U.S. patent application number 14/022681 was filed with the patent office on 2014-01-09 for lithium secondary battery of improved rate capability.
This patent application is currently assigned to LG Chem, Ltd.. The applicant listed for this patent is LG Chem, Ltd.. Invention is credited to Jong Ho Jeon, Shulkee Kim, Yoo Seok Kim, Doo Kyung Yang.
Application Number | 20140011098 14/022681 |
Document ID | / |
Family ID | 49383745 |
Filed Date | 2014-01-09 |
United States Patent
Application |
20140011098 |
Kind Code |
A1 |
Jeon; Jong Ho ; et
al. |
January 9, 2014 |
LITHIUM SECONDARY BATTERY OF IMPROVED RATE CAPABILITY
Abstract
Disclosed is a lithium secondary battery with improved rate
characteristics. More particularly, disclosed is a lithium
secondary battery including a cathode, an anode, a separator
disposed between the cathode and the anode, and an electrolyte,
wherein the electrolyte includes a mixed solvent of a cyclic
carbonate-based material and a propionate-based material, the
cathode includes a lithium manganese composite oxide represented by
Formula 1 below as a cathode active material, and the anode
includes a lithium metal oxide represented by Formula 2 below as an
anode active material: Li.sub.xM.sub.yMn.sub.2-yO.sub.4-zA.sub.z
(1) wherein 0.9.ltoreq.x.ltoreq.1.2, 0<y<2, and
0.ltoreq.z<0.2, M is at least one element selected from the
group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn,
Zr, Nb, Mo, Sr, Sb, W, Ti, and Bi; and A is at least one monovalent
or divalent anion, Li.sub.aM'.sub.bO.sub.4-xA.sub.c (2) wherein M'
is at least one element selected from the group consisting of Ti,
Cu, Pb, Sb, Zn, Fe, In, Al, and Zr; 0.1.ltoreq.a.ltoreq.4 and
0.2.ltoreq.b.ltoreq.4 wherein a and b are determined according to
oxidation number of M'; 0.ltoreq.c<0.2 wherein c is determined
according to oxidation number of A; and A is at least one
monovalent or divalent anion.
Inventors: |
Jeon; Jong Ho; (Daejeon,
KR) ; Kim; Yoo Seok; (Daejeon, KR) ; Yang; Doo
Kyung; (Daejeon, KR) ; Kim; Shulkee; (Daejeon,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG Chem, Ltd. |
Seoul |
|
KR |
|
|
Assignee: |
LG Chem, Ltd.
Seoul
KR
|
Family ID: |
49383745 |
Appl. No.: |
14/022681 |
Filed: |
September 10, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/KR2013/003294 |
Apr 18, 2013 |
|
|
|
14022681 |
|
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Current U.S.
Class: |
429/332 ;
429/330 |
Current CPC
Class: |
H01M 4/485 20130101;
H01M 2220/20 20130101; H01M 2300/0037 20130101; H01M 4/505
20130101; Y02T 10/70 20130101; H01M 10/0525 20130101; H01M 10/0569
20130101; Y02E 60/10 20130101; H01M 10/052 20130101 |
Class at
Publication: |
429/332 ;
429/330 |
International
Class: |
H01M 10/0569 20060101
H01M010/0569; H01M 10/052 20060101 H01M010/052 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2012 |
KR |
10-2012-0041297 |
Claims
1. A lithium secondary battery comprising a cathode, an anode, a
separator disposed between the cathode and the anode, and an
electrolyte, wherein the electrolyte comprises a mixed solvent of a
cyclic carbonate-based material and a propionate-based material,
the cathode comprises a lithium manganese composite oxide
represented by Formula I below as a cathode active material, and
the anode comprises a lithium metal oxide represented by Formula 2
below as an anode active material:
Li.sub.xM.sub.yMn.sub.2-yO.sub.4-zA.sub.z (1) wherein
0.9.ltoreq.x.ltoreq.1.2, 0<y<2, and 0.ltoreq.z<0.2; M is
at least one element selected from the group consisting of Al, Mg,
Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti,
and Bi; and A is at least one monovalent or divalent anion,
Li.sub.aM'.sub.bO.sub.4-cA.sub.c (2) wherein M' is at least one
element selected from the group consisting of Ti, Sn, Cu, Pb, Sb,
Zn, Fe, In, Al, and Zr; 0.1.ltoreq.a.ltoreq.4 and
0.2.ltoreq.b.ltoreq.4 wherein a and b are determined according to
oxidation number of M'; 0.ltoreq.c<0.2 wherein c is determined
according to oxidation number of A; and A is at least one
monovalent or divalent anion.
