A gel electrolyte composition, a gel electrolyte and a lithium ion battery

Abstract

The application discloses a gel electrolyte composition, a gel electrolyte and a lithium ion battery, and relates to the technical field of lithium batteries. The gel electrolyte composition with specific components is polymerized under the action of an initiator to obtain the gel electrolyte, the gel electrolyte has high ion conductivity and stability, and can enable the lithium ion battery to have low internal resistance, high cycle performance and high safety.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more particularly to a gel electrolyte composition, a gel electrolyte, and a lithium-ion battery. Background Technology

[0002] Currently, most commercially available lithium-ion batteries use liquid electrolytes, whose solvents are typically carbonate compounds. These compounds are highly reactive and flammable, making them prone to combustion and explosion when subjected to overcharging, overheating, short circuits, or impacts. This fails to meet the stringent safety requirements of large-scale industrial energy storage. Furthermore, liquid electrolytes pose a risk of leakage, leading to performance degradation or even battery failure, and their volatilization also affects long-term battery stability. All-solid-state batteries represent the future mainstream development direction; however, the technology is still immature, exhibiting low conductivity, interfacial compatibility issues with electrodes, and high interfacial impedance, all of which impact overall battery performance and cycle life. Their complex manufacturing process and high cost also limit their industrial application.

[0003] Gel electrolytes typically consist of a polymer matrix, an organic solvent, and a lithium electrolyte salt, with the organic solvent and lithium electrolyte salt immobilized within the network structure of the polymer matrix. Gel electrolytes represent a special state between solids and liquids, possessing the geometric shape, strength, and elasticity of solids, as well as the high ion diffusion rate of liquids. They can effectively reduce the risk of leakage and electrolyte evaporation, improving battery safety. Furthermore, with higher electrolyte content, the conductivity of gel electrolytes can approach that of liquid electrolytes, promising to provide high-power, high-energy-density, and high-specific-energy safe power sources for portable devices. This will drive the further development and application of lithium-ion battery technology in new energy vehicles, energy storage systems, and portable electronic devices, making it a major development direction in the near future. To meet the ever-increasing demands for safety, performance, and cost in lithium-ion batteries, it is necessary to develop gel electrolytes with high safety, high conductivity, and long cycle performance. Summary of the Invention

[0004] Based on the technical problems existing in the background art, the present invention proposes a gel electrolyte composition, a gel electrolyte and a lithium-ion battery. The gel electrolyte has high ionic conductivity, interfacial compatibility and stability, which enables the lithium-ion battery to have low internal resistance, long cycle performance and high safety.

[0005] This invention proposes a gel electrolyte composition comprising a polymeric monomer, a lithium salt, a sulfate ester film-forming additive, and a solvent;

[0006] The polymerizable monomers include a first monomer and a second monomer; the first monomer is an acrylate monomer containing one or two unsaturated double bond functional groups, and the second monomer is an acrylate monomer containing three or more unsaturated double bond functional groups.

[0007] The gel electrolyte composition satisfies the following conditions: 5%≤a%≤8%, 0.5%≤b%≤2%, 0.5%≤c%≤1%, and 3.25≤(a+b)c≤8.55;

[0008] Where a% is the mass percentage of the first monomer in the gel electrolyte composition;

[0009] b% represents the mass percentage of the second monomer in the gel electrolyte composition;

[0010] c% is the mass percentage of the sulfate ester film-forming additive in the gel electrolyte composition.

[0011] The gel electrolyte composition of this invention comprises polymeric monomers, lithium salts, sulfate-based film-forming additives, and solvents. Short-chain acrylate monomers containing one or two unsaturated double-bond functional groups are used to construct the polymer backbone, while multi-branched acrylate monomers containing three or more unsaturated double-bond functional groups are used for cross-linking. The combination of these two monomers forms a polymer matrix that can constrain the fluidity and volatility of the electrolyte, provide a certain mechanical strength, and does not significantly reduce the electrolyte's conductivity. The sulfate-based film-forming additives have a low film-forming potential, allowing film formation during the formation stage to generate a high-conductivity SEI film containing Li₂SO₃ and Li₂SO₄. This prevents monomers or other substances from continuing to react on the electrode surface and does not significantly degrade DCR and high-temperature storage performance, thus enhancing the cycle stability of the battery cell. By controlling the ratio of polymeric monomers and sulfate-based film-forming additives, this invention yields a gel electrolyte with excellent conductivity, mechanical properties, and high-temperature resistance. Furthermore, the system exhibits good stability and does not experience discoloration, hydrolysis, or excessive gelation, thus combining high conductivity, long cycle performance, and high safety.

