DESCRIPTION
COMPOSITION FOR GEL POLYMER ELECTROLYTE AND LITHIUM SECONDARY
BATTERY INCLUDING THE SAME

TECHNICAL FIELD

[0001] The present invention relates to a composition for a gel polymer electrolyte and a lithium secondary battery including the same, and more particularly, to a composition for a gel polymer electrolyte including a monomer having a functional group bondable to metal ions that are dissolved from a cathode, and a lithium secondary battery including the composition.

BACKGROUND ART

[0002] The application area of chargeable and dischargeable secondary batteries ■ is being increasingly expanded to electric vehicles as well as portable devices such as mobile phones, notebooks, and camcorders. Accordingly, secondary batteries have been actively developed. Also, research and development of battery design to improve capacity density and specific energy have been conducted during the development of the secondary batteries.

[0003] In general, it is known that battery safety improves
in the order of a liquid electrolyte, a gel polymer
electrolyte, and a solid polymer electrolyte, but battery !
performance decreases in the same order. An electrolyte in a liquid state, particularly, an ion conductive organic liquid electrolyte, in which a salt is dissolved in a non-aqueous organic solvent, has been mainly: used as an electrolyte for an electrochemical device, such as a typical battery using an

electrochemical reaction and an electric double-layer capacitor. However, when the electrolyte in a liquid state is used, an electrode material may degrade and the organic solvent is likely to be volatilized. Also, there may be limitations in safety - such as combustion due to ambient temperature and the temperature rise of the battery itself. [0004] It is known that the solid polymer electrolyte has not been commercialized yet due to poor battery performance. [0005] Since the gel polymer electrolyte may have excellent electrochemical safety, the thickness of the battery may be constantly maintained. Furthermore, since a contact between an electrode and the electrolyte may be excellent due to the inherent adhesion of a gel phase, a thin-film type battery may be prepared. Thus, the development of various gel polymer electrolytes is being expanded.

[0006] In the gel polymer electrolyte, since the size of lithium ions may be small, direct movement may not only be relatively easy, but also the lithium ions may easily move in the electrolyte solution due to a hopping phenomenon as illustrated in FIG. 1.

[0007] A lithium secondary battery including the gel polymer electrolyte generally uses a lithium' transition metal oxide, such as LiCo02, as a cathode active material. However, when the lithium secondary battery is used at a high voltage, metal ions may be dissolved. When the metal ions are dissolved, the metal ions may be reduced to a metallic state in an anode to block reaction sites of the anode. When the new metal is precipitated on the surface of the anode, an electrolyte solution produces a new solid electrolyte interface (SEI) layer on the surface of the metal, and thus,

the electrolyte solution is continuously consumed. Also, since the thickness of the SEI layer in the anode may be continuously increased to increase resistance, life characteristics of the lithium secondary battery may . be
decreased.

DISCLOSURE OF THE INVENTION TECHNICAL PROBLEM

[0008] The present invention provides a composition for a
gel. polymer electrolyte which may not only improve the
lifetime of a battery, but may also improve capacity
characteristics of the battery in both normal and high
voltage ranges by preventing the movement or decreasing the
movement speed of metal ions dissolved from a cathode to an
anode to reduce the precipitation of metal on the anode, and
a lithium secondary battery including the composition.

TECHNICAL SOLUTION

[0009.] According to an aspect of the present invention,
there is provided a composition for a gel polymer electrolyte
including i) an electrolyte solution solvent; ii) an j
ionizable lithium salt; iii) a polymerization initiator; and
iv) a monomer having a functional group bondable to metal
ions.

[0010] According to another aspect of the present invention,
there is provided a lithium secondary battery including a
cathode; an anode; a separator; and a gel polymer electrolyte,
wherein the gel polymer electrolyte is formed by polymerizing
the composition for a gel polymer electrolyte.

