Composition for forming gel polymer electrolyte, gel polymer electrolyte, and lithium secondary battery containing the gel polymer electrolyte

Abstract

The present invention provides a gel polymer electrolyte formation composition comprising a lithium salt, an organic solvent, and a crosslinking compound represented by the following chemical formula 1. [Chemical formula 1] JPEG2026513848000016.jpg37170 In the above chemical formula 1, L1, L2, L3, and L4 are independently selected from directly bonded or C1-C3 alkylene groups, L5 and L6 are independently selected from C1-C20 alkylene groups in which one or more methylene groups may be substituted with ether groups and one or more hydrogens are substituted with fluorine, and R1 and R2 are independently selected from hydrogen, C1-C3 alkyl groups, or halogens.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0124966 dated September 19, 2023, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a composition for forming a gel polymer electrolyte, a gel polymer electrolyte, and a lithium secondary battery containing the gel polymer electrolyte. [Background technology]

[0003] With the advancements in mobile electronic devices, electric vehicles (EVs), and grid-scale energy storage systems (ESS), the demand for high-energy-density lithium-ion batteries is rapidly increasing.

[0004] Generally, lithium-ion batteries consist of a positive electrode made of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte that acts as a medium for transferring lithium ions, and materials such as a separator.

[0005] The aforementioned lithium secondary battery uses a liquid electrolyte with high ionic conductivity and excellent electrochemical properties. However, this liquid electrolyte is highly flammable, highly reactive with electrode materials, and can cause side reactions, leading to leakage and other problems. Therefore, under abnormal operating conditions, it may cause fires or explosions.

[0006] Therefore, in recent years, research has attracted attention on developing more stable electrolytes to replace liquid electrolytes in order to improve the stability of lithium-ion batteries. For example, ionic liquid electrolytes, solid electrolytes, and gel polymer electrolytes have been proposed.

[0007] While the aforementioned ionic liquid electrolyte exhibits excellent thermal and oxidative stability, it is unstable on the surface of the negative electrode, has high viscosity resulting in poor wetting properties towards polyolefin separators, and is expensive. On the other hand, while the aforementioned solid electrolyte improves battery stability by eliminating flammable organic solvents, it suffers from a decrease in ionic conductivity around the electrolyte and a deterioration in lifespan due to increased interfacial resistance between the solid electrolyte and the electrode.

[0008] On the other hand, the gel polymer electrolyte is an electrolyte system in which a liquid electrolyte is encapsulated and impregnated within a polymer structure, and has the advantages of having high structural, thermal, and mechanical stability even over time, ensuring relatively high ionic conductivity, and having reasonable manufacturing costs.

[0009] In this case, the gel polymer electrolyte can be classified into physically crosslinked gel polymer electrolytes that form a polymer structure through the physical bonding of polymers, and chemically crosslinked gel polymer electrolytes that form a polymer structure through the chemical reaction of reactive oligomers or crosslinking agents. Since the bonding force of the physically crosslinked gel polymer electrolyte may weaken over time, the chemically crosslinked gel polymer electrolyte that forms a polymer structure through chemical bonding has higher structural, thermal, and mechanical stability.

[0010] However, the aforementioned chemically crosslinked gel polymer electrolyte still suffers from problems such as leakage, ignition, and explosion due to the large amount of liquid electrolyte contained within.

[0011] Therefore, there is an urgent need to develop gel polymer electrolytes that can improve all aspects of lithium secondary batteries, including stability and lifespan. [Overview of the project] [Problems that the invention aims to solve]

[0012] One objective of the present invention is to provide a gel polymer electrolyte forming composition that has excellent oxidation stability and flame retardancy, is effective in suppressing the amount of heat generated by electrodes, and can improve both the safety and lifespan performance of lithium secondary batteries.

[0013] Another objective of the present invention is to provide a gel polymer electrolyte that has excellent oxidation stability and flame retardancy, is effective in suppressing the amount of heat generated by electrodes, and can improve both the safety and lifespan performance of lithium secondary batteries.

[0014] Another object of the present invention is to provide a lithium secondary battery containing the aforementioned gel polymer electrolyte. [Means for solving the problem]

[0015] [1] One aspect of the present invention provides a composition for forming a gel polymer electrolyte, comprising a lithium salt, an organic solvent, and a crosslinking compound represented by the following chemical formula 1.

[0016] [Chemical formula 1] [ka]

[0017] In the above chemical formula 1, L1, L2, L3, and L4 are independently selected from directly bonded or C1-C3 alkylene groups, L5 and L6 are independently selected from C1-C20 alkylene groups in which one or more methylene groups may be substituted with ether groups and one or more hydrogens are substituted with fluorine, and R1 and R2 are independently selected from hydrogen, C1-C3 alkyl groups, or halogens.

[0018] [2] One aspect of the present invention provides the gel polymer electrolyte formation composition described in [1], further comprising a polymerization initiator.

[0019] [3] One aspect of the present invention provides a gel polymer electrolyte forming composition according to either [1] or [2], wherein the molecular weight of the crosslinked compound is 700 g / mol to 2,000 g / mol.

[0020] [4] One aspect of the present invention provides a gel polymer electrolyte forming composition according to any one of [1] to [3] above, wherein the crosslinking compound is contained in an amount of 1% to 30% by weight based on the total weight of the gel polymer electrolyte forming composition.

[0021] [5] One aspect of the present invention provides a gel polymer electrolyte forming composition according to any one of [1] to [4], wherein L1, L2, L3, and L4 in the chemical formula 1 are independently selected from directly bonded or methylene groups.

[0022] [6] One aspect of the present invention provides a gel polymer electrolyte forming composition according to any one of [1] to [5] above, wherein L1, L2, L3, and L4 in the chemical formula 1 are each methylene groups.

[0023] [7] One aspect of the present invention provides a gel polymer electrolyte forming composition according to any one of [1] to [6] above, wherein L5 and L6 are each independently represented by the following chemical formula 2.

[0024] [Chemical formula 2] *-[(CH2) n -(CF2) m -(CH2) p -(O) q -(CH2) r -(CF2) s -(CH2) t ] u -*

[0025] In Chemical Formula 2, n, m, p, r, s, and t are each an integer of 0 or more, q is 0 or 1, m + s is an integer of 1 or more, u is an integer of 1 or more, and the product of (n + m + p + q + r + s + t) and u is an integer of 1 to 20. However, when q is 1, n + m + p is an integer of 1 or more, and r + s + t is an integer of 1 or more.

[0026] [8] One aspect of the present invention provides a composition for forming a gel polymer electrolyte according to any one of [1] to [7], wherein the crosslinked compound represented by Chemical Formula 1 includes a crosslinked compound represented by the following Chemical Formula 1-1.

[0027] [Chemical Formula 1-1] [Chemical Structure]

[0028] [9] One aspect of the present invention provides a composition for forming a gel polymer electrolyte according to any one of [1] to [8], wherein the lithium salt includes at least one selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 , LiBOB (LiB(C2O4)2), LiCF3SO3, LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, and LiBETI (LiN(SO2CF2CF3)2).

[0029]

[10] One aspect of the present invention provides a composition for forming a gel polymer electrolyte according to any one of [1] to [9], wherein the organic solvent includes at least one selected from the group consisting of carbonate solvents, ester solvents, ether solvents, ketone solvents, aromatic hydrocarbon solvents, phosphate solvents, sulfone solvents, nitrile solvents, and ionic liquids.

[0030]

[11] One aspect of the present invention provides a gel polymer electrolyte forming composition according to any one of [1] to

[10] , further comprising the additive, wherein the additive comprises one or more selected from the group consisting of sultone compounds, halogen-substituted carbonate compounds, nitrile compounds, cyclic carbonate compounds, sulfite compounds, sulfone compounds, sulfate compounds, phosphate or phosphite compounds, borate compounds, and lithium salt compounds.

[0031]

[12] One aspect of the present invention provides a gel polymer electrolyte forming composition according to any one of [1] to

[11] , wherein the additive comprises a halogen-substituted carbonate compound, and the halogen-substituted carbonate compound is fluoroethylene carbonate.

[0032]

[13] One aspect of the present invention provides a gel polymer electrolyte comprising a lithium salt, an organic solvent, and a polymer matrix formed by a crosslinking reaction of a crosslinked compound represented by the following chemical formula 1.

[0033] [Chemical formula 1] [ka]

[0034] In the above chemical formula 1, L1, L2, L3, and L4 are independently selected from directly bonded or C1-C3 alkylene groups, L5 and L6 are independently selected from C1-C20 alkylene groups in which one or more methylene groups may be substituted with ether groups and one or more hydrogens are substituted with fluorine, and R1 and R2 are independently selected from hydrogen, C1-C3 alkyl groups, or halogens.