[0012] Preferably, the sulfate ester additive is selected from at least one compound as shown in Formula I:

[0013]

[0014] Formula I

[0015] In Formula I, R1 to R4 are each independently selected from any one of H, F, C1 to C6 alkyl, C2 to C6 alkenyl, C1 to C6 alkoxy, C1 to C6 acyloxy, C2 to C6 ester, C2 to C6 cyano, C2 to C4 cyclic sulfate, and C2 to C4 cyclic carbonate.

[0016] Preferably, the sulfate-based film-forming additive is selected from at least one of the compounds shown in 1-1 to 1-10:

[0017] , , , ,

[0018] 1-1 1-2 1-3 1-4 1-5

[0019] , , , ,

[0020] 1-6 1-7 1-8 1-9 1-10.

[0021] The sulfate ester additives shown in Formula I, such as those shown in 1-1 to 1-10, have lower LUMO energy levels, making electron transitions easier and facilitating electrochemical reactions. This allows for earlier reduction and formation of an SEI film on the negative electrode surface during the formation stage, further enhancing the battery's cycle stability. In particular, the use of the aforementioned sulfate ester film-forming additives 1-5 in the gel electrolyte composition of the present invention can significantly improve the battery's cycle life.

[0022] Preferably, the lithium salt comprises LiPF6 and LiFSI, wherein the mass percentage of LiPF6 in the gel electrolyte composition is 11.25% to 13.75%, and the mass percentage of LiFSI in the gel electrolyte composition is 1.5% to 4%. By selecting the specific lithium salts mentioned above and controlling the appropriate amount of the lithium salts, both conductivity and low cost can be achieved, and high-temperature performance can be improved.

[0023] Preferably, the lithium salt further includes at least one other lithium salt selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium difluorodioxalate, lithium difluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroantimonylate, lithium hexafluoroarsenate, lithium bis(pentafluoroethylsulfonyl)imino, lithium perchlorate, lithium tetrachloroaluminate, lithium trifluoromethanesulfonate, lithium fluorosulfonate, lithium chloroborane, lithium tetrafluorooxalatophosphate, and lithium trioxalatophosphate. The gel electrolyte composition of the present invention can incorporate the above-mentioned other lithium salts according to actual needs to obtain gel electrolytes capable of achieving different performance requirements.

[0024] Preferably, when the gel electrolyte composition includes other lithium salts, the total mass percentage of the other lithium salts in the gel electrolyte composition is 0.5% to 1.5%.

[0025] In this invention, the types of the first monomer, the second monomer, and the solvent are conventionally selected and can be adjusted according to actual needs.

[0026] Preferably, the first monomer is selected from at least one of methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, benzyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 2-phenoxyethyl methacrylate, and 2-propylheptyl methacrylate.

[0027] Preferably, the second monomer is selected from at least one of ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, bis(trimethylolpropane) tetraacrylate, and dipentaerythritol hexaacrylate.

[0028] Preferably, the solvent is selected from any three or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0029] The present invention also proposes a gel electrolyte, which is obtained by polymerization of the gel electrolyte composition in the presence of an initiator.

[0030] In this invention, the polymerization reaction conditions are conventionally selected. Preferably, the polymerization reaction conditions are: heating at 45~80°C for 3~24 hours.

[0031] In this invention, the type of initiator is conventionally selected. Preferably, the initiator is selected from any one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, di-tert-butyl peroxide, and methyl ethyl ketone peroxide.

