Gel polymer electrolyte, method for preparing the same, and semi-solid lithium ion battery

Abstract

This invention provides a gel polymer electrolyte, its preparation method, and a semi-solid-state lithium-ion battery. The preparation method includes: step S1, mixing a lithium salt with a solvent to obtain a lithium salt solution; step S2, mixing the lithium salt solution, a polymeric monomer, and an initiator and carrying out a polymerization reaction to obtain the gel polymer electrolyte; wherein the polymeric monomer has the structure shown in formula (I). The gel polymer electrolyte obtained in this application exhibits superior flame retardancy, thermal stability, ionic conductivity, and lower interfacial impedance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery manufacturing technology, and more specifically, to a gel polymer electrolyte, its preparation method, and a semi-solid lithium-ion battery. Background Technology

[0002] With the rapid growth in market demand for portable consumer electronics, energy storage products, and pure electric vehicles, the demand for liquid lithium-ion batteries is increasing. However, the flammability of their solvents poses a series of safety challenges for lithium-ion batteries, including electrolyte leakage, gas expansion, and even fire or explosion. Meanwhile, to improve energy density, high-voltage ternary cathode materials are widely used, but the solid electrolyte interphase (SEI) membrane between the cathode material and the electrolyte decreases with increasing voltage, accelerating capacity decay. Currently, flame retardants are added to electrolytes to address lithium-ion battery safety, improving safety in the event of thermal runaway due to battery abuse. To improve the non-flammability of electrolytes, solid polymer electrolytes have been extensively researched and applied in recent years.

[0003] Solid-state electrolytes improve the safety performance of lithium-ion batteries, but the polymer monomers currently used to prepare solid polymer electrolytes have poor oxidation resistance, and the resulting solid polymer electrolytes cannot maintain good cycle performance at high voltages.

[0004] Based on this, researching and developing a gel polymer electrolyte that can improve lithium-ion transport efficiency, reduce interfacial impedance, and enhance electrochemical and thermal stability, as well as its preparation method, is of great significance for improving the cycle performance of semi-solid lithium-ion batteries. Summary of the Invention

[0005] The main objective of this invention is to provide a gel polymer electrolyte, its preparation method, and a semi-solid lithium-ion battery, in order to solve the problems of low lithium-ion transport efficiency, high interfacial impedance, poor electrochemical stability and thermal stability of electrolytes in existing solid lithium-ion batteries, which makes it difficult to improve the cycle performance of solid lithium-ion batteries.

[0006] To achieve the above objectives, the present invention provides a method for preparing a gel polymer electrolyte, comprising: step S1, mixing a lithium salt with a solvent to obtain a lithium salt solution; and step S2, mixing the lithium salt solution, a polymeric monomer, and an initiator and carrying out a polymerization reaction to obtain a gel polymer electrolyte; wherein the polymeric monomer has the structure shown in formula (I):

[0007] ,

[0008] R1, R2, R3, and R4 are each independently selected from fluorine, C1 to C4. 10Fluorinated alkyl groups, or C1-C2 fluoroalkyl groups substituted with C1-C2 alkyl groups. 10 The fluoroalkyl group; R5 is selected from C1 to C2 alkyl groups or C1 to C2 fluoroalkyl groups.

[0009] Furthermore, R1, R2, R3 and R4 are each independently selected from fluorine, C1-C2 fluoroalkyl, or C1-C2 fluoroalkyl substituted with C1-C2 fluoroalkyl; R5 is selected from methyl, trifluoromethyl or pentafluoroethyl.

[0010] Furthermore, R1, R2, R3 and R4 are each independently selected from fluorine, trifluoromethyl, pentafluoroethyl, trifluoromethyl substituted with monofluoromethyl, or pentafluoroethyl substituted with trifluoroethyl; R5 is selected from methyl.

[0011] Furthermore, the polymerizing monomer is selected from one or more of monomers 1 to 3:

[0012] ,

[0013] ,

[0014] .

[0015] Furthermore, the lithium salt content in the lithium salt solution is 8–20 wt%.

[0016] Furthermore, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium bis(oxalate-borate), lithium difluoro(oxalate-borate), lithium difluoro(bis(oxalate-borate)) phosphate, and lithium tetrafluoro(oxalate-borate).

[0017] Furthermore, the solvent is selected from one or more of cyclic carbonates, chain carbonates, and carboxylic esters.

[0018] Further, the solvent includes cyclic carbonates and chain carbonates, and the weight percentage of cyclic carbonates in the solvent is 15 to 35 wt%; the weight percentage of chain carbonates in the solvent is 45 to 85 wt%; or, the solvent includes carboxylic acid esters, and the weight percentage of carboxylic acid esters in the solvent is 5 to 60 wt%.