[0035]

[14] One aspect of the present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and the gel polymer electrolyte described in

[13] . [Effects of the Invention]

[0036] A gel polymer electrolyte forming composition according to one aspect of the present invention is characterized by containing a crosslinking compound of a specific chemical formula. Since the crosslinking compound contains a fluorine group and a spirocyclic diphosphate group, the gel polymer electrolyte formed by the crosslinking reaction of the crosslinking compound can have excellent oxidation stability and flame retardancy, and has an excellent effect in suppressing the amount of heat generated by the electrodes. Therefore, a lithium secondary battery containing the gel polymer electrolyte forming composition or the gel polymer electrolyte can not only prevent leakage of organic solvents and short circuits in the battery, but also have excellent safety and lifespan performance. [Brief explanation of the drawing]

[0037] [Figure 1] This is a schematic diagram illustrating the synthesis process of the crosslinked compound related to Production Example 1. [Figure 2] These are the FT-IR spectral results of fluorinated ether monoacrylate (PFE-mono AC) and spirocyclic pentaerythritol diphosphate perfluorinated ether acrylate (SPDFA) prepared by steps 2 and 3 of Production Example 1. [Figure 3] This is the 1H NMR spectrum result of spirocyclic pentaerythritol bisphosphorate diphosphoryl chloride (SPDPC) produced by step 1 of production example 1. [Figure 4] This is the 1H NMR spectrum result of spirocyclic pentaerythritol diphosphate perfluorinated ether acrylate (SPDFA) prepared by step 3 of Production Example 1. [Figure 5] These are the FT-IR spectral analysis results for Example 1 and Example 2. [Figure 6] These are the measurement results of the ionic conductivity of the gel polymer electrolyte of Example 2 and the liquid electrolyte of Comparative Example 1, as measured by temperature. [Figure 7]This graph shows the current values ​​measured by linear sweep voltammetry (LSV) for the liquid electrolyte of Comparative Example 1 and the gel polymer electrolytes of Comparative Examples 4, 6, and 8, at an applied voltage (3.0~6.0V). [Figure 8] These are the charge-discharge curves for the lithium secondary battery of Example 3 after the 1st, 10th, 30th, 50th, 100th, 200th, and 300th cycles. [Figure 9] This graph shows the change in discharge capacity of the lithium secondary battery in Example 3 due to the cycle. [Figure 10] This photograph shows the results of the combustion test of the liquid electrolyte in Comparative Example 1 before (left) and after (right) the combustion test. [Figure 11] This photograph shows the results of the gel polymer electrolyte in Example 2 before (left) and after (right) the combustion test. [Figure 12] This photograph shows the results before (left) and after (right) storage of a polyethylene separator that is not impregnated with a gel polymer electrolyte according to one aspect of the present invention, when stored at 140°C. [Figure 13] This photograph shows the results before (left) and after (right) storage of a polyethylene separator impregnated with a gel polymer electrolyte according to one aspect of the present invention when stored at 140°C. [Figure 14] This graph shows the measured battery voltage over time when lithium secondary batteries from Example 3 and Comparative Example 2 were stored in a hot box at 140°C. [Figure 15] This graph shows the amount of heat generated due to the temperature of the negative electrode in the lithium secondary batteries of Example 3 and Comparative Example 2. [Figure 16] This graph shows the amount of heat generated due to the temperature of the positive electrode in the lithium secondary batteries of Example 3 and Comparative Example 2. [Modes for carrying out the invention]

[0038] The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0039] In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the presence of implemented features, figures, steps, components, or combinations thereof, and should be understood not to preemptively exclude the presence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0040] On the other hand, before describing the present invention, unless otherwise specifically mentioned in the present invention, "*" means a connected portion (bonding site) between identical or different atoms or the terminal parts of a chemical formula.

[0041] Furthermore, in this specification, when "a to b carbon atoms" is mentioned, "a" and "b" refer to the number of carbon atoms contained in a specific functional group. That is, the functional group may contain "a" to "b" carbon atoms. For example, "alkyl group with 1 to 5 carbon atoms" means alkyl groups containing 1 to 5 carbon atoms, i.e., CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2CH2-, (CH3)2CHCH2CH2-, etc.

[0042] Furthermore, in this specification, alkyl groups may be substituted or not. Unless otherwise defined, "substituted" means that at least one hydrogen bonded to a carbon is replaced by an element other than hydrogen, for example, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, a cycloalkynyl group having 3 to 12 carbon atoms, a heterocycloalkyl group having 3 to 12 carbon atoms, a heterocycloalkenyl group having 3 to 12 carbon atoms, a heterocycloalkynyl group having 2 to 12 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, a halogen atom, a fluoroalkyl group having 1 to 20 carbon atoms, a nitro group having 6 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a heteroaryl group having 2 to 20 carbon atoms, a haloaryl group having 6 to 20 carbon atoms, etc.

[0043] One embodiment of the present invention will be described in detail below.

[0044] Composition for forming gel polymer electrolytes One aspect of the present invention provides a composition for forming gel polymer electrolytes.

[0045] Specifically, the gel polymer electrolyte forming composition is characterized by comprising a lithium salt, an organic solvent, and a crosslinking compound represented by the following chemical formula 1.

[0046] [Chemical formula 1] [ka]

[0047] In the above chemical formula 1, L1, L2, L3, and L4 are independently selected from directly bonded or C1-C3 alkylene groups, L5 and L6 are independently selected from C1-C20 alkylene groups in which one or more methylene groups may be substituted with ether groups and one or more hydrogens are substituted with fluorine, and R1 and R2 are independently selected from hydrogen, C1-C3 alkyl groups, or halogens.

[0048] 1) Lithium salt In one aspect of the present invention, various lithium salts commonly used as electrolytes for lithium secondary batteries can be used without limitation. For example, the lithium salt may contain Li as a cation. + It includes, as an anion, F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - ClO4 - AlO4 - AlCl4 - PF6 - SbF6 - AsF6 - B 10 Cl 10 - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - , C4F9SO3 - CF3CF2SO3 - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - CH3SO3 - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - , and (CF3CF2SO2)2N - It may include at least one selected from the group consisting of the following.

[0049] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 The lithium salt may include at least one selected from the group consisting of LiBOB(LiB(C2O4)2), LiCF3SO3, LiFSI(LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, and LiBETI(LiN(SO2CF2CF3)2). Specifically, the lithium salt may include at least one selected from the group consisting of LiBF4, LiClO4, LiPF6, LiBOB(LiB(C2O4)2), LiCF3SO3, LiTFSI(LiN(SO2CF3)2), LiFSI((LiN(SO2F)2), and LiBETI(LiN(SO2CF2CF3)2).

[0050] The lithium salt may be included in the non-aqueous electrolyte at a concentration of 0.5 M to 5 M, specifically, 0.8 M to 4 M, and more specifically, 0.8 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the lithium ion transport fraction (Li + The transference number and the degree of lithium ion dissociation are improved, which can enhance the battery's output characteristics.

[0051] 2) Organic solvents The aforementioned organic solvent is not particularly limited as long as it is a non-aqueous solvent commonly used in lithium secondary batteries, and its decomposition due to oxidation reactions during the charging and discharging process of the secondary battery is minimized.

[0052] The organic solvent may include at least one selected from the group consisting of carbonate solvents, ester solvents, ether solvents, ketone solvents, aromatic hydrocarbon solvents, phosphate solvents, sulfone solvents, nitrile solvents, and ionic liquids. Specifically, the organic solvent may include at least one selected from the group consisting of carbonate solvents and ester solvents, and more specifically, a carbonate solvent.

[0053] If the organic solvent includes a carbonate-based solvent, the carbonate-based solvent may include a cyclic carbonate-based solvent, a linear carbonate-based solvent, or a mixture thereof.

[0054] The cyclic carbonate solvent is a highly viscous organic solvent with a high dielectric constant that readily dissociates lithium salts in electrolytes. Specifically, it may contain 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, fluoroethylene carbonate, and vinylene carbonate. More specifically, it may contain ethylene carbonate.

[0055] Furthermore, the linear carbonate solvent is an organic solvent having low viscosity and low dielectric constant, and may specifically 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, and more specifically, may include ethyl methyl carbonate (EMC).

[0056] The organic solvent may be a mixture of a cyclic carbonate solvent and a linear carbonate solvent. In this case, the cyclic carbonate solvent and the linear carbonate solvent may be mixed in a volume ratio of 10:90 to 40:60, specifically, in a volume ratio of 15:85 to 35:65. When the mixing ratio of the cyclic carbonate solvent and the linear carbonate solvent satisfies the above range, both high dielectric constant and low viscosity characteristics can be achieved, resulting in excellent ionic conductivity.

