U.S. patent application number 14/227820 was filed with the patent office on 2014-07-31 for method for preparing positive electrode active material for lithium secondary battery, positive electrode active material for lithium secondary battery, and lithium secondary battery including same.
This patent application is currently assigned to L&F Material Co., Ltd.. The applicant listed for this patent is L&F Material Co., Ltd.. Invention is credited to Su An Choi, Sang-Hoon Jeon, Seung-Won Lee.
Application Number | 20140212749 14/227820 |
Document ID | / |
Family ID | 49161388 |
Filed Date | 2014-07-31 |
United States Patent
Application |
20140212749 |
Kind Code |
A1 |
Choi; Su An ; et
al. |
July 31, 2014 |
Method for Preparing Positive Electrode Active Material for Lithium
Secondary Battery, Positive Electrode Active Material for Lithium
Secondary Battery, and Lithium Secondary Battery Including Same
Abstract
Disclosed are a method for preparing a positive electrode active
material for a lithium secondary battery and a positive electrode
active material for a lithium secondary battery, the method
including: preparing a mixture of a precursor represented by
Chemical Formula 1 below, a lithium composite oxide represented by
Chemical Formula 2 below and capable of
intercalating/deintercalating lithium ions, and a lithium feed
material; and firing the prepared mixture: A(OH).sub.2-a [Chemical
Formula 1] Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b
[Chemical Formula 2]
Inventors: |
Choi; Su An; (Gyeonggi-do,
KR) ; Lee; Seung-Won; (Daegu, KR) ; Jeon;
Sang-Hoon; (Daegu, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
L&F Material Co., Ltd. |
Gyeongsangbuk-Do |
|
KR |
|
|
Assignee: |
L&F Material Co., Ltd.
Gyeongsangbuk-Do
KR
|
Family ID: |
49161388 |
Appl. No.: |
14/227820 |
Filed: |
March 27, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/KR2012/002286 |
Mar 28, 2012 |
|
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14227820 |
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Current U.S.
Class: |
429/211 ;
252/182.1; 264/618; 429/223 |
Current CPC
Class: |
H01M 4/485 20130101;
Y02P 70/50 20151101; H01M 10/0525 20130101; C01P 2002/52 20130101;
C01P 2004/84 20130101; H01M 4/0471 20130101; H01M 4/505 20130101;
H01M 8/04 20130101; H01M 2004/028 20130101; Y02E 60/50 20130101;
C01G 53/50 20130101; Y02E 60/10 20130101; H01M 4/5825 20130101;
C01P 2006/40 20130101; C01D 15/02 20130101; H01M 4/131 20130101;
H01M 10/052 20130101; H01M 4/1391 20130101; H01M 4/525 20130101;
C01P 2004/61 20130101; C01P 2004/80 20130101 |
Class at
Publication: |
429/211 ;
429/223; 252/182.1; 264/618 |
International
Class: |
H01M 4/58 20060101
H01M004/58; H01M 4/04 20060101 H01M004/04; H01M 4/525 20060101
H01M004/525; C01D 15/02 20060101 C01D015/02; H01M 4/505 20060101
H01M004/505 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2012 |
KR |
10-2012-0025695 |
Claims
1. A method for preparing a positive electrode active material for
a lithium secondary battery, the method comprising: preparing a
mixture of a precursor represented by Chemical Formula 1 below, a
lithium composite oxide represented by Chemical Formula 2 below and
capable of intercalating/deintercalating lithium ions, and a
lithium feed material; and firing the prepared mixture:
A(OH).sub.2-a [Chemical Formula 1] wherein in Chemical Formula 1,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; and
-0.3.ltoreq.a.ltoreq.0.3, 0.5.ltoreq..alpha..ltoreq.0.64,
0.15.ltoreq..beta..ltoreq.0.29, and
0.21.ltoreq..gamma..ltoreq.0.35,
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
2] wherein in Chemical Formula 2,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.35.ltoreq..alpha.<0.5,
0.19.ltoreq..beta..ltoreq.0.34, and
0.31.ltoreq..gamma..ltoreq.0.46.
2. The method of claim 1, wherein the weight ratio of the precursor
represented by Chemical Formula 1 to the lithium composite oxide
represented by Chemical Formula 2 and capable of
intercalating/deintercalating lithium ions is 95/5 to 70/30.
3. The method of claim 1, wherein the precursor represented by
Chemical Formula 1 has a particle diameter of 8 to 12 .mu.m.
4. The method of claim 1, wherein the lithium composite oxide
represented by Chemical Formula 2 and capable of
intercalating/deintercalating lithium ions has a particle diameter
of 3 to 8 .mu.m.
5. The method of claim 1, wherein the lithium feed material is
nitrate, carbonate, acetate, oxalate, oxide, hydroxide, or sulfate,
which contains lithium, or a combination thereof.
6. The method of claim 1, wherein the precursor represented by
Chemical Formula 1 is represented by Chemical Formula 3 below:
A(OH).sub.2-a [Chemical Formula 3] wherein in Chemical Formula 3,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; and
-0.3.ltoreq.a.ltoreq.0.3, 0.5.ltoreq..alpha..ltoreq.0.61,
0.15.ltoreq..beta..ltoreq.0.26, and
0.24.ltoreq..gamma..ltoreq.0.35.
7. The method of claim 1, wherein the lithium composite oxide
represented by Chemical Formula 2 and capable of
intercalating/deintercalating lithium ions is represented by
Chemical Formula 4 below:
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
4] wherein in Chemical Formula 4,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.43.ltoreq..alpha.<0.5,
0.19.ltoreq..beta..ltoreq.0.26, and
0.31.ltoreq..gamma..ltoreq.0.38.
8. The method of claim 1, wherein in the firing of the prepared
mixture, the firing temperature is 800 to 1000.degree. C.
9. The method of claim 1, wherein the particle diameter of the
precursor represented by Chemical Formula 1 is larger than the
particle diameter of the lithium composite oxide represented by
Chemical Formula 2 and capable of intercalating/deintercalating
lithium ions.
10. The method of claim 1, wherein the amount of remaining
water-soluble lithium after the firing of the prepared mixture is
reduced to 20 to 50% based on the amount of remaining water-soluble
lithium when the precursor represented by Chemical Formula 1 is
fired alone.
11. The method of claim 1, wherein in the positive electrode active
material for a lithium secondary battery, which is obtained by
performing the firing of the prepared mixture, the surface Ni
content of a positive electrode active material derived from
Chemical Formula 1 is further reduced than the surface Ni content
of a positive electrode active material prepared by firing the
precursor represented by Chemical Formula 1 alone.
12. The method of claim 11, wherein the surface Ni content of the
positive electrode active material derived from Chemical Formula 1
is further reduced by less than 5% than the surface Ni content of
the positive electrode active material prepared by firing the
precursor represented by Chemical Formula 1 alone.
13. The method of claim 11, wherein, when ten particles of the
positive electrode active material derived from Chemical Formula 1
are randomly selected from the positive electrode active material
for a lithium secondary battery and surfaces thereof are analyzed,
the standard deviation of the Ni content is smaller than 1.00.
