U.S. patent application number 15/264829 was filed with the patent office on 2019-12-26 for positive electrode active material and secondary battery comprising the same.
This patent application is currently assigned to IUCF-HYU (INDUSTRY-UNIVERSITY COOPERATION FOUNDATION HANYANG UNIVERSITY). The applicant listed for this patent is IUCF-HYU (INDUSTRY-UNIVERSITY COOPERATION FOUNDATION HANYANG UNIVERSITY). Invention is credited to Hyung-Joo Noh, Yang-Kook SUN, Sung-June Youn.
Application Number | 20190393483 15/264829 |
Document ID | / |
Family ID | 58406809 |
Filed Date | 2019-12-26 |
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United States Patent
Application |
20190393483 |
Kind Code |
A9 |
SUN; Yang-Kook ; et
al. |
December 26, 2019 |
POSITIVE ELECTRODE ACTIVE MATERIAL AND SECONDARY BATTERY COMPRISING
THE SAME
Abstract
In the positive electrode active material according to the
inventive concept, A positive active material for lithium secondary
battery comprises a particle comprising M1, M2, and Li, wherein the
particle comprises a center, a surface, and an intermediate portion
between the center and the surface, wherein M1 and M2 are selected
from transition metal and are different each other, and wherein
concentrations of M1 and M2 have continuous concentration gradients
from the center to the intermediate portion.
Inventors: |
SUN; Yang-Kook; (Seoul,
KE) ; Noh; Hyung-Joo; (Bucheon-si, KR) ; Youn;
Sung-June; (Busan, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IUCF-HYU (INDUSTRY-UNIVERSITY COOPERATION FOUNDATION HANYANG
UNIVERSITY) |
Seoil |
|
KR |
|
|
Assignee: |
IUCF-HYU (INDUSTRY-UNIVERSITY
COOPERATION FOUNDATION HANYANG UNIVERSITY)
Seoul
KR
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20170092935 A1 |
March 30, 2017 |
|
|
Family ID: |
58406809 |
Appl. No.: |
15/264829 |
Filed: |
September 14, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14463170 |
Aug 19, 2014 |
9463984 |
|
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15264829 |
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13978067 |
Oct 8, 2013 |
8926860 |
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PCT/KR2011/010173 |
Dec 27, 2011 |
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14463170 |
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14926770 |
Oct 29, 2015 |
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13978067 |
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PCT/KR2014/003809 |
Apr 29, 2014 |
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14926770 |
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PCT/KR2014/003815 |
Apr 29, 2014 |
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PCT/KR2014/003809 |
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14926821 |
Oct 29, 2015 |
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PCT/KR2014/003815 |
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PCT/KR2014/003810 |
Apr 29, 2014 |
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14926821 |
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14926864 |
Oct 29, 2015 |
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PCT/KR2014/003810 |
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PCT/KR2014/003808 |
Apr 29, 2014 |
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14926864 |
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13978041 |
Oct 8, 2013 |
9493365 |
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PCT/KR2011/010175 |
Dec 27, 2011 |
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PCT/KR2014/003808 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01G 53/00 20130101;
C01G 53/50 20130101; C01G 53/006 20130101; C01P 2004/88 20130101;
C01P 2002/85 20130101; C01P 2004/84 20130101; H01M 2004/028
20130101; H01M 4/1391 20130101; H01M 4/131 20130101; H01M 4/505
20130101; C01P 2004/61 20130101; H01M 4/525 20130101; C01P 2006/40
20130101; C01G 53/42 20130101; H01M 4/364 20130101; C01G 53/44
20130101; C01D 15/02 20130101; C01P 2002/88 20130101; C01P 2004/03
20130101; H01M 4/485 20130101; H01M 4/366 20130101 |
International
Class: |
H01M 4/36 20060101
H01M004/36; C01G 53/00 20060101 C01G053/00; H01M 4/525 20060101
H01M004/525; H01M 4/505 20060101 H01M004/505 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 5, 2011 |
KR |
10-2011-0000841 |
Mar 10, 2011 |
KR |
10-2011-0021579 |
Nov 22, 2011 |
KR |
10-2011-0122542 |
Nov 22, 2011 |
KR |
10-2011-0122544 |
Apr 29, 2013 |
KR |
10-2013-0047797 |
Jul 31, 2013 |
KR |
10-2013-0091250 |
Apr 29, 2014 |
KR |
10-2014-0051571 |
Apr 29, 2014 |
KR |
10-2014-0051899 |
Apr 29, 2014 |
KR |
10-2014-0051935 |
Apr 29, 2014 |
KR |
10-2014-0051970 |
Oct 29, 2014 |
KR |
10-2014-0148503 |
Claims
1. A positive active material for lithium secondary battery
comprises: a particle comprising M1, M2, and Li, wherein the
particle comprises a center, a surface, and an intermediate portion
between the center and the surface, wherein M1 and M2 are selected
from transition metal and are different each other, and wherein
concentrations of M1 and M2 have continuous concentration gradients
from the center to the intermediate portion.
2. A positive active material for lithium secondary battery
according to claim 1, wherein the concentrations of M1 and M2 have
continuous concentration gradient in an entire region of the
particle.
3. A positive active material for lithium secondary battery
according to claim 2, wherein the particle further comprises M3,
wherein M3 is selected from transition metal and is different from
M1 and M2, and wherein a concentration of M3 is constant in the
entire region of the particle.
4. A positive active material for lithium secondary battery
according to claim 2, wherein the particle further comprises M3,
wherein M3 is selected from transition metal and is different from
M1 and M2, and wherein a concentration of M3 has a continuous
concentration gradient in the entire region of the particle.
5. A positive active material for lithium secondary battery
according to claim 4, wherein the concentration of M1 decreases in
the entire region of the particle, from the center to the surface,
and wherein the concentrations of M2 and M3 increase in the entire
region of the particle, from the center to the surface.
6. A positive active material for lithium secondary battery
according to claim 4, wherein the concentrations of M1 and M2
decrease in the entire region of the particle, from the center to
the surface, and wherein the concentration of M3 increases in the
entire region of the particle, from the center to the surface.
7. A positive active material for lithium secondary battery
according to claim 1, wherein the particle comprises a same
concentration portion in which the concentration of M1 is equal to
the concentration of M2, and wherein a distance between the center
and the same concentration portion is smaller than a distance
between the surface and the same concentration portion.
8. A positive active material for lithium secondary battery
according to claim 7, wherein the center comprises the same
concentration portion.
9. A positive active material for lithium secondary battery
according to claim 1, wherein M1 is Ni, and M2 is Co.
10. A positive active material for lithium secondary battery
according to claim 9, wherein the particle further comprises
Al.
11. A positive active material for lithium secondary battery
according to claim 1, wherein the concentrations of M1 and M2 from
the center to the intermediate portion have constant gradients.
12. A positive active material for lithium secondary battery
according to claim 1, wherein each of the concentrations of M1 and
M2 from the center to the intermediate portion has at least two
concentration gradients.
13. A positive active material for lithium secondary battery
according to claim 12, wherein the concentration gradients of M1
and M2 from the center to the intermediate portion have at least
one vertex.
14. A positive active material for lithium secondary battery
according to claim 1, wherein the concentration gradients of M1 and
M2 from the center to the intermediate portion have curved
shapes.
15. A positive active material for lithium secondary battery
according to claim 1, wherein the concentration of M1 decreases in
an entire region of the particle, from the center to the
intermediate portion, and wherein the concentration of M2 increases
in the entire region of the particle, from the center to the
intermediate portion.
16. A positive active material for lithium secondary battery
according to claim 1, wherein the particle further comprises M4,
wherein M4 comprises at least one of Fe, Na, Mg, Ca, Ti, V, Cr, Cu,
Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, or B and is different from
M1 and M2.
17. A positive active material for lithium secondary battery
according to claim 1, wherein the concentration of M1 from the
intermediate portion to the surface is constant, and wherein the
concentration of M2 from the intermediate portion to the surface is
constant.
18. A positive active material for lithium secondary battery
according to claim 17, wherein the concentration of M1 from the
intermediate portion to the surface is equal to the concentration
of M1 at the intermediate portion, and wherein the concentration of
M2 from the intermediate portion to the surface is equal to the
concentration of M2 at the intermediate portion.
19. A positive active material for lithium secondary battery
according to claim 17, wherein the concentration of M1 from the
intermediate portion to the surface is different from the
concentration of M1 at the intermediate portion, and wherein the
concentration of M2 from the intermediate portion to the surface is
different from the concentration of M2 at the intermediate
portion.
20. A positive active material for lithium secondary battery
according to claim 1, wherein the particle has a concentration
maintained portion and a concentration gradient portion between the
intermediate portion to the surface, wherein the concentrations of
M1 and M2 of the concentration maintained portion are constant, and
wherein the concentrations of M1 and M2 of the concentration
gradient portion have gradient.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 14/463,170 filed Aug. 19, 2014, which is a
continuation of U.S. patent application Ser. No. 13/978,067 filed
Oct. 8, 2013, now U.S. Pat. No. 8,926,860, which is a 371 of
PCT/KR2011/010173 filed Dec. 27, 2011, which claimed the priority
of KR Patent Application No. 10-2011-0000841 filed Jan. 5, 2011, KR
Patent Application No. 10-2011-0021579 filed Mar. 10, 2011 and KR
Patent Application No. 10-2011-0122542 filed Nov. 22, 2011,
contents of each of which are incorporated herein by reference in
their entirety.
[0002] This application is also a continuation-in-part of U.S.
patent application Ser. No. 14/926,770 filed Oct. 29, 2015, which
claims priority from Korean Patent Application No. 10-2014-0148503
filed on Oct. 29, 2014, and is a continuation-in-part of
International Application Nos. PCT/KR2014/003809 and
PCT/KR2014/003815 both filed on Apr. 29, 2014, which claim priority
from Korean Patent Application Nos. 10-2013-0047797 filed Apr. 29,
2013, 10-2014-0051899 filed Apr. 29, 2014, 10-2013-0091250 filed
Jul. 31, 2013, 10-2014-0051571 filed Apr. 29, 2014, and
10-2014-0051970 filed on Apr. 29, 2014, the entire contents of each
of which are incorporated herein by reference. This application
further claims priority from Korean Patent Application No.
10-2014-0148503 filed on Oct. 29, 2014, the entire contents of
which is incorporated herein by reference.
[0003] In addition, this application is a continuation-in-part of
U.S. patent application Ser. No. 14/926,821 filed Oct. 29, 2015,
which is a continuation of International Application No.
PCT/KR2014/003810 filed on Apr. 29, 2014, which claims priority
from Korean Patent Application Nos. 10-2013-0047797 filed Apr. 29,
2013 and 10-2014-0051395 filed Apr. 29, 2014, the entire contents
of each of which are incorporated herein by reference.
[0004] Furthermore, this application is a continuation-in-part of
U.S. patent application Ser. No. 14/926,864 filed Oct. 29, 2015,
which is a continuation of International Application No.
PCT/KR2014/003808 filed on Apr. 29, 2014, which claims priority
from Korean Patent Application Nos. 10-2013-0047797 filed Apr. 29,
2013 and 10-2014-0051935 filed Apr. 29, 2014, the entire contents
of each of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0005] Embodiments of the inventive concepts described herein
relates to a cathode active material with whole particle
concentration gradient for a lithium secondary battery, a method
for preparing same, and a lithium secondary battery having same,
and more specifically, to a cathode active material with whole
particle concentration gradient for a lithium secondary battery, a
method for preparing same, and a lithium secondary battery having
same, which has excellent lifetime characteristics and
charge/discharge characteristics through the stabilization of
crystal structure, and has thermostability even in high
temperatures.
[0006] In addition, embodiments of the inventive concepts described
herein relates to an cathode active material with whole particle
concentration gradient for a lithium secondary battery, a method
for preparing same, and a lithium secondary battery having same,
and more specifically, to a cathode active material with whole
particle concentration gradient for a lithium secondary battery, a
method for preparing same, and a lithium secondary battery having
same, which has excellent lifetime characteristics and
charge/discharge characteristics through the stabilization of
crystal structure without rapid change on the concentration of a
metal inside of the cathode active material particle, and has
thermostability even in high temperatures.
[0007] In addition, embodiments of the inventive concepts described
herein relate to a positive electrode active material for lithium
secondary battery, and more particularly, relate to a positive
electrode active material for lithium secondary battery including a
core portion in which concentrations of nickel, manganese, and
cobalt have gradients in a direction from the center to the surface
or concentrations of nickel, manganese, and cobalt are constant; a
concentration gradient portion which is formed on the outside of
the core portion and in which concentrations of nickel, manganese,
and cobalt have gradients; and a shell portion which is formed on
the outside of the concentration gradient portion and in which
concentrations of nickel, manganese, and cobalt are constant.
[0008] In addition, embodiments of the inventive concepts described
herein relate to a positive electrode active material for lithium
secondary battery, and more particularly, relate to a positive
electrode active material for lithium secondary battery including a
core portion in which concentrations of nickel, manganese, and
cobalt have gradients in a direction from the center to the surface
and a shell portion in which concentrations of nickel, manganese,
and cobalt are constant.
[0009] In addition, embodiments of the inventive concepts described
herein relate to a positive electrode active material and a
secondary battery including the same, and more particularly, relate
to a positive electrode active material including a concentration
gradient portion and a concentration maintained portion and a
secondary battery including the same.
[0010] In addition, embodiments of the inventive concepts described
herein relate to a positive electrode active material for lithium
secondary battery, and more particularly, relate to a positive
electrode active material for lithium secondary battery which
includes a first concentration gradient portion, a second
concentration gradient portion, and a first concentration
maintained portion. The first and second concentration gradient
portions have gradients of concentrations of nickel, manganese, and
cobalt in the direction from the center to the surface, and the
first concentration maintained portion has constant concentrations
of nickel, manganese, and cobalt between the first concentration
gradient portion and the second concentration gradient portion.
[0011] Embodiments of the inventive concepts described herein
relate to a positive electrode active material for lithium
secondary battery, and more particularly, relate to a positive
electrode active material for lithium secondary battery which
includes two core portions having gradients of concentrations of
nickel, manganese, and cobalt in the direction from the center to
the surface and in which the magnitudes of concentration gradients
of nickel, manganese, and cobalt are controlled in the two core
portions.
BACKGROUND OF THE INVENTION
[0012] On the strength of recent rapid development of electronics,
communications, computer industry, etc., the use of portable
electronic devices such as camcorders, mobile phones, notebook PCs
and the like becomes generalized. Accordingly, there is increasing
demand for batteries which are lightweight and highly reliable, and
can be used longer.
[0013] In particular, lithium secondary batteries, whose operating
voltage is 3.7 V or more, have higher energy density per unit
weight than nickel-cadmium batteries and nickel-hydrogen batteries.
Accordingly, the demand for the lithium secondary batteries as a
power source to drive the portable electronic communication devices
is increasing day by day.
[0014] Recently, studies on power sources for electric vehicles by
hybridizing an internal combustion engine and a lithium secondary
battery are actively conducted in the United States, Japan, Europe
and the like. The development of a plug-in hybrid (P-HEV) battery
used in the car with a mileage of less than 60 miles is actively
proceeding around United States. The P-HEV battery is a battery
having characteristics, which are nearly the characteristics of an
electric vehicle, and the biggest challenge is to develop
high-capacity batteries. In particular, the biggest challenge is to
develop cathode materials having higher tap density of 2.0 g/cc or
more and high capacity characteristics of 230 mAh/g or more.
[0015] The materials, which are currently available or under
development, are LiCoO.sub.2, LiNiO.sub.2, LiMnO.sub.2,
LiMn.sub.2O.sub.4, Li.sub.1+x[Mn.sub.2-xM.sub.x]O.sub.4,
LiFePO.sub.4 and the like. Of them, the LiCoO.sub.2 is an excellent
material having stable charge/discharge characteristics, excellent
electronic conductivity, high cell voltage, high stability and even
discharge voltage characteristics. However, because Co has low
reserves and is expensive and toxic to the human body, it is needed
to develop other cathode materials. Further, it has a defect of
very poor thermal properties by unstable crystal structure by
delithiation during discharging.
[0016] In order to improve it, there may be many attempts to shift
the exothermic onset temperature to the side of the higher
temperature and to make an exothermic peak broad in order to
prevent rapid heat-emitting, by substitute a part of the nickel
with transition metals. However, there is no satisfactory result
yet.
[0017] Namely, LiNi.sub.1-xCo.sub.xO.sub.2 (x=0.1-0.3) material,
wherein a part of the nickel is substituted with cobalt, shows
excellent charge/discharge characteristics and lifetime
characteristics, but the thermostability problem is not solved yet.
Furthermore, European Patent No. 0872450 discloses
Li.sub.aCo.sub.bMn.sub.cM.sub.dNi.sub.1-(b+c+d)O.sub.2 (M=B, Al,
Si. Fe, Cr, Cu, Zn, W, Ti, Ga)-type, where the Ni is substituted
with other metals as well as Co and Mn, but the thermostability of
the Ni-based material is not solved yet.
[0018] In order to eliminate these shortcomings, Korean Patent
Publication No. 2005-0083869 suggests lithium-transition metal
oxides having metal composition representing concentration
gradient. This method is a method that an internal materials with a
certain composition is synthesized and materials with other
composition is coated on the exterior thereof to obtain a bi-layer,
and is mixed with a lithium salt followed by heat-treatment. The
internal material may be commercially available lithium transition
metal oxides. However, in this method, the metal composition of the
cathode active material between the produced internal material and
the external material is discontinuously changed, and is not
continuously and gradually changed. Further, the powder synthesized
by the invention, which does not use ammonia as a chelating agent,
was not suitable for a cathode active material for a lithium
secondary battery due to its lower tap density.
[0019] In order to improve this problem, Korean Patent Publication
No. 2007-0097923 suggests a cathode active material, which has an
internal bulk part and an external bulk part, and the metal
ingredients have continuous concentration distribution depending on
their position at the external bulk part. However, in this method,
there was a need to develop a cathode active material of a new
structure having better stability and capacity because the
concentration is constant at the internal bulk part and the metal
composition is changed at the external bulk part.
SUMMARY OF THE INVENTION
[0020] In order to solve the above-described problems associated
with prior art, the present invention is objected to provide a
cathode active material, which has excellent lifetime
characteristics and charge/discharge characteristics through the
stabilization of crystal structure, and has thermostability even in
high temperatures.
[0021] Further, the present invention is objected to provide a
method for preparing the cathode active material for lithium
secondary battery.
[0022] Further, the present invention is objected to provide a
lithium secondary battery including the cathode active
material.
[0023] In order to accomplish one object of the present invention,
the present invention provides, in a cathode active material for a
lithium secondary battery, a cathode active material with whole
particle concentration gradient for a lithium secondary battery,
wherein the concentration of all metals making up the cathode
active material for a lithium secondary battery shows continuous
concentration gradient in the entire region, from the particle core
to the surface part.
[0024] In the present invention, the cathode active material for a
lithium secondary battery with whole particle concentration
gradient is characterized that it may comprise:
[0025] the core expressed by the following formula 1; and
[0026] the surface part expressed by the following formula 2,
[0027] wherein the concentrations of the M1, the M2 and the M3 have
continuous concentration gradient from the core to the surface.
Li.sub.a1M1.sub.x1M2.sub.y1M3z.sub.1M4.sub.wO.sub.2+.delta.
[Formula 1]
Li.sub.a2M1.sub.x2M2.sub.y2M3.sub.z2M4.sub.wO.sub.2+.delta.
[Formula 2]
[0028] (in the formulas 1 and 2, M1, M2 and M3 are selected from
the group consisting of Ni, Co, Mn and a combination thereof; M4 is
selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr,
Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and a combination
thereof; 0<a1.ltoreq.1.1, 0<a2.ltoreq.1.1,
0.ltoreq.x1.ltoreq.1, 0.ltoreq.x2.ltoreq.1, 0.ltoreq.y1.ltoreq.,
0.ltoreq.y2.ltoreq.1, 0.ltoreq.z1.ltoreq.1, 0.ltoreq.z2.ltoreq.1,
0.ltoreq.w.ltoreq.0.1, 0.0.ltoreq.8.ltoreq.0.02,
0.ltoreq.x1+y1+z1.ltoreq.1, 0.ltoreq.x2+y2+z2.ltoreq.,
x1.ltoreq.x2, y1.ltoreq.y2 and z2.ltoreq.z1.)
[0029] Further, the present invention provides a method for
preparing the cathode active material for a lithium secondary
battery comprises:
[0030] a first step of preparing a metal salt aqueous solution for
forming the core and a metal salt aqueous solution for forming the
surface part, which contain the M1, the M2 and the M3 as a metal
salt aqueous solution, wherein the concentrations of the M1, the M2
and the M3 are different each other;
[0031] a second step of forming precipitates by mixing the metal
salt aqueous solution for forming the core and the metal salt
aqueous solution for forming the surface part at a mixing ratio
from 100 v %:0 v % to 0 v %:100 v % with gradual change and by
mixing a chelating agent and a basic aqueous solution to a reactor
at the same time, wherein the concentrations of the M1, the M2 and
the M3 have continuous concentration gradient from the core to the
surface part;
[0032] a third step of preparing an active material precursor by
drying or heat-treating the obtained precipitates; and
[0033] a fourth step of mixing the active material precursor and a
lithium salt and then heat-treating thereof.
[0034] Further, the present invention provides a lithium secondary
battery comprising the cathode active material according to the
present invention.
[0035] In order to solve the above-described problems associated
with prior art, the present invention is objected to provide an
cathode active material with whole particle concentration gradient
for a lithium secondary battery, which has excellent lifetime
characteristics and charge/discharge characteristics through the
stabilization of crystal structure, and has thermostability even in
high temperatures.
[0036] Further, the present invention is objected to provide a
method for preparing the cathode active material for lithium
secondary battery.
[0037] Further, the present invention is objected to provide a
lithium secondary battery including the cathode active
material.
[0038] In order to accomplish one object of the present invention,
the present invention provides, in an cathode active material for a
lithium secondary battery, an cathode active material with whole
particle concentration gradient for a lithium secondary battery,
wherein the concentration of a metal making up the cathode active
material shows continuous concentration gradient in the entire
region, from the particle core to the surface part.
[0039] The cathode active material for a lithium secondary battery
is characterized that it may comprise:
[0040] the core expressed by the following formula 1; and
[0041] the surface part expressed by the following formula 2,
[0042] wherein the concentration of the M1 is constant from the
core to the surface part; and
[0043] the concentration of the M2 and the concentration of the M3
have continuous concentration gradient from the core to the
surface.
Li.sub.a1M1.sub.xM2.sub.y1M3.sub.z1M4.sub.wO.sub.2+.delta. [Formula
1]
Li.sub.a2M1.sub.xM2.sub.y2M3.sub.z2M4.sub.wO.sub.2+.delta. [Formula
2]
(in the formulas 1 and 2, M1, M2 and M3 are selected from the group
consisting of Ni, Co, Mn and a combination thereof; M4 is selected
from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge,
Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and a combination thereof;
0<a1.ltoreq.1.1, 0<a2.ltoreq.1.1, 0.ltoreq.x.ltoreq.1,
0.ltoreq.y1.ltoreq.1, 0.ltoreq.y2.ltoreq.1, 0.ltoreq.z1.ltoreq.1,
0.ltoreq.z2.ltoreq.1, 0.ltoreq.w.ltoreq.0.1,
0.0.ltoreq..delta..ltoreq.0.02, 0.ltoreq.x+y1+z1.ltoreq.1,
0<x+y2+z2.ltoreq.1, and y1.ltoreq.y2, z2.ltoreq.z1.
[0044] Further, the present invention provides a method for
preparing the cathode active material for a lithium secondary
battery comprises:
[0045] a first step of preparing a metal salt aqueous solution for
forming the core and a metal salt aqueous solution for forming the
surface part, which contain the M1, the M2 and the M3 as a metal
salt aqueous solution, wherein the concentration of the M1 is the
same each other, and the concentration of the M2 and the
concentration of the M3 are different each other;
[0046] a second step of forming precipitates by mixing the metal
salt aqueous solution for forming the core and the metal salt
aqueous solution for forming the surface part at a mixing ratio
from 100 v %:0 v % to 0 v %:100 v % with gradual change and by
mixing a chelating agent and a basic aqueous solution to a reactor
at the same time, wherein the concentration of the M1 is constant
from the core to the surface part, and the concentrations of the M2
and the M3 have continuous concentration gradient from the core to
the surface part;
[0047] a third step of preparing an active material precursor by
drying or heat-treating the obtained precipitates; and
[0048] a fourth step of mixing the active material precursor and a
lithium salt and then heat-treating thereof.
[0049] Further, the present invention provides a lithium secondary
battery comprising the cathode active material.
[0050] Embodiments of the inventive concepts may provide a positive
electrode active material having a new structure which includes a
core portion and a shell portion and in which the content of nickel
is increased to have a high capacity and the content of residual
lithium is decreased.
[0051] Embodiments of the inventive concepts may also provide a
positive electrode active material exhibiting high reliability and
a secondary battery including the same.
[0052] Embodiments of the inventive concepts may also provide a
secondary battery having a high capacity.
[0053] Embodiments of the inventive concepts may also provide a
secondary battery exhibiting high stability.
[0054] Embodiments of the inventive concepts may also provide a
secondary battery having a long cycle-life.
[0055] Embodiments of the inventive concepts may also provide a
secondary battery having an improved charge and discharge
efficiency.
[0056] Embodiments of the inventive concepts are not limited to
those described above.
[0057] One aspect of embodiments of the inventive concept is
directed to provide a positive electrode active material for
lithium secondary battery.
[0058] According to an embodiment of the inventive concept, the
positive electrode active material for lithium secondary battery
may include a core portion, a concentration gradient portion that
is formed on the outside of the core portion and has gradients of
concentrations of nickel, manganese, and cobalt, and a shell
portion that is formed on the outside of the concentration gradient
portion and has constant concentrations of nickel, manganese, and
cobalt.
[0059] According to an embodiment of the inventive concept, the
positive electrode active material for lithium secondary battery
includes the shell portion having the constant concentrations of
nickel, manganese, and cobalt on the outside of the core portion,
and thus it is possible to decrease the amount of residual lithium
on the surface of a particle although the concentration of nickel
in the inside of the particle is high.
[0060] According to an embodiment of the inventive concept, in the
positive electrode active material, the core portion may have
constant concentrations of nickel, manganese, and cobalt.
[0061] According to an embodiment of the inventive concept, in the
positive electrode active material, the concentration of nickel in
the core portion may be equal to the maximum value of the
concentration of nickel in the concentration gradient portion.
[0062] According to an embodiment of the inventive concept, in the
positive electrode active material, the core portion may have
gradients of concentrations of nickel, manganese, and cobalt.
[0063] In embodiments of the inventive concept, the fact that the
concentrations of nickel, manganese, and cobalt in the core portion
have gradients may mean that the concentrations of nickel,
manganese, and cobalt change depending on the distance from the
center of the positive electrode active material particle.
[0064] According to an embodiment of the inventive concept, in the
positive electrode active material, the core portion may have
constant magnitudes of concentration gradients of nickel,
manganese, and cobalt. According to embodiments of the inventive
concept, the magnitudes of concentration gradients of nickel,
manganese, and cobalt may be constant in the core portion, and thus
relational functions of the concentrations of nickel, manganese,
and cobalt according to the distance from the center may be
linear.
