U.S. patent application number 14/420428 was filed with the patent office on 2015-08-13 for cathode active material for secondary battery, method of manufacturing the same, and cathode for lithium secondary battery including the cathode active material.
This patent application is currently assigned to LG CHEM, LTD.. The applicant listed for this patent is LG Chem, Ltd.. Invention is credited to Seung Beom Cho, Wook Jang, Dong Kwon Lee, Jun Seok Nho.
Application Number | 20150228975 14/420428 |
Document ID | / |
Family ID | 53033515 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150228975 |
Kind Code |
A1 |
Lee; Dong Kwon ; et
al. |
August 13, 2015 |
CATHODE ACTIVE MATERIAL FOR SECONDARY BATTERY, METHOD OF
MANUFACTURING THE SAME, AND CATHODE FOR LITHIUM SECONDARY BATTERY
INCLUDING THE CATHODE ACTIVE MATERIAL
Abstract
The present invention relates to a cathode active material
including a lithium-containing transition metal oxide and two or
more metal composite oxide layers selected from the group
consisting of Chemical Formulae 1 to 3 which are coated on the
surface of the lithium-containing transition metal oxide, a method
of manufacturing the same, and a cathode for a secondary battery
including the cathode active material,
M(C.sub.2H.sub.5O.sub.2).sub.n [Chemical Formula 1]
M(C.sub.6H.sub.(8-n)O.sub.7) [Chemical Formula 2]
M(C.sub.6H.sub.(8-n)O.sub.7)(C.sub.2H.sub.5O.sub.2) [Chemical
Formula 3] (where M, as a metal desorbed from a metal precursor,
represents at least one metal selected from the group consisting of
Mg, Ca, Sr, Ba, Y, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ir,
Ni, Zn, Al, Ga, In, Si, Ge, Sn, La, and Ce, and n is an integer
between 1 and 4).
Inventors: |
Lee; Dong Kwon; (Daejeon,
KR) ; Cho; Seung Beom; (Daejeon, KR) ; Nho;
Jun Seok; (Daejeon, KR) ; Jang; Wook;
(Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG Chem, Ltd. |
Seoul |
|
KR |
|
|
Assignee: |
LG CHEM, LTD.
Seoul
KR
|
Family ID: |
53033515 |
Appl. No.: |
14/420428 |
Filed: |
September 30, 2014 |
PCT Filed: |
September 30, 2014 |
PCT NO: |
PCT/KR2014/009195 |
371 Date: |
February 9, 2015 |
Current U.S.
Class: |
429/188 ;
427/126.3; 429/213 |
Current CPC
Class: |
H01M 4/131 20130101;
H01M 4/1391 20130101; H01M 4/62 20130101; H01M 4/0416 20130101;
H01M 4/366 20130101; Y02E 60/10 20130101; H01M 4/0471 20130101 |
International
Class: |
H01M 4/485 20060101
H01M004/485; H01M 4/04 20060101 H01M004/04; H01M 10/052 20060101
H01M010/052; H01M 4/60 20060101 H01M004/60; H01M 4/131 20060101
H01M004/131 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2013 |
KR |
10-2013-0117036 |
Sep 29, 2014 |
KR |
10-2014-0130374 |
Claims
1. A cathode active material comprising: a lithium-containing
transition metal oxide; and two or more metal composite oxide
layers selected from the group consisting of Chemical Formulae 1 to
3 which are coated on a surface of the lithium-containing
transition metal oxide: M(C.sub.2H.sub.5O.sub.2).sub.n [Chemical
Formula 1] M(C.sub.6H.sub.(8-n)O.sub.7) [Chemical Formula 2]
M(C.sub.6H.sub.(8-n)O.sub.7)(C.sub.2H.sub.5O.sub.2) [Chemical
Formula 3] (where M, as a metal desorbed from a metal precursor,
represents at least one metal selected from the group consisting of
magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), yttrium
(Y), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb),
tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W),
manganese (Mn), iron (Fe), cobalt (Co), iridium (Ir), nickel (Ni),
zinc (Zn), aluminum (Al), gallium (Ga), indium (In), silicon (Si),
germanium (Ge), tin (Sn), lanthanum (La), and cerium (Ce), and n is
an integer between 1 and 4).
2. The cathode active material of claim 1, wherein the
lithium-containing transition metal oxide comprises one selected
from the group consisting of LiMO.sub.2 (M=Co, Mn, Ni,
Ni.sub.1/3Co.sub.1/3Mn.sub.1/3, Cr, or V), LiMO.sub.4 (M=CoMn, NiV,
CoV, CoP, FeP, MnP, NiP, or Mn.sub.2),
Li(Ni.sub.aCo.sub.bMn.sub.c)O.sub.2 (0<a<1, 0<b<1,
0<c<1, a+b+c=1), LiNi.sub.1-yCo.sub.yO.sub.2,
LiCo.sub.1-yMn.sub.yO.sub.2, LiNi.sub.1-yMn.sub.yO.sub.2
(O.ltoreq.=y.ltoreq.1), Li(Ni.sub.aMn.sub.bCo.sub.c)O.sub.4
(0<a<2, 0<b<2, 0<c<2, a+b+c=2),
LiMn.sub.2-zNi.sub.zO.sub.4, LiMn.sub.2-zCo.sub.zO.sub.4
(O<z<2), and LiV.sub.3O.sub.6.
3. The cathode active material of claim 1, wherein the
lithium-containing transition metal oxide is LiCoO.sub.2,
LiMnO.sub.2, LiCuO.sub.2, LiMn.sub.2O.sub.4,
LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.2,
LiNi.sub.0.6Mn.sub.0.2Co.sub.0.2O.sub.2, LiCoPO.sub.4, or
LiFePO.sub.4.