14. A positive electrode active material for a lithium secondary
battery, the positive electrode active material comprising: a
lithium composite oxide represented by Chemical Formula 5 below and
capable of intercalating/deintercalating lithium ions; and a
lithium composite oxide represented by Chemical Formula 2 below and
capable of intercalating/deintercalating lithium ions, wherein the
lithium composite oxide represented by Chemical Formula 5 below and
capable of intercalating/deintercalating lithium ions is prepared
from a precursor, and wherein the surface Ni content of the lithium
composite oxide represented by Chemical Formula 5 below and capable
of intercalating/deintercalating lithium ions is further reduced
than the surface Ni content of a lithium composite oxide prepared
by firing the precursor alone:
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
5] wherein in Chemical Formula 5,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.5.ltoreq..alpha.<0.64,
0.15.ltoreq..beta..ltoreq.0.29, and
0.21.ltoreq..gamma..ltoreq.0.35, and
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
2] wherein in Chemical Formula 2,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.35.ltoreq..alpha.<0.5,
0.19.ltoreq..beta..ltoreq.0.34, and
0.31.ltoreq..gamma..ltoreq.0.46.
15. The positive electrode active material of claim 14, wherein the
particle diameter of the lithium composite oxide represented by
Chemical Formula 5 and capable of intercalating/deintercalating
lithium ions is larger than the particle diameter of the lithium
composite oxide represented by Chemical Formula 2 and capable of
intercalating/deintercalating lithium ions.
16. The positive electrode active material of claim 14, wherein the
lithium composite oxide expressed by Chemical Formula 5 and capable
of intercalating/deintercalating lithium ions has a particle
diameter of 8 to 12 .mu.m.
17. The positive electrode active material of claim 14, wherein the
lithium composite oxide expressed by Chemical Formula 2 and capable
of intercalating/deintercalating lithium ions has a particle
diameter of 3 to 8 .mu.m.
18. The positive electrode active material of claim 14, wherein the
weight ratio of the lithium composite oxide represented by Chemical
Formula 5 and capable of intercalating/deintercalating lithium ions
to the lithium composite oxide represented by Chemical Formula 2
and capable of intercalating/deintercalating lithium ions is 95/5
to 70/30.
19. The positive electrode active material of claim 14, wherein the
lithium composite oxide represented by Chemical Formula 5 and
capable of intercalating/deintercalating lithium ions is
represented by Chemical Formula 6 below:
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
6] wherein in Chemical Formula 6,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.50.ltoreq..alpha.<0.61,
0.15.ltoreq..beta..ltoreq.0.26, and
0.24.ltoreq..gamma..ltoreq.0.35.
20. The positive electrode active material of claim 14, wherein the
lithium composite oxide represented by Chemical Formula 2 and
capable of intercalating/deintercalating lithium ions is
represented by Chemical Formula 4 below:
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
4] wherein in Chemical Formula 4,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.43.ltoreq..alpha.<0.5,
0.19.ltoreq..beta..ltoreq.0.26, and
0.31.ltoreq..gamma..ltoreq.0.38.
21. A lithium secondary battery comprising a positive electrode, an
anode, and an electrolyte, wherein the positive electrode includes
a current collector and a positive electrode active material layer
formed on the current collector, and wherein the positive electrode
active material layer contains the positive electrode active
material of claim 14.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 10-2012-0025695, and
PCT/KR2012/002286 filed in the Korean Intellectual Property Office
on Mar. 13, 2012, and Mar. 28, 2012, the entire contents of which
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] (a) Field of the Invention
[0003] The present invention relates to a method for preparing a
positive electrode active material for a lithium secondary battery,
a positive electrode active material for a lithium secondary
battery, and a lithium secondary battery including the same.
[0004] (b) Description of the Related Art
[0005] Recently, with respect to the trend of miniaturization and
lightweight of portable electronic devices, the batteries used as
power for the devices need to be have high performance and high
capacity.
[0006] Batteries generate electric power by using materials capable
of having an electrochemical reaction at positive and negative
electrodes. Of these batteries, a representative example is a
lithium secondary battery in which electric energy is generated due
to a change in a chemical potential when lithium ions are
intercalated/deintercalated at positive and negative
electrodes.
[0007] The lithium secondary battery is manufactured by using a
material capable of reversibly intercalating/deintercalating
lithium ions for positive electrode and negative electrode active
materials and charging an organic electrolyte or a polymer
electrolyte between a positive electrode and a negative
electrode.
[0008] As for the positive electrode active material for the
lithium secondary battery, a lithium composite compound is used,
and examples thereof may include metal composite oxides such as
LiCoO.sub.2, LiMn.sub.2O.sub.4, LiNiO.sub.2, and LiMnO.sub.2, which
have been researched.
[0009] Of these positive electrode active materials, Mn-based
positive electrode active materials, such as LiMn.sub.2O.sub.4 and
LiMnO.sub.2, are attractive since they are easy to synthesize, are
relatively cheap, have relatively excellent thermal stability at
the time of overcharging as compared with the other active
materials, and have less pollution on environment. However, these
materials have a drawback in that the capacity is small.
[0010] LiCoO.sub.2 is a representative positive electrode active
material that is currently commercialized on the market since it
has favorable electrical conductivity and a high battery voltage of
about 3.7 V as well as excellent cycle lifespan characteristics,
stability, and discharge capacity. However, LiCoO.sub.2 is not
priced competitively since it is expensive and thus accounts for
30% or more of the battery price.
[0011] LiNiO.sub.2 is difficult to synthesize even though it
provides the highest charge capacity in the above-mentioned
positive electrode active materials. Moreover, the high oxidation
state of nickel is a causative factor of deteriorating battery and
electrode lifespan characteristics. Moreover, the self discharge of
nickel is severe and reversibility of nickel is deteriorated.
Moreover, nickel insufficiently secures stability and thus is
difficult to commercialize.
[0012] For the improvement in stability and capacity of the
battery, JP 2011-216485 discloses a positive electrode active
material for a lithium secondary battery, in which lithium nickel
composite oxides having different particle size distributions and
different compositions are mixed. Here, the degree of improvement
is explained as a synergy effect due to the physical mixing of
different positive electrode active materials.
[0013] KR2012-0017004 discloses a positive electrode active
material for a lithium secondary battery, which is prepared by
mixing precursors having different compositions and firing the
mixture together with a lithium compound. However, since the firing
temperature needs to be varied depending on the compositional ratio
of Ni/Co/Mn in order to exhibit the maximum performance for the
compositions, the corresponding technology is restricted to a
mixture of precursors having very similar compositions.
[0014] The above information disclosed in this Background section
is only for enhancement of understanding of the background of the
invention and therefore it may contain information that does not
form the prior art that is already known in this country to a
person of ordinary skill in the art.
SUMMARY OF THE INVENTION
[0015] The present invention has been made in an effort to provide
a positive electrode active material having advantages of having
high capacity and high efficiency as well as improved high-rate
characteristic and long lifespan characteristics.