2. The lithium secondary battery according to claim 1, wherein the
propionate-based material is represented by Formula 3 below:
R.sub.1--COO--R.sub.2 (3) wherein R.sub.1 is a substituted or
unsubstituted ethyl group, and R.sub.2 is a substituted or
unsubstituted C.sub.1-C.sub.4 linear or branched alkyl group.
3. The lithium secondary battery according to claim 1, wherein the
Propionate-based material is one selected from the group consisting
of methyl propionate (MP), ethyl propionate (EP), propyl propionate
(PP), butyl propionate (BP), and combinations thereof.
4. The lithium secondary battery according to claim 1, wherein an
amount of the cyclic carbonate-based material is in a range of 1 wt
% to 30 wt % based on a total weight of the electrolyte.
5. The lithium secondary battery according to claim 1, wherein a
mixing weight ratio of the cyclic carbonate-based material to the
propionate-based material is in a range of 5 to 15:85 to 95.
6. The lithium secondary battery according to claim 5, wherein the
mixing weight ratio of the cyclic carbonate-based material to the
propionate-based material is 10:90.
7. The lithium secondary battery according to claim 1, wherein the
lithium manganese composite oxide of Formula 1 is a lithium nickel
manganese complex oxide (LNMO) represented by Formula 4 below:
Li.sub.xNi.sub.yMn.sub.2-yO.sub.4 (4) wherein
0.9.ltoreq.x.ltoreq.1.2 and 0.4.ltoreq.y.ltoreq.0.5.
8. The lithium secondary battery according to claim 7, wherein the
lithium nickel manganese composite oxide of Formula 4 is
LiNi.sub.0.5Mn.sub.1.5O.sub.4 or LiNi.sub.0.4Mn.sub.1.6O.sub.4.
9. The lithium secondary battery according to claim 1, wherein the
lithium metal oxide of Formula 2 is a lithium titanium oxide (LTO)
represented by Formula 5 below: Li.sub.aTi.sub.bO.sub.4 (5) wherein
0.5.ltoreq.a.ltoreq.3 and 1.ltoreq.b.ltoreq.2.5.
10. The lithium secondary battery according to claim 9, wherein the
lithium titanium oxide of Formula 5 is
Li.sub.1.33Ti.sub.1.67O.sub.4 and LiTi.sub.2O.sub.4.
11. A battery module comprising the lithium secondary battery
according to claim 1 as a unit cell.
12. A battery pack comprising the battery module according to claim
11.
13. A device comprising the battery pack according to claim 12.
14. The device according to claim 13, wherein the device is an
electric vehicle, a hybrid electric vehicle, a plug-in hybrid
electric vehicle, or a system for storing power.
Description
TECHNICAL FIELD
[0001] The present invention relates to a lithium secondary battery
with improved rate characteristics. More specifically, the present
invention relates to a lithium secondary battery including a
cathode, an anode, a separator disposed between the cathode and the
anode, and an electrolyte, wherein the electrolyte includes a mixed
solvent of a cyclic carbonate-based material and a propionate-based
material, the cathode includes a lithium manganese composite oxide
having a particular formula as a cathode active material, and the
anode includes a lithium metal oxide having a particular formula as
an anode active material.
BACKGROUND ART
[0002] As mobile device technology continues to develop and demand
therefor continues to increase, demand for secondary batteries as
energy sources is rapidly increasing. Among these secondary
batteries, lithium secondary batteries, which exhibit high energy
density and operating potential, have long cycle lifespan, and have
a low self-discharge rate, are commercially available and widely
used.
[0003] In addition, as recent interest in environmental problems is
increasing, research into electric vehicles (EVs), hybrid electric
vehicles (HEVs), and the like that can replace vehicles using
fossil fuels, such as gasoline vehicles, diesel vehicles, and the
like, which are one of the main causes behind air pollution, is
underway. As a power source of EVs, HEVs, and the like, a nickel
metal-hydride (Ni-MH) secondary battery is mainly used. However,
research into lithium secondary batteries having high energy
density, high discharge voltage, and high output stability is
actively carried out and some of the lithium secondary batteries
are commercially available.
[0004] A lithium secondary battery has a structure in which an
electrode assembly, which includes: a cathode prepared by coating a
cathode active material on a cathode current collector; an anode
prepared by coating an anode active material on an anode current
collector; and a porous separator disposed between the cathode and
the anode, is impregnated with a lithium salt-containing
non-aqueous electrolyte.