[0057] On the other hand, linear ester solvents and cyclic ester solvents may be used as ester solvents. Specifically, the linear ester solvent may include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate. Specifically, the cyclic ester solvent may include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0058] The ether-based solvent can be any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more of these, but is not limited to these.

[0059] The nitrile solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited to these.

[0060] The ionic liquid may contain one or more selected from the group consisting of diethylmethylammonium trifluoromethanesulfonate, dimethylpropylammonium trifluoromethanesulfonate, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, N-methyl-N-propylpiperidium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidium bis(trifluoromethanesulfonyl)imide, and methylpropylpiperidium trifluoromethanesulfonylimide.

[0061] Cyclohexanone may be used as the aforementioned ketone solvent.

[0062] Specific examples of the aforementioned aromatic hydrocarbon solvents include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, and toluene. The following may be selected from the group consisting of fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

[0063] The sulfone-based solvent may be at least one selected from the group consisting of dimethyl sulfone, diethyl sulfone, ethylmethyl sulfone, dipropyl sulfone, dibutyl sulfone, diphenyl sulfone, and dimethyl sulfoxide.

[0064] The phosphate solvent may be at least one selected from the group consisting of trimethyl phosphate, triethyl phosphate, tris(2-chloroethyl) phosphate, tris(2,2,2-trifluoroethyl) phosphate, tripropyl phosphate, triisopropyl phosphate, tributyl phosphate, trihexyl phosphate, triphenyl phosphate, tritlyl phosphate, methyl ethylene phosphate, and ethyl ethylene phosphate.

[0065] 3) Crosslinked compounds represented by chemical formula 1 The aforementioned crosslinking compound is characterized by being represented by the following chemical formula 1.

[0066] [Chemical formula 1] [ka]

[0067] In the above chemical formula 1, L1, L2, L3, and L4 are independently selected from directly bonded or C1-C3 alkylene groups, L5 and L6 are independently selected from C1-C20 alkylene groups in which one or more methylene groups may be substituted with ether groups and one or more hydrogens are substituted with fluorine, and R1 and R2 are independently selected from hydrogen, C1-C3 alkyl groups, or halogens.

[0068] The crosslinking compound contained in the gel polymer electrolyte forming composition is characterized in that acrylate groups are bonded to both ends of a spirocyclic diphosphate matrix, and fluorine-substituted linker groups (L5 and L6) are present between the spirocyclic diphosphate matrix and the acrylate groups. The polymer matrix formed by the crosslinking reaction of the crosslinking compound can have excellent oxidation stability and flame retardancy, thus enabling thermal safety, prevention of ignition or explosion, and excellent lifespan performance of lithium secondary batteries to which the gel polymer electrolyte is applied.

[0069] Specifically, the spirocyclic diphosphate matrix can vaporize upon heating to form radicals, and these radicals can scavenge OH radicals and H radicals, which are causes of battery ignition, thus effectively preventing ignition and improving flame retardancy. However, the spirocyclic diphosphate has poor oxidation stability, and stability becomes particularly problematic at high voltages, where it easily undergoes ring opening. This problem of reduced oxidation stability of the spirocyclic diphosphate, along with the failure to exhibit the aforementioned flame retardant effect, contributes to a decrease in the lifespan of lithium secondary batteries.

[0070] To solve these problems, a crosslinked compound according to one aspect of the present invention is characterized by the presence of fluorine-substituted linker groups (L5 and L6) between the spirocyclic diphosphate matrix and the acrylate group. The increase in electronegativity due to the fluorine-substituted linker groups significantly prevents the decomposition and ring-opening of the spirocyclic diphosphate, so that the crosslinked compound or the polymer matrix formed by the crosslinking reaction can exhibit excellent oxidation stability and flame retardancy. As a result, lithium secondary batteries containing the gel polymer electrolyte forming composition or a gel polymer electrolyte manufactured therefrom can exhibit both excellent safety and long lifespan.

[0071] In the above chemical formula 1, L1, L2, L3, and L4 may be independently selected from directly bonded or C1-C3 alkylene groups, specifically independently of each other, being directly bonded or methylene groups (-CH2-), and more specifically, being methylene groups from the viewpoint of improving the structural stability of the spirocyclic diphosphate.

[0072] In the aforementioned chemical formula 1, L5 and L6 are alkylene groups having 1 to 20 carbon atoms, in which one or more hydrogen atoms are substituted with fluorine. In the aforementioned chemical formula 1, L5 and L6 can function as linker groups that bond the spirocyclic diphosphate and the acrylate. Furthermore, L5 and L6 are alkylene groups having 1 to 20 carbon atoms, in which one or more hydrogen atoms are substituted with fluorine, and they have excellent electronegativity, which can prevent ring opening or decomposition of adjacent spirocyclic diphosphate rings and improve oxidation stability.

[0073] L5 and L6 may be, independently of each other, alkylene groups having 1 to 20 carbon atoms in which one or more hydrogen atoms are substituted with fluorine, more specifically, alkylene groups having 1 to 10 carbon atoms in which one or more hydrogen atoms are substituted with fluorine, or more specifically, alkylene groups having 5 to 10 carbon atoms in which one or more hydrogen atoms are substituted with fluorine. When they are within the above range, the structural stability of the crosslinked compound is improved, and the effect of preventing ring opening or decomposition of the spirocyclic diphosphate ring can be further improved.

[0074] Furthermore, L5 and L6 may independently have one or more methylene groups (or difluoromethylene groups) substituted with ether groups (-O-). Specifically, L5 and L6 may independently have one or more methylene groups substituted with ether groups or not.

[0075] L5 and L6 are not particularly limited and may be alkylene groups having 1 to 20 carbon atoms in which one or more hydrogen atoms are substituted with fluorine, independently of each other. For example, L5 and L6 may each be independently represented by the following chemical formula 2.

[0076] [Chemical formula 2] *-[(CH2) n -(CF2) m -(CH2) p -(O) q -(CH2) r -(CF2) s -(CH2) t ] u -*

[0077] In the above chemical formula 2, n, m, p, r, s, and t are each integers greater than or equal to 0, q is 0 or 1, m+s is an integer greater than or equal to 1, u is an integer greater than or equal to 1, and the product of (n+m+p+q+r+s+t) and u is an integer between 1 and 20, provided that when q is 1, n+m+p is an integer greater than or equal to 1 and r+s+t is an integer greater than or equal to 1.

[0078] In the chemical formula 2 above, when u is 2 or more, the units n, m, p, r, s, and t may be the same or different from each other.

[0079] In the above chemical formula 2, the product of (n+m+p+q+r+s+t) and u may be an integer between 1 and 20, more specifically an integer between 1 and 10, and more specifically an integer between 5 and 10.

[0080] Specifically, the crosslinking compound represented by chemical formula 1 may include the crosslinking compound represented by the following chemical formula 1-1.

[0081] [Chemical formula 1-1] [ka]

[0082] The molecular weight of the crosslinked compound may be between 700 g / mol and 2,000 g / mol, specifically between 850 g / mol and 1,200 g / mol.

[0083] The molecular weight can be measured using methods such as end-group determination, which involves quantitatively analyzing the functional groups at the ends of molecular chains to determine the molecular weight; comprehensive methods using physical properties such as osmotic pressure, vapor pressure depression, boiling point elevation, and freezing point depression (e.g., membrane osmosis method, vapor pressure osmosis method); light scattering, which uses the scattering of light; ultracentrifugation, which measures the molecular weight by analyzing the sedimentation velocity or concentration distribution after centrifuging a polymer solution; viscosity, which uses the viscosity of the polymer solution; and gel permeation chromatography (GPC) using high-performance liquid chromatography (HPLC).

[0084] The crosslinking compound may be present in an amount of 1% to 30% by weight based on the total weight of the gel polymer electrolyte forming composition. Specifically, the content of the crosslinking compound may be 1% or more by weight, 2% or more by weight, 3% or more by weight, 4% or more by weight, 5% or more by weight, 6% or more by weight, 7% or more by weight, or 8% or more by weight based on the total weight of the gel polymer electrolyte forming composition. The content of the crosslinking compound may be 30% or less by weight, 25% or less by weight, 20% or less by weight, 15% or less by weight, 12% or less by weight, or 11% or less by weight based on the total weight of the gel polymer electrolyte forming composition. More specifically, the crosslinking compound may be 3% to 30% by weight, 5% to 30% by weight, 5% to 25% by weight, or 8% to 15% by weight based on the total weight of the gel polymer electrolyte forming composition. When the conditions are within the above range, the oxidative stability and flame retardancy of the gel polymer electrolyte-forming composition or gel polymer electrolyte are exhibited at an excellent level, and it is preferable that an increase in resistance and a decrease in ionic conductivity due to excessive addition of crosslinking compounds can be prevented.

