[DESCRIPTION]
ELECTROLYTE FOR SECONDARY BATTERY AND LITHIUM
SECONDARY BATTERY INCLUDING THE SAME
[TECHNICAL FIELD]
5 The present invention relates to a rechargeable lithium secondary battery and
an electrolyte constituting the lithium secondary battery.
[BACKGROUND ART]
As energy source prices are increasing due to depletion of fossil fuels and
interest in environmental pollution is escalating, demand for environmentally-friendly
10 alternative energy sources is bound to play an increasing role in future life. Thus,
research into various power generation techniques such as nuclear energy, solar energy,
wind energy, tidal power, and the like, continues to be underway, and power storage
devices for more efficient use of the generated energy are also drawing much attention.
Specifically, demand for lithium secondary batteries as energy sources is
15 rapidly increasing as mobile device technology continues to develop and demand
therefor continues to increase. Recently, use of lithium secondary batteries as a power
source of electiic vehicles (EVs) and hybrid electric vehicles (HEVs) has been realized
. 1 -
and the market for lithium secondary batteries continues to expand to applications such
as auxiliary power suppliers through smart-grid technology.
A lithium secondary batteiy has a structure in which an electrode assembly,
which includes: a cathode prepared by coating a cathode active material on a cathode
5 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.
These lithium secondary batteries are generally manufactured by disposing a
polyolefin-based porous separator between a cathode including a cathode active
10 material, e.g., metal oxides such as lithium-cobalt based oxides, lithium-manganese
based oxides, lithium-nickel based oxides, or the like, an anode including an anode
active material, e.g., carbonaceous materials, and impregnating the resultant structure
with a non-aqueous electrolyte containing a lithium salt such as LiPFe or the like.
When the lithium secondary battery is charged, lithium ions of the cathode
15 active material are demtercalated 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 demtercalated 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.
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Recently, instead of using conventional materials as electrode active materials,
research into use of spinel-structure lithium nickel-based metal oxides as cathode active
materials or use of lithium titanium oxides and the like as anode active materials has
been conducted.
5 Reaction at an interface between the electrode and the electrolyte varies
according to kinds of electrode materials and electrolyte used in the lithium secondary
battery. Therefore, there is a need to develop electrolyte techniques that can be
suitably adapted to changes in electrode composition.
[DISCLOSURE]
10 [TECHNICAL PROBLEM]
Therefore, the present invention has been made to solve the above problems
and other technical problems that have yet to be resolved.
As a result of a variety of extensive and intensive studies and experiments, the
inventors of the present invention found that when a mixture of a cyclic carbonate and a
15 linear solvent is used as a non-aqueous electrolyte, the amount of the cyclic carbonate is
adjusted within a predetermined range, whereby a lithium secondary battery including
the same is stable at high voltages and has enhanced rate characteristics, thus
completing the present invention.
-3-
[TECHNICAL SOLUTION]
In accordance with one aspect of the present invention, provided is an
electrolyte for a lithium secondary battery which includes a non-aqueous solvent and a
lithium salt, wherein the non-aqueous solvent includes a cyclic carbonate and a linear
5 solvent, wherein the amount of the cyclic carbonate in the non-aqueous solvent is in the
range of 1 wt% to 30 wt% based on a total weight of the non-aqueous solvent.
The present invention also provides a lithium secondary battery in which an
electrode assembly including a cathode, an anode, and a separator disposed between the
cathode and the anode is accommodated in a battery case and the battery case is sealed.
10 The lithium secondary battery may include the electrolyte for a lithium secondary
battery.
Specifically, the lithium secondary battery may include an electrolyte for a
lithium secondary battery that may include a lithium metal oxide represented by
Formula (1) below as a cathode active material, a lithium metal oxide represented by
15 Formula (3) below as an anode active material, and a cyclic carbonate and a linear
solvent, as a non-aqueous solvent, wherein the amount of the cyclic carbonate in the
non-aqueous solvent is in the range of 1 wt% to 30 wt% based on the total weight of the
non-aqueous solvent.
-4-
In general, in a secondaiy 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
5 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 lowviscosity
solvent, and thus, there is a need to use a large amount of the cyclic carbonate
10 or use an additive for forming an anode protective film, such as vinylene carbonate
(VC).
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 compound represented by Formula (1) below as a cathode active material
15 and a compound represented by Formula (3) below as an anode active material,
problems occur as follows.
