Composition for gel polymer electrolyte, gel polymer electrolyte, and lithium secondary battery including gel polymer electrolyte

Abstract

The present invention provides a composition for a gel polymer electrolyte, a gel polymer electrolyte, and a lithium secondary battery, the composition for a gel polymer electrolyte comprising an electrolyte salt, an organic solvent, a polymerizable monomer, a polymerization initiator, and a polymerization inhibitor, the gel polymer electrolyte being prepared from the composition for a gel polymer electrolyte, the lithium secondary battery includes a gel polymer electrolyte.

Description

TECHNICAL FIELD

[0001] The present application relates to a gel polymer electrolyte composition, a gel polymer electrolyte, and a lithium secondary battery including the gel polymer electrolyte. BACKGROUND

[0002] In recent years, as the concern for environmental problems is increasing, exhaust gas emitted from vehicles using fossil fuels such as gasoline or diesel is pointed out as one of the main causes of air pollution, and as a method of replacing the same, a large amount of research is being conducted on electric vehicles (EV), hybrid electric vehicles (HEV), etc. At the same time, as a power source for such electric vehicles (EV), hybrid electric vehicles (HEV), etc., lithium secondary batteries having high discharge voltage and high power stability are mainly used.

[0003] Depending on the kind of electrolyte applied, such lithium secondary batteries are classified into lithium ion batteries applying a liquid electrolyte and lithium polymer batteries using a polymer electrolyte. The lithium ion battery has a problem that the battery design becomes complicated because of the risk of leakage and explosion due to the use of a liquid electrolyte. On the other hand, the lithium polymer battery has improved stability because of the use of a solid polymer electrolyte or a gel polymer electrolyte, and thus development of the lithium polymer battery is actively conducted in recent years.

[0004] The lithium secondary battery including the gel polymer electrolyte can be manufactured by a method of preparing a liquid gel polymer electrolyte composition by dissolving a polymerizable monomer and a polymerization initiator in a liquid electrolyte, injecting the gel polymer electrolyte composition into a battery case, and then impregnating into an electrode assembly including a cathode, an anode, and a separator under appropriate temperature and time conditions to form a gel polymer electrolyte, thereby manufacturing the lithium secondary battery.

[0005] In the process of impregnating the gel polymer electrolyte composition into the electrode assembly, the gel polymer electrolyte composition can be prematurely cured due to the reaction of the monomer with the polymerization initiator, which can cause the formation of a gel polymer electrolyte having a non-uniform crosslinking degree and surface, and thus can cause the secondary battery to have reduced performance due to liquid leakage, etc. Therefore, a technology for preventing the premature curing of the gel polymer electrolyte composition is required. SUMMARY

[0006] (I) Technical Problem to be Solved The present application aims to provide a gel polymer electrolyte composition including a polymerization inhibitor, a gel polymer electrolyte, and a lithium secondary battery including the gel polymer electrolyte.

[0007] (II) Technical Solution The composition for a gel polymer electrolyte according to the present application can include an electrolyte salt, an organic solvent, a polymerizable monomer, a polymerization initiator, and a polymerization inhibitor.

[0008] The polymerization inhibitor can include at least one selected from the group consisting of a hydroxyl or alkoxy group-containing aromatic compound, a quinone-based compound, a phenothiazine-based compound, and a nitrosobenzene-based compound.

[0009] The hydroxyl or alkoxy group-containing aromatic compound can include two or more hydroxyl groups or two or more alkoxy groups.

[0010] The hydroxyl or alkoxy group-containing aromatic compound can further include a nitro group or an alkyl group.

[0011] The hydroxyl or alkoxy group-containing aromatic compound can include a single ring or a condensed ring of two or more single rings condensed.

[0012] The polymerization inhibitor can include at least one selected from the group consisting of 4-methoxyphenol (MEHQ), 1,2-benzoquinone, 4-tert-butylcatechol (TBC), nitrosobenzene, picric acid, t-butylhydroquinone (TBHQ), hydroquinone, p-methoxyphenol, phenothiazine, tert-butylhydroquinone, 2,6-di-tert-butyl-p-cresol, 2-tert-butyl-1,4-benzoquinone, 6-tert-butyl-2,4-xylenol, 2,6-di-tert-butylphenol, 6-tert-butyl-2,4-xylenol, and 2,6-di-tert-butylphenol.

[0013] The content of the polymerization inhibitor can be 150 ppm or less, based on the total weight of the composition for a gel polymer electrolyte.

[0014] The polymerizable monomer can have a polymerizable functional group including at least one selected from a vinyl group, an epoxy group, an allyl group, an acrylic group, a (meth)acrylic group, an ether group, and a fluorine (F) group, and a phosphate group.

[0015] The polymerizable monomer can include 3 or more of the polymerizable functional groups.

[0016] The polymerizable monomer can include a phosphate group, an acrylate group, and an ether group.

[0017] The polymerizable monomer including the phosphate group can include an electron donating group (EGD).

[0018] The gel polymer electrolyte according to the present application can include a polymerizable polymer, an electrolyte salt, an organic solvent, a polymerization initiator, and a polymerization inhibitor.