[0085] 4) Polymerization initiator The aforementioned gel polymer electrolyte formation composition may further contain a polymerization initiator.

[0086] As the polymerization initiator, any conventional thermal polymerization initiator known in the field can be used. Specifically, the polymerization initiators are diisobutyl peroxide, t-amyl peroxydicarbonate, di(4-tert-butylcyclohexyl) peroxydicarbonate, diethylhexyl peroxydicarbonate, dibutyl peroxydicarbonate, diisopropyl peroxydicarbonate, dicetyl peroxydicarbonate, dimyristyl peroxydicarbonate, tert-butyl peroxypivalate, dilauroyl peroxide, and didecanoyl peroxide. peroxide), 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, tert-amylperoxy-2-ethylhexanoate, dibenzoyl peroxide, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxyethyl acetate, tert-butylperoxyisobutylate, and 1,It may contain at least one selected from the group consisting of 4-di(t-butylperoxycarbo)cyclohexane (1,4-di(tert-butylperoxycarbo)cyclohexane), specifically a liquid thermal initiator with a low starting temperature and low gas generation during the initial reaction, such as t-butylperoxypivalate.

[0087] The polymerization initiator is readily soluble in organic solvents and can decompose upon heating at 30°C to 80°C to form radicals. These radicals can accelerate the crosslinking reaction of the crosslinked compound, thereby forming a polymer matrix (network) with ensured mechanical strength and ionic conductivity.

[0088] The polymerization initiator may be included in the gel polymer electrolyte forming composition in an amount of 0.01 to 20 parts by weight, specifically 0.1 to 10 parts by weight, based on 100 parts by weight of the crosslinking compound. When the polymerization initiator is included within the above range, the gel polymer conversion rate can be increased to ensure the properties of the gel polymer electrolyte, pregel reaction can be prevented, and the wettability of the electrolyte to the electrode can be improved.

[0089] 5) Additives Furthermore, the gel polymer electrolyte forming composition according to one embodiment of the present invention may further contain additives that can form a more stable ionic conductivity film on the electrode surface, if necessary, in order to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and swelling improvement effect during high-temperature storage.

[0090] The additive may include one or more compounds selected from the group consisting of sultone compounds, halogen-substituted carbonate compounds, nitrile compounds, cyclic carbonate compounds, sulfite compounds, sulfone compounds, sulfate compounds, phosphate or phosphite compounds, borate compounds, and lithium salt compounds.

[0091] The sultone compound mentioned above includes at least one compound selected from the group consisting of 1,3-propanesultone (PS), 1,4-butanesultone, ethensultone, 1,3-propensultone (PRS), 1,4-butensultone, and 1-methyl-1,3-propensultone, and may be included in an amount of 5% by weight or less based on the total weight of the polymer electrolyte precursor composition. If the content of the sultone compound in the polymer electrolyte precursor composition exceeds 5% by weight, an excessively thick film may be formed on the electrode surface, potentially causing increased resistance and output degradation. Furthermore, an excessive amount of additives in the polymer electrolyte precursor composition may increase resistance and degrade the output characteristics.

[0092] Furthermore, examples of halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC), which may be included in an amount of 5% by weight or less based on the total weight of the polymer electrolyte precursor composition. If the content of halogen-substituted carbonate compounds in the polymer electrolyte precursor composition exceeds 5% by weight, the cell swelling performance may deteriorate.

[0093] Furthermore, the nitrile compounds include at least one compound selected from the group consisting of succinonitrile (SN), adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0094] The nitrile compound may be present in an amount of 8% by weight or less based on the total weight of the polymer electrolyte precursor composition. If the total weight of the nitrile compound in the polymer electrolyte precursor composition exceeds 8% by weight, the resistance may increase due to the increase in the film formed on the electrode surface, which may degrade the performance of the battery.

[0095] Furthermore, examples of the cyclic carbonate compound include vinylene carbonate (VC) or vinylethylene carbonate, and may be included in an amount of 5% by weight or less based on the total weight of the polymer electrolyte precursor composition. If the content of the cyclic carbonate compound in the polymer electrolyte precursor composition exceeds 5% by weight, the cell swelling suppression performance may deteriorate.

[0096] The sulfite compound mentioned above includes one or more compounds selected from the group consisting of ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethylpropylene sulfite, 4,5-diethylpropylene sulfite, 4,6-dimethylpropylene sulfite, 4,6-diethylpropylene sulfite, and 1,3-butylene glycol sulfite, and may be included in an amount of 5% by weight or less based on the total weight of the precursor composition.

[0097] The sulfone compound may be one or more compounds selected from the group consisting of divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone, and may be included in an amount of 5% by weight or less based on the total weight of the precursor composition.

[0098] Examples of the sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), and may be present in an amount of 5% by weight or less based on the total weight of the precursor composition.

[0099] The phosphate-based or phosphite-based compound may be one or more compounds selected from the group consisting of lithium difluoro(bisoxalato) phosphate, lithium difluorophosphate, tris(trimethylsilyl) phosphate (TMSPa), tris(trimethylsilyl) phosphite (TMSPi), tris(2,2,2-trifluoroethyl) phosphate (TFEPa), and tris(trifluoroethyl) phosphite (TFEPi), and may be included in an amount of 3% by weight or less based on the total weight of the polymer electrolyte precursor composition.

[0100] Examples of the borate-based compounds include tetraphenyl borate, lithium oxalyl difluoroborate (LiODFB), or lithium bisoxalate borate (LiB(C2O4)2, LiBOB), and may be included in an amount of 3% by weight or less based on the total weight of the polymer electrolyte precursor composition.

[0101] The lithium salt compound is a compound different from the lithium salt contained in the precursor composition, and examples include LiPO2F2 or LiBF4, and may be included in an amount of 3% by weight or less based on the total weight of the polymer electrolyte precursor composition.

[0102] Specifically, the additive may include halogen-substituted carbonate compounds, namely fluoroethylene carbonate (FEC).

[0103] Furthermore, two or more of the aforementioned additives may be included in a mixture, and the total weight of the additives may be 20% by weight or less, specifically 0.01% to 10% by weight, based on the total weight of the gel polymer electrolyte forming composition.

[0104] Gel polymer electrolytes Furthermore, one aspect of the present invention provides a gel polymer electrolyte. The gel polymer electrolyte can be produced from the aforementioned gel polymer electrolyte forming composition. More specifically, the gel polymer electrolyte may be formed by a crosslinking reaction of the aforementioned gel polymer electrolyte forming composition, or by a crosslinking reaction of a crosslinking compound contained in the aforementioned gel polymer electrolyte forming composition.

[0105] Specifically, the gel polymer electrolyte comprises a lithium salt, an organic solvent, and a polymer matrix formed by a crosslinking reaction of a crosslinking compound represented by the following chemical formula 1.

[0106] [Chemical formula 1] [ka]

[0107] In the above chemical formula 1, L1, L2, L3, and L4 are independently selected from directly bonded or C1-C3 alkylene groups, L5 and L6 are independently selected from C1-C10 alkylene groups in which one or more methylene groups may be substituted with ether groups and one or more hydrogens are substituted with fluorine, and R1 and R2 are independently selected from hydrogen, C1-C3 alkyl groups, or halogens.

[0108] The gel polymer electrolyte, by containing a polymer matrix formed by the crosslinked compound represented by chemical formula 1, can have excellent oxidation stability and flame retardancy. Therefore, lithium secondary batteries to which the gel polymer electrolyte is applied can have thermal safety, prevent ignition or explosion, and have excellent lifespan performance.

[0109] The specific details of the lithium salt, organic solvent, and crosslinking compound represented by chemical formula 1 are as described above.

[0110] Lithium-ion battery Furthermore, one aspect of the present invention provides a lithium secondary battery containing the aforementioned gel polymer electrolyte.

[0111] Specifically, one aspect of the present invention provides a lithium secondary battery including a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and the above-described gel polymer electrolyte. Alternatively, one aspect of the present invention provides a lithium secondary battery including a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and a gel polymer electrolyte formed from the above-described composition for forming a gel polymer electrolyte.

[0112] Specifically, the lithium secondary battery can be manufactured by manufacturing an electrode assembly with a separator interposed between the positive electrode and the negative electrode, and then injecting the assembled electrode assembly and the composition for forming a gel polymer electrolyte of one aspect of the present invention into a battery case and performing a crosslinking reaction (thermal polymerization) of the crosslinking compound.