[0032] In this invention, the amount of initiator is conventionally selected and can be adjusted according to actual needs. Preferably, the mass of the initiator is 0.01 to 0.02 times the sum of the masses of the first monomer and the second monomer.

[0033] The present invention also proposes a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and the aforementioned gel electrolyte.

[0034] In this invention, the method for preparing the lithium-ion battery may include, for example:

[0035] A positive electrode, a negative electrode, and a separator are stacked to obtain a battery cell; an initiator is added to a gel electrolyte composition and mixed evenly, then injected into the battery cell, heated at 45°C to 80°C for 3 to 24 hours, and cooled to obtain the lithium-ion battery.

[0036] The above-mentioned method for preparing lithium-ion batteries may also include conventional processing steps, such as vacuum baking the cell before liquid injection; and / or encapsulation and room temperature storage after liquid injection and before heating; and / or conventional formation, aging, and capacity testing after cooling.

[0037] This invention does not impose any special restrictions on the materials used for the positive electrode, negative electrode, and separator of lithium-ion batteries; conventional positive electrode, negative electrode, and separator materials in the art can be used.

[0038] Preferably, the positive electrode sheet includes a positive electrode active material, which is selected from any one or more combinations of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium cobalt oxide, lithium nickel manganese oxide, nickel cobalt manganese ternary material, and nickel cobalt aluminum ternary material.

[0039] Preferably, the negative electrode sheet includes a negative electrode active material, which is selected from any one or more combinations of lithium metal, graphite, silicon negative electrode material, silicon-carbon negative electrode material, silicon suboxide material and lithium titanate material.

[0040] Preferably, the diaphragm is selected from any one of the following: polyethylene film with or without ceramic coating, polypropylene film with or without ceramic coating, polyethylene-polypropylene composite film with or without ceramic coating, glass fiber diaphragm, and aramid diaphragm.

[0041] The beneficial effects of this invention are as follows:

[0042] The gel electrolyte composition of this invention constructs a polymer backbone using a suitable amount of short-chain acrylate monomers containing one or two unsaturated double bond functional groups, and crosslinks it with multi-branched acrylate monomers containing three or more unsaturated double bond functional groups. This constrains the fluidity and volatility of the electrolyte, provides a certain mechanical strength, and does not significantly reduce the conductivity of the electrolyte. Simultaneously, a suitable amount of sulfate-based film-forming additives is introduced to form a film during the formation stage, preventing monomers or other substances from continuing to react on the electrode surface and enhancing the cycle stability of the battery cell. Through the selection of raw materials such as lithium salts and solvents, low cost, high conductivity, and high-temperature resistance can be achieved. In summary, the gel electrolyte obtained by this invention combines high conductivity, long cycle performance, and high safety, and is also low in cost.

[0043] Furthermore, by further selecting sulfate ester additives with specific structures, the gel electrolyte composition of the present invention can also reduce and form an SEI film on the negative electrode surface earlier during the formation stage, thereby further improving the cycle stability of the battery. Detailed Implementation

[0044] The technical solution of the present invention will now be described in detail through specific embodiments.

[0045] Example 1

[0046] A gel electrolyte composition comprising: 0.8 wt% of compound 1-1, 6 wt% of methyl methacrylate, 1 wt% of pentaerythritol tetraacrylate, 12 wt% of lithium hexafluorophosphate (LiPF6), 3 wt% of lithium difluorosulfonyl imide (LiFSI), and solvent to a total of 100%, wherein the solvent is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 1:2:2;

[0047] The structure of compound 1-1 is as follows:

[0048] .

[0049] Preparation of gel electrolyte composition:

[0050] EC, EMC, and EMC are mixed evenly to obtain a solvent. LiPF6 and LiFSI are added to the above solvent and dissolved completely. Then, compound 1-1, methyl methacrylate, and pentaerythritol tetraacrylate are added and mixed evenly to obtain the final product.

[0051] Preparation of lithium-ion batteries:

[0052] The positive electrode, negative electrode and polypropylene separator are stacked to obtain a soft-pack lithium-ion battery cell with a capacity of 3Ah, a width of 56mm and a length of 60mm, and then vacuum baked at 85℃ for 48h.