[0019] The polymerization inhibitor can include at least one selected from an aromatic compound including a hydroxyl group or an alkoxy group, a quinone-based compound, a phenothiazine-based compound, and a nitroso-phenyl-based compound.

[0020] The polymerization inhibitor can include at least one selected from 4-methoxyphenol (MEHQ), 1,2-benzoquinone, 4-tert-butylcatechol (TBC), nitrosobenzene, picric acid, tert-butylhydroquinone (TBHQ), hydroquinone, p-methoxyphenol, phenothiazine, tert-butylhydroquinone, 2,6-di-tert-butyl-p-cresol, 2-tert-butyl-1,4-benzoquinone, 6-tert-butyl-2,4-dimethylphenol, 2,6-di-tert-butylphenol, 6-tert-butyl-2,4-dimethylphenol, and 2,6-di-tert-butylphenol.

[0021] The lithium secondary battery according to the present application can include the gel polymer electrolyte, and a positive electrode and a negative electrode impregnated with the gel polymer electrolyte.

[0022] (III) ADVANTAGEOUS EFFECTS The gel polymer electrolyte composition according to the present application includes a polymerization inhibitor, and thus can prevent the polymerizable monomers from being prematurely polymerized at room temperature.

[0023] The gel polymer electrolyte prepared from the gel polymer electrolyte composition can have a uniform cross-linking degree.

[0024] The storage property of the gel polymer electrolyte composition at room temperature can be improved, and the process property of the impregnation process of the gel polymer electrolyte composition can be improved.

[0025] The gel polymer electrolyte can have improved impregnation, and thus the gel polymer electrolyte can be uniformly impregnated into an electrode assembly.

[0026] By including the gel polymer electrolyte according to one embodiment of the present application, the performance of a secondary battery cell can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 FIG. 1 is a graph showing whether a polymerization inhibitor is dissolved in a gel polymer electrolyte composition according to an example and a comparative example of the present application.

[0028] Figure 2 FIG. 2 is a graph showing whether a polymerization inhibitor is detected in a gel polymer electrolyte composition according to an example and a comparative example of the present application.

[0029] Figure 3 FIG. 3 is a graph showing the amount of a polymerization inhibitor detected in a gel polymer electrolyte composition according to an example of the present application.

[0030] Figure 4 FIG. 4 is a graph showing whether a polymerization occurs in a gel polymer electrolyte composition according to an example and a comparative example of the present application when the gel polymer electrolyte composition is stored at room temperature.

[0031] Figure 5 FIG. 5 is a graph showing whether a polymerization occurs in a gel polymer electrolyte composition according to an example and a comparative example of the present application when the gel polymer electrolyte composition is polymerized at high temperature. BEST MODE FOR CARRYING OUT THE INVENTION

[0032] The gel polymer electrolyte composition according to the present application can include an electrolyte salt, an organic solvent, a polymerizable monomer, a polymerization initiator, and a polymerization inhibitor. In addition, the gel polymer electrolyte composition can further include an additive.

[0033] Electrolyte salt The electrolyte salt serves as a medium for transporting ions within a secondary battery, and can not be particularly limited as long as it is a substance generally used as an electrolyte salt for a secondary battery.

[0034] In an exemplary embodiment, the electrolyte salt can be a lithium salt, and for example, can include LiPF6 + as a cation, and can include at least one selected from the group consisting of F - , Cl - , Br - , BF4 - , I - , NO3 - , N(CN)2 - , ClO4 - , AlO4 -, AlCl4 - , PF6 - , SbF6 - , AsF6 - , BF2C2O4 - , BC4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - as an anion. In one embodiment, the electrolyte salt can include at least one selected from the group consisting of LiPF6, lithium bisperfluoroethanesulfonimide (LiN(SO2C2F5)2, LiBETI), lithium fluorosulfonyl imide (LiN(SO2F)2, LiFSI), lithium (bis)trifluoromethanesulfonimide (LiN(SO2CF3)2, LiTFSI), and lithium difluoro(oxalato) borate (LiDFOB).

[0035] In one embodiment, the electrolyte salt can be included in the gel polymer electrolyte composition at a concentration of about 0.5 M to about 2 M, specifically, at a concentration of about 0.8 M to about 1.5 M. By including the electrolyte salt in the gel polymer electrolyte composition at a concentration in the above range, an optimal corrosion-preventing thin film can be formed on the surface of the electrode, and the resistance caused by lithium ion loss at high rate charge and discharge can be reduced, and due to the increase in lithium ions in the gel polymer electrolyte composition, a higher ion transport property, i.e., ion transference number, of the lithium ions can be ensured, and the spreading resistance of the lithium ions can be reduced, thereby improving the cycle capacity property, ionic conductivity, and rate property.

[0036] Organic solvent The organic solvent is a non-aqueous organic solvent, and is not particularly limited as long as decomposition caused by oxidation reaction or the like during charge and discharge of the secondary battery can be minimized, and desired properties can be exhibited together with the additive.

[0037] In an exemplary embodiment, the organic solvent can include, for example, a carbonate-based organic solvent, an ether-based organic solvent, or an ester-based organic solvent, etc., which can be used alone or in a mixture of two or more.