[0019] Furthermore, the cyclic carbonate is selected from one or more of ethylene carbonate, propylene carbonate, and butene carbonate; the chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate; and the carboxylic acid ester is selected from one or more of methyl formate, ethyl formate, methyl acetate, and ethyl acetate.

[0020] Furthermore, the weight ratio of lithium salt to polymeric monomer in the lithium salt solution is (5-20):1; and / or, the weight ratio of polymeric monomer to initiator is (1-1000):(1-50).

[0021] Further, the initiator is selected from peroxide initiators and / or azo initiators; more preferably, the peroxide initiator is selected from one or more of benzoyl peroxide, benzoyl tert-butyl peroxide and methyl ethyl ketone peroxide; and the azo initiator is selected from one or more of azobisisobutyronitrile, dimethyl azobisisobutyrate and azobisisoheptanenitrile.

[0022] Further, step S2 includes: mixing lithium salt solution, polymerizing monomer, initiator and additive to obtain a polymerization reaction system, heating the polymerization reaction system to the reaction temperature to carry out the polymerization reaction, and obtaining gel polymer electrolyte.

[0023] Furthermore, the reaction temperature is 60–80℃, and the polymerization reaction time is 2–24 h.

[0024] Furthermore, the additive content is 0.1 to 20 wt% based on the total weight of the polymerization reaction system.

[0025] Furthermore, the additive is selected from one or more of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, and methanedisulfonate.

[0026] To achieve the above objectives, another aspect of the present invention provides a gel polymer electrolyte, which is prepared by the preparation method of the gel polymer electrolyte provided in this application; the ionic conductivity of the gel polymer electrolyte is 6 to 12 S / m.

[0027] Another aspect of the present invention provides a semi-solid lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, wherein the electrolyte is selected from the gel polymer electrolyte provided in this application.

[0028] By applying the technical solution of this invention, the preparation method described above enables the polymer monomers to undergo in-situ polymerization under the initiation of an initiator. The polymer monomers used in this application contain fluorine atoms and benzene ring structures. On the one hand, this introduces a large number of fluorine-containing groups into the gel polymer electrolyte. Under thermal runaway conditions in semi-solid lithium-ion batteries, these groups can decompose to generate fluorine free radicals. These fluorine free radicals can undergo a chain combustion reaction with hydrogen and hydroxyl free radicals in the gas phase, thereby improving the flame retardancy of the gel polymer electrolyte and thus enhancing the safety of the semi-solid lithium-ion battery. On the other hand, this inhibits the dissolution of transition metal elements in the positive electrode active material, mitigating irreversible phase transitions caused by high voltage, thereby reducing capacity loss in the semi-solid lithium-ion battery and improving its cycle performance. Furthermore, it improves the thermal stability of the gel polymer electrolyte. The polymer monomers used in this application also contain sulfonic acid groups. The introduction of these groups can improve the stability of the SEI film and chelate with anions in the lithium salt, thereby inhibiting anion migration, improving lithium-ion transport efficiency, and thus enhancing the electrochemical performance of the semi-solid lithium-ion battery.

[0029] Moreover, compared to other types, limiting the fluoroalkyl groups in R1, R2, R3, R4 and R5 in formula (I) to the above range is beneficial to reducing the impedance of the prepared gel polymer electrolyte, thereby reducing the internal resistance of the semi-solid lithium-ion battery and improving its electrochemical performance. Detailed Implementation

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0031] As described in the background section, existing solid-state lithium-ion battery electrolytes suffer from low lithium-ion transport efficiency, high interfacial impedance, and poor electrochemical and thermal stability, making it difficult to improve the cycle performance of solid-state lithium-ion batteries. To address these technical problems, this application provides a method for preparing a gel polymer electrolyte, comprising: step S1, mixing a lithium salt with a solvent to obtain a lithium salt solution; and step S2, mixing the lithium salt solution, a polymeric monomer, and an initiator and performing a polymerization reaction to obtain a gel polymer electrolyte; wherein the polymeric monomer has the structure shown in formula (I):

[0032] ,

[0033] R1, R2, R3, and R4 are each independently selected from fluorine, C1 to C4. 10 Fluorinated alkyl groups, or C1-C2 fluoroalkyl groups substituted with C1-C2 alkyl groups. 10 The fluoroalkyl group; R5 is selected from C1 to C2 alkyl groups or C1 to C2 fluoroalkyl groups.