[0065] In addition, according to embodiments of the inventive
concept, the magnitudes of concentration gradients of nickel,
manganese, and cobalt of the core portion may change depending on
the distance from the center of the positive electrode active
material particle. In other words, the relational function of the
concentrations of nickel, manganese, and cobalt and the according
to distance from the center may be curved. In other words, the rate
of change in concentrations of nickel, manganese, and cobalt at the
location having a distance D from the center in the core portion
may include a constant, a linear function, or a polynomial
function.
[0066] According to an embodiment of the inventive concept, in the
positive electrode active material, the core portion may include n
(5.gtoreq.n.gtoreq.1) core portions in which magnitudes of
concentration gradients of nickel, manganese, and cobalt are
represented by CSn-Ni, CSn-Mn, and CSn-Co, respectively. In a case
in which n is 2, the core portion may include a first core portion
in which magnitudes of concentration gradients of nickel,
manganese, and cobalt are represented by CS1-Ni, CS1-Mn, and
CS1-Co, respectively, and a second core portion in which magnitudes
of concentration gradients of nickel, manganese, and cobalt are
represented by CS2-Ni, CS2-Mn, and CS2-Co, respectively.
[0067] According to an embodiment of the inventive concept, in the
positive electrode active material, the concentration gradients of
nickel, manganese, and cobalt in the core portion may have linear
shapes or curved shapes.
[0068] According to an embodiment of the inventive concept, in the
positive electrode active material, the magnitudes |CSn-Ni|,
|CSn-Mn|, and |CSn-Co| of concentration gradients of nickel,
manganese, and cobalt in the n core portions and magnitudes
|CG-Ni|, |CG-Mn|, and |CG-Co| of concentration gradients of nickel,
manganese, and cobalt in the concentration gradient portion may
satisfy the following relational expressions.
|CSn Ni|.ltoreq.|CG-Ni|
|CSn-Mn|.ltoreq.|CG-Mn|
|CSn-Co|.ltoreq.|CG-Co|
[0069] In other words, according to an embodiment of the inventive
concept, in the positive electrode active material, the absolute
values of the magnitudes of concentration gradients in the
concentration gradient portion may be equal to or greater than the
absolute values of the magnitudes of concentration gradients in the
core portion.
[0070] According to an embodiment of the inventive concept, in the
positive electrode active material, the concentration gradient
portion may include n (5.gtoreq.n.gtoreq.1) concentration gradient
portions in which magnitudes of concentration gradients of nickel,
manganese, and cobalt are represented by CGn-Ni, CGn-Mn, and
CGn-Co, respectively.
[0071] According to an embodiment of the inventive concept, in the
positive electrode active material, the shell portion may include n
(5.gtoreq.n.gtoreq.1) shell portions in which concentrations of
nickel, manganese, and cobalt are represented by SCn-Ni, SCn-Mn,
and SCn-Co, respectively.
[0072] According to an embodiment of the inventive concept, in the
positive electrode active material, the concentrations SCn-Ni,
SCn-Mn, and SCn-Co of nickel, manganese, and cobalt in the n.sup.th
shell portion may satisfy the following relational expressions.
0.3.ltoreq.SCn-Ni.ltoreq.0.8
0.2.ltoreq.SCn-Mn.ltoreq.0.4
0.05.ltoreq.SCn-Co.ltoreq.0.2
[0073] According to an embodiment of the inventive concept, in the
positive electrode active material, the concentration of nickel in
the n.sup.th shell portion preferably may satisfy the following
relational expression.
0.5.ltoreq.SCn-Ni.ltoreq.0.7
[0074] According to an embodiment of the inventive concept, in the
positive electrode active material, the concentrations SC1-Ni,
SC1-Mn, and SC1-Co of nickel, manganese, and cobalt in the first
shell portion may be equal to the concentrations of nickel,
manganese, and cobalt of the outermost part of the concentration
gradient portion, namely, the contact point between the
concentration gradient portion and the first shell portion.
[0075] According to an embodiment of the inventive concept, in the
positive electrode active material, the concentration SC1-Ni of
nickel in the shell portion may be equal to the minimum value of
the concentration of nickel in the concentration gradient portion.
In other words, the concentration of nickel in the shell portion
may be continuously connected to the concentration gradient of
nickel in the concentration gradient portion.
[0076] According to an embodiment of the inventive concept, in the
positive electrode active material, the concentration SC1-Ni of
nickel in the shell portion may be different from the minimum value
of the concentration of nickel in the concentration gradient
portion. For example, the concentration SC1-Ni of nickel in the
shell portion may be higher than the minimum value of the
concentration of nickel in the concentration gradient portion. On
the other hand, the concentration SC1-Ni of nickel in the shell
portion may be lower than the minimum value of the concentration of
nickel in the concentration gradient portion. In other words, the
concentration SC1-Ni of nickel in the shell portion may be
discontinuous from the concentration gradient of nickel in the
concentration gradient portion.
[0077] According to an embodiment of the inventive concept, in the
positive electrode active material, the concentration gradients of
nickel, manganese, and cobalt in the concentration gradient portion
may have linear shapes or curved shapes.
[0078] According to an embodiment of the inventive concept, in the
positive electrode active material, the shell portion has a
thickness of from 0.1 .mu.m to 0.6 .mu.m. In the positive electrode
active material, an effect derived from the formation of the shell
portion may be not obtained when the thickness of the shell portion
is 0.1 .mu.m or less and the overall capacity rather may decrease
when the thickness is 0.6 .mu.m or more.
[0079] According to an embodiment of the inventive concept, in the
positive electrode active material, the volume of the shell portion
may be 30% or less of the total volume of the particle.
[0080] According to an embodiment of the inventive concept, in the
positive electrode active material, the content of Li.sub.2CO.sub.3
of the surface of the positive electrode active material may be
2,000 ppm or less.
[0081] According to an embodiment of the inventive concept, in the
positive electrode active material, the content of LiOH of the
surface of the positive electrode active material may be 2,000 ppm
or less.
[0082] According to an embodiment of the inventive concept, the
inventive concept is also directed to provide a lithium secondary
battery including the positive electrode active material described
above.
[0083] According to an embodiment of the inventive concept, a
positive electrode active material for lithium secondary battery
may include a core portion having gradients of concentrations of
nickel, manganese, and cobalt in a direction from a center to a
surface and a shell portion having constant concentrations of
nickel, manganese, and cobalt. The concentrations of nickel,
manganese, and cobalt in a center of the core portion may be
represented by CC1-Ni, CC1-Mn, and CC1-Co. The core portion may
include a first core portion in which magnitudes of concentration
gradients of nickel, manganese, and cobalt are represented by
CS1-Ni, CS1-Mn, and CS1-Co, respectively, and a second core portion
in which magnitudes of concentration gradients of nickel,
manganese, and cobalt are represented by CS2-Ni, CS2-Mn, and
CS2-Co, respectively. The concentration of the nickel CC1-Ni in the
center may be 0.95 or more, and the concentrations of nickel,
manganese, and cobalt in the shell portion may be represented by
SC-Ni, SC-Mn, and SC-Co, respectively. The concentration of nickel
SC-Ni in the shell portion may be 0.6 or less.
[0084] According to an embodiment of the inventive concept, in the
positive electrode active material, the magnitudes CS1-Ni, CS1-Mn,
and CS1-Co of concentration gradients of nickel, manganese, and
cobalt in the first core portion and the magnitudes CS2-Ni, CS2-Mn,
and CS2-Co of concentration gradients of nickel, manganese, and
cobalt in the second core portion may satisfy the following
relation expressions: CS1-Ni<0, CS1-Mn>0, CS1-Co>0,
CS2-Ni<0, CS2-Mn>0, and CS2-Co>0.
[0085] According to an embodiment of the inventive concept, in the
positive electrode active material, the concentrations of nickel,
manganese, and cobalt in the shell portion may be represented by
SC1-Ni, SC1-Mn, and SC1-Co, respectively, and the concentrations of
nickel, manganese, and cobalt in the shell portion may be
constant.
[0086] According to an embodiment of the inventive concept, in the
positive electrode active material, the concentrations SC1-Ni,
SC1-Mn, and SC1-Co of nickel, manganese, and cobalt in the shell
portion may be equal to the concentrations of nickel, manganese,
and cobalt of the outermost part of the core portion.
[0087] According to an embodiment of the inventive concept, in the
positive electrode active material, an average cobalt concentration
of the core portion and the shell portion may be 6%. In the
positive electrode active material according to the inventive
concept, the average concentration of cobalt may be the average
concentration of cobalt in the entire positive electrode active
material particle prepared according to the inventive concept. Rate
characteristics and capacity of the lithium secondary battery may
decrease when the average concentration of cobalt in the entire
particles is 6% or less.
[0088] According to an embodiment of the inventive concept, in the
positive electrode active material, the concentration of nickel at
the contact point between the first core portion and the second
core portion may be 0.9. In other words, the minimum value of the
concentration of nickel in the first core portion may be 0.9, and
the maximum value of the concentration of nickel in the second core
portion may be 0.9.
[0089] According to an embodiment of the inventive concept, in the
positive electrode active material, the volume of the shell portion
may be 30% or less of the total volume of the positive electrode
active material particle.
[0090] Still another aspect of embodiments of the inventive concept
is directed to provide a positive electrode active material.
[0091] According to an embodiment of the inventive concept, the
positive electrode active material may include a first element
formed of a plurality of metals including a first metal and a
second element composed of one or more first elements. The first
element may extend from a center part of the second element toward
a surface part of the second element. The second element may
include a concentration gradient portion in which a content of the
first metal changes, and a concentration maintained portion in
which a content of the first metal is constant.
[0092] According to an embodiment of the inventive concept, the
plurality of metals may further include a second metal. The content
of the second metal may decrease as the content of the first metal
increases in a direction from the center part to the surface part
in the concentration gradient portion. The content of the second
metal may increase as the content of the first metal decreases in
the direction from the center part to the surface part in the
concentration gradient portion.
[0093] According to an embodiment of the inventive concept, the
center part may include a region of the inside of the second
element and the first element may have a rod shape radiated from
the center part toward the surface part.
[0094] According to an embodiment of the inventive concept, an
average content of the first metal in the concentration gradient
portion may be higher than an average content of the first metal in
the concentration maintained portion.
[0095] According to an embodiment of the inventive concept, a
content of the first metal may continuously change in a direction
from the center part to the surface part.
[0096] According to an embodiment of the inventive concept, a
content of the first metal may discontinuously change between the
concentration gradient portion and the concentration maintained
portion.
[0097] According to an embodiment of the inventive concept, the
concentration maintained portion may include a first concentration
maintained portion and a second concentration maintained portion
having a content of the first metal different from that in the
first concentration maintained portion. A content of the first
metal may discontinuously change between the first concentration
maintained portion and the second concentration maintained
portion.
[0098] According to an embodiment of the inventive concept, the
content of the first metal in the concentration gradient portion
may gradually increase or decrease in a direction from the center
part to the surface part.
[0099] According to an embodiment of the inventive concept, each of
the concentration gradient portion and the concentration maintained
portion may be provided in plurality.
[0100] According to an embodiment of the inventive concept, the
first metal may be nickel (Ni) and the second metal may be
manganese (Mn).
[0101] Embodiments of the inventive concepts provide a positive
electrode active material having a new structure in which the
concentration of nickel has a gradient so as to have a high content
of nickel and a high capacity and to exhibit improved charge and
discharge characteristics and thermal stability.
[0102] One aspect of embodiments of the inventive concept is
directed to provide a positive electrode active material for
lithium secondary battery including: a first concentration gradient
portion having gradients of concentrations of nickel, manganese,
and cobalt in a direction from a center to a surface; a first
concentration maintained portion that is formed on the outside of
the first concentration gradient portion and has concentrations of
nickel, manganese, and cobalt which are maintained at a terminal of
the first concentration gradient portion; and a second
concentration gradient portion that is formed on the outside of the
first concentration maintained portion and has gradients of
concentrations of nickel, manganese, and cobalt in the direction
from the center to the surface.
[0103] In embodiments of the inventive concept, the fact that the
core portion has the gradients of concentrations of nickel,
manganese, and cobalt means that the concentrations of nickel,
manganese, and cobalt change depending on the distance from the
center of the positive electrode active material particle.
[0104] In the positive electrode active material according to
embodiments of the inventive concept, the core portion has constant
magnitudes of concentration gradients of nickel, manganese, and
cobalt. According to embodiments of the inventive concept, the
magnitudes of concentration gradients of nickel, manganese, and
cobalt are constant in the entire core portion, and thus the
functional relation between the concentrations of nickel,
manganese, and cobalt and the distance from the center may be
linear.
[0105] In addition, according to embodiments of the inventive
concept, the magnitudes of concentration gradients of nickel,
manganese, and cobalt may change depending on the distance from the
center on the basis of the magnitudes at the center of the positive
electrode active material particle in the core portion. In other
words, the functional relation between the concentrations of
nickel, manganese, and cobalt and the distance from the center may
be curved. In other words, the rate of change in concentrations of
nickel, manganese, and cobalt at the location having a distance D
from the center in the core portion may include a constant, a
linear function, or a polynomial function.
[0106] In the positive electrode active material according to
embodiments of the inventive concept, the first concentration
maintained portion is represented by the following Chemical Formula
1.
Li.sub.1+aNi.sub.x1Co.sub.y1Mn.sub.1-x1-y1-d1O.sub.2+d1 [Chemical
Formula 1]
[0107] In Chemical Formula 1, 0.6.ltoreq.x1.ltoreq.0.8,
0.05.ltoreq.y1.ltoreq.0.2, 0.1.ltoreq.1-x1-y1-d1.ltoreq.0.25,
0.01.ltoreq.a.ltoreq.0.1, and 0.01.ltoreq.d1.ltoreq.0.1.
[0108] The positive electrode active material according to
embodiments of the inventive concept may further include a second
concentration maintained portion that is formed on the outside of
the second concentration gradient portion and has concentrations of
nickel, manganese, and cobalt which are maintained.
[0109] In the positive electrode active material according to
embodiments of the inventive concept, the concentrations of nickel,
manganese, and cobalt in the second concentration maintained
portion are the same as the concentrations of nickel, manganese,
and cobalt at a terminal of the second concentration gradient
portion.
[0110] In the positive electrode active material according to
embodiments of the inventive concept, the concentrations of nickel,
manganese, and cobalt in the second concentration maintained
portion are discontinuous with respect to the concentrations of
nickel, manganese, and cobalt at a terminal of the second
concentration gradient portion.
[0111] In the positive electrode active material according to
embodiments of the inventive concept, the second concentration
maintained portion is represented by the following Chemical Formula
2.
Li.sub.1+aNi.sub.x2Co.sub.y2Mn.sub.1-x2-y2-d2O.sub.2+d2 [Chemical
Formula 2]
[0112] In Chemical Formula 2, 0.5.ltoreq.x2.ltoreq.0.6,
0.15.ltoreq.y2.ltoreq.0.25, 0.2.ltoreq.1-x2-y2-d2.ltoreq.0.35,
0.01.ltoreq.a.ltoreq.0.1, and 0.01.ltoreq.d2.ltoreq.0.1.
[0113] The positive electrode active material according to
embodiments of the inventive concept may further include a third
concentration maintained portion having constant concentrations of
nickel, manganese, and cobalt inside the first concentration
gradient portion in a center direction.
[0114] In the positive electrode active material according to
embodiments of the inventive concept, the third concentration
maintained portion is represented by the following Chemical Formula
3.
Li.sub.1+aNi.sub.x3Co.sub.y3Mn.sub.1-x3-y3-d3O.sub.2+d3 [Chemical
Formula 3]
[0115] In Chemical Formula 3, 0.7.ltoreq.x3.ltoreq.0.9,
0.15.ltoreq.y3.ltoreq.0.25, 0.2.ltoreq.1-x3-y3-d3.ltoreq.0.35,
0.01.ltoreq.a.ltoreq.0.1, and 0.01.ltoreq.d3.ltoreq.0.1.
[0116] In the positive electrode active material according to
embodiments of the inventive concept, the first concentration
maintained portion has a thickness of from 0.1 .mu.m to 0.6
.mu.m.
[0117] In the positive electrode active material according to
embodiments of the inventive concept, the second concentration
maintained portion has a thickness of from 0.1 .mu.m to 0.6
.mu.m.
[0118] In the positive electrode active material according to
embodiments of the inventive concept, an effect derived from the
formation of the shell portion is not obtained when the thickness
of each of the first and second concentration maintained portions
is smaller than 0.1 .mu.m, and the overall capacity rather
decreases when the thickness is greater than 0.6 .mu.m.
[0119] Another aspect of embodiments of the inventive concept is
directed to provide a positive electrode active material for
lithium secondary battery including: a first concentration gradient
portion having gradients of concentrations of nickel, manganese,
and cobalt in a direction from a center to a surface; a second
concentration gradient portion having gradients of concentrations
of nickel, manganese, and cobalt in the direction from the center
to the surface; and a first concentration maintained portion that
is positioned between the first concentration gradient portion and
the second concentration gradient portion and has concentrations of
nickel, manganese, and cobalt which are maintained.
[0120] In the positive electrode active material according to
embodiments of the inventive concept, the concentration of nickel
in the first concentration maintained portion may be the same as
the minimum value of the concentration of nickel in the first
concentration gradient portion.
[0121] In the positive electrode active material according to
embodiments of the inventive concept, the concentration of nickel
in the first concentration maintained portion may be the same as
the maximum value of the concentration of nickel in the second
concentration gradient portion.
In the positive electrode active material according to embodiments
of the inventive concept, the concentration of nickel in the first
concentration maintained portion may be different from the maximum
value of the concentration of nickel in the first concentration
gradient portion or the second concentration gradient portion. In
other words, the concentration of nickel in the first concentration
maintained portion may be discontinuous with respect to the
concentration gradient of nickel in the first concentration
gradient portion or the second concentration gradient portion.
[0122] Embodiments of the inventive concepts provide a positive
electrode active material having a new structure which includes a
core portion having gradients of concentrations of nickel,
manganese, and cobalt and in which the concentration gradients of
nickel, manganese, and cobalt have a vertex in the core
portion.
[0123] One aspect of embodiments of the inventive concept is
directed to provide a positive electrode active material for
lithium secondary battery which includes a core portion having
concentration gradients of nickel, manganese, and cobalt in a
direction from a center to a surface. Each of the concentration
gradients of nickel, manganese, and cobalt has at least one vertex
in the core portion.
[0124] In embodiments of the inventive concept, the fact that the
concentration gradient has a vertex may mean that the concentration
gradient has a vertex at which a negative value changes to a
positive value or a positive value changes to a negative value. For
example, the vertex may be a point at which the concentration of
nickel which has increased in the direction from the center to the
surface begins to decrease or may be a point at which the
concentration of nickel which has decreased in the direction from
the center to the surface begins to increase.
[0125] Alternatively, in embodiments of the inventive concept, the
vertex may be a point at which the concentration which has had a
(+) gradient begins to be constant. For example, the vertex may be
a point at which the concentration of nickel which has increased in
the direction from the center to the surface begins to be
constantly maintained or may be a point at which the concentration
of nickel which has decreased in the direction from the center to
the surface begins to be constantly maintained.
[0126] In the positive electrode active material according to
embodiments of the inventive concept, the core portion may include
a first core portion having magnitudes of the concentration
gradients of nickel, manganese, and cobalt which are represented by
CS1-Ni, CS1-Mn, and CS1-Co, respectively; and a second core portion
having magnitudes of the concentration gradients of nickel,
manganese, and cobalt which are represented by CS2-Ni, CS2-Mn,
CS2-Co, respectively. The magnitude CS1-Ni of the concentration
gradient of nickel in the first core portion and the magnitude
CS2-Ni of the concentration gradient of nickel in the second core
portion may satisfy the following Equation.
(CS1-Ni).times.(CS2-Ni)<0
[0127] In other words, in the positive electrode active material
according to embodiments of the inventive concept, the magnitude of
the concentration gradient of nickel in the second core portion may
be controlled to be negative when the magnitude of the
concentration gradient of nickel in the first core portion is
positive, and the magnitude of the concentration gradient of nickel
in the second core portion may be controlled to be positive when
the magnitude of the concentration gradient of nickel in the first
core portion is negative.
[0128] In the positive electrode active material according to
embodiments of the inventive concept, the magnitude CS1-Mn of the
concentration gradient of manganese in the first core portion and
the magnitude CS2-Mn of the concentration gradient of manganese in
the second core portion may satisfy the following Equation.
(CS1-Mn).times.(CS2-Mn)<0
[0129] In other words, in the positive electrode active material
according to embodiments of the inventive concept, the magnitude of
the concentration gradient of manganese in the second core portion
may be controlled to be negative when the magnitude of the
concentration gradient of manganese in the first core portion is
positive, and the magnitude of the concentration gradient of
manganese in the second core portion may be controlled to be
positive when the magnitude of the concentration gradient of
manganese in the first core portion is negative.
[0130] In the positive electrode active material according to
embodiments of the inventive concept, the magnitude CS1-Co of the
concentration gradient of cobalt in the first core portion and the
magnitude CS2-Co of the concentration gradient of cobalt in the
second core portion may satisfy the following Equation.
(CS1-Co).times.(CS2-Co)<0
[0131] In other words, in the positive electrode active material
according to embodiments of the inventive concept, the magnitude of
the concentration gradient of cobalt in the second core portion may
be controlled to be negative when the magnitude of the
concentration gradient of cobalt in the first core portion is
positive, and the magnitude of the concentration gradient of cobalt
in the second core portion may be controlled to be positive when
the magnitude of the concentration gradient of cobalt in the first
core portion is negative.
[0132] In the positive electrode active material according to
embodiments of the inventive concept, the core portion may further
include a first concentration maintained portion having constant
concentrations of nickel, manganese, and cobalt between the first
core portion and the second core portion.
[0133] In the positive electrode active material according to
embodiments of the inventive concept, the core portion may further
include a second concentration maintained portion having constant
concentrations of nickel, manganese, and cobalt inside the first
core portion in a center direction.
[0134] The positive electrode active material according to
embodiments of the inventive concept may further include a shell
portion having constant concentrations of nickel, manganese, and
cobalt on an outer peripheral surface of the core portion.
[0135] In the positive electrode active material according to
embodiments of the inventive concept, the shell portion may include
a first shell portion having constant concentrations of nickel,
manganese, and cobalt which are represented by SC1-Ni, SC1-Mn, and
SC1-Co, respectively; and a second shell portion having constant
concentrations of nickel, manganese, and cobalt which are
represented by SC2-Ni, SC2-Mn, and SC2-Co, respectively.
[0136] In the positive electrode active material according to
embodiments of the inventive concept, a volume of the shell portion
may be 30% or less of a total volume.
[0137] Another aspect of embodiments of the inventive concept is
directed to provide a lithium secondary battery including the
positive electrode active material according to embodiments of the
inventive concept.
[0138] In the cathode active material for a lithium secondary
battery according to the present invention, the concentrations of
all metals contained in the cathode active material are increased
or decreased with continuous concentration gradient from the core
to the surface part. Accordingly, the crystal structure is
stabilized and the thermostability is increased because there is no
phase boundary having rapid concentration change from the core to
the surface part.
[0139] In the cathode active material for a lithium secondary
battery according to the present invention, the concentration of
one metal is constant from the core to the surface part, and the
concentrations of the other two metals are increased or decreased
with continuous concentration gradient from the core to the surface
part.
[0140] Accordingly, the crystal structure of the particle is
stabilized and the thermostability is increased because there is no
phase boundary having rapid concentration change from the particle
core to the surface part.
[0141] Accordingly, the lithium secondary battery having the
cathode active material shows excellent capacity characteristics as
well as excellent lifetime characteristics and charge/discharge
characteristics, and has thermostability even in high temperatures.
Particularly, when the Ni concentration of the cathode active
material according to the present invention, which shows the whole
particle concentration gradient, is maintained constantly, a stable
active material showing high capacity can be prepared.
BRIEF DESCRIPTION OF DRAWINGS
[0142] The above and other objects and features of the present
invention will become apparent from the following description of
the invention taken in conjunction with the following accompanying
drawings, which respectively show:
[0143] FIGS. 1 to 6: the results measuring the atomic ratio in each
precursor particle prepared in Examples 1 to 6 of the present
invention, respectively;
[0144] FIGS. 7 to 12: the results measuring the atomic ratio in
each precursor particle prepared in Examples 1-1 to 1-6 of the
present invention after heat-treating, respectively;
[0145] FIGS. 13 to 18: the results of charging/discharging test and
the results measuring cycle characteristics of each battery
prepared by using the active materials prepared in Examples 1-1 to
1-6 of the present invention and the active materials prepared in
Comparative Examples 1-1 to 1-7, respectively; and
[0146] FIGS. 19 to 24: the results measuring heat flow of each
cathode including active materials prepared in Examples 1-1 to 1-6
of the present invention and active materials prepared in
Comparative examples 1-1 to 1-7, by charging at 4.3 V and then
heating at the speed of 10.degree. C./min by using a differential
scanning calorimeter (DSC), respectively.
[0147] FIGS. 25 to 29: the results measuring the atomic ratio in
each precursor particle prepared in Examples 2-1 to 2-5 of the
present invention, respectively;
[0148] FIGS. 30 to 34: the results measuring the atomic ratio in
each precursor particle prepared in Examples 2-1 to 2-5 of the
present invention after heat-treating, respectively;
[0149] FIGS. 35 to 39 and FIGS. 40 to 44: the surface images of
each precursor particle and the final active material prepared in
Examples 2-1 to 2-5 of the present invention measured by scanning
electron microscope, respectively;
[0150] FIGS. 45 to 48: the results of charging/discharging test and
the results measuring cycle characteristics of each battery
prepared by using the active material prepared in Examples 2-1 to
2-4 of the present invention, respectively;
[0151] FIG. 49: the result of charging/discharging test and the
result measuring cycle characteristics of each battery prepared by
using the active material, which has the same concentration
gradient and is prepared in Example 2-3 of the present invention
prepared by using a CSTR reactor, and Example 2-5 of the present
invention prepared by using a BATCH reactor, respectively;
[0152] FIGS. 50 to 53: the results measuring heat flow of each
cathode including active materials prepared in Examples 2-1 to 2-4
of the present invention and active materials prepared in
Comparative examples 2-1 to 2-4, by charging at 4.3 V and then
heating at the speed of 10.degree. C./min by using a differential
scanning calorimeter (DSC), respectively;
[0153] FIG. 54: the results measuring heat flow of each cathode
including the active material, which has the same concentration
gradient and is prepared in Example 2-3 of the present invention
prepared by using a CSTR reactor, and Example 2-5 of the present
invention prepared by using a BATCH reactor, by charging at 4.3 V
and then heating at the speed of 10.degree. C./min by using a
differential scanning calorimeter (DSC), respectively;
[0154] FIG. 55: the result measuring the atomic ratio in the
precursor particle prepared in Example 3-1 of the present
invention;
[0155] FIG. 56: the results measuring the atomic ratio in the
precursor particle prepared in Example 3-1 of the present invention
after heat-treating;
[0156] FIGS. 57 to 58: the surface images of the precursor particle
and the final active material prepared in Example 3-1 of the
present invention measured by scanning electron microscope;
[0157] FIG. 59: the results of charging/discharging test and the
results measuring cycle characteristics of the battery prepared by
using the active material prepared in Example 3-1 of the present
invention; and
[0158] FIG. 60: the results measuring heat flow of each cathode
including active materials prepared in Example 3-1 of the present
invention and active materials prepared in Comparative example 3-1,
by charging at 4.3 V and then heating at the speed of 10.degree.
