Modified polyionic liquid-based copolymer solid electrolyte, preparation method and application

Abstract

The present invention discloses a modified polyionic liquid-based copolymer solid electrolyte, a preparation method, and an application. The modified polyionic liquid-based copolymer solid electrolyte comprises a lithium salt and a modified polyionic liquid-based copolymer. The modified polyionic liquid-based copolymer has the following general structural formula: #imgabs0# wherein A is a cationic group containing a nitrogen element, B is an alkyl chain having a branched structure, and X is ‑ Selected from Cl ‑ Br ‑ , bis(trifluoromethanesulfonic acid) imide anion or difluorooxalatoborate anion, C is a carboxylate chain, and D is a ring or chain containing silicon or boron elements. The room temperature ionic conductivity of the modified polyionic liquid-based copolymer solid electrolyte provided by the present invention can reach up to 6×10 ‑4 Scm ‑1 It has the advantages of high temperature resistance and non-combustibility. In addition, the cationic group of the ionic liquid and the boron with a hole in the boroxane can form an electrostatic effect with the anion of the lithium salt, thereby inhibiting the migration of the anion and improving the migration of the Li ion.

Description

Technical Field

[0001] The present invention relates to a solid electrolyte, in particular to a modified polyionic liquid-based copolymer solid electrolyte and a preparation method thereof, as well as application in a lithium secondary battery, belonging to the technical field of lithium secondary batteries. Background Art

[0002] Energy is essential for maintaining human production and life. Since the new century, with the development of science and technology, energy has received increasing attention in production and life, and energy conversion and storage have become particularly important. Lithium-ion batteries are widely used due to their high energy density, high operating voltage, long cycle life, low self-discharge rate, no memory effect, fast charge and discharge, and environmental friendliness.

[0003] Currently, most commercial lithium-ion batteries on the market use liquid carbonate organic electrolytes. Because carbonate solvents are often flammable and have low flash points, lithium batteries are prone to leakage, combustion, and explosion. Replacing traditional liquid organic electrolytes with polymer electrolytes is a reliable solution for improving the safety performance of lithium-ion batteries. Consequently, polymer solid electrolytes are gaining increasing attention, particularly polyionic liquid solid electrolytes, which offer excellent heat resistance and flame retardancy.

[0004] Polyionic liquids (PILs) offer the advantages of ionic liquids, such as good thermal stability, non-combustion properties, and a wide electrochemical stability window, while also possessing the excellent processability and flexibility of polymers. They are very promising candidates for polymer matrices in solid electrolytes. However, these polymers also have their own drawbacks. For example, their highly regular structure makes their molecular chains difficult to move, resulting in low ionic conductivity at room temperature, making them unsuitable for practical applications.

[0005] In order to improve the ionic conductivity of polyionic liquid solid electrolytes, patent CN104140545A blends imidazolium ionic liquids containing unsaturated bonds at both ends with polymers such as polyvinylidene fluoride, and prepares ionic liquid / polymer electrolyte membranes by irradiation under gamma rays or electron beams, which solves the overflow problem of physically doped ionic liquids and improves the stability of polymer electrolytes. The literature ACS Appl. Mater. Interfaces 2020, 12, 23774-23780 copolymerizes the ionic liquid monomer 1-vinyl-3-propyl imidazole bis(trifluoromethylsulfonimide) salt with polyethylene glycol diacrylate monomer to reduce the crystalline area of ​​the polymer, increase the amorphous area, and improve the transmission of lithium ions in the polymer chain, obtaining a room temperature ionic conductivity of 1.4×10 -4 S cm -1However, to achieve application in all-solid-state batteries, the room-temperature ionic conductivity of the polyionic liquid-based polymer solid electrolytes prepared by these methods needs to be further improved. Summary of the Invention

[0006] The main purpose of the present invention is to provide a modified polyionic liquid-based copolymer solid electrolyte and a preparation method thereof, so as to overcome the deficiencies in the prior art.

[0007] Another object of the present invention is to provide an application of the modified polyionic liquid-based copolymer solid electrolyte in a lithium secondary battery.