[0034] The preparation method described in this application enables the monomers to undergo in-situ polymerization under the initiation of an initiator. The monomers used in this application contain fluorine atoms and benzene ring structures. On the one hand, this introduces a large number of fluorine-containing groups into the gel polymer electrolyte. Under thermal runaway conditions in semi-solid lithium-ion batteries, these groups can decompose to generate fluorine free radicals. These fluorine free radicals can undergo a chain combustion reaction with hydrogen and hydroxyl free radicals in the gas phase, thereby improving the flame retardancy of the gel polymer electrolyte and thus enhancing the safety of the semi-solid lithium-ion battery. On the other hand, this method can suppress the dissolution of transition metal elements in the positive electrode active material, mitigating irreversible phase transitions caused by high voltage, thereby reducing capacity loss and improving cycle performance of the semi-solid lithium-ion battery. Furthermore, it can improve the thermal stability of the gel polymer electrolyte. The monomers used in this application also contain sulfonic acid groups. The introduction of these groups can improve the stability of the SEI film and chelate with anions in the lithium salt, thereby inhibiting anion migration, improving lithium-ion transport efficiency, and thus enhancing the electrochemical performance of the semi-solid lithium-ion battery.

[0035] Moreover, compared to other types, limiting the fluoroalkyl groups in R1, R2, R3, R4 and R5 in formula (I) to the above range is beneficial to reducing the impedance of the prepared gel polymer electrolyte, thereby reducing the internal resistance of the semi-solid lithium-ion battery and improving its electrochemical performance.

[0036] In a preferred embodiment, R1, R2, R3, and R4 are each independently including, but not limited to, fluorine, C1-C2 fluoroalkyl groups, or C1-C2 fluoroalkyl groups substituted with C1-C2 fluoroalkyl groups; R5 includes, but is not limited to, methyl, trifluoromethyl, or pentafluoroethyl. Compared to other types, limiting the types of R1, R2, R3, R4, and R5 in formula (I) to the above-mentioned range is beneficial to improving the flame retardancy and thermal stability of the gel polymer electrolyte, and also beneficial to improving lithium-ion transport performance, thereby improving the safety, cycle performance, and electrochemical performance of the semi-solid-state lithium-ion battery.

[0037] To further improve the flame retardancy, thermal stability, and lithium-ion transport performance of the gel polymer electrolyte, in a preferred embodiment, R1, R2, R3, and R4 are each independently including but not limited to fluorine, trifluoromethyl, pentafluoroethyl, monofluoromethyl-substituted trifluoromethyl, or trifluoroethyl-substituted pentafluoroethyl; R5 includes but is not limited to methyl.

[0038] In a preferred embodiment, the polymerizing monomer includes, but is not limited to, one or more of monomers 1 to 3: ,

[0039] ,

[0040] .

[0041] The polymer monomers used in this application contain fluorine atoms and benzene ring structures. On the one hand, they can introduce a large number of fluorine-containing groups into the gel polymer electrolyte. Under the condition of thermal runaway in semi-solid lithium-ion batteries, these groups can decompose to generate fluorine free radicals. These fluorine free radicals can undergo a chain combustion reaction with hydrogen and hydroxyl free radicals in the gas phase, thereby improving the flame retardancy of the gel polymer electrolyte and thus improving the safety of the semi-solid lithium-ion battery. On the other hand, they can suppress the dissolution of transition metal elements in the positive electrode active material, reduce the irreversible phase transition caused by high voltage, thereby reducing the capacity loss of the semi-solid lithium-ion battery and improving its cycle performance. Furthermore, they can improve the thermal stability of the gel polymer electrolyte. The polymer monomers used in this application also contain sulfonic acid groups. The introduction of these groups can improve the stability of the SEI film and chelate with anions in lithium salts, thereby inhibiting anion migration, improving lithium-ion transport efficiency, and thus improving the electrochemical performance of the semi-solid lithium-ion battery.

[0042] In a preferred embodiment, the lithium salt content in the lithium salt solution is 8-20 wt%. The weight percentage of lithium salt includes, but is not limited to, the above range. Limiting it to the above range is beneficial to improving the lithium-ion transport performance of the gel polymer electrolyte and the migration of lithium ions in the semi-solid electrolyte, thereby improving the electrochemical performance of the semi-solid lithium-ion battery.

[0043] To further improve the migration of lithium ions in the semi-solid electrolyte, preferably, the lithium salt includes, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluorosulfonyl)imide (LiTFSI), lithium bis(oxalateborate)borate (LiBOB), lithium difluorooxalateborate (LiDFOB), lithium difluorobis(oxalateborate)phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiOTFP).

[0044] In a preferred embodiment, the solvent includes, but is not limited to, one or more of cyclic carbonates, linear carbonates, and carboxylic esters. Compared to other types, using the above-mentioned solvents is beneficial for improving the dispersibility of lithium salts, for the uniform distribution of lithium ions in the gel polymer electrolyte, and for the subsequent polymerization reaction, thereby increasing the yield of the gel polymer electrolyte.

