Composition for forming gel polymer electrolyte, gel polymer electrolyte, and lithium secondary battery comprising gel polymer electrolyte

Abstract

A composition for forming a gel polymer electrolyte includes a lithium salt, an organic solvent, and a crosslinking compound represented by Formula 1. In Formula 1, L1, L2, L3, and L4 are each independently selected from a directly bonded alkylene group or an alkylene group having 1 to 3 carbon atoms, L5 and L6 are each independently an alkylene group having 1 to 20 carbon atoms in which at least one methylene group is optionally substituted by an ether group and at least one hydrogen group is substituted by fluorine, and R1 and R2 are each independently selected from hydrogen, an alkyl group having 1 to 3 carbon atoms, or a halogen. [Formula 1]

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0124966, filed on September 19, 2023, the disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention relates to compositions for forming gel polymer electrolytes, gel polymer electrolytes, and lithium secondary batteries comprising said gel polymer electrolytes. Background Technology

[0004] The demand for high-energy-density lithium-ion batteries is rapidly increasing due to technological advancements in mobile electronic devices, electric vehicles (EVs), and grid-scale energy storage systems (ESS).

[0005] Generally, lithium secondary batteries can be made of materials such as a positive electrode made of lithium-containing transition metal oxides, a negative electrode capable of storing lithium, an electrolyte as a medium for transporting lithium ions, and a separator.

[0006] Liquid electrolytes, with their high ionic conductivity and excellent electrochemical performance, are used as electrolytes in lithium secondary batteries. However, due to their high flammability and reactivity with electrode materials, side reactions may occur. Furthermore, due to their low stability, such as leakage, liquid electrolytes may cause fires and explosions under abnormal operating conditions.

[0007] Therefore, in recent years, in order to improve the stability of lithium-ion batteries, research has been conducted to develop more stable electrolytes to replace liquid electrolytes. For example, ionic liquid electrolytes, solid electrolytes, and gel polymer electrolytes have been proposed.

[0008] Ionic liquid electrolytes possess excellent thermal and oxidative stability, but their drawbacks include instability on the negative electrode surface, poor wettability of polyolefin separators due to high viscosity, and high cost. Solid electrolytes improve battery stability by being free of flammable organic solvents, but the increased interfacial resistance between the solid electrolyte and the electrode leads to reduced ionic conductivity around the electrolyte and degraded battery life.

[0009] Gel polymer electrolytes are electrolyte systems in which liquid electrolytes are encapsulated and impregnated in a polymer structure. Their advantages include high structural, thermal and mechanical stability over time, high ionic conductivity, and reasonable manufacturing cost.

[0010] In this context, gel polymer electrolytes can be classified into physically cross-linked gel polymer electrolytes, which form polymer structures through physical bonding of polymers, and chemically cross-linked gel polymer electrolytes, which form polymer structures through chemical reactions of reactive oligomers or cross-linking agents. Since the binding force of physically cross-linked gel polymer electrolytes may weaken over time, chemically cross-linked gel polymer electrolytes, which form polymer structures through chemical bonding, exhibit higher structural, thermal, and mechanical stability.

[0011] However, because chemically cross-linked gel polymer electrolytes contain a large amount of liquid electrolytes, problems such as leakage, fire, and explosion still exist.

[0012] Therefore, there is an urgent need to develop a gel polymer electrolyte that can improve the overall performance of lithium secondary batteries, such as stability and lifespan. Summary of the Invention

[0013] Technical issues

[0014] One aspect of the present invention is to provide a composition for forming a gel polymer electrolyte that can simultaneously improve the safety and lifespan performance of a lithium secondary battery by having excellent oxidation stability and flame retardancy and the effect of suppressing electrode heat generation.

[0015] Furthermore, another aspect of the present invention is to provide a gel polymer electrolyte that can simultaneously improve the safety and lifespan performance of lithium secondary batteries by having excellent oxidation stability and flame retardancy and the effect of suppressing electrode heat generation.

[0016] Furthermore, another aspect of the present invention provides a lithium secondary battery comprising the above-described gel polymer electrolyte.

[0017] Technical solution

[0018] [1] 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 Formula 1.

[0019] [Formula 1]

[0020]

[0021] In Formula 1, L1, L2, L3 and L4 are each independently selected from directly bonded or alkylene groups having 1 to 3 carbon atoms, L5 and L6 are each independently selected from alkylene groups having 1 to 20 carbon atoms, wherein at least one methylene group is optionally substituted with an ether group and at least one hydrogen group is substituted with fluorine, and R1 and R2 are each independently selected from hydrogen, alkyl groups having 1 to 3 carbon atoms or halogens.

[0022] [2] The present invention provides the composition for forming a gel polymer electrolyte as described in [1] above, wherein the composition for forming a gel polymer electrolyte further comprises a polymerization initiator.

[0023] [3] The present invention provides a composition for forming a gel polymer electrolyte of at least one of [1] and [2] above, wherein the molecular weight of the crosslinking compound is from 700 g / mol to 2,000 g / mol.

[0024] [4] The present invention provides a composition for forming a gel polymer electrolyte according to at least one of [1] to [3] above, wherein the content of the crosslinking compound is from 1% to 30% by weight based on the total weight of the composition for forming the gel polymer electrolyte.

[0025] [5] The present invention provides a composition for forming a gel polymer electrolyte of at least one of [1] to [4] above, wherein, in Formula 1, L1, L2, L3 and L4 are each independently selected from direct bonding or methylene.

[0026] [6] The present invention provides a composition for forming a gel polymer electrolyte of at least one of [1] to [5] above, wherein, in Formula 1, L1, L2, L3 and L4 are each methylene groups.

[0027] [7] The present invention provides a composition for forming a gel polymer electrolyte of at least one of [1] to [6] above, wherein L5 and L6 are each independently represented by Formula 2.

[0028] [Equation 2]

[0029] *-[(CH2) n -(CF2) m -(CH2) p -(O) q -(CH2) r -(CF2) s -(CH2) t ] u -*

[0030] In Equation 2, n, m, p, r, s, and t are 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+s+t) and u is an integer from 1 to 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.

[0031] [8] The present invention provides a composition for forming a gel polymer electrolyte of at least one of [1] to [7] above, wherein the crosslinking compound represented by Formula 1 includes the crosslinking compound represented by Formula 1-1.

[0032] [Equation 1-1]

[0033]

[0034] [9] The present invention provides a composition for forming a gel polymer electrolyte according to at least one of [1] to [8] above, wherein the lithium salt comprises selected from LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 At least one of the group consisting of LiBOB (LiB(C2O4)2), LiCF3SO3, LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2 and LiBETI (LiN(SO2CF2CF3)2).

[0035]

[10] The present invention provides a composition for forming a gel polymer electrolyte according to at least one of [1] to [9] above, 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 ester solvents, sulfone solvents, nitrile solvents and ionic liquids.

[0036]

[11] The present invention provides a composition for forming a gel polymer electrolyte according to at least one of [1] to

[10] above, wherein the composition for forming a gel polymer electrolyte further comprises an additive, wherein the additive comprises at least one selected from the group consisting of sulfonyl lactones, halogen-substituted carbonates, nitrile compounds, cyclic carbonates, sulfites or salts, sulfones, sulfates or salts, phosphates or salts or phosphites or salts, borates or salts and lithium salts.

[0037]

[12] The present invention provides a composition for forming a gel polymer electrolyte according to at least one of [1] to

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

[0038]

[13] 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 crosslinking compound represented by Formula 1.

[0039] [Formula 1]

[0040]

[0041] In Formula 1, L1, L2, L3 and L4 are each independently selected from directly bonded or alkylene groups having 1 to 3 carbon atoms, L5 and L6 are each independently selected from alkylene groups having 1 to 10 carbon atoms with at least one methylene group optionally substituted with an ether group and at least one hydrogen group substituted with fluorine, and R1 and R2 are each independently selected from hydrogen, alkyl groups having 1 to 3 carbon atoms or halogens.

[0042]

[14] The present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode facing the positive electrode; a separator disposed between the positive electrode and the negative electrode; and the gel polymer electrolyte described above

[13] .

[0043] Beneficial effects

[0044] Because the composition of the present invention for forming a gel polymer electrolyte is characterized by containing a crosslinking compound of a specific chemical formula, wherein the crosslinking compound contains fluorine groups and spirocyclic diphosphate groups, the gel polymer electrolyte formed by the crosslinking reaction of the crosslinking compound can exhibit excellent oxidative stability and flame retardancy, and has an excellent effect on suppressing electrode heat generation. Therefore, lithium secondary batteries containing this composition for forming a gel polymer electrolyte or 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. Attached Figure Description

[0045] Figure 1 A schematic diagram illustrating the synthesis process of the crosslinked compound in Example 1.