4. The cathode active material of claim 1, wherein the two or more
metal composite oxide layers are formed in a single layer
structure, in which two or more metal composite oxides are
uniformly mixed, or a multilayer structure having two or more
layers in which two or more metal composite oxide layers are
sequentially stacked.
5. The cathode active material of claim 1, wherein a total
thickness of the two or more metal composite oxide layers is in a
range of 5 nm to 500 nm.
6. The cathode active material of claim 1, wherein an amount of
metal in the two or more metal composite oxide layers is in a range
of 0.01 wt % to 10 wt % based on a total weight of the
lithium-containing transition metal oxide.
7. The cathode active material of claim 1, wherein the two or more
metal composite oxide layers comprise a composite oxide of at least
one metal selected from the group consisting of Mg, Ca, Sr, Ba, Y,
Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ir, Ni, Zn, Al, Ga, In,
Si, Ge, Sn, La, and Ce.
8. A method of manufacturing a cathode active material that
comprises a metal composite oxide coating layer, the method
comprising steps of: a first step of preparing a metal glycolate
solution by performing two-steps heating process; a second step of
mixing lithium-containing transition metal oxide particles and the
metal glycolate solution and stirring in a paste state; a third
step of drying the paste-state mixture; and a fourth step of
performing a heat treatment on the dried mixture.
9. The method of claim 8, wherein the metal glycolate solution is
prepared by: preparing a mixed solution in which a metal precursor
and a chelating agent are dispersed in a glycol-based solvent;
performing primary heating on the mixed solution; and performing
secondary heating on the mixed solution.
10. The method of claim 9, wherein the metal glycolate solution
comprises a single material selected from the group consisting of
aluminum glycolate, zirconium glycolate, titanium glycolate,
calcium glycolate, and manganese glycolate, or a mixture of two or
more thereof.
11. The method of claim 9, wherein the performing of the primary
heating is performed in a temperature range of 150.degree. C. to
300.degree. C. for 1 hour to 48 hours.
12. The method of claim 9, wherein the performing of the secondary
heating is performed in a temperature range of 150.degree. C. to
300.degree. C. for 1 hour to 5 hours.
13. The method of claim 9, wherein the performing of the primary
heating and the performing of the secondary heating are performed
in an inert gas atmosphere.
14. The method of claim 8, wherein the drying (the third step) is
performed in a temperature range of 100.degree. C. to 200.degree.
C. for 1 hour to 4 hours.
15. The method of claim 8, wherein the performing of the heat
treatment (the fourth step) is performed in a temperature range of
200.degree. C. to 1,200.degree. C. for 1 hour to 3 hours.
16. A cathode for a secondary battery comprising: a cathode
collector; and the cathode active material of claim 1 coated on the
cathode collector.
17. A lithium secondary battery comprising: the cathode of claim
16; an anode; a separator disposed between the cathode and the
anode; and a lithium salt-containing non-aqueous electrolyte
solution.
Description
TECHNICAL FIELD
[0001] The present invention relates to a cathode active material
for a secondary battery, a method of manufacturing the same, and a
cathode for a lithium secondary battery including the cathode
active material, and more particularly, to a cathode active
material uniformly coated with two or more metal composite oxide
layers, a method of manufacturing the same, and a cathode for a
lithium secondary battery including the cathode active
material.
BACKGROUND ART
[0002] In line with the increasing use of mobile devices and
vehicles, demand for secondary batteries as their energy sources
has been rapidly increased. As the secondary batteries, lithium
secondary batteries having high energy density, high voltage, long
cycle life, and low self-discharging rate have been commercialized
and widely used.
[0003] A lithium secondary battery may be largely composed of a
cathode active material, an anode active material, a separator, and
an electrolyte. Specifically, a carbon material has been used as a
main component of the anode active material, and in addition,
research into using lithium metal, a sulfur compound, a silicon
compound, and a tin compound has been actively conducted. Also, a
layered structure, lithium-containing cobalt oxide (LiCoO.sub.2)
has been mainly used as the cathode active material, and in
addition, lithium metal compounds having a layered structure (the
metal includes manganese, cobalt, nickel, etc.), lithium-containing
manganese oxides having a spinel structure (LiMnO.sub.2 and
LiMn.sub.2O.sub.4), and lithium-containing nickel oxide
(LiNiO.sub.2) have been commercialized.
[0004] With respect to LiCoO.sub.2 which has currently been most
widely used among the above cathode active materials due to
excellent life characteristics and charge and discharge efficiency,
it has limitations in being applied to high-capacity batteries for
electric vehicles due to the fact that it has low structural
stability, has high raw material costs, and causes environmental
pollution. With respect to a lithium manganese oxide, such as
LiMnO.sub.2 and LiMn.sub.2O.sub.4, studied as an alternative
material of LiCoO.sub.2, it is inexpensive, but has disadvantages
in that electrical conductivity is low, capacity is low, and
electrode degradation rapidly occurs at high temperature. Also,
with respect to the lithium-containing nickel oxide, it has battery
characteristics of high discharge capacity, but has disadvantages
in that it is difficult to be synthesized by a simple solid-state
reaction and its cycle characteristics are low.
[0005] Therefore, there is an urgent need to develop a novel
cathode active material having excellent high-temperature
stability, lower manufacturing costs, and excellent cycle
characteristics.
DISCLOSURE OF THE INVENTION
Technical Problem
[0006] An aspect of the present invention provides a cathode active
material uniformly coated with two or more metal composite oxide
layers.
[0007] Another aspect of the present invention provides a method of
manufacturing the cathode active material.
[0008] Another aspect of the present invention provides a cathode
for a lithium secondary battery including the cathode active
material.
[0009] Another aspect of the present invention provides a secondary
battery in which cycle characteristics are improved by including
the cathode for a lithium secondary battery.