C./min by using a differential scanning calorimeter (DSC).
[0159] FIG. 61A illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a first embodiment of the inventive
concept.
[0160] FIG. 61B illustrates the positive electrode active material
containing the second element composed of the first element having
a rod shape according to a first embodiment of the inventive
concept.
[0161] FIG. 62 is a graph illustrating the change in content of the
first metal in the second element of the positive electrode active
material according to a first embodiment of the inventive
concept.
[0162] FIG. 63 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a second embodiment of the inventive
concept.
[0163] FIGS. 64 and 65 are graphs illustrating the change in
content of the first metal in the second element of the positive
electrode active material according to a second embodiment of the
inventive concept.
[0164] FIG. 66 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a third embodiment of the inventive
concept.
[0165] FIG. 67 is a graph illustrating the change in content of the
first metal in the second element of the positive electrode active
material according to a third embodiment of the inventive
concept.
[0166] FIG. 68 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a fourth embodiment of the inventive
concept.
[0167] FIGS. 69 and 70 are graphs illustrating the change in
content of the first metal in the second element of the positive
electrode active material according to a fourth embodiment of the
inventive concept.
[0168] FIG. 71 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a modified example of a fourth embodiment of
the inventive concept.
[0169] FIG. 72 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a fifth embodiment of the inventive
concept.
[0170] FIG. 73 is a graph illustrating the change in content of the
first metal in the second element of the positive electrode active
material according to a fifth embodiment of the inventive
concept.
[0171] FIG. 74 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a sixth embodiment of the inventive
concept.
[0172] FIGS. 75 and 76 are graphs illustrating the change in
content of the first metal in the second element of the positive
electrode active material according to a sixth embodiment of the
inventive concept.
[0173] FIG. 77 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a modified example of a sixth embodiment of
the inventive concept.
[0174] FIG. 78 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a seventh embodiment of the inventive
concept.
[0175] FIGS. 79 and 80 are graphs illustrating the change in
content of the first metal in the second element of the positive
electrode active material according to a seventh embodiment of the
inventive concept.
[0176] FIG. 81 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a modified example of a seventh embodiment of
the inventive concept.
[0177] FIG. 82 is a diagram for explaining a secondary battery
which contains the positive electrode active material according to
embodiments of the inventive concept.
[0178] FIG. 83 illustrates the concentrations of Ni, Mn, Co
depending on the distance from the center in the particles prepared
according to an embodiment of the inventive concept and Comparative
Example, which are measured by EDX.
[0179] FIG. 84 illustrates SEM images of the particles prepared
according to an embodiment of the inventive concept and Comparative
Example.
[0180] FIGS. 85 and 86 illustrate the measurement results on charge
and discharge characteristics, cycle-life characteristics, and DSC
characteristics of the batteries containing the active materials
prepared according to an embodiment of the inventive concept and
Comparative Example, respectively.
[0181] FIG. 87 illustrates the concentrations of Ni, Mn, Co
depending on the distance from the center in the particles prepared
according to an embodiment of the inventive concept and Comparative
Example, which are measured by EDX.
[0182] FIG. 88 illustrates the measurement results on charge and
discharge characteristics of the batteries containing the active
materials prepared according to an embodiment of the inventive
concept and Comparative Example.
[0183] FIGS. 89 and 90 illustrate the concentrations of Ni, Mn, Co
depending on the distance from the center in the particles prepared
according to embodiments of the inventive concept, which are
measured by EDX.
[0184] FIGS. 91 to 93 illustrate the measurement results on charge
and discharge characteristics, cycle-life characteristics, and DSC
characteristics of the particles prepared according to an
embodiment of the inventive concept and Comparative Example,
respectively.
[0185] FIGS. 94 to 96 illustrate the measurement results on charge
and discharge characteristics, cycle-life characteristics, and DSC
characteristics of the particles prepared according to an
embodiment of the inventive concept and Comparative Example,
respectively.
[0186] FIG. 97 illustrates the concentrations of Ni, Mn, Co
depending on the distance from the center in the particles prepared
according to an embodiment of the inventive concept, which are
measured by EDX.
[0187] FIGS. 98 to 100 illustrate the measurement results on charge
and discharge characteristics, cycle-life characteristics, and DSC
characteristics of the particles prepared according to an
embodiment of the inventive concept and Comparative Example,
respectively.
[0188] FIG. 101 illustrates the tap density and surface area by the
BET method of the particles prepared according to an embodiment of
the inventive concept and Comparative Example.
[0189] FIG. 102 illustrates the concentrations of Ni, Mn, Co
depending on the distance from the center in the particles prepared
according to an embodiment of the inventive concept, which are
measured by EDX.
[0190] FIGS. 103 to 105 illustrate the measurement results on
charge and discharge characteristics, cycle-life characteristics,
and DSC characteristics of the particles prepared according to an
embodiment of the inventive concept and Comparative Example,
respectively.
[0191] FIG. 106 illustrates the concentrations of Ni, Mn, Co
depending on the distance from the center in the particles prepared
according to an embodiment of the inventive concept, which are
measured by EDX.
[0192] FIGS. 107 to 109 illustrate the measurement results on
charge and discharge characteristics, cycle-life characteristics,
and DSC characteristics of the particles prepared according to an
embodiment of the inventive concept and Comparative Example,
respectively.
[0193] FIG. 110 illustrates the concentrations of Ni, Mn, Co
depending on the distance from the center in the particles prepared
according to an embodiment of the inventive concept measured by
EDX.
[0194] FIGS. 111 to 114 illustrate the measurement results on
charge and discharge characteristics, cycle-life characteristics,
and DSC characteristics of the batteries containing the active
materials prepared according to an embodiment of the inventive
concept and Comparative Example, respectively.
[0195] FIG. 115 illustrates the results of concentrations of Ni,
Mn, Co depending on the distance from the center in the particles
produced in Example of the inventive concept measured by EDX.
[0196] FIGS. 116 to 118 illustrate the results of charge and
discharge characteristics, lifespan characteristics, and DSC
characteristics measured on the particles produced in Example and
Comparative Examples of the inventive concept, respectively.
[0197] FIG. 119 illustrates the results of concentrations of Ni,
Mn, Co depending on the distance from the center in the particles
produced in Example of the inventive concept measured by EDX.
[0198] FIGS. 120 to 122 illustrate the results of charge and
discharge characteristics, lifespan characteristics, and DSC
characteristics measured on the particles produced in Example and
Comparative Examples of the inventive concept, respectively.
[0199] FIG. 123 illustrates the results of EDX measurement on the
cross-section of the active materials produced in Example and
Comparative Examples of the inventive concept.
[0200] FIGS. 124 and 125 illustrate the results of charge and
discharge characteristics and cycle-life characteristics measured
on the batteries which include the active materials produced in
Example and Comparative Examples of the inventive concept.
DETAILED DESCRIPTION OF THE INVENTION
[0201] The inventive concepts will now be described more fully
hereinafter with reference to the accompanying drawings, in which
exemplary embodiments of the inventive concepts are shown. The
advantages and features of the inventive concepts and methods of
achieving them will be apparent from the following exemplary
embodiments that will be described in more detail with reference to
the accompanying drawings. It should be noted, however, that the
inventive concepts are not limited to the following exemplary
embodiments, and may be implemented in various forms. Accordingly,
the exemplary embodiments are provided only to disclose the
inventive concepts and let those skilled in the art know the
category of the inventive concepts. In the drawings, embodiments of
the inventive concepts are not limited to the specific examples
provided herein and are exaggerated for clarity.
[0202] It will be understood that when an element such as a layer,
region or substrate is referred to as being "on" another element,
it can be directly on the other element or intervening elements may
be present. In contrast, the term "directly" means that there are
no intervening elements. In the drawings, the thicknesses of layers
and regions are exaggerated for clarity.
[0203] It will be understood that, although the terms "first",
"second", etc. may be used herein to describe various elements,
components, regions, layers and/or sections, these elements,
components, regions, layers and/or sections should not be limited
by these terms. These terms are only used to distinguish one
element, component, region, layer or section from another element,
component, region, layer or section. Thus, a first element,
component, region, layer or section discussed below could be termed
a second element, component, region, layer or section without
departing from the teachings of example embodiments. Exemplary
embodiments of aspects of the present inventive concepts explained
and illustrated herein include their complementary counterparts. As
used herein, the term "and/or" includes any and all combinations of
one or more of the associated listed items.
[0204] As used herein, the singular terms "a," "an" and "the" are
intended to include the plural forms as well, unless the context
clearly indicates otherwise. It will be further understood that the
terms "comprises", "comprising,", "includes" and/or "including",
when used herein, specify the presence of stated features,
integers, steps, operations, elements, and/or components, but do
not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof.
[0205] In addition, in explanation of the present invention, the
descriptions to the elements and functions of related arts may be
omitted if they obscure the subjects of the present invention.
[0206] The same reference numerals or the same reference
designators denote the same elements throughout the
specification.
[0207] In addition, the terms "to be constant" and/or "constant" as
described herein are interpreted to mean to be substantially
constant. In addition, the term "center part" as described herein
is interpreted to mean to include a region of the inside, but it is
not limited to the intermediate position and/or the central
position. In addition, the term "content" as described herein is
interpreted to include the atomic ratio and/or the
concentration.
[0208] In the present specification, that a concentration of a
metal has a concentration gradient may mean that the concentration
of the metal is substantially varied in a particle. In addition,
that a concentration of a metal is constant may mean that the
concentration of the metal is substantially constant in a
particle.
[0209] According to embodiments of the inventive concepts, a
positive active material for a lithium secondary battery may
include a particle including M1, M2, M3, and lithium (Li). The
particle may include a center, a surface, and an intermediate
portion disposed between the center and the surface.
[0210] M1, M2, and M3 may be transition metals of which kinds are
different from each other. For example, each of the M1, M2, and M3
may be nickel (Ni), cobalt (Co), manganese (Mn), or aluminum (Al).
Alternatively, in other embodiments, the particle may further
include M4 that is different from M1, M2, and M3. For example, M4
may include at least one of iron (Fe), sodium (Na), magnesium (Mg),
calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), copper
(Cu), zinc (Zn), germanium (Ge), strontium (Sr), silver (Ag),
barium (B a), zirconium (Zr), niobium (Nb), molybdenum (Mo),
aluminum (Al), gallium (Ga), or boron (B).
[0211] For example, the particle may include Li, Ni, Co, and Mn.
Alternatively, the particle may include Li, Ni, Co, and Al.
[0212] Concentrations of M1 and M2 may have continuous
concentration gradients from the center to at least the
intermediate portion.
[0213] In some embodiments, concentrations of M1, M2, and M3 may
have continuous concentration gradients in an entire region of the
particle. For example, the concentration of M1 (e.g., Ni) may
decrease from the center to the surface in the entire region of the
particle, and the concentrations of M2 (e.g., Co) and M3 (e.g., Mn)
may increase from the center to the surface in the entire region of
the particle. Alternatively, the concentrations of M1 (e.g., Ni)
and M2 (e.g., Co) may decrease from the center to the surface, and
the concentration of M3 (e.g., Mn) may increase from the center to
the surface.
[0214] In other embodiments, the concentrations of M1 (e.g., Co)
and M2 (e.g., Mn) may have continuous concentration gradients in
the entire region of the particle, and the concentration of M3
(e.g., Ni) may be substantially constant in the entire region of
the particle. For example, the concentration of M1 (e.g., Co) may
decrease from the center to the surface in the entire region of the
particle, the concentration of M2 (e.g., Mn) may increase from the
center to the surface in the entire region of the particle, and the
concentration of M3 (e.g., Ni) may be substantially constant in the
entire region of the particle.
[0215] In still other embodiments, the concentrations of M1 (e.g.,
Ni) and M2 (e.g., Co) may have continuous concentration gradients
in the entire region of the particle, the concentration of M3
(e.g., Al) may be substantially constant in the entire region of
the particle, and the concentration of M3 may be lower than the
concentrations of M1 and M2.
[0216] In yet other embodiments, the concentrations of M1, M2 and
M3 may have continuous concentration gradients from the center to
the intermediate portion and may be substantially constant from the
intermediate portion to the surface. In this case, for example, the
concentrations of M1, M2 and M3 from the intermediate portion to
the surface may be equal to the concentrations of M1, M2 and M3 at
the intermediate portion. In other words, the concentrations of M1,
M2 and M3 may be continuous from the center to the surface.
Alternatively, the concentrations of M1, M2 and M3 from the
intermediate portion to the surface may be different from the
concentrations of M1, M2 and M3 at the intermediate portion. In
other words, the concentrations of M1, M2 and M3 may be
discontinuous from the center to the surface.
[0217] In some embodiments, the particle may include a same
concentration portion. The concentration of M1 and the
concentration of M2 may be equal to each other in the same
concentration portion. A distance between the center and the same
concentration portion may be smaller than a distance between the
surface and the same concentration portion. For example, the same
concentration portion may be disposed between the center and the
intermediate portion. Alternatively, the same concentration portion
may be the center. In other words, the concentration of M1 and the
concentration of M2 may be equal to each other at the center of the
particle.
[0218] In some embodiments, the concentrations of M1, M2 and M3 may
have substantially constant concentration gradients from the center
to at least the intermediate portion. In other words, the
concentration gradients of M1, M2 and M3 may be constant from the
center to at least the intermediate portion. In certain
embodiments, the concentration gradients of M1, M2 and M3 may be
constant in the entire region of the particle.
[0219] In other embodiments, each of the concentrations of M1, M2
and M3 may have at least two concentration gradients from the
center to at least the intermediate portion. For example, a
magnitude of each of the concentration gradients of M1, M2 and M3
may decrease or increase from the center to at least the
intermediate portion. Alternatively, each of the concentrations of
M1, M2 and M3 from the center to at least the intermediate portion
may increase and then decrease or may decrease and then increase.
In this case, each of the concentration gradients of M1, M2 and M3
from the center to at least the intermediate portion may have a
vertex.
[0220] In still other embodiments, the concentrations of M1, M2 and
M3 from the center to at least the intermediate portion may have
curved shapes.
[0221] In some embodiments, at least one concentration gradient
portion and at least one concentration maintained portion may be
provided between the intermediate portion and the surface. The
concentrations of M1, M2 and M3 of the concentration gradient
portion may have gradients, and the concentrations of M1, M2 and M3
of the concentration maintained portion may be constant.
[0222] The first embodiment of the inventive concept will be
described with FIGS. 1 to 24.
[0223] Unlike the prior art that the metal concentration is
constant at the interior region, but the metal concentration shows
gradual concentration gradient at the exterior region, in the
cathode active material of the present invention, all metals making
up the cathode active material show continuous concentration
gradient in the whole region from the particle core to the surface
part.
[0224] Namely, in the cathode active material of the present
invention, the concentrations of all metals making up the cathode
active material are increased or decreased with continuous
concentration gradient in the whole region from the particle core
to the surface part.
[0225] The present invention is characterized that the
concentrations of the M1 and the M2 are increased with continuous
concentration gradient from the core to the surface part, and the
concentration of the M3 is decreased with continuous concentration
gradient from the core to the surface part.
[0226] Further, the present invention is characterized that the
concentration of the M2 is increased with continuous concentration
gradient from the core to the surface part, and the concentrations
of the M1 and the M3 are decreased with continuous concentration
gradient from the core to the surface part.
[0227] In the present invention, "metal concentration shows
continuous concentration gradient" refers that the concentration of
metal except for lithium exists with concentration distribution,
which is changed gradually from the core of the active material
particle to the surface part. The concentration gradient refers
that there may be metal concentration difference of 0.1 to 30 mol
%, preferably 0.1 to 20 mol %, more preferably 1 to 10 mol % per
0.1 .mum, from the particle core to the surface part. In the
present invention, the particle core refers to the range within the
diameter 0.2 .mum from the center of the active material particle,
and the particle surface part refers to the range within the
diameter 0.2 .mum from the outermost of the particle.
[0228] In the present invention, it is preferred that the
concentration gradients of the M1, the M2 and the M3 are constant
from the particle core to the surface part. Namely, in the present
invention, in terms of the structure stability, it is preferred
that the concentrations of the M1 and the M2 are continuously
increased as continuous concentration gradient form the core to the
surface part, and the concentration of the M3 is continuously
decreased as continuous concentration gradient from the core to the
surface part. Further, in the present invention, in terms of the
structure stability, it is preferred that the concentration of the
M2 is continuously increased as continuous concentration gradient
from the core to the surface part, and the concentrations of the M1
and the M3 are continuously decreased as continuous concentration
gradient from the core to the surface part.
[0229] In the present invention, the M1 may be Co, the M2 may be
Mn, and the M3 may be Ni. Namely, the concentration of the Ni is
decreased in the whole particle, the concentration of the Mn is
increased in the whole particle, and the concentration of the Co
shows concentration gradient in the whole particle, but any
structure of increase or decrease may be used.
[0230] In the present invention, it is preferred that the
concentration range of the M3 at the core, z1 may be
0.6.ltoreq.z1.ltoreq.1 so as to maintain the nickel concentration
in the core high, and the concentration difference of the nickel
between the core and the surface part of the M3 may be
0.2.ltoreq.|z2-z|.ltoreq.0.4 so as to show thermostability and to
prevent the capacity reduction.
[0231] In the present invention, it is preferred that the
concentration range of the M1 at the core, x1 may be
0.ltoreq.x1.ltoreq.0.2, and the concentration difference between
the core and the surface part of the M1 may be
0.05.ltoreq.|x2-x1|.ltoreq.0.1, so as to reduce the amount of the
Co and to prevent the capacity reduction at the same time.
[0232] In the present invention, it is preferred that the
concentration range of the M2 at the core, y1 may be
0.ltoreq.y1.ltoreq.0.1 and the Mn content a the surface par may be
0.2 or more, so as to have thermostability and the prevent the
capacity reduction at the same time, and the concentration
difference of the manganese between the core and the surface part
of the M2 may be 0.2.ltoreq.|y2-y|.ltoreq.0.4.
[0233] Hereinafter, an example method for preparing the cathode
active material of the present invention will be described.
[0234] First of all, a metal salt aqueous solution for forming the
core and a metal salt aqueous solution for forming the surface
part, which contain the M1, the M2 and the M3 as a metal salt
aqueous solution, wherein the concentrations of the M1, the M2 and
the M3 are different each other, are prepared.
[0235] The metal salt aqueous solution for forming the core and the
metal salt aqueous solution for forming the surface part may be
prepared by adding nickel salt, cobalt salt, manganese salt and
salts containing M to a solvent, or may be prepared by preparing
aqueous solution containing nickel salt, cobalt salt, manganese
salt and salts containing M, respectively followed by mixing
thereof for using. The metal salt may be sulfate, nitrate, acetate,
halide, hydroxide and the like, and it may be any salt, which can
be dissolved in water, without particular limitation.
[0236] Then, the metal salt aqueous solution for forming the core
and the metal salt aqueous solution for forming the surface part
are mixed together and simultaneously, the chelating agent and the
basic aqueous solution are mixed in a reactor so as to obtain a
precipitate wherein the concentrations of the M1, the M2 and the M3
have continuous concentration gradients from the core to the
surface part.
[0237] In the present invention, a precipitate having continuous
concentration gradient from the particle core to the surface part,
from the particle forming process through one coprecipitation
process, by mixing the metal salt aqueous solution for forming the
core and the metal salt aqueous solution for forming the surface
part from the initial stage of the particle forming process and
supplying thereof continuously at the same time. The produced
concentration gradient and its gradient may be controlled according
to the compositions and the mixing and supplying ratio of the metal
salt aqueous solution for forming the core and the metal salt
aqueous solution for forming the surface part. The entire particle
size may be controlled by adjusting the reaction time to 1 to 10
hours.
[0238] Further, the present invention is characterized that the
molar ratio of the chelating agent and the metal salt may be 0.2 to
1.0:1.
[0239] The chelating agent may be ammonia aqueous solution,
ammonium sulfate aqueous solution and a combination thereof. It is
preferred that the molar ratio of the chelating agent and the metal
salt may be 0.2 to 0.5:1, 0.2 to 0.4:1. The reason to set the molar
ratio of the chelating agent to 0.2 to 1.0 based on the metal
aqueous solution 1 mole, is that the chelating agent forms a
complex by reacting with metal at the ratio of 1:1 or more, but the
chelating agent remained after the reaction of sodium hydroxide and
the complex may be changed to intermediates and then recovered as
the chelating agent. Furthermore, the reason is that it is the best
condition for improving and stabilizing the crystallinity of the
cathode active material.
[0240] The concentration of the basic aqueous solution may be 2 M
to 10 M, preferably. If the concentration of the basic aqueous
solution is less than 2 M, particle forming may take longer, tap
density may be deteriorated, and the yield of the co-precipitation
reaction product may be reduced. And, if the concentration is over
10 M, it is not preferred because it may be difficult to form
homogeneous particles due to rapid particle growth by rapid
reaction, and the tap density may be also reduced.
[0241] In the second step, the reaction atmosphere of the
transition metal aqueous solution may be under a nitrogen flow, pH
may be within 10 to 12.5, reaction temperature is within 30 to
80.degree. C., and reaction stirring speed may be within 100 to
2000 rpm, preferably.
[0242] Then, in the third step, the obtained precipitate may be
dried or heat-treated to prepare an active material precursor. The
drying process may be conducted at 110.degree. C. to 400.degree. C.
for 15 to 30 hours.
[0243] Finally, the active material precursor and the lithium salt
are mixed and then heat-treated to obtain an active material.
[0244] It is preferred that the heat-treating process after mixing
the active material precursor and the lithium salt may be conducted
at 700.degree. C. to 1100.degree. C. The heat-treating atmosphere
may be in an oxidative atmosphere of air or oxygen or a reductive
atmosphere of nitrogen or hydrogen, preferably, and the
heat-treating time may be 10 to 30 hours, preferably. During this
heat-treating process, metal may be diffused even at the part where
the internal metal concentration is constant, and consequently, a
metal oxide having continuous metal concentration distribution from
the core to the surface may be obtained.
[0245] Before the heat-treating process, a pre-calcining process
may be conducted by maintaining at 250 to 650.degree. C. for 5 to
20 hours. Further, after the heat-treating process, an annealing
process may be conducted at 600 to 750.degree. C. for 10 to 20
hours.
[0246] Further, the present invention may further include a step of
adding sintering additives when mixing the active material
precursor and the lithium salt, preferably. The sintering additives
may be any one selected from the group consisting of compounds
containing ammonium ion, metal oxides, metal halides and a
combination thereof, preferably.
[0247] The compounds containing ammonium ion may be any one
selected from the group consisting of NH.sub.4F, NH.sub.4NO.sub.3,
(NH.sub.4).sub.2SO.sub.4, and a combination thereof, preferably;
the metal oxides may be any one selected from the group consisting
of B.sub.2O.sub.3, Bi.sub.2O.sub.3, and a combination thereof,
preferably; and the metal halides may be any one selected from the
group consisting of NiCl.sub.2, CaCl.sub.2, and a combination
thereof, preferably.
[0248] The sintering additives may be used in an amount of
0.01.about.0.2 mole based on the active material precursor 1 mole,
preferably. If the amount of the sintering additives is too low,
the sintering effect of the active material precursor may not be
improved a lot, and if the amount is higher than the said range,
the initial capacity during charging/discharging may be reduced or
the performance of the cathode active material may be
deteriorated.
[0249] Further, the present invention provides a lithium secondary
battery including the cathode active material according to the
present invention.
[0250] The lithium battery may include a cathode including the
cathode active material having the above constitution, an anode
including anode active material and a separator existing between
thereof. Further, it may include an electrolyte, which is immersed
in the cathode, the anode and the separator. The anode active
material may be a material which can reversibly absorb or release
lithium ions, preferably, for example, a material including
artificial graphite, natural graphite, graphitized carbon fiber,
amorphous Carbon, and metal lithium also can be used as a cathode
active material. The electrolyte may be a liquid electrolyte
containing lithium salts and non-aqueous organic solvent, or
polymer gel electrolyte.
EXAMPLES
[0251] Hereinafter, the present invention is explained by the
following Examples and Test Examples in more detail. The following
Examples and Test Examples are intended to further illustrate the
present invention, and the scope of the present invention cannot be
limited thereby in any way.
Examples 1
Example 1-1
[0252] In order to prepare a compound, wherein the Ni concentration
is continuously decreased from the core to the surface, the Co and
the Mn concentrations are continuously increased, a 2.4 M metal
aqueous solution, prepared by mixing nickel sulfate and cobalt
sulfate at the molar ratio of 80:20, as a metal salt aqueous
solution for forming the core and a metal aqueous solution
containing nickel sulfate, cobalt sulfate and manganese sulfate at
the molar ratio of 55:15:30 as a metal salt aqueous solution for
forming the surface part were prepared.
[0253] Distilled water 4 L was put into a coprecipitation reactor
(Capacity: 4 L, power of a rotation motor: 80 W); nitrogen gas was
supplied to the reactor at the speed of 0.5 L/min so as to remove
dissolved oxygen; and stirred at 1000 rpm while maintaining the
temperature of the reactor at 50.degree. C.
[0254] The metal salt aqueous solution for forming the core and the
metal salt aqueous solution for forming the surface part were mixed
at a certain ratio, and simultaneously supplied into the reactor at
the rate of 0.3 L/hour. Further, 3.6 M ammonia solution was
continuously supplied into the reactor at the rate of 0.03 L/hour.
Further, for adjusting pH, 4.8 M NaOH aqueous solution was supplied
to maintain pH in the reactor at 11. Then, the impeller speed of
the reactor was controlled to 1000 rpm, and the co-precipitation
reaction was conducted until the diameter of the obtained
precipitate became 1 .mum. At this time, the flow rate was
controlled to make the average retention time of the solution in
the reactor about 2 hours, and after the reaction reached to the
steady state, the reactant was kept at the steady state for a
certain time to so as to obtain a co-precipitated compound having
higher density. The compound was filtered, washed with water, and
dried with 110.degree. C. warm air dryer for 15 hours so as to
obtain an active material precursor.
[0255] LiNO.sub.3 as a lithium salt was mixed to the obtained
active material precursor, heated at a rate of 2.degree. C./min,
and then pre-calcined by maintaining at 280.degree. C. for 10 hours
followed by calcining at 750.degree. C. for 15 hours to obtain a
final active material particle. The size of the finally obtained
active material particle was 12 .mu.m.
Example 1-2 to Example 1-5
[0256] The procedure of Example 1-1 was repeated except for mixing
nickel sulfate, cobalt sulfate and manganese sulfate of the metal
salt aqueous solution for forming the core and the metal salt
aqueous solution for forming the surface part at the molar ratio as
listed in the following Table 1 so as to obtain an active material
particle.