[0046] Figure 2 The Fourier transform infrared (FT-IR) spectra of the fluorinated ether monoacrylate (PFE-mono AC) and spirocyclic pentaerythritol diphosphate perfluoroether acrylate (SPDFA) prepared in steps 2 and 3 of Preparation Example 1 are shown.

[0047] Figure 3 To prepare the spirocyclic pentaerythritol diphosphate diphosphonate chloride (SPDPC) prepared in step 1 of Example 1 1 Results of H nuclear magnetic resonance (NMR) spectroscopy.

[0048] Figure 4 For the preparation of the spirocyclic pentaerythritol diphosphate perfluoroether acrylate (SPDFA) prepared in step 3 of Example 1 1 Results of H NMR spectra.

[0049] Figure 5 The results are from the FT-IR spectral analysis of Examples 1 and 2.

[0050] Figure 6The results show the ionic conductivity measurements of the gel polymer electrolyte of Example 2 and the liquid electrolyte of Comparative Example 1 as a function of temperature.

[0051] Figure 7 This is a graph showing the current values ​​of the liquid electrolyte of Comparative Example 1 and the gel polymer electrolytes of Comparative Examples 4, 6 and 8 as a function of the applied voltage (3.0V to 6.0V) measured by linear sweep voltammetry (LSV).

[0052] Figure 8 The charge-discharge curves of the lithium secondary battery of Example 3 for the 1st, 10th, 30th, 50th, 100th, 200th, and 300th cycles are shown.

[0053] Figure 9 A graph illustrating the change in discharge capacity of the lithium secondary battery of Example 3 with cycling.

[0054] Figure 10 The photograph shows the results of the combustion test of the liquid electrolyte of Comparative Example 1 before (left) and after (right).

[0055] Figure 11 The photograph shows the results of the combustion test of the gel polymer electrolyte of Example 2 before (left) and after (right).

[0056] Figure 12 The photograph shows the results before (left) and after (right) storage of the polyethylene diaphragm without impregnation of the gel polymer electrolyte of the present invention at 140°C.

[0057] Figure 13 The photograph shows the results of storing the polyethylene diaphragm impregnated with the gel polymer electrolyte of the present invention at 140°C before (left) and after (right).

[0058] Figure 14 A graph showing the battery voltage measured over time when the lithium secondary batteries of Example 3 and Comparative Example 2 were stored in a hot box at 140°C.

[0059] Figure 15 A graph showing the heat generation of the lithium secondary batteries of Example 3 and Comparative Example 2 as a function of negative electrode temperature.

[0060] Figure 16 A graph showing the heat generation of the lithium secondary batteries of Example 3 and Comparative Example 2 as a function of positive electrode temperature. Detailed Implementation

[0061] It should be understood that the words or terms used in the specification and claims should not be interpreted as having the meanings defined in common dictionaries, and it should also be understood that, based on the principle that the inventors may appropriately define the meanings of words or terms to best interpret the invention, these words or terms should be interpreted as having meanings consistent with their meanings in the context of the relevant field and the technical ideas of the invention.

[0062] It will be further understood that the terms “comprising,” “including,” or “having” in this specification specify the presence of the said features, quantities, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0063] Before describing the present invention, unless otherwise stated in the present invention, the expression "*" indicates the portion (binding site) where the same or different atoms or chemical formulas are connected at their ends.

[0064] Furthermore, in the description of "a to b carbon atoms" in this specification, "a" and "b" each represent the number of carbon atoms contained in a specific functional group. That is, a functional group may include "a" to "b" carbon atoms. For example, the expression "alkyl group having 1 to 5 carbon atoms" indicates an alkyl group containing 1 to 5 carbon atoms, namely CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2CH2-, or (CH3)2CHCH2CH2-.

[0065] Furthermore, the alkyl groups in this specification may be entirely substituted or unsubstituted. Unless otherwise defined, the term "substituted" means that at least one hydrogen atom bonded to a carbon atom is substituted by an element other than hydrogen, such as 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 heterocyclic alkyl group having 3 to 12 carbon atoms, a heterocyclic alkenyl group having 3 to 12 carbon atoms, a heterocyclic alkynyl 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, an aryl group having 6 to 20 carbon atoms, a heteroaryl group having 2 to 20 carbon atoms, or a haloaryl group having 6 to 20 carbon atoms.

[0066] The invention will be described in more detail below.

[0067] Composition for forming gel polymer electrolytes

[0068] The present invention provides a composition for forming a gel polymer electrolyte.

[0069] Specifically, the composition for forming the gel polymer electrolyte is characterized by comprising a lithium salt, an organic solvent, and a crosslinking compound represented by Formula 1.

[0070] [Formula 1]

[0071]

[0072] In Formula 1, L1, L2, L3 and L4 are each independently selected from directly bonded or alkylene groups having 1 to 3 carbon atoms, L5 and L6 are each independently selected from alkylene groups having 1 to 20 carbon atoms in which at least one methylene group can be substituted with an ether group and at least one hydrogen group can be substituted with fluorine, and R1 and R2 are each independently selected from hydrogen, alkyl groups having 1 to 3 carbon atoms or halogens.

[0073] 1) Lithium salts

[0074] Various lithium salts commonly used in electrolytes for lithium secondary batteries can be used as the lithium salts used in this invention, without limitation. For example, the lithium salt may include Li + As a cation, and may include at least one selected from the group consisting of: 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 - .

[0075] Specifically, the lithium salt may include at least one selected from the group consisting of: LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 The lithium salts include LiBOB (LiB(C2O4)2), LiCF3SO3, LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, and LiBETI (LiN(SO2CF2CF3)2). Specifically, the lithium salts 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).

[0076] The concentration of lithium salt in non-aqueous electrolytes can range from 0.5 M to 5 M, particularly from 0.8 M to 4 M, and even more particularly from 0.8 M to 2.0 M. When the concentration of lithium salt meets the above range, the lithium-ion yield (Li) can be increased. + The output characteristics of a battery can be improved by adjusting the migration number and the degree of lithium-ion dissociation.

[0077] 2) Organic solvents

[0078] As an organic solvent, there are no particular restrictions on any non-aqueous solvent commonly used in lithium secondary batteries, as long as it can minimize the decomposition caused by oxidation reactions during the charging and discharging process of lithium secondary batteries.

[0079] Organic solvents may include at least one selected from the group consisting of carbonate solvents, ester solvents, ether solvents, ketone solvents, aromatic hydrocarbon solvents, phosphate ester solvents, sulfone solvents, nitrile solvents, and ionic liquids. More specifically, organic solvents may include at least one selected from the group consisting of carbonate solvents and ester solvents, and more specifically, may include carbonate solvents.

[0080] When the organic solvent includes carbonate solvents, the carbonate solvents may include cyclic carbonate solvents, linear carbonate solvents, or mixtures thereof.

[0081] Cyclic carbonate solvents are high-viscosity organic solvents that can effectively dissociate lithium salts in electrolytes due to their high dielectric constant. Specifically, cyclic carbonate organic solvents may 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-pentene carbonate, 2,3-pentene carbonate, and vinylene carbonate, and may more specifically include ethylene carbonate.

[0082] In addition, linear carbonate solvents are organic solvents with low viscosity and low dielectric constant. Specifically, linear carbonate organic solvents may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methyl ethyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate, and may more specifically include methyl ethyl carbonate (EMC).

[0083] The organic solvent can be a mixture of cyclic carbonate solvents and linear carbonate solvents. In this case, the volume ratio of the cyclic carbonate solvent to the linear carbonate solvent can be from 10:90 to 40:60, specifically from 15:85 to 35:65. When the mixing ratio of the cyclic carbonate solvent to the linear carbonate solvent meets the above range, both high dielectric constant and low viscosity characteristics can be achieved, along with excellent ionic conductivity characteristics.

[0084] As ester solvents, both straight-chain ester solvents and cyclic ester solvents can be used. Straight-chain ester solvents may specifically 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. Furthermore, cyclic ester solvents may specifically include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0085] As an ether solvent, any one or a mixture of two or more of the following can be used: 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), but the ether solvent is not limited thereto.

[0086] Nitrile solvents may be at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valerate, octanoic acid, heptanonitrile, cyclopentanoic acid, cyclohexanoic acid, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but are not limited thereto.