[0016] An exemplary embodiment of the present invention provides a
method for preparing a positive electrode active material for a
lithium secondary battery, the method including: preparing a
mixture of a precursor represented by Chemical Formula 1 below, a
lithium composite oxide represented by Chemical Formula 2 below and
capable of intercalating/deintercalating lithium ions, and a
lithium feed material; and firing the prepared mixture:
A(OH).sub.2-a [Chemical Formula 1]
[0017] wherein in Chemical Formula 1,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; and
-0.3.ltoreq.a.ltoreq.0.3, 0.5.alpha..ltoreq.64,
0.15.ltoreq..beta..ltoreq.0.29, and
0.21.ltoreq..gamma..ltoreq.0.35,
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
2]
[0018] wherein in Chemical Formula 2,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.35.ltoreq..alpha.<0.5,
0.19.ltoreq..beta..ltoreq.0.34, and
0.31.ltoreq..gamma..ltoreq.0.46.
[0019] The weight ratio of the precursor represented by Chemical
Formula 1 to the lithium composite oxide represented by Chemical
Formula 2 and capable of intercalating/deintercalating lithium ions
may be 95/5 to 70/30.
[0020] The precursor represented by Chemical Formula 1 may have a
particle diameter of 8 to 12 .mu.m.
[0021] The lithium composite oxide represented by Chemical Formula
2 and capable of intercalating/deintercalating lithium ions may
have a particle diameter of 3 to 8 .mu.m.
[0022] The lithium feed material may be nitrate, carbonate,
acetate, oxalate, oxide, hydroxide, or sulfate, which contains
lithium, or a combination thereof.
[0023] The precursor represented by Chemical Formula 1 may be
represented by Chemical Formula 3 below:
A(OH).sub.2-a [Chemical Formula 3]
[0024] In Chemical Formula 3,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; and
-0.3.ltoreq.a.ltoreq.0.3, 0.5.ltoreq..alpha..ltoreq.0.61,
0.15.beta..ltoreq.0.26, and 0.24.ltoreq..gamma.0.35.
[0025] The lithium composite oxide represented by Chemical Formula
2 and capable of intercalating/deintercalating lithium ions may be
represented by Chemical Formula 4 below:
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
4]
[0026] wherein in Chemical Formula 4,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.43.ltoreq..alpha.<0.5,
0.19.ltoreq..beta..ltoreq.0.26, and
0.31.ltoreq..gamma..ltoreq.0.38.
[0027] Here, in the firing of the prepared mixture, the firing
temperature may be 800 to 1000.degree. C.
[0028] The particle diameter of the precursor represented by
Chemical Formula 1 may be larger than the particle diameter of the
lithium composite oxide represented by Chemical Formula 2 and
capable of intercalating/deintercalating lithium ions.
[0029] The amount of remaining water-soluble lithium after the
firing of the prepared mixture may be reduced to 20 to 50% based on
the amount of remaining water-soluble lithium when the precursor
represented by Chemical Formula 1 is fired alone.
[0030] Here, in the positive electrode active material for a
lithium secondary battery, which is obtained by performing the
firing of the prepared mixture, the surface Ni content of a
positive electrode active material derived from Chemical Formula 1
may be further reduced than the surface Ni content of a positive
electrode active material prepared by firing the precursor
represented by Chemical Formula 1 alone.
[0031] The surface Ni content of the positive electrode active
material derived from Chemical Formula 1 may be further reduced by
less than 5% than the surface Ni content of the positive electrode
active material prepared by firing the precursor represented by
Chemical Formula 1 alone.
[0032] Here, when ten particles of the positive electrode active
material derived from Chemical Formula 1 are randomly selected from
the positive electrode active material for a lithium secondary
battery and surfaces thereof are analyzed, the standard deviation
of the Ni content may be smaller than 1.00.
[0033] Another embodiment of the present invention provides a
positive electrode active material for a lithium secondary battery,
the positive electrode active material including: a lithium
composite oxide represented by Chemical Formula 5 below and capable
of intercalating/deintercalating lithium ions; and a lithium
composite oxide represented by Chemical Formula 2 below and capable
of intercalating/deintercalating lithium ions, wherein the lithium
composite oxide represented by Chemical Formula 5 below and capable
of intercalating/deintercalating lithium ions is prepared from a
precursor, and wherein the surface Ni content of the lithium
composite oxide represented by Chemical Formula 5 below and capable
of intercalating/deintercalating lithium ions is further reduced
than the surface Ni content of a lithium composite oxide prepared
by firing the precursor alone:
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
5]
[0034] wherein in Chemical Formula 5,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.5.ltoreq..alpha.<0.64,
0.15.ltoreq..beta..ltoreq.0.29, and
0.21.ltoreq..gamma..ltoreq.0.35, and
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
2]
[0035] wherein in Chemical Formula 2,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.35.ltoreq..alpha.<0.5,
0.19.ltoreq..beta..ltoreq.0.34, and
0.31.ltoreq..gamma..ltoreq.0.46.
[0036] The particle diameter of the lithium composite oxide
represented by Chemical Formula 5 and capable of
intercalating/deintercalating lithium ions may be larger than the
particle diameter of the lithium composite oxide represented by
Chemical Formula 2 and capable of intercalating/deintercalating
lithium ions.
[0037] The lithium composite oxide expressed by Chemical Formula 5
and capable of intercalating/deintercalating lithium ions may have
a particle diameter of 8 to 12 .mu.m.
[0038] The lithium composite oxide expressed by Chemical Formula 2
and capable of intercalating/deintercalating lithium ions may have
a particle diameter of 3 to 8 .mu.m.
[0039] The weight ratio of the lithium composite oxide represented
by Chemical Formula 5 and capable of intercalating/deintercalating
lithium ions to the lithium composite oxide represented by Chemical
Formula 2 and capable of intercalating/deintercalating lithium ions
may be 95/5 to 70/30.
[0040] The lithium composite oxide represented by Chemical Formula
5 and capable of intercalating/deintercalating lithium ions may be
represented by Chemical Formula 6 below:
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
6]
[0041] wherein in Chemical Formula 6,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.50.ltoreq..alpha.<0.61,
0.15.ltoreq..beta..ltoreq.0.26, and
0.24.ltoreq..gamma..ltoreq.0.35.
[0042] The lithium composite oxide represented by Chemical Formula
2 and capable of intercalating/deintercalating lithium ions may be
represented by Chemical Formula 4 below:
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
4]
[0043] wherein in Chemical Formula 4,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.43.ltoreq..alpha.<0.5,
0.19.ltoreq..beta..ltoreq.0.26, and
0.31.ltoreq..gamma..ltoreq.0.38.
[0044] Yet another embodiment of the present invention provides a
lithium secondary battery including a positive electrode, an anode,
and an electrolyte, wherein the positive electrode includes a
current collector and a positive electrode active material layer
formed on the current collector, and wherein the positive electrode
active material layer contains the above-described positive
electrode active material according to an embodiment of the present
invention.
[0045] According to an embodiment of the present invention, there
can be obtained a positive electrode active material having high
capacity and high efficiency as well as improved high-rate
characteristics and long lifespan characteristics.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 is a schematic view of a lithium secondary
battery;
[0047] FIG. 2 is a discharge graph showing rate characteristics of
a battery of Example 1; and
[0048] FIG. 3 is a discharge graph showing rate characteristics of
a battery of Comparative Example 4.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0049] Hereinafter, embodiments of the present invention will be
described in detail. However, these embodiments are merely
exemplified, and the scope of protection of the present invention
is not limited thereto but defined by the appended claims.