ADVANTAGEOUS EFFECTS

[0011] A composition for a gel polymer electrolyte of the
present invention includes a monomer having a functional
group bondable to metal ions. Thus, when the composition is

used in a lithium secondary battery, since the precipitation of metal on an anode may be reduced by preventing the movement or decreasing the movement speed of metal ions dissolved from a cathode to the anode, the lifetime of the battery may not only be improved but capacity characteristics
* of the battery may also be improved in "both normal and high voltage ranges.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 illustrates a principle of the movement of lithium ions when a composition for a gel polymer electrolyte is used;

[0013] FIG. 2 compares degrees of precipitated metal on an anode according to the uses of a typical electrolyte solution and a composition for a gel polymer electrolyte according to an embodiment of the present invention;

[0014] FIG. 3 is a ' graph illustrating capacity characteristics of lithium secondary batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 3; [0015] FIG. 4 is a graph illustrating capacity characteristics of lithium secondary batteries prepared in Examples 5 and 6 and Comparative Examples 4 and 5; and [0016] FIG. 5 is a graph illustrating capacity characteristics of lithium' secondary batteries prepared in Examples 7 to 10 and Comparative Examples 6 to 8 at a high voltage of 4.3 V.
-
MODE FOR CARRYING OUT THE INVENTION

[0017] Hereinafter,- the present invention will be described in more detail to allow for a clearer understanding of the present invention.

[0018] It will be understood that words or terms used in the

specification and claims shall not be interpreted as the meaning defined in commonly used dictionaries. It will be further understood that the words or- terms should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the technical idea of the invention, based on the principle that an inventor may properly define the meaning of the words or terms to best explain the invention.

[0019] A composition for a gel polymer electrolyte according to an embodiment of the present invention may include an electrolyte solution solvent, an ionizable lithium salt, a polymerization initiator, and a monomer having a functional group bondable to metal ions.

[0020] The monomer having the functional group is acrylonitrile or an acrylate-based monomer, and preferably, the functional group may include any one selected from the
-». Q-O. 0. Cft>. O.
group consisting of
cN !M
\ L« r /
and ■ '-' ' which are substituted or unsubstituted with C!-C5'
alkyl or halogen, . or a mixture of two or more thereof.

[0021] Typical examples of the monomer having the functional group according to an embodiment of the present invention may be any one selected from the group consisting of the following compounds or a mixture of two or more thereof:
[0022] (1) 2-cyanoethyl acrylate;

[0023]

[0024] (2) 2-cyanoethoxyethyl acrylate;

[0025] CN
[0026] (3) acrylonitrile;
[0027] tiC^*
[0028] (4) ethyl (E)-3-(pyridin-2-yl)-acrylate;

[0030] (5) ethyl (E)-3-(4-pyridinyl)-2-propenoate;
0
[0031] N^"

[0032] (6) 2-propenoic acid, 3,3'-[2,2'-bipyridine]-4,4' -
diylbis-, dimethyl ester;
[0033] * "

[0034] (7) 2-propenoic acid, 2-[2,2'-bipyridine]-6-ylethyl
ester;

[0035] (8) 2-propenoic acid,. 2- [2,2' -bipyridine] -5-ylethyl
ester;

[0036] (9) 2-propenoic acid, 2-[2,2'-bipyridine]-4-ylethyl
ester;

[0037] (10) 2-propenoic acid, 1,1'-[ [2,2'-bipyridine]-4 , 4'-
diylbis(methylene)] ester;
[0038] (11) 2-propenoic acid, 1,10-phenanthroline-2,9-
diylbis(methylene) ester;
[0039] (12) 2-propenoic acid, 3-(1,10-phenanthroline-2-yl)-
,phenylmethyl ester; and *

[0040] (13) 2-propenoic acid, 2-[[(l-oxo-2-propenyl)oxy]methyl]-2-[(1,10-phenanthroline-5-ylmethoxy)methyl]-1,3-propanediyl ester.

[0041] Among these compounds,' any one selected from the group consisting of 2-cyanoethyl acrylate, 2-cyanoethoxyethyl acrylate, acrylonitrile, and ethyl (E)-3-(pyridin-2-yl)-acrylate, or a mixture of two or more thereof may be particularly used.

[0042] According to an embodiment of the present invention, since the monomer having the functional group includes the functional group in the monomer, the functional group may be stably fixed in " ' a gel ' structure in the ' gel polymer electrolyte.