Example 1-6
[0257] A cathode active material, which has the same composition
with Examples 1-1 was prepared by using a batch reactor.
[0258] Distilled water 2.5 L was put into a coprecipitation batch
reactor (Capacity: 8 L, power of a rotation motor: 180 W); nitrogen
gas was supplied to the reactor at the speed of 0.6 L/min so as to
remove dissolved oxygen; and stirred at 450 rpm while maintaining
the temperature of the reactor at 50.degree. C.
[0259] The metal salt aqueous solution for forming the core and the
metal salt aqueous solution for forming the surface part having the
same concentration with Example 1-3 were mixed at a certain ratio,
and simultaneously supplied into the reactor at the rate of 0.2
L/hour. Further, 4.8 M ammonia solution was continuously supplied
into the reactor at the rate of 0.1 L/hour. Further, for adjusting
pH, 10 M NaOH aqueous solution was supplied to maintain pH in the
reactor at 11. Then, the impeller speed of the reactor was
controlled to 450 rpm, and the reaction solution was supplied until
the total amount of the initially added distilled water, the added
metal aqueous solution, the ammonia solution and the NaOH solution
became 8 L. The compound was filtered, washed with water, and dried
with 110.degree. C. warm air dryer for 15 hours so as to obtain an
active material precursor.
[0260] LiNO.sub.3 as a lithium salt was mixed to the obtained
active material precursor, heated at a rate of 2.degree. C. min,
and then pre-calcined by maintaining at 280.degree. C. for 10 hours
followed by calcining at 750.degree. C. for 15 hours to obtain a
final active material. The size of the finally obtained active
material particle was 12 .mu.m.
TABLE-US-00001 TABLE 1-1 Metal salt aqueous solution Metal salt
aqueous solution for forming the core for forming the surface part
Ni Co Mn Ni Co Mn Example 1 90 10 0 55 15 30 Example 2 90 10 0 60
13 27 Example 3 90 10 0 65 05 33 Example 4 90 10 0 75 05 20 Example
5 85 10 5 70 05 25 Example 6 90 10 0 55 15 30
Comparative Example
[0261] An cathode active material, wherein the molar ratio of the
nickel, the cobalt and the manganese is as listed in the following
Table 1-2, respectively, and each concentration in the whole active
material is not changed so as to have constant composition, was
prepared.
TABLE-US-00002 TABLE 1-2 Ni Co Mn Comparative Example 1 80 07 13
Comparative Example 2 75 07 18 Comparative Example 3 70 09 21
Comparative Example 4 65 10 25 Comparative Example 5 75 07 18
Comparative Example 6 90 10 0 Comparative Example 7 85 10 5
Test Example 1-1
Confirmation of Concentration Gradient Structure in Precursor
Particle
[0262] In order to confirm the concentration gradient structure of
each metal from the core to the surface of the precursor particle
of the present invention, the atomic ratio in each precursor
particle prepared in Examples 1-1 to I-6 was measured by using EPMA
(Electron Probe Micro Analyzer) while moving form the core to the
surface part, and the results are shown in FIGS. 1 to 6,
respectively.
[0263] As shown in FIGS. 1 to 6, it was confirmed that in the case
of the precursors prepared in Examples 1-1 to 1-6, the Ni metal
concentration from the core to the surface was decreased, and the
Mn and Co concentrations were gradually increased with certain
gradient.
Test Example 1-2
Confirmation of Concentration Gradient Structure in Active Material
Particle after Heat-Treatment
[0264] In order to confirm whether each metal shows concentration
gradient from the particle core to the surface part after
heat-treating the precursor of the present invention, the atomic
ratio was measured by using EPMA (Electron Probe Micro Analyzer)
while moving from the core to the surface, and the results are
shown in FIGS. 7 to 12, respectively.
[0265] In FIGS. 6 to 9, it could be confirmed that: the Ni metal
concentration was decreased, and the concentrations of the Co and
the Mn at the core were little changed by the diffusion between the
metal salts, but the Co and Mn concentrations were gradually
increased with certain gradient.
Test Example 1-3
Measuring Charging/Discharging Capacity and Cycle
Characteristics
[0266] Cathodes were prepared by using the active materials
prepared in Examples 1-1 to 1-6 and the active materials prepared
in Comparative Examples 1-1 to 1-7, and applied to cylindrical
lithium secondary batteries, respectively.
[0267] For the batteries prepared by using the active materials
prepared in Examples 1-1 to 1-6, charging/discharging test and
cycle characteristics were measured, and the results are shown in
FIGS. 13 to 18. The charging/discharging was conducted 10 times per
each sample at the condition of 2.7.about.4.3 V and 0.2 C, and the
average value was taken.
[0268] In FIGS. 13 to 18, the results of charging/discharging of
Examples 1-1 to 1-6, Comparative Examples corresponding to each
bulk composition and Comparative Examples representing each core
composition are shown. In FIGS. 13 to 18, Examples 1-1 to 1-6
showed similar charging/discharging characteristics with
Comparative Examples corresponding to each bulk composition, but
Comparative Examples representing the core composition showed very
poor charging/discharging characteristics.
Test Example 1-4
Evaluation of Thermostability by DSC Measurement
[0269] The cathodes containing the active materials prepared in
Examples 1-1 to 1-6 and the active materials prepared in
Comparative Examples 1-1 to 1-4, were charged at 4.3 V,
respectively, and thermostability was measured by using a
differential scanning calorimeter (DSC) and heating at a rate of
10.degree. C./min. The results are shown in FIGS. 19 to 24.
[0270] As shown in FIGS. 19 to 24, the results of
charging/discharging of Examples 1-1 to 1-6, Comparative Examples
corresponding to each bulk composition and Comparative Examples
representing each core composition are shown.
[0271] As shown in FIGS. 19 to 24, when the active materials
prepared in Examples 1-1 to 1-6 according to the present invention
were contained, an exothermic peak was showed at the higher
temperature than Comparative Examples corresponding to each bulk
composition and Comparative Examples representing each core
composition. Thus, when the active materials prepared in Examples
1-1 to 1-6 according to the present invention were contained, the
thermostability was much improved than when the active materials
prepared in Comparative Examples 1-1 to 1-7 were contained.
[0272] Namely, in the present invention, the concentrations of all
metals are increased or decreased with continuous concentration
gradient from the core to the surface part. Accordingly, because
the structures are not rapidly changed and show stability, it could
be confirmed that the thermostability is largely increased.
[0273] The second embodiment of the inventive concept will be
described with FIGS. 25 to 60.
[0274] Unlike the prior art that the metal concentration is
constant at the interior region, but the metal concentration shows
gradual concentration gradient at the exterior region, in the
cathode active material of the present invention, a part of the
metal shows continuous concentration gradient at the whole region
from the particle core to the surface part, but the other one metal
shows constant metal concentration at the whole region from the
particle core to the surface part.
[0275] In the cathode active material particle of the present
invention, one of metals making up the cathode active material
shows constant metal concentration at the whole region from the
particle core to the surface part, but the other two metals show
decreased or increased continuous concentration gradient at the
whole region from the particle core to the surface part.
[0276] Namely, the present invention is characterized that the
concentration of the M2 is increased with continuous concentration
gradient from the core to the surface part, and the concentration
of the M3 is decreased with continuous concentration gradient from
the core to the surface part.
[0277] In the present invention, "metal concentration shows
continuous concentration gradient" refers that the concentration of
metal except for lithium exists with concentration distribution,
which is changed gradually from the core of the active material
particle to the surface part. The concentration gradient refers
that there may be metal concentration difference of 0.1 to 30 mol
%, preferably 0.1 to 20 mol %, more preferably 1 to 10 mol % per
0.1 .mum, from the particle core to the surface part. In the
present invention, the particle core refers to the range within the
diameter 0.2 .mum from the center of the active material particle,
and the particle surface part refers to the range within the
diameter 0.2 .mum from the outermost of the particle.
[0278] The present invention is characterized that the
concentration gradients of the M2 and the M3 should be constant
from the particle core to the surface, i.e., the concentrations of
the M2 and the M3 may be continuously changed at the whole
particle, preferably.
[0279] The present invention is characterized that the M1 is Ni,
the M2 is Mn and the M3 is Co. The Ni concentration is maintained
constantly so as to obtain high capacity, and the Mn concentration
becomes increased at the surface and the Co concentration becomes
decreased at the surface so as to obtain higher stability.
[0280] In the present invention, the constant concentration range
of the M1, i.e., Ni, x may be 0.4.ltoreq.x.ltoreq.1, and it is more
preferred that the Ni concentration should be maintained at high
concentration of 0.6.ltoreq.x.ltoreq.0.9.
[0281] In the present invention, when the M1 is Ni, the
concentration difference of the Co and the Mn between the particle
core and the particle surface may be 0.2.ltoreq.|y2-y1|0.4,
0.2.ltoreq.|z2-z1|.ltoreq.0.4, preferably, because there may be no
rapid concentration change. And the concentrations of the Mn and
the Co at the surface may be 0.2.ltoreq.y2.ltoreq.0.4,
0.ltoreq.z2.ltoreq.0.1, preferably. The Mn content at the surface
should be 0.2 or more to obtain thermostability and to prevent
capacity reduction.
[0282] The present invention is characterized that the M1 is Co,
the M2 is Mn and the M3 is Ni.
[0283] The present invention is characterized that the M1 is Mn,
the M2 is Co and the M3 is Ni.
[0284] Hereinafter, another method for preparing the cathode active
material of the present invention will be described.
[0285] First of all, a metal salt aqueous solution for forming the
core and a metal salt aqueous solution for forming the surface
part, which contain the M1, the M2 and the M3 as a metal salt
aqueous solution, wherein the concentration of the M1 is the same
each other, and the concentration of the M2 and the concentration
of the M3 are different each other, are prepared. The present
invention is characterized that in order to constantly maintain the
concentration of the M1 in the whole particle, the M1 concentration
may be maintained same at the metal salt aqueous solution for
forming the core and the metal salt aqueous solution for forming
the surface part.
[0286] The metal salt aqueous solution for forming the core and the
metal salt aqueous solution for forming the surface part may be
prepared by adding nickel salt, cobalt salt, manganese salt and
salts containing M to a solvent, or may be prepared by preparing
aqueous solution containing nickel salt, cobalt salt, manganese
salt and salts containing M, respectively followed by mixing
thereof for using. The metal salt may be sulfate, nitrate, acetate,
halide, hydroxide and the like, and it may be any salt, which can
be dissolved in water, without particular limitation.
[0287] Then, the metal salt aqueous solution for forming the core
and the metal salt aqueous solution for forming the surface part
are mixed together and simultaneously, the chelating agent and the
basic aqueous solution are mixed in a reactor so as to obtain a
precipitate wherein the M1 concentration is constant from the core
to the surface, and the M2 and M3 concentrations have continuous
concentration gradients from the core to the surface part. Namely,
the metal salt aqueous solution for forming the core and the metal
salt aqueous solution for forming the surface part are mixed at the
mixing ratio, which is gradually changed from 100 v %:0 v % to 0 v
%:100 v %, and simultaneously, the chelating agent and the basic
aqueous solution are mixed in a reactor, so as to form a
precipitate, wherein the M1 concentration is constant from the core
to the surface, and the M2 and M3 concentrations have continuous
concentration gradients from the core to the surface part.
[0288] In the present invention, a precipitate having continuous
concentration gradient from the particle core to the surface part,
from the particle forming process through one coprecipitation
process, by mixing the metal salt aqueous solution for forming the
core and the metal salt aqueous solution for forming the surface
part from the initial stage of the particle forming process and
supplying thereof continuously at the same time. The produced
concentration gradient and its gradient may be controlled according
to the compositions and the mixing ratio of the metal salt aqueous
solution for forming the core and the metal salt aqueous solution
for forming the surface part. The entire particle size may be
controlled by adjusting the reaction time to 1 to 10 hours.
[0289] Further, the present invention is characterized that the
molar ratio of the chelating agent and the metal salt may be 0.2 to
1.0:1.
[0290] The chelating agent may be ammonia aqueous solution,
ammonium sulfate aqueous solution and a combination thereof. It is
preferred that the molar ratio of the chelating agent and the metal
salt may be 0.2 to 0.5:1, 0.2 to 0.4:1. The reason to set the molar
ratio of the chelating agent to 0.2 to 1.0 based on the metal
aqueous solution 1 mole, is that the chelating agent forms a
complex by reacting with metal at the ratio of 1:1 or more, but the
chelating agent remained after the reaction of sodium hydroxide and
the complex may be changed to intermediates and then recovered as
the chelating agent. Furthermore, the reason is that it is the best
condition for improving and stabilizing the crystallinity of the
cathode active material.
[0291] The concentration of the basic aqueous solution may be 2 M
to 10 M, preferably. If the concentration of the basic aqueous
solution is less than 2 M, particle forming may take longer, tap
density may be deteriorated, and the yield of the co-precipitation
reaction product may be reduced. And, if the concentration is over
10 M, it is not preferred because it may be difficult to form
homogeneous particles due to rapid particle growth by rapid
reaction, and the tap density may be also reduced.
[0292] In the second step, the reaction atmosphere of the
transition metal aqueous solution may be under a nitrogen flow, pH
may be within 10 to 12.5, reaction temperature is within 30 to
80.degree. C., and reaction stirring speed may be within 100 to
2000 rpm, preferably.
[0293] Then, in the third step, the obtained precipitate may be
dried or heat-treated to prepare an active material precursor. The
drying process may be conducted at 110.degree. C. to 400.degree. C.
for 15 to 30 hours.
[0294] Finally, the active material precursor and the lithium salt
are mixed and then heat-treated to obtain an active material.
[0295] It is preferred that the heat-treating process after mixing
the active material precursor and the lithium salt may be conducted
at 700.degree. C. to 1100.degree. C. The heat-treating atmosphere
may be in an oxidative atmosphere of air or oxygen or a reductive
atmosphere of nitrogen or hydrogen, preferably, and the
heat-treating time may be 10 to 30 hours, preferably. During this
heat-treating process, metal may be diffused even at the part where
the internal metal concentration is constant at the initial stage
of the particle forming process, and consequently, a metal oxide
having continuous metal concentration distribution from the core to
the surface part in the whole particle may be obtained.
[0296] Before the heat-treating process, a pre-calcining process
may be conducted by maintaining at 250 to 650.degree. C. for 5 to
20 hours. Further, after the heat-treating process, an annealing
process may be conducted at 600 to 750.degree. C. for 10 to 20
hours.
[0297] Further, the present invention may further include a step of
adding sintering additives when mixing the active material
precursor and the lithium salt, preferably. The sintering additives
may be any one selected from the group consisting of compounds
containing ammonium ion, metal oxides, metal halides and a
combination thereof, preferably.
[0298] The compounds containing ammonium ion may be any one
selected from the group consisting of NH.sub.4F, NH.sub.4NO.sub.3,
(NH.sub.4).sub.2SO.sub.4, and a combination thereof, preferably;
the metal oxides may be any one selected from the group consisting
of B.sub.2O.sub.3, Bi.sub.2O.sub.3, and a combination thereof,
preferably; and the metal halides may be any one selected from the
group consisting of NiCl.sub.2, CaCl.sub.2, and a combination
thereof, preferably.
[0299] The sintering additives may be used in an amount of
0.01.about.0.2 mole based on the active material precursor 1 mole,
preferably. If the amount of the sintering additives is too low,
the sintering effect of the active material precursor may not be
improved a lot, and if the amount is higher than the said range,
the initial capacity during charging/discharging may be reduced or
the performance of the cathode active material may be
deteriorated.
[0300] Further, the present invention provides a lithium secondary
battery including the cathode active material according to the
present invention.
[0301] The lithium battery may include a cathode including the
cathode active material having the above constitution, a cathode
including cathode active material and a separator existing between
thereof. Further, it may include an electrolyte, which is immersed
in the cathode, the cathode and the separator. The cathode active
material may be a material which can reversibly absorb or release
lithium ions, preferably, for example, a material including
artificial graphite, natural graphite, graphitized carbon fiber,
Amorphous Carbon, and metal lithium also can be used as a cathode
active material. The electrolyte may be a liquid electrolyte
containing lithium salts and non-aqueous organic solvent, or
polymer gel electrolyte.
Examples 2
Case of Constant Nickel Concentration
Example 2-1
[0302] In order to prepare a compound, wherein the Ni concentration
is constant from the core to the surface, the Co concentration is
decreased, and the Mn concentration is increased, a 2.4 M metal
aqueous solution, prepared by mixing nickel sulfate and cobalt
sulfate at the molar ratio of 80:20, as a metal salt aqueous
solution for forming the core and a metal aqueous solution
containing nickel sulfate and manganese sulfate at the molar ratio
of 80:20 as a metal salt aqueous solution for forming the surface
part were prepared. Distilled water 4 L was put into a
coprecipitation reactor (Capacity: 4 L, power of a rotation motor:
80 W); nitrogen gas was supplied to the reactor at the speed of 0.5
L/min so as to remove dissolved oxygen; and stirred at 1000 rpm
while maintaining the temperature of the reactor at 50.degree.
C.
[0303] The metal salt aqueous solution for forming the core and the
metal salt aqueous solution for forming the surface part were mixed
at a certain ratio, and simultaneously supplied into the reactor at
the rate of 0.3 L/hour. Further, 3.6 M ammonia solution was
continuously supplied into the reactor at the rate of 0.03 L/hour.
Further, for adjusting pH, 4.8 M NaOH aqueous solution was supplied
to maintain pH in the reactor at 11. Then, the impeller speed of
the reactor was controlled to 1000 rpm, and the co-precipitation
reaction was conducted until the diameter of the obtained
precipitate became 1 .mum. At this time, the flow rate was
controlled to make the average retention time of the solution in
the reactor about 2 hours, and after the reaction reached to the
steady state, the reactant was kept at the steady state for a
certain time to so as to obtain a co-precipitated compound having
higher density. The compound was filtered, washed with water, and
dried with 110.degree. C. warm air dryer for 15 hours so as to
obtain an active material precursor.
[0304] LiNO.sub.3 as a lithium salt was mixed to the obtained
active material precursor, heated at a rate of 2.degree. C./min,
and then pre-calcined by maintaining at 280.degree. C. for 10 hours
followed by calcining at 750.degree. C. for 15 hours to obtain a
final active material particle. The size of the finally obtained
active material particle was 12 .mu.m.
Example 2-2 to Example 2-4
[0305] In order to prepare a compound, wherein the Ni concentration
is constant from the core to the surface, the Co concentration is
decreased and the Mn concentration is increased, the procedure of
Example 2-1 was repeated except for mixing nickel sulfate, cobalt
sulfate and manganese sulfate of the metal salt aqueous solution
for forming the core and the metal salt aqueous solution for
forming the surface part at the molar ratio as listed in the
following Table 3 so as to obtain an active material particle.
Example 2-5
[0306] An cathode active material, which has the same composition
and the same structure with Examples 2-3 was prepared by using a
batch reactor.
[0307] Distilled water 2.5 L was put into a coprecipitation batch
reactor (Capacity: 8 L, power of a rotation motor: 180 W); nitrogen
gas was supplied to the reactor at the speed of 0.6 L/min so as to
remove dissolved oxygen; and stirred at 450 rpm while maintaining
the temperature of the reactor at 50.degree. C.
[0308] The metal salt aqueous solution for forming the core and the
metal salt aqueous solution for forming the surface part having the
same concentration with Example 2-3 were mixed at a certain ratio,
and simultaneously supplied into the reactor at the rate of 0.2
L/hour. Further, 4.8 M ammonia solution was continuously supplied
into the reactor at the rate of 0.1 L/hour. Further, for adjusting
pH, 10 M NaOH aqueous solution was supplied to maintain pH in the
reactor at 11. Then, the impeller speed of the reactor was
controlled to 450 rpm, and the reaction solution was supplied until
the total amount of the initially added distilled water, the added
metal aqueous solution, the ammonia solution and the NaOH solution
became 8 L. The compound was filtered, washed with water, and dried
with 110.degree. C. warm air dryer for 15 hours so as to obtain an
active material precursor.
[0309] LiNO.sub.3 as a lithium salt was mixed to the obtained
active material precursor, heated at a rate of 2.degree. C./min,
and then pre-calcined by maintaining at 280.degree. C. for 10 hours
followed by calcining at 750.degree. C. for 15 hours to obtain a
final active material. The size of the finally obtained active
material particle was 12 .mu.m.
TABLE-US-00003 TABLE 3 Metal salt aqueous solution Metal salt
aqueous solution for forming the core for forming the surface part
Example 80 20 0 80 0 20 2-1 Example 75 25 0 75 02 23 2-2 Example 70
30 0 70 02 28 2-3 Example 65 35 0 65 02 33 2-4 Example 70 30 0 70
02 28 2-5
Comparative Example
[0310] An cathode active material, wherein the molar ratio of the
nickel, the cobalt and the manganese is as listed in the following
Table 4, respectively, and each concentration in the whole active
material is not changed so as to have constant composition, was
prepared.
TABLE-US-00004 TABLE 4 Ni Co Mn Comparative Example 2-1 80 07 13
Comparative Example 2-2 75 07 18 Comparative Example 2-3 70 09 21
Comparative Example 2-4 65 10 25
Test Example 2-1
Confirmation of Formation of Concentration Gradient in Precursor
Particle
[0311] In order to confirm the concentration gradient structure of
each metal from the core to the surface of the precursor particle
of the present invention, the atomic ratio in each precursor
particle prepared in Examples 2-1 to 2-5 was measured by using EPMA
(Electron Probe Micro Analyzer) while moving form the core to the
surface part, and the results are shown in FIGS. 25 to 29,
respectively.
[0312] In FIGS. 25 to 28, it was confirmed that the Ni metal
concentration from the core to the surface was constant, and there
was concentration gradient, where the Mn concentration was
gradually increased with certain gradient, but the Co concentration
was gradually decreased with certain gradient.
[0313] Further, for Example 2-5 prepared by using the batch type
reactor, as shown in FIG. 29, it was confirmed that the Ni metal
concentration from the core to the surface was constant, and there
was concentration gradient, where the Mn concentration was
gradually increased with certain gradient, but the Co concentration
was gradually decreased with certain gradient.
Test Example 2-2
Confirmation of Formation of Concentration Gradient in Active
Material Particle after Heat-Treatment
[0314] In order to confirm whether each metal shows concentration
gradient from the particle core to the surface part after
heat-treating the precursor of the present invention, the particles
prepared in Examples 2-1 to 2-5 were heat-treated. And then the
atomic ratio was measured by using EPMA (Electron Probe Micro
Analyzer) while moving from the core to the surface, and the
results are shown in FIGS. 30 to 34, respectively.
[0315] In FIGS. 30 to 33, it could be confirmed that: the Ni metal
concentration was constant from the core to the surface, and the
precursor showed the concentration of the aqueous solution for
forming the core; but after heat-treatment, the Co and Mn
concentrations in the core were same each other, and later there
was concentration gradient, where the Mn concentration was
gradually increased with certain gradient, but the Co concentration
was gradually decreased with certain gradient.
[0316] Further, as shown in FIG. 34, for Example 2-5 prepared by
using the batch type reactor, it was confirmed that the Ni metal
concentration from the core to the surface was constant, and there
was concentration gradient, where the Mn concentration was
gradually increased with certain gradient, but the Co concentration
was gradually decreased with certain gradient.
[0317] In FIGS. 30 to 34, unlike the precursor, becoming the
concentrations of the Mn and the Co in the core the same was
resulted from diffusion between metal salts in the heat-treatment
process.
Test Example 2-3
Confirmation of Surface Image of Particles of Precursor and Active
Material
[0318] Surface images of the precursors and the final active
materials prepared in Examples 2-1 to 2-5 were taken by using a
scanning electron microscope, and the results are shown in FIGS. 35
to 39 and FIGS. 40 to 44.
[0319] Each of the pictures is a surface image with different
magnification, and it could be confirmed that each particle was
homogeneously formed.
Test Example 2-4
Measuring Charging/Discharging Capacity and Cycle
Characteristics
[0320] Cathodes were prepared by using the active materials
prepared in Examples 2-1 to 2-5 and the active materials prepared
in Comparative Examples 2-1 to 2-4, and applied to cylindrical
lithium secondary batteries, respectively.
[0321] For the batteries prepared by using the active materials
prepared in Examples 2-1 to 2-4, charging/discharging test and
cycle characteristics were measured, and the results are shown in
FIGS. 45 to 48. The charging/discharging was conducted 10 times per
each sample at the condition of 2.7.about.4.3 V and 0.2 C, and the
average value was taken.
[0322] In FIGS. 45 to 48, Example 2-1 and Comparative Example 2-1,
Example 2-2 and Comparative Example 2-2, Example 2-3 and
Comparative Example 2-3, and Example 2-4 and Comparative Example
2-4 have the same molar ratio of the nickel contained in the whole
particle, respectively, thereby showing similar initial
charging/discharging capacity and cycle characteristics. However,
Examples 2-1 to 2-5 showing concentration gradient showed better
performance than Comparative Examples 2-1 to 2-4.
[0323] Further, in FIG. 49, when comparing Example 2-3 prepared by
using a CSTR reactor and Example 2-5 prepared by using a BATCH
reactor, which show the same concentration gradient, they showed
identical charge/discharge characteristics.
Test Example 2-5
Evaluation of Thermostability by DSC Measurement
[0324] The cathodes containing the active materials prepared in
Examples 2-1 to 2-4 and the active materials prepared in
Comparative Examples 2-1 to 2-4, were charged at 4.3 V,
respectively, and thermostability was measured by using a
differential scanning calorimeter (DSC) and heating at a rate of
10.degree. C./min. The results are shown in FIGS. 50 to 53.
[0325] As shown in FIGS. 50 to 53, when the active materials
prepared in Examples 2-1 to 2-4 according to the present invention
were contained, an exothermic peak was showed at the higher
temperature in the differential scanning calorimeter (DSC) than
when the active materials prepared in Comparative Examples 2-1 to
2-4 were contained. Thus, when the active materials prepared in
Examples 2-1 to 2-4 according to the present invention were
contained, the thermostability was much improved than when the
active materials prepared in Comparative Examples 2-1 to 2-4 were
contained.
[0326] Namely, in the present invention, the concentration of one
metal is constant, and the concentrations of the other two metals
are increased or decreased with continuous concentration gradient
from the core to the surface part. Accordingly, because the
concentrations of the metals inside of the particle are not rapidly
changed and show table structure, it could be confirmed that the
thermostability is largely increased.
[0327] Further, in FIG. 54, when comparing Example 2-3 prepared by
using a CSTR reactor and Example 2-5 prepared by using a BATCH
reactor, which show the same concentration gradient, they showed
DSC peaks at the same temperature.
Examples 3
Case of Constant Cobalt Concentration
Example 3-1
[0328] In order to prepare a compound, wherein the Co concentration
is constant from the core to the surface, the NI concentration is
decreased, and the Mn concentration is increased, a 2.4 M metal
aqueous solution, prepared by mixing nickel sulfate and cobalt
sulfate at the molar ratio of 90:10, as a metal salt aqueous
solution for forming the core and a metal aqueous solution
containing nickel sulfate, cobalt sulfate and manganese sulfate at
the molar ratio of 65:10:25 as a metal salt aqueous solution for
forming the surface part were prepared, and a precursor was
prepared as described in Example 3-1.