[0087] The ionic liquid may include at least one selected from the group consisting of: diethylmethylammonium trifluoromethanesulfonate, dimethylpropylammonium trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)imide N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium, bis(trifluoromethanesulfonyl)imide N-methyl-N-propylpiperidineonium, bis(trifluoromethanesulfonyl)imide N-butyl-N-methylpyrrolidineonium, and trifluoromethanesulfonylimide methylpropylpiperidineonium.

[0088] Cyclohexanone can be used as a ketone solvent.

[0089] Specific examples of aromatic hydrocarbon solvents can be selected from the group consisting of: 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. 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.

[0090] The sulfone solvent may be at least one selected from the group consisting of: dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, dipropyl sulfone, dibutyl sulfone, diphenyl sulfone, and dimethyl sulfoxide.

[0091] Phosphate ester solvents may be at least one selected from the group consisting of: trimethyl phosphate, triethyl phosphate, tri(2-chloroethyl) phosphate, tri(2,2,2-trifluoroethyl) phosphate, tripropyl phosphate, triisopropyl phosphate, tributyl phosphate, trihexyl phosphate, triphenyl phosphate, tricresyl phosphate, methyl vinyl phosphate, and ethyl vinyl phosphate.

[0092] 3) Crosslinked compounds represented by Formula 1

[0093] The cross-linked compound is characterized by being represented by the following formula 1.

[0094] [Formula 1]

[0095]

[0096] In Formula 1, L1, L2, L3 and L4 are each independently selected from directly bonded or alkylene groups having 1 to 3 carbon atoms, L5 and L6 are each independently selected from alkylene groups having 1 to 20 carbon atoms in which at least one methylene group can be substituted with an ether group and at least one hydrogen group can be substituted with fluorine, and R1 and R2 are each independently selected from hydrogen, alkyl groups having 1 to 3 carbon atoms or halogens.

[0097] The crosslinking compound contained in the composition for forming the gel polymer electrolyte is characterized in that acrylate groups are bonded to both ends of the spirocyclic diphosphate matrix, and there are fluorine-substituted linking groups (L5 and L6) between the spirocyclic diphosphate matrix and the acrylate groups. Since the polymer matrix formed by the crosslinking reaction of the crosslinking compound has excellent oxidative stability and flame retardancy, the thermal safety of the lithium secondary battery using the gel polymer electrolyte can be guaranteed and fire or explosion can be prevented, and excellent life performance can be achieved.

[0098] Specifically, spirocyclic diphosphates can form free radicals during vaporization upon heating. These free radicals can scavenge OH and H radicals that cause battery ignition, thus effectively preventing fire and improving flame retardancy. However, spirocyclic diphosphates suffer from poor oxidative stability, particularly at high voltages, and are prone to ring-opening. The reduced oxidative stability of spirocyclic diphosphates and their inability to achieve the aforementioned flame-retardant effects lead to a decline in the lifespan performance of lithium-ion batteries.

[0099] To address these issues, the crosslinking compound of the present invention is characterized by the presence of fluorinated linking groups (L5 and L6) between the spirocyclic diphosphate matrix and the acrylate groups. Since the electronegativity increases with the fluorinated linking groups, the decomposition and ring-opening of the spirocyclic diphosphate can be prevented at an excellent level. Therefore, the polymer matrix formed from this crosslinking compound or its crosslinking reaction can exhibit excellent oxidative stability and flame retardant properties. Consequently, lithium secondary batteries containing this composition for forming a gel polymer electrolyte or gel polymer electrolyte prepared therefrom can simultaneously exhibit excellent safety and lifespan performance.

[0100] In Formula 1, L1, L2, L3 and L4 are each independently selected from directly bonded or alkylene groups having 1 to 3 carbon atoms. Specifically, they can each be directly bonded or methylene (-CH2-). More specifically, from the perspective of improving the structural stability of spirocyclic diphosphates, they can be methylene groups.

[0101] In Formula 1, L5 and L6 are alkylene groups having 1 to 20 carbon atoms, wherein at least one hydrogen atom is substituted with fluorine. L5 and L6 can be used as linking groups connecting the spirocyclic diphosphate and the acrylate in Formula 1. Furthermore, since L5 and L6, as alkylene groups having 1 to 20 carbon atoms with at least one hydrogen atom substituted with fluorine, have excellent electronegativity, they can prevent ring-opening or decomposition of adjacent spirocyclic diphosphates and can improve oxidative stability.

[0102] L5 and L6 can each independently be at least one alkylene group having 1 to 20 carbon atoms with hydrogen substituted by fluorine, particularly at least one alkylene group having 1 to 10 carbon atoms with hydrogen substituted by fluorine, and even more particularly at least one alkylene group having 5 to 10 carbon atoms with hydrogen substituted by fluorine. When L5 and L6 are within the above ranges, the effect of preventing ring-opening or decomposition of the above-mentioned spirocyclic diphosphate can be further improved while enhancing the structural stability of the crosslinked compound.

[0103] Furthermore, L5 and L6 each independently have at least one methylene group (or difluoromethylene group) that can be substituted by an ether group (-O-). Specifically, L5 and L6 each independently have at least one methylene group (or difluoromethylene group) that can be substituted by an ether group (-O-) or not substituted.

[0104] L5 and L6 can each independently be an alkylene group having 1 to 20 carbon atoms, with at least one hydrogen atom substituted by fluorine, but there are no particular limitations. For example, L5 and L6 can each independently be represented by the following formula 2.

[0105] [Equation 2]

[0106] *-[(CH2) n -(CF2) m -(CH2) p -(O) q -(CH2) r -(CF2) s -(CH2) t ] u -*

[0107] In Equation 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+s+t) and u is an integer from 1 to 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.

[0108] In Equation 2, when u is 2 or more, the n, m, p, r, s and t of each unit can be the same or different from each other.

[0109] In Equation 2, the product of (n+m+p+q+s+t) and u can be an integer from 1 to 20, especially an integer from 1 to 10, and even more especially an integer from 5 to 10.

[0110] Specifically, the crosslinking compound represented by Formula 1 may include the crosslinking compound represented by Formula 1-1 below.

[0111] [Equation 1-1]

[0112]

[0113] The molecular weight of the cross-linked compound can be from 700 g / mol to 2,000 g / mol, specifically from 850 g / mol to 1,200 g / mol.

[0114] Molecular weight can be determined using the following methods: end-group quantitative methods to obtain molecular weight by quantitative analysis of functional groups at the ends of molecular chains; colligative methods (membrane permeation, vapor pressure permeation, etc.) using physical properties such as osmotic pressure, vapor pressure drop, boiling point elevation, and freezing point depression; light scattering methods using light scattering; ultracentrifugation methods to measure molecular weight by analyzing the sedimentation rate or concentration distribution of polymer solutions after centrifugation; viscometry methods using the viscosity of polymer solutions; and gel permeation chromatography (GPC) using high performance liquid chromatography (HPLC).

[0115] Based on the total weight of the composition used to form the gel polymer electrolyte, the content of the crosslinking compound can be from 1% to 30% by weight. Specifically, based on the total weight of the composition used to form the gel polymer electrolyte, the amount of the crosslinking compound can be 1% or more, 2% or more, 3% or more, 4% or more, 5% or more, 6% or more, 7% or more, or 8% or more. Based on the total weight of the composition used to form the gel polymer electrolyte, the amount of the crosslinking compound can be less than 30% by weight, less than 25% by weight, less than 20% by weight, less than 15% by weight, less than 12% by weight, or less than 11% by weight. More specifically, based on the total weight of the composition used to form the gel polymer electrolyte, the amount of the crosslinking compound can be in the range of 3% to 30% by weight, 5% to 30% by weight, 5% to 25% by weight, or 8% to 15% by weight. When the amount of crosslinking compound is within the above range, it is ideal to prevent the increase in resistance and decrease in ionic conductivity caused by excessive addition of crosslinking compound, while enabling the above-mentioned composition for forming gel polymer electrolyte or gel polymer electrolyte to exhibit excellent levels of oxidative stability and flame retardancy.

[0116] 4) Polymerization initiator

[0117] The composition used to form the gel polymer electrolyte may also contain a polymerization initiator.