First, when the compound of Formula (1) is used as a cathode active material, a
cathode operates at a high voltage with respect to lithium and thus the electrolyte is
decomposed due to low oxidation voltage of vinylene carbonate (VC) and components
-5-
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
5 lithium salt, may occur.
Second, when an electrolyte including 30 wt% or more of cyclic carbonate is
applied to a lithium secondary battery including the compound of Formula (3) below as
an anode active material used to achieve high-rate charge/discharge, lifespan
characteristics and rate characteristics are worse than when a smaller amount of the
10 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
15 are rather enhanced when the electrolyte includes a small amount of the cyclic
carbonate.
Thus, the inventors of the present invention repeatedly performed intensive
studies and discovered that when the compound of Formula (3) below is used as an
anode active material and the electrolyte including a mixed solvent of a small amount of
-6-
a cyclic carbonate and a linear solvent is used, problems in terms of reduction at the
anode including the compound of Formula (3) below having high stability for reduction
of the electrolyte do not occur due to high reduction potential, and lifespan and rate
characteristics may be enhanced. In addition, the inventors discovered that when a
5 high-voltage cathode active material, e.g., the compound of Formula (1) below, 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.
When the amount of the cyclic carbonate is less than 1 wt%, improvement in
10 ionic conductivity, which is a strong point of cyclic carbonate-based materials, may not
be obtained. On the other hand, when the amount of the cyclic carbonate exceeds 30
wt%, the amount of the linear solvent is relatively small and thus desired effects, i.e.,
improvement in lifespan characteristics and stability of oxidation at a surface of a highvoltage
cathode, may not be achieved.
15 In a specific embodiment, a weight ratio of the cyclic carbonate to the linear
solvent may be 10-20: 80-90, for example, 10: 90.
The cyclic carbonate may be any ring-type carbonate. For example, the cyclic
carbonate may be propylene carbonate, ethylene carbonate (EC), butylene carbonate,
vinylene carbonate, or any combination thereof, but is not limited thereto.
-7-
The linear solvent is not particularly limited, and may be, for example, a linear
carbonate or a linear ester.
For example, the linear carbonate may be dimethyl carbonate (DMC), diethyl
carbonate (DEC), ethylmethyl carbonate (EMC), or any combination thereof, but is not
5 limited thereto.
Preferably, a mixture of DMC and EC may be used.
As confirmed in Experimental Example 1, when the mixture of DMC and EC
is used, superior lifespan characteristics may be obtained as compared to a case in
which a mixture of EMC, DMC, and EC is used. In addition, it can be confirmed that
10 when a mixture of EMC and EC is used, lifespan characteristics are deteriorated as
compared to a case in which the mixture of DMC and EC is used.
The lithium secondary battery may be a lithium ion battery or a lithium ion
polymer battery.
The cathode or anode may be fabricated using a manufacturing method
15 including the following processes.
The electrode manufacturing method includes: preparing a binder solution by
dispersing or dissolving a binder in a solvent; preparing an electrode slurry by mixing
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the binder solution, an electrode active material, and a conductive material; coating the
electrode sluny on a current collector; drying the electrode; and compressing the
electrode to a uniform thickness.
In some cases, the electrode manufacturing method may further include drying
5 a rolled electrode.
Preparation of the binder solution is a process of preparing a binder solution by
dispersing or dissolving a binder in a solvent.
The binder may be any binder known in the art and, in particular, may be
selected from the group consisting of fluorine resins, polyolefins, styrene-butadiene
10 rubbers, carboxymethyl cellulose, mussel protein (dopamine), silanes, ethylcellulose,
. methylceltulose, hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, and
acryl-based copolymers.
The solvent may be optionally used according to the kind of the binder and
may be, for example, an organic solvent such as isopropyl alcohol, N-
15 methylpyrrolidone (NMP), acetone, or the like, or water.
In a specific embodiment, a binder solution for a cathode may be prepared by
dispersing or dissolving PVdF in NMP.
-9-
The electrode active material and the conductive material may be mixed with
or dispersed in the binder solution to prepare the electrode slurry. The electrode slurry
may be transferred to a storage tank and stored until the electrode slurry is used in the
coating process. To prevent the electrode slurry from hardening, the electrode slurry
5 may be continuously stirred in the storage tank.
