U.S. patent application number 16/230895 was filed with the patent office on 2019-12-05 for composite cathode active material, cathode and lithium battery including the same, and method of preparing the composite cathode.
The applicant listed for this patent is Samsung Electronics Co., Ltd., Samsung SDI Co., Ltd.. Invention is credited to Sungjin AHN, Dongjin HAM, San MOON, Jinhwan PARK, Jayhyok SONG, Donghee YEON.
Application Number | 20190372109 16/230895 |
Document ID | / |
Family ID | 65023750 |
Filed Date | 2019-12-05 |
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United States Patent
Application |
20190372109 |
Kind Code |
A1 |
MOON; San ; et al. |
December 5, 2019 |
COMPOSITE CATHODE ACTIVE MATERIAL, CATHODE AND LITHIUM BATTERY
INCLUDING THE SAME, AND METHOD OF PREPARING THE COMPOSITE CATHODE
ACTIVE MATERIAL
Abstract
A composite cathode active material includes: a secondary
including a core including a plurality of primary particles; and a
shell on the core, wherein the plurality of primary particles
include a nickel-containing lithium transition metal oxide doped
with a first metal, and wherein at least one grain boundary between
the plurality of primary particles includes a first composition
including the first metal.
Inventors: |
MOON; San; (Hwaseong-si,
KR) ; SONG; Jayhyok; (Suwon-si, KR) ; AHN;
Sungjin; (Anyang-si, KR) ; YEON; Donghee;
(Seoul, KR) ; HAM; Dongjin; (Anyang-si, KR)
; PARK; Jinhwan; (SEOUL, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Samsung Electronics Co., Ltd.
Samsung SDI Co., Ltd. |
Suwon-si
Yongin-si |
|
KR
KR |
|
|
Family ID: |
65023750 |
Appl. No.: |
16/230895 |
Filed: |
December 21, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/0471 20130101;
H01M 4/1391 20130101; C01P 2002/52 20130101; H01M 4/525 20130101;
H01M 4/62 20130101; H01M 4/382 20130101; C01P 2004/84 20130101;
C01G 53/50 20130101; C01P 2004/04 20130101; H01M 4/131 20130101;
H01M 4/366 20130101; H01M 4/0497 20130101; H01M 10/052 20130101;
H01M 10/0525 20130101 |
International
Class: |
H01M 4/36 20060101
H01M004/36; H01M 4/04 20060101 H01M004/04; H01M 4/1391 20060101
H01M004/1391; H01M 4/38 20060101 H01M004/38; H01M 4/62 20060101
H01M004/62; H01M 4/131 20060101 H01M004/131; H01M 4/525 20060101
H01M004/525; H01M 10/0525 20060101 H01M010/0525 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 4, 2018 |
KR |
10-2018-0064480 |
Claims
1. A composite cathode active material, comprising: a secondary
particle comprising a core comprising a plurality of primary
particles; and a shell on the core, wherein the plurality of
primary particles comprise a nickel-containing lithium transition
metal oxide doped with a first metal, and wherein at least one
grain boundary between the plurality of primary particles comprises
a first composition comprising the first metal.
2. The composite cathode active material of claim 1, wherein the
nickel-containing lithium transition metal oxide comprises a first
phase and the first composition comprises a second phase which is
different from the first phase.
3. The composite cathode active material of claim 2, wherein the
second phase has a monoclinic crystalline structure.
4. The composite cathode active material of claim 3, wherein the
monoclinic crystalline structure belongs to a C2/m, C12/c1, or C2/c
space group.
5. The composite cathode active material of claim 1, wherein the
first metal comprises Zr, Mn, Si, Mo, Pd, Co, Ni, Ti, Sn, Mo, Ir,
Pt, Ru, or a combination thereof.
6. The composite cathode active material of claim 1, wherein the
first composition comprises lithium, the first metal, and oxygen,
and, the first composition comprises about 1.7 moles to about 2.3
moles of lithium, about 0.7 moles to about 1.3 moles of the first
metal, and about 2.7 moles to about 3.3 moles of oxygen, per mole
of the first composition.
7. The composite cathode active material of claim 1, wherein the
first composition is represented by Formula 1:
Li.sub.aM1.sub.bO.sub.c <Formula 1> wherein, in Formula 1, M1
comprises Zr, Mn, Si, Mo, Pd, Co, Ni, Ti, Sn, Mo, Ir, Pt, Ru, or a
combination thereof, 1.9.ltoreq.a.ltoreq.2.1,
0.9.ltoreq.b.ltoreq.1.1, and 2.9.ltoreq.c.ltoreq.3.1.
8. The composite cathode active material of claim 1, wherein the
core comprises a first inner region and a second inner region,
wherein the first inner region extends from a center of the core to
halfway between the center of the core and a surface of the core,
and the second inner region extends from halfway between the center
of the core and the surface of the core to the surface of the core,
and about 50% or greater of the grain boundaries in the first inner
region comprise the first composition, and about 50% or greater of
the grain boundaries in the second inner region comprise the first
composition.
9. The composite cathode active material of claim 1, wherein at
least one grain boundary between the plurality of primary particles
has a substantially rectilinear form.
10. The composite cathode active material of claim 1, wherein at
least one grain boundary between adjacent primary particles among
the plurality of primary particles, extends in a direction parallel
to adjacent surfaces of the adjacent primary particles, and at
least one grain boundary extends in a direction different from a
tangential direction of an outer surface of the core of the
secondary particle.
11. The composite cathode active material of claim 1, wherein the
core comprises a first grain boundary and a second grain boundary,
and each of the first grain boundary and the second grain boundary
are adjacent to a same primary particle, and wherein the first
grain boundary and the second grain boundary intersect at an angle
determined by a shape of the primary particle.
12. The composite cathode active material of claim 1, wherein the
core comprises a plurality of grain boundaries amongst the
plurality of primary particles, wherein each grain boundary of the
plurality of grain boundaries extends in a direction parallel to a
surface of an adjacent primary particle, and wherein each grain
boundary of the plurality of grain boundaries extends in a
different direction from each other.
13. The composite cathode active material of claim 1, wherein an
average grain boundary length is in a range of about 50 nanometers
to about 1000 nanometers and an average grain boundary thickness is
in a range of about 1 nanometer to about 50 nanometers, and wherein
a length direction of the grain boundary is parallel to adjacent
surfaces of adjacent primary particles, and thickness direction of
the grain boundary is perpendicular to adjacent surfaces of
adjacent primary particles.
14. The composite cathode active material of claim 1, wherein the
shell comprises the first composition comprising the first
metal.
15. The composite cathode active material of claim 1, wherein the
shell comprises a second composition comprising a second metal.
16. The composite cathode active material of claim 15, wherein the
second metal comprises Zr, Co, Mg, Mn, Si, Mo, Pd, Co, Ni, Ti, Sn,
Mo, Ir, Pt, Ru, or a combination thereof.
17. The composite cathode active material of claim 1, wherein the
shell has a thickness of about 300 nanometers or less.
18. The composite cathode active material of claim 1, wherein an
amount of the first metal in the secondary particle is about 1 mole
percent or less with respect to total moles of the transition metal
and the first metal in the nickel-containing lithium transition
metal oxide.
19. The composite cathode active material of claim 1, wherein the
nickel-containing lithium transition metal oxide comprises lithium,
nickel, the first metal, a third metal, and oxygen, wherein, the
nickel-containing lithium transition metal oxide comprises about
0.1 mole to about 1.3 moles of lithium, about 0.7 moles to about
0.99 moles of nickel, about 0.001 moles to about 0.01 moles of the
first metal, about 0.01 mole to about 0.3 moles of the third metal,
and about 1.7 moles to about 2.3 moles of oxygen, per mole of the
nickel-containing lithium transition metal oxide.
20. The composite cathode active material of claim 1, wherein the
nickel-containing lithium transition metal oxide is represented by
Formula 2: Li.sub.aMO.sub.2 Formula 2 wherein, in Formula 2,
0.9.ltoreq.a.ltoreq.1.1, M comprises nickel, the first metal, and
an element comprising a Group 2 to Group 13 element which is
different from the first metal, and an amount of nickel in M is
about 70 mole percent to less than 100 mole percent based on total
moles of M in the lithium transition metal oxide.
21. The composite cathode active material of claim 1, wherein the
nickel-containing lithium transition metal oxide is represented by
Formula 3: Li.sub.aNi.sub.bM1.sub.cM2.sub.dM3.sub.eO.sub.2 Formula
3 wherein, in Formula 3, 0.9.ltoreq.a.ltoreq.1.1, 0.7<b<1.0,
0<c<0.3, 0<d<0.3, 0.ltoreq.e<0.1, b+c+d+e=1, and M1,
M2, and M3 differ from one another and are each independently an
element selected from Mn, V, Cr, Fe, Co, Zr, Re, Al, B, Ru, Ti, Nb,
Mo, Mg, and Pt.
22. The composite cathode active material of claim 1, wherein the
nickel-containing lithium transition metal oxide is represented by
Formula 4: Li.sub.aNi.sub.bCO.sub.cMn.sub.dM3.sub.eO.sub.2 Formula
4 wherein, in Formula 4, 0.9.ltoreq.a.ltoreq.1.1, 0.7<b<1.0,
0<c<0.1, 0<d<0.1, 0.ltoreq.e<0.01, b+c+d+e=1, and M3
comprises Zr, V, Cr, Fe, Re, Al, B, Ru, Ti, Nb, Mo, Mg, Pt, or a
combination thereof.
23. The composite cathode active material of claim 1, wherein the
nickel-containing lithium transition metal oxide is represented by
Formula 5: aLi.sub.2MnO.sub.3-(1-a)LiMO.sub.2 Formula 5 wherein, in
Formula 5, 0<a<1, and M comprises at least two elements
selected from Ni, Co, Mn, V, Cr, Fe, Zr, Re, Al, B, Ru, Ti, Nb, Mo,
Mg, and Pt.
24. The composite cathode active material of claim 1, wherein an
area of pores in a cross-section of the composite cathode active
material is about 1% or less with respect to the total area of the
cross-section.
25. A cathode comprising the composite cathode active material
according to claim 1.
26. A lithium battery comprising, the cathode according to claim
25, an anode, and an electrolyte between the cathode and the
anode.
27. A method of preparing a composite cathode active material, the
method comprising: providing a first solution comprising a first
metal precursor; combining the first solution with a
nickel-containing lithium transition metal oxide precursor to
prepare a second solution comprising a precipitate; separating the
precipitate from the second solution and drying the precipitate to
prepare a dried product; mixing the dried product and a lithium
precursor compound to prepare a mixture; and thermally treating the
mixture to thereby prepare the composite cathode active
material.
28. The method of claim 28, wherein a porosity of the composite
cathode active material is less than a porosity of the
nickel-containing lithium transition metal oxide precursor.
29. The method of claim 27, wherein the nickel-containing lithium
transition metal oxide precursor comprises primary particles having
a needle shape.
30. The method of claim 27, wherein the composite cathode active
material comprises: a secondary particle comprising a core
comprising a plurality of particles, and a shell on the core,
wherein the plurality of primary particles comprise the
nickel-containing lithium transition metal oxide doped with the
first metal, and wherein at least one grain boundary between the
plurality of primary particles comprises the first metal.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to an the benefit of Korean
Patent Application No. 10-2018-0064480, filed on Jun. 4, 2018, in
the Korean Intellectual Property Office, and all the benefits
accruing therefrom under 35 U.S.C. .sctn. 119, the content of which
is incorporated herein by reference in its entirety.
BACKGROUND
1. Field
[0002] The present disclosure relates to a composite cathode active
material, a cathode and a lithium battery, each including the
composite cathode active material, and a method of preparing the
composite cathode active material.
2. Description of the Related Art
[0003] To adapt to the trend toward devices having a smaller size
and increased performance, it is advantageous to provide a lithium
battery having a high energy density, a small size, and a low
weight. That is, a lithium battery having a high capacity is
desirable.