[0043] For example, in a case where, a complex is formed by respectively adding a cyano group and acrylate to the composition for a gel polymer electrolyte (gel electrolyte solution) and. polymerizing, the complex itself may move in the composition for a gel polymer electrolyte so that reduction may occur at an anode and metal may be precipitated. However, according to an embodiment of the present invention, in a case where 2-cyanoethylacrylate is used as the monomer having the functional group, since a cyano group is included in the monomer having the functional group, the cyano group itself may not ""move in the gel structure.

[0044] That is, according to an embodiment of the present invention, as illustrated in FIG. 2, in a case where the monomer having the functional group is used in the composition for a gel polymer electrolyte, the monomer having the functional group may be bonded to metal ions dissolved from a cathode to reduce the precipitation of metal on an

anode, different from a case of using a typical electrolyte . solution in which metal ions dissolved from the cathode is precipitated on the anode. Thus, charge and discharge efficiency of a lithium secondary battery may be improved and good cycle characteristics may be exhibited. In addition, in a case where the composition for a gel polymer electrolyte including the monomer having the functional group is used in a lithium secondary battery, capacity characteristics may be improved in both normal and high voltage ranges. ' [0045] The expression "normal voltage" used in the present specification denotes a case in which a charge voltage of the lithium secondary battery is in a range of 3:0 V .to less than 4.3 V, and the expression "high voltage" denotes a case in which a charge voltage is in a range of 4.3 V to 5.0 V. [0046]

[0047] The monomer having the functional group may be
included in an amount of 0.1 wt% to 10 wt%, for example, 0.5
wt% to 5 wt% based on a total weight of the composition for a
gel polymer electrolyte. In the case that the amount of the
monomer having the functional group is less than 0.1 wt%,
gelation may be difficult and thus, characteristics of the;
gel polymer electrolyte may not be exhibited. In the case in which the amount of the monomer is greater than 10 wt%, resistance may increase due to the excessive amount of the monomer and thus, battery performance may decrease. [0048] Also, according to an embodiment of the present invention, the composition for a gel polymer electrolyte may further include a monomer having 2 to 6 acrylate groups, and the monomer may be a branched monomer.

[0049] Examples of the branched monomer may be any one

selected from the" group consisting of ditrimethylolpropane tetraacrylate, _dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate, or a mixture of two or more thereof.

[0050] The branched monomer may be included in an amount of
i
0.1 wt% to 10 wt%, preferably, 0.5 wt% to 5 wt% based on the ''
total weight of the composition for a gel polymer electrolyte. ,
[0051] According to an embodiment of the present invention,
in a case where the composition for a gel polymer electrolyte
further includes the branched monomer, the monomer having the
functional group and the branched monomer are mixed and
reacted' at a temperature ranging from 30°C to 100°C for 2
minutes to 12 hours to prepare a polymerizable monomer. In
this case, a content ratio (weight ratio) of the monomer
having the functional group to the branched monomer, for
example, may be in a range of 1:0.1, to 1:10. However, the
present invention is not limited thereto.

[0052]' Examples of the ionizable lithium salt included in
the composition for a gel polymer electrolyte according to an
embodiment of the present invention may be any one selected
from the group consisting of LiPFg, LiBF^, LiSbFg, LiAsFe,
LiCl04, LiN(C2F5S02)2, LiN (CF3S02) 2, CF3S03Li, LiC {CF3S02) 3. and
LiC^BOs/ or a mixture of two or more thereof. However,, the
present invention is not limited thereto.
[0053] Also, any electrolyte solution solvent typically used
in an electrolyte solution for a lithium secondary battery
may be used as the electrolyte solution solvent used
according to an embodiment of the present invention without
limitation, and for example, ether, ester, amide, linear
carbonate, or cyclic carbonate may be used alone or in a

mixture of two or more thereof.