[0113] Since the composition for forming a gel polymer electrolyte and the gel polymer electrolyte are as described above, the positive electrode, negative electrode, and separator will be described below.

[0114] 1) Positive electrode The positive electrode may contain a positive electrode active material.

[0115] The lithium transition metal oxide is a compound capable of reversible intercalation and deintercalation of lithium, and includes lithium cobalt-based oxides (e.g., LiCoO2, etc.), lithium nickel-based oxides (e.g., LiNiO2, etc.), lithium manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-nickel-manganese-based oxides (e.g., LiN i1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2MnY2O2(where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4(where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r1 )O2(where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4(where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), lithium-nickel-cobalt-manganese-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2(where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2 + r3 + s2 = 1), etc.), high-nickel lithium transition metal composite oxides, over-lithiated manganese-rich oxides, lithium iron phosphate (e.g., LiFePO4, etc.), and at least one selected from the group consisting of over-lithiated layered oxides (Overlithiated layered oxide, OLO) may be included.

[0116] The high-nickel lithium transition metal composite oxide may contain 50 mol% or more, specifically 60 mol% or more of nickel based on the total number of moles of transition metals contained in the lithium transition metal composite oxide. Specifically, the high-nickel lithium transition metal composite oxide may contain, as transition metals, nickel; and at least one selected from manganese, cobalt, and aluminum, and contain the nickel at 50 mol% or more, specifically 60 mol% or more, more specifically 60 mol% to 90 mol% based on the total number of moles of the transition metals.

[0117] Furthermore, the lithium transition metal oxide may be a compound represented by the following chemical formula 5.

[0118] [Chemical formula 5] Li 1+x (Ni a Co b Mn c M d )O2

[0119] In the above chemical formula 5, M is one or more selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and 1+x, a, b, c, and d are the atomic fractions of independent elements, where 0≦x≦0.2 and 0.50≦a<1, 0 <b≦0.30、0<c≦0.30、0≦d≦0.1、a+b+c+d=1である。

[0120] Preferably, a, b, c, and d are 0.60 ≤ a ≤ 0.95, 0.025 ≤ b ≤ 0.25, 0.025 ≤ c ≤ 0.25, and 0 ≤ d ≤ 0.05, respectively. Alternatively, a, b, c, and d may be 0.80 ≤ a ≤ 0.95, 0.025 ≤ b ≤ 0.15, 0.025 ≤ c ≤ 0.15, and 0 ≤ d ≤ 0.05, respectively. Alternatively, a, b, c, and d may be 0.85 ≤ a ≤ 0.90, 0.05 ≤ b ≤ 0.10, 0.05 ≤ c ≤ 0.10, and 0 ≤ d ≤ 0.03, respectively.

[0121] The lithium transition metal oxide may be a manganese-perlithified oxide. The manganese-perlithified oxide may contain 50 mol% or more of Mn in the total metal excluding lithium, and the molar ratio of lithium to the transition metal may be greater than 1.

[0122] Specifically, the perlithitated manganese-rich oxide may be a compound represented by the following chemical formula 6.

[0123] [Chemical formula 6] Li 1+s [Ni t Cou Mn v M 1 w O 2+z

[0124] In Chemical Formula 6, 0.05≦s≦1, 0≦t≦0.5, 0≦u≦0.3, 0.5≦v<1.0, 0≦w≦0.2, 0≦z≦1 may be satisfied. Preferably, 0.05≦s≦1.0, 0.1≦t≦0.5, 0≦u≦0.1, 0.5≦v<1.0, 0≦w≦0.2, 0≦z≦1 may be satisfied, and more preferably, 0.10≦s≦0.50, 0.1≦t≦0.5, 0≦u≦0.1, 0.6≦v<1.0, 0≦w≦0.1, 0≦z≦0.50 may be satisfied. M 1 may be one or more selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.

[0125] More specifically, the over-lithiated manganese-rich oxide may be a compound represented by the following Chemical Formula 6-1.

[0126] [Chemical Formula 6-1] X Li2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M 1 w O2

[0127] In Chemical Formula 6-1, 0.1≦x≦0.5, 0.5≦y<1, 0≦z≦0.3, 0≦w≦0.2 may be satisfied, preferably, 0.2≦x≦0.5, 0.5≦y<1, 0≦z≦0.1, 0≦w≦0.2, and more preferably, 0.3≦x≦0.5, 0.6≦y<1, 0≦z≦0.1, 0≦w≦0.2 may be satisfied. M 1 may be one or more selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.

[0128] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector. In this case, the positive electrode active material layer includes the positive electrode active material.

[0129] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity. Specifically, the positive electrode current collector may contain at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloy, preferably aluminum.

[0130] The thickness of the positive electrode current collector is typically 3 to 500 μm.

[0131] The positive electrode current collector may have fine irregularities formed on its surface to strengthen the bonding force with the negative electrode active material. For example, the positive electrode current collector can be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0132] The positive electrode active material layer is disposed on at least one side of the positive electrode current collector. Specifically, the positive electrode active material layer may be disposed on one or both sides of the positive electrode current collector.

[0133] The positive electrode active material may be included in the positive electrode active material layer in an amount of 80% to 99% by weight, preferably 92% to 98.5% by weight, taking into consideration the sufficient capacity of the positive electrode active material.

[0134] The positive electrode active material layer may further include a binder and / or a conductive material along with the positive electrode active material.

[0135] The binder is a component that assists in the binding of the active material to the conductive material and to the current collector, and specifically may contain at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-dientelpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

[0136] The binder may be included in the positive electrode active material layer in an amount of 1% to 20% by weight, preferably 1.2% to 10% by weight, from the viewpoint of ensuring sufficient binding force between components such as the positive electrode active material.

[0137] The conductive material is used to assist and improve the conductivity of a secondary battery and is not particularly limited as long as it does not cause chemical changes and is conductive. Specifically, the positive electrode conductive material may contain at least one selected from the group consisting of graphite such as natural graphite 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 metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives, and preferably contains carbon black in order to improve conductivity.

[0138] The conductive material may be included in the positive electrode active material layer in an amount of 1% to 20% by weight, preferably 1.2% to 10% by weight, in order to ensure sufficient electrical conductivity.

[0139] The thickness of the positive electrode active material layer may be 30 μm to 400 μm, preferably 40 μm to 110 μm.

[0140] The positive electrode can be manufactured by coating a positive electrode slurry containing a positive electrode active material and selectively a binder, conductive material, and solvent for forming the positive electrode slurry onto the positive electrode current collector, followed by drying and rolling.

[0141] The solvent for forming the positive electrode slurry may include an organic solvent such as NMP (N-methyl-2-pyrrolidone). The solid content of the positive electrode slurry may be 40% to 90% by weight, specifically 50% to 80% by weight.

[0142] 2) Negative electrode The negative electrode faces the positive electrode.

[0143] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector.

[0144] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0145] The negative electrode current collector typically has a thickness of 3 to 500 μm.

[0146] The negative electrode current collector may have its surface textured to enhance the bonding force of the negative electrode active material. For example, the negative electrode current collector can be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0147] The negative electrode active material layer is disposed on at least one side of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one or both sides of the negative electrode current collector.

[0148] The aforementioned negative electrode active material layer may contain a negative electrode active material.

[0149] The negative electrode active material is a material capable of reversibly intercalating / deintercalating lithium ions, and may include at least one selected from the group consisting of carbon-based active materials, metalloid-based active materials, and lithium metal. Specifically, it may include at least one selected from carbon-based active materials and metalloid-based active materials.

[0150] The carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and preferably includes at least one selected from the group consisting of artificial graphite and natural graphite.

[0151] The average particle size (D) of the carbon-based active material 50 The thickness of the ) may be 10 μm to 30 μm, preferably 15 μm to 25 μm, in order to ensure structural stability during charging and discharging and to reduce side reactions with the electrolyte.

[0152] Specifically, the metalloid active material may include: at least one metalloid selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an alloy of lithium with at least one metalloid selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an oxide of at least one metalloid selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; lithium titanium oxide (LTO); lithium vanadium oxide; and the like.

[0153] More specifically, the metalloid-based active material may include a silicon-based active material.

[0154] The silicon-based active material is SiO x The compound may contain compounds represented by (0 ≤ x < 2). SiO2 does not react with lithium ions and therefore cannot store lithium. For this reason, x is preferably within the above range, and more preferably, the silicon-based active material may be SiO2.

[0155] The average particle size (D) of the silicon-based active material 50 The thickness of the ) may be 1 μm to 30 μm, preferably 2 μm to 15 μm, in order to ensure structural stability during charging and discharging and to reduce side reactions with the electrolyte.