[0008] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0009] An embodiment of the present invention provides a modified polyionic liquid-based copolymer solid electrolyte, which includes a lithium salt and a modified polyionic liquid-based copolymer. The general structural formula of the modified polyionic liquid-based copolymer is as follows:

[0010]

[0011] Wherein, A is a cationic group having nitrogen element, B is an alkyl chain containing two or more carbon branched structures, and X - Selected from C1 - Br - 、Bistrifluoromethanesulfonic acid imide anion (Tf2N - ) or difluorooxalatoborate anion (DFOB - ), C contains a carboxylate (-COO-) structure, D is a ring or chain containing silicon or boron elements, n=10 to 1000, and m=10 to 1000.

[0012] In some embodiments, the content of lithium salt in the solid electrolyte is 5 to 40 wt %, and the content of the modified polyionic liquid-based copolymer is 60 to 95 wt %.

[0013] Furthermore, the modified polyionic liquid-based copolymer comprises an ionic liquid polymer segment and a silicone / boroxane-containing polymer segment, wherein the content of the ionic liquid polymer in the modified polyionic liquid-based copolymer is 50-90 wt%, and the content of the silicone / boroxane-containing polymer is 10-50 wt%.

[0014] In some embodiments, the number average molecular weight of the modified polyionic liquid-based copolymer is 1,000 to 50,000, preferably 1,000 to 10,000, and the lithium ion transference number is greater than 0.5.

[0015] Furthermore, the room temperature ionic conductivity of the modified polyionic liquid-based copolymer solid electrolyte can reach up to 6×10 -4 S cm -1 .

[0016] An embodiment of the present invention further provides a method for preparing the aforementioned modified polyionic liquid-based copolymer solid electrolyte, which comprises:

[0017] Providing a cationic ionic liquid monomer having at least one active group and containing two or more carbon branched substituent groups, and a monomer having at least one active group and a boroxane or siloxane;

[0018] A polymer electrolyte precursor solution comprising the cationic ionic liquid monomer, a monomer having at least one active group and boroxane or siloxane, a lithium salt and an initiator is subjected to copolymerization reaction under heating or light conditions to obtain the modified polyionic liquid-based copolymer solid electrolyte.

[0019] In some embodiments, the cationic ionic liquid monomer includes an ionic liquid monomer such as an imidazole, pyrrole, pyridine, piperidine or quaternary ammonium salt.

[0020] In some embodiments, the polymerization temperature of the copolymerization reaction is 40 to 80° C., the polymerization time is 6 to 12 hours, and the illumination time is 2 to 10 minutes.

[0021] An embodiment of the present invention further provides a lithium secondary battery comprising the aforementioned modified polyionic liquid-based copolymer solid electrolyte.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) The present invention provides a novel modified polyionic liquid-based copolymer solid electrolyte. The polymer chain structure is cleverly designed by copolymerizing a cationic ionic liquid monomer containing one or more active groups and branched substituent groups with a monomer containing one or more active groups and a boroxane / siloxane. By increasing the size of the side chains, the free volume of the copolymer is increased, the mobility of the main chain is promoted, and the crystallinity and glass transition temperature of the polymer are reduced. Simultaneously, the polar groups on the side chains, such as carbonyl, carboxyl, boroxane / siloxane, and the cationic ionic liquid groups, promote the dissociation of lithium salts and the conduction of lithium ions through the polymer main / side chains. Furthermore, the cationic groups of the ionic liquid and the boron with a hole in the boroxane can form electrostatic interactions with the anions of the lithium salt, thereby inhibiting the migration of anions and enhancing the migration of lithium ions.

[0024] 2) The room temperature ionic conductivity of the modified polyionic liquid-based copolymer solid electrolyte provided by the present invention can reach up to 6×10 -4 S cm-1 , with the advantages of high temperature resistance and non-combustibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 1 is a schematic structural diagram of a modified polyionic liquid-based copolymer solid electrolyte in a typical embodiment of the present invention;

[0027] Figure 2 Schematic diagram of the preparation reaction of each reaction monomer and copolymer electrolyte in each step of Examples 1-12 of the present invention;

[0028] Figure 3 Schematic diagram of the preparation reaction of each reaction monomer and copolymer electrolyte in each step in Examples 13-15 of the present invention;