[0053] Add 1% of azobisisobutyronitrile (AIBN) equivalent to the total mass of methyl methacrylate and pentaerythritol tetraacrylate to the above gel electrolyte composition, mix well, then inject into the above battery cell, encapsulate, leave at room temperature, then heat at 60°C for 6 hours, cool to room temperature, and after formation, aging, and capacity testing, obtain a lithium-ion battery.

[0054] The preparation method of the positive electrode in the above-mentioned lithium-ion battery is as follows:

[0055] LiNi, a 7-series NCM cathode active material 0.7 CO 0.1 Mn 0.2 O2, conductive carbon black Super P, polyvinylidene fluoride binder, and carbon nanotubes (CNTs) were mixed evenly in a mass ratio of 97.5:0.5:1:1 to obtain a positive electrode slurry, which was then coated on both sides of an aluminum foil, with a single-sided areal density of 185 g / m³. 2 After pre-drying at 70℃ for 24 hours and rolling, the positive electrode is obtained by drying at 80℃ for 24 hours under vacuum.

[0056] The preparation method of the negative electrode in the above-mentioned lithium-ion battery is as follows:

[0057] A negative electrode slurry was prepared by uniformly mixing graphite (the negative electrode active material), conductive carbon black Super P, carboxymethyl cellulose thickener CMC, and binder SBR (styrene-butadiene rubber latex) at a mass ratio of 95:1.5:1.0:2.5. This slurry was then coated onto both sides of a copper foil, with a single-sided surface density of 40 g / m³. 2 After pre-drying at 100℃ for 24 hours and rolling, the negative electrode sheet is obtained by drying at 85℃ under vacuum for 24 hours.

[0058] Example 2

[0059] The only difference between Example 2 and Example 1 is that compound 1-1 is replaced with compound 1-3, the structure of which is as follows:

[0060] .

[0061] Example 3

[0062] The only difference between Example 3 and Example 1 is that compound 1-1 is replaced with compound 1-5, the structure of which is as follows:

[0063] .

[0064] Example 4

[0065] The only difference between Example 4 and Example 1 is that compound 1-1 is replaced with compound 1-6, the structure of which is as follows:

[0066] .

[0067] Example 5

[0068] The only difference between Example 5 and Example 1 is that compound 1-1 is replaced with compound 1-7, the structure of which is as follows:

[0069] .

[0070] Example 6

[0071] The only difference between Example 6 and Example 1 is that compound 1-1 is replaced with compound 1-9, the structure of which is as follows:

[0072] .

[0073] Example 7

[0074] The only difference between Example 7 and Example 1 is that compound 1-1 is replaced with compound 1-10, the structure of which is as follows:

[0075] .

[0076] Example 8

[0077] A gel electrolyte composition comprising: 0.8 wt% of compound 1-1, 6 wt% of propyl methacrylate, 1 wt% of pentaerythritol tetraacrylate, 12 wt% of lithium hexafluorophosphate (LiPF6), 2 wt% of lithium difluorosulfonyl imide (LiFSI), and solvent to a total of 100%, wherein the solvent is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 1:2:2.

[0078] Preparation of gel electrolyte composition:

[0079] EC, EMC, and EMC are mixed evenly to obtain a solvent. LiPF6 and LiFSI are added to the above solvent and dissolved completely. Then, compound 1-1, propyl methacrylate, and pentaerythritol tetraacrylate are added and mixed evenly to obtain the final product.

[0080] Preparation of lithium-ion batteries:

[0081] The positive electrode, negative electrode and polypropylene separator are stacked to obtain a soft-pack lithium-ion battery cell with a capacity of 3Ah, a width of 56mm and a length of 60mm, and then vacuum baked at 85℃ for 48h.

[0082] Azobisisoheptanenitrile (1% of the total mass of propyl methacrylate and pentaerythritol tetraacrylate) was added to the above gel electrolyte composition, mixed evenly, and then injected into the above battery cell. The mixture was then encapsulated, placed at room temperature, heated at 60°C for 6 hours, cooled to room temperature, and subjected to formation, aging, and capacity testing to obtain a lithium-ion battery.