Technical Solution
[0010] According to an aspect of the present invention, there is
provided a cathode active material including:
[0011] a lithium-containing transition metal oxide; and
[0012] two or more metal composite oxide layers selected from the
group consisting of Chemical Formulae 1 to 3 which are coated on a
surface of the lithium-containing transition metal oxide:
M(C.sub.2H.sub.5O.sub.2).sub.n [Chemical Formula 1]
M(C.sub.6H.sub.(8-n)O.sub.7) [Chemical Formula 2]
M(C.sub.6H.sub.(8-n)O.sub.7)(C.sub.2H.sub.5O.sub.2) [Chemical
Formula 3]
[0013] (where M, as a metal desorbed from a metal precursor,
represents at least one metal selected from the group consisting of
magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), yttrium
(Y), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb),
tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W),
manganese (Mn), iron (Fe), cobalt (Co), iridium (Ir), nickel (Ni),
zinc (Zn), aluminum (Al), gallium (Ga), indium (In), silicon (Si),
germanium (Ge), tin (Sn), lanthanum (La), and cerium (Ce), and n is
an integer between 1 and 4).
[0014] According to another aspect of the present invention, there
is provided a method of manufacturing a cathode active material
including the steps of: a first step of preparing a metal glycolate
solution by performing two-steps heating process; a second step of
mixing lithium-containing transition metal oxide particles and the
metal glycolate solution and stirring in a paste state; a third
step of drying the paste-state mixture; and a fourth step of
performing a heat treatment on the dried mixture.
[0015] According to another aspect of the present invention, there
is provided a cathode for a secondary battery including a cathode
collector and the cathode active material of the present invention
coated on the cathode collector, and a lithium secondary battery
including the cathode.
Advantageous Effects
[0016] According to a method of the present invention, a cathode
active material having improved conductivity and density may be
manufactured by including two or more metal composite oxide layers
that are coated to a uniform thickness. Also, a secondary battery
having improved cycle characteristics may be prepared by including
the cathode active material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a field-emission scanning electron microscope
(FE-SEM) image of a cathode active material according to Example 1
of the present invention;
[0018] FIG. 2 is an FE-SEM image of a cathode active material
according to Example 2 of the present invention; and
[0019] FIG. 3 is a graph comparing cycle characteristics of
secondary batteries according to Experimental Example 1 of the
present invention.
MODE FOR CARRYING OUT THE INVENTION
[0020] Hereinafter, the present invention will be described in
detail.
[0021] Recently, the need for using a cathode of a lithium ion
secondary battery at a high voltage increases, and accordingly,
research into methods for preparing a cathode active material
having excellent high-temperature stability, low manufacturing
costs, excellent capacity, and excellent cycle characteristics has
emerged. For example, in order to improve thermal stability and
cycle characteristics, a method of coating the surface of a cathode
active material with two or more metal oxides using a typical dry
or wet coating method has been proposed. However, since it is
difficult to coat two or more metal composite oxides to have a
uniform thickness by the typical method, the degree of improvement
is still insufficient. For example, the dry coating method has
advantages in that the process is simple and cost is low, but has
disadvantages in that it is difficult to form two or more metal
composite oxide coating layers having a uniform thickness on the
surface of a cathode active material. The wet coating method may
form a metal oxide coating layer having a uniform thickness.
However, the wet coating method has disadvantages in that anions
capable of degrading battery characteristics may not only remain on
the surface of the metal oxide coating layer, but it may also be
difficult to coat two or more metal composite oxide layers having a
uniform thickness which may further improve charge and discharge
efficiency.
[0022] Accordingly, the present invention aims at providing a
cathode active material coated with two or more metal composite
oxides having a uniform thickness, a method of manufacturing the
same, and a secondary battery including the cathode active
material.
[0023] Specifically, according to an embodiment of the present
invention, provided is a cathode active material including:
[0024] a lithium-containing transition metal oxide; and
[0025] two or more metal composite oxide layers selected from the
group consisting of Chemical Formulae 1 to 3 which are coated on a
surface of the lithium-containing transition metal oxide:
M(C.sub.2H.sub.5O.sub.2).sub.n [Chemical Formula 1]
M(C.sub.6H.sub.(8-n)O.sub.7) [Chemical Formula 2]
M(C.sub.6H.sub.(8-n)O.sub.7)(C.sub.2H.sub.5O.sub.2) [Chemical
Formula 3]
[0026] (where M, as a metal desorbed from a metal precursor,
represents at least one metal selected from the group consisting of
magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), yttrium
(Y), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb),
tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W),
manganese (Mn), iron (Fe), cobalt (Co), iridium (Ir), nickel (Ni),
zinc (Zn), aluminum (Al), gallium (Ga), indium (In), silicon (Si),
germanium (Ge), tin (Sn), lanthanum (La), and cerium (Ce), and n is
an integer between 1 and 4).
[0027] Also, in the cathode active material of the present
invention, the lithium-containing transition metal oxide may
include one selected from the group consisting of LiMO.sub.2 (M=Co,
Mn, Ni, Ni.sub.1/3Co.sub.1/3Mn.sub.1/3, Cr, or V), LiMO.sub.4
(M=CoMn, NiV, CoV, CoP, FeP, MnP, NiP, or Mn.sub.2),
Li(Ni.sub.aCo.sub.bMn.sub.c)O.sub.2 (0<a<1, 0<b<1,
0<c<1, a+b+c=1), LiNi.sub.1-yCo.sub.yO.sub.2,
LiCo.sub.1-yMn.sub.yO.sub.2, LiNi.sub.1-yMn.sub.yO.sub.2 (O=y=1),
Li(Ni.sub.aMn.sub.bCo.sub.c)O.sub.4 (0<a<2, 0<b<2,
0<c<2, a+b+c=2), LiMn.sub.2-zNi.sub.zO.sub.4,
LiMn.sub.2-zCo.sub.zO.sub.4 (O<z<2), and
LiV.sub.3O.sub.6.