[0050] In an embodiment of the present invention, there is provided
a method for preparing a positive electrode active material for a
lithium secondary battery, the method including: preparing a
mixture of a precursor represented by Chemical Formula 1 below, a
lithium composite oxide represented by Chemical Formula 2 below and
capable of intercalating/deintercalating lithium ions, and a
lithium feed material; and firing the prepared mixture:
A(OH).sub.2-a [Chemical Formula 1]
[0051] wherein in Chemical Formula 1,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; and
-0.3.ltoreq.a.ltoreq.0.3, 0.5.ltoreq..alpha..ltoreq.0.64,
0.15.ltoreq..beta..ltoreq.0.29, and
0.21.ltoreq..gamma..ltoreq.0.35,
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
2]
wherein in Chemical Formula 2,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.35.ltoreq..alpha.<0.5,
0.19.ltoreq..beta..ltoreq.0.34, and
0.31.ltoreq..gamma..ltoreq.0.46.
[0052] The weight ratio of the precursor represented by Chemical
Formula 1 to the lithium composite oxide represented by Chemical
Formula 2 and capable of intercalating/deintercalating lithium ions
(precursor/lithium composite oxide) may be 95/5 to 70/30. When this
range is satisfied, the amount of lithium remaining after the
firing can be reduced and discharge capacity characteristics of the
battery can be improved.
[0053] The prepared positive electrode active material has two
different composition groups of
Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma., and, of the particles
having the two compositions, a particle having a higher Ni content
may be a positive electrode active material particle in which the
Ni content is higher in an inside than a surface.
[0054] This may be different from the conventional art in which
positive electrode active materials with different compositions of
Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.are individually fired and
then mixed at a predetermined ratio.
[0055] As in an embodiment of the present invention, when the
lithium feed material is added to the mixture of the precursor and
the lithium composite oxide and then the firing is conducted, the
lithium feed material reacts with the precursor and the lithium
composite oxide.
[0056] The mixing of active materials according to the conventional
art corresponds to simple physical mixing, which has some
limitations in the improvement of powder characteristics and
battery characteristics.
[0057] As in an embodiment of the present invention, the chemical
reaction of the precursor, the lithium composite compound (e.g.,
heterogeneous active material), and Li is performed by mixing a
lithium feed material with the precursor and the lithium composite
compound, which have different compositions of
Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma., followed by firing, so
that the chemical reaction of the precursor, lithium composite
oxide, and lithium leads to a concentration gradient between two
different compositions of
Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma..
[0058] Here, of the particles having the different compositions, a
particle having a higher Ni content may be a positive electrode
active material particle in which the Ni content is lower in an
inside than a surface.
[0059] Besides this chemical concentration gradient reaction,
lithium reacts with a composition having a higher Mn content more
selectively due to the presence of Mn which has been known to have
excellent reactivity with lithium, thereby fundamentally preventing
the generation of remaining water-soluble lithium in the
composition having a higher Ni content.
[0060] The particle diameter of the lithium composite oxide
represented by Chemical Formula 2 and capable of
intercalating/deintercalating lithium ions may be smaller than the
particle diameter of the precursor represented by Chemical Formula
1. This can offset a negative effect such as the power down which
may result from lithium composite oxide represented by Chemical
Formula 2 and having a relatively higher Mn content.
[0061] Since the lithium composite oxide represented by Chemical
Formula 2 and capable of intercalating/deintercalating lithium ions
has a higher Mn content and a smaller particle diameter than the
precursor represented by Chemical Formula 1, Mn elution is more
likely to occur. Therefore, the Mn elution can be controlled by
appropriately adjusting the mixed ratio of the lithium composite
oxide having a higher Mn content.
[0062] More specifically, the particle diameter of the precursor
represented by Chemical Formula 1 may be 8 to 12 .mu.m.
[0063] In addition, the particle diameter of the lithium composite
oxide represented by Chemical Formula 2 and capable of
intercalating/deintercalating lithium ions may be 3 to 8 .mu.m.
[0064] The lithium feed material is nitrate, carbonate, acetate,
oxalate, oxide, hydroxide, or sulfate, which contains lithium, or a
combination thereof, but is not limited thereto.
[0065] More specifically, the precursor represented by Chemical
Formula 1 may be represented by Chemical Formula 3 below:
A(OH).sub.2-a [Chemical Formula 3]
[0066] wherein in Chemical Formula 3,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; and
-0.3.ltoreq.a.ltoreq.0.3, 0.5.ltoreq..alpha..ltoreq.0.61,
0.15.ltoreq..beta..ltoreq.0.26, and 0.24.ltoreq..gamma.0.35.
[0067] More specifically, the lithium composite oxide represented
by Chemical Formula 2 and capable of intercalating/deintercalating
lithium ions may be represented by Chemical Formula 4 below:
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
4]
[0068] wherein in Chemical Formula 4,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05, and
0.ltoreq.b.ltoreq.0.05; and 0.43.ltoreq..alpha.<0.5,
0.19.ltoreq..beta..ltoreq.0.26, and
0.31.ltoreq..gamma..ltoreq.0.38.
[0069] In the firing of the prepared mixture, the firing
temperature may be 800 to 1000.degree. C. The range may be
appropriate to simultaneously fire the precursor and the lithium
composite oxide according to an embodiment of the present
invention.
[0070] The amount of remaining water-soluble lithium after the
firing of the prepared mixture may be 20 to 50% based on the amount
of remaining water-soluble lithium when the precursor represented
by Chemical Formula 1 is fired alone.
[0071] The reduction of the remaining lithium can solve many of
problems, such as instability of electrode plate slurry and gas
generation after application to the battery, which result from a
high amount of remaining lithium in the conventional art.
[0072] In the positive electrode active material for a lithium
secondary battery, which is obtained by performing the firing of
the prepared mixture, the surface Ni content of a positive
electrode active material derived from Chemical Formula 1 may be
further reduced than the surface Ni content of a positive electrode
active material prepared by firing the precursor represented by
Chemical Formula 1 alone.
[0073] The surface Ni content of the positive electrode active
material derived from Chemical Formula 1 may be further reduced by
less than 5% than the surface Ni content of the positive electrode
active material prepared by firing the precursor represented by
Chemical Formula 1 alone.
[0074] When ten particles of the positive electrode active material
derived from Chemical Formula 1 are randomly selected from the
positive electrode active material for a lithium secondary battery
and surfaces thereof are analyzed, the standard deviation of the Ni
content may be smaller than 1.00.
[0075] Descriptions thereof are shown as described above, and thus
will be omitted.