[0054] Among these materials, the cyclic carbonate, the linear carbonate, or a carbonate compound as a mixture thereof may be representatively included. Specific examples of the cyclic carbonate may be any one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, and a halide thereof, or a. mixture of two
■ or more thereof. Also, specific examples of the linear carbonate may be any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), . ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), and ethylpropyl carbonate

[0072] Li[LixNiaCobMnc]02 (where 0
[0074] LiMn2-xMx04 (where M is one or more elements selected from the group consisting of nickel (Ni), cobalt (Co),' iron (Fe) , phosphorus (P), sulfur (S) , zirconium (Zr), titanium (Ti), and aluminum (Al), and 0 [0076] Lii+aCOxMi-xAX* (where M is one or.' more elements

selected from the group consisting of Al, magnesium (Mg), Ni, Co, manganese (Mn), Ti, gallium (Ga), copper (Cu) , vanadium (V), niobium (Nb) , Zr, cerium (Ce) , indium (In), zinc (Zn), and yttrium (Y) , X is one or more elements selected from the ■ group consisting of oxygen (0), fluorine (F), and nitrogen (N) , A is P, S, or a mixed element thereof, O^a^O. 2, and 0.5^x^1).

[0077] The cathode active material may satisfy 0.4

[0091] An electrolyte solution was prepared by dissolving
LiPFg in a non-aqueous electrolyte solution solvent having a
composition, in which a volume ratio of ethylene carbonate
(EC) to ethylmethyl carbonate (EMC) was 1:2, to obtain a
LiPF6 concentration of 1 M. A composition fox a gel polymer
electrolyte was prepared by adding 5 parts by weight of a polymerizable monomer (2.5 parts by weight of 2-cyanoethyl acrylate and 2.5 parts by weight of ditrimetylolpropane tetraacrylate) and 0.25 parts by weight of t-butylperoxy-2-ethylhexanoate as a polymerization initiator based on 100 parts by weight of the electrolyte solution. [0092]
[0093] < Preparation of Coin-type Secondary Battery>

[0094] Cathode Preparation

[0095] A cathode mixture slurry was prepared by adding 94 wt% of LiCoO? as a cathode active material, 3 wt% of carbon

black as a conductive agent, and 3 wt% of polyvinylidene fluoride (PVdF) as a binder to N-methyl-2-pyrrolidone (NMP) as a solvent. An about 20 um thick aluminum (Al) thin film as a cathode current collector was coated with the cathode mixture slurry and dried, arid the Al thin film was then roll-pressed to prepare a cathode.

[0096] Anode Preparation

[0097] An anode mixture slurry was prepared by adding 96 wt%. of carbon powder as an anode active material, 3 wt% of PVdF as a binder, and 1 wt% of carbon black as a conductive agent to NMP as a solvent. A 10 um thick copper (Cu) thin film as an anode current collector was coated with the anode mixture slurry and dried, and the Cu thin film was then' roll-pressed to prepare an anode.

[0098] Battery Preparation

[0099] A battery was assembled using the cathode, the anode, and a separator formed of three layers of polypropylene/polyethylene/polypropylene (PP/PE/PP), and the prepared composition for a gel polymer electrolyte was injected into the assembled battery. Then, a coin-type secondary battery was prepared by heating the assembled
battery to 80°C for 2 minutes to 30 minutes.

[00100]

[00101] Example 2

[00102] A coin-type secondary battery was prepared in the
same manner as- in Example 1 except that 2-cyanoethoxyethyl
acrylate was used instead of 2-cyanoethyl acrylate in ■ the
preparation of the composition for a gel polymer electrolyte
of Example 1.
[00103]

[00104] Example 3

[00105] A coin-type secondary battery was prepared in the same manner as in Example 1' except that acrylonitrile was used instead of 2-cyanoethyl acrylate in the preparation of the composition for a gel polymer electrolyte of Example 1.

[00106]

[00107] Example 4

[00108] A coin-type secondary battery was prepared in the same manner as in Example 1 except that ethyl (E)-3- (pyridin-2-yl)-acrylate was used instead of 2-cyanoethyl acrylate in the preparation of the composition for a gel polymer electrolyte of Example 1.

[00109]

[00110] Example 5

[00111] A coin-type secondary battery was prepared in the same manner as in Example 1 except that a mixture, in which LiMn204 and Li {Nio.33Coo.33Mno.33) O2 was mixed at a weight ratio of 3:7, was used as a cathode active material in the preparation of the coin-type secondary battery of Example 1.