[0045] To further improve the dispersibility of lithium salts and the degree of lithium ion dissociation in the electrolyte, and to further improve the yield of gel polymer electrolytes, preferably, the solvent includes cyclic carbonates and chain carbonates, and the weight percentage of cyclic carbonates in the solvent is 15-35 wt%; the weight percentage of chain carbonates in the solvent is 45-85 wt%; or, the solvent includes carboxylic acid esters, and the weight percentage of carboxylic acid esters in the solvent is 5-60 wt%.

[0046] To further improve the dispersibility of lithium salts, increase the degree of dissociation and uniform distribution of lithium ions in the gel polymer electrolyte, and further improve the yield of the gel polymer electrolyte, preferably, cyclic carbonates include, but are not limited to, one or more of ethylene carbonate, propylene carbonate, and butene carbonate; chain carbonates include, but are not limited to, one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate; and carboxylic acid esters include, but are not limited to, one or more of methyl formate, ethyl formate, methyl acetate, and ethyl acetate.

[0047] In a preferred embodiment, the weight ratio of lithium salt to polymeric monomer in the lithium salt solution is (5-20):1. The weight ratio of lithium salt to polymeric monomer includes, but is not limited to, the above range. Limiting it to this range is beneficial for improving the ionic conductivity of the gel polymer electrolyte, as well as for improving the stability of the SEI film and suppressing the growth of lithium dendrites, thereby improving the cycle performance and electrochemical performance of the semi-solid-state lithium-ion battery. Preferably, the weight ratio of lithium salt to polymeric monomer in the lithium salt solution is (10-20):1.

[0048] In a preferred embodiment, the weight ratio of the monomer to the initiator is (1-1000):(1-50). The weight ratio of the monomer to the initiator includes, but is not limited to, the above range. Limiting it to this range is beneficial for improving the polymerization reaction efficiency and also for improving the microstructure of the gel polymer electrolyte, thereby improving the overall performance of the gel polymer electrolyte, such as its ionic conductivity. Preferably, the weight ratio of the monomer to the initiator is (1-1000):(1-20).

[0049] In order to further improve the polymerization efficiency and to further improve the microstructure of the gel polymer electrolyte and enhance its comprehensive properties such as ionic conductivity, in a preferred embodiment, the initiator includes, but is not limited to, peroxide initiators and / or azo initiators.

[0050] To further improve the polymerization reaction efficiency and to further improve the microstructure of the gel polymer electrolyte and enhance its comprehensive properties such as ionic conductivity, preferably, the peroxide initiator includes, but is not limited to, one or more of benzoyl peroxide, benzoyl tert-butyl peroxide and methyl ethyl ketone peroxide; and the azo initiator includes, one or more of azobisisobutyronitrile, dimethyl azobisisobutyrate and azobisisoheptanenitrile.

[0051] In a preferred embodiment, step S2 includes: mixing a lithium salt solution, a polymerizing monomer, an initiator, and an additive to obtain a polymerization reaction system; heating the polymerization reaction system to the reaction temperature to carry out a polymerization reaction to obtain a gel polymer electrolyte. Introducing additives into the polymerization reaction system helps to improve the ionic conductivity of the subsequently prepared gel polymer electrolyte, reduce interfacial impedance, and improve electrochemical and thermal stability, thereby improving the cycle life of the semi-solid-state lithium-ion battery.

[0052] In a preferred embodiment, the reaction temperature is 60–80°C, and the polymerization reaction time is 2–24 h. The reaction temperature and reaction time include, but are not limited to, the above ranges. Limiting them to these ranges is beneficial for improving the polymerization reaction efficiency and also for improving the microstructure of the gel polymer electrolyte, thereby increasing the ionic conductivity of the gel polymer electrolyte, reducing interfacial impedance, and improving its overall performance, including electrochemical stability and thermal stability.

[0053] To further improve the overall performance of the gel polymer electrolyte, preferably, the weight percentage of the additive is 0.1 to 20 wt% based on the total weight of the polymerization reaction system.

[0054] To further improve the overall performance of the gel polymer electrolyte, preferably, the additives include, but are not limited to, one or more of the following: vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, and methanedisulfonate.