[0005] These lithium secondary batteries generally use metal oxides
as a cathode active material, such as lithium cobalt-based oxides,
lithium manganese-based oxides, lithium nickel-based oxides, and
the like and carbonaceous materials as an anode active material,
and such lithium secondary battery is manufactured by disposing a
polyolefin-based porous separator between an anode and a cathode
and impregnating the resultant structure with a non-aqueous
electrolyte containing a lithium salt such as LiPF.sub.6 or the
like. When the lithium secondary battery is charged, lithium ions
of the cathode active material are deintercalated and then are
intercalated into a carbon layer of the anode. When the lithium
secondary battery is discharged, the lithium ions of the carbon
layer are deintercalated and then are intercalated into the cathode
active material. In this regard, the non-aqueous electrolyte acts
as a medium through which lithium ions migrate between the anode
and the cathode.
[0006] Such electrolyte basically requires stability within an
operating voltage range of a battery, i.e., 0 to 4.2 V, and the
capability to transfer ions at a sufficiently high rate. To satisfy
the requirements, a mixed solvent prepared by appropriately mixing
a cyclic carbonate compound such as ethylene carbonate, propylene
carbonate, or the like, with a linear carbonate compound such as
dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, or
the like is used as an electrolyte solvent.
[0007] However, lithium secondary batteries have high operating
potentials and thus high energy may instantaneously flow therein.
Accordingly, when a lithium secondary battery is overcharged to 4.2
V or higher, the electrolyte starts to decompose, and when the
temperature of the electrolyte increases, the electrolyte may
readily reach an ignition point, which results in high possibility
of combustion.
[0008] In addition, recently, instead of using conventional
materials as electrode active materials, research into use of
spinel-structure lithium manganese composite oxides as cathode
active materials or use of lithium metal oxides, e.g., lithium
titanium oxides as anode active materials is underway.
[0009] In particular, among lithium manganese composite oxides,
spinel-structure lithium nickel manganese composite oxides having
formula Li.sub.xNi.sub.yMn.sub.2-yO.sub.4, where y=0.01 to 0.6,
which are used as active materials for high-voltage applications
since they have an average voltage of 4.7 V, reach oxidation
potential of an electrolyte and thus the electrolyte is oxidized,
resulting in generation of by-products such as gas and the like,
which deteriorates secondary battery safety.
[0010] Therefore, there is a need to develop an electrolyte that
does not cause these problems, is stable at high voltages, and
improves rate characteristics.
DISCLOSURE
Technical Problem
[0011] Therefore, the present invention has been made to solve the
above problems and other technical problems that have yet to be
resolved.
[0012] As a result of a variety of extensive and intensive studies
and experiments, the inventors of the present invention found that,
as described below, when an electrolyte including a mixed solvent
of a cyclic carbonate-based material and a propionate-based
material is applied to a lithium secondary battery that includes a
lithium manganese composite oxide as a cathode active material and
a lithium metal oxide as an anode active material, desired effects
can be achieved, thus completing the present invention.
Technical Solution
[0013] In accordance with one aspect of the present invention,
provided is a lithium secondary battery including a cathode, an
anode, a separator disposed between the cathode and the anode, and
an electrolyte, wherein the electrolyte includes a mixed solvent of
a cyclic carbonate-based material and a propionate-based material,
the cathode includes a lithium manganese composite oxide
represented by Formula 1 below as a cathode active material, and
the anode includes a lithium metal oxide represented by Formula 2
below as an anode active material:
Li.sub.xM.sub.yMn.sub.2-yO.sub.4-zA.sub.z (1) [0014] wherein
0.9.ltoreq.x.ltoreq.1.2, 0<y<2, 0.ltoreq.z<0.2; M is at
least one element selected from the group consisting of Al, Mg, Ni,
Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti, and
Bi; and A is at least one monovalent or divalent anion, and
[0014] Li.sub.aM'.sub.bO.sub.4-cA.sub.c (2) [0015] wherein M' is at
least one element selected from the group consisting of Ti, Sn, Cu,
Pb, SU, Zn, Fe, In, Al, and Zr; 0.1.ltoreq.a.ltoreq.4 and
0.2.ltoreq.b.ltoreq.4 wherein a and b are determined according to
oxidation number of M'; 0.ltoreq.c<0.2 wherein c is determined
according to oxidation number of A; and A is at least one
monovalent or divalent anion.
[0016] In general, in a secondary battery that uses graphite as an
anode active material and, as an electrolyte solvent, a mixed
solvent including a low-viscosity linear carbonate, e.g., dimethyl
carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate
(DEC) and a cyclic carbonate, when the electrolyte includes 30 wt %
or less of the cyclic carbonate, problems in terms of formation of
an anode protective film (e.g., solid electrolyte interface (SEI)
film) occur and thus lifespan characteristics are dramatically
deteriorated. In addition, when a linear ester is used instead of
the linear carbonate, reduction at the anode excessively occurs
relative to a carbonate-based low-viscosity solvent, and thus,
there is a need to use a large amount of the cyclic carbonate or
use an additive for forming an anode protective film, such as
vinylene carbonate (VC) or the like.