[0004] To implement such a lithium battery, research has been
conducted to identify cathode active materials having high
capacity. A nickel-based (e.g., nickel-containing) cathode active
material may have poor lifetime characteristics and poor thermal
stability due to side reactions caused by a high amount of residual
surface lithium and mixing of cations.
[0005] Therefore, there is a need for a method of preventing
performance deterioration in a battery including a nickel-based
cathode active material.
SUMMARY
[0006] Provided is a novel composite cathode active material which
may prevent performance deterioration of a battery by suppressing a
side reaction on a surface of, and inside of, the composite cathode
active material.
[0007] Provided is a cathode including the composite cathode active
material.
[0008] Provided is a lithium battery including the cathode.
[0009] Provided is a method of preparing the composite cathode
active material.
[0010] Additional aspects will be set forth in part in the
description which follows and, in part, will be apparent from the
description, or may be learned by practice of the presented
embodiments.
[0011] According to an aspect of an embodiment, a composite cathode
active material includes: a secondary particle including a core
including a plurality of primary particles; and a shell on the
core, wherein the plurality of primary particles include a
nickel-containing lithium transition metal oxide doped with a first
metal, and wherein a grain boundary between the plurality of
primary particles includes a first composition including the first
metal.
[0012] According to an aspect of another embodiment, a cathode
includes the above-described composite cathode active material.
[0013] According to an aspect of another embodiment, a lithium
battery includes the above-described cathode, an anode, and an
electrolyte between the cathode and the anode.
[0014] According to an aspect of another embodiment, a method of
preparing a composite cathode active material includes: providing a
first solution including a first metal precursor; combining the
first solution with a nickel-containing lithium transition metal
oxide precursor to prepare a second solution including a
precipitate; separating the precipitate from the second solution
and drying the precipitate to prepare a dried product; mixing the
dried product and a lithium precursor compound to prepare a
mixture; and thermally treating the mixture to thereby prepare the
composite cathode active material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] These and/or other aspects will become apparent and more
readily appreciated from the following description of the
embodiments, taken in conjunction with the accompanying drawings in
which:
[0016] FIG. 1A is a schematic view that partially illustrates an
internal structure of a composite cathode active material according
to an embodiment;
[0017] FIG. 1B is a schematic cross-sectional view of a composite
cathode active material according to an embodiment;
[0018] FIG. 2 a graph of intensity (arbitrary units, a.u.) versus
diffraction angle (degrees 2-theta), illustrating the X-ray
diffraction (XRD) spectra of first composite cathode active
materials prepared in Examples 1 to 3 and Comparative Example
1;
[0019] FIGS. 3A a 3D are high-angle annular dark-field scanning
transmission electron microscopy (HAADF STEM) and energy dispersive
X-ray spectroscopy (EDS) images of cross-sections of a second
composite cathode active material prepared in Comparative Example
3;
[0020] FIGS. 4A to 4D are HAADF STEM and EDS images of
cross-sections of the second composite cathode active material of
Example 2;
[0021] FIG. 5A is a scanning electron microscope (SEM) image of a
cross-section of the second composite cathode active material
prepared in Comparative Example 3 before being assembled into a
lithium battery;
[0022] FIG. 5B is a SEM image of a cross-section of the second
composite cathode active material prepared in Example 2 before
being assembled into a lithium battery;
[0023] and
[0024] FIG. 6 is a schematic view of a lithium battery according to
an embodiment.
DETAILED DESCRIPTION
[0025] The present inventive concept will now be described more
fully with reference to the accompanying drawings, in which example
embodiments are shown. The present inventive concept may, however,
be embodied in many different forms, should not be construed as
being limited to the embodiments set forth herein, and should be
construed as including all modifications, equivalents, and
alternatives within the scope of the present inventive concept;
rather, these embodiments are provided so that this inventive
concept will be thorough and complete, and will fully convey the
effects and features of the present inventive concept and ways to
implement the present inventive concept to those skilled in the
art.
[0026] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the inventive concept. As used herein, the singular forms "a", "an"
and "the" are intended to include the plural forms as well, unless
the context clearly indicates otherwise. It will be further
understood that the terms "comprises" and/or "comprising," when
used in this specification, specify the presence of stated
features, integers, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof. The sign "/" used herein may be construed as
meaning of "and" or "or" depending on the situation. "At least one"
is not to be construed as limiting "a" or "an." "Or" means
"and/or." As used herein, the term "and/or" includes any and all
combinations of one or more of the associated listed items.
[0027] In the drawings, the size or thickness of each layer,
region, or element are arbitrarily exaggerated or reduced for
better understanding or ease of description, and thus the present
inventive concept is not limited thereto. Throughout the written
description and drawings, like reference numbers and labels will be
used to denote like or similar elements. It will also be understood
that when an element such as a layer, a film, a region or a
component is referred to as being "on" another layer or element, it
can be "directly on" the other layer or element, or intervening
layers, regions, or components may also be present. In contrast,
when an element is referred to as being "directly on" another
element, there are no intervening elements present. Although the
terms "first", "second", etc., may be used herein to describe
various elements, components, regions, and/or layers, these
elements, components, regions, and/or layers should not be limited
by these terms. These terms are used only to distinguish one
component from another, not for purposes of limitation.
[0028] Furthermore, relative terms, such as "lower" or "bottom" and
"upper" or "top," may be used herein to describe one element's
relationship to another element as illustrated in the Figures. It
will be understood that relative terms are intended to encompass
different orientations of the device in addition to the orientation
depicted in the Figures. For example, if the device in one of the
figures is turned over, elements described as being on the "lower"
side of other elements would then be oriented on "upper" sides of
the other elements. The exemplary term "lower," can therefore,
encompasses both an orientation of "lower" and "upper," depending
on the particular orientation of the figure. Similarly, if the
device in one of the figures is turned over, elements described as
"below" or "beneath" other elements would then be oriented "above"
the other elements. The exemplary terms "below" or "beneath" can,
therefore, encompass both an orientation of above and below.
[0029] "About" or "approximately" as used herein is inclusive of
the stated value and means within an acceptable range of deviation
for the particular value as determined by one of ordinary skill in
the art, considering the measurement in question and the error
associated with measurement of the particular quantity (e.g., the
limitations of the measurement system). For example, "about" can
mean within one or more standard deviations, or within .+-.30%,
20%, 10%, or 5% of the stated value.
[0030] Hereinafter, embodiments of a composite cathode active
material, a method of preparing the same, and a cathode and a
lithium battery each including the composite cathode active
material will be described in detail.
[0031] In accordance with an aspect of the inventive concept, a
composite cathode active material includes: a core including a
plurality of primary particles; and a shell on the core, wherein at
least one grain boundary between the plurality of primary particles
includes a first composition including a first metal, and the
plurality of primary particles include a nickel-based
(nickel-containing) lithium transition metal oxide, and the
nickel-based lithium transition metal oxide is doped with the first
metal. That is, the nickel-based lithium transition metal oxide may
have a layered crystalline structure, and the nickel-based lithium
transition metal oxide may be doped with the first metal. The grain
boundaries may be disposed between adjacent primary particles among
the plurality of primary particles. As used herein the term "grain
boundary" refers to the interface between adjacent particles
(grains or crystallites).
[0032] Referring to FIG. 1A, a composite cathode active material
400 according to an embodiment may include a secondary particle 300
including a core 100 and a shell 200 on the core 100. The core 100
may include a plurality of primary particles 10 and a grain
boundary 20 between adjacent primary particles among the plurality
of primary particles 10. For example, the primary particles 10 may
be crystallites each having the same crystalline structure. The
primary particles 10 may include a nickel-based lithium transition
metal oxide doped with a first metal and having a layered
crystalline structure. For example, the shell 200 may be a coating
layer on a portion of a surface of the core 100, or on the entire
surface of the core 100. The grain boundary 20 between adjacent
primary particles among the plurality of primary particles 10 may
include a first composition including the first metal. The
secondary particle 300 may be an aggregate of the plurality of
primary particles 10 (core) having a coating layer (shell)
thereon.
[0033] By the inclusion of the grain boundaries 20 including the
first composition between adjacent primary particles among the
plurality of primary particles 10 in the core 100 of the composite
cathode active material 400, lithium ion conduction within the core
100 may be facilitated, and the release of nickel ions from the
primary particles 10 in the core 100 into an electrolyte solution
that has permeated into the core 100, may be suppressed. A side
reaction between the primary particles 10 and the electrolyte
solution in the core 100 may be suppressed. Accordingly, a lithium
battery including the composite cathode active material 400 may
have improved cycle characteristics. A residual surface lithium
content of the plurality of primary particles 10 in the core 100
may be reduced, and deterioration of the composite cathode active
material 400 may be suppressed. Further, due to reduced gas
generation, the lithium battery may have improved thermal
stability. The first composition in the grain boundaries 20 between
the adjacent primary particles 10 may prevent damage to the surface
of the primary particles 10, which may occur during washing of the
composite cathode active material 400, and may prevent the
deterioration of lifetime characteristics in the lithium battery.
The first composition, present in the grain boundaries 20 between
the adjacent primary particles 10, may withstand a volume change
which occurs in the primary particles during a charge/discharge
process. The first composition in the grain boundaries may also
suppress cracking from occurring between the primary particles 10,
and suppress mechanical strength reduction of the composite cathode
active material 400, thereby preventing deterioration of the
lithium battery. Since the nickel-containing lithium transition
metal oxide in the primary particles 10 is doped with the first
metal, the nickel-containing lithium transition metal oxide may
have a stabilized crystalline structure, and thus a lithium battery
including the composite cathode active material may have improved
cycle characteristics.
[0034] In the composite cathode active material according to one or
more embodiments, an amount of nickel in the nickel-containing
lithium transition metal oxide may be about 70 mole percent (mol %)
or greater, about 71 mol % or greater, about 75 mol % or greater,
about 80 mol % or greater, about 85 mol % or greater, about 90 mol
% or greater, about 93 mol % or greater, about 95 mol % or greater,
or about 97 mol % or greater based on the total moles of transition
metals in the nickel-containing lithium transition metal oxide. For
example, the amount of nickel in the nickel-containing lithium
transition metal oxide is about 70 mol % to less than 100 mol %, or
about 80 mol % to about 99 mol % or about 85 mol % to about 98 mol
%. When the amount of nickel in the nickel-containing lithium
transition metal oxide is about 70 mol % or greater, a high
capacity may be implemented. Accordingly, a high-capacity lithium
battery may be implemented.
[0035] The first composition in the grain boundaries 20 may include
a first phase and a second phase. The second phase is different
from the first phase. The first phase corresponds to the
nickel-containing lithium transition metal oxide. In other words,
the primary particle may include the first phase, and the grain
boundary may include a second phase. The second phase may have, for
example, a monoclinic crystalline structure. Since the first
composition has the monoclinic crystalline structure,
two-dimensional migration of lithium ions may be possible in the
grain boundaries including the first composition, such that lithium
ion conduction in the core 100 may be facilitated, thus leading to
improved high-rate characteristics. The first composition may have
a monoclinic crystalline structure belonging to a C2/m, C12/c1, or
C2/c space group. As the first composition has a monoclinic
crystalline structure belonging to the C2/m, C12/c1, or C2/c space
group, a lithium battery including the composite cathode active
material may have further improved cycle characteristics and
thermal stability. For example, the first phase may include a phase
having a trigonal crystalline structure, and the second phase may
include a phase having a monoclinic crystalline structure. The
first phase and the second phase may belong to different space
groups. The first phase and the second phase may have different
chemical compositions.
[0036] The first metal in the first composition may include, for
example, Zr, Mn, Si, Mo, Pd, Co, Ni, Ti, Sn, Mo, Ir, Pt, Ru, or a
combination thereof. When the first composition includes the first
metal, a lithium battery including the composite cathode active
material may have further improved charge/discharge
characteristics.