[0055] The second aspect of this application also provides a method for preparing a polymeric monomer with the structure shown in formula (I). The method includes: step S1, sulfonating reactant 1 with concentrated sulfuric acid at 60–80°C to obtain intermediate 1; step S2, reacting intermediate 1 with sulfuric acid at 100–120°C under anhydrous conditions to obtain intermediate 2; step S3, esterifying reactant 2 with methanol under concentrated sulfuric acid catalysis and reflux at 70–80°C to obtain intermediate 3; and step S4, reacting intermediate 3 and intermediate 2 under sodium carbonate catalysis at 80–100°C to obtain the polymeric monomer shown in formula (I). The synthetic route is as follows:

[0056]

[0057] A third aspect of this application also provides a gel polymer electrolyte, which is prepared by the method described above. The gel polymer electrolyte has an ionic conductivity of 6–12 S / m. It should be noted that, due to the specific nature of the materials field and limitations of existing testing and characterization methods, it is difficult to comprehensively and quantitatively characterize the complex microstructure of the obtained gel polymer electrolyte. However, experiments show that the gel polymer electrolyte obtained in this application exhibits superior flame retardancy, thermal stability, ionic conductivity, and lower interfacial impedance.

[0058] A fourth aspect of this application also provides a semi-solid-state lithium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, wherein the electrolyte is selected from the gel polymer electrolyte provided in this application.

[0059] The gel polymer electrolyte provided in this application has excellent flame retardancy, thermal stability, ionic conductivity, and low interfacial impedance. Its application in semi-solid lithium-ion batteries can improve their safety, cycle performance, and electrochemical performance.

[0060] In a preferred embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on its surface; the positive electrode current collector includes, but is not limited to, aluminum foil or carbon-coated aluminum foil; the positive electrode active material layer includes a positive electrode active material, which includes, but is not limited to, one or more of lithium cobalt oxide, lithium manganese oxide, and lithium nickel cobalt manganese oxide. Compared to other types, using the above-mentioned types of positive electrode current collectors and positive electrode active materials is beneficial to improving the electrochemical performance and cycle performance of semi-solid-state lithium-ion batteries.

[0061] In a preferred embodiment, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on its surface; the negative electrode current collector includes, but is not limited to, copper foil or carbon-coated copper foil; the negative electrode active material layer includes a negative electrode active material, which includes, but is not limited to, one or more of artificial graphite, natural graphite, and hard carbon. Compared to other types, using the above-mentioned types of negative electrode current collectors and negative electrode active materials is beneficial to improving the electrochemical performance and cycle performance of semi-solid-state lithium-ion batteries.

[0062] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0063] (I) Preparation Examples

[0064] Preparation Example 1

[0065] A method for preparing a gel polymer electrolyte, comprising:

[0066] (1) LiPF6, ethylene carbonate, dimethyl carbonate and methyl formate are mixed to obtain a lithium salt solution; the weight percentage of LiPF6 in the lithium salt solution is 14wt%; the weight ratio of ethylene carbonate, dimethyl carbonate and methyl formate is 25:65:10.

[0067] (2) Mix 100g of the lithium salt solution obtained in step (1), 1g of monomer 1 and 0.02g of initiator benzoyl peroxide, heat to 70℃ for polymerization reaction, and obtain gel polymer electrolyte after 6h reaction; wherein, the weight ratio of LiPF6 to monomer 1 in the lithium salt solution is 14:1; the weight ratio of monomer 1 to initiator is 50:1;

[0068] The chemical structure of monomer 1 is as follows:

[0069] .

[0070] Preparation Example 2

[0071] The difference from Preparation Example 1 is that monomer 1 in step (2) is replaced with monomer 2, and the chemical structure of monomer 2 is as follows:

[0072] .

[0073] Preparation Example 3

[0074] The difference from Preparation Example 1 is that monomer 1 in step (2) is replaced with monomer 3, and the chemical structure of monomer 3 is as follows:

[0075] .

[0076] Preparation Example 4

[0077] The difference from Preparation Example 1 is that the weight percentage of LiPF6 in the lithium salt solution is 8 wt%.

[0078] Preparation Example 5

[0079] The difference from Preparation Example 1 is that the weight percentage of LiPF6 in the lithium salt solution is 20 wt%.

[0080] Preparation Example 6

[0081] The difference from Preparation Example 1 is that the weight percentage of LiPF6 in the lithium salt solution is 5 wt%.

[0082] Preparation Example 7

[0083] The difference from Preparation Example 1 is that an equal amount of LiFSI is used to replace LiPF6 in step (1).

[0084] Preparation Example 8

[0085] The difference from Preparation Example 1 is that an equal amount of LiTFSI is used to replace LiPF6 in step (1).

[0086] Preparation Example 9

[0087] The difference from the preparation example 1 is that in step (1), LiPF6, propylene carbonate, diethyl carbonate and ethyl formate are mixed to obtain a lithium salt solution; the weight percentage of LiPF6 in the lithium salt solution is 14wt%; the weight ratio of propylene carbonate, diethyl carbonate and ethyl formate is 15:45:40.