Examples of the electrode active material include, but are not limited to,
layered compounds such as lithium cobalt oxide (IJC0O2) and lithium nickel oxide
(LiNi02), or compounds substituted with one or more transition metals; lithium
manganese oxides such as compounds of Formula Lii+yMn2-y04 where 03, LiMn203, and LiMn02; lithium copper oxide (Li2Cu02); vanadium oxides
such as LiV308, L1V3O4, V2O5, and CU2V2O7; Ni-site type lithium nickel oxides of
Formula LiNii.yMy02 where M = Co, Mn, AI, Cu, Fe, Mg, B, or Ga, and 0.014)3; metal composite oxides such as LixFe203
where 00.2),
-11-
lifespan characteristics of the lithium secondary battery may be rather deteriorated due
to an unstable crystal structure of the compound of Formula (1).
Specifically, the spinel-structure lithium metal oxide of Formula (1) may be a
lithium metal oxide represented by Formula (2) below:
5 LixNiyMn2-y04 (2)
wherein 0.9< x< 1.2 and 0.4^ y< 0.5.
More specifically, the lithium metal oxide may be LiNio.5Mn1.5O4 or
LiNio.4Mn1.6O4.
In addition, in a non-restrictive embodiment, the electrode active material may
10 include a lithium metal oxide represented by Formula (3) below:
LiaM,
b04.cAc (3)
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^ a^ 4 and 0.2£ b£ 4 wherein a and b are determined according to
15 oxidation number of M';
0£ c<0.2 wherein c is determined according to oxidation number; and
-12-
A is at least one monovalent or divalent anion.
The lithium metal oxide of Formula (3) may be represented by Formula (4)
below:
LiaTib04 (4)
5 wherein 0.5* a< 3 and 1< b< 2,5.
Examples of the lithium metal oxide include, but are not limited to,
Lio.sTi2.2O4, Li2.67Ti1.33O4, LiTi204, Li1.33Ti1.67O4, and Li1.14Ti1.71O4.
In a non-restrictive embodiment, the lithium metal oxide may be Li1.33Ti1.67O4
or LiTi204. In this regard, Li1.33Ti1.67O4 has a spinel stnacture having a small change in
10 crystal structure during charge/discharge and high reversibility.
The lithium metal oxide may be prepared using a manufacturing method
known in the art, for example, solid-state reaction, a hydrothermal method, a sol-gel
method, or the like. A detailed description of known manufacturing methods is
omitted.
15 The lithium metal oxide may be in the form of a secondary particle in which
primary particles are agglomerated with one another.
The secondary particle may have a diameter of 200 nm to 30 um.
-13-
When the diameter of the secondary particle is less than 200 nm, reduction in
adhesion is caused during an anode fabrication process. To address this problem, a
larger amount of a binder needs to be used, which is not desirable in terms of energy
density. On the other hand, when the diameter of the secondary particle exceeds 30
5 urn, diffusion rate of lithium ions is slow and thus it may be difficult to achieve high
output.
The amount of the lithium metal oxide may be equal to or greater than 50 wt%
to equal to or less than 100 wt% based on a total weight of the anode active material.
The conductive material is not particularly limited so long as it has suitable
10 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
15 powder; conductive whiskers such as zinc oxide and potassium titanate; conductive
metal oxides such as titanium oxide; and polyphenylene derivatives.
The electrode slurry may further optionally include a filler or the like, as
desired.
-14-
The filler is not particularly limited so long as it is a fibrous material that does
not cause chemical changes in the fabricated batteiy. Examples of the filler include
olefln-based polymers such as polyethylene and polypropylene; and fibrous materials
such as glass fiber and carbon fiber.
5 The coating of the electrode slurry on a current collector is a process of coating
the electrode slurry on a current collector in a predetermined pattern and to a uniform
thickness by passing through a coater head.
The coating of the electrode slurry on a current collector may be performed by
applying the electrode slurry to the current collector and uniformly dispersing the
10 electrode sluny thereon using a doctor blade. The coating process may be performed
by, for example, die casting, comma coating, screen printing, or the like. In another
embodiment, the electrode sluny may be molded on a separate substrate and then
adhered to a current collector via pressing or lamination.
The current collector is not particularly limited so long as it does not cause
15 chemical changes in the fabricated secondary batteiy and has high conductivity. For
example, the current collector may be made of copper, stainless steel, aluminum, nickel,
titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel,
titanium, silver, or the like, or aluminum-cadmium alloys. A cathode current collector
may have fine irregularities at a surface thereof to increase adhesion between a cathode
-15-
active material and the cathode current collector and be used in any of various forms
including films, sheets, foils, nets, porous structures, foams, and non-woven fabrics.