[0076] In another embodiment of the present invention, there is
provided a positive electrode active material for a lithium
secondary battery, the positive electrode active material
including: a lithium composite oxide represented by Chemical
Formula 5 below and capable of intercalating/deintercalating
lithium ions; and a lithium composite oxide represented by Chemical
Formula 2 below and capable of intercalating/deintercalating
lithium ions, wherein the lithium composite oxide represented by
Chemical Formula 5 below and capable of
intercalating/deintercalating lithium ions is prepared from a
precursor, and wherein the surface Ni content of the lithium
composite oxide represented by Chemical Formula 5 below and capable
of intercalating/deintercalating lithium ions is further reduced
than the surface Ni content of a lithium composite oxide prepared
by firing the precursor alone:
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
5]
[0077] wherein in Chemical Formula 5,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.5.ltoreq..alpha.<0.64,
0.15.ltoreq..beta..ltoreq.0.29, and 0.21.ltoreq..beta..ltoreq.0.35,
and
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
2]
[0078] wherein in Chemical Formula 2,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; and -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05, 0.35.ltoreq..alpha.<0.5,
0.19.ltoreq..beta..ltoreq.0.34, and
0.31.ltoreq..gamma..ltoreq.0.46.
[0079] The particle diameter of the lithium composite oxide
represented by Chemical Formula 2 and capable of
intercalating/deintercalating lithium ions may be smaller than the
particle diameter of the lithium composite oxide represented by
Chemical Formula 5 and capable of intercalating/deintercalating
lithium ions.
[0080] Descriptions thereof overlap the above descriptions of the
method for preparing a positive electrode active material for a
lithium secondary battery according to the embodiment of the
present invention, and thus will be omitted.
[0081] More specifically, the particle diameter of the lithium
composite oxide represented by Chemical Formula 5 and capable of
intercalating/deintercalating lithium ions may be 8 to 12
.mu.m.
[0082] More specifically, the particle diameter of the lithium
composite oxide represented by Chemical Formula 2 and capable of
intercalating/deintercalating lithium ions may be 3 to 8 .mu.m.
[0083] The weight ratio of the lithium composite oxide represented
by Chemical Formula 5 and capable of intercalating/deintercalating
lithium ions to the lithium composite oxide represented by Chemical
Formula 2 and capable of intercalating/deintercalating lithium ions
(Chemical Formula 5/Chemical Formula 2) may be 95/5 to 70/30.
[0084] When this range is satisfied, the amount of lithium
remaining after the firing can be reduced and discharge capacity
characteristics of the battery can be improved.
[0085] More specifically, the lithium composite oxide represented
by Chemical Formula 5 and capable of intercalating/deintercalating
lithium ions may be represented by Chemical Formula 6 below.
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
6]
[0086] wherein in Chemical Formula 6,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; -0.05.ltoreq.z.ltoreq.0.1, 0.ltoreq.a.ltoreq.0.05,
0.ltoreq.b.ltoreq.0.05; and 0.50.ltoreq..alpha.<0.61,
0.15.ltoreq..beta..ltoreq.0.26, and
0.24.ltoreq..beta..ltoreq.0.35.
[0087] More specifically, the lithium composite oxide represented
by Chemical Formula 2 and capable of intercalating/deintercalating
lithium ions may be represented by Chemical Formula 4 below:
Li[Li.sub.zA.sub.(1-z-a)D.sub.a]E.sub.bO.sub.2-b [Chemical Formula
4]
[0088] In Chemical Formula 4,
A=Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma.; D is at least one
element selected from the group consisting of Mg, Al, B, Zr, and
Ti; E is at least one element selected from the group consisting of
P, F, and S; -0.05.ltoreq.z.ltoreq.0.1; 0.ltoreq.a.ltoreq.0.05;
0.ltoreq.b.ltoreq.0.05; and 0.43.ltoreq..alpha.<0.5,
0.19.ltoreq..beta..ltoreq.0.26, and
0.31.ltoreq..gamma..ltoreq.0.38.
[0089] In still another embodiment of the present invention, there
is provided a lithium secondary battery including a positive
electrode, an anode, and an electrolyte, wherein the positive
electrode includes a current collector and a positive electrode
active material layer formed on the current collector, and wherein
the positive electrode active material layer contains the
above-described positive electrode active material according to an
embodiment of the present invention.
[0090] Descriptions of the positive electrode active material are
the same as those in the embodiment of the present invention, and
thus will be omitted.
[0091] The positive electrode active material layer may contain a
binder and a conductor.
[0092] The binder serves to favorably bind positive electrode
active material particles to each other and favorably bind the
positive electrode active material to the current collector.
Examples thereof may include polyvinyl alcohol, carboxymethyl
cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl
chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a
polymer including ethylene oxide, polyvinyl pyrrolidone,
polyurethane, polytetrafluoroethylene, polyvinylidene fluoride,
polyethylene, polypropylene, a styrene-butadiene rubber, an
acrylated styrene-butadiene rubber, an epoxy resin, nylon, and the
like, but are not limited thereto.
[0093] The conductor is used to give conductivity to the
electrodes, and any material that does not cause a chemical change
and corresponds to an electronically conductive material may be
used in batteries. As an example of the conductor, a conductive
material containing a carbon based material, such as natural
graphite, artificial graphite, carbon black, acetylene black,
Ketjen black, or carbon fiber; a metal based material, such as a
metal powder or a metal fiber of copper, nickel, aluminum, silver,
or the like; a conductive polymer such as a polyphenylene
derivative; or a mixture thereof, may be used.
[0094] The negative electrode includes a current collector and a
negative electrode active material layer formed on the current
collector, and the negative electrode active material layer
contains a negative electrode active material.
[0095] Examples of the negative electrode active material may
include a material capable of reversibly
intercalating/deintercalating lithium ions, lithium, a lithium
alloy, a material capable of doping and dedoping lithium, and a
transition metal oxide.
[0096] The material capable of reversibly
intercalating/deintercalating lithium ions is a carbon-based
material. Any carbon-based negative electrode active material that
can be generally used in a lithium ion secondary battery may be
used, and representative examples thereof may include crystalline
carbon, amorphous carbon, and a mixture thereof. Examples of the
crystalline carbon may include formless, plate type, flake type,
spherical, or fiber type natural graphite and artificial graphite.
Examples of the amorphous carbon may include soft carbon
(low-temperature fired carbon), hard carbon, mesophase pitch
carbide, fired coke, and the like.
[0097] The lithium alloy may be an alloy of lithium and a metal
selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg,
Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.
[0098] Examples of the material capable of doping and dedoping
lithium may include Si, SiO.sub.x (0<x<2), Si--Y alloys
(wherein Y is an element selected from the group consisting of
alkali metals, alkali earth metals, Group 13 elements, Group 14
elements, transition elements, rare earth elements, and
combinations thereof, but is not Si), Sn, SnO.sub.2, Sn--Y (wherein
Y is an element selected from the group consisting of alkali
metals, alkali earth metals, Group 13 elements, Group 14 elements,
transition elements, rare earth elements, and combinations thereof,
but is not Si), and the like, and at least one of these materials
may be used in a mixture with SiO.sub.2. Here, the element Y may be
selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y,
Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb,
Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In,
Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.
[0099] Examples of the transition metal oxide may include vanadium
oxides, lithium-vanadium oxides, and the like.
[0100] The negative electrode active material layer also contains a
binder, and may further optionally contain a conductor.
[0101] The binder serves to favorably bind negative electrode
active material particles to each other and favorably bind a
negative electrode active material to a current collector. Examples
thereof may include polyvinyl alcohol, carboxymethyl cellulose,
hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl
chloride, polyvinyl fluoride, a polymer including ethylene oxide,
polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene,
polyvinylidene fluoride, polyethylene, polypropylene, a
styrene-butadiene rubber, an acrylated styrene-butadiene rubber, an
epoxy resin, nylon, and the like, but are not limited thereto.