[0038] In an exemplary embodiment, the carbonate-based organic solvent can include at least one of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent.

[0039] In one embodiment, the cyclic carbonate-based organic solvent can include at least 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, vinyl ethylene carbonate, and fluoroethylene carbonate (FEC). The cyclic carbonate-based organic solvent can include a mixed solvent of ethylene carbonate having a high dielectric constant and propylene carbonate having a relatively low melting point compared to ethylene carbonate.

[0040] In one embodiment, the linear carbonate-based organic solvent is a solvent having low viscosity and low dielectric constant, and can include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate.

[0041] In an exemplary embodiment, the ether-based organic solvent can include any one or a mixture of two or more selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether.

[0042] In an exemplary embodiment, the ester-based organic solvent can include at least one selected from the group consisting of linear ester-based organic solvents and cyclic ester-based organic solvents.

[0043] In one embodiment, the linear ester-based organic solvent can include any one or a mixture of two or more selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0044] In one embodiment, specific examples of the cyclic ester-based organic solvent can include any one or a mixture of two or more selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-hexalactone, σ-valerolactone, and ε-hexalactone.

[0045] Polymerizable monomer The polymerizable monomer can have a polymerizable functional group including at least one group selected from a vinyl group, an epoxy group, an allyl group, an acrylic acid group, a (meth)acrylic acid group, an ether group, and fluorine (F) that can undergo a polymerization reaction, and a phosphate ester group, and can be converted into a gel phase by polymerization or cross-linking. Among them, the acrylic acid group can include an acrylate group, and the (meth)acrylic acid group can include an acrylic acid group and a methacrylic acid group.

[0046] The polymerizable monomer is not particularly limited as long as it is a substance generally used as a monomer for a gel polymer electrolyte.

[0047] In an exemplary embodiment, the polymeric monomer can include three or more of the polymeric functional groups. Specifically, the polymeric monomer can include a phosphate group, an acrylate group, and an ether group. More specifically, the polymeric monomer can include, for example, selected from tetraethylene glycol diacrylate, polyethylene glycol diacrylate (molecular weight of 50 to 20,000), 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxylate tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, poly(ethylene glycol) diglycidyl ether, 1,5-hexadiene diepoxide, glycerol propoxylate triglycidyl ether, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane, 4-vinylcyclohexene dioxide, butyl glycidyl ether, diglycidyl 1,2-cyclohexanedicarboxylate, diglycidyl 1,3-cyclohexanedicarboxylate, diglycidyl 1,4-cyclohexanedicarboxylate, diglycidyl 1,2,3-cyclohexanetricarboxylate, diglycidyl 1,2,5-cyclohexanetricarboxylate, diglycidyl 1,3,5-cyclohexanetricarboxylate, diglycidyl 1,2,4-cyclohexanetricarboxylate, diglycidyl 1,2,3,5-cyclohexanetetracarboxylate, diglycidyl 1,2,3,6-cyclohexanetetracarboxylate, diglycidyl 1,2,4,5-cyclohexanetetracarboxylate, diglycidyl 1,2,4,6-cyclohexanetetracarboxylate, diglycidyl 1,2,3,4-cyclohexanetetracarboxylate, diglycidyl 1,2,3,5-cyclohexanetetracarboxylate, diglycidyl 1,2,3,6-cyclohexanetetracarboxylate, diglycidyl 1,2,4,5-cyclohexanetetracarboxylate, diglycidyl 1,2,4,6-cyclohexanetetracarboxylate, diglycidyl 1,2,3,4-cyclohexanetetracarboxylate, diglycidyl 1,2,3,4,5-cyclohexanepentacarboxylate, diglycidyl 1,2,3,4,6-cyclohexanepentacarboxylate, diglycidyl 1,2,3,5,6-cyclohexanepentacarboxylate, diglycidyl 1,2,4,5,6-cyclohexanepentacarboxylate, diglycidyl 1,2,4,5,6-cyclohexanepentacarboxylate, diglycidyl 1,2,3,4,5,6-cyclohexanehexacarboxylate, and the like.2-cyclohexanedicarboxylate), ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and glycidyl methacrylate.

[0048] In addition, the polymerizable monomer including the phosphoric acid ester group having flame retardancy can impart flame retardancy to the gel polymer electrolyte prepared from the gel polymer electrolyte composition.

[0049] In one embodiment, the polymerizable monomer including the phosphoric acid ester group can include an electron-donating group (EGD).

[0050] In one embodiment, the content of the polymerizable monomer can be about 2% by weight to about 30% by weight, specifically, about 2% by weight to about 20% by weight, more specifically, about 4% by weight to about 10% by weight, based on the total weight of the gel polymer electrolyte composition. By having the content of the polymerizable monomer in the above range, based on the total weight of the gel polymer electrolyte composition, the polymerizable monomer can form a sufficient crosslinking network, and the ionic conductivity of the electrolyte can be improved, thereby the capacity exertion and the capacity retention rate of the secondary battery can be improved.