[0083] The positive electrode, negative electrode, and separator of the lithium-ion battery are the same as in Example 1.

[0084] Example 9

[0085] A gel electrolyte composition comprising: 0.6 wt% of compound 1-1, 7 wt% of benzoyl methacrylate, 1.5 wt% of trimethylolpropane triacrylate, 12 wt% of lithium hexafluorophosphate (LiPF6), 3 wt% of lithium difluorosulfonyl imide (LiFSI), and solvent to a total of 100%, wherein the solvent is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 1:2:2.

[0086] Preparation of gel electrolyte composition:

[0087] EC, EMC, and EMC are mixed evenly to obtain a solvent. LiPF6 and LiFSI are added to the above solvent and dissolved completely. Then, compound 1-1, benzoyl methacrylate, and trimethylolpropane triacrylate are added and mixed evenly to obtain the final product.

[0088] Preparation of lithium-ion batteries:

[0089] The positive electrode, negative electrode and glass fiber separator are stacked to obtain a soft-pack lithium-ion battery cell with a capacity of 3Ah, a width of 56mm and a length of 60mm, and then vacuum baked at 85℃ for 48h.

[0090] Add 1% benzoyl peroxide, equivalent to the total mass of benzoyl methacrylate and trimethylolpropane triacrylate, to the above gel electrolyte composition, mix well, then inject into the above battery cell, encapsulate, place at room temperature, then heat at 80°C for 8 hours, cool to room temperature, and after formation, aging, and capacity testing, obtain a lithium-ion battery.

[0091] The positive electrode, negative electrode, and separator of the lithium-ion battery are the same as in Example 1.

[0092] Comparative Example 1

[0093] Comparative Example 1 uses a conventional electrolyte, prepared as follows:

[0094] Weigh the raw materials according to the following mass percentages: 12wt% lithium hexafluorophosphate (LiPF6), 3wt% lithium difluorosulfonyl imide (LiFSI), and make up to 100% solvent, wherein the solvent is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 1:2:2; mix EC, EMC, and EMC evenly to obtain the solvent, add LiPF6 and LiFSI to the above solvent and dissolve them completely to obtain the electrolyte.

[0095] Preparation of lithium-ion batteries:

[0096] The positive electrode, negative electrode and polypropylene separator are stacked to obtain a soft-pack lithium-ion battery cell with a capacity of 3Ah, a width of 56mm and a length of 60mm, and then vacuum baked at 85℃ for 48h.

[0097] The electrolyte is injected into the above-mentioned battery cell, which is then packaged, left to stand at room temperature, and then subjected to formation, aging, and capacity testing to obtain a lithium-ion battery.

[0098] The positive electrode, negative electrode, and separator of the lithium-ion battery are the same as in Example 1.

[0099] Comparative Example 2

[0100] A gel electrolyte composition comprising: 6 wt% methyl methacrylate, 1 wt% pentaerythritol tetraacrylate, 12 wt% lithium hexafluorophosphate (LiPF6), 3 wt% lithium difluorosulfonyl imide (LiFSI), and solvent to a total of 100%, wherein the solvent is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 1:2:2.

[0101] Preparation of gel electrolyte composition:

[0102] EC, EMC, and EMC are mixed evenly to obtain a solvent. LiPF6 and LiFSI are added to the above solvent and dissolved completely. Then, methyl methacrylate and pentaerythritol tetraacrylate are added and mixed evenly to obtain the final product.

[0103] The preparation method of the lithium-ion battery, the positive electrode, the negative electrode and the separator are the same as in Example 1.

[0104] Comparative Example 3

[0105] A gel electrolyte composition comprising: 2 wt% of compound 1-1, 6 wt% of methyl methacrylate, 1 wt% of pentaerythritol tetraacrylate, 12 wt% of lithium hexafluorophosphate (LiPF6), 3 wt% of lithium difluorosulfonyl imide (LiFSI), and solvent to a total of 100%, wherein the solvent is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 1:2:2.