[0329] LiNO.sub.3 as a lithium salt was mixed to the obtained
active material precursor, heated at a rate of 2.degree. C./min,
and then pre-calcined by maintaining at 280.degree. C. for 10 hours
followed by calcining at 750.degree. C. for 15 hours to obtain a
final active material particle. The size of the finally obtained
active material particle was 12 .mu.m.
[0330] As Comparative Example 3-1, a precursor containing the
nickel, cobalt and manganese at the molar ratio of 72:10:18,
wherein each metal concentration is the same in the whole particle
was prepared.
TABLE-US-00005 TABLE 5 Ni Co Mn Comparative Example 3-1 72 10
18
Test Example 3-1
Confirmation of Formation of Concentration Gradient in Precursor
Particle
[0331] In order to confirm the concentration gradient structure of
each metal from the core to the surface of the precursor particle
of the present invention, the atomic ratio of the precursor
particle prepared in Example 3-1 was measured by using EPMA
(Electron Probe Micro Analyzer) while moving form the core to the
surface part as described in Test Example 3-1, and the results is
shown in FIG. 55.
[0332] In FIG. 55, it could be confirmed that: the Co metal
concentration was constant from the core to the surface, the Mn
concentration was gradually increased with certain gradient, but
the Ni concentration was gradually decreased with certain
gradient.
Test Example 3-2
[0333] Confirmation of Formation of Concentration Gradient in
Active Material Particle after Heat-Treatment
[0334] In order to confirm whether each metal shows concentration
gradient from the core to the surface part after heat-treating the
precursor particle of the present invention, the atomic ratio of
the particle prepared in Example 3-1 was measured by using EPMA
(Electron Probe Micro Analyzer) while moving from the core to the
surface as described in Test Example 3-2, and the result is shown
in FIG. 56.
Test Example 3-3
Confirmation of Surface Image of Particles of Precursor and Active
Material
[0335] Surface images of the precursors and the final active
materials prepared in Example 3-1 and Comparative Example 3-1 were
taken by using a scanning electron microscope, and the results are
shown in FIGS. 57 to 58.
[0336] Each of the pictures is a surface image with different
magnification, and it could be confirmed that each particle was
homogeneously formed.
Test Example 3-4
Measuring Charging/Discharging Capacity and Cycle
Characteristics
[0337] Cathodes were prepared by using the active material prepared
in Example 3-1 and the active material prepared in Comparative
Example 3-1, and applied to cylindrical lithium secondary
batteries, respectively.
[0338] For the batteries prepared by using the active material
prepared in Example 3-1 and the active material prepared in
Comparative Example 3-1, charging/discharging test and cycle
characteristics were measured, and the results are shown in FIG.
59. The charging/discharging was conducted 10 times per each sample
at the condition of 2.7.about.4.3 V and 0.2 C, and the average
value was taken.
[0339] In FIG. 59, Example 3-1 and Comparative Example 3-1 have the
same molar ratio of the nickel contained in the whole particle,
respectively, thereby showing similar initial charging/discharging
capacity and cycle characteristics.
[0340] However, Example 3-1 showing concentration gradient showed
better performance than Comparative Example 3-1.
Test Example 3-5
Evaluation of Thermostability by DSC Measurement
[0341] The cathodes containing the active materials prepared in
Example 3-1 and Comparative Example 3-1 were charged at 4.3 V,
respectively, and thermostability was measured by using a
differential scanning calorimeter (DSC) and heating at a rate of
10.degree. C./min. The results are shown in FIG. 60.
[0342] As shown in FIG. 60, the cathode containing the active
material prepared in Example 3-1 according to the present invention
showed an exothermic peak at the higher temperature in the
differential scanning calorimeter (DSC) than the cathode containing
the active material prepared in Comparative Example 3-1. Thus, in
the cathode containing the active material prepared in Example 3-1
according to the present invention, wherein the Co was contained
constantly, the Ni was decreased with continuous concentration
gradient, and the Mn was increased with continuous concentration
gradient, and the cathode containing the active material prepared
in Comparative Example 3-1 were the same in the composition. But,
the active material prepared in Example 3-1, wherein the metal
concentration showed concentration gradient in the whole particle,
showed much improved thermostability than the active material
prepared in Comparative Example 3-1, wherein the metal
concentration was constant in the whole particle.
[0343] Namely, in the present invention, the concentration of one
metal is constant, and the concentrations of the other two metals
are increased or decreased with continuous concentration gradient
from the core to the surface part. Accordingly, because the
concentrations of the metals inside of the particle are not rapidly
changed and show table structure, it could be confirmed that the
thermostability is largely increased.
[0344] The third embodiment of the inventive concept will be
described with FIGS. 61A to 114.
[0345] FIG. 61A illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a first embodiment of the inventive concept.
FIG. 61B illustrates the positive electrode active material
containing the second element composed of the first element having
a rod shape according to a first embodiment of the inventive
concept. FIG. 62 is a graph illustrating the change in content of
the first metal in the second element of the positive electrode
active material according to a first embodiment of the inventive
concept.
[0346] Referring to FIG. 61A, FIG. 61B, and FIG. 62, the second
element of the positive electrode active material according to the
first embodiment of the inventive concept may include a center part
10 and a surface part 20. The center part 10 may include a region
of the intermediate position, the central position, and/or the
inside of the second element, as described in the boilerplate of
the description. The surface part 20 may be the exterior surface of
the second element.
[0347] The second element is illustrated as a sphere in FIG. 61A
and FIG. 61B. However, embodiments of the inventive concepts are
not limited thereto. In another embodiment, the second element may
have a shape with an oval cross section.
[0348] The second element may be composed of one or more first
elements 30. In other words, the second element may be formed by
aggregation of the first elements 30. The first element 30 may
extend from the center part 10 toward the surface part 20. In other
words, the first element 30 may have a rod shape radiated from the
center part 10 toward the surface part 20.
[0349] The pathway for a metal ion (e.g., lithium ion) and an
electrolyte may be provided between the first elements 30 having
the rod shape, namely, between the first elements 30 extending in a
direction D from the center part 10 to the surface part 20 of the
second element. This enables the positive electrode active material
according to an embodiment of the inventive concept to improve the
charge and discharge efficiency of a secondary battery.
[0350] The first element 30 may be formed of a plurality of metals
including a first metal, a second metal, and a third metal. Hence,
the second element containing the first element 30 may include the
plurality of metals including the first to third metals. For
example, the first metal may be nickel (Ni), the second metal may
be manganese (Mn), and the third metal may be cobalt (Co). In this
case, the second element may be formed of a compound of lithium,
nickel, manganese, and cobalt.
[0351] The second element may include a concentration gradient
portion 110 in which the content of the first metal changes, and a
concentration maintained portion 120 in which the content of the
first metal is constant. The concentration maintained portion 120
may surround the concentration gradient portion 110. In other
words, the concentration gradient portion 110 may correspond to the
core of the second element and the concentration maintained portion
120 may correspond to the shell of the second element.
[0352] The second element including the concentration gradient
portion 110 and the concentration maintained portion 120 may be
prepared by controlling the contents of an aqueous solution
containing the first metal, an aqueous solution containing the
second metal, and an aqueous solution containing the third metal.
For example, in a case in which the aqueous solution containing the
first metal includes nickel sulfate, the aqueous solution
containing the second metal includes manganese sulfate, and the
aqueous solution containing the third metal includes cobalt
sulfate, nickel-manganese-cobalt hydroxide is prepared using nickel
sulfate, manganese sulfate, cobalt sulfate, and a coprecipitation
reactor. The second element containing lithium, nickel, manganese,
and cobalt may be prepared by mixing the nickel, manganese, cobalt
hydroxide with lithium hydroxide and heating and sintering the
mixture.
[0353] The content of the first metal in the concentration gradient
portion 110 may gradually decrease in the direction D from the
center part 10 to the surface part 20. The content of at least one
of the second metal or the third metal in the concentration
gradient portion 110 may gradually increase in a case in which the
content of the first metal in the concentration gradient portion
110 gradually decreases. According to an embodiment of the
inventive concept, the content 200 of the second metal may
gradually increase in the direction D from the center part 10 to
the surface part 20 in a case in which the content of the first
metal gradually decreases in the direction D from the center part
10 to the surface part 20, as illustrated in (a) of FIG. 62. In
this case, the content of the third metal may increase, be
maintained, or decrease.
[0354] According to an embodiment of the inventive concept, the
content of the first metal may continuously change between the
concentration gradient portion 110 and the concentration maintained
portion 120 as illustrated in (a) of FIG. 62. In this case, the
minimum value of the content of the first metal in the
concentration gradient portion 110 may be substantially equal to
the average value of the content of the first metal in the
concentration maintained portion 120. As described above, the
minimum value of the content of the first metal in the
concentration gradient portion 110 may be the value of the content
of the first metal at a part of the outside of the concentration
gradient portion 110 close to the concentration maintained portion
120 in a case in which the content of the first metal in the
concentration gradient portion 110 gradually decreases in the
direction D from the center part 10 to the surface part 20.
[0355] Alternatively, according to another embodiment of the
inventive concept, the content of the first metal may
discontinuously change between the concentration gradient portion
110 and the concentration maintained portion 120, as illustrated in
(b) of FIG. 62. In this case, the minimum value of the content of
the first metal in the concentration gradient portion 110 may be
different from the average value of the content of the first metal
in the concentration maintained portion 120. The content 210 or 220
of the first metal in the concentration maintained portion 120 may
be higher or lower than the minimum value of the content of the
first metal in the concentration gradient portion 110, namely, the
value of the content of the first metal at a part of the outside of
the concentration gradient portion 110 close to the concentration
maintained portion 120.
[0356] According to an embodiment of the inventive concept, the
contents of the second metal and the third metal in the
concentration maintained portion 120 may be constant.
Alternatively, according to another embodiment of the inventive
concept, the content of at least one of the second metal or the
third metal may change in the concentration maintained portion
120.
[0357] Unlike the first embodiment of the inventive concept
described above, a rate of change in content of the first metal may
change in the concentration gradient portion in a second embodiment
of the inventive concept. Hereinafter, this will be described with
reference to FIGS. 63 to 65.
[0358] FIG. 63 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a second embodiment of the inventive concept,
and FIGS. 64 and 5 are graphs illustrating the change in content of
the first metal in the second element of the positive electrode
active material according to a second embodiment of the inventive
concept.
[0359] Referring to FIGS. 63 to 65, a second element of a positive
electrode active material according to the second embodiment of the
inventive concept may be composed of one or more first elements 30
extending from the center part 10 toward the surface part 20 as
described with reference to FIG. 61B. The first element 30 may be
formed of a plurality of metals including the first metal to the
third metal as described with reference to FIG. 61A, FIG. 61B, and
FIG. 62.
[0360] The second element may include a first concentration
gradient portion 110a in which the content of the first metal
changes, a second concentration gradient portion 110b which has a
rate of change in content of the first metal different from the
rate of change in content of the first metal in the first
concentration gradient portion 110a, and a concentration maintained
portion 120 in which the content of the first metal is constant.
The second concentration gradient portion 110b may surround the
first concentration gradient portion 110a, and the concentration
maintained portion 120 may surround the second concentration
gradient portion 110b.
[0361] According to an embodiments of the inventive concept, as
illustrated in (a) and (b) of FIG. 64, the content of the first
metal in the first concentration gradient portion 110a and the
content of the first metal in the second concentration gradient
portion 110b may gradually decrease in the direction D from the
center part 10 to the surface part 20. For example, in the
direction D from the center part 10 to the surface part 20, the
rate of decrease in content of the first metal in the first
concentration gradient portion 110a may be smaller than the rate of
decrease in content of the first metal in the second concentration
gradient portion 110b, as illustrated in (a) of FIG. 64.
Alternatively, for another example, in the direction D from the
center part 10 to the surface part 20, the rate of decrease in
content of the first metal in the first concentration gradient
portion 110a may be greater than the rate of decrease in content of
the first metal in the second concentration gradient portion 110b,
as illustrated in (b) of FIG. 64.
[0362] According to another embodiment of the inventive concept, as
illustrated in (a) and (b) of FIG. 65, one of the content of the
first metal in the first concentration gradient portion 110a and
the content of the first metal in the second concentration gradient
portion 110b may increase and the other thereof may decrease in the
direction D from the center part 10 to the surface part 20. For
example, in the direction D from the center part 10 to the surface
part 20, the content of the first metal in the first concentration
gradient portion 110a may increase and the content of the first
metal in the second concentration gradient portion 110b may
decrease, as illustrated in (a) of FIG. 65. Alternatively, for
another example, in the direction D from the center part 10 to the
surface part 20, the content of the first metal in the first
concentration gradient portion 110a may decrease and the content of
the first metal in the second concentration gradient portion 110b
may increase, as illustrated in (b) of FIG. 65.
[0363] In a case in which the contents of the first metal in the
first and second concentration gradient portions 110a and 110b
gradually decrease or increase in the direction D from the center
part 10 to the surface part 20, the contents of the second metal in
the first and second concentration gradient portions (110a and
110b) may gradually increase or decrease in the direction D from
the center part 10 to the surface part 20, as described with
reference to FIG. 62.
[0364] According to an embodiment of the inventive concept, as
illustrated in FIGS. 64 and 65, the content of the first metal may
continuously change between the second concentration gradient
portion 110b and the concentration maintained portion 120. In this
case, the minimum value or the maximum value of the content of the
first metal in the second concentration gradient portion 110b may
be equal to the average value of the content of the first metal in
the concentration maintained portion 120. Alternatively, according
to another embodiment of the inventive concept, as described with
reference to (b) of FIG. 62, the content of the first metal may
discontinuously change between the second concentration gradient
portion 110b and the concentration maintained portion 120. In this
case, the minimum value or the maximum value of the content of the
first metal in the second concentration gradient portion 110b may
be different from the average value of the content of the first
metal in the concentration maintained portion 120.
[0365] Unlike the embodiments of the inventive concept described
above, the concentration maintained portion may include a first
concentration maintained portion and a second concentration
maintained portion which have different contents of the first metal
from each other in according to a third embodiment of the inventive
concept. Hereinafter, this will be described with reference to
FIGS. 66 and 67.
[0366] FIG. 66 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a third embodiment of the inventive concept,
and FIG. 67 is a graph illustrating the change in content of the
first metal in the second element of the positive electrode active
material according to a third embodiment of the inventive
concept.
[0367] Referring to FIGS. 66 and 67, a second element of a positive
electrode active material according to a third embodiment of the
inventive concept may be composed of one or more first elements 30
extending from the center part 10 toward the surface part 20, as
described with reference to FIG. 61B. The first element 30 may be
formed of a plurality of metals including the first metal to the
third metal as described with reference to FIG. 61A, FIG. 61B, and
FIG. 62.
[0368] The second element may include the concentration gradient
portion 110 in which the content of the first metal changes, a
first concentration maintained portion 120a in which the content of
the first metal is constant, and a second concentration maintained
portion 120b in which the content of the first metal is constant
but different from the content of the first metal in first
concentration maintained portion 120a. The first concentration
maintained portion 120a may surround the concentration gradient
portion 110. The second concentration maintained portion 120b may
surround the first concentration maintained portion 120a.
[0369] According to an embodiment of the inventive concept, the
content of the first metal in the concentration gradient portion
110 may gradually decrease in the direction D from the center part
10 to the surface part 20. In this case, the content of the second
metal in the concentration gradient portion 110 may gradually
increase as described with reference to FIG. 62.
[0370] The content of the first metal may discontinuous change
between the first concentration maintained portion 120a and the
second concentration maintained portion 120b. According to an
embodiment of the inventive concept, the content of the first metal
in the first concentration maintained portion 120a may be lower
than a content 310 of the first metal in the second concentration
maintained portion 120b. Alternatively, unlike this, according to
another embodiment of the inventive concept, the content of the
first metal in the first concentration maintained portion 120a may
be higher than a content 320 of the first metal in the second
concentration maintained portion 120b.
[0371] According to an embodiment of the inventive concept, the
content of the first metal may continuous change between the
concentration gradient portion 110 and the first concentration
maintained portion 120a, as illustrated in FIG. 67. In this case,
the minimum value of the content of the first metal in the
concentration gradient portion 110 may be equal to the average
value of the content of the first metal in the first concentration
maintained portion 120a. Alternatively, according to another
embodiment of the inventive concept, the content of the first metal
in the concentration gradient portion 110 may be discontinuous with
the average value of the content of the first metal in the first
concentration maintained portion 120a, as described with reference
to (b) of FIG. 62. In this case, the minimum value of the content
of the first metal in the concentration gradient portion 110 may be
different from the average value of the content of the first metal
in the first concentration maintained portion 120a.
[0372] Unlike the embodiments of the inventive concept described
above, according to a fourth embodiment of the inventive concept,
an outer portion of the second element may correspond to a
concentration gradient portion. Hereinafter, this will be described
with reference to FIGS. 68 to 70.
[0373] FIG. 68 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a fourth embodiment of the inventive concept,
and FIGS. 69 and 10 are graphs illustrating the change in content
of the first metal in the second element of the positive electrode
active material according to a fourth embodiment of the inventive
concept.
[0374] Referring to FIGS. 68 to 70, the second element of the
positive electrode active material according to the fourth
embodiment of the inventive concept may be composed of one or more
first elements 30 extending from the center part 10 toward the
surface part 20 as described with reference to FIG. 61B. The first
element 30 may be formed of a plurality of metals including the
first metal to the third metal as described with reference to FIG.
61A, FIG. 61B, and FIG. 62.
[0375] The second element may include a first concentration
gradient portion 110a in which the content of the first metal
changes, a concentration maintained portion 120 in which the
content of the first metal is constant, and a second concentration
gradient portion 110b in which the content of the first metal
changes. The concentration maintained portion 120 may surround the
first concentration gradient portion 110a, and the second
concentration gradient portion 110b may surround the concentration
maintained portion 120.
[0376] According to an embodiment of the inventive concept, as
illustrated in (a) of FIG. 69, the content of the first metal in
the first concentration gradient portion 110a and the content of
the first metal in the second concentration gradient portion 110b
may gradually decrease in the direction D from the center part 10
to the surface part 20. According to another embodiment of the
inventive concept, as illustrated in (b) of FIG. 69, the content of
the first metal in the first concentration gradient portion 110a
and the content of the first metal in the second concentration
gradient portion 110b may gradually increase in the direction D
from the center part 10 to the surface part 20.
[0377] Alternatively, according to still another embodiment of the
inventive concept, in the direction D from the center part 10 to
the surface part 20, the content of the first metal in the first
concentration gradient portion 110a may gradually decrease and the
content of the first metal in the second concentration gradient
portion 110b may gradually increase, as illustrated in (a) of FIG.
70. In this case, the content of the first metal at a part
including the interface between the first concentration gradient
portion 110a and the second concentration gradient portion 110b may
be highest in the inside of the second element.
[0378] Alternatively, according to yet still another embodiments of
the inventive concept, in the direction D from the center part 10
to the surface part 20, the content of the first metal in the first
concentration gradient portion 110a may gradually increase and the
content of the first metal in the second concentration gradient
portion 110b may gradually decrease, as illustrated in (b) of FIG.
70. In this case, the content of the first metal at a part
including the interface between the first concentration gradient
portion 110a and the second concentration gradient portion 110b may
be lowest in the inside of the second element.
[0379] In a case in which the contents of the first metal in the
first and second concentration gradient portions 110a and 110b
gradually decrease or increase in the direction D from the center
part 10 to the surface part 20, the contents of the second metal in
the first and second concentration gradient portions (110a and
110b) may gradually increase or decrease in the direction D from
the center part 10 to the surface part 20, as described with
reference to FIG. 62.
[0380] According to an embodiment of the inventive concept, as
illustrated in FIGS. 69 and 70, the content of the first metal may
continuously change between the first concentration gradient
portion 110a and the concentration maintained portion 120 and
between the concentration maintained portion 120 and the second
concentration gradient portion 110b. In this case, the maximum
values or the minimum values of the contents of the first metal in
the first and second concentration gradient portions 110a and 110b
may be equal to the average value of the content of the first metal
in the concentration maintained portion 120. Alternatively,
according to another embodiment of the inventive concept, the
content of the first metal may discontinuously change between the
first concentration gradient portion 110a and the concentration
maintained portion 120 and between the concentration maintained
portion 120 and the second concentration gradient portion 110b.
[0381] Unlike the fourth embodiment of the inventive concept
described above, according to a modified example of the fourth
embodiment of the inventive concept, a second concentration
maintained portion may surround the second concentration gradient
portion 110b of the second element according to the fourth
embodiment of the inventive concept described with reference to
FIG. 68. Hereinafter, this will be described with reference to FIG.
61.
[0382] FIG. 61 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a modified example of a fourth embodiment of
the inventive concept.
[0383] Referring to FIG. 61, a second element of a positive
electrode active material according to a modified example of the
fourth embodiment of the inventive concept may be composed of one
or more first elements 30 extending from the center part 10 toward
the surface part 20 as described with reference to FIG. 61B. The
first element 30 may be formed of a plurality of metals including
the first metal to the third metal as described with reference to
FIG. 61A, FIG. 61B, and FIG. 62.
[0384] The second element may include the first concentration
gradient portion 110a in which the content of the first metal
changes, the first concentration maintained portion 120a in which
the content of the first metal is constant, the second
concentration gradient portion 110b in which the content of the
first metal changes, and the second concentration maintained
portion 120b in which the content of the first metal is constant.
The first concentration maintained portion 120a may surround the
first concentration gradient portion 110a, the second concentration
gradient portion 110b may surround the first concentration
maintained portion 120a, and the second concentration maintained
portion 120b may surround the second concentration gradient portion
110b.
[0385] The first concentration gradient portion 110a, the first
concentration maintained portion 120a, and the second concentration
gradient portion 110b may respectively correspond to the first
concentration gradient portion 110a, the concentration maintained
portion 120, and the second concentration gradient portion 110b,
which are described with reference to FIGS. 68 to 70.
[0386] In a case in which the contents of the first metal in the
first and second concentration gradient portions 110a and 110b are
the same as described with reference to FIG. 69, the average value
of the content of the first metal in the second concentration
maintained portion 120b may be different from the average value of
the content of the first metal in the first concentration
maintained portion 120a. In a case in which the contents of the
first metal in the first and second concentration gradient portions
110a and 110b are the same as described with reference to FIG. 70,
the average value of the content of the first metal in the second
concentration maintained portion 120b may be the same as or
different from the average value of the content of the first metal
in the first concentration maintained portion 120a.
[0387] According to an embodiment of the inventive concept, the
content of the first metal may continuously change between the
second concentration gradient portion 110b and the second
concentration maintained portion 120b. In this case, the maximum
value or the minimum value of the content of the first metal in the
second concentration gradient portion 110b may be equal to the
average value of the content of the first metal in the second
concentration maintained portion 120b. Alternatively, according to
another embodiment of the inventive concept, the content of the
first metal may discontinuously change between the second
concentration gradient portion 110b and the second concentration
maintained portion 120b.
[0388] Unlike the embodiments of the inventive concept described
above, according to a fifth embodiment of the inventive concept, a
concentration gradient portion may be disposed between
concentration maintained portions. Hereinafter, this will be
described with reference to FIGS. 62 and 63.
[0389] FIG. 62 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a fifth embodiment of the inventive concept.
FIG. 63 is a graph illustrating the change in content of the first
metal in the second element of the positive electrode active
material according to a fifth embodiment of the inventive
concept.
[0390] Referring to FIGS. 62 and 63, a second element of a positive
electrode active material according to the fifth embodiment of the
inventive concept may be composed of one or more first elements 30
extending from the center part 10 toward the surface part 20 as
described with reference to FIG. 61B. The first element 30 may be
formed of a plurality of metals including the first metal to the
third metal as described with reference to FIG. 61A, FIG. 61B, and
FIG. 62.
[0391] The second element may include the first concentration
maintained portion 120a in which the content of the first metal is
constant, the concentration gradient portion 110 in which the
content of the first metal changes, and the second concentration
maintained portion 120b in which the content of the first metal is
constant. The concentration gradient portion 110 may surround the
first concentration maintained portion 120a and the second
concentration maintained portion 120b may surround the
concentration gradient portion 110.
[0392] According to an embodiment of the inventive concept, the
content of the first metal in the concentration gradient portion
110 may gradually decrease in the direction D from the center part
10 to the surface part 20, as illustrated in (a) of FIG. 73. In
this case, the content of the first metal in the first
concentration maintained portion 120a may be higher than the
content of the first metal in the second concentration maintained
portion 120b.
[0393] Alternatively, according to another embodiment of the
inventive concept, the content of the first metal in the
concentration gradient portion 110 may gradually increase in the
direction D from the center part 10 to the surface part 20, as
illustrated in (b) of FIG. 73. In this case, the content of the
first metal in the first concentration maintained portion 120a may
be lower than the content of the first metal in the second
concentration maintained portion 120b.
[0394] In a case in which the content of the first metal in the
concentration gradient portion 110 gradually decreases or increases
in the direction D from the center part 10 to the surface part 20,
the content of the second metal in the concentration gradient
portion 110 may gradually increase or decrease in the direction D
from the center part 10 to the surface part 20, as described with
reference to FIG. 62.
[0395] According to an embodiment of the inventive concept, the
content of the first metal may continuously change between the
first maintained concentration portion 120a and the concentration
gradient portion 110 and between the concentration gradient portion
110 and the second concentration maintained portion 120b. In this
case, the maximum value and the minimum value of the content of the
first metal in the concentration gradient portion 110 may be equal
to the average values of the contents of the first metal in the
concentration maintained portions 120a and 120b (or 120b and 120a),
respectively. Alternatively, according to another embodiment of the
inventive concept, the content of the first metal may
discontinuously change between the first maintained concentration
portion 120a and the concentration gradient portion 110 and between
the concentration gradient portion 110 and the second concentration
maintained portion 120b.
[0396] Unlike the embodiments of the inventive concept described
above, according to a sixth embodiment of the inventive concept,
concentration gradient portions may surround a plurality of
concentration maintained portions. Hereinafter, this will be
described with reference to FIGS. 74 to 76.
[0397] FIG. 74 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a sixth embodiment of the inventive concept.
FIGS. 75 and 76 are graphs illustrating the change in content of
the first metal in the second element of the positive electrode
active material according to a sixth embodiment of the inventive
concept.
[0398] Referring to FIGS. 74 to 76, a second element of a positive
electrode active material according to the sixth embodiment of the
inventive concept may be composed of one or more first elements 30
extending from the center part 10 toward the surface part 20 as
described with reference to FIG. 61B. The first element 30 may be
formed of a plurality of metals including the first metal to the
third metal as described with reference to FIG. 61A, FIG. 61B, and
FIG. 62.
[0399] The second element may include the first concentration
maintained portion 120a in which the content of the first metal is
constant, the first concentration gradient portion 110a in which
the content of the first metal changes, the second concentration
maintained portion 120b in which the content of the first metal is
constant, and the second concentration gradient portion 110b in
which the content of the first metal changes. The first
concentration gradient portion 110a may surround the first
concentration maintained portion 120a, the second concentration
maintained portion 120b may surround the first concentration
gradient portion 110a, and the second concentration gradient
portion 110b may surround the second concentration maintained
portion 120b.