[0037] In the composite cathode active material according to one or
more embodiments, the first composition may include lithium, a
first metal, and oxygen. For example, per mole of the first
composition, the first composition may include about 1.7 moles to
about 2.3 moles of lithium, about 0.7 mole to about 1.3 moles of
the first metal, and about 2.7 moles to about 3.3 moles of oxygen.
For example, per mole of the first composition, the first
composition may include about 1.8 moles to about 2.2 moles of
lithium, about 0.8 mole to about 1.2 moles of the first metal, and
about 2.8 moles to about 3.2 moles of oxygen. For example, per mole
of the first composition, the first composition may include about
1.9 moles to about 2.1 moles of lithium, about 0.9 mole to about
1.1 mole of the first metal, and about 2.9 moles to about 3.1 moles
of oxygen.
[0038] The first composition may have, for example, a composition
represented by Formula 1.
Li.sub.aM1.sub.bO.sub.c Formula 1
[0039] In Formula 1, M1 may include Zr, Mn, Si, Mo, Pd, Co, Ni, Ti,
Sn, Mo, Ir, Pt, Ru, or a combination thereof, and
1.9.ltoreq.a.ltoreq.2.1, 0.91.ltoreq.b.ltoreq.1.1, and
2.9.ltoreq.c.ltoreq.3.1.
[0040] In the composite cathode active material according to one or
more embodiments, the core may include a first inner region and
second inner region. The first inner region extends from a center
of the core to halfway between the center of the core and a surface
of the core, and a second inner region extends from halfway between
the center of the core and the surface of the core to the surface
of the core. About 50% or greater of the grain boundaries in the
first inner region may include the first composition, and about 50%
or greater of the grain boundaries in the second inner region may
include the first composition. For example, about 51% or greater,
about 55% or greater, about 60% or greater, about 70% or greater,
about 80% or greater, about 85% or greater, about 90% or greater,
about 95% or greater, or about 98% or greater of the grain
boundaries in the first inner region may include the first
composition. For example, about 51% or greater, about 55% or
greater, about 60% or greater, about 70% or greater, about 80% or
greater, about 85% or greater, about 90% or greater, about 95% or
greater, or about 98% or greater of the grain boundaries in the
second inner region may include the first composition. As referred
to herein, the percentage (%) of the grain boundaries including the
first composition refers to a percentage of the area of grain
boundaries including the first composition with respect to a total
area of the grain boundaries, as measured by exposing a
cross-section of the core. That is, most of the grain boundaries in
the first inner region and in the second inner region of the core
may include the first composition.
[0041] In the composite cathode active material according to one or
more embodiments, the core may include the first composition
dispersed at a uniform concentration throughout the core. In some
embodiments, the first composition may have a continuous or
discontinuous concentration gradient that changes from a center
portion to a surface portion of the core. For example, a
concentration of the first composition in the first inner region of
the core may be lower than that a concentration of the first
composition in the second inner region of the core. For example, a
concentration of the first composition in the first inner region of
the core may be greater than a concentration of the first
composition in the second inner region of the core. The first
composition may be discontinuously dispersed inside of the
core.
[0042] Referring to FIG. 1B, in the core 100 of the composite
cathode active material 400, the grain boundaries 20 may have a
substantially rectilinear form. Since the primary particles 10
adjacent to the grain boundaries 20 include the nickel-based
(nickel containing) lithium transition metal oxide having a layered
crystalline structure, the primary particles 10 may have a
polyhedral shape, and thus the grain boundary 20 between adjacent
primary particles 10 may have a rectilinear form.
[0043] Referring to FIG. 1B, in the composite cathode active
material 400, the grain boundary 20 in the core 100 may extend in a
direction 21 parallel to a surface of the adjacent primary particle
10, and the direction 21 in which the grain boundary 20 is extended
may be different from a tangential direction 101 of a nearest outer
surface of the core 100. That is, the grain boundary may extend in
a direction different from a tangential direction 101 of the outer
surface of the core.
[0044] Referring to FIG. 1B, in the composite cathode active
material 400, the core 100 may include a first grain boundary 32
and a second grain boundary 33. Each of the first grain boundary 32
and the second grain boundary 33 may be directly adjacent to the
same primary particle 30 among the plurality of primary particles
10, and the first grain boundary 32 and the second grain boundary
33 may intersect at an angle (a) that is determined by a shape of
the primary particle 30. The angle (a) at which the first grain
boundary 32 and the second grain boundary 33 intersect may be in a
range of greater than about 0 degree to less than about 180
degrees, or, for example, about 10 degrees to about 170 degrees,
about 20 degrees to about 160 degrees, about 30 degrees to about
150 degrees, about 40 degrees to about 140 degrees, about 50
degrees to about 130 degrees, about 60 degrees to about 120
degrees, about 70 degrees to about 110 degrees, or about 80 degrees
to about 110 degrees.
[0045] Referring to FIG. 1B, in the composite cathode active
material 400, the core 100 may include a plurality of grain
boundaries 32 and 42 amongst (adjacent to) the plurality of primary
particles 30 and 40. Each grain boundary of the plurality of grain
boundaries 32 and 42 extends in directions 31 and 41 that are
parallel to surfaces of the primary particles 30 and 40 adjacent to
the plurality of grain boundaries 32 and 42. Also, each grain
boundary of the plurality of grain boundaries 32 and 42, extends in
a different direction from each other.
[0046] Referring to FIG. 1B, in the composite cathode active
material 400, the grain boundaries 20, 32, and 42 may have an
average grain boundary length in a range of about 50 nanometers
(nm) to about 1000 nm and an average grain boundary thickness in a
range of about 1 nm to about 200 nm. Length directions 21, 31, and
41 of the grain boundaries may be parallel to surfaces of the
adjacent primary particles 10, 30, and 40, and a thickness
direction of the grain boundaries 20, 32, and 42 may be
perpendicular to surfaces of the adjacent primary particles 10, 30,
and 40. For example, the average grain boundary length may be in a
range of about 50 nm to about 950 nm, about 100 nm to about 900 nm,
about 150 nm to about 800 nm, or about 200 nm to about 700 nm. For
example, the average grain boundary thickness may be in a range of
about 2 nm to about 100 nm, about 5 nm to about 100 nm, about 10 nm
to about 100 nm, or about 20 nm to about 100 nm. When the average
grain boundary length and the average grain boundary thickness are
within these ranges, further improved charge/discharge
characteristics may be provided. The average grain boundary length
may refer to an average of the lengths d1 of the grain boundaries
extending in a direction. The average grain boundary thickness may
refer to an average of the thicknesses d2 of the grain
boundaries.
[0047] In the composite cathode active material according to one or
more embodiments, an average particle diameter of the primary
particles may be in a range of about 50 nm to about 500 nm, about
50 nm to about 450 nm, about 50 nm to about 400 nm, about 50 nm to
about 350 nm, about 50 nm to about 300 nm, about 50 nm to about 250
nm, or about 50 nm to about 200 nm. However, embodiments are not
limited thereto. The average particle diameter of the primary
particles 10 may be varied as long as it provides improved
charge/discharge characteristics. As used herein, average particle
diameter refers to a size, e.g., a dimension, such as a length or
width dimension, as measured along a major surface.
[0048] In the composite cathode active material according to one or
more embodiments, an average particle diameter of the core,
corresponding to the aggregate of the plurality of primary
particles, may be in a range of about 1 micrometer (.mu.m) to about
30 .mu.m, about 2 .mu.m to about 28 .mu.m, about 4 .mu.m to about
26 .mu.m, about 6 .mu.m to about 24 .mu.m, about 8 .mu.m to about
22 .mu.m, about 10 .mu.m to about 20 .mu.m, about 12 .mu.m to about
18 .mu.m, about 12 .mu.m to about 16 .mu.m, or about 13 .mu.m to
about 15 .mu.m. However, embodiments are not limited thereto. The
average particle diameter of the core 100 may be varied as long as
it may provide improved charge/discharge characteristics.
[0049] In the composite cathode active material according to one or
more embodiments, the shell may include the first composition
including the first metal. The first composition may be disposed in
the shell, which is present on the surface of the core, as well as
in the grain boundaries of the core. In some embodiments, the first
composition may form the shell, which is provided as a coating of
the surface of the core. The first composition in the shell may
have the same composition and the same crystalline structure as the
first composition disposed in the grain boundaries of the core. For
example, the first composition in the shell may have a monoclinic
crystalline structure belonging to the C2/m, C12/c1, or C2/c space
group. For example, the first composition in the shell may have the
composition represented by Formula 1 as described above.
[0050] In the composite cathode active material according to one or
more embodiments, the shell may further include a second
composition including a second metal, the second composition having
the same or different composition and/or the same or different
crystalline structure as those of the first composition, as long as
it does not deteriorate charge/discharge characteristics of the
lithium battery. That is, the shell may include the second
composition in addition to the first composition. The second
composition may have an amorphous structure, a layered crystalline
structure, a spinel crystalline structure, an olivine crystalline
structure, or a combination thereof. By the additional inclusion of
the second composition, a residual surface lithium content of the
core may be reduced, and a side reaction between the core and the
electrolyte may be more effectively prevented. The second metal in
the second composition may include Zr, Co, Mg, Mn, Si, Mo, Pd, Co,
Ni, Ti, Sn, Mo, Ir, Pt, Ru, or a combination thereof. However,
embodiments are not limited thereto. Any metal that may be capable
of improving the cycle characteristics of the composite active
material by being coated on the surface of the core may be
used.
[0051] In the composite cathode active material according to one or
more embodiments, the shell may have a multilayer structure
including a first coating layer containing the first composition
and a second coating layer containing the second composition. The
first coating layer and the second coating layer may be
sequentially stacked on the surface of the core, may be arranged in
different regions parallel to one another on the surface of the
core, or may have a combination of these stacked and parallel
configurations.
[0052] In the composite cathode active material according to one or
more embodiments, the shell may have a thickness of about 300 nm or
less, about 250 nm or less, about 200 nm or less, about 150 nm or
less, about 100 nm or less, about 90 nm or less, about 80 nm or
less, about 70 nm or less, about 60 nm or less, about 50 nm or
less, about 40 nm or less, about 30 nm or less, about 20 nm or
less, or about 10 nm or less, or from about 1 nm to about 300 nm,
or from about 5 nm to about 200 nm, or from about 5 nm to about 100
nm. When the thickness of the shell is within these ranges, a
lithium battery including the composite cathode active material may
have further improved cycle characteristics and thermal
stability.
[0053] In the composite cathode active material according to one or
more embodiments, a total amount of the first metal in the
secondary particles including the core and the shell may be about 2
mol % or less, about 1.5 mol % or less, about 1.0 mol % or less,
about 0.95 mol % or less, about 0.9 mol % or less, about 0.85 mol %
or less, about 0.8 mol % or less, about 0.75 mol % or less, about
0.7 mol % or less, about 0.65 mol % or less, or about 0.6 mol % or
less, with respect to the total number of moles of the transition
metal and the first metal of the nickel-containing lithium
transition metal oxide. For example, the amount of the first metal
in the second particles including the core and the shell may be
about 0.01 mol % or greater, about 0.05 mol % or greater, about 0.1
mol % or greater, about 0.15 mol % or greater, about 0.2 mol % or
greater, or about 0.25 mol % or greater, with respect to a total
number of moles of the transition metal and the first metal in the
nickel-containing lithium transition metal oxide. When the amount
of the first metal is within these ranges, a lithium battery
including the composite cathode active material may have further
improved cycle characteristics and thermal stability.
[0054] In the composite cathode active material according to one or
more embodiments, the nickel-containing lithium transition metal
oxide may include lithium, nickel, the first metal, an additional
(third) metal, and oxygen. The additional (third) metal may refer
to any metal other than lithium, nickel, and the first metal, and
may be, for example a transition metal.