[0028] Specifically, typical examples of the lithium-containing
transition metal oxide may be LiCoO.sub.2, LiNiO.sub.2,
LiMnO.sub.2, LiCuO.sub.2, LiMn.sub.2O.sub.4,
LiNi.sub.1/3Mn.sub.1/3CO.sub.1/3O.sub.2,
LiNi.sub.0.6Mn.sub.0.2Co.sub.0.2O.sub.2, LiCoPO.sub.4, or
LiFePO.sub.4.
[0029] Also, in the cathode active material of the present
invention, the two or more metal composite oxide layers may be
formed in a single layer structure, in which two or more metal
composite oxides are uniformly mixed, or a multilayer structure
having two or more layers in which each of two or more metal
composite oxides is sequentially stacked.
[0030] A total thickness of the two or more metal composite oxide
layers may be in a range of 5 nm to 500 nm. In the case that the
thickness of the two or more metal composite oxide layers is less
than 5 nm, an effect of protecting a cathode material may be
reduced. In the case in which the thickness of the two or more
metal composite oxide layers is greater than 500 nm, since the two
or more metal composite oxide layers may obstruct lithium-ion
movement, battery capacity and output may be reduced.
[0031] Also, an amount of metal in the two or more metal composite
oxide layers may be in a range of 0.01 wt % to 10 wt % based on a
total weight of the lithium-containing transition metal oxide. In
the case that the amount of the metal in the two or more metal
composite oxide layers is less than 0.01 wt %, the protective
effect due to the coating may be reduced. In the case in which the
amount of the metal in the two or more metal composite oxide layers
is greater than 10 wt %, since an excessive amount of the metal is
coated, the two or more metal composite oxide layers may adversely
affect the rate capacity and output of the battery.
[0032] Furthermore, the present invention may provide a method of
manufacturing a cathode active material including the two or more
metal composite oxide layers.
[0033] Specifically, the method may include the steps of:
[0034] a first step of preparing a metal glycolate solution by
performing two-steps heating process;
[0035] a second step of mixing lithium-containing transition metal
oxide particles and the metal glycolate solution and stirring in a
paste state;
[0036] a third step of drying the paste-state mixture; and
[0037] a fourth step of performing a heat treatment on the dried
mixture.
[0038] In this case, in the method of the present invention, the
first step of preparing a metal glycolate solution by performing
two-steps heating process may be performed by a method including
preparing a mixed solution by dispersing a metal precursor and a
chelating agent in a glycol-based solvent; performing primary
heating on the mixed solution; and performing secondary heating on
the mixed solution.
[0039] During the preparation of the metal glycolate solution (the
first step), the glycol-based solvent is a component added to
function as a reactant which forms a metal organo-compound by
combining (reacting) with a metal desorbed from the metal precursor
during a heating process. Typical examples of the glycol-based
solvent may include solvents having a boiling point (bp) of
120.degree. C. to 400.degree. C., for example, a single material
selected from the group consisting of ethylene glycol (bp
197.degree. C.), propylene glycol (bp 188.degree. C.), diethylene
glycol (bp 245.degree. C.), triethylene glycol (bp 285.degree. C.),
and polyethylene glycol, or a mixture of two or more thereof, but
the present invention is not particularly limited thereto. In the
case that a solvent having a boiling point of less than 120.degree.
C. is used as the glycol-based solvent, since the binding reaction
with the metal desorbed from the metal precursor does not occur,
the metal organo-compound may be difficult to be formed.
[0040] Also, during the preparation of the metal glycolate solution
(the first step), the metal precursor is not particularly limited
so long as it includes a typical metal, and for example, the metal
precursor may include a single material selected form the group
consisting of acetate, hydroxide, nitrate, nitride, sulfate,
sulfide, alkoxide, and halide, which include at least one metal
selected form the group consisting of Mg, Ca, Sr, Ba, Y, Ti, Zr, V,
Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ir, Ni, Zn, Al, Ga, In, Si, Ge, Sn,
La, and Ce, or a mixture of two or more thereof. Specifically,
typical examples of the metal precursor may be aluminum acetate,
zirconium nitride, or manganese acetate.
[0041] During the preparation of the metal glycolate solution (the
first step), the chelating agent is a component added to facilitate
the binding between the glycol-based solvent and the metal by more
easily desorbing the metal from the metal precursor, and typical
examples of the chelating agent may include a single material
selected from the group consisting of citric acid,
ethylenediaminetetraacetic acid (EDTA), oxalic acid, and gluconic
acid, or a mixture of two or more thereof.
[0042] Also, during the preparation of the metal glycolate solution
(the first step), a content ratio (parts by weight) of the metal
precursor: the glycol-based solvent: the chelating agent may be in
a range of 1:1:0.1 to 1:500:20, for example, 1:1:0.1 to
1:100:20.
[0043] In the case that the amount of the glycol-based solvent is
less than 1 part by weight, the metal desorbed from the metal
precursor may not entirely react with the glycol-based solvent to
remain in a state of the metal precursor. Also, in the case in
which the amount of the glycol-based solvent is greater than 500
parts by weight, since a large amount of the glycol-based solvent
not participating in the reaction must be removed by being
evaporated during the heating after the reaction, the consumption
of energy and the glycol-based solvent may be large and side
reactions may occur in a solvent evaporation process. Furthermore,
in the case that the amount of the chelating agent is less than 0.1
parts by weight, the effect of the chelating agent may not be
sufficiently obtained. In the case in which the amount of the
chelating agent is greater than 20 parts by weight, since a large
amount of the chelating agent preferentially react with the metal
precursor to inhibit the reaction between the glycol-based solvent
and the metal precursor, a desired yield of the metal
organo-compound may be reduced.