[0400] According to an embodiment of the inventive concept, as
illustrated in (a) of FIG. 75, the contents of the first metal in
the first and second concentration gradient portions 110a and 110b
may gradually decrease in the direction D from the center part 10
to the surface part 20. Alternatively, according to another
embodiment of the inventive concept, as illustrated in (b) of FIG.
75, the contents of the first metal in the first and second
concentration gradient portions 110a and 110b may gradually
increase in the direction D from the center part 10 to the surface
part 20.
[0401] Alternatively, according to still another embodiments of the
inventive concept, in the direction D from the center part 10 to
the surface part 20, the content of the first metal in the first
concentration gradient portion 110a may gradually increase and the
content of the first metal in the second concentration gradient
portion 110b may gradually decrease, as illustrated in (a) of FIG.
76. Alternatively, according to yet still another embodiments of
the inventive concept, in the direction D from the center part 10
to the surface part 20, the content of the first metal in the first
concentration gradient portion 110a may gradually decrease and the
content of the first metal in the second concentration gradient
portion 110b may gradually increase, as illustrated in (b) of FIG.
76.
[0402] In a case in which the contents of the first metal in the
first and second concentration gradient portions 110a and 110b
gradually decrease or increase in the direction D from the center
part 10 to the surface part 20, the contents of the second metal in
the first and second concentration gradient portions (110a and
110b) may gradually increase or decrease in the direction D from
the center part 10 to the surface part 20 as described with
reference to FIG. 62.
[0403] The content of the first metal may continuously or
discontinuously change between the first maintained concentration
portion 120a and the first concentration gradient portion 110a,
between the first concentration gradient portion 110a and the
second concentration maintained portion 120b, and between the
second concentration maintained portion 120b and the second
concentration gradient portion 110b.
[0404] Unlike the sixth embodiment of the inventive concept
described above, according to a modified example of the sixth
embodiment of the inventive concept, a third concentration
maintained portion may surround the second concentration gradient
portion 110b of the second element according to the sixth
embodiment of the inventive concept described with reference to
FIG. 74. Hereinafter, this will be described with reference to FIG.
77.
[0405] FIG. 77 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a modified example of a sixth embodiment of
the inventive concept.
[0406] Referring to FIG. 77, a second element of a positive
electrode active material according to a modified example of the
sixth embodiment of the inventive concept may be composed of one or
more first elements 30 extending from the center part 10 toward the
surface part 20 as described with reference to FIG. 61A. The first
element 30 may be formed of a plurality of metals including the
first metal to the third metal as described with reference to FIG.
61A, FIG. 61B, and FIG. 62.
[0407] The second element may further include a third concentration
maintained portion 120c which has a constant content of the first
metal and surrounds the second concentration gradient portion 110b
in addition to the first concentration maintained portion 120a, the
first concentration gradient portion 110a, the second concentration
maintained portion 120b, and the second concentration gradient
portion 110b described with reference to FIG. 74.
[0408] In a case in which the contents of the first metal in the
first and second concentration gradient portions 110a and 110b are
the same as described with reference to FIG. 75, the average value
of the content of the first metal in the third concentration
maintained portion 120c may be different from the average values of
the contents of the first metal in the first and second
concentration maintained portions 120a and 120b. Unlike this, in a
case in which the contents of the first metal in the first and
second concentration gradient portions 110a and 110b are the same
as described with reference to FIG. 76, the average value of the
content of the first metal in the third concentration maintained
portion 120c may be the same as or different from at least one of
the average values of the contents of the first metal in the first
and second concentration maintained portions 120a and 120b.
[0409] According to an embodiment of the inventive concept, the
content of the first metal may continuously change between the
second concentration gradient portion 110b and the second
concentration maintained portion 120b. In this case, the minimum
value or maximum value of the content of the first metal in the
second concentration gradient portion 110b may be equal to the
average value of the content of the first metal in the third
concentration maintained portion 120c. Unlike this, according to
another embodiment of the inventive concept, the content of the
first metal may discontinuously change between the second
concentration gradient portion 110b and the third concentration
maintained portion 120c.
[0410] Unlike the embodiments of the inventive concept described
above, according to a seventh embodiment of the inventive concept,
a first concentration gradient portion and a second concentration
gradient portion which have different rates of change in content of
the first metal from each other may compose an outer portion of the
second element. Hereinafter, this will be described with reference
to FIGS. 78 to 80.
[0411] FIG. 78 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a seventh embodiment of the inventive
concept. FIGS. 79 and 80 are graphs illustrating the change in
content of the first metal in the second element of the positive
electrode active material according to a seventh embodiment of the
inventive concept.
[0412] Referring to FIGS. 78 to 80, a second element of a positive
electrode active material according to the seventh embodiment of
the inventive concept may be composed of one or more first elements
30 extending from the center part 10 toward the surface part 20 as
described with reference to FIG. 61B. The first element 30 may be
formed of a plurality of metals including the first metal to the
third metal as described with reference to FIG. 61A, FIG. 61B, and
FIG. 62.
[0413] The second element may include the concentration maintained
portion 120 in which the content of the first metal is constant,
the first concentration gradient portion 110a in which the content
of the first metal changes, and the second concentration gradient
portion 110b in which the content of the first metal changes. The
first concentration gradient portion 110a may surround the
concentration maintained portion 120 and the second concentration
gradient portion 110b may surround the first concentration gradient
portion 110a.
[0414] According to an embodiment of the inventive concept, as
illustrated in (a) of FIG. 79, the content of the first metal in
the first concentration gradient portion 110a and the content of
the first metal in the second concentration gradient portion 110b
may gradually decrease in the direction D from the center part 10
to the surface part 20. Alternatively, according to another
embodiment of the inventive concept, as illustrated in (b) of FIG.
79, the content of the first metal in the first concentration
gradient portion 110a and the content of the first metal in the
second concentration gradient portion 110b may gradually increase
in the direction D from the center part 10 to the surface part
20.
[0415] Alternatively, according to still another embodiment of the
inventive concept, in the direction D from the center part 10 to
the surface part 20, the content of the first metal in the first
concentration gradient portion 110a may gradually increase and the
content of the first metal in the second concentration gradient
portion 110b may gradually decrease, as illustrated in (a) of FIG.
80. In this case, the content of the first metal at a part
including the interface between the first concentration gradient
portion 110a and the second concentration gradient portion 110b may
be highest in the inside of the second element.
[0416] Alternatively, according to yet still another embodiment of
the inventive concept, in the direction D from the center part 10
to the surface part 20, the content of the first metal in the first
concentration gradient portion 110a may gradually decrease and the
content of the first metal in the second concentration gradient
portion 110b may gradually increase, as illustrated in (b) of FIG.
80. In this case, the content of the first metal at a part
including the interface between the first concentration gradient
portion 110a and the second concentration gradient portion 110b may
be lowest in the inside of the second element.
[0417] In a case in which the contents of the first metal in the
first and second concentration gradient portions 110a and 110b
gradually decrease or increase in the direction D from the center
part 10 to the surface part 20, the contents of the second metal in
the first and second concentration gradient portions 110a and 110b
may gradually increase or decrease in the direction D from the
center part 10 to the surface part 20 as described with reference
to FIG. 62.
[0418] According to an embodiment of the inventive concept, the
content of the first metal may continuously change between the
first concentration gradient portion 110a and the concentration
maintained portion 120. In this case, the minimum value or maximum
value of the content of the first metal in the first concentration
gradient portion 110a may be equal to the average value of the
content of the first metal in the concentration maintained portion
120. Alternatively, according to another embodiment of the
inventive concept, the content of the first metal may
discontinuously change between the first concentration gradient
portion 110a and the concentration maintained portion 120.
[0419] Unlike the seventh embodiment according to the inventive
concept, according to a modified example of the seventh embodiment
of the inventive concept, a second concentration maintained portion
may surround the second concentration gradient portion 110b of the
second element according to the seventh embodiment of the inventive
concept described with reference to FIG. 78. Hereinafter, this will
be described with reference to FIG. 81.
[0420] FIG. 81 illustrates the cross section of the second element
for explaining the second element of the positive electrode active
material according to a modified example of a seventh embodiment of
the inventive concept.
[0421] Referring to FIG. 81, a second element of a positive
electrode active material according to a modified example of the
seventh embodiment of the inventive concept may be composed of one
or more first elements 30 extending from the center part 10 toward
the surface part 20 as described with reference to FIG. 61B. The
first element 30 may be formed of a plurality of metals including
the first metal to the third metal as described with reference to
FIG. 61A, FIG. 61B, and FIG. 62.
[0422] The second element may include the first concentration
maintained portion 120a in which the content of the first metal is
constant, the first and second concentration gradient portions 110a
and 110b in which the content of the first metal changes, and the
second concentration maintained portion 120b in which the content
of the first metal is constant. The first concentration gradient
portion 110a may surround the first concentration maintained
portion 120a, the second concentration gradient portion 110b may
surround the first concentration gradient portion 110a, and the
second concentration maintained portion 120b may surround the
second concentration gradient portion 110b.
[0423] The first concentration maintained portion 120a, the first
concentration gradient portion 110a, and the second concentration
gradient portion 110b may respectively correspond to the
concentration maintained portion 120, the first concentration
gradient portion 110a, and the second concentration gradient
portion 110b which are described with reference to FIGS. 78 to
80.
[0424] In a case in which the contents of the first metal in the
first and second concentration gradient portions 110a and 110b are
the same as described with reference to FIG. 79, the average value
of the content of the first metal in the second concentration
maintained portion 120b may be different from the average value of
the content of the first metal in the first concentration
maintained portion 120a. In a case in which the contents of the
first metal in the first and second concentration gradient portions
110a and 110b are the same as described with reference to FIG. 80,
the average value of the content of the first metal in the second
concentration maintained portion 120b may be the same as or
different from the average value of the content of the first metal
in the first concentration maintained portion 120a.
[0425] According to an embodiment of the inventive concept, the
content of the first metal may continuously change between the
second concentration gradient portion 110b and the second
concentration maintained portion 120b. In this case, the minimum
value or maximum value of the content of the first metal in the
second concentration gradient portion 110b may be the same as the
average value of the content of the first metal in the second
concentration maintained portion 120b. Unlike this, according to
another embodiment of the inventive concept, the content of the
first metal may discontinuously change between the second
concentration gradient portion 110b and the second concentration
maintained portion 120b.
[0426] As described above, the second element according to the
embodiments of the inventive concept may include the concentration
gradient portion in which the content of the first metal changes
and the concentration maintained portion in which the content of
the first metal is constant. Hence, the first element can be formed
in a rod shape, and at the same time, the content of the first
metal in the second element can be controlled. This makes it
possible to provide the positive electrode active material in which
the characteristics (e.g., capacity and/or safety) are maximized
due to the first metal.
[0427] The positive electrode active material containing the second
element according to the embodiments of the inventive concept
described above may be included in a positive electrode of a
secondary battery. Hereinafter, a secondary battery which contains
the positive electrode active material according to the
aforementioned embodiments of the inventive concept will be
described.
[0428] FIG. 82 is a diagram for explaining a secondary battery
which contains the positive electrode active material according to
embodiments of the inventive concept.
[0429] Referring to FIG. 82, a secondary battery which contains the
positive electrode active material according to embodiments of the
inventive concept may include a positive electrode 410, a negative
electrode 420 facing the positive electrode 410, a separation layer
440 disposed between the positive electrode 410 and the negative
electrode 420, and an electrolyte 430 filling a space between the
positive electrode 410 and the negative electrode 420.
[0430] The positive electrode 410 may contain the positive
electrode active material according to the aforementioned
embodiments described above.
[0431] The negative electrode 420 may contain a negative electrode
active material. For example, the negative electrode active
material may include at least one of a carbon material (e.g.,
graphite or hard carbon), a metal material (e.g., Li, Na, Mg, Al,
Si, In, Ti, Pb, Ga, Ge, Sn, Bi, Sb, or an alloy thereof), silicon,
silicon oxide, or a Ti-based oxide (e.g.,
Li.sub.4Ti.sub.5O.sub.12).
[0432] The separation layer 440 may include at least one of a
polyolefin-based resin, a fluorine-based resin, a polyester-based
resin, a polyacrylonitrile resin, or a micro-porous layer formed of
a cellulose-based material, or the separation membrane 440 may be
obtained by coating at least one of these layers with an inorganic
material such as ceramic.
[0433] The electrolyte 430 may be impregnated into the separation
layer 440, the positive electrode 410, and/or the negative
electrode 420. The electrolyte 430 may be a gel polymer-type
electrolyte or a liquid electrolyte.
Examples 4
Examples 4-1 to 4-6
[0434] Into a coprecipitation reactor (volume: 16 L, output of
rotary motor: 80 W or more), 2.5 L of distilled water was
introduced, N.sub.2 gas was then supplied thereto at a rate of 2
L/min, and the distilled water was stirred at 400 rpm while
maintaining the temperature of the reactor at 45.degree. C.
[0435] A first aqueous metal solution and a second aqueous metal
solution were prepared by mixing nickel sulfate, cobalt sulfate,
and manganese sulfate so as to have a composition of
Ni.sub.x1Co.sub.y1Mn.sub.z1OH.sub.2 (X1, Y1, Z1) and a composition
of Ni.sub.x2Co.sub.y2Mn.sub.z2OH.sub.2 (x2, y2, z2), respectively,
the first aqueous metal solution and the second aqueous metal
solution were continuously introduced into the reactor at 0.7 L/hr
while mixing them and changing the mixing ratio thereof, and an
ammonia solution having a concentration of 25 mol was also
continuously introduced into the reactor at 0.07 L/hr, thereby
forming the core portion and the concentration gradient portion
which had a concentration gradient. In addition, a sodium hydroxide
solution having a concentration of 5 mol was supplied into the
reactor in order to adjust the pH so that the pH was maintained at
11.5. The speed of impeller was controlled at 400 rpm.
[0436] Thereafter, only the second aqueous metal solution was
supplied into the reactor for a certain period of time to form the
shell portion having constant concentrations of nickel, manganese,
and cobalt on the outside of the core portion and the concentration
gradient portion which had a concentration gradient, thereby
producing a composite metal hydroxide.
[0437] The concentrations of the aqueous metal solutions in
Examples 4-1 to 4-6 are as presented in the following Table 6.
TABLE-US-00006 TABLE 6 First aqueous Second aqueous metal solution
metal solution Ni Co Mn Ni Co Mn Example 75 0 25 55 20 25 4-1
Example 70 0 30 50 20 30 4-2 Example 78 0 22 54 19 27 4-3 Example
90 0 10 54 15 31 4-4 Example 90 5 5 65 10 25 4-5 Example 96 0 1 54
15 31 4-6
[0438] The composite metal hydroxide thus prepared was filtered,
washed with water, and then dried for 12 hours in a hot air dryer
at 110.degree. C. The composite metal hydroxide and lithium
hydroxide (LiOH) were mixed at a molar ratio of 1:1, the mixture
was subjected to the preliminary firing by heating at a temperature
rise rate of 2.degree. C./min and then maintaining at 450.degree.
C. for 10 hours and then fired at from 700 to 900.degree. C. for 10
hours, thereby obtaining a positive electrode active material
powder.
Comparative Examples 4-1 to 4-3
[0439] In Comparative Example 4-1, the positive electrode active
material particles containing only the core portion and the
concentration gradient portion which had a concentration gradient
were prepared in the same manner as in Example 4-1 except that the
shell portion having constant concentrations of nickel, manganese,
and cobalt was not formed.
[0440] In Comparative Example 4-2, composite oxide particles having
constant concentrations of nickel, manganese, and cobalt was
prepared using an aqueous metal solution having a composition of
Ni.sub.55Co.sub.20Mn.sub.25OH.sub.2 which corresponds to the
composition of the shell portion in Example 4-1. In Comparative
Example 4-3, composite oxide particles having constant
concentrations of nickel, manganese, and cobalt was prepared using
an aqueous metal solution having a composition of
Ni.sub.65Co.sub.10Mn.sub.25OH.sub.2 which corresponds to the
composition of the shell portion in Example 4-5.
<Experimental Example> Taking of EDX Image
[0441] The concentrations of Ni, Mn, and Co depending on the
distance from the center in the particles prepared in Example 4-1
and Comparative Example 4-1 were measured by EDX, and the results
are illustrated in FIG. 83. From FIG. 83, it can be seen that the
magnitude of the concentration gradient in the core portion and the
concentration gradient portion is constant as the core portion and
the concentration gradient portion have a concentration gradient, a
shell portion that is continuous with respect to the core portion
and the concentration gradient portion and has constant
concentrations of nickel, manganese, and cobalt is formed, and the
functional relation of the concentration to the distance is linear
in the core portion and the concentration gradient portion in the
case of the particles according to Example of the inventive
concept.
Experimental Example: Taking of SEM Image
[0442] The images of the particles prepared in Example 4-5 and
Comparative Example 1-3 were taken using a SEM, and the results are
illustrated in FIG. 84.
<Experimental Example> Measurement of Residual Lithium
[0443] Into 100 ml of distilled water, 10 g of the active material
particles prepared in Example 1-1 and Comparative Example 1-1 were
added, respectively, stirred for 10 minutes, then filtered, and
subjected to the titration with 10% hydrochloric acid, thereby
determining the amount of residual lithium. The amounts of LiOH and
Li.sub.2CO.sub.3 measured are as presented in the following Table
7.
TABLE-US-00007 TABLE 7 Residual LiOH Li.sub.2CO.sub.3 Sum Example
4-1 4728 2101 6829 Comparative Example 4-1 5728 2733 8461
<Experimental Example> Measurement of Charge and Discharge
Characteristics, Cycle-Life Characteristics, and DSC
[0444] The charge and discharge characteristics, cycle-life
characteristics, and DSC characteristics of the batteries
containing the active materials prepared in Examples 4-1 to 4-6 and
Comparative Examples 4-1 to 4-3 were measured, and the results are
presented in the following Table 8 and illustrated in FIGS. 85 and
86.
TABLE-US-00008 TABLE 8 Cycle-life Discharge characteristics
capacity (100.sup.th) DSC Example 4-1 189 mAh/g 95.2% 288.degree.
C. Example 4-2 184 mAh/g 96.2% 298.degree. C. Example 4-3 190 mAh/g
96.0% 289.degree. C. Example 4-4 195 mAh/g 96.1% 288.degree. C.
Example 4-5 203 mAh/g 94.3% 266.degree. C. Example 4-6 196 mAh/g
95.2% 286.degree. C. Comparative 191 mAh/g 96.7% 273.degree. C.
Example 4-1 Comparative 176 mAh/g 89.2% 267.degree. C. Example 4-2
Comparative 186 mAh/g 90.4% 272.degree. C. Example 4-3
Examples 4-7 to 4-10
[0445] Into a coprecipitation reactor (volume: 16 L, output of
rotary motor: 80 W or more), 2.5 L of distilled water was
introduced, N.sub.2 gas was then supplied thereto at a rate of 2
L/min, and the distilled water was stirred at 400 rpm while
maintaining the temperature of the reactor at 45.degree. C.
[0446] A first aqueous metal solution and a second aqueous metal
solution were prepared by mixing nickel sulfate, cobalt sulfate,
and manganese sulfate so as to have a composition of
Ni.sub.x1Co.sub.y1Mn.sub.z1OH.sub.2 (X1, Y1, Z1) and a composition
of Ni.sub.x2Co.sub.y2Mn.sub.z2OH.sub.2 (x2, y2, z2), respectively,
the first aqueous metal solution and the second aqueous metal
solution were continuously introduced into the reactor at 0.7 L/hr
while mixing them and changing the mixing ratio thereof, and an
ammonia solution having a concentration of 25 mol was also
continuously introduced into the reactor at 0.07 L/hr, thereby
forming the core portion and the concentration gradient portion
which had a concentration gradient. In addition, a sodium hydroxide
solution having a concentration of 5 mol was supplied into the
reactor in order to adjust the pH so that the pH was maintained at
11.5. The speed of impeller was controlled at 400 rpm.
[0447] Thereafter, a third aqueous metal solution prepared by
mixing nickel sulfate, cobalt sulfate, and manganese sulfate so as
to have a constant composition of
Ni.sub.x3Co.sub.y3Mn.sub.z3OH.sub.2 was supplied into the reactor
to form the shell portion in which the concentrations of nickel,
manganese, and cobalt were constant but different from those at the
outermost part of the core portion and the concentration gradient
portion, thereby producing a composite metal hydroxide.
[0448] The concentrations of the aqueous metal solutions in
Examples 4-7 to 4-10 are as presented in the following Table 9.
TABLE-US-00009 TABLE 9 First aqueous Second aqueous Third aqueous
Thickness metal solution metal solution metal solution of shell Ni
Co Mn Ni Co Mn Ni Co Mn portion Example 85 6 9 62 13 25 48 20 32
0.5 .mu.m 4-7 Example 85 6 9 62 13 25 48 20 32 1.0 .mu.m 4-8
Example 90 5 5 65 10 25 40 30 30 0.3 .mu.m 4-9 Example 90 5 5 65 10
25 50 20 30 0.3 .mu.m 4-10
[0449] The composite metal hydroxide thus prepared was filtered,
washed with water, and then dried for 12 hours in a hot air dryer
at 110.degree. C. The composite metal hydroxide and lithium
hydroxide (LiOH) were mixed at a molar ratio of 1:1, the mixture
was subjected to the preliminary firing by heating at a temperature
rise rate of 2.degree. C./min and then maintaining at 450.degree.
C. for 10 hours and then fired at from 700 to 900.degree. C. for 10
hours, thereby obtaining a positive electrode active material
powder.
Comparative Examples 4-4 and 4-5
[0450] In Comparative Example 4-4, positive electrode active
material particles were prepared in the same manner as in Example
4-7 except that the shell portion was not formed.
[0451] In Comparative Example 4-5, positive electrode active
material particles were prepared in the same manner as in Example
4-9 except that the shell portion was not formed.
<Experimental Example> Taking of EDX Image
[0452] The concentrations of Ni, Mn, and Co depending on the
distance from the center in the particles prepared in Example 4-7
and Comparative Example 4-4 were measured by EDX, and the results
are illustrated in FIG. 87.
[0453] From FIG. 87, it can be seen that the magnitude of the
concentration gradient in the core portion and the concentration
gradient portion is constant as a shell portion having constant
concentrations of nickel, manganese, and cobalt that is formed on
the outside of the core portion having a concentration gradient and
the functional relation of the concentration to the distance is
linear in the core portion and the concentration gradient portion
in the case of the particles according to Example of the inventive
concept.
<Experimental Example> Measurement of Charge and Discharge
Characteristics, Cycle-Life Characteristics, and DSC
[0454] The charge and discharge characteristics, cycle-life
characteristics, and DSC characteristics of the batteries
containing the active materials prepared in Examples 3-7 to 3-10
and Comparative Examples 4-4 and 4-5 were measured, and the results
are presented in the following Table 10.
TABLE-US-00010 TABLE 10 Cycle-life Discharge characteristics
capacity (100.sup.th) DSC Example 4-7 196 mAh/g 96.3% 289.degree.
C. Example 4-8 192 mAh/g 97.7% 297.degree. C. Example 4-9 196 mAh/g
96.3% 289.degree. C. Example 4-10 192 mAh/g 97.7% 297.degree. C.
Comparative 199 mAh/g 94.3% 271.degree. C. Example 4-4 Comparative
204 mAh/g 93.2% 263.degree. C. Example 4-5
[0455] The charge and discharge characteristics of the batteries
containing the active materials prepared in Example 4-7 and
Comparative Example 4-4 were measured, and the results are
illustrated in FIG. 88.
Examples 4-11 to 4-20
[0456] In order to produce particles having different magnitudes of
concentration gradient in the core portion and the concentration
gradient portion, first, a first aqueous metal solution and a
second aqueous metal solution were prepared by mixing nickel
sulfate, cobalt sulfate, and manganese sulfate so as to have a
composition of Ni.sub.x1Co.sub.y1Mn.sub.z1OH.sub.2 (X1, Y1, Z1) and
a composition of Ni.sub.x2Co.sub.y2Mn.sub.z2OH.sub.2 (x2, y2, z2),
respectively, the first aqueous metal solution and the second
aqueous metal solution were continuously introduced into the
reactor at 0.7 L/hr while mixing them and changing the mixing ratio
thereof, and an ammonia solution having a concentration of 25 mol
was also continuously introduced into the reactor at 0.07 L/hr,
thereby forming the core portion having a first magnitude of
concentration gradient.
[0457] Thereafter, a third aqueous metal solution was prepared by
mixing nickel sulfate, cobalt sulfate, and manganese sulfate so as
to have a constant composition of
Ni.sub.x3Co.sub.y3Mn.sub.z3OH.sub.2, the third aqueous metal
solution and the second aqueous metal solution were continuously
introduced into the reactor at 0.7 L/hr while mixing them and
changing the mixing ratio thereof, and an ammonia solution having a
concentration of 25 mol was also continuously introduced into the
reactor at 0.07 L/hr, thereby forming the concentration gradient
portion having a second magnitude of concentration gradient.
[0458] Thereafter, only the third aqueous metal solution prepared
by mixing nickel sulfate, cobalt sulfate, and manganese sulfate so
as to have a constant composition of
Ni.sub.x3Co.sub.y3Mn.sub.z3OH.sub.2 was supplied into the reactor
to form the shell portion in which the concentrations of nickel,
manganese, and cobalt were constant and the same as those at the
outermost part of the concentration gradient portion having a
second magnitude of concentration gradient. The concentrations of
the aqueous metal solutions thus prepared in Examples 4-11 to 4-20
are as presented in the following Table 11.
TABLE-US-00011 TABLE 11 Third aqueous metal solution First aqueous
Second aqueous Thickness metal solution metal solution of shell Ni
Co Mn Ni Co Mn Ni Co Mn portion Example 85 6 9 62 13 25 48 20 32
0.3 .mu.m 4-11 Example 85 6 9 62 13 25 48 20 32 0.5 .mu.m 4-12
Example 90 5 5 65 10 25 40 30 30 0.5 .mu.m 4-13 Example 90 5 5 65
10 25 50 20 30 0.2 .mu.m 4-14 Example 85 1 14 76 9 15 64 11 25 0.3
.mu.m 4-15 Example 90 1 9 80 8 12 65 10 25 0.5 .mu.m 4-16 Example
95 1 4 84 7 9 66 9 25 0.4 .mu.m 4-17 Example 95 2 3 77 7 16 63 11
26 0.5 .mu.m 4-18 Example 98 1 1 95 2 3 65 10 25 0.3 .mu.m 4-19
Example 95 2 3 85 5 10 55 18 27 0.5 .mu.m 4-20
[0459] The composite metal hydroxide thus prepared was filtered,
washed with water, and then dried for 12 hours in a hot air dryer
at 110.degree. C. The composite metal hydroxide and lithium
hydroxide (LiOH) were mixed at a molar ratio of 1:1, the mixture
was subjected to the preliminary firing by heating at a temperature
rise rate of 2.degree. C./min and then maintaining at 450.degree.
C. for 10 hours and then fired at from 700 to 900.degree. C. for 10
hours, thereby obtaining a positive electrode active material
powder.