[0055] In the composite cathode active material according to one or
more embodiments, per mole of the nickel-containing lithium
transition metal oxide, the nickel-containing lithium transition
metal oxide may include about 0.1 mole to about 1.3 moles of
lithium, about 0.7 mole to about 0.99 mole of nickel, about 0.001
mole to about 0.01 mole of the first metal, about 0.01 mole to
about 0.3 mole of the additional (third) transition metal, and
about 1.7 moles to about 2.3 moles of oxygen. For example, per mole
of the nickel-containing lithium transition metal oxide, the
nickel-containing lithium transition metal oxide may include about
0.7 mole to about 1.3 moles of lithium, about 0.7 mole to about
0.99 mole of nickel, about 0.001 mole to about 0.01 mole of the
first metal, about 0.01 mole to about 0.3 mole of the additional
(third) transition metal, and about 1.7 moles to about 2.3 moles of
oxygen.
[0056] For example, the nickel-containing lithium transition metal
oxide may be represented by Formula 2.
Li.sub.aMO.sub.2 Formula 2
[0057] In Formula 2, 0.9.ltoreq.a.ltoreq.1.1, M may include nickel,
a first metal, and at least one other element selected from Group 2
to Group 13 elements other than the first metal, and a nickel
content in M may be about 70 mol % to less than 100 mol %.
[0058] For example, the nickel-containing lithium transition metal
oxide may be represented by Formula 3.
Li.sub.aNi.sub.bM1.sub.cM2.sub.dM3.sub.eO.sub.2 Formula 3
[0059] In Formula 3, 0.9.ltoreq.a.ltoreq.1.1, 0.7<b<1.0,
0<c<0.3, 0<d<0.3, 0.ltoreq.e<0.1, b+c+d+e=1, and M1,
M2, and M3 may differ from one another and may each be
independently an element selected from manganese (Mn), vanadium
(V), chromium (Cr), iron (Fe), cobalt (Co), zirconium (Zr), rhenium
(Re), aluminum (Al), boron (B), ruthenium (Ru), titanium (Ti),
niobium (Nb), molybdenum (Mo), magnesium (Mg), and platinum (Pt).
The nickel-containing lithium transition metal oxide of Formula 3
includes a first metal as a dopant in the nickel-containing lithium
transition metal oxide.
[0060] For example, the nickel-containing lithium transition metal
oxide may be represented by Formula 4:
Li.sub.aNi.sub.bCo.sub.cMn.sub.dM3.sub.eO.sub.2 Formula 4
[0061] In Formula 4, 0.9.ltoreq.a.ltoreq.1.1, 0.7<b<1.0,
0<c<0.3, 0<d<0.3, 0.ltoreq.e<0.1, b+c+d+e=1, and M3
may include zirconium (Zr), vanadium (V), chromium (Cr), iron (Fe),
rhenium (Re), aluminum (Al), boron (B), ruthenium (Ru), titanium
(Ti), niobium (Nb), molybdenum (Mo), magnesium (Mg), platinum (Pt),
or a combination thereof. The nickel-containing lithium transition
metal oxide of Formula 4 includes a first metal as a dopant in the
nickel-containing lithium transition metal oxide.
[0062] In the composite cathode active material according to one or
more embodiments, the nickel-containing lithium transition metal
oxide may include at least one of a first layered crystalline phase
belonging to the C2/m, C12/c1, or C2/c space group, and a second
layered crystalline phase belonging to the R-3m space group. The
nickel-containing lithium transition metal oxide according to one
or more embodiments may be a composite of the first layered
crystalline phase and the second layered crystalline phase.
[0063] For example, the nickel-containing lithium transition metal
oxide may include a first layered crystalline phase having a
composition represented by Formula 4a and belonging to the C2/m,
C12/c1, or C2/c space group, and a second layered crystalline phase
having a composition represented by Formula 4b and belonging to the
R-3m space group.
Li.sub.2MnO.sub.3 Formula 4a
LiMO.sub.2 Formula 4b
[0064] In Formulae 4a and 4b,
[0065] M may be at least two elements selected from nickel (Ni),
cobalt (Co), manganese (Mn), vanadium (V), chromium (Cr), iron
(Fe), zirconium (Zr), rhenium (Re), aluminum (Al), boron (B),
ruthenium (Ru), titanium (Ti), niobium (Nb), molybdenum (Mo),
magnesium (Mg), and platinum (Pt). At least a portion of M may be
Ni. The amount of Ni in M may be about 70 mol % or greater, for
example, about 71 mol % or greater, about 75 mol % or greater,
about 80 mol % or greater, about 85 mol % or greater, about 90 mol
% or greater, about 93 mol % or greater, about 95 mol % or greater,
or about 97 mol % or greater, based on the total moles of the
elements in M. The second layered crystalline phase of Formula 4b
may be doped with a first metal.
[0066] For example, the nickel-containing lithium transition metal
oxide may be represented by Formula 5.
aLi.sub.2MnO.sub.3-(1-a)LiMO.sub.2 Formula 5
[0067] In Formula 5, 0<a<1, and M may include at least two
elements selected from nickel (Ni), cobalt (Co), manganese (Mn),
vanadium (V), chromium (Cr), iron (Fe), zirconium (Zr), rhenium
(Re), aluminum (Al), boron (B), ruthenium (Ru), titanium (Ti),
niobium (Nb), molybdenum (Mo), magnesium (Mg), and platinum (Pt).
At least a portion of M may be Ni. A Ni content in M may be about
70 mol % or greater, for example, about 71 mol % or greater, about
75 mol % or greater, about 80 mol % or greater, about 85 mol % or
greater, about 90 mol % or greater, about 93 mol % or greater,
about 95 mol % or greater, or about 97 mol % or greater, based on
the total moles of the elements in M. The nickel-containing lithium
transition metal oxide of Formula 5 includes a first metal which is
doped in the nickel-containing lithium transition metal oxide.
[0068] In the composite cathode active material according to one or
more embodiments, the area of pores in a cross-section of the
composite cathode active material, before use in a lithium battery,
i.e., not subjected to charging and discharging, may be 1% or less,
about 0.95% or less, about 0.90% or less, about 0.85% or less, or
about 0.80% or less of a total area of the cross-section. The area
of pores in the total area of the cross-section of the composite
cathode active material corresponds to a porosity. As used herein,
the term "porosity" is used to refer to a measure of the empty
space (i.e., voids or pores) in the secondary particle and is
represented by Equation 1.
Porosity [%]=(Area occupied by pores/Total cross-sectional area of
a secondary particle).times.100% <Equation 1>
[0069] In Equation 1, the area occupied by pores refers to a total
area of the pores in the secondary particle, and which appears as
black dots in FIGS. 5A and 5B.
[0070] In accordance with another aspect of the inventive concept,
a cathode includes a composite cathode active material according to
any of the above-described embodiments.
[0071] The cathode may be prepared as follows. A composite cathode
active material according to any of the above-described
embodiments, a conducting agent, a binder, and a solvent may be
mixed together to prepare a cathode active material composition.
The cathode active material composition may be directly coated on
an aluminum current collector to prepare a cathode plate having a
cathode active material film. In some embodiments, the cathode
active material composition may be cast on a separate support to
form a cathode active material film. This cathode active material
film may then be separated from the support and laminated on an
aluminum current collector to prepare a cathode plate (or a
cathode) having the cathode active material film.
[0072] The conducting agent may include carbon black, graphite
particulates, natural graphite, artificial graphite, acetylene
black, Ketjen black, carbon fibers, carbon nanotubes, a metal
powder, metal fiber, or metal tubes of copper, nickel, aluminum, or
silver, or a conducting polymer such as a polyphenylene derivative,
or a combination thereof, but embodiments are not limited thereto.
Any material suitable for use as a conducting agent may be
used.
[0073] Examples of the binder include a vinylidene
fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride
(PVDF), polyacrylonitrile, polymethyl methacrylate,
polytetrafluoroethylene (PTFE), a styrene-butadiene rubber polymer,
or a combination thereof, but embodiments are not limited thereto.
Any material suitable for use as a binding agent may be used.
Examples of the solvent include N-methyl-pyrrolidone (NMP),
acetone, or water, but embodiments are not limited thereto. Any
material suitable for use as a solvent may be used.
[0074] In some embodiments, pores may be formed in the cathode
plate by further adding a plasticizing agent to the cathode active
material composition.
[0075] The amounts of the composite cathode active material, the
conducting agent, the binder, and the solvent may be determined by
those of skill in the art without undue experimentation. At least
one of the conducting agent, the binder, and the solvent may be
omitted according to the use and the structure of the lithium
secondary battery.
[0076] The cathode may include an additional (e.g., second) cathode
active material in addition to the composite cathode active
material used above.
[0077] The second cathode active material may be any material
suitable for use as a cathode active material for a lithium battery
and, may be for example, a lithium-containing metal oxide. For
example, the second cathode active material may include a lithium
composite oxide including a metal selected from among Co, Mn, Ni,
or a combination thereof. In some embodiments, the second cathode
active material may be a compound represented by one of the
following formulae: Li.sub.aA.sub.1-bB.sub.bD.sub.2 (wherein
0.90.ltoreq.a.ltoreq.1 and 0.ltoreq.b.ltoreq.0.5);
Li.sub.aE.sub.1-bB.sub.bO.sub.2-cD.sub.c (wherein
0.90.ltoreq.a.ltoreq.1, 0.ltoreq.b.ltoreq.0.5, and
0.ltoreq.c.ltoreq.0.05); LiE.sub.2-bB.sub.bO.sub.4-cD.sub.c
(wherein 0.ltoreq.b.ltoreq.0.5 and 0.ltoreq.c.ltoreq.0.05);
Li.sub.aNi.sub.1-b-cCO.sub.bB.sub.cD.sub..alpha. (wherein
0.90.ltoreq.a.ltoreq.1, 0.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.05, and 0<.alpha.<2);
Li.sub.aNi.sub.1-b-cCo.sub.bB.sub.cO.sub.2-aF.sub..alpha. (wherein
0.90.ltoreq.a.ltoreq.1, 0.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.05, and 0<.alpha..ltoreq.2);
Li.sub.aNi.sub.1-b-cCO.sub.bB.sub.cO.sub.2-.alpha.F.sub..alpha.
(wherein 0.90.ltoreq.a.ltoreq.1, 0.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.05, and 0<.alpha..ltoreq.2);
Li.sub.aNi.sub.1-b-cMn.sub.bB.sub.cD.sub..alpha. (wherein
0.90.ltoreq.a.ltoreq.1, 0.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.05, and 0<.alpha..ltoreq.2);
Li.sub.aNi.sub.1-b-cMn.sub.bB.sub.cO.sub.2-.alpha.F.sub..alpha.
(wherein 0.90.ltoreq.a.ltoreq.1, 0.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.05, and 0<.alpha..ltoreq.2);
Li.sub.aNi.sub.1-b-cMn.sub.bB.sub.cO.sub.2-.alpha.F.sub.2 (wherein
0.90.ltoreq.a.ltoreq.1, 0.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.05, and 0<.alpha.<2);
Li.sub.aNi.sub.bE.sub.cG.sub.dO.sub.2 (wherein
0.90.ltoreq.a.ltoreq.1, 0.ltoreq.b.ltoreq.0.9,
0.ltoreq.c.ltoreq.0.5, and 0.001.ltoreq.d.ltoreq.0.1);
Li.sub.aNi.sub.bCo.sub.cMn.sub.dGeO.sub.2 (wherein
0.90.ltoreq.a.ltoreq.1, 0.ltoreq.b.ltoreq.0.9,
0.ltoreq.c.ltoreq.0.5, 0.ltoreq.d.ltoreq.0.5, and
0.001.ltoreq.e.ltoreq.0.1); Li.sub.aNiG.sub.bO.sub.2 (wherein
0.90.ltoreq.a.ltoreq.1 and 0.001.ltoreq.b.ltoreq.0.1);
Li.sub.aCoG.sub.bO.sub.2 (wherein 0.90.ltoreq.a.ltoreq.1 and
0.001.ltoreq.b.ltoreq.0.1); Li.sub.aMnG.sub.bO.sub.2 (wherein
0.90.ltoreq.a<1 and 0.001.ltoreq.b.ltoreq.0.1);
Li.sub.aMn.sub.2G.sub.bO.sub.4 (wherein 0.90.ltoreq.a.ltoreq.1 and
0.001.ltoreq.b.ltoreq.0.1); QO.sub.2; QS.sub.2; LiQS.sub.2;
V.sub.2O.sub.5; LiV.sub.2O.sub.5; LiIO.sub.2; LiNiVO.sub.4;
Li.sub.(3-f)J.sub.2(PO.sub.4).sub.3 (wherein 0.ltoreq.f.ltoreq.2);
Li.sub.(3-f)Fe.sub.2(PO.sub.4).sub.3 (wherein 0.ltoreq.f.ltoreq.2);
and LiFePO.sub.4. A combination comprising at least one of the
foregoing may also be used.