[00112]

[00113] Example 6

[00114] A coin-type secondary battery was prepared in the same manner as in Example 1 except that 2-cyanoethoxyethyl acrylate was used instead of 2-cyanoethyl acrylate in the preparation of the composition for a gel polymer electrolyte of Example 1, and a mixture, in which LiMn204 and Li (Nio.33Coo.33Mno.33) O2 was mixed at a weight ratio of 3:7, was used as a cathode active material in the preparation of a coin-type secondary battery.

[00115]

[00116] Example 7

[00117] A coin-type secondary battery was prepared in the
same manner as in Example 1 except that
Li [Li0.29^10.l^Coo.nMno.^e] O2 was used instead of LiCoC>2 as a
cathode active material in.the preparation of the cathode of
Example 1.

[00118]

[00119] Example 8

[00120] A coin-type secondary battery was prepared in the
same manner as in Example 1 except that 2-cyanoethoxyethyl
acrylate was used instead of 2-cyanoethyl acrylate in the
preparation of the composition for a gel polymer "electrolyte
of Example 1, and Li [Lio.29Nio.14Coo.nMno.46] O2 was used instead
of LiCo02 as a cathode active material in the preparation of
a cathode.

[00121]

[00122] Example 9

[00123] A coin-type secondary battery was prepared in the
same manner as in Example 1 except that acrylonitrile was
used instead of 2-cyanoethyl acrylate in the preparation of
the composition for a gel polymer electrolyte of Example 1,
and Li [Lio.29Nio.i4Co0.iiMn0.46]02 was used instead of LiCoC>2 as a
cathode active material in the preparation of a cathode.

[00124]

[00125] Example 10

[00126] A coin-type secondary battery was prepared in the
same manner as in Example 1 except that ethyl (E)-3-(pyridin-
2-yl)-acrylate was used instead of 2-cyanoethyl. acrylate in
the preparation of the composition for .a gel polymer
electrolyte of Example 1, and Li [Lio.29Nio.i4Coo.nMno.46302 was

used instead of LiCo02 as a cathode active material in the
preparation of a cathode.

[00127]

[00128] Comparative Example 1

[00129] A coin-type secondary battery was. prepared in the
same manner as in Example 1 except that a polymerizable
monomer and a polymerization initiator were not used in the
preparation of the composition for a gel polymer electrolyte
of Example 1.

[00130]

[00131] Comparative Example 2

[00132] A coin-type secondary battery was prepared in the
same manner as in Example 1 except that 5 parts by weight of
ditrimetylolpropane tetraacrylate was used alone instead of
using 5 parts by weight of a polymerizable monomer prepared
by mixing 2.5 parts by weight of 2-cyanoethyl acrylate and
2.5 parts by weight of ditrimetylolpropane tetraacrylate in
the preparation .of the composition for a gel polymer
electrolyte of Example 1.

[00133]

[00134] Comparative Example 3

[00135] A coin-type secondary battery was prepared in the
same manner as in Example 1 except that 5 parts by weight of
dipentaerythritol pentaacrylate was used alone instead of
using 5 parts by weight of a polymerizable.monomer prepared'
by mixing 2.5 parts by weight of 2-cyanoethyl acrylate and
2.5 parts by weight of ditrimetylolpropane tetraacrylate in
the preparation of the composition for a gel polymer
electrolyte of Example 1.

[00136]

[00137] Comparative Example 4

[00138] A coin-type secondary battery was prepared in the same manner as in Example 5 except that a polymerizable monomer and a polymerization initiator were not used in the preparation of the composition for a gel polymer electrolyte of Example 5.

[00139]

[00140] Comparative Example 5

[00141] A coin-type secondary battery was prepared in the same manner as in Example 5 except that 5 parts by weight of ditrimetylolpropane tetraacrylate was used alone instead of using 5 parts by weight of a polymerizable monomer prepared by mixing 2.5 parts by weight of 2-cyanoethyl acrylate and 2.5 parts by weight of ditrimetylolpropane tetraacrylate in the preparation of the composition for a gel polymer electrolyte of Example 5.