[0029] Figure 4 Schematic diagram of the preparation reaction of each reaction monomer and copolymer electrolyte in each step in Example 16 of the present invention;

[0030] Figure 5 This is the H NMR spectrum of the cationic ionic liquid monomer A containing unsaturated bonds and branched substituent groups in Example 1 of the present invention;

[0031] Figure 6 This is the H NMR spectrum of the unsaturated acrylate monomer B containing cyclic boroxine in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] In response to the shortcomings of the existing technology, the inventors of this case have proposed the technical solution of the present invention after long-term research and extensive practice. It mainly provides a modified polyionic liquid-based copolymer solid electrolyte. The modified polyionic liquid-based copolymer solid electrolyte is produced by copolymerizing a cationic ionic liquid monomer containing one or more active groups and branched substituent groups, a monomer containing one or more active groups and boroxane / siloxane, and a lithium salt under UV light or heating.

[0033] The technical solution, its implementation process and principles are further explained below.

[0034] One aspect of the present invention provides a modified polyionic liquid-based copolymer solid electrolyte, which is copolymerized by a cationic ionic liquid monomer having one or more active groups and branched substituent groups and a monomer containing one or more active groups and boroxane / siloxane, and has the general structural formula: The main chain is a carbon-carbon chain, and the side chain is an ionic liquid R1 containing a branching group and an R2 repeating unit containing a siloxane / boroxane.

[0035] For more details, see Figure 1 As shown, another aspect of the embodiment of the present invention provides a modified polyionic liquid-based copolymer solid electrolyte comprising a lithium salt and a modified polyionic liquid-based copolymer, wherein the modified polyionic liquid-based copolymer has the following general structural formula:

[0036]

[0037] Wherein, A is a cationic group having a nitrogen element, B is an alkyl chain containing two or more carbon branched structures (each branched structure contains two to ten carbons), X - Selected from Cl - Br - 、Bistrifluoromethanesulfonic acid imide anion (Tf2N - ) or difluorooxalatoborate anion (DFOB - ), C contains a carboxylate structure (-COO-), D is a ring or chain containing silicon or boron elements, n=10 to 1000, and m=10 to 1000.

[0038] In some preferred embodiments, A includes an imidazole group, a pyrrole group, a pyridine group, a piperidine group, or a quaternary ammonium salt, but is not limited thereto.

[0039] Further, B is 2-ethylhexyl, but is not limited thereto.

[0040] Furthermore, C is an acrylate chain, and D is a cyclic borane group or a silane group, but is not limited thereto.

[0041] In some preferred embodiments, the structure of the modified polyionic liquid-based copolymer is shown in any one of the following:

[0042]

[0043] In some preferred embodiments, the content of lithium salt in the solid electrolyte is 5 to 40 wt%, and the content of the modified polyionic liquid-based copolymer is 60 to 95 wt%.

[0044] In some preferred embodiments, the modified polyionic liquid-based copolymer comprises an ionic liquid polymer segment and a silicone / boroxane-containing polymer segment, wherein the content of the ionic liquid polymer in the modified polyionic liquid-based copolymer is 50 to 90 wt%, and the content of the silicone / boroxane-containing polymer is 10 to 50 wt%.

[0045] In some preferred embodiments, the number average molecular weight of the modified polyionic liquid-based copolymer is 1,000 to 50,000, preferably 1,000 to 10,000, and the lithium ion transference number is greater than 0.5.

[0046] Furthermore, the room temperature ionic conductivity of the modified polyionic liquid-based copolymer solid electrolyte can reach up to 6×10 -4 S cm -1 , with the advantages of high temperature resistance and non-combustibility.

[0047] In summary, the structural design principle of the modified polyionic liquid-based copolymer solid electrolyte provided by the present invention is: from the perspective of polymer chain structure design, a cationic ionic liquid monomer containing one or more active groups and branched substituent groups is copolymerized with a monomer containing one or more active groups and boroxane / siloxane. By increasing the size of the side chain, the free volume of the copolymer is increased, the mobility of the main chain is promoted, and the crystallinity and glass transition temperature of the polymer are reduced. At the same time, the polar groups on the side chain, such as carbonyl, carboxyl, boroxane / siloxane, etc., and the cationic ionic liquid groups can promote the dissociation of lithium salts and the conduction of lithium ions through the main / side chains of the polymer. In addition, the cationic groups of the ionic liquid and the boron with a hole in the boroxane can also form electrostatic interactions with the anions of the lithium salt, thereby inhibiting the migration of anions and improving the migration of Li ions.