[0102] The conductor is used to give conductivity to the
electrodes, and any material that does not cause a chemical change
and corresponds to an electronically conductive material may be
used in batteries. As an example of the conductor, a conductive
material containing a carbon based material, such as natural
graphite, artificial graphite, carbon black, acetylene black,
Ketjen black, or carbon fiber; a metal based material, such as a
metal powder or a metal fiber of copper, nickel, aluminum, silver,
or the like; a conductive polymer such as a polyphenylene
derivative; or a mixture thereof, may be used.
[0103] As for the current collector, at least one selected from the
group consisting of a copper foil, a nickel foil, a stainless steel
foil, a titanium foil, a nickel foam, a copper foam, a polymer
substrate coated with a conductive metal, or a combination thereof
may be used.
[0104] Al may be used for the current collector, but is not limited
thereto.
[0105] The negative electrode and positive electrode are
manufactured by mixing an active material, a conductor, and a
binder in a solvent to prepare an active material composition and
then coating the active material composition on a current
collector. Since the electrode manufacturing method is well known
in the art, detailed descriptions thereof will be omitted in the
present specification. Examples of the solvent may include
[0106] N-methylpyrrolidone, but are not limited thereto.
[0107] The electrolyte contains a non-aqueous organic solvent and a
lithium salt.
[0108] The non-aqueous organic solvent serves as a medium through
which ions involved in an electrochemical reaction of a battery can
move.
[0109] Examples of the non-aqueous organic solvent may include
carbonate-based, ester-based, ether-based, ketone-based,
alcohol-based, and aprotic solvent. Examples of the carbonate based
solvent may include dimethyl carbonate (DMC), diethyl carbonate
(DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC),
ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene
carbonate (EC), propylene carbonate (PC), butylene carbonate (BC),
and the like. Examples of the ester-based solvent may include
methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate,
methyl propionate, ethyl propionate, .gamma.-butyrolactone,
decanolide, valerolactone, mevalonolactone, caprolactone, and the
like. Examples of the ether-based solvent may include dibutyl
ether, tetraglyme, diglyme, dimethoxy ethane, 2-methyl
tetrahydrofuran, tetrahydrofuran, and the like. Examples of the
ketone-based solvent may include cyclohexanone and the like. In
addition, examples of the alcohol-based solvent may include ethyl
alcohol, isopropyl alcohol, and the like. Examples of the aprotic
solvent may include nitriles including R--CN(R is a C2-C20
straight, branched, or cyclic hydrocarbon group which may include a
double bonded aromatic ring or an ether bond), amides including
dimethylformamide, dioxolanes including 1,3-dioxolane, sulfolanes,
and the like.
[0110] The non-aqueous organic solvents may be used alone or in a
combination of two or more. When they are used in a combination of
two or more, the mixing ratio thereof may be appropriately
controlled according to the desired battery performance, which may
be widely understood by those worked in the art.
[0111] In addition, when the carbonate-based solvent is used, it is
favorable to use cyclic carbonate and chained carbonate in a
mixture thereof. In this case, the cyclic carbonate and the chained
carbonate are mixed at a volume ratio of 1:1 to 1:9, so that the
performance of the electrolyte can be favorably exhibited.
[0112] The non-aqueous organic solvent according to an embodiment
of the present invention may further contain an aromatic
hydrocarbon-based organic solvent in addition to the
carbonate-based solvent. Here, the carbonate-based solvent and the
aromatic hydrocarbon based organic solvent may be mixed at a volume
ratio of 1:1 to 30:1.
[0113] As the aromatic hydrocarbon-based organic solvent, an
aromatic hydrocarbon-based compound of Chemical Formula 7 below may
be used:
##STR00001##
[0114] (wherein in Chemical Formula 7, R.sub.1 to R.sub.6 each are
independently hydrogen, halogen, C.sub.1-C.sub.10 alkyl group, a
holoalkyl group, or a combination thereof).
[0115] The aromatic hydrocarbon-based organic solvent may be
selected from the group consisting of benzene, fluorobenzene,
1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene,
1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene,
1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene,
1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, Iodo benzene,
1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene,
1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene,
1,2-difluorotoluene, 1,3-difluorotoluene, 1,4-difluorotoluene,
1,2,3-trifluorotoluene, 1,2,4-trifluorotoluene, chlorotoluene,
1,2-dichlorotoluene, 1,3-dichlorotoluene, 1,4-dichlorotoluene,
1,2,3-trichlorotoluene, 1,2,4-trichlorotoluene, iodotoluene,
1,2-diiodotoluene, 1,3-diiodotoluene, 1,4-diiodotoluene,
1,2,3-triiodotoluene, 1,2,4-triiodotoluene, xylene, and a
combination thereof.
[0116] The non-aqueous electrolyte may further contain vinylene
carbonate or an ethylene carbonate-based compound of Chemical
Formula 8 below in order to improve the battery lifespan:
##STR00002##
[0117] (wherein in Chemical Formula 8, R.sub.7 and R.sub.8 each are
independently hydrogen, a halogen group, a cyano group (CN), a
nitro group (NO.sub.2), or a C.sub.1-C.sub.5 fluoroalkyl group, and
at least one of R.sub.7 and R.sub.8 is a halogen group, a cyano
group (CN), a nitro group (NO.sub.2), or a C.sub.1-C.sub.5
fluoroalkyl group).
[0118] Representative examples of the ethylene carbonate-based
compound may include difluoroethylene carbonate, chloroethylene
carbonate, dichloroethylene carbonate, bromoethylene carbonate,
dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene
carbonate, fluoroethylene carbonate, and the like. When these
lifespan improving additives are further used, the use amounts
thereof may be appropriately controlled.
[0119] The lithium salt is dissolved in the organic solvent to act
as a lithium ion supply source in the battery, thereby enabling a
basic operation of a lithium secondary battery and promoting the
movement of lithium ions between a positive electrode and a
negative electrode. Representative examples of the lithium salt
include, as a supporting electrolyte salt, at least one selected
from the group consisting of LiPF.sub.6, LiBF.sub.4, LiSbF.sub.6,
LiAsF.sub.6, LIC.sub.4F.sub.9SO.sub.3, LIClO.sub.4, LiAlO.sub.2,
LiAlCl.sub.4, LiN(C.sub.xF.sub.2x+1SO.sub.2,
C.sub.yF.sub.2y+1SO.sub.2, here, x and y are a natural number),
LiCl, LiI, and LiB(C.sub.2O.sub.4).sub.2 (lithium bis(oxalato)
borate; LiBOB). The concentration of the lithium salt is preferably
0.1 to 2.0 M. If the concentration of the lithium salt falls within
the above range, the electrolyte has appropriate electrical
conductivity and viscosity, so that the electrolyte performance can
be excellent and the lithium ions can be effectively moved.
[0120] A separator may be disposed between the positive electrode
and the negative electrode depending on the kind of lithium
secondary battery. As for the separator, polyethylene,
polypropylene, polyvinylidene fluoride or multi-layers of two or
more layers thereof may be used. Mixed multi-layers thereof such as
a polyethylene/polypropylene double-layered separator, a
polyethylene/polypropylene/polyethylene triple-layered separator,
polypropylene/polyethylene/polypropylene triple-layered separator,
and the like may be used.