[0017] However, the inventors of the present invention confirmed
that when the same composition as that of the above-described
electrolyte is applied to a secondary battery that uses a lithium
manganese composite oxide as a cathode active material and a
lithium metal oxide as an anode active material, problems occur as
follows.
[0018] First, when the lithium manganese composite oxide is used as
a cathode active material, a cathode is driven at a high voltage
versus lithium and thus the electrolyte is decomposed due to low
oxidation voltage of VC and components of the cathode active
material, e.g., a transition metal, oxygen, and the like, are
eluted and the eluted components are deposited on a surface of the
anode, whereby battery performance is deteriorated. Or, secondary
problems, such as deterioration of battery performance due to
decomposition of components of the electrolyte, e.g., a solvent or
a lithium salt, may occur.
[0019] Second, when an electrolyte including 30 wt % or more of
cyclic carbonate is applied to a lithium secondary battery
including the lithium metal oxide as an anode active material used
to achieve high-rate charge/discharge characteristics, improvement
in rate characteristics is lower than when a smaller amount of the
cyclic carbonate is used. As is common knowledge in the art, as
conductivity of lithium ions increases, high-rate charge/discharge
characteristics of a battery are enhanced. In addition, when the
amount of the cyclic carbonate is about 30 wt % or less, e.g., in
the range of 10 to 20 wt %, it can be confirmed that ionic
conductivity is reduced, whereas rate characteristics are rather
enhanced when the electrolyte includes a small amount of the cyclic
carbonate.
[0020] Thus, the inventors of the present invention repeatedly
performed intensive studies and discovered that when the lithium
metal oxide is used as an anode active material and the electrolyte
including a mixed solvent of a small amount of a cyclic
carbonate-based material and a propionate-based material is used,
problems in terms of reduction at the anode having high stability
for reduction of the electrolyte do not occur due to high reduction
potential, and rate characteristics may be enhanced. In addition,
the inventors discovered that when a cathode active material for
high-voltage application, e.g., the lithium manganese composite
oxide, is used, elution of components of the cathode active
material and generation of by-products such as carbon dioxide or
carbon monoxide due to surface reaction may be suppressed or
reduced.
[0021] In a specific embodiment, the propionate-based material,
which is one of the components of the mixed solvent, may be
represented by Formula 3 below:
R.sub.1--COO--R.sub.2 (3) [0022] wherein R.sub.1 is a substituted
or unsubstituted ethyl group, and R.sub.2 is a substituted or
unsubstituted C.sub.1-C.sub.4 linear or branched alkyl group.
[0023] For example, the propionate-based material may be selected
from the group consisting of methyl propionate (MP), ethyl
propionate (EP), propyl propionate (PP), butyl propionate (BP), and
combinations thereof. More specifically, the propionate-based
material may be MP.
[0024] The propionate-based material enables appropriate
coordination of lithium ions and thus has high ionic conductivity
at room temperature and low temperatures. In addition, when the
lithium secondary battery is charged, the propionate-based material
increases resistance to an electrolyte decomposition reaction,
whereby overall performance, in particular rate characteristics, of
the battery is enhanced.
[0025] In a specific embodiment, the cyclic carbonate-based
material constituting the mixed solvent together with the
propionate-based material may be selected from the group consisting
of ethylene carbonate (EC), propylene carbonate (PC), butylene
carbonate (BC), fluoroethylene carbonate (FEC),
.gamma.-butyrolactone, and combinations thereof, but is not limited
thereto. The cyclic carbonate-based material satisfactorily
dissolves lithium ions and thus may increase ionic conductivity of
the electrolyte.
[0026] In this regard, the amount of the cyclic carbonate-based
material may be in the range of 1 wt % to 30 wt % based on a total
weight of the electrolyte.
[0027] When the amount of the cyclic carbonate-based material is
less than 1 wt %, improvement in ionic conductivity, which is a
strong point of cyclic carbonate-based materials, is not obtained.
On the other hand, when the amount of the cyclic carbonate exceeds
30 wt %, the amount of the propionate-based material is relatively
small and thus desired effects, i.e., improvement in rate
characteristics and stability of oxidation at a surface of a
high-voltage cathode, cannot be achieved.