[00142]

[00143] Comparative Example 6

[00144] A coin-type secondary battery was prepared in the same manner as in Example 7 except that a polymerizable monomer and a polymerization initiator were not used in the preparation of the composition for a gel polymer electrolyte of Example 7.

[00145]

[00146] Comparative Example 7

[00147] A coin-type secondary battery was prepared in the same manner as in Example 7 except that 5 parts by weight of ditrimetylolpropane tetraacrylate was used alone instead of using 5 parts by weight of a polymerizable monomer prepared by mixing 2.5 parts by weight of 2-cyanoethyl acrylate and

2.5 parts by weight of ditrimetylolpropane tetraacrylate in
the preparation of the composition for a gel polymer
electrolyte of Example 7.

[00148]

[00149] Comparative Example 8

[00150] A coin-type secondary battery was prepared in the
same manner as in Example 7 except that 5 parts by weight of
dipentaerythritol pentaacrylate was used alone instead of
using 5 parts by weight of a polymerizable' monomer prepared
by mixing 2.5 parts by weight of 2-cyanoethyl acrylate and
2.5 parts by weight of ditrimetylolpropane tetraacrylate in
the preparation of the composition for a gel polymer
electrolyte of Example 7.

[00151] I

[00152] Experimental Example 1: Capacity Characteristics 1

[00153] The lithium secondary batteries (battery capacity:
5.5 mAh) prepared in Examples 1 to 4 and Comparative Examples
1 to 3 were charged at a constant current of 0.7 C to a
voltage of 4.2 V at 55°C. Thereafter, the lithium secondary
batteries were charged at a constant voltage of 4.2 V and the
charge was terminated when a charge current became 0.275 mA.
After the batteries were left standing for 10 minutes, the
batteries were discharged at a constant current of 0.5 C to a
voltage of 3.0 V. The charge and discharge were repeated for
100 cycles and battery capacities were then measured. The
results thereof are presented in FIG. 3.

[00154] Specifically, as illustrated in FIG. 3, capacities of
Examples 1 to 4 and Comparative Examples 1 to 3 were similar
to one another within less than a 5th cycle. However, the
capacities of Comparative Examples 1 to 3 were rapidly

decreased after about a 20th" cycle. In contrast/ the
capacities of Examples 1 to 4 were almost not changed .to the
20th cycle. Also, with respect to Examples 1 to 4, slopes of
the changes in capacity were relatively slow to a 100th cycle,
and Examples 1 to 4 exhibited capacities that were 2 to 3 times or more those of Comparative Examples 1 to 3.

[00155] Therefore, it may be understood that the discharge capacities of the batteries prepared in Examples 1 to 4 after the 100th cycle were significantly improved in comparison to those of the batteries prepared in Comparative Examples 1 to 3.

[00156]

[00157] Experimental Example 2: Capacity Characteristics 2

[00158] The lithium secondary batteries {battery capacity: 2.5 mAh) prepared in Examples 5 and 6 and Comparative Examples 4 and 5 were charged at a constant current of 0.7 C to a voltage of 4.2 V at 45°C. Thereafter, the lithium secondary batteries were charged at a constant voltage of 4.2 V and the charge was terminated when a charge current became 0.125 mA. After the batteries were left standing for 10 minutes, the batteries were discharged at a constant current of 0.5 C to a voltage of 3.0 V. The charge and discharge were repeated for 100 cycles and battery capacities were then measured. The results thereof are presented in FIG. 4. [00159] Specifically, as illustrated in FIG. 4, capacities of Examples 5 and 6 and Comparative Examples 4 and 5 were almost similar to one another within less than a 50th cycle. However, the capacities of Comparative Examples 4 and 5 began to decrease after about a 60th cycle and were rapidly decreased in an 80th cycle. In contrast, with respect to Examples 5 and

6, slopes of the changes in-capacity were almost maintained to a 100th cycle, and - in the 100th cycle, Examples 5 and 6 exhibited capacities that were 2 to 3 times or more those of Comparative Examples 4 and 5.

[00160] Therefore, it may be understood that the discharge capacities of the batteries prepared in Examples 5 and 6 after the 100th cycle were significantly improved in comparison to those of the batteries prepared in Comparative Examples 4 and
5.