[0051] Polymerization initiator The polymerization initiator can be a thermal polymerization initiator or a photopolymerization initiator. The polymerization initiator can be decomposed by heat or light to form radicals, and the radicals can initiate the polymerization reaction between the polymerizable monomers.

[0052] In an exemplary embodiment, the polymerization initiator can include organic peroxide compounds or hydroperoxide compounds such as benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, t-butyl peroxypivalate, cumyl hydroperoxide, and hydrogen peroxide; and one or more azo compounds selected from 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methyl butyronitrile), 2,2'-azobis(iso-butyronitrile) (AIBN), and 2,2'-azobisdimethyl-Valeronitrile (AMVN).

[0053] In one embodiment, the polymerization initiator can be decomposed to form radicals at a heat or temperature of about 50°C to about 90°C, and can initiate a polymerization reaction between the polymerizable monomers.

[0054] In one embodiment, the content of the polymerization initiator can be about 0.025% to about 0.3% by weight, based on the total weight of the gel polymer electrolyte composition. When the content of the polymerization initiator exceeds about 0.3% by weight, based on the total weight of the gel polymer electrolyte composition, a polymerization reaction between the polymerizable monomers can be initiated before reaching a curing temperature of the gel polymer electrolyte composition, which can cause the gel polymer electrolyte composition to be cured prematurely. When the content of the polymerization initiator is less than about 0.025% by weight, based on the total weight of the gel polymer electrolyte composition, a polymerization reaction between the polymerizable monomers can not be sufficiently initiated, which can cause the polymerizable monomers to not form a sufficient crosslinked network.

[0055] Polymerization inhibitor The polymerization inhibitor can prevent premature polymerization between the polymerizable monomers. Specifically, the polymerization inhibitor can rapidly react with radicals formed by the polymerization initiator to stabilize the radicals, which can prevent premature polymerization between the polymerizable monomers.

[0056] In an exemplary embodiment, the polymerization inhibitor can include at least one selected from the group consisting of a hydroxyl or alkoxy group-containing aromatic compound, a quinone-based compound, a phenothiazine-based compound, and a nitrosophenyl compound.

[0057] In an exemplary embodiment, the hydroxyl or alkoxy group-containing aromatic compound can include 2 or more hydroxyl groups or 2 or more alkoxy groups.

[0058] In an exemplary embodiment, the hydroxyl or alkoxy group-containing aromatic compound can further include a nitro group or an alkyl group.

[0059] In an exemplary embodiment, the hydroxyl or alkoxy group-containing aromatic compound can include a monocyclic ring or a condensed ring of 2 or more monocyclic rings.

[0060] Specifically, the hydroxyl or alkoxy group-containing aromatic compound can include, for example, at least one selected from the group consisting of 4-methoxyphenol (MEHQ), 4-tert-butylcatechol (TBC), picric acid, tert-butylhydroquinone (TBHQ), hydroquinone, p-methoxyphenol, tert-butylhydroquinone, 6-tert-butyl-2,4-dimethylphenol, 2,6-di-tert-butylphenol, and dibutylhydroxytoluene (BHT).

[0061] Specifically, the quinone-based compound can include, for example, 1,2-benzoquinone or 2-tert-butyl-1,4-benzoquinone, the phenothiazine-based compound can include, for example, phenothiazine, and the nitrosophenyl compound can include, for example, nitrosobenzene.

[0062] In an exemplary embodiment, the content of the polymerization inhibitor can be about 150 ppm or less, specifically, about 5 ppm to about 100 ppm, more specifically, about 10 ppm to about 100 ppm, about 15 ppm to about 80 ppm, about 20 ppm to 80 ppm, or about 20 ppm to about 50 ppm, based on the total weight of the gel polymer electrolyte composition. When the content of the polymerization inhibitor is within the above range, the premature polymerization between the polymerizable monomers can be inhibited, and at the same time, the solubility of the polymerization inhibitor and the solidification of the gel polymer electrolyte composition can be excellent, so that a gelled gel polymer electrolyte having a uniform crosslinking degree and surface, in which a liquid electrolyte is not separated from the gel, can be formed.

[0063] Additives The additive can be included in the gel polymer electrolyte composition to prevent decomposition of the gel polymer electrolyte composition in a high power environment during preparation of the gel polymer electrolyte, to induce negative electrode collapse, and to form a more stable ion conductive thin film on the electrode surface, etc.

[0064] In an exemplary embodiment, the additive can include at least one selected from a sultone-based compound, a sulfite-based compound, a sulfone-based compound, a sulfate-based compound, a halogen-substituted carbonate-based compound, a nitrile-based compound, a cyclic carbonate-based compound, a phosphate-based compound, a borate-based compound, a lithium salt-based compound, and a fluorine-based compound.

[0065] As described above, the polymerizable monomers can be prematurely polymerized by the polymerization initiator. In particular, when the polymerizable monomers include the phosphonate group-containing monomer having flame retardancy, since the phosphonate group-containing monomer includes an electron-donating group, premature polymerization between the polymerizable monomers can be further accelerated, which can occur at room temperature.