Comparative Examples 4-6 and 4-7
[0460] In Comparative Example 1-6, composite oxide particles having
constant concentrations of nickel, manganese, and cobalt in the
entire particle were prepared using an aqueous metal solution
having a composition of Ni.sub.80Co.sub.7Mn.sub.13OH.sub.2 which
corresponds to the average composition of Example 4-11.
[0461] In Comparative Example 4-7, particles of a composite oxide
which was represented by LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2
and known to have a capacity of 200 mAh/g were used.
<Experimental Example> Taking of EDX Image
[0462] The concentrations of Ni, Mn, and Co depending on the
distance from the center in the particles prepared in Example 4-11
were measured by EDX, and the results are illustrated in FIG. 89.
From FIG. 89, it can be seen that the concentration is linear with
respect to the distance from the center, the magnitudes of the
concentration gradient in the core portion and the concentration
gradient portion are different from each other, and a shell portion
having constant concentrations of nickel, manganese, and cobalt is
formed on the outside of the concentration gradient portion in the
case of the particles according to Example of the inventive
concept.
[0463] The concentrations of Ni, Mn, and Co depending on the
distance from the center in the particles prepared in Example 4-13
were measured by EDX, and the results are illustrated in FIG. 90.
From FIG. 90, it can be seen that the concentration to the distance
from the center has two straight lines having different
inclinations, the magnitudes of the concentration gradient in the
core portion and the concentration gradient portion are different
from each other, and a shell portion having constant concentrations
of nickel, manganese, and cobalt is formed on the outside of the
core portion and the concentration gradient portion in the case of
the particles according to Example of the inventive concept.
<Experimental Example> Measurement of Charge and Discharge
Characteristics, Cycle-Life Characteristics, and DSC
[0464] The charge and discharge characteristics, cycle-life
characteristics, and DSC characteristics of the batteries
containing the active materials prepared in Examples 4-11 to 4-20
and Comparative Examples 4-6 and 4-7 were measured, and the results
are presented in the following Table 12.
TABLE-US-00012 TABLE 12 Cycle-life Discharge characteristics
capacity (100.sup.th) DSC Example 4-11 221 mAh/g 94.9% 250.degree.
C. Example 4-12 211 mAh/g 95.3% 257.degree. C. Example 4-13 201
mAh/g 96.6% 280.degree. C. Example 4-14 205 mAh/g 96.1% 277.degree.
C. Example 4-15 204 mAh/g 94.3% 274.degree. C. Example 4-16 212
mAh/g 94.9% 272.degree. C. Example 4-17 216 mAh/g 94.2% 268.degree.
C. Example 4-18 207 mAh/g 94.8% 271.degree. C. Example 4-19 220
mAh/g 92.3% 256.degree. C. Example 4-20 209 mAh/g 95.5% 272.degree.
C. Comparative 203 mAh/g 79.2% 233.degree. C. Example 4-6
Comparative 198 mAh/g 90.8% 221.degree. C. Example 4-7
[0465] The charge and discharge characteristics, cycle-life
characteristics, and DSC characteristics of the particles prepared
in Example 4-11 and Comparative Example 4-6 were measured, and the
results are illustrated in FIGS. 91 to 93, respectively.
[0466] From FIGS. 91 to 93, it has been confirmed that the average
composition of the particles in Example 4-11 is the same as the
composition of the particles in Comparative Example 1-6, but the
charge and discharge characteristics, cycle-life characteristics,
and thermal stability are greatly improved in Example 4-11 since
the particles in Example 4-11 includes the core portion, and the
concentration gradient portion, and the shell portion which has
constant concentrations of nickel, manganese, and cobalt and is
formed on the outside of the core portion.
[0467] The charge and discharge characteristics, cycle-life
characteristics, and DSC characteristics of the particles prepared
in Example 4-13 and Comparative Example 4-7 were measured, and the
results are illustrated in FIGS. 94 to 96, respectively. From FIGS.
94 to 96, it has been confirmed that the average composition of the
particles in Example 4-13 is the same as the composition of the
particles in Comparative Example 4-7, but the charge and discharge
characteristics, cycle-life characteristics, and DSC
characteristics are greatly improved in Example 4-13 as compared to
those in Comparative Example 4-7 since the particles in Example
4-13 includes the core portion, and the concentration gradient
portion, and the shell portion.
Examples 4-21 to 4-28
[0468] In order to produce particles having different magnitudes of
concentration gradient in the core portion and the concentration
gradient portion, first, a first aqueous metal solution and a
second aqueous metal solution were prepared by mixing nickel
sulfate, cobalt sulfate, and manganese sulfate so as to have a
composition of Ni.sub.x1Co.sub.y1Mn.sub.z1OH.sub.2 (X1, Y1, Z1) and
a composition of Ni.sub.x2Co.sub.y2Mn.sub.z2OH.sub.2 (x2, y2, z2),
respectively, the first aqueous metal solution and the second
aqueous metal solution were continuously introduced into the
reactor at 0.7 L/hr while mixing them and changing the mixing ratio
thereof, and an ammonia solution having a concentration of 25 mol
was also continuously introduced into the reactor at 0.07 L/hr,
thereby forming the core portion having a first concentration
gradient.
[0469] Thereafter, a third aqueous metal solution prepared by
mixing nickel sulfate, cobalt sulfate, and manganese sulfate so as
to have a constant composition of
Ni.sub.x3Co.sub.y3Mn.sub.z3OH.sub.2 and the second aqueous metal
solution were continuously introduced into the reactor at 0.7 L/hr
while mixing them and changing the mixing ratio thereof, and an
ammonia solution having a concentration of 25 mol was also
continuously introduced into the reactor at 0.07 L/hr, thereby
forming the concentration gradient portion having a second
concentration gradient.
[0470] Thereafter, only a fourth aqueous metal solution prepared by
mixing nickel sulfate, cobalt sulfate, and manganese sulfate so as
to have a constant composition of
Ni.sub.x4Co.sub.y4Mn.sub.z4OH.sub.2 was supplied into the reactor
to form the shell portion having constant concentrations of nickel,
manganese, and cobalt.
[0471] The concentrations of the aqueous metal solutions thus
prepared in Examples 4-21 to 4-28 are as presented in the following
Table 13.
TABLE-US-00013 TABLE 13 Fourth aqueous metal solution First aqueous
Second aqueous Third aqueous Thickness metal solution metal
solution metal solution of shell Ni Co Mn Ni Co Mn Ni Co Mn Ni Co
Mn portion Example 95 2 3 90 4 6 67 9 24 60 15 25 0.3 .mu.m 4-21
Example 95 2 3 85 5 10 67 11 22 60 13 27 0.4 .mu.m 4-22 Example 96
2 2 91 4 5 70 10 20 63 12 25 0.5 .mu.m 4-23 Example 95 2 3 90 4 6
67 9 24 56 17 27 0.2 .mu.m 4-24 Example 96 2 2 85 5 10 67 11 22 55
15 30 0.3 .mu.m 4-25 Example 95 2 3 90 4 6 75 8 17 57 16 27 0.5
.mu.m 4-26 Example 96 2 2 91 3 6 80 7 13 57 16 27 0.4 .mu.m 4-27
Example 85 5 10 80 7 13 55 15 30 45 20 35 0.5 .mu.m 4-28
[0472] The composite metal hydroxide thus prepared was filtered,
washed with water, and then dried for 12 hours in a hot air dryer
at 110.degree. C. The composite metal hydroxide and lithium
hydroxide (LiOH) were mixed at a molar ratio of 1:1, the mixture
was subjected to the preliminary firing by heating at a temperature
rise rate of 2.degree. C./min and then maintaining at 450.degree.
C. for 10 hours and then fired at from 700 to 900.degree. C. for 10
hours, thereby obtaining a positive electrode active material
powder.
Comparative Example 4-8
[0473] In Comparative Example 1-8, composite oxide particles having
constant concentrations of nickel, manganese, and cobalt in the
entire particle were prepared using an aqueous metal solution
having a composition of Ni.sub.76Co.sub.8Mn.sub.16OH.sub.2 which
corresponds to the average composition of Example 4-24.
<Experimental Example> Taking of EDX Image
[0474] The image of the cross section of the particles prepared in
Example 21 was taken using a TEM, and the concentrations of Ni, Mn,
and Co depending on the distance from the center in the particles
were measured by EDX, and the results are illustrated in FIG.
97.
[0475] From FIG. 97, it can be seen that the concentration is
linear with respect to the distance from the center, the magnitudes
of the concentration gradients of nickel, manganese, and cobalt in
the core portion are constant, and the magnitudes of the
concentration gradients are different in the concentration gradient
portion, and the magnitudes of the concentration gradient in the
core portion and the concentration gradient portion are two
different from each other in the case of the particles according to
Example of the inventive concept.
<Experimental Example> Measurement of Charge and Discharge
Characteristics, Cycle-Life Characteristics, and DSC
[0476] The charge and discharge characteristics, cycle-life
characteristics, and DSC characteristics of the batteries
containing the active materials prepared in Examples 4-21 to 4-28
and Comparative Examples 4-6 and 4-8 were measured, and the results
are presented in the following Table 14.
TABLE-US-00014 TABLE 14 Cycle-life Discharge characteristics
capacity (100.sup.th) DSC Example 4-21 220 mAh/g 95.9% 260.degree.
C. Example 4-22 215 mAh/g 95.2% 262.degree. C. Example 4-23 223
mAh/g 93.7% 257.degree. C. Example 4-24 212 mAh/g 96.2% 270.degree.
C. Example 4-25 211 mAh/g 96.0% 271.degree. C. Example 4-26 221
mAh/g 93.9% 263.degree. C. Example 4-27 225 mAh/g 94.2% 253.degree.
C. Example 4-28 195 mAh/g 97.8% 291.degree. C. Comparative 203
mAh/g 79.2% 237.degree. C. Example 4-6 Comparative 195 mAh/g 82.5%
233.degree. C. Example 4-8
[0477] The charge and discharge characteristics, cycle-life
characteristics, and DSC characteristics of the particles prepared
in Example 4-24 and Comparative Example 4-8 were measured, and the
results are illustrated in FIGS. 98 to 100, respectively.
[0478] From FIGS. 98 to 100, it has been confirmed that the average
composition of the particles in Example 4-24 is the same as the
composition of the particles in Comparative Example 4-8, but the
charge and discharge characteristics, cycle-life characteristics,
and DSC characteristics are greatly improved in Example 4-24 as
compared to Comparative Example since the particles in Example 4-24
includes the core portion and the concentration gradient portion in
which the concentrations of nickel, manganese, and cobalt have
gradients and the shell portion in which the concentrations of
nickel, manganese, and cobalt are constant.
<Experimental Example> Measurement of Residual Lithium
[0479] The amounts of residual LiOH and Li.sub.2CO.sub.3 in the
particles prepared in Example 4-21 and Comparative Example 1-6 were
measured, and the results are as presented in the following Table
15.
TABLE-US-00015 TABLE 15 Residual LiOH Li.sub.2CO.sub.3 Sum Example
4-21 5927 3950 9877 Comparative 9469 11466 20935 Example 4-6
<Experimental Example> Measurement of Tap Density and BET
Surface Area
[0480] The tap density and surface area by the BET method of the
particles prepared in Example 4-21 and Comparative Example 4-6 are
as presented in the following Table 16 and illustrated in FIG. 101,
respectively.
TABLE-US-00016 TABLE 16 Tap density Example 4-21 2.54 Comparative
2.37 Example 4-6
[0481] It can be seen that the tap density is greatly improved in
the active material particles prepared in Example of the inventive
concept as compared to Comparative Example.
Examples 5
Examples 5-1 to 5-4: Case Having Constant Concentration in Core
Portion
[0482] Into a coprecipitation reactor (volume: 16 L, output of
rotary motor: 80 W or more), 2.5 L of distilled water was
introduced, N.sub.2 gas was then supplied thereto at a rate of 2
L/min, and the distilled water was stirred at 400 rpm while
maintaining the temperature of the reactor at 45.degree. C.
[0483] A first aqueous metal solution was prepared by mixing nickel
sulfate, cobalt sulfate, and manganese sulfate so as to have
concentrations of Ni.sub.x1Co.sub.y1Mn.sub.z1OH.sub.2 (X1, Y1, Z1),
the first aqueous metal solution was continuously introduced into
the reactor at 0.7 L/hr, and an ammonia solution having a
concentration of 25 mol was also continuously introduced into the
reactor at 0.07 L/hr, thereby forming the inner core portion having
constant concentrations of nickel, manganese, and cobalt.
[0484] A second aqueous metal solution was prepared so as to have a
composition of Ni.sub.x2Co.sub.y2Mn.sub.z2OH.sub.2 (x2, y2, z2),
the first aqueous metal solution and the second aqueous metal
solution were continuously introduced into the reactor at 0.7 L/hr
while mixing them and changing the mixing ratio thereof, and an
ammonia solution having a concentration of 25 mol was also
continuously introduced into the reactor at 0.07 L/hr, thereby
forming the first concentration gradient portion having a
concentration gradient. In addition, a sodium hydroxide solution
having a concentration of 5 mol was supplied into the reactor in
order to adjust the pH so that the pH was maintained at 11.5. The
speed of impeller was controlled at 400 rpm.
[0485] Thereafter, a third aqueous metal solution was prepared by
mixing nickel sulfate, cobalt sulfate, and manganese sulfate so as
to have a constant composition of
Ni.sub.x3Co.sub.y3Mn.sub.z3OH.sub.2, and the third aqueous metal
solution and the second aqueous metal solution were continuously
introduced into the reactor at 0.7 L/hr while mixing them and
changing the mixing ratio thereof, and an ammonia solution having a
concentration of 25 mol was also continuously introduced into the
reactor at 0.07 L/hr, thereby forming the second concentration
gradient portion having a concentration gradient. In addition, a
sodium hydroxide solution having a concentration of 5 mol was
supplied into the reactor in order to adjust the pH so that the pH
was maintained at 11.5. The speed of impeller was controlled at 400
rpm.
[0486] Thereafter, only the third aqueous metal solution was
supplied into the reactor to form the shell portion.
[0487] The concentrations of the aqueous metal solutions in
Examples 5-1 to 5-4 are as presented in the following Table 17.
TABLE-US-00017 TABLE 17 Third aqueous metal solution First aqueous
Second aqueous Thickness metal solution metal solution of shell Ni
Co Mn Ni Co Mn Ni Co Mn portion Example 95 2 3 85 6 9 67 9 24 0.5
.mu.m 5-1 Example 98 0 2 88 4 8 67 9 24 0.3 .mu.m 5-2 Example 85 5
10 78 6 16 60 15 25 0.5 .mu.m 5-3 Example 97 0 3 82 5 13 55 15 30
0.3 .mu.m 5-4
[0488] The composite metal hydroxide thus prepared was filtered,
washed with water, and then dried for 12 hours in a hot air dryer
at 110.degree. C. The composite metal hydroxide and lithium
hydroxide (LiOH) were mixed at a molar ratio of 1:1, the mixture
was subjected to the preliminary firing by heating at a temperature
rise rate of 2.degree. C./min and then maintaining at 450.degree.
C. for 10 hours and then fired at from 700 to 900.degree. C. for 10
hours, thereby obtaining a positive electrode active material
powder.
Comparative Examples 5-1 and 5-2
[0489] In Comparative Example 5-1, positive electrode active
material particles having constant concentrations of nickel,
manganese, and cobalt in the entire particle were prepared using an
aqueous metal solution having a composition of
Ni.sub.82Co.sub.5Mn.sub.13OH.sub.2 which corresponds to the average
composition of the entire particle in Example 5-2.
[0490] In Comparative Example 5-2, positive electrode active
material particles having constant concentrations of nickel,
manganese, and cobalt in the entire particle were prepared using an
aqueous metal solution having a composition of
Ni.sub.76Co.sub.7Mn.sub.17OH.sub.2 which corresponds to the average
composition of the entire particle in Example 5-4.
<Experimental Example> Taking of EDX Image
[0491] The concentrations of Ni, Mn, and Co depending on the
distance from the center in the particles prepared in Example 5-2
were measured by EDX, and the results are illustrated in FIG.
102.
[0492] From FIG. 102, it can be seen that the first concentration
gradient portion and the second concentration gradient portion are
disposed between the inner core portion and the outermost shell
portion which have constant concentrations of nickel, manganese,
and cobalt in the case of the particles according to Example of the
inventive concept.
<Experimental Example> Measurement of Charge and Discharge
Characteristics, Cycle-Life Characteristics, and DSC
[0493] The charge and discharge characteristics, cycle-life
characteristics, and DSC characteristics of the batteries
containing the active materials prepared in Examples 5-1 to 5-4 and
Comparative Examples 5-1 and 5-2 were measured, and the results are
presented in the following Table 18.
TABLE-US-00018 TABLE 18 Cycle-life Discharge characteristics
capacity (100.sup.th) DSC Example 5-1 217.6 mAh/g 93.6%
263.5.degree. C. Example 5-2 220.1 mAh/g 93.1% 259.6.degree. C.
Example 5-3 205.3 mAh/g 94.8% 272.7.degree. C. Example 5-4 211.8
mAh/g 94.3% 268.2.degree. C. Comparative 209.3 mAh/g 81.7%
243.6.degree. C. Example 5-1 Comparative 198.7 mAh/g 83.2%
247.3.degree. C. Example 5-2
[0494] The charge and discharge characteristics, cycle-life
characteristics, and DSC characteristics of the particles prepared
in Example 5-2 and Comparative Example 5-1 were measured, and the
results are illustrated in FIGS. 103 to 105, respectively.
[0495] From FIGS. 103 to 105, it has been confirmed that the
average composition of the particles in Example 5-2 is the same as
the composition of the particles in Comparative Example 5-1, but
the charge and discharge characteristics, cycle-life
characteristics, and thermal stability are greatly improved in
Example 5-2 as compared to Comparative Example 5-1 since the
particles in Example 5-2 includes the inner core portion, and the
first concentration gradient portion, the second concentration
gradient portion, and the shell portion continuous to the second
concentration gradient portion although the average concentrations
of nickel, manganese, and cobalt thereof are the same as those of
the particles in Comparative Example 5-1.
Examples 5-5 to 5-7
[0496] Into a coprecipitation reactor (volume: 16 L, output of
rotary motor: 80 W or more), 2.5 L of distilled water was
introduced, N.sub.2 gas was then supplied thereto at a rate of 2
L/min, and the distilled water was stirred at 400 rpm while
maintaining the temperature of the reactor at 45.degree. C.
[0497] A first aqueous metal solution was prepared by mixing nickel
sulfate, cobalt sulfate, and manganese sulfate so as to have
concentrations of Ni.sub.x1Co.sub.y1Mn.sub.z1OH.sub.2 (X1, Y1, Z1),
the first aqueous metal solution was continuously introduced into
the reactor at 0.7 L/hr, and an ammonia solution having a
concentration of 25 mol was also continuously introduced into the
reactor at 0.07 L/hr, thereby forming the inner core portion having
constant concentrations of nickel, manganese, and cobalt.
[0498] A second aqueous metal solution was prepared so as to have a
composition of Ni.sub.x2Co.sub.y2Mn.sub.z2OH.sub.2 (x2, y2, z2),
the first aqueous metal solution and the second aqueous metal
solution were continuously introduced into the reactor at 0.7 L/hr
while mixing them and changing the mixing ratio thereof, and an
ammonia solution having a concentration of 25 mol was also
continuously introduced into the reactor at 0.07 L/hr, thereby
forming the first concentration gradient portion having a
concentration gradient. In addition, a sodium hydroxide solution
having a concentration of 5 mol was supplied into the reactor in
order to adjust the pH so that the pH was maintained at 11.5. The
speed of impeller was controlled at 400 rpm.
[0499] Thereafter, a third aqueous metal solution was prepared by
mixing nickel sulfate, cobalt sulfate, and manganese sulfate so as
to have a constant composition of
Ni.sub.x3Co.sub.y3Mn.sub.z3OH.sub.2 and only the third aqueous
metal solution was supplied into the reactor to form the shell
portion. In addition, a sodium hydroxide solution having a
concentration of 5 mol was supplied into the reactor in order to
adjust the pH so that the pH was maintained at 11.5. The speed of
impeller was controlled at 400 rpm.
[0500] The concentrations of the aqueous metal solutions in
Examples 5-5 to 5-7 are as presented in the following Table 19.
TABLE-US-00019 TABLE 19 Third aqueous metal solution First aqueous
Second aqueous Thickness metal solution metal solution of shell Ni
Co Mn Ni Co Mn Ni Co Mn portion Example 98 0 2 69 8 23 59 11 30 0.5
.mu.m 5-5 Example 90 3 7 70 10 20 50 15 35 0.3 .mu.m 5-6 Example 80
10 10 60 15 25 40 20 40 0.3 .mu.m 5-7
[0501] The composite metal hydroxide thus prepared was filtered,
washed with water, and then dried for 12 hours in a hot air dryer
at 110.degree. C. The composite metal hydroxide and lithium
hydroxide (LiOH) were mixed at a molar ratio of 1:1, the mixture
was subjected to the preliminary firing by heating at a temperature
rise rate of 2.degree. C./min and then maintaining at 450.degree.
C. for 10 hours and then fired at from 700 to 900.degree. C. for 10
hours, thereby obtaining a positive electrode active material
powder.
Comparative Examples 5-3 and 5-4
[0502] In Comparative Example 5-3, positive electrode active
material particles having constant concentrations of nickel,
manganese, and cobalt in the entire particle were prepared using an
aqueous metal solution having a composition of
Ni.sub.81Co.sub.5Mn.sub.14OH.sub.2 which corresponds to the average
composition of the entire particle in Example 5-5.
[0503] In Comparative Example 5-4, positive electrode active
material particles having constant concentrations of nickel,
manganese, and cobalt in the entire particle were prepared using an
aqueous metal solution having a composition of
Ni.sub.68Co.sub.13Mn.sub.19OH.sub.2 which corresponds to the
average composition of the entire particle in Example 5-4.
<Experimental Example> Taking of EDX Image
[0504] The concentrations of Ni, Mn, and Co depending on the
distance from the center in the particles prepared in Example 5-5
were measured by EDX, and the results are illustrated in FIG.
106.
[0505] From FIG. 106, it can be seen that the concentration
gradient portion is formed on the outside of the inner core portion
and the shell portion having constant concentrations of nickel,
manganese, and cobalt is formed on the concentration gradient
portion in the case of the particles according to Example of the
inventive concept.
<Experimental Example> Measurement of Charge and Discharge
Characteristics, Cycle-Life Characteristics, and DSC
[0506] The charge and discharge characteristics, cycle-life
characteristics, and DSC characteristics of the batteries
containing the active materials prepared in Examples 5-5 to 5-7 and
Comparative Examples 5-3 and 5-4 were measured, and the results are
presented in the following Table 20.
TABLE-US-00020 TABLE 20 Cycle-life Discharge characteristics
capacity (100.sup.th) DSC Example 5-5 220.4 mAh/g 94.7%
269.7.degree. C. Example 5-6 215.7 mAh/g 94.9% 272.2.degree. C.
Example 5-7 201.8 mAh/g 96.3% 286.4.degree. C. Comparative 206.7
mAh/g 84.8% 234.3.degree. C. Example 5-3 Comparative 193.2 mAh/g
88.3% 271.6.degree. C. Example 5-4
[0507] The charge and discharge characteristics, cycle-life
characteristics, and DSC characteristics of the particles prepared
in Example 5-5 and Comparative Example 5-3 were measured, and the
results are illustrated in FIGS. 107 to 109, respectively.
[0508] From FIGS. 107 to 109, it has been confirmed that the
average composition of the particles in Example 5-5 is the same as
the composition of the particles in Comparative Example 5-3, but
the charge and discharge characteristics, cycle-life
characteristics, and thermal stability are greatly improved in
Example 5-5 as compared to Comparative Example 5-3 since the
particles in Example 5-5 includes the shell portion having a
constant concentration on the outside of the inner core portion and
the first concentration gradient portion.
<Experimental Example> Measurement of Residual Lithium
[0509] The amounts of LiOH and Li.sub.2CO.sub.3 were measured in
order to determine the amount of residual lithium in the particles
prepared in Example 5-5 and Comparative Example 4-3, and the
results are as presented in the following Table 21.
TABLE-US-00021 TABLE 21 Sample LiOH Li.sub.2CO.sub.3 Sum of
residual lithium Comparative 7124 5397 12521 Example 5-3 Example
5-5 3512 2699 6211
[0510] It has been confirmed that residual lithium is improved by
nearly 50% in the active material according to Example 5-5 of the
inventive concept as compared to the active material prepared in
Comparative example 5-3.
Examples 6
Examples 6-1 and 6-2
[0511] In order to produce particles having two concentration
gradients in the core portion, first, a first aqueous metal
solution and a second aqueous metal solution were prepared by
mixing nickel sulfate, cobalt sulfate, and manganese sulfate so as
to have a composition of Ni.sub.x1Co.sub.y1Mn.sub.z1OH.sub.2 (X1,
Y1, Z1) and a composition of Ni.sub.x2Co.sub.y2Mn.sub.z2OH.sub.2
(x2, y2, z2), respectively, the first aqueous metal solution and
the second aqueous metal solution were continuously introduced into
the reactor at 0.7 L/hr while mixing them and changing the mixing
ratio thereof, and an ammonia solution having a concentration of 25
mol was also continuously introduced into the reactor at 0.07 L/hr,
thereby forming the core portion having a first concentration
gradient.
[0512] Thereafter, a third aqueous metal solution prepared by
mixing nickel sulfate, cobalt sulfate, and manganese sulfate so as
to have a constant composition of
Ni.sub.x3Co.sub.y3Mn.sub.z3OH.sub.2 and the second aqueous metal
solution were continuously introduced into the reactor at 0.7 L/hr
while mixing them and changing the mixing ratio thereof, and an
ammonia solution having a concentration of 25 mol was also
continuously introduced into the reactor at 0.07 L/hr, thereby
forming the core portion having a second concentration
gradient.
[0513] Thereafter, an aqueous solution for the formation of shell
portion that was prepared by mixing nickel sulfate, cobalt sulfate,
and manganese sulfate so as to have a constant composition of
Ni.sub.x4Co.sub.y4Mn.sub.z4OH.sub.2 was supplied into the reactor
to form the shell portion having a concentration that is different
from the concentration at the end of the core portion having a
second concentration gradient.
[0514] The concentrations of the aqueous metal solutions thus
prepared in Examples 6-1 and 6-2 are as presented in the following
Table 22.
TABLE-US-00022 TABLE 22 First aqueous Second aqueous Third aqueous
Fourth aqueous Thickness metal solution metal solution metal
solution metal solution of shell Ni Co Mn Ni Co Mn Ni Co Mn Ni Co
Mn portion Example 98 2 2 90 4 6 69 08 23 60 12 28 0.5 .mu.m 6-1
Example 98 2 2 90 4 6 70 7 23 60 10 30 0.5 .mu.m 6-2
[0515] The composite metal hydroxide thus prepared was filtered,
washed with water, and then dried for 12 hours in a hot air dryer
at 110.degree. C. The composite metal hydroxide and lithium
hydroxide (LiOH) were mixed at a molar ratio of 1:1, the mixture
was subjected to the preliminary firing by heating at a temperature
rise rate of 2.degree. C./min and then maintaining at 450.degree.