[0118] Commonly known thermal polymerization initiators in the art can be used as polymerization initiators. Specifically, polymerization initiators may include those selected from diisobutyl peroxide, tert-amyl peroxide dicarbonate, di(4-tert-butylcyclohexyl) peroxide dicarbonate, diethylhexyl peroxide dicarbonate, dibutyl peroxide dicarbonate, diisopropyl peroxide dicarbonate, di(hexadecyl) peroxide dicarbonate, dimyristyl peroxide dicarbonate, tert-butyl peroxypentanoate, dilauroyl peroxide, didecanoyl peroxide, 2,5-dimethyl-2,5-di(2-ethylhexyl)peroxide, etc. At least one of the following groups: (oxidized) hexane, 1,1,3,3-tetramethyl butyl peroxide-2-ethylhexanoate, tert-amyl peroxide-2-ethylhexanoate, benzoyl peroxide, tert-butyl peroxide-2-ethylhexanoate, tert-butyl peroxide-ethylacetate, tert-butyl peroxide-isobutyrate, and 1,4-di(tert-butylperoxycarbon)cyclohexane, specifically a liquid thermal initiator having a low initiation temperature, and may include tert-butyl peroxyneoplastate, which produces almost no gas during the initiation reaction.

[0119] Polymerization initiators are readily soluble in organic solvents and can decompose upon heating at temperatures ranging from 30°C to 80°C to form free radicals. These free radicals promote the cross-linking reaction of cross-linking compounds, resulting in a polymer matrix (network) with guaranteed mechanical strength and ionic conductivity.

[0120] Based on 100 parts by weight of the crosslinking compound, the content of the polymerization initiator in the composition used to form the gel polymer electrolyte can be from 0.01 parts by weight to 20 parts by weight, specifically from 0.1 parts by weight to 10 parts by weight. If the content of the polymerization initiator is within the above range, the properties of the gel polymer electrolyte can be guaranteed by increasing the gel polymer conversion rate, and the wettability of the electrolyte to the electrode can be improved by preventing the pre-gel reaction.

[0121] 5) Additives

[0122] Furthermore, if necessary, the composition of the present invention for forming a gel polymer electrolyte may further include additives that can form a more stable ion-conducting film on the electrode surface, so as to further improve the low-temperature high-rate discharge characteristics, high-temperature stability, overcharging prevention, and expansion during high-temperature storage.

[0123] The additive may include at least one selected from the group consisting of: sulfonyl lactones, halogen-substituted carbonates, nitriles, cyclic carbonates, sulfites or salts, sulfones, sulfates or salts, phosphates or salts or phosphites or salts, borates or salts, and lithium salts.

[0124] The sulfonyl compounds may include at least one compound selected from the group consisting of 1,3-propanesulfonyl (PS), 1,4-butanesulfonyl, vinylsulfonyl, 1,3-propenesulfonyl (PRS), 1,4-butenesulfonyl, and 1-methyl-1,3-propenesulfonyl, and their content may be less than 5% by weight based on the total weight of the polymer electrolyte precursor composition. When the content of sulfonyl compounds in the polymer electrolyte precursor composition exceeds 5% by weight, increased resistance and deteriorated output may occur due to an excessively thick film formed on the electrode surface, and excessive additives in the polymer electrolyte precursor composition may also lead to increased resistance, thereby deteriorating the output characteristics.

[0125] Furthermore, the halogen-substituted carbonate compounds may include fluoroethylene carbonate (FEC), and their content may be less than 5% by weight based on the total weight of the polymer electrolyte precursor composition. If the amount of halogen-substituted carbonate compounds in the polymer electrolyte precursor composition exceeds 5% by weight, the cell expansion performance may deteriorate.

[0126] In addition, nitrile compounds may include at least one selected from the group consisting of: succinate (SN), adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valerate, octanoic acid, heptanonitrile, cyclovalerate, cyclohexanoic acid, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0127] Based on the total weight of the polymer electrolyte precursor composition, the content of nitrile compounds can be less than 8% by weight. If the total amount of nitrile compounds in the polymer electrolyte precursor composition exceeds 8% by weight, battery performance may deteriorate due to the increased film formed on the electrode surface, which increases resistance.

[0128] Furthermore, the cyclic carbonate compounds may include vinylene carbonate (VC) or vinylene carbonate, and their content may be less than 5% by weight based on the total weight of the polymer electrolyte precursor composition. If the amount of cyclic carbonate compounds in the polymer electrolyte precursor composition exceeds 5% by weight, the cell expansion suppression performance may deteriorate.

[0129] The sulfite or salt compound may include at least one compound 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-dimethyl propylene sulfite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, and 1,3-butanediol sulfite, and its content may be less than 5% by weight based on the total weight of the precursor composition.

[0130] The sulfone compounds may include at least one compound selected from the group consisting of divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone, and the content may be less than 5% by weight based on the total weight of the precursor composition.

[0131] The sulfate ester or salt compound may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyltrimethyl sulfate (MTMS), and its content may be less than 5% by weight based on the total weight of the precursor composition.

[0132] The phosphate ester or salt or phosphite or salt compound may include at least one compound selected from the group consisting of lithium difluorodioxazophosphate, lithium difluorophosphate, tri(trimethylsilyl) phosphate (TMSPa), tri(trimethylsilyl) phosphite (TMSPi), tri(2,2,2-trifluoroethyl) phosphate (TFEPa), and tri(trifluoroethyl) phosphite (TFEPi), and its content may be less than 3% by weight based on the total weight of the polymer electrolyte precursor composition.

[0133] The borate ester or salt compound may include tetraphenylborate, lithium oxaloyl difluoroborate (LiODFB) or lithium dioxaloyl borate (LiB(C2O4)2, LiBOB), and its content may be less than 3% by weight based on the total weight of the polymer electrolyte precursor composition.

[0134] The lithium salt compound is a compound different from the lithium salt contained in the precursor composition. The lithium salt compound may include LiPO2F2 or LiBF4, and its content may be less than 3% by weight based on the total weight of the polymer electrolyte precursor composition.

[0135] Specifically, additives may include halogen-substituted carbonate compounds, such as fluoroethylene carbonate (FEC).

[0136] In addition, it may also contain two or more other additives, and the total weight of the additives contained may be less than 20% by weight, specifically from 0.01% to 10% by weight, based on the total weight of the polymer electrolyte precursor composition.

[0137] Gel polymer electrolyte

[0138] Furthermore, the present invention also provides a gel polymer electrolyte. The gel polymer electrolyte can be prepared from the composition described above for forming the gel polymer electrolyte. More specifically, the gel polymer electrolyte can be formed by a crosslinking reaction of the composition described above for forming the gel polymer electrolyte or by a crosslinking reaction of the crosslinking compound contained in the composition described above for forming the gel polymer electrolyte.

[0139] Specifically, the gel polymer electrolyte comprises: a lithium salt; an organic solvent; and a polymer matrix formed by the crosslinking reaction of a crosslinking compound represented by Formula 1.

[0140] [Formula 1]

[0141]

[0142] In Formula 1, L1, L2, L3 and L4 are each independently selected from directly bonded or alkylene groups having 1 to 3 carbon atoms, L5 and L6 are each independently selected from alkylene groups having 1 to 10 carbon atoms, wherein at least one methylene group may be substituted with an ether group and at least one hydrogen group may be substituted with fluorine, and R1 and R2 are each independently selected from hydrogen, alkyl groups having 1 to 3 carbon atoms or halogens.

[0143] Because gel polymer electrolytes have excellent oxidative stability and flame retardancy due to the polymer matrix formed by crosslinking compounds represented by Formula 1, the thermal safety of lithium secondary batteries using gel polymer electrolytes can be ensured and fire or explosion can be prevented, and excellent life performance can be achieved.

[0144] The lithium salt, organic solvent, and crosslinked compound represented by Formula 1 are described in detail above.

[0145] Lithium secondary batteries

[0146] Furthermore, the present invention provides a lithium secondary battery comprising the above-described gel polymer electrolyte.

[0147] Specifically, the present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode facing the positive electrode; a separator disposed between the positive electrode and the negative electrode; and the aforementioned gel polymer electrolyte. Furthermore, the present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode facing the positive electrode; a separator disposed between the positive electrode and the negative electrode; and a gel polymer electrolyte formed from the aforementioned composition for forming the gel polymer electrolyte.

[0148] Specifically, after preparing an electrode assembly by disposing a separator between a positive electrode and a negative electrode, the assembled electrode assembly is placed in a battery case, and the composition for forming a gel polymer electrolyte of the present invention is injected, and a crosslinking reaction (thermal polymerization) of a crosslinking compound is carried out, thereby preparing a lithium secondary battery.

[0149] Since the composition for forming a gel polymer electrolyte and the gel polymer electrolyte have been described above, the positive electrode, the negative electrode, and the separator will be described below.