[0066] However, in an exemplary embodiment, the gel polymer electrolyte composition includes the polymerization inhibitor, and thus can prevent premature polymerization between the polymerizable monomers at room temperature. Accordingly, the gel polymer electrolyte prepared from the gel polymer electrolyte composition can have flame retardancy while having a uniform crosslinking degree. Thus, storability of the gel polymer electrolyte composition at room temperature can be improved, and processability of the impregnation process of the gel polymer electrolyte composition can be improved. Ultimately, impregnability of the gel polymer electrolyte can be improved, and thus the gel polymer electrolyte can be uniformly impregnated into an electrode assembly, and thus performance of a secondary battery cell can be improved.

[0067] Hereinafter, a preparation process of a gel polymer electrolyte prepared from the gel polymer electrolyte composition will be described. While the process is described, effects of the gel polymer electrolyte composition of the present application by including the polymerization inhibitor will be described in more detail.

[0068] First, the electrolyte salt, the polymerizable monomers, the polymerization inhibitor, and the additive can be dissolved in the organic solvent.

[0069] In one embodiment, the organic solvent is stirred with the electrolyte salt, the polymerizable monomers, the polymerization inhibitor, and the additive at room temperature for about 1 hour or more, and thus the electrolyte salt, the polymerizable monomers, the polymerization inhibitor, and the additive can be dissolved in the organic solvent.

[0070] After that, the polymerization initiator is dissolved in the organic solvent at room temperature, so that the gel polymer electrolyte composition can be prepared.

[0071] After that, the gel polymer electrolyte composition can be stored at room temperature for a certain period of time before being injected into a battery case. Since the gel polymer electrolyte composition contains the polymerization inhibitor, premature polymerization between the polymerizable monomers at room temperature can be prevented, so that it can be stored in a liquid phase without being converted into a gel phase. In one embodiment, the gel polymer electrolyte composition can be stored at a temperature of about 30°C or less for about 24 hours.

[0072] After that, the gel polymer electrolyte composition is injected into a battery case, and then the gel polymer electrolyte composition is impregnated into an electrode assembly including a positive electrode and a negative electrode at room temperature for a certain period of time, so that a gel polymer electrolyte can be prepared. Since the gel polymer electrolyte composition contains the polymerization inhibitor, premature polymerization between the polymerizable monomers at room temperature can be prevented, so that the gel polymer electrolyte can be uniformly impregnated into the electrode assembly. In one embodiment, the impregnation process can be performed at a temperature of about 30°C or less for about 10 hours or more.

[0073] After that, the gel polymer electrolyte composition is cured by increasing the temperature, so that the gel polymer electrolyte can be formed. Since the polymerization inhibitor prevents premature polymerization during the process of storage at room temperature and impregnation into the electrode assembly of the gel polymer electrolyte composition, when the gel polymer electrolyte composition is cured by increasing the temperature, the gel polymer electrolyte having a uniform crosslinking degree can be formed.

[0074] In an exemplary embodiment, the impregnation process can further include a degassing process. The degassing process can remove gas present in the battery case before the gel polymer electrolyte composition is cured.

[0075] Thus, the gel polymer electrolyte can be prepared.

[0076] When the gel polymer electrolyte composition does not include the polymerization inhibitor, the polymerizable monomers can be prematurely polymerized when the gel polymer electrolyte composition is stored at room temperature, thereby possibly causing at least a portion of the gel polymer electrolyte composition to solidify. Thereafter, since the solidified gel polymer electrolyte composition is injected into the battery case, the gel polymer electrolyte composition can be completely solidified before reaching the process temperature and process time in the impregnation process. Thus, a gel polymer electrolyte having a non-uniform degree of crosslinking can be formed, thereby possibly causing the gel polymer electrolyte to be non-uniformly impregnated into the electrode assembly.

[0077] However, in the exemplary embodiment, since the gel polymer electrolyte composition includes the polymerization inhibitor, premature polymerization between the polymerizable monomers can be prevented when the gel polymer electrolyte composition is stored at room temperature. Thus, storability of the gel polymer electrolyte composition can be improved.

[0078] Further, since the uncured gel polymer electrolyte composition is injected into the battery case, the gel polymer electrolyte composition can be solidified at the process temperature and process time in the impregnation process. Thus, a gel polymer electrolyte having a uniform degree of crosslinking can be formed, thereby allowing the gel polymer electrolyte to be uniformly impregnated into the electrode assembly. That is, processability of the impregnation process of the gel polymer electrolyte composition can be improved.

[0079] In addition, the gel polymer electrolyte can include a polymerizable polymer formed by crosslinking the polymerizable monomers, the electrolyte salt, the organic solvent, the polymerization initiator, and the polymerization inhibitor.

[0080] Further, the secondary battery can include the gel polymer electrolyte, and the positive electrode and the negative electrode impregnated with the gel polymer electrolyte.

[0081] The positive electrode is not particularly limited, and the positive electrode can include a lithium-transition metal oxide such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), or lithium nickel oxide (LiNiO2), or a lithium-transition metal composite oxide in which a portion of the transition metal is substituted with another transition metal, as a positive electrode active material.