[0048] Another aspect of an embodiment of the present invention provides a method for preparing a modified polyionic liquid-based copolymer solid electrolyte, comprising:

[0049] Providing a cationic ionic liquid monomer having at least one reactive group and two or more branched substituent groups (each branch having two to ten carbon atoms), and a monomer having at least one reactive group and a boroxane or siloxane;

[0050] A polymer electrolyte precursor solution comprising the cationic ionic liquid monomer, a monomer having at least one active group and boroxane or siloxane, a lithium salt and an initiator is subjected to copolymerization reaction under heating or light conditions to obtain the modified polyionic liquid-based copolymer solid electrolyte.

[0051] In some preferred embodiments, the cationic ionic liquid monomer includes cationic ionic liquids such as imidazoles, pyrroles, pyridines, piperidines or quaternary ammonium salts, and the ionic liquid monomer contains one or more reactive groups, which can be but are not limited to vinyl groups, allyl groups and the like.

[0052] More specifically, the structure of the cationic ionic liquid monomer can be:

[0053]

[0054] More specifically, the structure of the monomer having an active group and boroxane or siloxane is shown in any one of the following:

[0055]

[0056] In some preferred embodiments, the mass ratio of the cationic ionic liquid monomer to the monomer having one active group and boroxane or siloxane is 1:1 to 9:1.

[0057] In some preferred embodiments, the preparation method of the cationic ionic liquid monomer containing one or more active groups and branched substituent groups is as follows:

[0058] 1) An ionic liquid containing an active group and an alkyl bromide having a branched alkyl group are dissolved in ethyl acetate and reacted. After the reaction is completed, rotary distillation is performed, and after the distillation is completed, the product is washed with n-hexane and then rotary distilled again to obtain the product.

[0059] 2) Dissolve the product obtained in step 1) in chloroform, dissolve the lithium salt in deionized water, slowly add dropwise, and stir for 24 hours. After stirring, wash with plenty of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate to obtain a cationic ionic liquid monomer having active groups and branched substituents.

[0060] In some preferred embodiments, the polymer monomer containing active groups and boroxane / siloxane can be purchased or homemade, wherein the preparation method of the polymer monomer containing active groups and boroxane can be referred to as follows:

[0061] Under an argon atmosphere, trimethyl borate and an alkane containing two hydroxyl groups are dissolved in anhydrous acetonitrile, stirred for 2 hours, and then a carboxylate with a double bond and a hydroxyl group is added. Stirring is continued to obtain an unsaturated acrylic ester monomer containing a cyclic boroxane.

[0062] In some preferred embodiments, the modified polyionic liquid-based copolymer solid electrolyte is produced by copolymerizing a cationic ionic liquid monomer containing one or more active groups and branched substituent groups, a monomer containing one or more active groups and boroxane / siloxane, and a lithium salt under UV light or heating. The active groups can be but are not limited to vinyl, allyl and other groups. The polymerization temperature of the copolymerization reaction is 40-80°C, the polymerization time is 6-12h, and the illumination time under 365nm ultraviolet light is 2-10min.

[0063] In some preferred embodiments, the initiator comprises a thermal initiator and / or a photoinitiator.

[0064] Furthermore, the initiator can be any one or a combination of two or more thermal initiators such as azobisisobutyronitrile, azobisisoheptanenitrile, dibenzoyl peroxide, dialkyl peroxide, isopropylbenzene hydroperoxide, and tert-butyl hydroperoxide, or can be any one or a combination of two or more photoinitiators such as 2-hydroxy-methylphenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl-1-propanone, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, but is not limited thereto.

[0065] In some preferred embodiments, the mass ratio of the initiator to the cationic ionic liquid monomer to the monomer having one reactive group and boroxane or siloxane is 0.1-5:100. That is, the amount of the initiator is 0.1-5 wt% of the total weight of the two monomers.