[0150] 1) Positive electrode

[0151] The positive electrode may include a positive electrode active material.

[0152] Lithium transition metal oxides are compounds capable of reversibly intercalating and deintercalating lithium, and among them, the lithium transition metal oxides may include at least one selected from the group consisting of: lithium cobalt oxides (e.g., LiCoO2, etc.), lithium nickel oxides (e.g., LiNiO2, etc.), lithium manganese oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium nickel manganese oxides (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni z O4 (where 0 < Z < 2), etc.), lithium nickel cobalt oxides (e.g., LiNi 1- Y1 Co Y1 O2 (where 0 < Y1 < 1), lithium manganese cobalt oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co z1 O4 (where 0 < Z1 < 2), etc.), lithium nickel manganese cobalt oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, and p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, and 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 aluminum (Al), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), tantalum (Ta), magnesium (Mg), and molybdenum (Mo)), p2, q2, r3, and s2 are the atomic fractions of each independent element, where 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), high-nickel lithium transition metal composite oxides, over-lithiated manganese-rich oxides, lithium iron phosphate (such as LiFePO4, etc.), over-lithiated layered oxides (OLO).

[0153] The high-nickel lithium transition metal composite oxide may include nickel accounting for more than 50 mol% of the total moles of transition metals contained in the lithium transition metal composite oxide. Specifically, it may include more than 60 mol% of nickel. Specifically, the high-nickel lithium transition metal composite oxide includes nickel and at least one selected from manganese, cobalt, and aluminum as transition metals, and based on the total moles of transition metals, it may include more than 50 mol%, especially more than 60 mol%, more especially 60 mol% to 90 mol% of nickel.

[0154] In addition, the lithium transition metal oxide may be a compound represented by the following formula 5.

[0155] [Formula 5]

[0156] Li 1+x (Ni a Co b Mn c M d )O2

[0157] In formula 5, M is at least one selected from the group consisting of tungsten (W), copper (Cu), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), zirconium (Zr), zinc (Zn), aluminum (Al), indium (In), tantalum (Ta), yttrium (Y), lanthanum (La), strontium (Sr), gallium (Ga), scandium (Sc), gadolinium (Gd), samarium (Sm), calcium (Ca), cerium (Ce), niobium (Nb), magnesium (Mg), boron (B), and molybdenum (Mo)), 1 + x, a, b, c, and d are the atomic fractions of each independent element, where 0 ≤ x ≤ 0.2, 0.50 ≤ a < 1, 0 < b ≤ 0.30, 0 < c ≤ 0.30, 0 ≤ d ≤ 0.1 and a + b + c + d = 1.

[0158] Preferably, a, b, c, and d can satisfy 0.60≤a≤0.95, 0.025≤b≤0.25, 0.025≤c≤0.25, and 0≤d≤0.05, respectively. Furthermore, a, b, c, and d can satisfy 0.80≤a≤0.95, 0.025≤b≤0.15, 0.025≤c≤0.15, and 0≤d≤0.05, respectively. Additionally, a, b, c, and d can satisfy 0.85≤a≤0.90, 0.05≤b≤0.10, 0.05≤c≤0.10, and 0≤d≤0.03, respectively.

[0159] Lithium transition metal oxides can be overlithiated manganese-rich oxides. Among all metals other than lithium, overlithiated manganese-rich oxides can include more than 50 mol% manganese (Mn), and the molar ratio of lithium to the transition metal can be greater than 1.

[0160] Specifically, the overlithiated manganese-rich oxide can be a compound represented by Formula 6 below.

[0161] [Formula 6]

[0162] Li 1+s [Ni t Co u Mn v M 1 w O 2+z

[0163] In Equation 6, 0.05≤s≤1, 0≤t≤0.5, 0≤u≤0.3, 0.5≤v<1.0, 0≤w≤0.2 and 0≤z≤1; preferably, 0.05≤s≤1.0, 0.1≤t≤0.5, 0≤u≤0.1, 0.5≤v<1.0, 0≤w≤0.2 and 0≤z≤1; 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 and 0≤z≤0.50. M 1 It can be at least one of the following: 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.

[0164] More specifically, the overlithiated manganese-rich oxide can be a compound represented by the following formula 6-1.

[0165] [Equation 6-1]

[0166] XLi2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M 1 wO2

[0167] In Equation 6-1, 0.1≤X≤0.5, 0.5≤y<1, 0≤z≤0.3 and 0≤w≤0.2, preferably, 0.2≤X≤0.5, 0.5≤y<1, 0≤z≤0.1 and 0≤w≤0.2, more preferably, 0.3≤X≤0.5, 0.6≤y<1, 0≤z≤0.1 and 0≤w≤0.2. M 1 It can be at least one of the following: 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.

[0168] The positive electrode may include: a positive electrode current collector; and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. In this case, the positive electrode active material layer may include a positive electrode active material.

[0169] There are no particular limitations on the positive electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. Specifically, the positive electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and aluminum-cadmium alloys, and may preferably include aluminum.

[0170] Positive current collectors can typically have a thickness ranging from 3 μm to 500 μm.

[0171] Micro-textures can be formed on the surface of the positive current collector to improve the adhesion of the positive electrode active material. For example, the positive current collector can be used in various shapes, such as membranes, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc.

[0172] The positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer may be disposed on one surface or two surfaces of the positive electrode current collector.

[0173] Considering that the positive electrode active material exhibits sufficient capacity, the content of the positive electrode active material in the positive electrode active material layer can be from 80% to 99% by weight, preferably from 92% to 98.5% by weight.

[0174] The positive electrode active material layer may also include a binder and / or a conductive agent together with the aforementioned positive electrode active material.

[0175] The adhesive is a component that assists in the bonding of the conductive agent with the active material and with the current collector. Specifically, it may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

[0176] From the perspective of ensuring sufficient bonding between components such as positive electrode active materials, the content of binder in the positive electrode active material layer can be from 1% to 20% by weight, preferably from 1.2% to 10% by weight.

[0177] Conductive agents can be used to assist and improve the conductivity in secondary batteries without particular limitations, as long as they are conductive and do not cause chemical changes. Specifically, the positive electrode conductive agent may include at least one selected from the group consisting of: graphite, such as natural or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers, such as carbon fibers or metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives, preferably including carbon black from the perspective of improving conductivity.

[0178] From the perspective of ensuring sufficient conductivity, the content of conductive agent in the positive electrode active material layer can be from 1% to 20% by weight, preferably from 1.2% to 10% by weight.

[0179] The positive electrode active material layer can have a thickness of 30 μm to 400 μm, preferably 40 μm to 110 μm.

[0180] The positive electrode can be prepared by coating a positive electrode slurry, which includes a positive electrode active material and optionally a binder, a conductive agent and a solvent for forming the positive electrode slurry, onto a positive electrode current collector, and then drying and calendering the coated positive electrode current collector.

[0181] Solvents used to form the cathode slurry may include organic solvents such as NMP (N-methyl-2-pyrrolidone). The solids content of the cathode slurry may be from 40% to 90% by weight, specifically from 50% to 80% by weight.

[0182] 2) Negative electrode

[0183] The negative electrode can face the positive electrode.

[0184] The negative electrode may include a negative electrode current collector and a layer of negative electrode active material disposed on at least one surface of the negative electrode current collector.

[0185] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. Specifically, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel that has been surface-treated with one of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used as negative electrode current collectors.

[0186] Negative electrode current collectors can typically have a thickness ranging from 3 μm to 500 μm.

[0187] Micro-textured irregularities can be formed on the surface of the negative electrode current collector to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes, such as membranes, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc.

[0188] The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one surface or two surfaces of the negative electrode current collector.

[0189] The negative electrode active material layer may include a negative electrode active material.

[0190] The negative electrode active material is a material capable of reversibly inserting / deintercalating lithium ions, wherein it may include at least one selected from the group consisting of carbon-based active materials, (quasi-)metallic active materials and lithium metal, specifically including at least one of carbon-based active materials and (quasi-)metallic active materials.

[0191] Carbon-based active materials 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 may preferably include at least one selected from the group consisting of artificial graphite and natural graphite.

[0192] From the perspective of ensuring structural stability during charging and discharging and reducing side reactions with the electrolyte, the average particle size (D50) of carbon-based active materials can be 10 μm to 30 μm, preferably 15 μm to 25 μm.