[0044] Also, during the preparation of the metal glycolate solution
(the first step), an additive may be further included in the mixed
solution.
[0045] The additive may improve the yield of metal composite oxide
by being included as a catalyst component which promotes the
reaction between the metal desorbed from the metal precursor and
the glycol-based solvent. The additive may be a component which
does not remain later in a coating layer by being entirely
evaporated and removed during the heating. Typical examples of the
additive may include a single material selected from the group
consisting of formaldehyde, acetaldehyde, and glycolic acid, or a
mixture of two or more thereof.
[0046] The additive may be included in an amount of 0.1 parts by
weight to 20 parts by weight based on total 1 part by weight of the
metal precursor. In the case that the amount of the additive is
greater than 20 parts by weight, there may be a possibility that a
large amount of byproducts may be formed due to the occurrence of
side reactions.
[0047] Also, during the preparation of the metal glycolate solution
(the first step), the performing of the primary heating may be
performed at a temperature below a boiling point of the
glycol-based solvent, as a temperature at which the reaction is
initiated, to a temperature above the boiling point. Specifically,
the performing of the primary heating may be performed in a
temperature range of 100.degree. C. to 300.degree. C., for example,
110.degree. C. to 230.degree. C., for 1 hour to 48 hours, for
example, 5 hours to 20 hours. The performing of the primary heating
may be performed in which a time at which all metal of the metal
precursor react with the glycol-based solvent to form the metal
organo-compound is set as a termination point.
[0048] A viscosity of the mixed solution after the primary heating
may be in a range of about 1 cps (centipoise) to about 1,000 cps,
and specifically, the mixed solution may have a viscosity similar
to the glycol-based solvent.
[0049] Furthermore, during the preparation of the metal glycolate
solution (the first step), the performing of the secondary heating
may be immediately performed with no time interval, such as a
cooling process, after the primary heating. In this case, the
performing of the secondary heating may be performed at a
temperature near the boiling point of the glycol-based solvent or
thereabove. Specifically, the performing of the secondary heating
may be performed in a temperature range of 100.degree. C. to
300.degree. C., for example, 170.degree. C. to 250.degree. C., for
1 hour to 5 hours. For example, in the case that ethylene glycol is
used as the glycol-based solvent, the performing of the secondary
heating may be performed at a temperature of about 180.degree. C.
or more for 1 hour to 5 hours.
[0050] The performing of the secondary heating may be performed
until a termination point at which the glycol-based solvent used as
a reactant is sufficiently removed to form a metal glycolate
solution. Thus, the performing of the secondary heating may be
referred to as "heating and concentrating". In this case, the metal
glycolate solution may have a viscosity of 1 cps to 15,000 cps,
specifically, 200 cps to 5,000 cps, for example, 1,000 cps to 3,000
cps.
[0051] During the preparation of the metal glycolate solution (the
first step), the performing of the primary heating and the
performing of the secondary heating may be performed in an inert
gas atmosphere such as argon (Ar).
[0052] In the case that the metal glycolate solution is prepared by
the method including the performing of the secondary heating, a
concentration of the coating solution may be easily adjusted during
the preparation of the cathode active material including the metal
coating layer, and thus, the effectiveness of coating may be
improved by controlling coating conditions according to the
concentration of the coating solution.
[0053] As described above, in the first step, a glycol-based
solvent (e.g., ethylene glycol), a metal precursor, and a chelating
agent (e.g., citric acid) are mixed to prepare a mixed solution,
and coordination bonds are then formed between oxygen of the
glycol-based solvent and the chelating agent and metal ions
desorbed from the metal precursor while hydrogen of the
glycol-based solvent and the chelating agent is desorbed during
heating (concentrating) the mixed solution. As a result, a metal
glycolate coating solution including a metal organo-compound as a
main component as following formula 1 to 3 is obtained while a
metal desorbed from the metal precursor, the glycol-based solvent,
and the chelating agent are combined together.
[0054] Typical examples of the metal glycolate solution prepared by
the above method may include a single material selected from the
group consisting of aluminum glycolate, zirconium glycolate,
titanium glycolate, calcium glycolate, and manganese glycolate, or
a mixture of two or more thereof.
[0055] Also, in the method of manufacturing a cathode active
material of the present invention, the mixing of the
lithium-containing transition metal oxide particles and the metal
glycolate solution and the stirring in a paste state (the second
step) may be performed at a revolution speed of 500 rpm to 2,000
rpm and a rotation speed of 500 rpm to 2,000 rpm, specifically, at
a revolution speed of 1,500 rpm and a rotation speed of 1,500 rpm
using a paste mixer.
[0056] Furthermore, the drying of the paste-state mixture (the
third step), as a step performed for evaporating a solvent in the
paste-state mixture, may be performed in a temperature range of
100.degree. C. to 200.degree. C., specifically, at a temperature of
180.degree. C. for 1 hour to 4 hours, for example, 2 hours.
[0057] Subsequently, in the method of manufacturing a cathode
active material of the present invention, the performing of the
heat treatment (the fourth step) may be performed in a temperature
range of about 200.degree. C. to about 1,200.degree. C.,
specifically, at a temperature of 180.degree. C. for 1 hour to 3
hours, for example, 1 hour in an air (oxidation) atmosphere.
[0058] In the case that the heat treatment temperature is greater
than 1,200.degree. C., a phenomenon may occur in which oxygen
present in the lithium-containing transition metal oxide
constituting the cathode active material is desorbed in a gaseous
form, and in the case in which the heat treatment temperature is
equal to or less than 200.degree. C., a uniform metal oxide coating
layer may not be formed.