[0088] Preparation Example 10

[0089] The difference from Preparation Example 1 is that in step (1), LiPF6, propylene carbonate, diethyl carbonate and ethyl formate are mixed to obtain a lithium salt solution; the weight percentage of LiPF6 in the lithium salt solution is 14wt%; the weight ratio of propylene carbonate, diethyl carbonate and ethyl formate is 35:45:20.

[0090] Preparation Example 11

[0091] The difference from the preparation example 1 is that in step (1), LiPF6, propylene carbonate and diethyl carbonate are mixed to obtain a lithium salt solution; the weight percentage of LiPF6 in the lithium salt solution is 14wt%; the weight ratio of propylene carbonate and diethyl carbonate is 15:85.

[0092] Preparation Example 12

[0093] The difference from the preparation example 1 is that in step (1), LiPF6, propylene carbonate, diethyl carbonate and ethyl formate are mixed to obtain a lithium salt solution; the weight percentage of LiPF6 in the lithium salt solution is 14wt%; the weight ratio of propylene carbonate, diethyl carbonate and ethyl formate is 40:45:15.

[0094] Preparation Example 13

[0095] The difference from Preparation Example 1 is that the weight ratio of LiPF6 to monomer 1 in the lithium salt solution is 5:1; and the weight ratio of monomer 1 to initiator is 50:1.

[0096] Preparation Example 14

[0097] The difference from Preparation Example 1 is that the weight ratio of LiPF6 to monomer 1 in the lithium salt solution is 20:1; and the weight ratio of monomer 1 to initiator is 1000:1.

[0098] Preparation Example 15

[0099] The difference from Preparation Example 1 is that the weight ratio of LiPF6 to monomer 1 in the lithium salt solution is 25:1; and the weight ratio of monomer 1 to initiator is 40:1.

[0100] Preparation Example 16

[0101] The difference from the preparation example 1 is that in step (2), the reaction temperature of the polymerization reaction is 60°C and the time is 24h.

[0102] Preparation Example 17

[0103] The difference from the preparation example 1 is that in step (2), the reaction temperature of the polymerization reaction is 80°C and the time is 2h.

[0104] Preparation Example 18

[0105] The difference from the preparation example 1 is that in step (2), the reaction temperature of the polymerization reaction is 30°C and the time is 30h.

[0106] Preparation Example 19

[0107] A method for preparing a gel polymer electrolyte, comprising:

[0108] (1) A lithium salt solution was prepared using the same method as in Preparation Example 1;

[0109] (2) Mix 100g of the lithium salt solution obtained in step (1), 1g of monomer 1, 0.02g of initiator benzoyl peroxide and additive vinylene carbonate to obtain a polymerization reaction system. Heat the polymerization reaction system to 70°C for polymerization reaction. After reacting for 4 hours, a gel polymer electrolyte is obtained. The weight ratio of LiPF6 to monomer 1 in the lithium salt solution is 14:1. The weight ratio of monomer 1 to initiator is 50:1. The weight percentage of additive vinylene carbonate is 0.1wt% based on the total weight of the polymerization reaction system.

[0110] Preparation Example 20

[0111] The difference from Preparation Example 19 is that tris(trimethylsilane)borate is used instead of vinylene carbonate; and the weight percentage of tris(trimethylsilane)borate is 20 wt% based on the total weight of the polymerization reaction system.

[0112] Preparation Example 21

[0113] The difference from Preparation Example 19 is that tris(trimethylsilane) phosphate is used instead of vinylene carbonate; and the weight percentage of tris(trimethylsilane) phosphate is 25 wt% based on the total weight of the polymerization reaction system.

[0114] Preparation of Comparative Example 1

[0115] The difference from Preparation Example 1 is that an equal amount of monomer D1 (CAS: 45115-53-5) is used to replace monomer 1 in step (2). The chemical structure of monomer D1 is as follows:

[0116] .

[0117] Preparation of Comparative Example 2

[0118] The difference from Preparation Example 1 is that an equal amount of monomer D2 (CAS: 36405-47-7) is used to replace monomer 1 in step (2). The chemical structure of monomer D2 is as follows:

[0119] .

[0120] (II) Application Examples

[0121] Application Example 1

[0122] A method for preparing a semi-solid-state lithium-ion battery, comprising:

[0123] (1) Lithium nickel cobalt manganese oxide, conductive carbon black Super P and binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:1.5:1.5 and dispersed in NMP to prepare a positive electrode slurry. The positive electrode slurry is coated on both sides of an aluminum foil and then baked, rolled and cut to obtain a positive electrode sheet.

[0124] The negative electrode active material artificial graphite, conductive carbon black Super P and binder SBR are mixed in a weight ratio of 92:4:4 and dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of a copper foil and then baked, rolled and cut to obtain a negative electrode sheet.