[0028] In a specific embodiment, a mixing weight ratio of the
cyclic carbonate-based material to the propionate-based material
may be in the range of 5 to 15:85 to 95, and, more specifically,
10:90. The inventors of the present invention discovered that the
above-described mixing weight ratio is an optimum range that
enables improvement in performance, e.g., charge/discharge
characteristics and the like of a secondary battery.
[0029] A linear carbonate is not used as one of the essential
components of the mixed solvent, but a small amount of the linear
carbonate may be used within a scope that does not deviate from the
objective of the present invention.
[0030] The present invention also provides a method of
manufacturing the lithium secondary battery. The method is not much
different from manufacturing methods known in the art and, in
particular, includes: manufacturing an electrode assembly including
a cathode fabricated by coating a cathode active material on a
cathode current collector, an anode fabricated by coating an anode
active material on an anode current collector, and a porous
separator disposed therebetween; and impregnating the electrode
assembly with an electrolyte including the mixed solvent.
[0031] The electrode assembly may be a jellyroll (winding-type)
electrode assembly in which long sheet-shaped cathodes and anodes
are wound with separators therebetween, a stack-type electrode
assembly in which a plurality of cathodes and anodes cut to have
certain sizes arc sequentially stacked with separators
therebetween; and a stack/folding-type electrode assembly in which
Bi-cells or full cells formed by stacking cathodes and anodes
having certain sizes with separators therebetween arc wound using a
long, continuous separator sheet.
[0032] The cathode is fabricated by coating a mixture of a cathode
active material, a conductive material, and a binder on a cathode
current collector and drying and pressing the coated cathode
current collector. As desired, the mixture may further include a
filler.
[0033] As described above, the cathode active material may include
a lithium manganese composite oxide. In a specific embodiment, the
lithium manganese composite oxide may be a lithium nickel manganese
complex oxide (LNMO) represented by Formula 4 below, for example,
LiNi.sub.0.5Mn.sub.1.5O.sub.4 or LiNi.sub.0.4Mn.sub.1.6O.sub.4:
Li.sub.xNi.sub.yMn.sub.2-yO.sub.4 (4) [0034] wherein
0.9.ltoreq.x.ltoreq.1.2 and 0.4.ltoreq.y.ltoreq.0.5.
[0035] In addition to the lithium manganese composite oxide, the
cathode active material may include other active materials.
Examples of other active materials include, but are not limited to,
layered compounds such as lithium cobalt oxide (LiCoO.sub.2) and
lithium nickel oxide (LiNiO.sub.2), or compounds substituted with
one or more transition metals; lithium manganese oxides such as
compounds of Formula Li.sub.1+xMn.sub.2-xO.sub.4 where
0.ltoreq.x.ltoreq.0.33, LiMnO.sub.3, LiMn.sub.2O.sub.3, and
LiMnO.sub.2; lithium copper oxide (Li.sub.2CuO.sub.2); vanadium
oxides such as LiV.sub.3O.sub.8, LiV.sub.3O.sub.4, V.sub.2O.sub.5,
and Cu.sub.2V.sub.2O.sub.7; Ni-site type lithium nickel oxides of
Formula LiNi.sub.1-xM.sub.xO.sub.2 where M=Co, Mn, Al, Cu, Fe, Mg,
B, or Ga, and 0.01.ltoreq.x.ltoreq.0.3; lithium manganese composite
oxides of Formula LiMn.sub.2-xM.sub.xO.sub.2 where M=Co, Ni, Fe,
Cr, Zn, or Ta, and 0.01.ltoreq.x.ltoreq.0.1), or Formula
Li.sub.2Mn.sub.3MO.sub.8 where M=Fe, Co, Ni, Cu, or Zn; and
LiMn.sub.2O.sub.4 in which some of the Li atoms are substituted
with alkaline earth metal ions; disulfide compounds; and
Fe.sub.2(MoO.sub.4).sub.3. In this case, the amount of the lithium
manganese composite oxide may be in the range of 40 to 100 wt %
based on a total weight of the cathode active material.
[0036] The cathode current collector is generally fabricated to a
thickness of 3 to 500 .mu.m. The cathode current collector is not
particularly limited so long as it does not cause chemical changes
in the secondary battery and has high conductivity. For example,
the cathode current collector may be made of stainless steel,
aluminum, nickel, titanium, sintered carbon, or aluminum or
stainless steel that is surface-treated with carbon, nickel,
titanium, silver, or the like. The cathode current collector may
have fine irregularities at a surface thereof to increase adhesion
between the cathode active material and the cathode current
collector. In addition, the cathode current collector may be used
in any of various forms including films, sheets, foils, nets,
porous structures, foams, and non-woven fabrics.