[0193] Specifically, the (quasi-)metallic active material may include: at least one (quasi-)metal selected from the group consisting of copper (Cu), nickel (Ni), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), silicon (Si), antimony (Sb), lead (Pb), indium (In), zinc (Zn), barium (Ba), radium (Ra), germanium (Ge), aluminum (Al), vanadium (V), titanium (Ti), and tin (Sn); an alloy of lithium and at least one (quasi-)metal 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 (quasi-)metal 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 titanate oxide (LTO); or lithium vanadium oxide.

[0194] More specifically, the (quasi-)metallic active material may include a silicon-based active material.

[0195] The silicon-based active material may include a compound represented by SiO x (0 < x < 2). For SiO2, since it does not react with lithium ions, it cannot store lithium. Therefore, it is preferred that x is within the above range. More preferably, the silicon-based active material may be SiO.

[0196] From the perspective of ensuring the structural stability during charge and discharge processes and reducing side reactions with the electrolyte, the average particle size (D50) of the silicon-based active material may be 1 μm to 30 μm, preferably 2 μm to 15 μm.

[0197] The content of the negative electrode active material in the negative electrode active material layer may be 60% to 99% by weight, preferably 75% to 95% by weight.

[0198] The negative electrode active material layer may further include a binder and / or a conductive agent together with the negative electrode active material.

[0199] The adhesive is used to enhance the adhesion between the negative electrode active material layer and the negative electrode current collector to improve battery performance. The adhesive may include, 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and materials in which hydrogen is replaced by lithium (Li), Na, or Ca, and may also include various copolymers thereof.

[0200] The binder content in the negative electrode active material layer can be from 0.5% to 10% by weight, preferably from 1% to 5% by weight.

[0201] There are no particular restrictions on conductive agents, as long as they are conductive and do not cause chemical changes in the battery. For example, conductive materials such as: graphite such as natural or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives.

[0202] The content of the conductive agent in the negative electrode active material layer can be from 0.5% to 10% by weight, preferably from 1% to 5% by weight.

[0203] The negative electrode active material layer can have a thickness of 10 μm to 100 μm, preferably 50 μm to 80 μm.

[0204] The negative electrode can be prepared by coating at least one surface of the negative electrode current collector with a negative electrode slurry containing a negative electrode active material, a binder, a conductive agent and / or a solvent for forming the negative electrode slurry, and then drying and calendering the coated negative electrode current collector.

[0205] From the perspective of facilitating the dispersion of the negative electrode active material, binder, and / or conductive agent, the solvent for forming the negative electrode slurry may, for example, include at least one selected from the group consisting of distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol, and isopropanol, specifically NMP. The solids content of the negative electrode slurry may be from 30% to 80% by weight, specifically from 40% to 70% by weight.

[0206] 3) Diaphragm

[0207] Furthermore, conventional porous polymer membranes commonly used as separators, such as porous polymer membranes prepared from polyolefin polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers), can be used alone or in laminations as separators, and typical porous nonwoven fabrics, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers, can be used, but the invention is not limited thereto. In addition, coated separators comprising ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators having single-layer or multi-layer structures can optionally be used.

[0208] The shape of the lithium secondary battery of the present invention is not particularly limited, but cylindrical, prismatic, pouch or coin-shaped batteries made from cans can be used.

[0209] The present invention will now be described in detail with reference to specific embodiments. However, the following embodiments are merely illustrative of the invention, and the scope of the invention is not limited thereto. It will be apparent to those skilled in the art that various modifications and changes can be made within the scope and spirit of the invention. Such modifications and changes fall within the scope of the claims included herein.

[0210] Examples and Comparative Examples

[0211] Preparation Example 1: Preparation of Crosslinked Compounds: Synthesis of Spirocyclic Pentaerythritol Diphosphate Perfluoroether Acrylate (SPDFA, Formula 1-1)

[0212] (1) Step 1: Synthesis of spirocyclic pentaerythritol diphosphate diphosphonate chloride (SPDPC)

[0213] Figure 1 A schematic diagram (step 2) of the synthesis of spirocyclic pentaerythritol diphosphate diphosphoryl chloride (SPDPC) from pentaerythritol and phosphorus oxychloride is shown. First, pentaerythritol (6.81 g, 50 mmol) was placed in a double-jacketed container 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 temperature of the mixture was raised to 80°C, stirred for 2 hours, and then raised to 110°C for 20 hours. The resulting compound was filtered, washed with tetrahydrofuran and ethanol, and then dried under vacuum at 80°C for 12 hours to obtain spirocyclic pentaerythritol diphosphate diphosphoryl chloride. The chemical structure of the product was confirmed by nuclear magnetic resonance (NMR) spectroscopy.

[0214] [Confirmation of the chemical structure of spirocyclic pentaerythritol diphosphate diphosphoyl chloride (NMR)]

[0215] 1 H NMR (DMSO), δ (ppm): 4.25-4.1 (dd, 4H)

[0216] 31 P NMR (CDCl3), δ (ppm): -7.95

[0217] (2) Step 2: Synthesis of fluorinated ether monoacrylate (PFE-mono AC)

[0218] A schematic diagram of the synthesis of fluorinated ether monoacrylate (PFE-mono AC) from perfluoroether diol (PFE-OH) is shown below. Figure 1 As shown in Step 2. First, 10 g of 1H,1H,8H,8H-perfluoro-3,6-dioxaoctane-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-jacketed container. After adding all reactants and 4.15 g of triethylamine (TEA) catalyst to THF at 0 °C, the reaction temperature was raised to 25 °C and the reaction was carried out for 12 hours. After vacuum drying of the THF solvent in the resulting solution, unreacted substances and byproducts were removed by column chromatography, and the chemical structure of the obtained product was confirmed by NMR spectroscopy.

[0219] [Confirmation of the chemical structure of fluorinated ether monoacrylate (NMR)]

[0220] 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)

[0221] (3) Step 3: Synthesis of spirocyclic pentaerythritol diphosphate perfluoroether acrylate (SPDFA)

[0222] A schematic diagram of the synthesis of spirocyclic pentaerythritol diphosphate perfluoroether acrylate (SPDFA) is shown below. Figure 1 As shown in step 3. First, 10.0 g of the prepared pentaerythritol diphosphate diphosphonate chloride (SPDPC) 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-jacketed container. After adding all reactants and 18.2 g of triethylamine catalyst to THF at 0 °C, the reaction temperature was raised to 25 °C and the reaction was carried out for 48 hours (2 days). After vacuum drying of the acetonitrile solvent in the resulting solution, unreacted substances and byproducts were completely removed by column chromatography. Figure 2 Fourier transform infrared (FT-IR) results and Figure 3 In1 The chemical structure of the obtained product was confirmed by 1H NMR spectroscopy. The molecular weight of the prepared spirocyclic pentaerythritol diphosphate perfluoroether acrylate (SPDFA) was 952.4 g / mol.

[0223] Specifically, Figure 2 The FT-IR spectra of perfluoroether monoacrylate (PFE-mono AC) and spirocyclic pentaerythritol diphosphate perfluoroether acrylate (SPDFA) prepared via steps 2 and 3 are shown. Furthermore, Figure 3 The spirocyclic pentaerythritol diphosphate diphosphonate chloride (SPDPC) prepared in step 1 1 1H NMR spectral results. In addition... Figure 4 The spirocyclic pentaerythritol diphosphate perfluoroether acrylate (SPDFA) prepared in step 3 1 1H NMR spectral results.

[0224] Example 1: Preparation of a composition for forming a gel polymer electrolyte

[0225] Lithium hexafluorophosphate (LiPF6) at a concentration of 1.15 M 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 prepare a liquid electrolyte. The amount of FEC added to the liquid electrolyte was 5% by weight. 9 g of the liquid electrolyte was mixed with 1 g of spirocyclic pentaerythritol diphosphate perfluoroether acrylate (SPDFA) crosslinking compound, and 0.01 g (based on 1 part by weight of crosslinking compound per 100 parts by weight) of tert-butyl peroxypentanoate (polymerization initiator) was added and stirred to prepare a composition for forming a gel polymer electrolyte.

[0226] Example 2: Preparation of Gel Polymer Electrolytes

[0227] The composition prepared in Example 1 for forming a gel polymer electrolyte was thermally crosslinked at 70°C for 1 hour to prepare a gel polymer electrolyte (SPDFA GPE) with a polymer matrix formed by crosslinking compounds.