[0156] The negative electrode active material may be included in the negative electrode active material layer in an amount of 60% to 99% by weight, preferably 75% to 95% by weight.

[0157] The negative electrode active material layer may further include a binder and / or a conductive material together with the negative electrode active material.

[0158] The binder is used to improve the performance of the battery by improving the adhesion between the negative electrode active material layer and the negative electrode current collector, and may contain, for example, at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and substances in which the hydrogen of these substances is substituted with Li, Na, or Ca, or may contain various copolymers thereof.

[0159] The binder may be included in the negative electrode active material layer in an amount of 0.5% to 10% by weight, preferably 1% to 5% by weight.

[0160] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. Examples include graphite such as natural graphite 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 metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0161] The conductive material may be included in the negative electrode active material layer in an amount of 0.5% to 10% by weight, preferably 1% to 5% by weight.

[0162] The thickness of the negative electrode active material layer may be 10 μm to 100 μm, preferably 50 μm to 80 μm.

[0163] The negative electrode can be manufactured by coating at least one surface of a negative electrode current collector with a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, and / or a solvent for forming the negative electrode slurry, followed by drying and rolling.

[0164] The solvent for forming the negative electrode slurry may include, for example, at least one selected from the group consisting of distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol, and isopropyl alcohol, specifically NMP, in order to facilitate the dispersion of the negative electrode active material, binder, and / or conductive material. The solid content of the negative electrode slurry may be 30% to 80% by weight, specifically 40% to 70% by weight.

[0165] 3) Separator Furthermore, the separator may be a conventional porous polymer film, such as a porous polymer film made from polyolefin polymers like ethylene monopolymer, propylene monopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, used alone or in a laminated configuration. Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used, but is not limited to these. In addition, a coated separator containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be used selectively as a single-layer or multi-layer structure.

[0166] The external shape of a lithium secondary battery according to one embodiment of the present invention is not particularly limited, but may be cylindrical, rectangular, pouch-shaped, or coin-shaped using a can.

[0167] An embodiment of the present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative for understanding the present invention and are not intended to limit the scope of the present invention. It will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the described concept and technical idea, and it goes without saying that such variations and modifications fall within the scope of the appended claims.

[0168] Examples and Comparative Examples Manufacturing Example 1: Manufacturing of Crosslinked Compounds: Synthesis of Spirocyclic Pentaerythritol Diphosphate Perfluorinated Ether Acrylate (SPDFA, Chemical Formula 1-1) (1) Step 1: Synthesis of spirocyclic pentaerythritol bisphosphorate diphosphoryl chloride (SPDPC) Figure 1 shows a schematic diagram of the synthesis of spirocyclic pentaerythritol bisphosphorate diphosphoryl chloride (SPDPC) from pentaerythritol and phosphorus oxychloride (Step 1). First, pentaerythritol (6.81 g, 50 mmol) was placed in a double jacket and cooled to 0°C. Then, phosphorus oxychloride (53.67 g, 350 mmol) was slowly added dropwise while stirring. After the addition was complete, the mixed solution was raised to 80°C and stirred for 2 hours, then raised to 110°C and the reaction was allowed to proceed for 20 hours. After the reaction was complete, the compound was filtered, washed with tetrahydrofuran and ethanol, and vacuum-dried at 80°C for 12 hours to obtain spirocyclic pentaerythritol bisphosphorate diphosphoryl chloride. The chemical structure of the product was confirmed by NMR spectroscopy.

[0169] [Confirmation of the chemical structure of spirocyclic pentaerythritol bisphosphorate diphosphoryl chloride (NMR)] 1 H NMR (DMSO), δ (ppm): 4.25-4.1 (dd, 4H) 31 P NMR (CDCl3), δ (ppm): -7.95

[0170] (2) Step 2: Synthesis of fluorinated ether monoacrylate (PFE-mono AC) Figure 1 (Step 2) shows a schematic diagram of the synthesis of fluorinated ether monoacrylate (PFE-mono AC) from fluorinated ether diol (PFE-OH). First, 10 g of 1H,1H,8H,8H-perfluoro-3,6-dioxaoctan-1,8-diol (PFE-OH) and 3.08 g of acryloyl chloride were dissolved in 56.6 ml of tetrahydrofuran (THF) solvent and placed in a double jacket. After adding all of the reactants and 4.15 g of triethylamine (TEA) catalyst to the THF at 0°C, the reaction temperature was raised to 25°C and the reaction was allowed to proceed for 12 hours. After vacuum drying the THF solvent in the generated solution, unreacted and by-reactants were completely removed via a column process, and the chemical structure of the obtained product was confirmed by NMR spectroscopy.

[0171] [Confirmation of the chemical structure of fluorinated ether monoacrylate (NMR)] 1 H NMR (CDCl3), δ (ppm) : 6.54-6.5 (dd, 1H), 6.22-6.16 (dd, 1H), 6.05-5.98 (dd, 1H), 4.6-4.55 (t, 2H), 3.95-3.9 (q, 2H), 2.54-5.48 (t, 1H)

[0172] (3) Step 3: Synthesis of spirocyclic pentaerythritol diphosphate perfluorinated ether acrylate (SPDFA) A schematic diagram of the synthesis of spirocyclic pentaerythritol diphosphate perfluorinated ether acrylate (SPDFA) is shown in Figure 1 (Step 3). First, 10.0 g of the spirocyclic pentaerythritol bisphosphorate diphosphoryl chloride (SPDPC) prepared above and 9.8 g of fluorinated ether monoacrylate (PFE-mono AC) were dissolved in 192.6 ml of acetonitrile solvent and placed in a double jacket. After adding all the reactants and 18.2 g of triethylamine catalyst at 0°C, the reaction temperature was raised to 25°C and the reaction proceeded for 48 hours (2 days). After vacuum drying the acetonitrile solvent in the resulting solution, unreacted and by-reactants were completely removed by column chromatography, and the chemical structure of the obtained product was recorded in FT-IR in Figure 2 and in Figure 4. 1 This was confirmed by the 1H NMR spectrum. The molecular weight of the spirocyclic pentaerythritol diphosphate perfluorinated ether acrylate (SPDFA) prepared as described above was 952.4 g / mol.

[0173] Specifically, Figure 2 shows the FT-IR spectral results of fluorinated ether monoacrylate (PFE-mono AC) and spirocyclic pentaerythritol diphosphate perfluorinated ether acrylate (SPDFA) produced by steps 2 and 3. Figure 3 shows the FT-IR spectral results of spirocyclic pentaerythritol bisphosphorate diphosphoryl chloride (SPDPC) produced by step 1. 1 Figure 4 shows the 1H NMR spectrum results of the spirocyclic pentaerythritol diphosphate perfluorinated ether acrylate (SPDFA) produced in step 3. 1 This is the result of the 1H NMR spectrum.

[0174] Example 1: Preparation of a composition for forming a gel polymer electrolyte A 1.15 M lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC) (volume ratio: 30 / 50 / 20), and then fluoroethylene carbonate (FEC) was added to produce a liquid electrolyte. The FEC was added to the liquid electrolyte at a content of 5% by weight. 9 g of the liquid electrolyte and 1 g of a spirocyclic pentaerythritol diphosphate perfluorinated ether acrylate (SPDFA) crosslinked compound were mixed, and 0.01 g of t-butyl peroxypivalate, a polymerization initiator, was added (1 part by weight per 100 parts by weight of the crosslinked compound) and the mixture was stirred to produce a gel polymer electrolyte formation composition.

[0175] Example 2: Production of gel polymer electrolytes The gel polymer electrolyte-forming composition produced in Example 1 was thermally crosslinked at 70°C for 1 hour to produce a gel polymer electrolyte (SPDFA GPE) in which a polymer matrix was formed by the crosslinking compound.

[0176] Example 3: Manufacturing of a lithium secondary battery Cathode active material (Li[Ni 0.6 Co 0.2 Mn 0.2 A positive electrode slurry was prepared by adding 2O2, a conductive material (Super P), and a binder (PVdF) in a weight ratio of 95:3:2 to N-methylpyrrolidone (NMP) solvent. The positive electrode slurry was applied to one surface of an aluminum positive electrode current collector with a thickness of 15 μm, and the positive electrode was prepared by drying and rolling.

[0177] A negative electrode slurry was prepared by adding a negative electrode active material (graphite), a conductive material (Super P), and a binder (PVdF) in a weight ratio of 90:3:7 to an N-methylpyrrolidone solvent. The negative electrode slurry was applied to one surface of a 15 μm thick copper negative electrode current collector, and the negative electrode was manufactured by drying and rolling.