[0059] After the performing of the heat treatment (the fourth
step), a metal oxide layer derived from the metal glycolate
solution is formed to a uniform thickness on the surface of the
lithium-containing transition metal oxide. In this case, two or
more metal composite oxide layers may be formed on the surface of
the cathode active material according to the type of the metal
glycolate solution.
[0060] In the method of manufacturing a cathode active material of
the present invention, the metal oxide layer coated on the surface
of the cathode active material after the performing of the heat
treatment (the fourth step) may include an oxide layer of at least
one metal selected from the group consisting of Mg, Ca, Sr, Ba, Y,
Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ir, Ni, Zn, Al, Ga, In,
Si, Ge, Sn, La, and Ce.
[0061] As described above, in the method of the present invention,
the metal glycolate solution and cathode active material particles
are mixed and then heat-treated. Thus, the surface of the cathode
active material, for example, the surface of the lithium-containing
transition metal oxide, of the secondary battery may be coated with
two or more metal composite oxides having a uniform thickness.
Therefore, the effect of anions may not only be minimized, but
various metal composite oxides may also be coated. In addition,
since a uniform carbon coating layer may be further formed on the
surface of the cathode active material without additional supply of
a carbon source by controlling an oxidation/reduction heat
treatment atmosphere as a subsequent process, a cathode active
material having improved thermal stability, capacity
characteristics, and cycle characteristics and a secondary battery
including the cathode active material may be manufactured.
[0062] That is, since the metal oxide layer may act as an
electrical resistance layer exhibiting significant internal
resistance during high-rate discharge, such as a short circuit
during the operation of the secondary battery, to obstruct the
introduction of electrons into a lithium-containing transition
metal oxide core, the metal oxide layer may also suppress the
intercalation of lithium ions. That is, since the metal oxide layer
may decrease the rate at which a large amount of lithium ions and
electrons released from an anode during internal short circuit are
intercalated into the cathode active material, the metal oxide
layer may prevent the generation of heat due to the generation of
instantaneous overcurrent and may improve the stability of the
battery. If only a portion of the surface of the lithium-containing
transition metal oxide is coated with the metal oxide, lithium ions
and electrons may be intercalated into the lithium-containing
transition metal oxide through a portion which is not coated with
the metal oxide. Thus, the above-described effect, such as the
decrease in the movement speed of lithium ions and electrons, may
not be obtained, but an area through which lithium ions and
electrons pass may also be decreased to further increase the local
movement speed of the lithium ions and electrons due to a nozzle
effect. Thus, the metal oxide layer may adversely affect the
stability of the battery by promoting the local generation of heat.
However, according to the present invention, since the surface of
the lithium-containing transition metal oxide is uniformly coated
with a metal oxide, the flow of lithium ions may be suppressed by
maximizing the action of the metal oxide layer as a resistor when
the overcurrent flows. In particular, the cathode active material
of the present invention including the lithium-containing
transition metal oxide coated with a metal oxide may decrease the
surface energy of the lithium-containing transition metal oxide to
change into a stable state, and thus, thermal stability may be
improved by suppressing side reactions between the
lithium-containing transition metal oxide and an electrolyte
solution.
[0063] Also, the present invention provides a cathode for a
secondary battery including a cathode collector and the cathode
active material of the present invention coated on the cathode
collector.
[0064] In this case, the cathode collector is generally fabricated
to have a thickness of about 3 .mu.m to about 500 .mu.m. The
cathode collector is not particularly limited so long as it has
high conductivity without causing adverse chemical changes in the
batteries. The cathode collector may be formed of, for example,
stainless steel, aluminum, nickel, titanium, fired carbon, or
aluminum or stainless steel that is surface-treated with one of
carbon, nickel, titanium, silver, or the like. The collector may
have an uneven surface to improve the bonding strength of a cathode
active material and may have any of various shapes such as that of
a film, a sheet, a foil, a net, a porous body, a foam body, a
non-woven fabric body, and the like.
[0065] Also, the cathode active material may further include a
binder and a conductive agent in addition to the cathode active
material coated with a metal oxide layer of the present
invention.
[0066] The binder is a component that assists in the binding
between the active material and the conductive agent and in the
binding with the collector. The binder is commonly added in an
amount of 1 wt % to 30 wt % based on a total weight of a mixture
including the cathode active material. Examples of the binder may
include polyvinylidene fluoride, polyvinyl alcohol,
carboxymethylcellulose (CMC), starch, hydroxypropylcellulose,
regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene,
polyethylene, polypropylene, an ethylene-propylene-diene terpolymer
(EPDM), a sulfonated EPDM, a styrene butadiene rubber, a fluoro
rubber, various copolymers, and the like.
[0067] Also, the conductive agent is commonly added in an amount of
1 wt % to 30 wt % based on the total weight of the mixture
including the cathode active material. Any conductive agent may be
used without particular limitation so long as it has suitable
conductivity without causing adverse chemical changes in the
batteries. For example, the conductive agent may include a
conductive material such as: graphite such as natural graphite and
artificial graphite; carbon black such as acetylene black, Ketjen
black, channel black, furnace black, lamp black, and thermal black;
conductive fibers such as carbon fibers and metal fibers; metal
powder such as fluorocarbon powder, aluminum powder, and nickel
powder; conductive whiskers such as zinc oxide whiskers and
potassium titanate whiskers; conductive oxide such as titanium
oxide; or polyphenylene derivatives.
[0068] Also, according to an embodiment of the present invention, a
lithium secondary battery composed of the cathode including the
cathode active material, an anode, a separator, and a lithium
salt-containing non-aqueous electrolyte solution is provided.
[0069] The anode, for example, is prepared by coating an anode
collector with an anode material including an anode active material
and then drying the anode collector. If necessary, components, such
as the conductive agent, the binder, and a filler, may be included
in the anode material.