[0037] The conductive material is typically added in an amount of 1
to 30 wt % based on the total weight of the mixture including the
cathode active material. There is no particular limit as to the
conductive material, so long as the conductive material has
conductivity and does not cause chemical changes in the fabricated
battery. Examples of conductive materials include graphite such as
natural or artificial graphite; carbon black such as carbon black,
acetylene black, Ketjen black, channel black, furnace black, lamp
black, and thermal black; conductive fibers such as carbon fibers
and metallic fibers; metallic powders such as carbon fluoride
powder, aluminum powder, and nickel powder; conductive whiskers
such as zinc oxide and potassium titanate; conductive metal oxides
such as titanium oxide; and polyphenylene derivatives.
[0038] The binder is a component assisting in binding between the
electrode active material and the conductive material and in
binding of the electrode active material to the corresponding
current collector. The binder is typically added in an amount of 1
to 30 wt % based on the total weight of the mixture including the
cathode active material. Examples of the binder include
polyvinylidene fluoride, polyvinyl alcohols, carboxymethylcellulose
(CMC), starch, hydroxypropylcellulose, regenerated cellulose,
polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene,
polypropylene, ethylene-propylene-diene terpolymer (EPDM),
sulfonated EPDM, styrene butadiene rubber, fluorine rubber, and
various copolymers.
[0039] The filler is optionally used as a component to inhibit
cathode expansion. The filler is not particularly limited so long
as it is a fibrous material that does not cause chemical changes in
the fabricated battery. Examples of the filler include olefin-based
polymers such as polyethylene and polypropylene; and fibrous
materials such as glass fiber and carbon fiber.
[0040] The anode is manufactured by coating an anode active
material on an anode current collector and drying and pressing the
coated anode current collector. In some eases, the conductive
material, the binder, the filler, or the like may be further
optionally used.
[0041] As described above, the anode active material may include a
lithium metal oxide. In a specific embodiment, the lithium metal
oxide may be lithium titanium oxide (LTO) represented by Formula 5
below, for example, Li.sub.0.8Ti.sub.2.2O.sub.4,
Li.sub.2.67Ti.sub.1.33O.sub.4, LiTi.sub.2O.sub.4,
Li.sub.1.33Ti.sub.1.67O.sub.4, Li.sub.1.14Ti.sub.1.71O.sub.4, or
the like, but is not limited thereto. More specifically, the LTO
may have a spinel structure with less change in crystal structure
during charge/discharge and high reversibility, e.g.,
Li.sub.1.33Ti.sub.1.67O.sub.4 or LiTi.sub.2O.sub.4:
Li.sub.aTi.sub.bO.sub.4 (5) [0042] wherein 0.5.ltoreq.a.ltoreq.3
and 1.ltoreq.b.ltoreq.2.5.
[0043] A method of preparing the lithium titanium oxide of Formula
5 is known in the art. For example, the method includes adding
titanium oxide or the like as a titanium source to a solution
prepared by dissolving a lithium salt as a lithium source, such as
lithium hydroxide, lithium oxide, lithium carbonate, or the like in
water according to an atomic percent of lithium to titanium,
stirring and drying the mixture to prepare a precursor of the
lithium titanium oxide and sintering the prepared precursor.
[0044] The anode active material may also include other active
materials in addition to the lithium metal oxide. Examples of other
active materials include, but are not limited to, carbon such as
hard carbon and graphite-based carbon; metal composite oxides such
as Li.sub.xFe.sub.2O.sub.3 where 0.ltoreq.x.ltoreq.1,
Li.sub.xWO.sub.2 where 0.ltoreq.x.ltoreq.1, and
Sn.sub.xMe.sub.1-xMe'.sub.yO.sub.z where Me: Mn, Fe, Pb or Ge; Me':
Al, B, P, Si, Group I, Group II and Group III elements, or
halogens; 0.ltoreq.x.ltoreq.1; 1.ltoreq.y.ltoreq.3; and
1.ltoreq.z.ltoreq.8; lithium metals; lithium alloys; silicon-based
alloys; tin-based alloys; metal oxides such as SnO, SnO.sub.2, PbO,
PbO.sub.2, Pb.sub.2O.sub.3, Pb.sub.3O.sub.4, Sb.sub.2O.sub.3,
Sb.sub.2O.sub.4, Sb.sub.2O.sub.5, GeO, GeO.sub.2, Bi.sub.2O.sub.3,
Bi.sub.2O.sub.4, and Bi.sub.2O.sub.5; conductive polymers such as
polyacetylene; Li--Co--Ni based materials; titanium oxides. In this
case, the amount of the lithium metal oxide may be, for example, 40
to 100 wt % based on a total weight of the anode active
material.