[0178] An electrode assembly was manufactured by interposing a polyethylene porous separator between the positive electrode and negative electrode manufactured as described above. The electrode assembly was then placed in a battery case, and the gel polymer electrolyte forming composition of Example 1 was poured into the battery case and sealed. After heat treatment at 70°C, a lithium secondary battery was manufactured in which a gel polymer electrolyte was formed from the gel polymer electrolyte forming composition.

[0179] Comparative Example 1: Manufacturing of Liquid Electrolytes A liquid electrolyte was prepared by dissolving 1.15 M lithium hexafluorophosphate (LiPF6) in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) (volume ratio: 30 / 50 / 20), and then adding fluoroethylene carbonate (FEC). The fluoroethylene was added to the liquid electrolyte at a content of 5% by weight.

[0180] Comparative Example 2: Manufacturing of Lithium-ion Rechargeable Batteries A lithium secondary battery was manufactured in the same manner as in Example 3, except that the liquid electrolyte of Comparative Example 1 was used instead of the gel polymer electrolyte forming composition of Example 1, and no further heat treatment was performed to form the gel polymer electrolyte.

[0181] Comparative Example 3: Production of a composition for forming a gel polymer electrolyte A gel polymer electrolyte-forming composition was prepared in the same manner as in Example 1, except that 1 g of the compound represented by the following chemical formula A was added to the gel polymer electrolyte-forming composition instead of 1 g of the spirocyclic pentaerythritol diphosphate perfluorinated ether acrylate (SPDFA) crosslinking compound.

[0182] [Chemical formula A] [ka] (In the above chemical formula A, n1 is 3.)

[0183] Comparative Example 4: Production of Gel Polymer Electrolytes The gel polymer electrolyte-forming composition produced in Comparative Example 3 was thermally crosslinked at 70°C for 1 hour to produce a gel polymer electrolyte (SPDFA GPE) in which a polymer matrix was formed by the crosslinking compound.

[0184] Comparative Example 5: Production of a composition for forming a gel polymer electrolyte A gel polymer electrolyte-forming composition was prepared in the same manner as in Example 1, except that 1 g of the compound represented by the following chemical formula B was added to the gel polymer electrolyte-forming composition instead of 1 g of the spirocyclic pentaerythritol diphosphate perfluorinated ether acrylate (SPDFA) crosslinking compound.

[0185] [Chemical formula B] [ka] (In the above chemical formula B, m1 is 3.)

[0186] Comparative Example 6: Production of Gel Polymer Electrolytes The gel polymer electrolyte-forming composition produced in Comparative Example 5 was thermally crosslinked at 70°C for 1 hour to produce a gel polymer electrolyte (SPDFA GPE) in which a polymer matrix was formed by the crosslinking compound.

[0187] Comparative Example 7: Production of a composition for forming a gel polymer electrolyte A gel polymer electrolyte-forming composition was prepared in the same manner as in Example 1, except that 1 g of the compound represented by the following chemical formula C was added to the gel polymer electrolyte-forming composition instead of 1 g of the spirocyclic pentaerythritol diphosphate perfluorinated ether acrylate (SPDFA) crosslinking compound.

[0188] [Chemical formula C] [ka]

[0189] Comparative Example 8: Production of Gel Polymer Electrolytes The gel polymer electrolyte-forming composition produced in Comparative Example 7 was thermally crosslinked at 70°C for 1 hour to produce a gel polymer electrolyte (SPDFA GPE) in which a polymer matrix was formed by the crosslinking compound.

[0190] Experimental example Experimental Example 1: Confirmation of Crosslinking Reaction of Gel Polymer Electrolytes To confirm whether the crosslinking reaction of the gel polymer electrolyte (SPDFA GPE) in Example 2 proceeded well, FT-IR spectral analysis was performed. The results are shown in Figure 5.

[0191] C=C(1635cm) of SPDFA in Example 1 -1 The double bond peak was confirmed to disappear in the SPDFA GPE of Example 2. This confirms the completion of the crosslinking reaction and the formation of the gel polymer electrolyte.

[0192] Experimental Example 2: Measurement of Ionic Conductivity The gel polymer electrolyte of Example 2 and the liquid electrolyte of Comparative Example 1 were subjected to a 10-10 volts test using a CH instrument (CHI 600D) at an amplitude of 50 mV. 6 The AC impedance between sandwich-type electrodes was measured in the frequency range of Hz, and the measured values ​​were analyzed using a frequency response analyzer to determine the ionic conductivity with respect to temperature. The results are shown in Figure 6.

[0193] Referring to Figure 6, the gel polymer electrolyte of Example 2 is 4 × 10 at room temperature. -3 S cm -1 It exhibited the above-mentioned high ionic conductivity.

[0194] Experimental Example 3: Evaluation of Electrochemical Stability To compare the electrochemical stability of the gel polymer electrolyte of Example 2 with the liquid electrolyte of Comparative Example 1, and the gel polymer electrolytes of Comparative Examples 4, 6, and 8, the current value due to the applied voltage was measured by linear sweep voltammetry (LSV) (scanning speed 1 mV / s), and the results are shown in Figure 7. Specifically, Figure 7 is a graph (oxidation scan) showing the values ​​for the x-axis range of 3.0 to 6.0 V.

[0195] Referring to Figure 7, it can be seen that the gel polymer electrolyte of Example 2 exhibits improved electrochemical stability compared to the liquid electrolyte of Comparative Example 1, Comparative Example 4, Comparative Example 6, and Comparative Example 8, due to the characteristic structure of the crosslinking compound according to Chemical Formula 1.

[0196] Experimental Example 4: Evaluation of Cycle Characteristics The lithium secondary battery of Example 3, manufactured as described above, was charged to 4.2V at 25°C with a constant current of 0.1C, and then discharged to 2.5V with a constant current of 0.1C. This process constituted one cycle, and four cycles of the activation step were performed.

[0197] Subsequently, the battery was charged to 4.2V at 25°C with a constant current of 0.2C, and then discharged to 2.5V with a constant current of 0.2C. This cycle was defined as one charge-discharge cycle, and 300 such cycles were performed.

[0198] Figure 8 shows the charge-discharge curves of the lithium secondary battery of Example 3 for the 1st, 10th, 30th, 50th, 100th, 200th, and 300th cycles. Figure 9 shows a graph of the change in discharge capacity of the lithium secondary battery of Example 3 over the course of cycles.

[0199] The lithium secondary battery of Example 3, which uses the gel polymer electrolyte of Example 2, was found to perform stable charge-discharge cycles.

[0200] Experimental Example 5: Evaluation of Flame Retardant Properties (1) Experimental Example 5-1 To evaluate the flame retardancy of the gel polymer electrolyte produced in Example 2 and the liquid electrolyte of Comparative Example 1, combustion experiments were conducted using a flame torch.

[0201] Figure 10 shows photographs of the results before (left) and after (right) the combustion test of the liquid electrolyte of Comparative Example 1. Figure 11 shows photographs of the results before (left) and after (right) the combustion test of the gel polymer electrolyte of Example 2.

[0202] Referring to Figure 10, the liquid electrolyte of Comparative Example 1 exhibits high flammability when a flame torch is applied.

[0203] In contrast, referring to Figure 11, it can be seen that the gel polymer electrolyte of Example 2 exhibits excellent self-extinguishing properties and flame-retardant properties, meaning it does not burn in fire.

[0204] (2) Experimental Example 5-2 To evaluate the flame retardancy of the gel polymer electrolyte produced in Example 2, the liquid electrolyte of Comparative Example 1, and the gel polymer electrolytes of Comparative Examples 4, 6, and 8, combustion experiments were conducted using a flame torch.

[0205] The gel polymer electrolyte produced in Example 2, the liquid electrolyte of Comparative Example 1, and the gel polymer electrolytes of Comparative Examples 4, 6, and 8 were subjected to a self-extinguish time experiment, in which 1 g of each electrolyte was ignited and the time until the sample burned was measured to evaluate its flame retardancy. The results are shown in Table 1 below.

[0206] [Table 1]

[0207] Referring to Table 1 above, it can be seen that the gel polymer electrolyte for lithium secondary batteries produced in Example 2 of the present invention does not ignite, whereas the liquid electrolyte of Comparative Example 1 and the gel polymer electrolytes of Comparative Examples 4, 6, and 8 exhibit inferior flame retardancy compared to the gel polymer electrolyte of Example 2, which exhibited completely non-flammable properties.

[0208] Experimental Example 6: Evaluation of Separator Contraction Degree Two identical polyethylene separators were prepared.