[0125] Prepare a 15μm thick PP material separator;

[0126] (2) The positive electrode, negative electrode and separator prepared in step (1) are wound to obtain a bare cell;

[0127] (3) The bare cell is placed in an aluminum-plastic packaging film, and the polymerization reaction system containing lithium salt solution, monomer 1 and initiator benzoyl peroxide obtained in step (2) of preparation example 1 is injected into the bare cell; it is left to stand at 25°C for 24 hours; the polymerization reaction is carried out at 70°C for 4 hours to obtain a semi-solid lithium-ion battery.

[0128] Application Example 2

[0129] The difference from Application Example 1 is that, referring to Preparation Example 2, monomer 1 is replaced with monomer 2.

[0130] Application Example 3

[0131] The difference from Application Example 1 is that, referring to Preparation Example 3, monomer 1 is replaced with monomer 3.

[0132] Application Examples 4 to 6

[0133] The difference from Application Example 1 is that the weight percentage of LiPF6 in the lithium salt solution is as described in Preparation Examples 4 to 6.

[0134] Application Examples 7 and 8

[0135] The difference from Application Example 1 is that the lithium salt types are referred to in Preparation Examples 7 and 8 respectively.

[0136] Application Examples 9 to 12

[0137] The difference from Application Example 1 is that the types and proportions of solvents are as described in Preparation Examples 9 to 12.

[0138] Application Examples 13 to 15

[0139] The difference from Application Example 1 is that the weight ratio of LiPF6 to monomer 1 is as described in Preparation Examples 13 to 15.

[0140] Application Examples 16 to 18

[0141] The difference from Application Example 1 is that the reaction temperature and time of the polymerization reaction are as described in Preparation Examples 16 to 18.

[0142] Application Example 19

[0143] A method for preparing a semi-solid-state lithium-ion battery, comprising:

[0144] (1) Prepare the positive electrode, negative electrode and separator, and the specific method is the same as in Application Example 1;

[0145] The bare battery cell was placed in an aluminum-plastic packaging film, and the polymerization reaction system containing lithium salt solution, monomer 1, initiator benzoyl peroxide and additive vinylene carbonate obtained in step (2) of preparation example 19 was injected into the bare battery cell; it was left to stand at 25°C for 24 hours; and the polymerization reaction was carried out at 70°C for 8 hours to obtain a semi-solid lithium-ion battery.

[0146] Application Examples 20 and 21

[0147] The difference from Application Example 19 is that the types of additives were replaced according to Preparation Examples 20 and 21, respectively.

[0148] Application Comparative Example 1

[0149] The difference from Application Example 1 is that, referring to Comparative Example 1, the monomer type is replaced by monomer D1.

[0150] Application Comparative Example 2

[0151] The difference from Application Example 1 is that, referring to Comparative Example 2, the monomer type is replaced by monomer D2.

[0152] The semi-solid lithium-ion batteries prepared in the above application embodiments and application comparative examples of this application were subjected to thermal box performance tests and cycle performance tests.

[0153] (1) The performance test of the hot box is as follows: At 25℃, the battery is charged to 4.25V with a constant current and constant voltage of 0.5C and a cutoff current of 0.05C. Then, the battery cell is fixed with iron clamps and placed in the hot box. The box is heated from room temperature to the point of battery thermal runaway at a heating rate of 5℃ / min. The starting temperature of battery thermal runaway is recorded. The higher the starting temperature, the higher the battery safety.

[0154] (2) Cyclic performance test is as follows: voltage range is 2.5~4.4V, number of cycles is 500, test temperature is 25℃ and 45℃.

[0155] The test results are shown in Table 1.

[0156] Table 1

[0157]

[0158] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0159] The preparation method described in this application enables the monomers to undergo in-situ polymerization under the initiation of an initiator. The monomers used in this application contain fluorine atoms and benzene ring structures. On the one hand, this introduces a large number of fluorine-containing groups into the gel polymer electrolyte. Under thermal runaway conditions in semi-solid lithium-ion batteries, these groups can decompose to generate fluorine free radicals. These fluorine free radicals can undergo a chain combustion reaction with hydrogen and hydroxyl free radicals in the gas phase, thereby improving the flame retardancy of the gel polymer electrolyte and thus enhancing the safety of the semi-solid lithium-ion battery. On the other hand, this method can suppress the dissolution of transition metal elements in the positive electrode active material, mitigating irreversible phase transitions caused by high voltage, thereby reducing capacity loss and improving cycle performance of the semi-solid lithium-ion battery. Furthermore, it can improve the thermal stability of the gel polymer electrolyte. The monomers used in this application also contain sulfonic acid groups. The introduction of these groups can improve the stability of the SEI film and chelate with anions in the lithium salt, thereby inhibiting anion migration, improving lithium-ion transport efficiency, and thus enhancing the electrochemical performance of the semi-solid lithium-ion battery.