[0078] In the formulae above, A may include nickel (Ni), cobalt
(Co), manganese (Mn), or a combination thereof; B may include
aluminum (Al), nickel (Ni), cobalt (Co), manganese (Mn), chromium
(Cr), iron (Fe), magnesium (Mg), strontium (Sr), vanadium (V), a
rare earth element, or a combination thereof; D may include oxygen
(O), fluorine (F), sulfur (S), phosphorus (P), or a combination
thereof; E may include cobalt (Co), manganese (Mn), or a
combination thereof; F may include fluorine (F), sulfur (S),
phosphorus (P), or a combination thereof; G may include aluminum
(Al), chromium (Cr), manganese (Mn), iron (Fe), magnesium (Mg),
lanthanum (La), cerium (Ce), strontium (Sr), vanadium (V), or a
combination thereof; Q may include titanium (Ti), molybdenum (Mo),
manganese (Mn), or a combination thereof; I may include chromium
(Cr), vanadium (V), iron (Fe), scandium (Sc), yttrium (Y), or a
combination thereof; and J may include vanadium (V), chromium (Cr),
manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), or a
combination thereof.
[0079] The compounds listed above as second cathode active
materials may have a surface coating layer (hereinafter, also
referred to as "coating layer"). In other embodiments, a mixture of
a compound without a coating layer and a compound having a coating
layer, the compounds being selected from the compounds listed
above, may be used. In some embodiments, the coating layer may
include a compound of a coating element, for example, an oxide, a
hydroxide, an oxyhydroxide, an oxycarbonate, and/or a
hydroxycarbonate of the coating element. In some embodiments, the
compounds for the coating layer may be amorphous or crystalline. In
some embodiments, the coating element for the coating layer may
include magnesium (Mg), aluminum (Al), cobalt (Co), potassium (K),
sodium (Na), calcium (Ca), silicon (Si), titanium (Ti), vanadium
(V), tin (Sn), germanium (Ge), gallium (Ga), boron (B), arsenic
(As), zirconium (Zr), or a combination thereof. In some
embodiments, the coating layer may be formed on a surface of the
second cathode active material using any method that does not
adversely affect the physical properties of the cathode active
material when a compound of the coating element is used. For
example, the coating layer may be formed using a spray coating
method or a dipping method. The coating methods are well understood
by those of ordinary skill in the art, and thus a detailed
description thereof will be omitted.
[0080] According to another embodiment, a lithium battery may
include a cathode including a composite cathode active material
according to any of the above-described embodiments. The lithium
battery may be prepared in the following manner.
[0081] First, a cathode may be prepared according to the
above-described method.
[0082] Next, an anode may be prepared as follows. The anode may be
prepared in the same manner as applied to the cathode, except that
an anode active material is used instead of the composite cathode
active material. A conducting agent, a binder, and a solvent, which
may be used to prepare an anode active material composition, may be
the same as those used to prepare the cathode active material
composition.
[0083] For example, an anode active material, a conducting agent, a
binder, and a solvent may be mixed together to prepare the anode
active material composition. The anode active material composition
may be directly coated on a copper current collector to prepare an
anode plate (or an anode). In some embodiments, the anode active
material composition may be cast on a separate support to form an
anode active material film. This anode active material film may
then be separated from the support and laminated on a copper
current collector to prepare an anode plate.
[0084] The anode active material may be any material suitable for
use as an anode active material for a lithium battery. Examples of
the anode active material may include lithium metal, a metal
alloyable with lithium, a transition metal oxide, a non-transition
metal oxide, a carbonaceous material, or a combination thereof.
[0085] For example, the metal alloyable with lithium may be Si, Sn,
Al, Ge, Pb, Bi, Sb, an Si--Y' alloy (wherein Y' may be an alkali
metal, an alkaline earth metal, a Group 13 element, a Group 14
element, a Group 15 element, a Group 16 element, a transition
metal, a rare earth element, or a combination thereof, but is not
Si), an Sn--Y' alloy (wherein Y' may be an alkali metal, an
alkaline earth metal, a Group 13 element, a Group 14 element, a
Group 15 element, a Group 16 element, a transition metal, a rare
earth element, or a combination thereof, but is not Sn), or a
combination thereof. Examples of the element Y' may include 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, or a
combination thereof.
[0086] Examples of the transition metal oxide may include a lithium
titanium oxide, a vanadium oxide, and a lithium vanadium oxide.
[0087] Examples of the non-transition metal oxide may include
SnO.sub.2 and SiO.sub.x (wherein 0<x<2).
[0088] The carbonaceous material may be crystalline carbon,
amorphous carbon, or a combination thereof. Examples of the
crystalline carbon may include graphite, such as natural graphite
or artificial graphite in nonshaped, plate, flake, spherical, or
fibrous form. Examples of the amorphous carbon may include soft
carbon (carbon calcined at a low temperature), hard carbon,
meso-phase pitch carbonization product, and calcined cokes.
[0089] The amounts of the anode active material, the conducting
agent, the binder, and the solvent may be determined by those of
skill in the art without undue experimentation.
[0090] Next, a separator to be disposed between the cathode and the
anode may be prepared. The separator for the lithium battery may be
any separator suitable for use in a lithium battery. In some
embodiments, the separator may have low resistance to migration of
ions in an electrolyte and have good electrolyte-retaining ability.
Examples of the separator include glass fiber, polyester,
Teflon.TM., polyethylene, polypropylene, PTFE, or a combination
thereof, each of which may be a non-woven fabric or a woven fabric.
For example, a rollable separator including polyethylene or
polypropylene may be used for a lithium ion battery. A separator
having good organic electrolyte solution-retaining ability may be
used for a lithium ion polymer battery. For example, the separator
may be manufactured in the following manner.
[0091] In some embodiments, a polymer resin, a filler, and a
solvent may be mixed together to prepare a separator composition.
Then, the separator composition may be directly coated on an
electrode, and dried to form the separator. In some embodiments,
the separator composition may be cast on a support and then dried
to form a separator film. This separator film may then be separated
from the support and laminated on an electrode to form the
separator.
[0092] The polymer resin used to manufacture the separator may be
any material suitable for use as a binder for an electrode plate.
Examples of the polymer resin include a
vinylidenefluoride/hexafluoropropylene copolymer, PVDF,
polyacrylonitrile, polymethylmethacrylate, or a combination
thereof.
[0093] Then, an electrolyte is prepared.
[0094] In some embodiments, the electrolyte may be an organic
electrolyte solution. In some embodiments, the electrolyte may be
in a solid phase. Examples of the electrolyte are lithium oxide and
lithium oxynitride. Any material suitable for use as a solid
electrolyte may be used. In some embodiments, the solid electrolyte
may be formed on the anode by, for example, sputtering.
[0095] In some embodiments, the organic electrolyte solution may be
prepared by dissolving a lithium salt in an organic solvent.
[0096] The organic solvent may be any solvent suitable for use as
an organic solvent in a lithium battery. In some embodiments, the
organic solvent may include propylene carbonate, ethylene
carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl
carbonate, diethyl carbonate, methylethyl carbonate, methylpropyl
carbonate, ethylpropyl carbonate, methylisopropyl carbonate,
dipropyl carbonate, dibutyl carbonate, benzonitrile, acetonitrile,
tetrahydrofuran, 2-methyltetrahydrofuran, .gamma.-butyrolactone,
dioxolane, 4-methyldioxorane, N,N-dimethyl formamide, dimethyl
acetamide, dimethylsulfoxide, dioxane, 1,2-dimethoxyethane,
sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene
glycol, dimethyl ether, or a combination thereof.
[0097] In some embodiments, the lithium salt may be any material
suitable for use as a lithium salt in a lithium battery. In some
embodiments, the lithium salt may include LiPF.sub.6, LiBF.sub.4,
LiSbFe, LiAsFe, LiClO.sub.4, LiCF.sub.3SO.sub.3,
Li(CF.sub.3SO.sub.2).sub.2N, LiC.sub.4F.sub.9SO.sub.3, LiAlO.sub.2,
LiAlCl.sub.4,
LiN(C.sub.xF.sub.2x+1SO.sub.2)(C.sub.yF.sub.2y+1SO.sub.2) (wherein
x and y may each independently be a natural number), LiCl, LiI, or
a combination thereof.
[0098] Referring to FIG. 6, a lithium battery 1 according to an
embodiment may include a cathode 3, an anode 2, and a separator 4.
In some embodiments, the cathode 3, the anode 2, and the separator
4 may be wound or folded, and then sealed in a battery case 5. In
some embodiments, the battery case 5 may be filled with an organic
electrolyte solution and sealed with a cap assembly 6, thereby
completing the manufacture of the lithium battery 1. In some
embodiments, the battery case 5 may have a cylindrical,
rectangular, or thin-film shape. For example, the lithium battery 1
may be a large-sized thin-film-type battery. In some embodiments,
the lithium battery 1 may be a lithium ion battery.
[0099] In some embodiments, the separator 4 may be disposed between
the cathode 3 and the anode 2 to form a battery assembly. In some
embodiments, the battery assembly may be stacked in a bi-cell
structure and impregnated with the electrolyte solution. In some
embodiments, the resultant assembly may be put into a pouch and
hermetically sealed, thereby completing the manufacture of a
lithium ion polymer battery.
[0100] In some embodiments, a plurality of battery assemblies may
be stacked to form a battery pack, which may be used in any device
that benefits from high capacity and high output, for example, in a
laptop computer, a smartphone, or an electric vehicle.
[0101] The lithium battery 1 may have improved lifetime
characteristics and high-rate characteristics, and thus may be used
in an electric vehicle (EV), for example, in a hybrid vehicle such
as a plug-in hybrid electric vehicle (PHEV). The lithium battery
may be applicable to the high-power storage field. For example, the
lithium battery may be used in an electric bicycle or a power
tool.
[0102] In accordance with another aspect of the inventive concept,
a method of preparing the composite cathode active material
according to the one or more embodiments include: providing (e.g.,
preparing) a first solution including a first metal precursor;
combining (e.g. mixing) the first solution and a nickel-containing
lithium transition metal oxide precursor to prepare a second
solution including a precipitate; separating the precipitate from
the second solution and drying the precipitate to prepare a dried
product; mixing the dried product and a lithium precursor compound
to prepare a mixture; and thermally treating the mixture to thereby
prepare the composite cathode active material.
[0103] The first metal precursor may be an oxychloride, oxynitrate,
or nitrate of the first metal. However, embodiments are not limited
thereto. The first metal precursor may be any suitable dissociative
salt including the first metal. For example, the first metal
precursor may include ZrO(NO.sub.3).sub.2,
ZrO(NO.sub.3).sub.2.H.sub.2O, Zr(NO.sub.3).sub.2, ZrOCl.sub.2,
ZrOCl.sub.2.H.sub.2O, or a combination thereof. The first solution
and the second solution may include a solvent that may dissolve the
first metal precursor and the nickel-containing lithium transition
metal oxide precursor. The type of solvent is not specifically
limited, and any suitable solvent may be used. For example, the
solvent may be distilled water.