Specifically, the cathode current collector may be a metal current collector, e.g., an Al
current collector, and an anode current collector may be a metal current collector, e.g., a
5 Cu current collector. The electrode current collector may be a metal foil, e.g., Al foil
or Cu foil.
The drying process is a process of removing solvent and moisture from the
electrode slurry to diy the electrode slurry coated on the current collector.
Specifically, the drying process is performed in a vacuum oven at 50 to 200D for one
10 day or less.
The electrode manufacturing method may further include a cooling process
after the drying process. The cooling process may be performed by slow cooling up to
room temperature so that a recrystallized structure of the binder is satisfactorily formed.
To increase capacity density of the coating-completed electrode and increase
15 adhesion between the current collector and the corresponding active material, the
electrode may be compressed to a desired thickness by passing between two hightemperature
heated rolls. This process is referred to as a rolling process.
-16-
Before passing between the two high-temperature heated rolls, the electrode
may be subjected to a preheating process. The preheating process is a process to
preheat the electrode before passing between the rolls in order to enhance compression
of the electrode.
5 The rolling-completed electrode may be dried in a vacuum oven at 50 to 200 •
for one day or less, within a temperature range that is equal to or greater than a melting
point of the binder. The rolled electrode may be cut to a uniform length and then
dried.
After the drying process, a cooling process may be performed. The cooling
10 process may be performed by slow cooling to room temperature such that a
recrystallized structure of the binder is satisfactorily formed.
The separator may be an insulating thin film having high ion permeability and
mechanical strength. The separator typically has a pore diameter of 0.01 to 10 um and
a thickness of 5 to 300 um.
15 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, Kraft paper, or the like may be used. Applicable commercially
available separators include Celgard type products (Celgard® 2400, 2300: Hoechest
-17-
Celanese Corp.), polypropylene separators (Ube Industries Ltd., Pall RAI's products),
polyethylene type separators (Tonen or Entek), and the like.
>
In some cases, the separator may be coated with a gel polymer electrolyte in
order to increase stability of the lithium secondaiy battery. Examples of gel polymers
5 include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile.
Examples of the electrode assembly include a jelly-roll type electrode assembly
(or a winding-type electrode assembly), a stack-type electrode assembly, and a
stack/folding electrode assembly, which are known in the art.
As used herein, the stack/folding electrode assembly may be understood to
10 include stack/folding electrode assemblies manufactured by arranging a unit cell having
a structure in which a separator is disposed between a cathode and an anode on a
separator sheet and folding or winding the separator sheet.
In addition, the electrode assembly may include an electrode assembly in
which a structure having any one of a cathode and an anode disposed between
15 separators is laminated in a stacked state by thermal bonding.
The lithium salt is a material that is readily soluble in the non-aqueous
electrolyte and examples thereof include LiCl, LiBr, Lil, LiC104, LiBF-i, LiBioClio,
LiPF6, UCF3SO3, UCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3U, CF3SO3L1, LiSCN,
-18-
LiC(CF3S02)3, (CF3S02)2NLi, chloroborane lithium, lower aliphatic carboxylic acid
lithium, lithium tetraphenyl borate, and imide.
In addition, in order to improve charge/discharge characteristics and flame
retardancy, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether,
5 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
10 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), fluoropropylene
carbonate (FPC), or the like.
The lithium secondary battery according to the present invention may be used
15 in battery cells used as a power source of small devices and may also be suitable for use
as a unit cell in medium and large battery modules including a plurality of battery cells.
The present invention also provides a battery pack including the battery
module as a power source of a medium and large device. Examples of medium and
large devices include, but are not limited to, electric vehicles (EVs), hybrid electric
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vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and apparatuses for storing
power.
Structures and manufacturing methods of the battery module and the battery
pack are known in the art, and thus, a detailed description thereof is omitted.
5 [EFFECTS OF INVENTION]
As apparent from the fore-going, the present invention provides a lithium
secondary battery including the compound of Formula (1) and/or the compound of
Formula (3) as an electrode active material and thus may have improved lifespan
characteristics.
10 The lithium secondaiy battery according to the present invention also improves
the rate characteristic by the increased ion conductivity.
[BEST MODE]
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
15 invention and should not be construed as limiting the scope and spirit of the present
invention.

-20-
Solids including Li(Nio.5Mn 1.5)04 (available from BASF): Super P (available
from Timcal): PVdF(Solef® 6020), in a weight ratio of 90:5:5, were mixed with NMP
as a solvent to prepare a cathode slurry. The cathode slurry was coated on Al foil
having a thickness of 20 um to manufacture a cathode having a loading amount of 1.0
5 mAh/cm .