[0106] The preparation method of the gel electrolyte composition is the same as in Example 1.

[0107] The preparation method of the lithium-ion battery, the positive electrode, the negative electrode and the separator are the same as in Example 1.

[0108] Comparative Example 4

[0109] A gel electrolyte composition comprising: 1 wt% of compound 1-1, 10 wt% of methyl methacrylate, 2 wt% of pentaerythritol tetraacrylate, 12 wt% of lithium hexafluorophosphate (LiPF6), 3 wt% of lithium difluorosulfonyl imide (LiFSI), and solvent to a total of 100%, wherein the solvent is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 1:2:2.

[0110] The preparation method of the gel electrolyte composition is the same as in Example 1.

[0111] The preparation method of the lithium-ion battery, the positive electrode, the negative electrode and the separator are the same as in Example 1.

[0112] Test case

[0113] The lithium-ion batteries prepared in the examples and comparative examples were subjected to cycle tests and internal resistance tests, respectively. The test methods are as follows:

[0114] Battery Cycle Test

[0115] Under conditions of 25℃ / 45℃, the lithium-ion battery was charged at a constant current of 0.5C to the cutoff voltage of 4.35V, then charged at a constant voltage of 0.05C to the cutoff voltage, and then discharged at a constant current of 0.5C to the cutoff voltage of 2.5V. This charge-discharge cycle was repeated, and the discharge capacity at the end of each cycle was recorded. The capacity retention rate of the Nth cycle was calculated using the following formula: Capacity retention rate of the Nth cycle = Discharge capacity at the end of the Nth cycle / Discharge capacity of the first cycle × 100%; the maximum number of cycles in which the capacity retention rate remained ≥80% was taken as the battery's cycle life (cycles).

[0116] Battery internal resistance test

[0117] The lithium-ion battery was charged at a constant current of 0.33C to the cutoff voltage of 4.35V, and then charged at a constant voltage until the current dropped to 0.05C. The battery was then discharged at a current of 0.33C to 50% SOC, and then discharged at a current of 2C I for 10s. The voltage changes U1-U2 were recorded, and the DCR value was calculated using the formula (U1-U2) / I.

[0118] Coin cells using the gel electrolyte compositions or electrolytes from the examples and comparative examples were prepared and their conductivity was tested. The method for assembling coin cells using the gel electrolyte composition was as follows: the cell was assembled in the order of negative electrode shell, stainless steel sheet, polypropylene separator, stainless steel sheet, and positive electrode shell. An initiator was added to the gel electrolyte composition and mixed thoroughly, then injected into the cell, ensuring the injection amount completely wetted the separator. The cell was heated at 60°C for 6 hours, cooled to room temperature, and the resulting coin cell was subjected to EIS testing. The method for assembling coin cells using the electrolyte was as follows: the cell was assembled in the order of negative electrode shell, stainless steel sheet, polypropylene separator, stainless steel sheet, and positive electrode shell. The electrolyte was injected into the cell, ensuring the injection amount completely wetted the separator, and the resulting coin cell was subjected to EIS testing.

[0119] The EIS test results are calculated using the following formula: σ=L / RS, where L is the diaphragm thickness, S is the facing area, and R is the focal point of the EIS test curve and the real axis.

[0120] The test results are shown in Table 1:

[0121] Table 1

[0122]

[0123] As can be seen from the data in Table 1, the gel electrolyte prepared by the present invention by selecting appropriate polymer monomers and sulfate ester film-forming additives in suitable proportions exhibits high ionic conductivity, interfacial compatibility, and stability. This reduces battery internal resistance and improves battery cycle performance and safety. In particular, the sulfate ester film-forming additive used in Example 3 demonstrates this advantage. The LUMO energy level is -1.879248 eV, and the HUMO energy level is -10.2612 eV. It is easily reduced, resistant to oxidation, and can generate LiF and Li₂SO₄. x The composite SEI membrane exhibits excellent overall performance in the ternary system, significantly improving the cycle life of the battery. Compared with the conventional electrolyte of Comparative Example 1, the gel electrolyte of this invention has a similar room temperature conductivity, while the cycle life of the electrolyte of Comparative Example 1 is far lower than that of the gel electrolyte of this invention. Compared with Comparative Example 2, the gel electrolyte of Comparative Example 2 did not contain sulfate ester film-forming additives, resulting in significantly worse cycle performance. Compared with the gel electrolytes of Comparative Examples 3-4, which have different ratios of polymer monomers and sulfate ester film-forming additives, the electrochemical performance of the gel electrolytes of Comparative Examples 3-4 is comprehensively reduced, far inferior to that of the gel electrolyte of this invention.