[0121] Lithium secondary batteries may be classified into lithium
ion batteries, lithium ion polymer batteries, and lithium polymer
batteries according to the kinds of a separator and an electrolyte
used therein. The lithium secondary batteries may be classified
into cylindrical, prismatic, coin-type, and pouch-type batteries
according to the shape. The secondary batteries may be classified
into bulk type and thin film type batteries according to the size.
Since structures and manufacturing methods of these batteries are
widely known in the art, descriptions thereof will be omitted.
[0122] FIG. 1 is a schematic view showing a representative
structure of a lithium secondary battery of the present invention.
Referring to FIG. 1, a lithium secondary battery 1 includes a
battery container 5 having a positive electrode 3, a negative
electrode 2, and a separator 4 disposed between the positive
electrode 3 and the negative electrode 2, which are impregnated
with an electrolyte, and a sealing member 6 sealing the battery
container 5.
[0123] Hereinafter, examples and comparative examples of the
present invention will be described. However, the following
examples are merely for illustrating the present invention, but the
present invention is not limited thereto.
EXAMPLES
Synthetic Example 1
Preparation of Lithium Composite Oxide
[0124] Li.sub.2CO.sub.3 (Product name: SQM) and
Ni.sub.0.47Co.sub.0.20Mn.sub.0.33(OH).sub.2(D50: 5 .mu.m) were
mixed at a weight ratio of 1:1.03 (Metal:Li) using a mixer. The
obtained mixture was fired for a total of 20 hours while the time
rise reaction time was 6 hours in air and the time for a
maintenance period was 7 hours at 950.degree. C., thereby preparing
a fired material.
[0125] The obtained fired material was slowly cooled and then
reduced to powder, thereby obtaining a lithium composite oxide
powder for mixing and firing according to an embodiment of the
present invention.
Example 1
Preparation of Positive Electrode Active Material Through Mixing
and Firing
[0126] Li.sub.2CO.sub.3 (Product name: SQM) and
Ni.sub.0.55Co.sub.0.20Mn.sub.0.25(OH).sub.2 were mixed at a weight
ratio of 1:1.03 (Metal:Li) using a mixer.
[0127] After the final firing,
LiNi.sub.0.47Co.sub.0.20Mn.sub.0.33O.sub.2 was further added
thereto such that the weight ratio of
LiNi.sub.0.55Co.sub.0.20Mn.sub.0.25O.sub.2 and
Li.sub.0.47Co.sub.0.20Mn.sub.0.33O.sub.2 of Synthetic Example 1 was
90:10.
[0128] The obtained mixture was fired for a total of 20 hours while
the time rise reaction time was 6 hours in air and the time for a
maintenance period was 7 hours at 940.degree. C., thereby preparing
a fired material.
[0129] The obtained fired material was slowly cooled and then
reduced to powder, thereby preparing a positive electrode active
material.
Example 2
Preparation of Positive Electrode Active Material Through Mixing
and Firing
[0130] A positive electrode active material was prepared by the
same method as in Example 1, except that
LiNi.sub.0.47CO.sub.0.20Mn.sub.0.33O.sub.2 was added such that the
weight ratio of LiNi.sub.0.55CO.sub.0.20Mn.sub.0.25O.sub.2 and
LiNi.sub.0.47CO.sub.0.20Mn.sub.0.33O.sub.2 was 80:20, followed by
mixing and firing.
Example 3
Preparation of Positive Electrode Active Material Through Mixing
and Firing
[0131] A positive electrode active material was prepared by the
same method as in Example 1, except that
LiNi.sub.0.47CO.sub.0.20Mn.sub.0.33O.sub.2 was added such that the
weight ratio of LiNi.sub.0.55CO.sub.0.20Mn.sub.0.25O.sub.2 and
LiNi.sub.0.47CO.sub.0.20Mn.sub.0.33O.sub.2 was 70:30, followed by
mixing and firing.
Example 4
Preparation of Positive Electrode Active Material Through Mixing
and Firing
[0132] A positive electrode active material was prepared by the
same method as in Example 1, except that Ti--Zr-codoped
Li.sub.0.47Co.sub.0.20Mn.sub.0.33O.sub.2 prepared by further
dry-mixing Ni.sub.0.47Co.sub.0.20Mn.sub.0.33(OH).sub.2 with
ZrO.sub.2 powder and TiO.sub.2 powder at a weight ratio of
100:0.27:0.33 and firing the mixture was used.
Comparative Example 1
[0133] Li.sub.2CO.sub.3 (Product name: SQM) and
LiNi.sub.0.55CO.sub.0.20Mn.sub.0.25O.sub.2(OH).sub.2 were mixed at
a weight ratio of 1:1.03 (Metal:Li) using a mixer.
[0134] The obtained mixture was fired for a total of 20 hours while
the time rise reaction time was 6 hours in air and the time for a
maintenance period was 7 hours at 940.degree. C., thereby preparing
a fired material. The obtained fired material was slowly cooled,
and then reduced to powder, thereby preparing a positive electrode
active material.
Comparative Example 2
[0135] LiNi.sub.0.47CO.sub.0.20Mn.sub.0.33O.sub.2 prepared in
Synthetic Example 1 was used for a positive electrode active
material.
Comparative Example 3
[0136] Li.sub.2CO.sub.3 (Product name: SQM) and
Ni.sub.0.55Co.sub.0.20Mn.sub.0.25(OH).sub.2 and
Ni.sub.0.47Co.sub.0.20Mn.sub.0.33(OH).sub.2 were mixed at a weight
ratio of 1:1.03 (Metal:Li) using a mixer.
[0137] Here, the mixing was conducted such that the weight ratio of
Ni.sub.0.55Co.sub.0.20Mn.sub.0.25(OH).sub.2 and
Ni.sub.0.47Co.sub.0.20Mn.sub.0.33(OH).sub.2 was 90:10.
[0138] The obtained mixture was fired for a total of 20 hours while
the time rise reaction time was 6 hours in air and the time for a
maintenance period was 7 hours at 940.degree. C., thereby preparing
a fired material.
[0139] The obtained fired material was slowly cooled and then
reduced to powder, thereby preparing a positive electrode active
material.
Comparative Example 4
[0140] A positive electrode active material in which
LiNi.sub.0.55CO.sub.0.20Mn.sub.0.25O.sub.2 prepared in Comparative
Example 1 and LiNi.sub.0.47Co.sub.0.20Mn.sub.0.33O.sub.2 prepared
in Synthetic example 1 were mixed at a weight ratio of 90:10 was
used.
Experimental Example 1
Manufacture of Coin Cells
[0141] Each positive electrode slurry was prepared by adding 95 wt
% of the positive electrode active material prepared in each of
Examples 1 to 4 and Comparative Examples 1 to 4, 2.5 wt % of carbon
black as a conductor, and 2.5 wt % of PVDF as a binder to 5.0 wt %
of N-methyl-2-pyrolidone (NMP) as a solvent.