[00161]

[00162] Experimental Example 3: Capacity Characteristics 3 (High Voltage)

[00163] The lithium secondary batteries (battery capacity: 4.3 mAh) prepared in Examples 7 to 10 and Comparative Examples 6 to 8 were charged at a constant current of 0.7 C to a voltage of 4.3 V at 55°C. Thereafter, the ■• lithium secondary batteries were charged-at a constant voltage of 4.3 V and the charge was terminated when a charge current became 0.215 mA. After the batteries were left standing for 10 minutes, the batteries were discharged at a constant current of 0.5 C to a voltage of 3.0 V. The charge and discharge were repeated for 40 cycles and battery capacities were then measured. The results thereof are presented in FIG. 5.

[00164] Specifically, referring to FIG. 5, capacities of Examples 7 -to 10 and Comparative Examples 6 to 8 were similar to one another within less than about a 5th cycle. However, the capacity of Comparative Example 6 was rapidly decreased after about the 5th cycle, and the capacities of Comparative Examples 7 and 8 were rapidly decreased after a 30th cycle and a 20th cycle, respectively. In contrast, changes in the

capacities of Examples 7 to 10 to a 4 0 cycle were relatively lower than those of Comparative Examples 6 to 8. In particular, with respect to Examples 8 and 9 using 2-cyanoethoxyethyl acrylate and acrylonitrile, the capacities were almost not changed at a high voltage to the 4 0th cycle, and Examples 8 to 9 exhibited capacities that were 2 to 4 times or more those of Comparative Examples 6 to 8.

[00165] Therefore, it may be understood that the discharge capacities of the batteries prepared in Examples 7 to 10 that were charged at a high voltage of 4.3 V after the 40th cycle were significantly improved in comparison to those of the secondary batteries prepared in Comparative Examples 6 to 8.- •

[00166]
INDUSTRIAL APPLICABILITY

[00167] In a case where a composition for a gel polymer electrolyte of the present invention is used in a lithium secondary battery, since the precipitation of metal on an anode may be reduced by preventing the movement or decreasing the movement speed of metal ions dissolved from a cathode to the anode, the lifetime of the battery may not only be improved but capacity characteristics of the battery may also be improved in both normal and high voltage ranges. Thus, the composition for a gel polymer electrolyte may be suitable for secondary batteries.

CLAIMS
1. A composition for a gel polymer electrolyte, the
composition comprising:
ionizable lithium salt; iii) a polymerization initiator; and
i) an electrolyte solution solvent; ii) an iv) a monomer having .a functional group bondable to metal ions.
2.
3. The composition for a gel polymer electrolyte of claim 1, wherein the monomer having the functional group is acfylonitrile or an acrylate-based monomer.
4. The composition for a gel polymer electrolyte of claim 1, wherein the functional group comprises any one selected from the group consisting of
-w. oo. o, <£b. O (o)
and * ' which are
substituted or unsubstituted with Ci-C5 alkyl or halogen, or a mixture of two or more- thereof.
4. The composition for a gel polymer electrolyte of
claim 1, wherein the monomer 'having the functional group is
any one selected from the group consisting of the following
compounds or a mixture of'two or more thereof:
(1) 2-cyanoethyl acrylate;
(2) 2-cyanoethoxyethyl acrylate;
(3) acrylonitrile;
(4) ethyl (E)-3-Cpyridin-2-yl)-acrylate;
(5) ethyl (E)-3-(4-pyridinyl)-2-propenoate;
(6) 2-propenoic acid, 3,3'-[2,2'-bipyridine]-4,4'-