[0124] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A gel electrolyte composition, characterized in that, The gel electrolyte composition includes polymeric monomers, lithium salts, sulfate ester film-forming additives, and solvents; The polymerizable monomers include a first monomer and a second monomer; the first monomer is an acrylate monomer containing one or two unsaturated double bond functional groups, and the second monomer is an acrylate monomer containing three or more unsaturated double bond functional groups. The gel electrolyte composition satisfies the following conditions: 5%≤a%≤8%, 0.5%≤b%≤2%, 0.5%≤c%≤1%, and 3.25≤(a+b)c≤8.55; Where a% is the mass percentage of the first monomer in the gel electrolyte composition; b% represents the mass percentage of the second monomer in the gel electrolyte composition; c% is the mass percentage of the sulfate ester film-forming additive in the gel electrolyte composition.

2. The gel electrolyte composition according to claim 1, characterized in that, The sulfate ester film-forming additive is selected from at least one compound as shown in Formula I: Formula I In Formula I, R1 to R4 are each independently selected from any one of H, F, C1 to C6 alkyl, C2 to C6 alkenyl, C1 to C6 alkoxy, C1 to C6 acyloxy, C2 to C6 ester, C2 to C6 cyano, C2 to C4 cyclic sulfate, and C2 to C4 cyclic carbonate.

3. The gel electrolyte composition according to claim 1, characterized in that, The sulfate ester film-forming additive is selected from at least one of the compounds shown in 1-1 to 1-10: 、 、 、 、 1-1 1-2 1-3 1-4 1-5 、 、 、 、 1-6 1-7 1-8 1-9 1-10 。 4. The gel electrolyte composition according to claim 1, characterized in that, The lithium salt includes LiPF6 and LiFSI, wherein the mass percentage of LiPF6 in the gel electrolyte composition is 11.25% to 13.75%, and the mass percentage of LiFSI in the gel electrolyte composition is 1.5% to 3%.

5. The gel electrolyte composition according to claim 4, characterized in that, The lithium salt further includes at least one other lithium salt selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium difluorodioxalatophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium bis(pentafluoroethylsulfonyl)imino, lithium perchlorate, lithium tetrachloroaluminate, lithium trifluoromethanesulfonate, lithium fluorosulfonate, lithium chloroborane, lithium tetrafluorooxalatophosphate, and lithium trioxalatophosphate.

6. The gel electrolyte composition according to claim 5, characterized in that, The other lithium salts constitute 0.5% to 1.5% of the total mass of the gel electrolyte composition.

7. The gel electrolyte composition according to claim 1, characterized in that, The first monomer is selected from at least one of methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, benzyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 2-phenoxyethyl methacrylate, and 2-propylheptyl methacrylate; The second monomer is selected from at least one of ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, bis(trimethylolpropane) tetraacrylate, and dipentaerythritol hexaacrylate; The solvent is selected from any three or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate.

8. A gel electrolyte, characterized in that, The gel electrolyte is obtained by polymerization of the gel electrolyte composition according to any one of claims 1 to 7 in the presence of an initiator.

9. The gel electrolyte according to claim 8, characterized in that, The polymerization reaction is carried out under the following conditions: heating at 45~80℃ for 3~24h; The mass of the initiator is 0.01 to 0.02 times the sum of the masses of the first monomer and the second monomer; the initiator is selected from any one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, di-tert-butyl peroxide, and methyl ethyl ketone peroxide.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and a gel electrolyte as described in claim 8 or 9.

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