[0070] The anode collector is generally fabricated to have a
thickness of about 3 .mu.m to about 500 .mu.m. The anode collector
is not particularly limited so long as it has conductivity without
causing adverse chemical changes in the batteries. The anode
collector may be formed of, for example, copper, stainless steel,
aluminum, nickel, titanium, fired carbon, copper or stainless steel
that is surface-treated with one of carbon, nickel, titanium,
silver, or the like, an aluminum-cadmium alloy, or the like. Also,
like the cathode collector, the anode collector may have a fine
roughness surface to improve bonding strength with an anode active
material. The anode collector may have various shapes such as a
film, a sheet, a foil, a net, a porous body, a foam body, a
non-woven fabric body, and the like.
[0071] The separator is disposed between the cathode and the anode,
and a thin insulating film having high ion permeability and
mechanical strength is used. The separator typically has a pore
diameter of 0.01 .mu.m to 10 .mu.m and a thickness of 5 .mu.m to
300 .mu.m.
[0072] For example, sheets or non-woven fabrics formed of an
olefin-based polymer such as polypropylene; glass fibers or
polyethylene, which have chemical resistance and hydrophobicity,
are used as the separator. When a solid electrolyte, such as a
polymer, is used as an electrolyte, the solid electrolyte may also
serve as the separator.
[0073] The lithium salt-containing non-aqueous electrolyte solution
is formed of an electrolyte and a lithium salt, and a non-aqueous
organic solvent or an organic solid electrolyte may be used as the
electrolyte solution.
[0074] Examples of the non-aqueous organic solvent may include
aprotic organic solvents, such as N-methyl-2-pyrrolidone, propylene
carbonate, ethylene carbonate, butylene carbonate, dimethyl
carbonate, diethyl carbonate, .gamma.-butyrolactone, 1,2-dimethoxy
ethane, tetrahydroxyfuran, 2-methyl tetrahydrofuran, dimethyl
sulfoxide, 1,3-dioxolane, formamide, diemthylformamide, dioxolane,
acetonitrile, nitromethane, methyl formate, methyl acetate,
phosphate triester, trimethoxy methane, a dioxolane derivative,
sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, a
propylene carbonate derivative, a tetrahydrofuran derivative,
ether, methyl propionate, and ethyl propionate.
[0075] Examples of the organic solid electrolyte may include a
polyethylene derivative, a polyethylene oxide derivative, a
polypropylene oxide derivative, a phosphate ester polymer, poly
agitation lysine, polyester sulfide, polyvinyl alcohol,
polyvinylidene fluoride, and a polymer containing an ionic
dissociation group.
[0076] The lithium salt is a material that is readily soluble in
the non-aqueous electrolyte and for example, may include LiCi,
LiBr, LiI, LiClO.sub.4, LiBF.sub.4, LiB.sub.10Cl.sub.10,
LiPF.sub.6, LiCF.sub.3SO.sub.3, LiCF.sub.3CO.sub.2, LiAsF.sub.6,
LiSbF.sub.6, LiAlCl.sub.4, CH.sub.3SO.sub.3Li, CF.sub.3SO.sub.3Li,
(CF.sub.3SP.sub.2).sub.2NLi, chloroborane lithium, lower aliphatic
carboxylic acid lithium, lithium tetraphenyl borate and imide.
[0077] Also, in order to improve charge/discharge characteristics
and flame retardancy, pyridine, triethylphosphite, triethanolamine,
cyclic ether, ethylenediamine, n-glyme, hexaphosphoric triamide, a
nitrobenzene derivative, sulfur, a quinone imine dye, N-substituted
oxazolidinone, N,N-substituted imidazolidine, ethylene glycol
dialkyl ether, an ammonium salt, pyrrole, 2-methoxy ethanol, and
aluminum trichloride, for example, may be added to the electrolyte
solution. In some cases, halogen-containing solvents, such as
carbon tetrachloride and ethylene trifluoride, may be further
included in order to impart incombustibility, and carbon dioxide
gas may be further included in order to improve high-temperature
storage characteristics.
[0078] Hereinafter, the present invention will be described in
detail, according to specific examples. The invention may, however,
be embodied in many different forms and should not be construed as
being limited to the embodiments set forth herein. Rather, these
example embodiments are provided so that this description will be
thorough and complete, and will fully convey the scope of the
present invention to those skilled in the art.
EXAMPLES
Preparation Example 1
Preparation of Metal Glycolate Solution
[0079] 40 g of zirconium nitride (ZrN) and 10 g of citric acid
(C.sub.6H.sub.8O.sub.7) were stirred in 200 g of an ethylene glycol
(C.sub.2H.sub.6O.sub.2) solution to prepare a mixed solution. The
mixed solution was primarily heated at a temperature of 150.degree.
C. for 5 hours, and then secondarily heated at a temperature of
180.degree. C. for 1 hour to prepare a zirconium glycolate
solution.
Preparation Example 2
Preparation of Metal Glycolate Solution
[0080] 30 g of titanium isopropoxide
(Ti(OCH(CH.sub.3).sub.2).sub.4) and 10 g of citric acid
(C.sub.6H.sub.8O.sub.7) were stirred in 200 g of an ethylene glycol
(C.sub.2H.sub.6O.sub.2) solution to prepare a mixed solution. The
mixed solution was primarily heated at a temperature of 150.degree.
C. for 5 hours, and then secondarily heated at a temperature of
180.degree. C. for 1 hour to prepare a titanium glycolate
solution.