diylbis-, dimethyl.ester;
(7) 2-propenoic acid, 2-[2,2'-bipyridine]-6-ylethyl ester;
(8) 2-propenoic acid, 2-[2,2'-bipyridine]-5-ylethyl ester;
(9) 2-propenoic acid, 2-[2,2'-bipyridine]-4-ylethyl ester;
(10) 2-propenoic' acid, 1,1'-[[2,2'-bipyridine]-4,4'-
diylbis(methylene)] ester;
(11) 2-propenoic acid, 1,10-phenanthroline-2,9-
diylbis(methylene) ester;
(12) 2-propenoic acid, 3-(1,10-phenanthroline-2-yl) -
,phenylmethyl ester; and
(13) 2-propenoic acid, 2-[ [ (l-oxo-2-
propenyl)oxy]methyl]-2-[(1,10-phenanthroline-5-
ylmethoxy)methyl]-1,3-propanediyl ester.
'5. The composition for a gel polymer electrolyte of claim 1, further comprising a monomer having 2 to 6 acrylate groups,
wherein the monomer is a branched monomer.
6. The composition for a gel polymer electrolyte of claim 5, wherein the branched monomer is any one selected from the group consisting of ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate, or a mixture of two or more thereof.
7. The composition for a gel polymer electrolyte of claim 1, wherein the"monomer having the functional group is included in an amount of 0.1 wt% to 10 wt% based on a total weight of the composition.

8. The composition for a gel polymer electrolyte of claim 5, wherein the branched monomer is included in an amount of 0.1 wt% to 10 wt% based on the total weight of the composition.
9. The composition for a gel polymer electrolyte of claim 5,- wherein a content ratio (weight ratio) of the monomer having the functional group to the branched monomer is in a range of 1:0.1 to 1:10.
10. The composition for a gel polymer electrolyte of claim 1, wherein the lithium salt is any one selected from the group consisting of LiPF6, L.iBF4, LiSbF6, LiAsF6, LiC104, L-iN(C2F5S02)2, LiN(CF3S02)2, CF3S03Li, LiC (CF3S02) 3, and LiC4B0B, or a mixture of two or more thereof.
11. The composition for a gel polymer electrolyte of claim 1, wherein the electrolyte solution solvent is linear carbonate, cyclic carbonate, or a combination thereof.
12. The composition for a gel polymer electrolyte of
. claim 11, wherein the linear carbonate comprises any one
selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, and ethylpropyl carbonate, or a mixture of two or more thereof, and the cyclic carbonate comprises any one selected from the group consisting of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate,- and a halide thereof, or a mixture of two or more thereof.
13. A lithium secondary battery comprising:
a cathode;
an anode;

a separator; and
a gel polymer electrolyte,
wherein the gel polymer electrolyte is formed by polymerizing the composition for a gel polymer electrolyte of claim 1.
14. The lithium secondary battery of claim 13,
wherein the composition for a gel polymer electrolyte further
comprises a monomer having 2 to 6 acrylate groups,
wherein the monomer is a branched monomer.
15. The lithium secondary battery of claim 14, wherein the branched monomer is any one selected from the group consisting of ' ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate, or a mixture of two or more thereof.
16. The lithium secondary battery of claim 13, wherein a charge voltage of the lithium secondary battery Is in a range of 3.0 V to 5.0 V.
17. The lithium secondary battery of claim 16, wherein the charge voltage of the lithium secondary battery is in a range, of 4.3 V to 5.0 V.
18. The lithium secondary battery of claim 17, wherein a cathode active material for the cathode is any one selected from the group consisting of compounds of Chemical Formulas 1 to 3, or a mixture of two or more thereof:

Li[LixNiaCObMnc]02 (where 0 , . • ■
LiMn2-xMx04 (where M is one or more elements selected from the group consisting of nickel (Ni), cobalt (Co), iron

(Fe) , phosphorus . (F) , sulfur (S) ,' zirconium (Zr) , titanium (Ti), and aluminum (Al), and 0
Lii+aCoxMi-xAX4 (where M is one or more elements selected
from the group consisting ■ of Al, magnesium (Mg) , ■ Ni, Co,
manganese (Mn), Ti, gallium (Ga), copper (Cu), vanadium (V),
niobium (Nb) , Zr, cerium (Ce) , indium (In) , zinc . (Zn) , and
yttrium (Y) , X is one or more elements selected from the
group consisting of oxygen (0) , fluorine (F) , and nitrogen
(N) , A is P, S, or a mixed element thereof, O^a^O. 2, and
0.5^x^1). s
19. The lithium' secondary battery of claim 16,
wherein a cathode active material for the cathode is any one
selected from the group consisting of LiCo02, LiNi02, LiMn02,
LiMn204, .. LiNi1_yCoyO2(0%