[0045] The anode current collector is generally fabricated to a
thickness of 3 to 500 .mu.m. The anode current collector is not
particularly limited so long as it does not cause chemical changes
in the fabricated secondary battery and has conductivity. For
example the anode current collector may be made of copper,
stainless steel, aluminum, nickel, titanium, sintered carbon,
copper or stainless steel that is surface-treated with carbon,
nickel, titanium, silver, or the like, or an aluminum-cadmium
alloy. In addition, similarly to the cathode current collector, the
anode current collector may have fine irregularities at a surface
thereof to increase adhesion between the anode active material and
the anode current collector. In addition, the anode current
collector may be used in any of various forms including films,
sheets, foils, nets, porous structures, foams, and non-woven
fabrics.
[0046] The separator is disposed between the cathode and the anode
and, as the separator, an insulating thin film having high ion
permeability and mechanical strength is used. The separator
typically has a pore diameter of 0.01 to 10 .mu.m and a thickness
of 5 to 300 .mu.m. As the separator, sheets or non-woven fabrics
made of an olefin polymer such as polypropylene, glass fibers or
polyethylene, which have chemical resistance and hydrophobicity,
are used. When a solid electrolyte such as a polymer is employed as
the electrolyte, the solid electrolyte may also serve as both the
separator and electrolyte.
[0047] The lithium salt included in the electrolyte is a material
that is readily soluble in the non-aqueous electrolyte. Examples of
lithium salts include, but are not limited to, LiCl, LiBr,
LiClO.sub.4, LiBF.sub.4, LiB.sub.10Cl.sub.10, LiPF.sub.6,
LiCF.sub.3O.sub.3, LiCF.sub.3CO.sub.2, LiAsF.sub.6, LiSbF.sub.6,
LiAlCl.sub.4, CH.sub.3SO.sub.3Li, (CF.sub.3SO.sub.2).sub.2NLi,
chloroborane lithium, lower aliphatic carboxylic acid lithium,
lithium tetraphenyl borate, and imide.
[0048] In addition, in order to improve charge/discharge
characteristics and flame retardancy, for example, pyridine,
triethylphosphite, triethanolamine, cyclic ether, ethylenediamine,
n-glyme, hexaphosphoric triamide, nitrobenzene derivatives, sulfur,
quinone imine dyes, N-substituted oxazolidinone, N,N-substituted
imidazolidine, ethylene glycol dialkyl ether, ammonium salts,
pyrrole, 2-methoxy ethanol, aluminum trichloride, or the like may
be added to the electrolyte. In some cases, in order to impart
incombustibility, the electrolyte may further include a
halogen-containing solvent such as carbon tetrachloride and
ethylene trifluoride. In addition, in order to improve
high-temperature storage characteristics, the electrolyte may
further include carbon dioxide gas, fluoro-ethylene carbonate
(FEC), propene sultone (PRS), or the like.
[0049] The present invention also provides a battery module
including the lithium secondary battery as a unit battery, a
battery pack including the battery module, and a device including
the battery pack.
[0050] Examples of such devices include, but are not limited to,
electric motor-driven power tools; electric vehicles (EVs), hybrid
electric vehicles (HEVs), and plug-in hybrid electric vehicles
(PHEVs); electric two-wheeled vehicles such as e-bikes and
e-scooters; electric golf carts; and systems for storing power.
Effects of Invention
[0051] As apparent from the fore-going, a lithium secondary battery
according to the present invention uses an electrolyte including a
mixed solvent of a cyclic carbonate-based material and a
propionate-based material, which is stable even when applied to a
lithium secondary battery including a lithium manganese composite
oxide, which is used in high-voltage applications, as a cathode
active material and a lithium metal oxide having high operating
potential as an anode active material, and thus, has enhanced rate
characteristics.
BEST MODE
[0052] Now, the present invention will be described in more detail
with reference to the following examples. These examples are
provided only for illustration of the present invention and should
not be construed as limiting the scope and spirit of the present
invention.
Example 1
[0053] Li.sub.1.33Ti.sub.1.67O.sub.4 as an anode active material,
Denka black as a conductive material, and PVdF as a binder were
added to NMP in a weight ratio of 95:2.5:2.5 and the components
were mixed to prepare an anode composite material. Thereafter, the
anode composite material was coated on copper foil having a
thickness of 20 .mu.m and the coated copper foil was rolled and
dried, thereby completing manufacture of an anode.
[0054] Separately, LiNi.sub.0.5Mn.sub.1.5O.sub.4 as a cathode
active material, Denka black as a conductive material, and PVdF as
a binder were added to NMP in a weight ratio of 95:2.5:2.5 and the
components were mixed to prepare a cathode composite material.