[0104] In the preparing of the second solution, an amount of the
first solution may be about 500 parts by weight or less, about 400
parts by weight or less, about 300 parts by weight or less, about
200 parts by weight or less, about 100 parts by weight or less,
about 50 parts by weight or less, about 45 parts by weight or less,
about 40 parts by weight or less, about 35 parts by weight or less,
about 30 parts by weight or less, about 25 parts by weight or less,
about 20 parts by weight or less, or about 10 parts by weight or
less, each with respect to 100 parts by weight of the
nickel-containing lithium transition metal oxide precursor. For
example, the amount of the first solution may be about 10 parts by
weight to about 500 parts by weight, or about 50 parts by weight to
about 300 parts by weight, or about 50 parts by weight to about 200
parts by weight. When the concentration of the nickel-containing
lithium transition metal oxide precursor in the second solution is
increased, the first metal may be uniformly distributed on the
surface and the inside of the composite cathode active
material.
[0105] An amount of the first metal precursor in the second
solution may be about 0.1 mole or less, about 0.05 mole or less,
about 0.03 mole or less, about 0.02 mole or less, or about 0.01
mole or less, per mole of the nickel-containing lithium transition
metal oxide precursor. For example, the amount of the first metal
precursor in the second solution may be about 0.005 mole to about
0.1 mole, or about 0.005 mole to about 0.05 mole, or about 0.02
mole to about 0.05 mole, per mole of the nickel-containing lithium
transition metal oxide precursor.
[0106] In the preparing of the dried product, the precipitate may
be separated from the second solution by removing the solvent from
the second solution. The precipitate may then be dried in an oven
at a temperature of about 120.degree. C. to about 150.degree. C.
for about 1 hour to about 30 hours to prepare the dried product.
However, the temperature or time range is not limited thereto. The
temperature and the time may be varied in order to prepare the
dried product from the precipitate, as long as the temperature
and/or time do not interfere with the formation of the first
composition including the first metal on the core surface and in
the grain boundaries inside the core of the composite cathode
active material, and doping of the first metal in the
nickel-containing lithium transition metal oxide.
[0107] The thermal treating of the dried product may be performed
at a temperature in a range of about 650.degree. C. to about
800.degree. C., about 650.degree. C. to about 750.degree. C., or
about 700.degree. C. to about 750.degree. C., under an oxidative
atmosphere including an oxidative gas such as oxygen or air. The
thermal treatment time may be in a range of about 3 hours to about
20 hours, about 3 hours to about 15 hours, about 3 hours to about
10 hours, about 3 hours to about 7 hours, or about 4 hours to about
6 hours. However, the temperature, atmosphere, or thermal treatment
time are not limited thereto and may be varied within the scope to
facilitate formation of the first composition including the first
metal on the core surface and in the grain boundaries inside the
core of the composite cathode active material, and doping of the
first metal in the nickel-containing lithium transition metal
oxide.
[0108] In the method of preparing the composite cathode active
material according to one or more embodiments, a porosity of the
composite cathode active material may be less than a porosity of
the nickel-containing lithium transition metal oxide precursor.
That is, the composite cathode active material may have a more
compact structure than the nickel-containing lithium transition
metal oxide precursor. The primary particles of the
nickel-containing lithium transition metal oxide precursor may have
a needle shape (needle-like). Due to the inclusion of the
needle-like shaped primary particles, the nickel-containing lithium
transition metal oxide precursor may have a high porosity. However,
due to the formation of the first composition at grain boundaries
between the primary particles of the nickel-containing lithium
transition metal oxide precursor, the pores between the primary
particles in the composite cathode active material may be
reduced.
[0109] One or more embodiments of the present disclosure will now
be described in detail with reference to the following examples.
However, these examples are only for illustrative purposes and are
not intended to limit the scope of the one or more embodiments of
the present disclosure.
EXAMPLES
Preparation of Composite Cathode Active Material
Example 1: Ni88+Zr 0.3 Mol %, Wet Method
(Preparation of First Composite Cathode Active Material: Before
Washing)
[0110] A first aqueous solution of zirconium oxynitrate
(ZrO(NO.sub.3).sub.2) as a first metal precursor dissolved in
distilled water was prepared.
Ni.sub.0.88Co.sub.0.08Mn.sub.0.04(OH).sub.2 (Reshine New Material,
Co, Ltd., China) powder, as a nickel-containing lithium transition
metal oxide precursor, was added into the first aqueous solution
and stirred at about 25.degree. C. for about 10 minutes to prepare
a second aqueous solution. A molar ratio of
Ni.sub.0.88Co.sub.0.08Mn.sub.0.04(OH).sub.2 to zirconium oxynitrate
in the second aqueous solution was about 1:0.003. In the second
aqueous solution, 100 parts by weight of the nickel-containing
lithium transition metal oxide precursor
(Ni.sub.0.88Co.sub.0.08Mn.sub.0.04(OH).sub.2) with respect to 100
parts by weight of distilled water was added. The added
Ni.sub.0.88Co.sub.0.08Mn.sub.0.04(OH).sub.2 powder included
secondary particles including aggregated primary particles having a
needle-like shape. A co-precipitate of zirconium oxynitrate and
Ni.sub.0.88Co.sub.0.08Mn.sub.0.04(OH).sub.2 was filtered from the
second aqueous solution. The filtered co-precipitate was dried in
an oven at about 120.degree. C. for about 12 hours. The dried
co-precipitate (Zr-coprecipitated
Ni.sub.0.88Co.sub.0.08Mn.sub.0.04(OH).sub.2) and LiOH.H.sub.2O as a
lithium precursor were mixed in a molar ratio of about 1:1 to about
1:1.09 to prepare a mixture. The mixture was put into a furnace and
then thermally treated at about 750.degree. C. for about 20 hours
while oxygen was flowed thereinto (primary thermal treatment) to
thereby prepare a first composite cathode active material.
[0111] Through the primary thermal treatment, a Zr-doped
Li(Ni.sub.0.88Co.sub.0.08Mn.sub.0.04).sub.1-xZr.sub.xO.sub.2
(wherein 0<x<0.003) core was obtained, and a
Li.sub.2ZrO.sub.3 coating layer having a monoclinic crystalline
structure was formed in the grain boundaries between adjacent
primary particles among the plurality of primary particles inside
of the core, and on the surface of the core.
(Preparation of Second Composite Cathode Active Material: After
Washing)
[0112] A washing step, wherein 100 parts by weight of distilled
water was added to 100 parts by weight of the first composite
cathode active material, stirred, and then removed to remove
residual lithium, was conducted one time. Subsequently, 100 parts
by weight of the first composite cathode active material was added
to 100 parts by weight of distilled water and stirred for about 8
minutes. Then, a 1 molar (M) Co.sub.3Mg.sub.1 (a 3:1 mole ratio
mixed solution of Co(NO.sub.3).sub.2 and Mg(NO.sub.3).sub.2)
aqueous solution was added thereto, further stirred for about 10
minutes, and then filtered to isolate a precipitate. The filtered
precipitate was dried in an oven at about 150.degree. C. for about
3 hours to prepare a dried product. The dried product was put into
a furnace and then thermally treated at about 720.degree. C. for
about 5 hours while oxygen was flowed thereinto (secondary thermal
treatment) to thereby prepare a second composite cathode active
material.
[0113] Through the secondary thermal treatment, the second
composite cathode active material including Co and Mg additionally
coated on the core surface was obtained. A content of Co and Mg
coated on the second composite cathode active material was about
0.75 weight percent (wt %) based on the total weight of the second
composite cathode active material.
[0114] Referring to FIG. 4D, the second composite cathode active
material was found to still retain the Li.sub.2ZrO.sub.3 layer
having a monoclinic crystalline structure in the grain boundaries
between adjacent primary particles inside of the core, and on the
surface of the core.
Example 2: Ni88+Zr 0.45 Mol %, Wet Method
[0115] A first composite cathode active material and a second
composite cathode active material were prepared in the same manner
as in Example 1, except that a molar ratio of
Ni.sub.0.88Co.sub.0.08Mn.sub.0.04(OH).sub.2 to zirconium oxynitrate
in the second aqueous solution was about 1:0.0045.
[0116] Through the primary thermal treatment, the first composite
cathode active material was obtained. The first composite cathode
active material thus obtained included a Zr-doped
Li(Ni.sub.0.88Co.sub.0.08Mn.sub.0.04).sub.1-xZr.sub.xO.sub.2
(wherein 0<x<0.0045) core and a Li.sub.2ZrO.sub.3 layer
having a monoclinic crystalline structure was present in the grain
boundaries between adjacent primary particles among the plurality
of primary particles inside of the core, and on the surface of the
core.
Example 3: Ni88+Zr 0.6 Mol %, Wet Method
[0117] A first composite cathode active material and a second
composite cathode active material were prepared in the same manner
as in Example 1, except that a molar ratio of
Ni.sub.0.88Co.sub.0.08Mn.sub.0.04(OH).sub.2 to zirconium oxynitrate
in the second aqueous solution was about 1:0.006.
[0118] Through the primary thermal treatment, the first composite
cathode active material was obtained. The first composite cathode
active material thus obtained included a Zr-doped
Li(Ni.sub.0.88Co.sub.0.08Mn.sub.0.04).sub.1-xZr.sub.xO.sub.2
(wherein 0<x<0.006) core and a Li.sub.2ZrO.sub.3 coating
layer having a monoclinic crystalline structure in the grain
boundaries between adjacent primary particles among the plurality
of primary particles the inside of the core, and on the surface of
the core.
Comparative Example 1: Ni.sub.88, Dry Method
(Preparation of First Composite Cathode Active Material: Before
Washing)
[0119] Ni.sub.0.88Co.sub.0.08Mn.sub.0.04(OH).sub.2 as a
nickel-containing lithium transition metal oxide precursor and
LiOH.H.sub.2O as a lithium precursor were mixed in a molar ratio of
about 1:1 to prepare a mixture. The mixture was put into a furnace
and then thermally treated at about 750.degree. C. for about 20
hours while oxygen was flowed thereinto (primary thermal treatment)
to thereby prepare a first composite cathode active material.
Through the primary thermal treatment, the first composite cathode
active material including a
LiNi.sub.0.88Co.sub.0.08Mn.sub.0.04O.sub.2 core was obtained.
(Preparation of Second Composite Cathode Active Material: After
Washing)
[0120] A washing step, wherein 100 parts by weight of distilled
water was added to 100 parts by weight of the first composite
cathode active material, stirred, and then removed to remove
residual lithium, was conducted one time. Subsequently, 100 parts
by weight of the first composite cathode active material was added
to 100 parts by weight of distilled water and stirred for about 8
minutes. Then, a 1 M Co.sub.3Mg.sub.1 (a 3:1 mole ratio mixed
solution of Co(NO.sub.3).sub.2 and Mg(NO.sub.3).sub.2) aqueous
solution was added thereto, further stirred for about 10 minutes,
and then filtered to isolate a precipitate. The filtered
precipitate was dried in an oven at about 150.degree. C. for about
3 hours to prepare a dried product. The dried product was put into
a furnace and then thermally treated at about 720.degree. C. for
about 5 hours while oxygen was flowed thereinto (secondary thermal
treatment) to thereby prepare a second composite cathode active
material.
[0121] Through the secondary thermal treatment, the second
composite cathode active material including Co and Mg additionally
coated on the core surface was obtained. A content of Co and Mg
coated on the second composite cathode active material was about
0.75 wt % based on a total weight of the second composite cathode
active material.