[0228] Example 3: Preparation of Lithium Secondary Batteries

[0229] The positive electrode active material (Li[Ni) 0.6 Co 0.2 Mn 0.2O2), conductive agent (Super P), and binder (PVdF) were added to N-methylpyrrolidone (NMP) solvent in a weight ratio of 95:3:2 to prepare a positive electrode slurry. The positive electrode slurry was then coated onto one surface of an aluminum positive electrode current collector with a thickness of 15 μm, dried, and rolled to prepare the positive electrode.

[0230] A negative electrode slurry was prepared by adding the negative electrode active material (graphite), conductive agent (Super P), and binder (PVdF) to an N-methylpyrrolidone solvent at a weight ratio of 90:3:7. The negative electrode slurry was then coated onto one surface of a copper negative electrode current collector with a thickness of 15 μm, dried, and calendered to prepare the negative electrode.

[0231] A porous polyethylene membrane is disposed between the positive and negative electrodes prepared above to prepare an electrode assembly. The electrode assembly is housed in a battery case. The composition for forming a gel polymer electrolyte of Example 1 is injected into the battery case. The battery case is sealed and then heat-treated at 70°C to prepare a lithium secondary battery in which a gel polymer electrolyte is formed by the composition for forming a gel polymer electrolyte.

[0232] Comparative Example 1: Preparation of Liquid Electrolytes

[0233] Lithium hexafluorophosphate (LiPF6) at a concentration of 1.15 M 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 prepare a liquid electrolyte. The amount of fluoroethylene carbonate added to the liquid electrolyte was 5% by weight.

[0234] Comparative Example 2: Preparation of Lithium Secondary Batteries

[0235] The lithium secondary battery was prepared in the same manner as in Example 3, except that the liquid electrolyte of Comparative Example 1 was used instead of the composition for forming the gel polymer electrolyte of Example 1, and no separate heat treatment for forming the gel polymer electrolyte was performed.

[0236] Comparative Example 3: Preparation of a composition for forming a gel polymer electrolyte

[0237] The composition for forming the gel polymer electrolyte was prepared in the same manner as in Example 1, except that 1 g of the compound represented by Formula A was added to the composition for forming the gel polymer electrolyte in place of 1 g of the spirocyclic pentaerythritol diphosphate perfluoroether acrylate (SPDFA) crosslinking compound.

[0238] [Formula A]

[0239]

[0240] (In equation A, n1 is 3)

[0241] Comparative Example 4: Preparation of Gel Polymer Electrolytes

[0242] The composition prepared in Comparative Example 3 for forming a gel polymer electrolyte was thermally crosslinked at 70°C for 1 hour to prepare a gel polymer electrolyte (SPDFA GPE) with a polymer matrix formed by crosslinking compounds.

[0243] Comparative Example 5: Preparation of a composition for forming a gel polymer electrolyte

[0244] The composition for forming the gel polymer electrolyte was prepared in the same manner as in Example 1, except that 1 g of the compound represented by Formula B was added to the composition for forming the gel polymer electrolyte in place of 1 g of the spirocyclic pentaerythritol diphosphate perfluoroether acrylate (SPDFA) crosslinking compound.

[0245] [Formula B]

[0246]

[0247] (In equation B, m1 is 3)

[0248] Comparative Example 6: Preparation of Gel Polymer Electrolytes

[0249] The composition prepared in Comparative Example 5 for forming a gel polymer electrolyte was thermally crosslinked at 70°C for 1 hour to prepare a gel polymer electrolyte (SPDFA GPE) with a polymer matrix formed by crosslinking compounds.

[0250] Comparative Example 7: Preparation of a composition for forming a gel polymer electrolyte

[0251] The composition for forming the gel polymer electrolyte was prepared in the same manner as in Example 1, except that 1 g of the compound represented by formula C and 1 g of the spirocyclic pentaerythritol diphosphate perfluoroether acrylate (SPDFA) crosslinking compound were added to the composition for forming the gel polymer electrolyte.

[0252] [Formula C]

[0253]

[0254] Comparative Example 8: Preparation of Gel Polymer Electrolytes

[0255] The composition prepared in Comparative Example 7 for forming a gel polymer electrolyte was thermally crosslinked at 70°C for 1 hour to prepare a gel polymer electrolyte (SPDFA GPE) with a polymer matrix formed by crosslinking compounds.

[0256] Experimental Example

[0257] Experimental Example 1: Confirmation of the cross-linking reaction of gel polymer electrolytes

[0258] To confirm whether the crosslinking reaction of the gel polymer electrolyte (SPDFA GPE) in Example 2 proceeded well, FT-IR spectroscopy analysis was performed. The results are shown below. Figure 5 middle.

[0259] It has been confirmed that in the SPDFA GPE of Example 2, the C = C(1635cm) of the SPDFA of Example 1 is equal to that of Example 1. -1 The disappearance of the double bond peak confirms that the cross-linking reaction has been completed and a gel polymer electrolyte has been formed.

[0260] Experimental Example 2: Measurement of Ionic Conductivity

[0261] The gel polymer electrolyte of Example 2 and the liquid electrolyte of Comparative Example 1 were tested using a CH instrument (CHI 600D) at 10 Hz to 10 Hz. 6 The AC impedance between sandwich electrodes was measured within a frequency range of Hz and an amplitude of 50 mV. The measured values ​​were analyzed using a frequency response analyzer to measure the ionic conductivity as a function of temperature. The results are shown in... Figure 6 middle.

[0262] See Figure 6 The gel polymer electrolyte of Example 2 exhibits a strength of 4 × 10⁻⁶ at room temperature. -3 Scm -1 The above-mentioned high ionic conductivity.

[0263] Experimental Example 3: Electrochemical Stability Assessment

[0264] To compare the electrochemical stability of the gel polymer electrolyte of Example 2, the liquid electrolyte of Comparative Example 1, and the gel polymer electrolytes of Comparative Examples 4, 6, and 8, the current values ​​as a function of applied voltage were measured by linear sweep voltammetry (LSV) (scan rate 1 mV / s), and the results are shown below. Figure 7 middle. Figure 7 This is a graph (oxidation scan) showing the values ​​of the x-axis over the range of 3.0V to 6.0V.

[0265] See Figure 7 As can be seen, due to the characteristic structure of the cross-linked compound of Formula 1, the gel polymer electrolyte of Example 2 exhibits improved electrochemical stability compared with the liquid electrolyte of Comparative Example 1 and the gel polymer electrolytes of Comparative Examples 4, 6 and 8.

[0266] Experiment Example 4: Cyclic Characteristic Evaluation

[0267] The lithium secondary battery of Example 3 prepared above was charged to 4.2V at a constant current of 0.1C at 25°C and discharged to 2.5V at a constant current of 0.1C for one cycle, and the formation process was carried out for 4 cycles.

[0268] Then, the lithium secondary battery will be charged to 4.2V at a constant current of 0.2C at 25°C and discharged to 2.5V at a constant current of 0.2C as one cycle, and 300 cycles of charging and discharging will be performed.

[0269] Figure 8 The charge-discharge curves of the lithium secondary battery of Example 3 for the 1st, 10th, 30th, 50th, 100th, 200th, and 300th cycles are shown. Figure 9 A graph showing the change in discharge capacity of the lithium secondary battery of Example 3 with cycling is shown.

[0270] For the lithium secondary battery of Example 3 using the gel polymer electrolyte of Example 3, it is known that the charge and discharge cycles proceed stably.

[0271] Experiment Example 5: Flame Retardant Properties Evaluation

[0272] (1) Experimental Example 5-1

[0273] To evaluate the flame retardant properties of the gel polymer electrolyte prepared in Example 2 and the liquid electrolyte in Comparative Example 1, a combustion test was conducted using a flame torch.

[0274] Figure 10 The photograph shows the results of the combustion test of the liquid electrolyte of Comparative Example 1 before (left) and after (right). Figure 11 The photograph shows the results of the combustion test of the gel polymer electrolyte of Example 2 before (left) and after (right).

[0275] See Figure 10 When a flamethrower is used, the liquid electrolyte of Comparative Example 1 exhibits high flammability.

[0276] Conversely, see Figure 11 It can be seen that the gel polymer electrolyte of Example 2 exhibits excellent self-extinguishing properties and flame-retardant properties of non-combustible gel polymer electrolyte.

[0277] (2) Experimental Example 5-2

[0278] To evaluate the flame retardant properties of the gel polymer electrolyte prepared in Example 2, the liquid electrolyte of Comparative Example 1, and the gel polymer electrolytes of Comparative Examples 4, 6, and 8, a combustion test was conducted using a flame torch.