[0160] Moreover, compared to other types, limiting the fluoroalkyl groups in R1, R2, R3, R4 and R5 in formula (I) to the above range is beneficial to reducing the impedance of the prepared gel polymer electrolyte, thereby reducing the internal resistance of the semi-solid lithium-ion battery and improving its electrochemical performance.

[0161] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0162] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a gel polymer electrolyte, characterized in that, The preparation method includes: Step S1: Mix the lithium salt with a solvent to obtain a lithium salt solution; Step S2: The lithium salt solution, polymerizing monomer and initiator are mixed and polymerized to obtain a gel polymer electrolyte; The polymeric monomer has the structure shown in formula (I): ， R1, R2, R3, and R4 are each independently selected from fluorine, C1 to C4. 10 Fluorinated alkyl groups, or C1-C2 fluoroalkyl groups substituted with C1-C2 alkyl groups. 10 Fluorinated alkyl groups; R5 is selected from C1-C2 alkyl groups or C1-C2 fluoroalkyl groups.

2. The method for preparing the gel polymer electrolyte according to claim 1, characterized in that, R1, R2, R3 and R4 are each independently selected from fluorine, C1-C2 fluoroalkyl, or C1-C2 fluoroalkyl substituted with C1-C2 fluoroalkyl; R5 is selected from methyl, trifluoromethyl or pentafluoroethyl.

3. The method for preparing the gel polymer electrolyte according to claim 1, characterized in that, R1, R2, R3 and R4 are each independently selected from fluorine, trifluoromethyl, pentafluoroethyl, monofluoromethyl-substituted trifluoromethyl, or trifluoroethyl-substituted pentafluoroethyl; R5 is selected from methyl.

4. The method for preparing the gel polymer electrolyte according to claim 1, characterized in that, The polymeric monomer is selected from one or more of monomers 1 to 3: 、 、 。 5. The method for preparing the gel polymer electrolyte according to any one of claims 1 to 4, characterized in that, The lithium salt in the lithium salt solution has a weight percentage of 8-20 wt%. Preferably, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium bis(oxalate-borate), lithium difluorooxalate-borate, lithium difluorobis(oxalate-phosphate), and lithium tetrafluorooxalate-phosphate.

6. The method for preparing the gel polymer electrolyte according to any one of claims 1 to 4, characterized in that, The solvent is selected from one or more of cyclic carbonates, linear carbonates, and carboxylic acid esters; Preferably, the solvent comprises the cyclic carbonate and the chain carbonate, and the weight percentage of the cyclic carbonate in the solvent is 15-35 wt%; the weight percentage of the chain carbonate in the solvent is 45-85 wt%; or, the solvent comprises the carboxylic acid ester, and the weight percentage of the carboxylic acid ester in the solvent is 5-60 wt%. Preferably, the cyclic carbonate is selected from one or more of ethylene carbonate, propylene carbonate, and butene carbonate; the chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate; and the carboxylic acid ester is selected from one or more of methyl formate, ethyl formate, methyl acetate, and ethyl acetate.

7. The method for preparing the gel polymer electrolyte according to claim 6, characterized in that, The weight ratio of lithium salt to polymeric monomer in the lithium salt solution is (5-20):1; and / or, The weight ratio of the polymerizable monomer to the initiator is (1-1000):(1-50). Preferably, the initiator is selected from peroxide initiators and / or azo initiators; more preferably, the peroxide initiator is selected from one or more of benzoyl peroxide, benzoyl tert-butyl peroxide and methyl ethyl ketone peroxide; and the azo initiator is selected from one or more of azobisisobutyronitrile, dimethyl azobisisobutyrate and azobisisoheptanenitrile.

8. The method for preparing the gel polymer electrolyte according to claim 6 or 7, characterized in that, Step S2 includes: mixing the lithium salt solution, the polymerizing monomer, the initiator and the additive to obtain a polymerization reaction system, heating the polymerization reaction system to the reaction temperature to carry out the polymerization reaction, and obtaining the gel polymer electrolyte; Preferably, the reaction temperature is 60–80°C, and the polymerization reaction time is 2–24 hours. Preferably, the additive has a weight percentage of 0.1–20 wt% based on the total weight of the polymerization reaction system. More preferably, the additive is selected from one or more of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, and methanedisulfonate.

9. A gel polymer electrolyte, characterized in that, The gel polymer electrolyte is prepared by the method of any one of claims 1 to 8; the ionic conductivity of the gel polymer electrolyte is 6 to 12 S / m.

10. A semi-solid-state lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, characterized in that, The electrolyte is selected from the gel polymer electrolyte of claim 9.

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