Comparative Example 2: Ni88+Zr 0.3 Mol %, Dry Method
(Preparation of First Composite Cathode Active Material: Before
Washing)
[0122] Zirconium hydroxide (Zr(OH).sub.4) as a first metal
precursor, Ni.sub.0.88Co.sub.0.08Mn.sub.0.04(OH).sub.2 (Reshine New
Material Co. Ltd., China) as a nickel-containing lithium transition
metal oxide precursor, and LiOH.H.sub.2O as a lithium precursor
were mixed in a molar ratio of about 0.003:1:1 to prepare a
mixture. The mixture was put into a furnace and then thermally
treated at about 750.degree. C. for about 20 hours while oxygen was
flowed thereinto (primary thermal treatment) to thereby prepare a
first composite cathode active material.
(Preparation of Second Composite Cathode Active Material: After
Washing)
[0123] 100 parts by weight of distilled water was added to 100
parts by weight of the first composite cathode active material,
stirred, and then washed with water one time to remove residual
lithium. Subsequently, 100 parts by weight of the first cathode
active material was added to 100 parts by weight of distilled water
and stirred for about 8 minutes. Then, a 1M Co.sub.3Mg.sub.1 (a
mixed solution of Co(NO.sub.3).sub.2 and Mg(NO.sub.3).sub.2)
aqueous solution was added thereto and further stirred for about 10
minutes, and then filtered to isolate a precipitate. The filtered
precipitate was dried in an oven at about 150.degree. C. for about
3 hours to prepare a dried product. The dried product was put into
a furnace and then thermally treated at about 720.degree. C. for
about 5 hours while oxygen was flowed thereinto (secondary thermal
treatment) to thereby prepare a second composite cathode active
material.
[0124] Through the secondary thermal treatment, the second
composite cathode active material including Co and Mg coated on its
surface was obtained. A content of Co and Mg coated on the second
composite cathode active material was about 0.75 wt %.
Comparative Example 3: Ni88+Zr 0.45 Mol %, Dry Method
[0125] A first composite cathode active material and a second
composite cathode active material were prepared in the same manner
as in Comparative Example 2, except that zirconium hydroxide
(Zr(OH).sub.4) as a first metal precursor,
Ni.sub.0.88Co.sub.0.08Mn.sub.0.04(OH).sub.2 (Reshine New Material
Co. Ltd., China) as a nickel-containing lithium transition metal
oxide precursor, and LiOH.H.sub.2O as a lithium precursor were
mixed in a molar ratio of about 0.0045:1:1 to prepare a
mixture.
Comparative Example 4: Ni88+Zr 0.6 Mol %, Dry Method
[0126] A first composite cathode active material and a second
composite cathode active material were prepared in the same manner
as in Comparative Example 2, except that zirconium hydroxide
(Zr(OH).sub.4) as a first metal precursor,
Ni.sub.0.88Co.sub.0.08Mn.sub.0.04(OH).sub.2 (Reshine New Material
Co. Ltd., China) as a nickel-containing lithium transition metal
oxide precursor, and LiOH.H.sub.2O as a lithium precursor were
mixed in a molar ratio of about 0.006:1:1 to prepare a mixture.
Manufacture of Lithium Battery (Half Cell): Using First Composite
Cathode Active Material
Example 4
Manufacture of Cathode
[0127] The first composite cathode active material prepared in
Example 1, a carbon conducting material (Denka Black), and
polyvinylidene fluoride (PVdF) were mixed at a weight ratio of
92:4:4 to prepare a mixture, and the mixture was mixed with
N-methylpyrrolidone (NMP) in an agate mortar to prepare a slurry.
The slurry was bar-coated on an aluminum current collector having a
thickness of 15 .mu.m, dried at room temperature, dried once more
in a vacuum at 120.degree. C., and then roll-pressed and punched to
manufacture a cathode plate having a thickness of 55 .mu.m.
(Manufacture of Coin Cell)
[0128] A coin cell was manufactured using the cathode plate
manufactured above, lithium metal as a counter electrode, a PTFE
separator, and an electrolyte solution prepared by dissolving 1.25
M of LiPF.sub.6 in a mixture of ethylene carbonate (EC),
ethylmethyl carbonate (EMC), and dimethyl carbonate (DMC) at a
volume ratio of 3:4:3.
Examples 5 and 6
[0129] Coin cells were manufactured in the same manner as in
Example 4, except that the first composite cathode active materials
prepared in Examples 2 and 3 were used, respectively, instead of
the first composite cathode active material prepared in Example
1.
Comparative Examples 5 to 8
[0130] Coin cells were manufactured in the same manner as in
Example 4, except that the first composite cathode active materials
prepared in Comparative Examples 1 to 4 were used, respectively,
instead of the first composite cathode active material prepared in
Example 1.
Manufacture of Lithium Battery (Half Cell): Using Second Composite
Cathode Active Material
Example 7
(Manufacture of Cathode)
[0131] The second composite cathode active material prepared in
Example 1, a carbonaceous conducting agent (Denka Black), and
polyvinylidene fluoride (PVdF) were mixed in a weight ratio of
92:4:4 to prepare a mixture. The mixture was mixed with
N-methyl-pyrrolidone (NMP) by using an agate mortar to prepare a
slurry. The slurry was bar-coated on an aluminum current collector
having a thickness of about 15 .mu.m, dried at room temperature,
dried further in a vacuum at 120.degree. C., and then roll-pressed
and punched to manufacture a cathode plate having a thickness of
about 55 .mu.m.
(Manufacture of Coin Cell)
[0132] The cathode plate was used as a cathode, a lithium metal was
used as a counter electrode, a PTFE separator was used as a
separator, and a solution prepared by dissolving 1.15 M of
LiPF.sub.6 in a solvent mixture including ethylene carbonate (EC),
ethylmethylcarbonate (EMC) and dimethyl carbonate (DMC) in a volume
ratio of 3:4:3 was used as an electrolyte to manufacture a coin
cell.
Examples 8 and 9
[0133] Coin cells were manufactured in the same manner as in
Example 7, except that the second composite cathode active
materials prepared in Examples 2 and 3 were used, respectively,
instead of the second composite cathode active material prepared in
Example 1.
Comparative Examples 9 to 12
[0134] Coin cells were manufactured in the same manner as in
Example 7, except that the second composite cathode active
materials prepared in Comparative Examples 1 to 4 were used,
respectively, instead of the second composite cathode active
material prepared in Example 1.
Evaluation Example 1: X-Ray Diffraction (XRD) Spectrum
Evaluation
[0135] Referring to FIG. 2, in the XRD spectra of the first
composite cathode active materials of Examples 1 to 3 and
Comparative Example 1, the (104) peak diffraction angle exhibited
by the first composite cathode active materials of Examples 1 to 3
was shifted to a lower angle due to the doping of Zr, as compared
with the first composite cathode active material of Comparative
Example 1. This indicates that a lattice expansion occurred due to
the deposition of Zr at the octahedral site of a transition metal
layer in the layered structure of the nickel-containing lithium
transition metal oxide, thus further stabilizing the layered
structure.
[0136] In addition, when the doping concentration of Zr was
increased as in Examples 2 and 3, relative to Example 1, a further
peak shift did not occur. This indicates that a part of the Zr
added to prepare the first composite cathode active materials in
Examples 1 to 3 was doped, and the remaining Zr was used to form a
second phase (Li.sub.2ZrO.sub.3). The second phase
(Li.sub.2ZrO.sub.3) had a monoclinic crystalline structure.
Evaluation Example 2: Residual Surface Lithium Content
Measurement
[0137] Residual surface lithium contents in the second composite
cathode active materials prepared in Examples 1 to 3 and
Comparative Example 1 were measured. The results are shown in Table
1.
[0138] The residual surface lithium contents were measured as an
amount of Li from such as Li.sub.2CO.sub.3 and LiOH remaining on
the surface of each second composite cathode active material by
using a wet method (or a titration method).
[0139] Details of the measurement method are disclosed in JP
2016-081903 (see paragraph [0054]), the content of which is
incorporated herein by reference.
TABLE-US-00001 TABLE 1 Residual surface lithium content Example
[ppm*] Comparative Example 1 2197 Example 1 1582 Example 2 1324
Example 3 998 *parts per million (ppm)
[0140] Referring to Table 1, the second composite cathode active
materials of Examples 1 to 3 were found to include lower amounts of
residual surface lithium as compared to the second composite
cathode active material of Comparative Example 1.
[0141] This is attributed to the residual surface lithium on the
nickel-containing lithium transition metal oxide material forming
the coating layer having a monoclinic crystalline structure on the
surface and inside of the core by reaction with the first metal
precursor.
[0142] Therefore, in a lithium battery including any of the second
composite cathode active materials of Examples 1 to 3, gas
generation during charging and discharging and lifetime
characteristic deterioration may be suppressed as compared to a
lithium battery including the second composite cathode active
material of Comparative Example 1.
Evaluation Example 3: Evaluation of Inner and Surface Compositions
of Core
[0143] FIGS. 3A to 3D are high-angle annular dark-field scanning
transmission electron microscope (HAADF STEM) and energy dispersive
X-ray spectroscope (EDS) images of cross-sections of the second
composite cathode active material of Comparative Example 3,
including the core as an aggregate of the primary particles. FIG.
3D is a magnified high-resolution image of a cross-section of a
core of the second composite active material of Comparative Example
3.
[0144] FIGS. 4A to 4D are HAADF STEM and EDS images of
cross-sections of the second composite cathode active material of
Example 2 including the core as an aggregate of the plurality of
primary particles. FIG. 4D is a magnified high-resolution image of
a cross-section of a core of the second composite cathode active
material of Example 2.
[0145] Referring to FIGS. 3C and 4C, the second composite cathode
active materials of Comparative Example 3 and Example 2 were found
to have a uniform distribution of Ni in the core.
[0146] However, as shown in FIGS. 3B and 4B, it was found that the
second composite cathode active material of Comparative Example 3
did not include Zr in the core, while the second composite cathode
active material of Example 2 included Zr distributed in the
core.
[0147] Referring to FIG. 3D, in the second composite cathode active
material of Comparative Example 3, no additional phase including Zr
appeared at the grain boundaries between the primary particles in
the core or on the core surface.
[0148] However, as illustrated in FIG. 4D, in the second composite
cathode active material of Example 2, an additional phase including
Zr appeared at the grain boundaries between the primary particles
in the core and on the core surface. Accordingly, it was confirmed
that Li.sub.2ZrO.sub.3 was uniformly coated on the core surface and
at the grain boundaries between the primary particles inside the
core of the second composite cathode active material of Example
2.
[0149] In the composite cathode active materials of Comparative
Examples 2 to 4 prepared using a dry method, the introduction of Zr
at the grain boundaries between the primary particles in the core
did not occur, whereas in the composite cathode active materials of
Examples 1 to 3 prepared using a wet method, Zr was introduced at
the grain boundaries present between almost all of the primary
particles in the core.
Evaluation Example 4: Porosity Evaluation
[0150] A cross-section of a secondary particle in each of the
second composite cathode active materials prepared in Comparative
Example 3 and Example 2 was analyzed by SEM. The SEM images of the
second composite active materials of Comparative Example 3 and
Example 2 are shown in FIGS. 5A and 5B, respectively. A total area
of the single secondary particle and a total area of pores in the
secondary particle were measured based on f the SEM images of each,
and by using an image analyzer, and a percent porosity was
calculated using Equation 1.
Porosity [%]=(Area occupied by pores/Total cross-sectional area of
a secondary particle).times.100% Equation 1
[0151] The secondary particle of the second composite cathode
active material prepared in Comparative Example 3 had a porosity of
about 5.44%, whereas the secondary particle of the second composite
cathode active material prepared in Example 2 had a porosity of
about 0.76%. The second composite cathode active material of
Example 2 prepared using a wet method was found to have a
remarkably low porosity, due to the Zr-containing first composition
disposed at the grain boundaries between the primary particles, as
compared with the second composite cathode active material of
Comparative Example 3 prepared using a dry method.