C. for 10 hours and then fired at from 700 to 900.degree. C. for 10
hours, thereby obtaining a positive electrode active material
powder.
Comparative Example 6-1
[0516] In Comparative Example 6-1, composite oxide particles having
constant concentrations of nickel, manganese, and cobalt in the
entire particle were prepared using an aqueous metal solution
having a composition of Ni.sub.80Co.sub.6Mn.sub.14OH.sub.2.
<Experimental Example> Taking of EDX Image
[0517] The concentrations of Ni, Mn, and Co depending on the
distance from the center in the particles prepared in Example 6-1
were measured by EDX, and the results are illustrated in FIG.
110.
[0518] From FIG. 110, it can be seen that the core portion has two
magnitudes of concentration gradient and the shell portion in which
the concentration at the end is maintained is formed in the case of
the particles according to Example of the inventive concept.
<Experimental Example> Measurement of Charge and Discharge
Characteristics, Cycle-Life Characteristics, and DSC
[0519] The charge and discharge characteristics, cycle-life
characteristics, and DSC characteristics of the batteries
containing the active materials prepared in Examples 6-1 and 6-2
and Comparative Example 6-1 were measured, and the results are
presented in the following Table 23 and illustrated in FIGS. 111 to
114.
TABLE-US-00023 TABLE 23 Cycle-life Discharge characteristics
capacity (100.sup.th) DSC Example 6-1 223 mAh/g 95.5% 270.degree.
C. Example 6-2 222 mAh/g 95.9% 275.degree. C. Comparative 207 mAh/g
84.8% 234.degree. C. Example 6-1
[0520] From Table 23 above and FIG. 111 illustrating the charge and
discharge characteristics, it has been confirmed that the capacity
of the battery including the positive electrode active material
according to the inventive concept is 220 mAh/g or more, and from
FIG. 114, it can be seen that the thermal stability thereof is
greatly improved in the DSC characteristics as the ignition
temperature is higher than that in Comparative Example by
40.degree. C. or higher although a high content of nickel is
contained to have a high capacity.
<Experimental Example> Measurement of Residual Lithium
[0521] The amounts of residual LiOH and Li.sub.2CO.sub.3 in the
particles prepared in Example 6-1 and Comparative Example 6-1 were
measured, and the results are as presented in the following Table
24.
TABLE-US-00024 TABLE 24 Residual LiOH Li.sub.2CO.sub.3 Sum
Comparative 7124 5397 12521 Example 6-1 Example 6-1 3208 3095
6307
[0522] From Table 24 above, it has been confirmed that residual
lithium in Example 3-1 of the inventive concept has decreased to
about 50% of that in Comparative example.
<Experimental Example> Measurement of Tap Density and BET
Surface Area
[0523] The tap density of the particles prepared in Example 6-1 and
Comparative Example 6-1 are as presented in the following Table
25.
TABLE-US-00025 TABLE 25 Tap density Example 6-1 2.52 Comparative
2.62 Example 6-1
[0524] In the positive electrode active material according to
embodiments of the inventive concept, a shell portion having a
constant concentration is formed on the surface of the core portion
in which concentrations of nickel, manganese, and cobalt have
gradients, and thus the positive electrode active material exhibits
excellent cycle-life characteristics and charge and discharge
characteristics, has a stabilized crystal structure while having a
high capacity, and is structurally stabilized even when being used
at a high voltage.
[0525] In addition, according to an embodiment of the inventive
concept, the positive electrode active material includes a first
element containing a first metal and a second element composed of
one or more first elements. The second element may include a
concentration gradient portion having a content of the first metal
changed and a concentration maintained portion having a constant
content of the first metal. Consequently, it is possible to provide
a positive electrode active material containing the second element
with characteristics improved by the first metal as the content of
the first metal in the second element can be controlled.
Examples 7
[0526] The forth embodiment of the inventive concept will be
described with FIGS. 115 to 122.
[0527] Into a coprecipitation reactor (volume: 16 L, output of
rotary motor: 80 W or more), 2.5 L of distilled water was
introduced, N.sub.2 gas was then supplied thereto at a rate of 2
L/min, and the distilled water was stirred at 400 rpm while
maintaining the temperature of the reactor at 45.degree. C.
[0528] A first aqueous metal solution and a second aqueous metal
solution were prepared by mixing nickel sulfate, cobalt sulfate,
and manganese sulfate so as to have a composition of
Ni.sub.x1Co.sub.y1Mn.sub.z1OH.sub.2 (X1, Y1, Z1) and a composition
of Ni.sub.x2Co.sub.y2Mn.sub.z2OH.sub.2 (x2, y2, z2), respectively,
the first aqueous metal solution and the second aqueous metal
solution were continuously introduced into the reactor at 0.7 L/hr
while mixing them and changing the mixing ratio thereof, and an
ammonia solution having a concentration of 25 mol was also
continuously introduced into the reactor at 0.7 L/hr, thereby
forming the first concentration gradient portion. In addition, a
sodium hydroxide solution having a concentration of 5 mol was
supplied into the reactor in order to adjust the pH so that the pH
was maintained at 11.5. The speed of impeller was controlled at 400
rpm.
[0529] Thereafter, only the second aqueous metal solution was
supplied into the reactor for a certain period of time to form the
first concentration maintained portion in which the concentrations
of nickel, manganese, and cobalt at the outermost part of the first
concentration gradient portion are maintained on the outside of the
first concentration gradient portion in a thickness of from 0.2 to
1 .mu.m.
[0530] Thereafter, a third aqueous metal solution prepared by
mixing nickel sulfate, cobalt sulfate, and manganese sulfate so as
to have constant concentrations of
Ni.sub.x3Co.sub.y3Mn.sub.z3OH.sub.2 was supplied into the reactor
while mixing them and changing the mixing ratio of the third
aqueous metal solution to the second aqueous metal solution,
thereby forming the second concentration gradient portion on the
outside of the first concentration maintained portion.
[0531] Thereafter, only the third aqueous metal solution was
supplied into the reactor for a certain period of time to form the
second concentration maintained portion on the outside of the
second concentration gradient portion.
[0532] The concentrations of the aqueous metal solutions in
Examples 7-1 to 7-4 are as presented in the following Table 26.
TABLE-US-00026 TABLE 26 Thickness of second First aqueous Second
aqueous Third aqueous concentration metal solution metal solution
metal solution maintained Ni Co Mn Ni Co Mn Ni Co Mn portion
Example 95 2 3 80 7 13 54 15 31 0.3 .mu.m 7-1 Example 85 5 10 70 10
20 55 18 27 0.5 .mu.m 7-2 Example 85 3 12 73 10 17 58 14 28 0.4
.mu.m 7-3 Example 80 7 13 69 12 19 57 13 30 0.2 .mu.m 7-4
[0533] The composite metal hydroxide thus produced was filtered,
washed with water, and then dried for 12 hours in a hot air dryer
at 110.degree. C. The composite metal hydroxide and lithium
hydroxide (LiOH) were mixed at a molar ratio of 1:1, the mixture
was subjected to the preliminary firing by heating at a temperature
rise rate of 2.degree. C./min and then maintaining at 450.degree.
C. for 10 hours and then fired at from 700 to 900.degree. C. for 10
hours, thereby obtaining a positive electrode active material
powder.
Comparative Examples
[0534] In Comparative Example 7-1, particles are produced in the
same manner as in Example 7-1 except that a first aqueous metal
solution and a second aqueous metal solution were prepared by
mixing nickel sulfate, cobalt sulfate, and manganese sulfate so as
to have concentration gradients from the center part to the surface
part of the entire particle and a composition of
Ni.sub.85Co.sub.5Mn.sub.10OH.sub.2 and a composition of
Ni.sub.57Co.sub.16Mn.sub.27OH.sub.2, respectively, and the first
aqueous metal solution and the second aqueous metal solution were
mixed while changing the mixing ratio thereof.
[0535] In Comparative Example 7-2, positive electrode active
material particles having constant concentrations of nickel,
manganese, and cobalt in the entire particle were produced using an
aqueous metal solution having a composition of
Ni.sub.62Co.sub.14Mn.sub.24OH.sub.2 which corresponds to the
average composition of the particle in Example 7-2.
[0536] In Comparative Example 7-3, positive electrode active
material particles having constant concentrations of nickel,
manganese, and cobalt in the entire particle were produced using an
aqueous metal solution having a composition of
Ni.sub.55Col.sub.8Mn.sub.27OH.sub.2.
<Experimental Example> Taking of EDX Image
[0537] The concentrations of Ni, Mn, and Co depending on the
distance from the center in the particles produced in Example 7-2
were measured by EDX, and the results are illustrated in FIG.
115.
[0538] In FIG. 115, a particle structure in which the first
concentration gradient portion, the concentration maintained
portion, and the second concentration gradient portion are formed
has been confirmed in the case of the particles according to
Example of the inventive concept, and it can be seen that the
magnitudes of the concentration gradients in the first
concentration gradient portion and the second concentration
gradient portion are constant as the functional relations between
the first concentration gradient portion and the distance and
between the second concentration gradient portion and the distance
are linear, respectively.
<Experimental Example> Measurement of Battery
Characteristics
[0539] The charge and discharge characteristics, lifespan
characteristics, DSC characteristics, and tap density of the
batteries which included the active materials produced in Examples
7-1 to 7-4 and Comparative Examples 1 to 3 were measured, and the
results are presented in the following Table 27.
TABLE-US-00027 TABLE 27 Lifespan Capacity characteristics Tap
(mAh/g) -2.7 (%) -2.7 DSC den- to -4.3 V, to -4.3 V, (.degree. C.)
-4.3 V sity 0.1 C 0.5 C, 100.sup.th cycle cut off (g/cc) Example
7-1 199.8 95.0 281.9 2.59 Example 7-2 194.4 95.6 285.2 2.60 Example
7-3 200.7 94.8 277.8 2.58 Example 7-4 196.1 95.4 283.3 2.59
Comparative 193.1 95.3 284.5 2.58 Example 7-1 Comparative 183.7
90.8 268.0 2.50 Example 7-2 Comparative 178.1 95.0 286.8 2.51
Example 7-3
[0540] The charge and discharge characteristics, lifespan
characteristics, and DSC characteristics of the particles produced
in Example 7-2 and Comparative Example 7-2 were measured, and the
results are illustrated in FIGS. 116 to 118, respectively.
[0541] In FIGS. 116 to 118, it has been confirmed that the
composition of particles in Comparative Example 7-2 is the same as
the average composition of the particles in Example 7-2 but the
charge and discharge characteristics, lifespan characteristics, and
thermal stability are greatly improved in Example 7-2 as compared
to those in Comparative Example 7-2 since the particles in Example
7-2 includes the first concentration gradient portion, the first
concentration maintained portion, the second concentration gradient
portion, and the second concentration maintained portion that is
continuous with respect to the second concentration gradient
portion.
Examples
[0542] Into a coprecipitation reactor (volume: 16 L, output of
rotary motor: 80 W or more), 2.5 L of distilled water was
introduced, N.sub.2 gas was then supplied thereto at a rate of 2
L/min, and the distilled water was stirred at 400 rpm while
maintaining the temperature of the reactor at 45.degree. C.
[0543] A first aqueous metal solution and a second aqueous metal
solution were prepared by mixing nickel sulfate, cobalt sulfate,
and manganese sulfate so as to have a composition of
Ni.sub.x1Co.sub.y1Mn.sub.z1OH.sub.2 (X1, Y1, Z1) and a composition
of Ni.sub.x2Co.sub.y2Mn.sub.z2OH.sub.2 (x2, y2, z2), respectively,
the first aqueous metal solution and the second aqueous metal
solution were continuously introduced into the reactor at 0.7 L/hr
while mixing them and changing the mixing ratio thereof, and an
ammonia solution having a concentration of 25 mol was also
continuously introduced into the reactor at 0.7 L/hr, thereby
forming the first concentration gradient portion. In addition, a
sodium hydroxide solution having a concentration of 5 mol was
supplied into the reactor in order to adjust the pH so that the pH
was maintained at 11.5. The speed of impeller was controlled at 400
rpm.
[0544] Thereafter, only the second aqueous metal solution was
supplied into the reactor for a certain period of time to form the
first concentration maintained portion in which the concentrations
of nickel, manganese, and cobalt of the first concentration
gradient portion are maintained on the outside of the first
concentration gradient portion in a thickness of from 0.2 to 1
.mu.m.
[0545] Thereafter, a third aqueous metal solution prepared by
mixing nickel sulfate, cobalt sulfate, and manganese sulfate so as
to have constant concentrations of
Ni.sub.x3Co.sub.y3Mn.sub.z3OH.sub.2 was supplied into the reactor
while mixing them and changing the mixing ratio of the third
aqueous metal solution to the second aqueous metal solution,
thereby forming the second concentration gradient portion on the
outside of the first concentration maintained portion.
[0546] Thereafter, only a fourth aqueous metal solution prepared by
mixing nickel sulfate, cobalt sulfate, and manganese sulfate so as
to have constant concentrations of
Ni.sub.x4Co.sub.y4Mn.sub.z4OH.sub.2 was supplied into the reactor
for a certain period of time to form the second concentration
maintained portion having discontinuous concentrations of nickel,
manganese, and cobalt on the outside of the second concentration
gradient portion.
[0547] The concentrations of the aqueous metal solutions in
Examples 7-5 to 7-8 are as presented in the following Table 28.
TABLE-US-00028 TABLE 28 Thickness of second First aqueous Second
aqueous Third aqueous Fourth aqueous concentration metal solution
metal solution metal solution metal solution maintained Ni Co Mn Ni
Co Mn Ni Co Mn Ni Co Mn portion Example 93 2 5 82 6 12 65 13 22 59
12 29 0.3 .mu.m 7-5 Example 90 3 7 80 6 14 63 11 26 57 13 30 0.4
.mu.m 7-6 Example 85 5 10 73 10 17 61 12 27 55 17 28 0.5 .mu.m 7-7
Example 80 5 10 70 11 19 60 19 21 56 15 29 0.2 .mu.m 7-8
[0548] The composite metal hydroxide thus produced was filtered,
washed with water, and then dried for 12 hours in a hot air dryer
at 110.degree. C. The composite metal hydroxide and lithium
hydroxide (LiOH) were mixed at a molar ratio of 1:1, the mixture
was subjected to the preliminary firing by heating at a temperature
rise rate of 2.degree. C./min and then maintaining at 450.degree.
C. for 10 hours and then fired at from 700 to 900.degree. C. for 10
hours, thereby obtaining a positive electrode active material
powder.
Comparative Examples
[0549] In Comparative Example 7-4, positive electrode active
material particles having constant concentrations of nickel,
manganese, and cobalt in the entire particle were produced using an
aqueous metal solution having a composition of
Ni.sub.65Co.sub.12Mn.sub.23OH.sub.2 which corresponds to the
average composition of the entire particle in Example 7-7.
[0550] In Comparative Example 7-5, positive electrode active
material particles having constant concentrations of nickel,
manganese, and cobalt in the entire particle were produced using an
aqueous metal solution having a composition of
Ni.sub.65Co.sub.12Mn.sub.23OH.sub.2 which corresponds to the
composition of the second concentration gradient portion in Example
7-7.
<Experimental Example> Taking of EDX Image
[0551] The concentrations of Ni, Mn, and Co depending on the
distance from the center in the particles produced in Example 7-7
were measured by EDX, and the results are illustrated in FIG.
119.
[0552] In FIG. 119, it has been confirmed that the first
concentration gradient portion, the first concentration maintained
portion, the second concentration gradient portion, and the second
concentration maintained portion that is discontinuous with respect
to the second concentration gradient portion are formed in the case
of the particles according to Example of the inventive concept.
[0553] In addition, it can be seen that the magnitudes of the
concentration gradients in the first concentration gradient portion
and the second concentration gradient portion are constant since
the functions of concentration according to distance in the first
and second concentration gradient portions are linear.
<Experimental Example> Measurement of Charge and Discharge
Characteristics, Lifespan Characteristics, and DSC
[0554] The charge and discharge characteristics, lifespan
characteristics, DSC characteristics, and tap density of the
batteries which included the active materials produced in Examples
7-5 to 7-7 and Comparative Examples 7-4 and 7-5 were measured, and
the results are presented in the following Table 29.
TABLE-US-00029 TABLE 29 Lifespan Capacity characteristics Tap
(mAh/g) -2.7 (%) -2.7 DSC den- to -4.3 V, to -4.3 V, (.degree. C.)
-4.3 V sity 0.1 C 0.5 C, 100.sup.th cycle cut off (g/cc) Example
7-5 205.9 94.7 275.9 2.58 Example 7-6 203.3 94.9 278.8 2.59 Example
7-7 200.2 95.3 280.5 2.60 Example 7-8 197.5 95.6 284.2 2.59
Comparative 187.6 90.1 263.3 2.50 Example 7-4 Comparative 178.8
95.1 287.1 2.49 Example 7-5
[0555] The charge and discharge characteristics, lifespan
characteristics, and DSC characteristics of the particles produced
in Example 7-7 and Comparative Example 7-4 were measured, and the
results are illustrated in FIGS. 120 to 122, respectively.
[0556] In FIGS. 120 to 122, it has been confirmed that the
composition of particles in Comparative Example 7-4 is the same as
the average composition of the particles in Example 7-7 but the
charge and discharge characteristics, lifespan characteristics, and
thermal stability are greatly improved in Example 7-7 as compared
to those in Comparative Example 7-4 since the particles in Example
7-7 includes the first concentration gradient portion, the first
concentration maintained portion, the second concentration gradient
portion, and the second concentration maintained portion.
[0557] The positive electrode active material according to
embodiments of the inventive concept includes the first
concentration maintained portion between the first concentration
gradient portion and the second concentration gradient portion
which have concentration gradients of nickel, manganese, and cobalt
and the second concentration maintained portion on the outside of
the second concentration gradient portion, thus the content of Ni
contained in the particle is high so that the capacity is high, the
crystal structure is stabilized by the concentration gradient so
that excellent lifespan characteristics and charge and discharge
characteristics are exhibited, and the positive electrode active
material is structurally stabilized even when being used at a high
voltage.
[0558] The fifth embodiment of the inventive concept will be
described with FIGS. 123 to 125.
Examples 8
[0559] Into a coprecipitation reactor (volume: 16 L, output of
rotary motor: 80 W or more), 2.5 L of distilled water was
introduced, N.sub.2 gas was then supplied thereto at a rate of 2
L/min, and the distilled water was stirred at 400 rpm while
maintaining the temperature of the reactor at 45.degree. C.
[0560] A first aqueous metal solution prepared by mixing nickel
sulfate, cobalt sulfate, and manganese sulfate so as to have a
composition of Ni.sub.x1Co.sub.y1Mn.sub.z1OH.sub.2 (X1, Y1, Z1) and
a second aqueous metal solution prepared by mixing nickel sulfate,
cobalt sulfate, and manganese sulfate so as to have a composition
of Ni.sub.x2Co.sub.y2Mn.sub.z2OH.sub.2 (x2, y2, z2) were
continuously introduced into the reactor at 0.7 L/hr while mixing
them and changing the mixing ratio of the second aqueous metal
solution to the first aqueous metal solution from 0 to 100, and an
ammonia solution having a concentration of 25 mol was also
continuously introduced into the reactor at 0.7 L/hr, thereby
forming a core portion having a concentration gradient. In
addition, a sodium hydroxide solution having a concentration of 5
mol was supplied into the reactor in order to adjust the pH so that
the pH was maintained at 11.5. The speed of impeller was controlled
at 400 rpm.
[0561] A third aqueous metal solution prepared by mixing nickel
sulfate, cobalt sulfate, and manganese sulfate so as to have
constant concentrations of Ni.sub.x3Co.sub.y3Mn.sub.z3OH.sub.2 was
supplied into the reactor while mixing them and changing the mixing
ratio of the third aqueous metal solution to the second aqueous
metal solution from 0 to 100, thereby forming a second core
portion. After the second core portion having a desired thickness
was formed, only the third aqueous metal solution was supplied into
the reactor to form a shell portion having a constant concentration
that was the same as the final concentration of the second core
portion, thereby producing a composite metal hydroxide.
[0562] The concentrations of the aqueous metal solutions in
Examples 8-1 to 8-3 are as presented in the following Table 30.
TABLE-US-00030 TABLE 30 First aqueous Second aqueous Third aqueous
metal solution metal solution metal solution Thickness Ni Co Mn Ni
Co Mn Ni Co Mn of shell Example 75 5 20 90 7 3 65 10 25 0.5 .mu.m
8-1 Example 86 0 14 96 0 4 54 15 31 0.4 .mu.m 8-2 Example 80 10 10
95 2 3 45 20 35 0.3 .mu.m 8-3
[0563] The composite metal hydroxide thus produced was filtered,
washed with water, and then dried for 12 hours in a hot air dryer
at 110.degree. C. The composite metal hydroxide and lithium
hydroxide (LiOH) were mixed at a molar ratio of 1:1, the mixture
was subjected to the preliminary firing by heating at a temperature
rise rate of 2.degree. C./min and then maintaining at 450.degree.
C. for 10 hours and then fired at from 700 to 900.degree. C. for 10
hours, thereby obtaining a positive electrode active material
powder.
Examples
[0564] The first core portion was formed in the same manner as in
Examples above, the second core portion was then formed by mixing
the third aqueous metal solution and the second aqueous metal
solution while changing the mixing ratio thereof, and only a fourth
aqueous metal solution prepared by mixing nickel sulfate, cobalt
sulfate, and manganese sulfate so as to have constant
concentrations of Ni.sub.x4Co.sub.y4Mn.sub.z4OH.sub.2 was supplied
into the reactor to form the shell portion.
[0565] The concentrations of the aqueous metal solutions prepared
in Examples 8-4 and 8-5 are as presented in the following Table
31.
TABLE-US-00031 TABLE 31 First aqueous Second aqueous Third aqueous
Fourth aqueous metal solution metal solution metal solution metal
solution Thickness Ni Co Mn Ni Co Mn Ni Co Mn Ni Co Mn of shell
Example 80 5 15 90 5 5 50 20 30 40 20 40 0.5 .mu.m 8-4 Example 75
10 15 95 2 3 65 15 20 55 15 30 0.3 .mu.m 8-5
[0566] The composite metal hydroxide thus produced was filtered,
washed with water, and then dried for 12 hours in a hot air dryer
at 110.degree. C. The composite metal hydroxide and lithium
hydroxide (LiOH) were mixed at a molar ratio of 1:1, the mixture
was subjected to the preliminary firing by heating at a temperature
rise rate of 2.degree. C./min and then maintaining at 450.degree.
C. for 10 hours and then fired at from 700 to 900.degree. C. for 10
hours, thereby obtaining a positive electrode active material
powder.
Comparative Examples
[0567] In Comparative Example 8-1, particles having a constant
concentration in the entire particle were produced by supplying an
aqueous metal solution having a composition represented by
Ni.sub.70Co.sub.9Mn.sub.21OH.sub.2 which corresponds to the average
composition of the entire particle in Example 8-2.
[0568] In Comparative Example 8-2, particles were produced in the
same manner as in Example 8-2 except that the first core portion
was not formed in Example 8-2.
[0569] In Comparative Example 8-3, particles having a constant
concentration in the entire particle were produced by supplying an
aqueous metal solution having a composition represented by
Ni.sub.60Co.sub.15Mn.sub.25OH.sub.2 which corresponds to the
average composition of the entire particle in Example 8-4.
<Experimental Example> Taking of EDX Image
[0570] The concentrations of Ni, Mn, and Co depending on the
distance from the center in the particles produced in Example 8-2
were measured by EDX, and the results are illustrated in FIG.
123.
[0571] From FIG. 123, it has been confirmed that the magnitudes of
the concentration gradients of the metals in the first core portion
and the magnitudes of the concentration gradients of the metals in
the second core portion are reversed in the case of the particles
according to Example of the inventive concept.
<Experimental Example> Measurement of Charge and Discharge
Characteristics, Cycle-Life Characteristics, and DSC
[0572] The charge and discharge characteristics, cycle-life
characteristics, and DSC characteristics of the batteries which
included the active materials produced in Examples 8-1 to 8-5 and
Comparative Examples 8-1 to 8-3 were measured, and the results are
presented in the following Table 32 and illustrated in FIGS. 124
and 125.
TABLE-US-00032 TABLE 32 Cycle-Life Discharge characteristics
characteristics (100.sup.th) DSC Example 8-1 208.3 mAh/g 94.7%
273.5.degree. C. Example 8-2 199.7 mAh/g 95.0% 280.7.degree. C.
Example 8-3 194.8 mAh/g 95.6% 288.9.degree. C. Example 8-4 187.6
mAh/g 96.3% 296.3.degree. C. Example 8-5 205.9 mAh/g 95.2%
281.6.degree. C. Comparative 185.3 mAh/g 88.2% 268.2.degree. C.
Example 8-1 Comparative 195.9 mAh/g 95.2% 283.5.degree. C. Example
8-2 Comparative 178.7 mAh/g 91.2% 267.6.degree. C. Example 8-3
[0573] In FIGS. 124 and 125, it has been confirmed that the
capacity and the cycle-life characteristics until 100.sup.th cycle
are greatly improved in the active materials produced in Examples
of the inventive concept as compared to the active materials
produced in Comparative Examples.
[0574] The positive electrode active material according to
embodiments of the inventive concept exhibits excellent cycle-life
characteristics and excellent charge and discharge characteristics
as the magnitudes of concentration gradients of nickel, manganese,
and cobalt are controlled in two core portions having the
concentration gradients, and thus the positive electrode active
material has a stabilized crystal structure as well as a high
capacity and is structurally stabilized even when being used at a
high voltage.
[0575] While the inventive concept has been described with
reference to exemplary embodiments, it will be apparent to those
skilled in the art that various changes and modifications may be
made without departing from the spirit and scope of the inventive
concept. Therefore, it should be understood that the above
embodiments are not limiting, but illustrative.
[0576] According to a embodiment of the inventive concept, in the
cathode active material for a lithium secondary battery according
to the present invention, the concentrations of all metals
contained in the cathode active material are increased or decreased
with continuous concentration gradient from the core to the surface
part. Accordingly, the crystal structure is stabilized and the
thermostability is increased because there is no phase boundary
having rapid concentration change from the core to the surface
part.
[0577] According to a embodiment of the inventive concept, in the
cathode active material for a lithium secondary battery according
to the present invention, the concentration of one metal is
constant from the core to the surface part, and the concentrations
of the other two metals are increased or decreased with continuous
concentration gradient from the core to the surface part.
Accordingly, the crystal structure of the particle is stabilized
and the thermostability is increased because there is no phase
boundary having rapid concentration change from the particle core
to the surface part.
[0578] Accordingly, the lithium secondary battery having the
cathode active material shows excellent capacity characteristics as
well as excellent lifetime characteristics and charge/discharge
characteristics, and has thermostability even in high temperatures.
Particularly, when the Ni concentration of the cathode active
material according to the present invention, which shows the whole
particle concentration gradient, is maintained constantly, a stable
active material showing high capacity can be prepared.
[0579] While the invention has been described with respect to the
above specific embodiments, it should be recognized that various
modifications and changes may be made and also fall within the
scope of the invention as defined by the claims that follow.
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