[0209] One of two polyethylene separators was impregnated with the gel polymer electrolyte-forming composition of Example 1, and then a crosslinking reaction was carried out at 70°C for 1 hour to produce a polyethylene separator impregnated with the gel polymer electrolyte. The other polyethylene separator was left untreated.

[0210] Polyethylene separators that were not impregnated with gel polymer electrolytes (no treatment was applied) were stored at 140°C for 30 minutes. Figure 12 shows a photograph of the polyethylene separator before storage at 140°C on the left and a photograph of the polyethylene separator after storage at 140°C for 30 minutes on the right.

[0211] Furthermore, polyethylene separators impregnated with gel polymer electrolytes were stored at 140°C for 30 minutes. Figure 13 shows a photograph of the polyethylene separator before storage at 140°C on the left and a photograph of the polyethylene separator after storage at 140°C for 30 minutes on the right.

[0212] Referring to Figure 12, a polyethylene separator without a gel polymer electrolyte according to one aspect of the present invention was found to exhibit significant shrinkage at high temperatures. On the other hand, referring to Figure 13, a polyethylene separator without a gel polymer electrolyte according to one aspect of the present invention showed very little shrinkage when stored at 140°C, confirming that it has high thermal stability at high temperatures.

[0213] Experimental Example 7: Short-circuit test of lithium secondary battery The lithium secondary batteries of Example 3 and Comparative Example 2 were charged to 4.2 V at a constant current of 0.1 C at 25°C, stored in a hot box at 140°C, and the battery voltage was measured over time. The results are shown in FIG. 14.

[0214] Referring to FIG. 14, the lithium secondary battery of Example 3 to which the gel polymer electrolyte of Example 2 was applied maintained the battery voltage stably even at high temperatures as compared with the lithium secondary battery of Comparative Example 2 using the liquid electrolyte of Comparative Example 1. From such results, it can be seen that when applying the gel polymer electrolyte according to one aspect of the present invention, the phenomenon of fine internal short circuit of the lithium secondary battery can be suppressed, and the thermal stability of the lithium secondary battery can be remarkably improved.

[0215] Experimental Example 8: Measurement of electrode heat generation amount In the lithium secondary batteries of Example 3 and Comparative Example 2, in order to compare the heat generation amounts of the electrodes due to the electrolyte, the heat generation amounts of the negative electrode and the positive electrode were measured by differential scanning calorimetry (DSC).

[0216] Specifically, the lithium secondary batteries of Example 3 and Comparative Example 2 manufactured above were charged to 4.2 V at a constant current of 0.1 C at 25°C, and discharged to 2.5 V at a constant current of 0.1 C as one cycle, and an activation step of 4 cycles was performed. Then, at 25°C, it was charged to 4.2 V at a constant current of 0.2 C, discharged to 2.5 V at a constant current of 0.2 C for one cycle of charge and discharge, and after being fully charged at a constant current of 0.2 C, the lithium secondary battery was disassembled to recover the positive electrode and negative electrode materials, and then the heat generation amount was measured by a DSC experiment. The DSC experiment was performed by heating from 0°C to 300°C at a rate of 10°C / min.

[0217] The DSC experiment results for the negative electrode are shown in FIG. 15, and the DSC experiment results for the positive electrode are shown in FIG. 16.

[0218] Referring to Figures 15 and 16, it can be seen that the lithium secondary battery of Example 3 exhibits a significant reduction in the heat generated at both the negative and positive electrodes compared to Comparative Example 2. From these results, it can be seen that the gel polymer electrolyte forming composition or gel polymer electrolyte according to one embodiment of the present invention can significantly improve the thermal safety of lithium secondary batteries.

Claims

1. Lithium salts and Organic solvents and A composition for forming a gel polymer electrolyte, comprising a crosslinking compound represented by the following chemical formula 1. [Chemical formula 1] 【Chemistry 1】 (In the above chemical formula 1, L １ , L ２ , L ３ , and L ４ These are independently of each other, directly bonded, or selected from alkylene groups having 1 to 3 carbon atoms. L ５ and L ６ These are alkylene groups having 1 to 20 carbon atoms, in which one or more methylene groups may be substituted with ether groups, and one or more hydrogen atoms may be substituted with fluorine. R １ and R ２ These elements are independently selected from hydrogen, an alkyl group having 1 to 3 carbon atoms, or a halogen.

2. The gel polymer electrolyte formation composition according to claim 1, further comprising a polymerization initiator.

3. The gel polymer electrolyte formation composition according to claim 1, wherein the molecular weight of the crosslinked compound is 700 g / mol to 2,000 g / mol.

4. The gel polymer electrolyte forming composition according to claim 1, wherein the crosslinking compound is contained in an amount of 1% to 30% by weight based on the total weight of the gel polymer electrolyte forming composition.

5. In the above Chemical Formula 1, L １ , L ２ , L ３ and L ４ are each independently selected from a direct bond or a methylene group, and the composition for forming a gel polymer electrolyte according to Claim 1.

6. In the above chemical formula 1, L １ , L ２ , L ３ , and L ４ The gel polymer electrolyte formation composition according to claim 1, wherein each of these is a methylene group.

7. Said L ５ and L ６ The gel polymer electrolyte formation composition according to any one of claims 1 to 6, wherein each of the components is independently represented by the following chemical formula 2. [Chemical formula 2] *-[(CH ２ ) ｎ -(CF ２ ) ｍ -(CH ２ ) ｐ -(O) ｑ -(CH ２ ) ｒ -(CF ２ ) ｓ -(CH ２ ) ｔ ] ｕ -* (In the above chemical formula 2, n, m, p, r, s, and t are each non-negative integers. q is either 0 or 1, m+s is an integer greater than or equal to 1, u is an integer greater than or equal to 1, The product of (n+m+p+q+r+s+t) and u is an integer between 1 and 20. However, when q is 1, n + m + p is an integer greater than or equal to 1, and r + s + t is an integer greater than or equal to 1.

8. The gel polymer electrolyte forming composition according to any one of claims 1 to 6, wherein the crosslinking compound represented by the chemical formula 1 comprises the crosslinking compound represented by the following chemical formula 1-1. [Chemical formula 1-1] 【Chemistry 2】

9. The lithium salts mentioned above are LiCl, LiBr, LiI, and LiBF. ４ LiClO ４ LiAlO ４ LiAlCl ４ LiPF ６ LiSbF ６ LiAsF ６ LiB １０ Cl １０ , LiBOB(LiB(C ２ O ４ ) ２ ), LiCF ３ SO ３ , LiFSI (LiN(SO ２ F) ２ ), LiCH ３ SO ３ LiCF ３ CO ２ LiCH ３ CO ２ , and LiBETI(LiN(SO ２ CF ２ CF ３ ) ２ A gel polymer electrolyte forming composition according to any one of claims 1 to 6, comprising at least one selected from the group consisting of ).

10. The gel polymer electrolyte formation composition according to any one of claims 1 to 6, wherein the organic solvent comprises at least one selected from the group consisting of carbonate solvents, ester solvents, ether solvents, ketone solvents, aromatic hydrocarbon solvents, phosphate solvents, sulfone solvents, nitrile solvents, and ionic liquids.

11. It also contains additives, The gel polymer electrolyte formation composition according to any one of claims 1 to 6, wherein the additive comprises one or more selected from the group consisting of sultone compounds, halogen-substituted carbonate compounds, nitrile compounds, cyclic carbonate compounds, sulfite compounds, sulfone compounds, sulfate compounds, phosphate or phosphite compounds, borate compounds, and lithium salt compounds.

12. The aforementioned additive includes a halogen-substituted carbonate compound. The gel polymer electrolyte formation composition according to claim 11, wherein the halogen-substituted carbonate compound is fluoroethylene carbonate.

13. A gel polymer electrolyte comprising a lithium salt, an organic solvent, and a polymer matrix formed by a crosslinking reaction of a crosslinking compound represented by the following chemical formula 1. [Chemical formula 1] 【Transformation 3】 (In the above chemical formula 1, L １ , L ２ , L ３ , and L ４ These are independently of each other, directly bonded, or selected from alkylene groups having 1 to 3 carbon atoms. L ５ and L ６ These are alkylene groups having 1 to 20 carbon atoms, in which one or more methylene groups may be substituted with ether groups, and one or more hydrogen atoms may be substituted with fluorine. R １ and R ２ These elements are independently selected from hydrogen, an alkyl group having 1 to 3 carbon atoms, or a halogen.

14. Positive electrode and, A negative electrode opposite the positive electrode, A separator interposed between the positive electrode and the negative electrode, A lithium secondary battery comprising the gel polymer electrolyte described in claim 13.

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