[0082] For example, the lithium-transition metal oxide can include nickel (Ni), and can further include at least one selected from cobalt (Co) or manganese (Mn). For example, the positive active material can include an NCM-based positive active material; a Mn-rich based positive active material; or a Li rich layered oxides (LLO) / Over Lithiated Oxides / Over-lithiated layered oxide / OLO / LLOs-based positive active material. For example, the lithium-transition metal oxide can have a structure represented by the following Chemical Formula 1 to Chemical Formula 3.

[0083] [Chemical Formula 1] Li a Ni b M 1-b O2 In the Chemical Formula 1, 0.9≤a≤1.2, b≥0.5, and M is at least one of Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Zr. Specifically, in the Chemical Formula 1, it can be 0.95≤a≤1.08, and b can be 0.6 or more, 0.8 or more, more than 0.8, 0.9 or more, or 0.98 or more. Specifically, in the Chemical Formula 1, M can include Co, Mn, or Al, more specifically, M can include Co and Mn, and can further include Al according to selection.

[0084] [Chemical Formula 2] pLi2MnO3·(1-p)Li q JO2 In the Chemical Formula 2, it can be 0

[0085] [Chemical Formula 3] Li 1+x M 1-x O2 In the Chemical Formula 3, 0≤x≤0.4, and M is at least one of Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ni, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Zr. Specifically, in the Chemical Formula 3, M can include Ni, Co, Mn, or Al, more specifically, can include Ni, Co, and Mn, and can further include Al according to selection.

[0086] Further, the positive active material can be a lithium iron phosphate (LFP)-based positive active material represented by the chemical formula LiFePO4.

[0087] Further, the lithium-transition metal oxide can be a secondary particle substantially formed as one particle by assembling or aggregating a plurality of primary particles, or can be in a single particle form. The single particle form can be, for example, a meaning excluding a secondary particle substantially formed as one particle by assembling or aggregating a plurality of primary particles (e.g., more than 10). However, the single particle form does not exclude a single particle in the range of 2 to 10, which is attached or closely adhered to each other to substantially have a whole form (e.g., transformed into a structure of a single particle). In some embodiments, the positive active material can include both a secondary particle form and a single particle form.

[0088] The negative electrode is not particularly limited, and the negative electrode can include a carbon-based active material such as artificial graphite, natural graphite, etc., a silicon oxide (SiO x ; 0 < x < 2), a Si-C composite, a pure Si, etc., a silicon-based active material, lithium metal, a lithium metal alloy, etc., a metal as a negative active material.

[0089] In addition, the lithium secondary battery can be a negative electrode-free secondary battery. That is, it can be a battery in which a negative active material layer is not formed on a negative current collector during battery assembly. When the negative electrode-free lithium secondary battery is initially charged or primary charged, the main positive active material and the sacrificial positive active material are delithiated, lithium ions generated from the positive active material are reduced on the negative current collector, and thus a lithium layer of a lithium metal layer or a solid lithium layer can be formed. DETAILED DESCRIPTION

[0090] Hereinafter, the present application will be described in more detail by examples. The following examples merely show one example of the present application and are not intended to limit the present application.

[0091] Examples 1 to 4 and Comparative Examples 1 to 3 A composition in which LiPF6, ethylene carbonate, and methyl ethyl carbonate are mixed (wherein LiPF6, ethylene carbonate, and methyl ethyl carbonate are 12.3% by weight, 31.5% by weight, and 56.2% by weight, respectively, based on the total weight of LiPF6, ethylene carbonate, and methyl ethyl carbonate) was stirred with a polymerizable monomer and a polymerization inhibitor at room temperature for 2 hours, so that the polymerizable monomer and the polymerization inhibitor were dissolved in the above composition. Thereafter, a polymerization initiator was dissolved at room temperature, thereby preparing a composition for a gel polymer electrolyte.

[0092] 2-[(Dimethoxyphosphoryl)oxy]ethyl acrylate was used as the polymerizable monomer, and the content thereof in the composition for a gel polymer electrolyte was 7.5% by weight.

[0093] Tert-butyl peroxy pivalate was used as the polymerization initiator, and the content thereof in the composition for a gel polymer electrolyte was 1% by weight of the total weight of the polymerizable monomer.

[0094] 4-Methoxyphenol was used as the polymerization inhibitor, and the content thereof in the composition for a gel polymer electrolyte is shown in Table 1 below.

[0095] [Table 1] Whether the polymerization inhibitor was dissolved An organic solvent was stirred with an electrolyte salt, a polymerizable monomer, and a polymerization inhibitor at room temperature (25°C) for 2 hours, so that the electrolyte salt, the polymerizable monomer, and the polymerization inhibitor were dissolved in the organic solvent, and then a polymerization initiator was added to the organic solvent at room temperature. Thereafter, the organic solvent to which the polymerization initiator was added was left to stand at room temperature, whether the polymerization inhibitor was dissolved in the composition for a gel polymer electrolyte was evaluated (see Figure 1 ), and the results thereof are shown in Table 2 below.

[0096] Whether the polymerization inhibitor was detected and the detected amount of the polymerization inhibitor The polymerization inhibitor and the composition for a gel polymer electrolyte of Example 1 to Example 3 and Comparative Example 2 were subjected to high performance liquid chromatography (HPLC) analysis. Whether the polymerization inhibitor was detected and the detected amount of the polymerization inhibitor in the composition for a gel polymer electrolyte were confirmed by HPLC analysis (see Figure 2 and Figure 3 ), and the results thereof are shown in Table 2 below.