[0279] Self-extinguishing time tests were conducted on the gel polymer electrolyte prepared in Example 2, the liquid electrolyte of Comparative Example 1, and the gel polymer electrolytes of Comparative Examples 4, 6, and 8. In these tests, 1 g of each electrolyte was ignited, and the time until the sample ignited was measured to evaluate flame retardancy. The results are shown in Table 1 below.

[0280] [Table 1]

[0281] Self-extinguishing time (seconds) Example 2 0 Comparative Example 1 34.2 Comparative Example 4 2.5 Comparative Example 6 1.8 Comparative Example 8 6.1

[0282] Referring to Table 1, the gel polymer electrolyte for lithium secondary batteries prepared in Example 2 of the present invention did not ignite. However, it can be seen that the liquid electrolyte of Comparative Example 1 and the gel polymer electrolytes of Comparative Examples 4, 6 and 8 exhibited worse flame retardant properties than the gel polymer electrolyte of Example 2. The gel polymer electrolyte of Example 2 exhibited completely non-flammable properties.

[0283] Experiment Example 6: Assessment of Diaphragm Shrinkage

[0284] Prepare two identical polyethylene diaphragms.

[0285] After impregnating one of the two polyethylene membranes with the composition of Example 1 for forming a gel polymer electrolyte, a crosslinking reaction was carried out at 70°C for 1 hour to prepare a polyethylene membrane impregnated with the gel polymer electrolyte. The other polyethylene membrane was left untreated.

[0286] The polyethylene diaphragm without impregnation of gel polymer electrolyte (without any treatment) was stored at 140°C for 30 minutes. Figure 12 The left side shows a photo of the polyethylene diaphragm before it was stored at 140°C, while Figure 12 The right side shows a photograph of the polyethylene diaphragm after being stored at 140°C for 30 minutes.

[0287] In addition, the polyethylene diaphragm impregnated with the gel polymer electrolyte was stored at 140°C for 30 minutes. Figure 13 The left side shows a photo of the polyethylene diaphragm before it was stored at 140°C. Figure 13 The right side shows a photograph of the polyethylene diaphragm after being stored at 140°C for 30 minutes.

[0288] See Figure 12 It was found that polyethylene diaphragms without the gel polymer electrolyte of the present invention exhibited significant shrinkage at high temperatures. See also Figure 13 It can be confirmed that polyethylene diaphragms without the gel polymer electrolyte of the present invention exhibit very low shrinkage when stored at 140°C and have high thermal stability at high temperatures.

[0289] Experiment Example 7: Short Circuit Test of Lithium Secondary Battery

[0290] The lithium secondary batteries of Example 3 and Comparative Example 2 were charged to 4.2V at a constant current of 0.1C at 25°C, and then stored in a hot box at 140°C to measure the battery voltage over time. The results are shown in... Figure 14 middle.

[0291] See Figure 14 Compared to the lithium secondary battery of Comparative Example 2, which used the liquid electrolyte of Comparative Example 1, the lithium secondary battery of Example 3, which used the gel polymer electrolyte of Example 2, maintained a stable battery voltage even at high temperatures. Based on these results, it can be seen that by suppressing microscopic internal short circuits in the lithium secondary battery when using the gel polymer electrolyte of the present invention, the thermal stability of the lithium secondary battery can be significantly improved.

[0292] Experiment Example 8: Measurement of Electrode Heat Generation

[0293] In the lithium secondary batteries of Example 3 and Comparative Example 2, differential scanning calorimetry (DSC) was used to measure the heat generation of the negative and positive electrodes to compare the heat generation of the electrodes with different electrolytes.

[0294] Specifically, the lithium secondary batteries prepared in Example 3 and Comparative Example 2 were subjected to a formation process of 4 cycles, consisting of charging to 4.2V at 25°C with a constant current of 0.1C and discharging to 2.5V at 0.1C as one cycle. Subsequently, each lithium secondary battery was charged to 4.2V at 25°C with a constant current of 0.2C and discharged to 2.5V for one charge-discharge cycle. After being fully charged at a constant current of 0.2C, each lithium secondary battery was disassembled to recover the positive and negative electrode materials. The heat generation was then measured using a DSC test. The DSC test was conducted by heating from 0°C to 300°C at a rate of 10°C / min.

[0295] The DSC test results of the negative electrode are as follows Figure 15 As shown, the DSC test results for the positive electrode are as follows: Figure 16 As shown.

[0296] See Figure 15 and Figure 16 It can be seen that the heat generation of both the negative and positive electrodes of the lithium secondary battery in Example 3 is significantly lower than that of the lithium secondary battery in Comparative Example 2. Based on these results, it is evident that the composition for forming the gel polymer electrolyte of the present invention, or the gel polymer electrolyte itself, can significantly improve the thermal safety of lithium secondary batteries.

Claims

1. A composition for forming a gel polymer electrolyte, the composition comprising: Lithium salts; Organic solvents; and The cross-linked compound represented by Formula 1: [Formula 1] in, In Formula 1, L1, L2, L3, and L4 are each independently selected from directly bonded or alkylene groups having 1 to 3 carbon atoms. L5 and L6 are each independently an alkylene group having 1 to 20 carbon atoms, in which at least one methylene group is optionally substituted with an ether group and at least one hydrogen group is substituted with fluorine. R1 and R2 are each independently selected from hydrogen, alkyl groups having 1 to 3 carbon atoms, or halogens.

2. The composition for forming a gel polymer electrolyte as claimed in claim 1, further comprising a polymerization initiator.

3. The composition for forming a gel polymer electrolyte as described in claim 1, wherein, The molecular weight of the crosslinked compound is from 700 g / mol to 2,000 g / mol.

4. The composition for forming a gel polymer electrolyte as described in claim 1, wherein, Based on the total weight of the composition for forming the gel polymer electrolyte, the content of the crosslinking compound is from 1% to 30% by weight.

5. The composition for forming a gel polymer electrolyte as described in claim 1, wherein, In Formula 1, L1, L2, L3 and L4 are each independently selected from direct bonding or methylene.

6. The composition for forming a gel polymer electrolyte as claimed in claim 1, wherein, In Formula 1, L1, L2, L3 and L4 are each methylene groups.

7. The composition for forming a gel polymer electrolyte as claimed in claim 1, wherein, L5 and L6 are each independently represented by Equation 2: [Equation 2] *-[(CH2) n -(CF2) m -(CH2) p -(O) q -(CH2) r -(CF2) s -(CH2) t ] u -* In Equation 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+s+t) and u is an integer from 1 to 20. The condition is 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.

8. The composition for forming a gel polymer electrolyte as claimed in claim 1, wherein, The cross-linked compounds represented by Formula 1 include those represented by Formula 1-1: [Equation 1-1] 9. The composition for forming a gel polymer electrolyte as claimed in claim 1, wherein, The lithium salt includes those selected from LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, and LiB. 10 Cl 10 At least one of the group consisting of LiBOB (LiB(C2O4)2), LiCF3SO3, LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2 and LiBETI (LiN(SO2CF2CF3)2).

10. The composition for forming a gel polymer electrolyte as claimed in claim 1, 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 ester solvents, sulfone solvents, nitrile solvents, and ionic liquids.

11. The composition for forming a gel polymer electrolyte as claimed in claim 1, further comprising additives, in, The additive comprises at least one selected from the group consisting of sulfonyl lactones, halogen-substituted carbonates, nitriles, cyclic carbonates, sulfites or salts, sulfones, sulfates or salts, phosphates or salts or phosphites or salts, borates or salts, and lithium salts.

12. The composition for forming a gel polymer electrolyte as described in claim 11, wherein, The additives include halogen-substituted carbonate compounds. The halogen-substituted carbonate compound is fluoroethylene carbonate.

13. A gel polymer electrolyte, comprising: Lithium salts; organic solvents; And the polymer matrix formed by the crosslinking reaction of the crosslinking compound represented by Formula 1: [Formula 1] In Formula 1, L1, L2, L3, and L4 are each independently selected from directly bonded or alkylene groups having 1 to 3 carbon atoms. L5 and L6 are each independently an alkylene group having 1 to 10 carbon atoms, in which at least one methylene group is optionally substituted with an ether group and at least one hydrogen group is substituted with a fluorine group. R1 and R2 are each independently selected from hydrogen, alkyl groups having 1 to 3 carbon atoms, or halogens.

14. A lithium secondary battery, comprising: positive electrode; The negative electrode facing the positive electrode; A diaphragm is disposed between the positive electrode and the negative electrode; as well as The gel polymer electrolyte of claim 13.

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