[0142] The positive electrode slurry was coated on an aluminum (Al)
thin film as a positive electrode current collector with a
thickness of 20 to 40 .mu.m and then vacuum-dried, followed by roll
pressing, thereby preparing a positive electrode.
[0143] Li-metal was used for a negative electrode.
[0144] A coin cell type half cell was manufactured by using the
thus prepared positive electrode, the Li-metal as a counter
electrode, and 1.15 M LiPF6EC:DMC (1:1 vol %) as an electrolyte.
Then, the charge-discharge test was conducted at 3.0 V to 4.3
V.
Evaluation on Characteristics of Coin Cells
[0145] Table 1 below shows evaluation results of battery
characteristics of coin cells manufactured in the experiment
example.
TABLE-US-00001 TABLE 1 Remaining water- Formation soluble discharge
Rate Lifespan lithium capacity Efficiency (1.0 C/ characteristics
LiNi.sub.0.55Co.sub.0.20Mn.sub.0.25O.sub.2/LiNi.sub.0.47Co.sub.0.20Mn.sub-
.0.33O.sub.2 (wt %) (mAh/g) (%) 0.1 C, %) (30CY/1CY, %) Example 1
90/10 0.245 174.11 89.32 92.41 89.27 Example 2 80/20 0.230 173.88
89.27 91.86 89.12 Example 3 70/30 0.212 173.18 88.99 91.58 89.40
Example 4 90/10 0.251 174.03 89.62 92.73 90.88 Comparative 100/0
0.352 173.20 88.61 89.92 89.30 Example 1 Comparative 0/100 0.182
168.30 89.58 90.61 91.20 Example 2 Comparative 90/10 0.302 172.48
88.57 89.76 89.11 Example 3 Comparative 90/10 0.325 172.52 88.70
89.86 89.26 Example 4
[0146] Examples 1 to 3 showed equivalent or higher Formation
discharge capacity as compared with Comparative Example 1 using a
single composition.
[0147] This feature cannot be expressed in the case of the mixture
of lithium composite oxides (Comparative Example 4), which
corresponds to the conventional art. This is construed as a result
of a selective Li reaction induced by adding a Li compound to a
mixture of a precursor and a lithium composite oxide and performing
firing in an embodiment of the present invention.
[0148] Further, it can be confirmed that, in consideration of
remaining water-soluble lithium values in Examples 1 to 3, the
examples of the present invention have a remarkable effect in
reducing the remaining water-soluble lithium even though the
remaining water-soluble lithium values were calculated to reflect
the mixing ratios by using the remaining water-soluble lithium
values in Comparative Examples 1 and 2.
[0149] Examples 1 to 3 showed excellent efficiency and rate
characteristics and equivalent or higher lifespan characteristics,
as compared with Comparative Example 1.
[0150] In addition, when compared with Example 1, Example 4 in
which a positive electrode material substituted with a transition
metal was used can be confirmed to have improved lifespan and rate
characteristics, which result from transition metal
substitution.
[0151] Comparative Example 3, in which precursors having different
compositions were mixed and then fired at a particular temperature,
which corresponds one of the conventional arts, showed reduced
efficiency, rate characteristics and/or lifespan characteristics as
compared with Examples 1 to 4.
[0152] In order to obtain the optimum performance in the
composition Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma., the firing
temperature needs to be varied depending on the ratio of Ni/Co/Mn.
However, when precursors having different compositions are mixed
and fired, the firing temperature needs to be selected to be
optimum to a particular composition or the firing temperature needs
to be set by a temperature between or among individual optimum
firing temperatures for different compositions, and thus the
optimum battery performance cannot be exhibited.
[0153] In addition, Comparative Example 4 in which lithium
composite oxides having different compositions are mixed could not
show an effect in reducing the remaining water-soluble lithium,
which corresponds to an effect of Examples 1 to 4, and showed
reduced effects in Formation discharge capacity, efficiency, rate
characteristics, and the like, as compared with Examples 1 to
4.
Experimental Example 2
EDS Analysis on Precursor and Positive Electrode Active
Material
[0154] Ten precursor particles having a composition of
Ni.sub.0.55Co.sub.0.20Mn.sub.0.25 and ten particles of Comparative
Example 1 are randomly selected and then EDS analysis (energy
dispersive spectrometer, x-act, OXFORD Inc.) was performed thereon.
Table 2 shows the mean and standard deviation of EDS value for each
case.
[0155] Ten particles having relatively a higher Ni content were
randomly selected from the positive electrode active material
obtained in Example 1. The surface analysis results thereof were
expressed as Examples 1-1 to 1-10. Ten particles having relatively
a higher Ni content were randomly selected from the positive
electrode active material obtained in Comparative Example 3. The
surface analysis results thereof were expressed as Comparative
Examples 3-1 to 3-10.
TABLE-US-00002 TABLE 2 EDS Ni (mole %) Standard Sample Mean
deviation Ni.sub.0.55Co.sub.0.20Mn.sub.0.25 precursor 55.41
.+-.0.65 Comparative Example 1 55.37 .+-.0.46 Example 1 54.29
.+-.0.55 Example1-1 54.31 Example1-2 53.89 Example1-3 54.59
Example1-4 53.69 Example1-5 54.12 Example1-6 54.99 Example1-7 55.12
Example1-8 54.76 Example1-9 53.74 Example1-10 53.67 Comparative
Example 3 52.23 .+-.1.17 Comparative Example 3-1 52.04 Comparative
Example 3-2 53.38 Comparative Example 3-3 52.92 Comparative Example
3-4 50.49 Comparative Example 3-5 52.39 Comparative Example 3-6
52.12 Comparative Example 3-7 51.19 Comparative Example 3-8 52.27
Comparative Example 3-9 51.06 Comparative Example 3-10 54.47
[0156] Example 1, as an embodiment of the present invention, in
which the positive electrode active material was prepared by mixing
and firing the precursor and the lithium composite oxide, has two
different composition groups of
Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma., and Table 2 obtained
from EDS analysis results showed that, of the particles having the
two compositions, the surface Ni content of particles having a
higher Ni content was further reduced as compared with Comparative
Example 1 in which the mixing and firing were not performed. In
addition, Comparative Example 3, as one of the conventional arts,
in which precursors having different compositions were mixed and
fired, has two different composition groups of
Ni.sub..alpha.Co.sub..beta.Mn.sub..gamma., and, it can be seen
that, of the particles having the two compositions, the surface Ni
content of particles having a higher Ni content was largely
reduced.
Experimental Example 3
Analysis of Remaining Water-Soluble Lithium
[0157] In Examples 1 to 4 and Comparative Examples 1 to 4, the
remaining water-soluble lithium was analyzed by using
titration.
[0158] The present invention is not limited to the embodiments but
may be implemented into different forms, and those skilled in the
art will understand that the present invention may be implemented
in alternative embodiments without changing technical spirits and
necessary characteristics of the present invention. Thus, the
embodiments described above should be construed as being
exemplified and not limiting the present disclosure.
[0159] While this invention has been described in connection with
what is presently considered to be practical exemplary embodiments,
it is to be understood that the invention is not limited to the
disclosed embodiments, but, on the contrary, is intended to cover
various modifications and equivalent arrangements included within
the spirit and scope of the appended claims.
* * * * *