[0152] The second composite cathode active material of Example 2
was also found to have a remarkably small specific surface area
(BET), due to the Zr-containing first composition disposed at the
grain boundaries between the primary particles, as compared with
the second composite cathode active material of Comparative Example
3.
Evaluation Example 5: Charge-Discharge Characteristics Evaluation
(when First Composite Cathode Active Material was Used)
[0153] The lithium batteries of Examples 4 to 6 and Comparative
Examples 5 to 8 were charged at about 25.degree. C. with a constant
current (CC) of 0.1 C rate until a voltage of 4.35 volts (V) (with
respect to Li) was reached, and then with a constant voltage of
4.35 V (constant voltage mode) until a cutoff current of 0.05 C
rate was reached, followed by discharging with a constant current
of 0.1 C rate until a voltage of 2.8 V (with respect to Li) was
reached (1.sup.st cycle, formation cycle).
[0154] After the 1.sup.st cycle, the lithium batteries were charged
at about 25.degree. C. with a constant current of 1.0 C rate until
a voltage of 4.35 V (with respect to Li) was reached, and then with
a constant voltage of 4.35 V (constant voltage mode) until a cutoff
current of 0.05 C rate was reached, followed by discharging with a
constant current of 0.2 C rate until a voltage of 2.8 V (with
respect to Li) was reached (2.sup.nd cycle).
[0155] After the 2.sup.nd cycle, the lithium batteries were charged
at about 25.degree. C. with a constant current of 0.33 C rate until
a voltage of 4.35 V (with respect to Li) was reached, and then with
a constant voltage of 4.35 V (constant voltage mode) until a cutoff
current of 0.05 C rate was reached, followed by discharging with a
constant current of 0.3 C rate until a voltage of 2.8 V (with
respect to Li) was reached (3.sup.rd cycle).
[0156] After the 3.sup.rd cycle, the lithium batteries were charged
at about 25.degree. C. with a constant current of 0.33 C rate until
a voltage of 4.35 V (with respect to Li) was reached, and then with
a constant voltage of 4.35 V (constant voltage mode) until a cutoff
current of 0.05 C rate was reached, followed by discharging with a
constant current of 1 C rate until a voltage of 2.8 V (with respect
to Li) was reached (4th cycle).
[0157] After the 4.sup.th cycle, the lithium batteries were charged
at about 25.degree. C. with a constant current of 0.33 C rate until
a voltage of 4.35 V (with respect to Li) was reached, and then with
a constant voltage of 4.35 V (constant voltage mode) until a cutoff
current of 0.05 C rate was reached, followed by discharging with a
constant current of 2 C rate until a voltage of 2.8 V (with respect
to Li) was reached (5.sup.th cycle).
[0158] After the 5.sup.th cycle, the lithium batteries were charged
at about 25.degree. C. with a constant current of 0.33 C rate until
a voltage of 4.35 V (with respect to Li) was reached, and then with
a constant voltage of 4.35 V (constant voltage mode) until a cutoff
current of 0.05 C rate was reached, followed by discharging with a
constant current of 3 C rate until a voltage of 2.8 V (with respect
to Li) was reached (6.sup.th cycle).
[0159] After the 6.sup.th cycle, the lithium batteries were charged
at about 25.degree. C. with a constant current of 0.33 C rate until
a voltage of 4.35 V (with respect to Li) was reached, and then with
a constant voltage of 4.35 V (constant voltage mode) until a cutoff
current of 0.05 C rate was reached, followed by discharging with a
constant current of 1 C rate until a voltage of 2.8 V (with respect
to Li) was reached (7.sup.th cycle). This cycle was repeated under
the same conditions up to and including the 56.sup.th cycle (50
times repetition). A rest time of about 10 minutes was allowed
after each charge/discharge cycle for the entire charge/discharge
cycles.
[0160] The charge-discharge test results are shown in Table 2. A
capacity retention rate at the 56.sup.th cycle is defined by
Equation 2.
Capacity retention rate [%]=[Discharge capacity at 56.sup.th
cycle/Discharge capacity at 7.sup.th cycle].times.100% Equation
2
TABLE-US-00002 TABLE 2 Capacity retention rate Example [%]
Comparative Example 5 (Zr = 0 mol %) 77.4 Comparative Example 6 (Zr
= 0.3 mol %) 89.2 Comparative Example 7 (Zr = 0.45 mol %) 89.2
Comparative Example 8 (Zr = 0.6 mol %) 89.4 Example 4 (Zr = 0.3 mol
%) 94.9 Example 5 (Zr = 0.45 mol %) 93.6 Example 6 (Zr = 0.6 mol %)
95.0
[0161] Referring to Table 2, the lithium batteries of Examples 4 to
6 were found to have remarkably improved capacity retention rate,
as compared with the lithium battery of Comparative Example 5.
Without being limited by theory, the improvement in the lifetime
characteristics are attributed to the doping of Zr in the
crystalline structure of the nickel-containing lithium transition
metal oxide of the first composite cathode active material used in
the lithium batteries of Examples 4 to 6, leading to improvement in
the structural stability of the first composite cathode active
material.
[0162] The lithium batteries of Examples 4 to 6 were also found to
have improved capacity retention rate, as compared with the lithium
batteries of Comparative Examples 6 to 8. Without being limited by
theory, these improved lifetime characteristics are attributed to
the fact that a second phase (monoclinic phase, Li.sub.2ZrO.sub.3)
was disposed in the grain boundaries between the primary particles
inside the core as well as on the core surface of the first
composite cathode active material used in the lithium batteries of
Examples 4 to 6, to coat the primary particles in the core, thereby
suppressing a side reaction between the primary particles and an
electrolyte and also suppressing the release of a transition metal
from the primary particles. Further, two-dimensional transfer paths
of lithium ions were secured due to the second phase on the surface
and the inside of the core.
Evaluation Example 6: Charge-Discharge Characteristics Evaluation
(when Second Composite Cathode Active Material was Used)
[0163] The lithium batteries of Examples 7 to 9 and Comparative
Examples 9 to 12 were charged at about 25.degree. C. with a
constant current (CC) of 0.1 C rate until a voltage of 4.35 V (with
respect to Li) was reached, and then with a constant voltage of
4.35 V (constant voltage mode) until a cutoff current of 0.05 C
rate was reached, followed by discharging with a constant current
of 0.1 C rate until a voltage of 2.8 V (with respect to Li) was
reached (1.sup.st cycle, formation cycle).
[0164] After the 1.sup.st cycle, the lithium batteries were charged
at about 25.degree. C. with a constant current of 1.0 C rate until
a voltage of 4.35 V (with respect to Li) was reached, and then with
a constant voltage of 4.35 V (constant voltage mode) until a cutoff
current of 0.05 C rate was reached, followed by discharging with a
constant current of 0.2 C rate until a voltage of 2.8 V (with
respect to Li) was reached (2.sup.nd cycle).
[0165] After the 2.sup.nd cycle, the lithium batteries were charged
at about 25.degree. C. with a constant current of 0.33 C rate until
a voltage of 4.35 V (with respect to Li) was reached, and then with
a constant voltage of 4.35 V (constant voltage mode) until a cutoff
current of 0.05 C rate was reached, followed by discharging with a
constant current of 0.3 C rate until a voltage of 2.8 V (with
respect to Li) was reached (3.sup.rd cycle).
[0166] After the 3.sup.rd cycle, the lithium batteries were charged
at about 25.degree. C. with a constant current of 0.33 C rate until
a voltage of 4.35 V (with respect to Li) was reached, and then with
a constant voltage of 4.35 V (constant voltage mode) until a cutoff
current of 0.05 C rate was reached, followed by discharging with a
constant current of 1 C rate until a voltage of 2.8 V (with respect
to Li) was reached (4.sup.th cycle).
[0167] After the 4.sup.th cycle, the lithium batteries were charged
at about 25.degree. C. with a constant current of 0.33 C rate until
a voltage of 4.35 V (with respect to Li) was reached, and then with
a constant voltage of 4.35 V (constant voltage mode) until a cutoff
current of 0.05 C rate was reached, followed by discharging with a
constant current of 2 C rate until a voltage of 2.8 V (with respect
to Li) was reached (5.sup.th cycle).
[0168] After the 5.sup.th cycle, the lithium batteries were charged
at about 25.degree. C. with a constant current of 0.33 C rate until
a voltage of 4.35 V (with respect to Li) was reached, and then with
a constant voltage of 4.35 V (constant voltage mode) until a cutoff
current of 0.05 C rate was reached, followed by discharging with a
constant current of 3 C rate until a voltage of 2.8 V (with respect
to Li) was reached (6.sup.th cycle).
[0169] After the 6.sup.th cycle, the lithium batteries were charged
at about 25.degree. C. with a constant current of 0.33 C rate until
a voltage of 4.35 V (with respect to Li) was reached, and then with
a constant voltage of 4.35 V (constant voltage mode) until a cutoff
current of 0.05 C rate was reached, followed by discharging with a
constant current of 1 C rate until a voltage of 2.8 V (with respect
to Li) was reached (7.sup.th cycle). This cycle was repeated under
the same conditions to and including the 56.sup.th cycle (50 times
repetition). A rest time of about 10 minutes was allowed after each
charge/discharge cycle for the entire charge/discharge cycles.
[0170] The charge-discharge test results are shown in Table 3. A
capacity retention rate at the 56.sup.th cycle is defined by
Equation 2, and high-rate characteristics are defined by Equation
3.
Capacity retention rate [%]=[Discharge capacity at 56.sup.th
cycle/Discharge capacity at 7.sup.th cycle].times.100% Equation
2
High-rate characteristics [%]=[Discharge capacity at 4.sup.th cycle
(1C rate)/Discharge capacity at 1.sup.st cycle (0.1C
rate)].times.100% Equation 3
TABLE-US-00003 TABLE 3 High-rate Capacity characteristics retention
rate Example [%] [%] Comparative Example 9 91.8 88.0 (Zr = 0 mol %)
Comparative Example 11 92.1 89.5 (Zr = 0.45 mol %) Comparative
Example 12 93.1 93.1 (Zr = 0.6 mol %) Example 8 92.7 92.6 (Zr =
0.45 mol %) Example 9 93.7 93.9 (Zr = 0.6 mol %)
[0171] Referring to Table 3, the lithium batteries of Example 8 and
9 were found to have remarkably improved lifetime characteristics
(capacity retention rate), as compared with the lithium battery of
Comparative Example 9. The lithium batteries of Examples 8 and 9
also had improved high-rate characteristics and lifetime
characteristics, based on the same amount of Zr, as compared with
the lithium batteries of Comparative Example 11 and 12,
respectively. Without being limited by theory, these improved
high-rate characteristics and lifetime characteristics are
attributed to the fact that a second phase (monoclinic phase,
Li.sub.2ZrO.sub.3) was disposed at the grain boundaries between the
primary particles inside the core of the second composite cathode
active material used in the lithium batteries of Examples 8 and 9,
to coat the primary particles, thereby suppressing surface damage
of the positive active material which may occur during a washing
process, effectively withstanding a volume change of the primary
particles during charging and discharging, and facilitating
conduction of lithium ions in the core.
[0172] As described above, according to the one or more
embodiments, a composite cathode active material may include a
composition having a different phase inside and on a surface of the
core, and a lithium transition metal oxide doped with a first
metal, and thus may improve charge and discharge characteristics of
a lithium battery.
[0173] It should be understood that embodiments described herein
should be considered in a descriptive sense only and not for
purposes of limitation. Descriptions of features or aspects within
each embodiment should be considered as available for other similar
features or aspects in other embodiments.
[0174] While one or more embodiments have been described with
reference to the figures, it will be understood by those of
ordinary skill in the art that various changes in form and details
may be made therein without departing from the spirit and scope as
defined by the following claims.
* * * * *