Thereafter, the cathode material was coated on aluminum foil having
a thickness of 20 .mu.m and the coated aluminum foil was rolled and
dried, thereby completing manufacture of a cathode.
[0055] Afterwards, a polyethylene film (Celgard, thickness :20
.mu.m) was disposed as a separator between the anode and the
cathode, and a liquid electrolyte containing 1M LiPF.sub.6 in a
mixed solvent of ethylene carbonate and methyl propionate in a
weight ratio of 10:90 was injected thereinto, thereby completing
manufacture of a 2016 coin cell.
Example 2
[0056] A 2016 coin cell was manufactured in the same manner as in
Example 1, except that a liquid electrolyte containing 1M
LiPF.sub.6 in a mixed solvent of propylene carbonate and methyl
propionate in a weight ratio of 10:90 was used.
Comparative Example 1
[0057] A 2016 coin cell was manufactured in the same manner as in
Example 1, except that a liquid electrolyte containing 1M
LiPF.sub.6 in a mixed solvent of ethylene carbonate, ethyl methyl
carbonate, and dimethyl carbonate in a volume ratio of 30:30:40 was
used.
Comparative Example 2
[0058] A 2016 coin cell was manufactured in the same manner as in
Example 1, except that a liquid electrolyte containing 1M
LiPF.sub.6 in a mixed solvent of ethylene carbonate and dimethyl
carbonate in a weight ratio of 10:90 was used.
Comparative Example 3
[0059] A 2016 coin cell was manufactured in the same manner as in
Example 1, except that a liquid electrolyte containing 1M
LiPF.sub.6 in a mixed solvent of propylene carbonate and dimethyl
carbonate in a weight ratio of 10:90 was used.
Example 3
[0060] A 2016 coin cell was manufactured in the same manner as in
Example 1, except that a liquid electrolyte containing 1M
LiPF.sub.6 in a mixed solvent of ethylene carbonate and methyl
propionate in a weight ratio of 30:70 was used.
Comparative Example 4
[0061] A 2016 coin cell was manufactured in the same manner as in
Example 1, except that a liquid electrolyte containing 1M
LiPF.sub.6 in a mixed solvent of ethylene carbonate and methyl
propionate in a weight ratio of 50:50 was used.
Experimental Example
[0062] A rate test was performed on the 2016 coin cells
manufactured according to Examples 1 to 3 and Comparative Examples
1 to 4, and results are shown in Table 1 below.
TABLE-US-00001 TABLE 1 LTO/LNMO (1.5~3.5 V, coin full 3C/3C 5C/5C
10C/10C 20C/20C cell) Rate test vs. vs. vs. vs. (1Crate = 1.49 mA)
3C/3C 3C/3C 3C/3C 3C/3C Example 1 EC/MP 10:90 wt %, 1M 100% 99% 85%
50% LiPF.sub.6 1.49 mAh Example 2 PC/MP 10:90 wt %, 1M 100% 99% 79%
50% LiPF.sub.6 1.36 mAh Comparative EC/EMC/DMC 100%, 95% 12% 9%
Example 1 30:30:40 vol %, 1M 1.30 mAh LiPF.sub.6 Comparative EC/DMC
10:90 wt %, 100% 99% 56% 17% Example 2 1M LiPF.sub.66 1.48 mAh
Comparative PC/DMC 10:90 wt %, 100% 98% 51% 14% Example 3 1M
LiPF.sub.6 1.47 mAh Example 3 EC/MP 30:70 wt %, 1M 100% 98% 63% 12%
LiPF.sub.6 1.47 mAh Comparative EC/MP 50:50 wt %, 1M 100% 96% 10%
7% Example 4 LiPF.sub.6 1.47 mAh
[0063] Referring to Table 1, it can be confirmed that the 2016 coin
cells of Examples 1 and 2 that use MP, which is a propionate-based
material, exhibit superior rate characteristics to those of the
2016 coin cells of Comparative Examples 1 to 3 that use DMC, which
is a linear carbonate-based material.
[0064] In addition, by comparison between the 2016 coin cells of
Examples 1 to 3 and the 2016 coin cell of Comparative Example 4, it
can be confirmed that when the amount of EC, which is a cyclic
carbonate-based material, is 30 wt % or less, the coin cells
including EC within the above-described range exhibit superior rate
characteristics. This is assumed to be because ion mobility
decreases since the amount of the propionate-based material
relatively decreases as the amount of the cyclic carbonate-based
material increases, and, in particular, when the amount of the
cyclic carbonate-based material is above a certain amount,
dissociation of lithium ions decreases.
[0065] Although the preferred embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
* * * * *