[0097] In addition, as to whether the polymerization inhibitor was detected, since the polymerization inhibitor appeared as a peak at 6.413 minutes (min), when the peak area of the polymerization inhibitor was 0.000, it was determined that the polymerization inhibitor was not detected.Figure 2 The peak appeared at a time close to 6.413 minutes, and it was determined that the polymerization inhibitor was detected.

[0098] Further, Figure 3 The detection amounts according to the contents of the added polymerization inhibitors in the gel polymer electrolytes of Example 1, Example 2, and Example 4 are shown in Table 2.

[0099] [Table 2] Whether polymerization occurs at normal temperature (25°C) The gel polymer electrolyte compositions of Example 1 to Example 4 and Comparative Example 1 and Comparative Example 2 were stored at normal temperature (25°C). Whether polymerization of the gel polymer electrolyte compositions occurred was confirmed at 0 hours, 3 hours, 8 hours, and 24 hours (see Figure 4 ), and the results thereof are shown in Table 3 below.

[0100] Whether polymerization occurs at high temperature (70°C) The gel polymer electrolyte compositions of Example 1 to Example 4 and Comparative Example 1 and Comparative Example 2 were polymerized at high temperature (70°C). Whether polymerization of the gel polymer electrolyte compositions occurred was confirmed at 10 minutes and 30 minutes (see Figure 5 ), and the results thereof are shown in Table 3 below.

[0101] [Table 3] From Table 2 and Figure 1 it can be seen that the polymerization inhibitors of Example 1 to Example 4 and Comparative Example 2 are dissolved in the organic solvent, and the polymerization inhibitor of Comparative Example 3 is saturated and swells in the organic solvent. From this, it can be seen that when the content of the polymerization inhibitor in the gel polymer electrolyte composition is 10 ppm to 80 ppm, the polymerization inhibitor is smoothly dissolved in the organic solvent.

[0102] Further, from Table 2 and Figure 2 it can be seen that the gel polymer electrolyte compositions of Example 1 to Example 3 have peaks at a time close to 6.413 minutes, but the gel polymer electrolyte composition of Comparative Example 1 does not have a peak at a time close to 6.413 minutes. From this, it can be seen that the gel polymer electrolyte composition of the present application contains a polymerization inhibitor.

[0103] In addition, from Figure 3 , the higher the content of the added polymerization inhibitor in the gel polymer electrolyte composition, the more the amount of the detected polymerization inhibitor.

[0104] Further, from Table 3 and Figure 4As can be seen, when the gel polymer electrolyte compositions of Examples 1 to 4 and Comparative Examples 1 and 2 were stored at room temperature, the gel polymer electrolyte compositions of Examples 1 to 4 did not polymerize even after 0 hours, 3 hours, 8 hours, and 24 hours. In addition, the gel polymer electrolyte compositions of Comparative Examples 1 and 2 did not polymerize after 0 hours, but polymerized after 3 hours, 8 hours, and 24 hours. As such, when the content of the polymerization inhibitor in the gel polymer electrolyte composition is 20 ppm to 80 ppm, even if the gel polymer electrolyte composition is stored at room temperature for 24 hours, the gel polymer electrolyte composition does not polymerize. That is, it can be seen that the gel polymer electrolyte composition of the present application contains 20 ppm to 80 ppm of the polymerization inhibitor, is stored in a liquid state, and is injected into the battery case.

[0105] In addition, according to Table 3 and Figure 5 As can be seen, when the gel polymer electrolyte compositions of Examples 1 to 4 and Comparative Examples 1 and 2 were polymerized at high temperature, the gel polymer electrolyte compositions of Examples 1 to 4 did not polymerize after 10 minutes, but polymerized after 30 minutes. In addition, it was confirmed that the gel polymer electrolyte compositions of Comparative Examples 1 and 2 polymerized after 10 minutes and 30 minutes.

[0106] As such, when the content of the polymerization inhibitor in the gel polymer electrolyte composition is 20 ppm to 80 ppm, even if the gel polymer electrolyte composition is polymerized at high temperature for 10 minutes, the gel polymer electrolyte composition does not polymerize, but when the gel polymer electrolyte composition is polymerized at high temperature for 30 minutes, the gel polymer electrolyte composition polymerizes.

[0107] That is, it can be confirmed that, since the impregnation process of the present application is performed for at least 10 minutes or more, and the gel polymer electrolyte composition contains 20 ppm to 80 ppm of the polymerization inhibitor, the gel polymer electrolyte does not prematurely polymerize, and when cured, the gel polymer electrolyte having a uniform crosslinking degree can be formed. In addition, it can be seen that even if the gel polymer electrolyte composition contains 20 ppm to 80 ppm of the polymerization inhibitor, the gel polymer electrolyte composition does not permanently polymerize.

[0108] Although the embodiments of the present application have been described in detail above, this is merely exemplary and those skilled in the art will understand that various modifications and other embodiments can be made thereto. Accordingly, the technical scope of the present application should be determined by the technical idea of the claims.