Separately, solids including Lij.33Ti1.67O4 (available from Posco ESM; T30):
Super P (available from Timcal): PVdF(SolefS) 6020), in a weight ratio of 90:5:5, were
mixed with NMP as a solvent to prepare an anode sluny. The anode slurry was coated
onto Al foil having a thickness of 20 urn to manufacture an anode having a loading
10 amount of 1.0 mAh/cm2.
Battery cells each including the cathode, the anode, and a polyethylene
membrane as a separator (Celgard, thickness: 20 um) and including electrolytes having
compositions shown in Table 1 below were manufactured.

Example 1
Example 2
Electrolyte
Carbonate electrolyte containing 1M LiPFe in EC:DMC
(5:95 weight ratio)
Carbonate electrolyte containing 1M LiPF6 in EC:DMC
(10:90 weight ratio)
-21-
Example 3
Example 4
Comparative
Example 1
Comparative
Example 2
Comparative
Example 3
Carbonate electrolyte containing 1M LiPF6 in EC:DMC
(20:80 weight ratio)
Carbonate electrolyte containing 1M LiPF6 in EC:DMC
(30:70 weight ratio)
Carbonate electrolyte containing 1M LiPF6 in EC:DMC
(50:50 weight ratio)
Carbonate electrolyte containing 1M LiPFg in EC:EMC
(50:50 weight ratio)
Carbonate electrolyte containing 1M LiPF6 in
EC:EMC:DMC (30:30:40 weight ratio)
Experimental Example>
200 charge/discharge cycles were performed using the battery cells
manufactured according to Examples 1 to 4 and Comparative Examples 1 to 3 at 1.5 to
3.5 V and 3 C. Capacity retention ratio of each battery cell after 200 cycles is shown
5 in Table 2 below. Referring to Table 2, it can be confirmed that the battery cells of
Examples 1 to 4 including the electrolyte containing EC: DMC in a weight ratio that is
equal to or less than 30:70 exhibit excellent lifespan characteristics when compared to
the battery cells of Comparative Examples 1 to 3.

LTO/LNMO (1.5 ~ 3.5V, coin full-cell)
3C/3 C-rate cycle life test (1Crate=
1.49mA)
200m Capacity retention (%, vs. 1st),
Capacity (mAh): 1st -> 200th
-22-
Example 1
Example 2
Example 3
Example 4
Comparative Example 1
Comparative Example 2
Comparative Example 3
92.5%, 1.48mAh -> 1.37mAh
96.5%, 1.48mAh -> 1.43mAh
95.8%, 1.47mAh-> 1.41mAh
93.3%, 1.39mAh -> 1.30mAh
57.7%, 1.08mAli -> 0.62mAh
39%, 1.06mAh -> 0.41mAh
86.1%, 1.30mAh-> 1.12mAh
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.
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[CLAIMS]
[Claim l] An electrolyte for a secondary battery, the electrolyte comprising a
non-aqueous solvent and a lithium salt, wherein the non-aqueous solvent comprises a
cyclic carbonate and a linear solvent, wherein an amount of the cyclic carbonate in the
non-aqueous solvent is in a range of 1 wt% to 30 wt% based on a total weight of the
non-aqueous solvent.
[Claim 2] The electrolyte according to claim 1, wherein the linear solvent is a
linear carbonate or a linear ester.
[Claim 3] The electrolyte according to claim 2, wherein the linear carbonate is
one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate
(DEC), ethylmethyl carbonate (EMC), and combinations thereof.
[Claim 43 The electrolyte according to claim 3, wherein the linear carbonate is
DMC.
[Claim 5] The electrolyte according to claim 1, wherein the cyclic carbonate is
one selected from the group consisting of ethylene carbonate (EC), propylene carbonate
(PC), vinylene carbonate (VC), and combinations thereof.
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[Claim 6] The electrolyte according to claim 5, wherein the cyclic carbonate is
EC.
[Claim 7] A lithium secondary battery comprising the electrolyte according to
any one of claims 1 to 6 and an electrode assembly comprising a cathode, an anode, and
a polymer membrane disposed between the cathode and the anode, the electrode
assembly being accommodated in a battery case.
[Claim 8] The lithium secondary battery according to claim 7, wherein the
cathode comprises a spinel-structure lithium metal oxide represented by Formula (1)
below:
LixMyMn2-y04_zAz (1)
wherein 0.9* x^ 1.2, 0