Preparation Example 3
Preparation of Metal Glycolate Solution
[0081] 20 g of calcium acetate (Ca(C.sub.2H.sub.3O.sub.2).sub.2)
and 10 g of citric acid (C.sub.6H.sub.8O.sub.7) were stirred in 200
g of an ethylene glycol (C.sub.2H.sub.6O.sub.2) solution to prepare
a mixed solution. The mixed solution was primarily heated at a
temperature of 140.degree. C. for 5 hours, and then secondarily
heated at a temperature of 180.degree. C. for 1 hour to prepare a
calcium glycolate solution.
Preparation Example 4
Preparation of Metal Glycolate Solution
[0082] 40 g of aluminum acetate (Al(C.sub.2H.sub.3O.sub.2).sub.3)
and 20 g of citric acid (C.sub.6H.sub.8O.sub.7) were stirred in 200
g of an ethylene glycol (C.sub.2H.sub.6O.sub.2) solution to prepare
a mixed solution. The mixed solution was primarily heated at a
temperature of 140.degree. C. for 5 hours, and then secondarily
heated at a temperature of 180.degree. C. for 1 hour to prepare an
aluminum glycolate solution.
Example 1
Preparation of Cathode Active Material
[0083] While adding 1 g of the zirconium glycolate solution of
Preparation Example 1 and 1 g of the aluminum glycolate solution of
Preparation Example 4 to 8 g of ethanol and stirring,
LiNi.sub.0.6Mn.sub.0.2Co.sub.0.2O.sub.2 was added thereto and
stirred in a paste state. The stirred paste was dried at
180.degree. C. for 2 hours and then heat-treated at 800.degree. C.
in air for 1 hour to manufacture cathode active material particles
coated with a metal composite oxide layer formed of zirconium oxide
and aluminum oxide.
[0084] The results of field-emission scanning electron microscope
(FE-SEM) and energy dispersive spectrometer (EDS) analysis of the
surface of the manufactured cathode active material are presented
in Table 1 below (see FIG. 1).
TABLE-US-00001 TABLE 1 Element Wt % Al 1.06 Zr 1.05 Ni 27.87 Mn
8.68 Co 9.16 O 52.19 Total 100
[0085] Referring to FIG. 1, amounts of elements in a portion marked
as "spectrum 18" in an FE-SEM image were analyzed by EDS. As a
result, it may be understood that cathode materials of Ni, Mn, and
Co were present in the form of an oxide and the amounts of Al and
Zr, as a composite coating material, were analyzed to be 1.06 wt %
and 1.05 wt %, respectively. Furthermore, it may be confirmed that
the surface of the cathode active material was very clean in the
FE-SEM image, and thus, it may be understood that the composite
coating of Al and Zr was very uniform.
Example 2
Preparation of Cathode Active Material
[0086] While adding 1 g of the titanium glycolate solution of
Preparation Example 2 and 1 g of the calcium glycolate solution of
Preparation Example 3 to 8 g of ethanol and stirring,
LiNi.sub.0.6Mn.sub.0.2Co.sub.0.2O.sub.2 was added thereto and
stirred in a paste state. The stirred paste was dried at
180.degree. C. for 2 hours and then heat-treated at 800.degree. C.
in air for 1 hour to manufacture cathode active material particles
coated with a metal composite oxide layer formed of calcium oxide
and titanium oxide.
[0087] The results of FE-SEM and EDS analysis of the surface of the
manufactured cathode active material are presented in Table 2 below
(see FIG. 2).
TABLE-US-00002 TABLE 2 Element Wt % Ti 1.39 Ca 1.29 Ni 28.78 Mn
9.91 Co 9.29 O 49.35 Total 100
[0088] Referring to FIG. 2, amounts of elements in a portion marked
as "spectrum 18" in an FE-SEM image were analyzed by EDS. As a
result, it may be understood that cathode materials of Ni, Mn, and
Co were present in the form of an oxide and the amounts of Ti and
Ca, as a composite coating material, were analyzed to be 1.39 wt %
and 1.29 wt %, respectively. Furthermore, it may be confirmed that
the surface of the cathode active material was very clean in the
FE-SEM image, and thus, it may be understood that the composite
coating of AL and Zr was very uniform.
Example 3
Preparation of Cathode and Secondary Battery
[0089] A slurry was prepared by adding 90 wt % of the cathode
active material particles of Example 2, 6 wt % of carbon black as a
conductive agent, and 4 wt % of polyvinylidene fluoride (PVDF) as a
binder to N-methyl-pyrrolidone (NMP). An aluminum (Al) foil as a
cathode collector was coated with the slurry, and the coated Al
foil was then rolled and dried to prepare a cathode for a lithium
secondary battery.
[0090] Subsequently, a porous polyethylene separator was disposed
between the cathode and a graphite-based anode, and a lithium
salt-containing electrolyte solution was injected to prepare a
secondary battery cell.
Comparative Example 1
[0091] A slurry was prepared by adding 90 wt % of
LiNi.sub.0.6Mn.sub.0.2Co.sub.0.2O.sub.2 as a cathode active
material, 6 wt % of carbon black as a conductive agent, and 4 wt %
of PVDF as a binder to NMP. An Al foil as a cathode collector was
coated with the slurry, and the coated Al foil was then rolled and
dried to prepare a cathode for a lithium secondary battery in which
a metal coating layer was not formed.
[0092] Subsequently, a porous polyethylene separator was disposed
between the cathode and a graphite-based anode, and a lithium
salt-containing electrolyte solution was injected to prepare a
secondary battery cell.
Experimental Example 1
Comparison of Cycle Life Characteristics
[0093] Cycle life characteristics of the secondary battery cell of
Example 3 and the secondary battery cell of Comparative Example 1
were measured. Referring to FIG. 3, it may be confirmed that the
cycle life characteristics of the lithium secondary battery of
Example 3 including a metal composite oxide layer was improved in
comparison to that of the secondary battery of Comparative Example
1 which does not include a metal coating layer.
* * * * *