[0109] The specific embodiments described in the examples are only one example and do not limit the scope of the examples in any way. Furthermore, unless otherwise specified, the constituent elements of the application are not essential to the application.

[0110] In the specification of the examples, particularly in the claims, the use of the term "said" and similar referential terms can correspond to both the singular and the plural. Furthermore, when a range is recited in the examples, the disclosure applies to each value belonging to the above-mentioned range (unless otherwise recited to the contrary), which is equivalent to reciting each value constituting the above-mentioned range in the detailed description. Finally, as to the steps constituting the method according to the examples, unless the order is explicitly recited or otherwise recited to the contrary, the above-mentioned steps can be performed in an appropriate order. The examples are not necessarily limited to the recited order of the above-mentioned steps. In the examples, the use of all examples or exemplary terms (e.g., etc.) is only intended to detail the examples, and the scope of the examples is not limited by the above-mentioned examples or exemplary terms unless otherwise defined in the claims. Furthermore, those skilled in the art will understand that various modifications, combinations, and changes can be made within the scope of the claims or their equivalents according to design conditions and factors.

Claims

1. A composition for a gel polymer electrolyte, comprising an electrolyte salt, an organic solvent, a polymerizable monomer, a polymerization initiator, and a polymerization inhibitor.

2. The gel polymer electrolyte composition according to claim 1, wherein, The polymerization inhibitor includes at least one selected from the group consisting of a hydroxyl or alkoxy-containing aromatic compound, a quinone-based compound, a phenothiazine-based compound, and a nitrosophenyl compound.

3. The gel polymer electrolyte composition according to claim 2, wherein, The hydroxyl or alkoxy-containing aromatic compound contains 2 or more hydroxyl groups or contains 2 or more alkoxy groups.

4. The gel polymer electrolyte composition according to claim 2, wherein, The hydroxyl or alkoxy-containing aromatic compound further contains a nitro group or an alkyl group.

5. The gel polymer electrolyte composition according to claim 2, wherein, The hydroxyl or alkoxy-containing aromatic compound contains a monocyclic ring or a condensed ring of 2 or more monocyclic rings.

6. The gel polymer electrolyte composition according to claim 1, wherein, The polymerization inhibitor includes at least one selected from the group consisting of 4-methoxyphenol (MEHQ), 1,2-benzoquinone, 4-tert-butylcatechol (TBC), nitrosobenzene, picric acid, tert-butylhydroquinone (TBHQ), hydroquinone, p-methoxyphenol, phenothiazine, tert-butylhydroquinone, 2,6-di-tert-butyl-p-cresol, 2-tert-butyl-1,4-benzoquinone, 6-tert-butyl-2,4-dimethylphenol, 2,6-di-tert-butylphenol, 6-tert-butyl-2,4-dimethylphenol, and 2,6-di-tert-butylphenol.

7. The gel polymer electrolyte composition according to claim 1, wherein, The content of the polymerization inhibitor is 150 ppm or less, based on the total weight of the composition for a gel polymer electrolyte.

8. The gel polymer electrolyte composition according to claim 1, wherein, The polymerizable monomer has a polymerizable functional group containing at least one selected from the group consisting of a vinyl group, an epoxy group, an allyl group, an acrylic acid group, a (meth)acrylic acid group, an ether group, and fluorine (F), and a phosphate ester group.

9. The gel polymer electrolyte composition according to claim 8, wherein, The polymerizable monomer contains 3 or more of the polymerizable functional groups.

10. The gel polymer electrolyte composition according to claim 8, wherein, The polymerizable monomer contains a phosphate ester group, an acrylic ester group, and an ether group.

11. The gel polymer electrolyte composition according to claim 8, wherein, The polymerizable monomer containing the phosphate ester group contains an electron-donating group (EGD).

12. A gel polymer electrolyte comprising a polymerizable polymer, an electrolyte salt, an organic solvent, a polymerization initiator, and a polymerization inhibitor.

13. The gel polymer electrolyte of claim 12, wherein, The polymerization inhibitor includes at least one selected from the group consisting of a hydroxyl or alkoxy-containing aromatic compound, a quinone-based compound, a phenothiazine-based compound, and a nitrosophenyl compound.

14. The gel polymer electrolyte of claim 12, wherein, The polymerization inhibitor includes at least one selected from the group consisting of 4-methoxyphenol (MEHQ), 1,2-benzoquinone, 4-tert-butylcatechol (TBC), nitrosobenzene, picric acid, tert-butylhydroquinone (TBHQ), hydroquinone, p-methoxyphenol, phenothiazine, tert-butylhydroquinone, 2,6-di-tert-butyl-p-cresol, 2-tert-butyl-1,4-benzoquinone, 6-tert-butyl-2,4-dimethylphenol, 2,6-di-tert-butylphenol, 6-tert-butyl-2,4-dimethylphenol, and 2,6-di-tert-butylphenol.

15. A lithium secondary battery comprising: The gel polymer electrolyte according to any one of claims 12 to 14; and a positive electrode and a negative electrode impregnated with the gel polymer electrolyte.

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