[0066] Furthermore, the lithium salt includes any one or a combination of two or more of lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), lithium hexafluorophosphate, lithium bis(oxalatoborate), etc., but is not limited thereto.

[0067] Furthermore, the mass ratio of the lithium salt to the cationic ionic liquid monomer to the monomer having one active group and boroxane or siloxane is 5-40:100, that is, the amount of the lithium salt is 5-40 wt% of the total of the two monomers.

[0068] Another aspect of the embodiments of the present invention further provides a lithium secondary battery comprising any one of the aforementioned modified polyionic liquid-based copolymer solid electrolytes.

[0069] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments and the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The experimental methods in the following examples where specific conditions are not specified are generally based on conventional conditions or the conditions recommended by the manufacturer.

[0070] Example 1: The schematic diagram of the preparation reaction of each reaction monomer and copolymer electrolyte in each step of this example is shown in FIG. Figure 2 As shown:

[0071] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer A)

[0072] Dissolve 10 g of 1-vinylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill the mixture at 60°C for 40 minutes. Wash the mixture three times with 20 ml of n-hexane (separation), and rotary distill the mixture at 60°C for 40 minutes to yield 23.12 g (75.72%) of the product.

[0073] Dissolve 20g of the product from the previous step in 80ml of chloroform; dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24h. After the reaction is complete, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it contains no bromide ions. Rotary evaporate at 70°C for 40min, then dry in a vacuum oven at 70°C for 12h to obtain 31.50g (93%) of a reddish-brown, transparent liquid. For its H NMR spectrum, see [see 'H NMR spectrum']. Figure 5 .

[0074] (2) Preparation of unsaturated acrylate monomer containing cyclic boroxane (monomer B)

[0075] Under argon atmosphere, dissolve 10 ml of trimethyl borate and 6 ml of 1,2-propylene glycol in 40 ml of anhydrous acetonitrile, stir at 65°C for 2 h, add 6.5 ml of hydroxyethyl methacrylate, and continue stirring at 70°C for 4 h to obtain a pink liquid. Its H NMR spectrum can be found at Figure 6 .

[0076] (3) Composition of polymer electrolyte precursor solution: the mass ratio of monomer A to monomer B is 3:1, lithium salt: lithium bis(trifluoromethanesulfonyl imide): 30 wt% of the total mass of monomer A and monomer B, thermal initiator: azobisisobutyronitrile (1% of the total mass of monomer A and monomer B).

[0077] (4) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A thermal initiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was dropped onto a glass fiber membrane and heated at 60°C in a vacuum for 9 hours to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 6.0×10 -4 S cm -1 .

[0078] Example 2 For the schematic diagram of the preparation reaction of each reaction monomer and copolymer electrolyte in each step of this example, please refer to Figure 2 As shown:

[0079] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer A)

[0080] Dissolve 10 g of 1-vinylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill the mixture at 60°C for 40 minutes. Wash the mixture three times with 20 ml of n-hexane (separation), and rotary distill the mixture at 60°C for 40 minutes to yield 23.12 g (75.72%) of the product.

[0081] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 31.50g (93%) of a reddish-brown, transparent liquid.

[0082] (2) Preparation of unsaturated acrylate monomer containing cyclic boroxane (monomer B)

[0083] Under argon atmosphere, 10 ml of trimethyl borate and 6 ml of 1,2-propylene glycol were dissolved in 40 ml of anhydrous acetonitrile, stirred at 65 °C for 2 h, 6.5 ml of hydroxyethyl methacrylate was added, and stirring was continued at 70 °C for 4 h to obtain a pink liquid.

[0084] (3) Composition of polymer electrolyte precursor solution: the mass ratio of monomer A to monomer B is 1:1, lithium salt: lithium bis(trifluoromethanesulfonyl)imide: 5 wt% of the total mass of monomer A and monomer B), thermal initiator: azobisisobutyronitrile (0.1% of the total mass of monomer A and monomer B).

[0085] (4) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A thermal initiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was dropped onto a glass fiber membrane and heated in a vacuum at 40°C for 6 hours to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 2.5×10 -5 S cm -1 .

[0086] Example 3: The schematic diagram of the preparation reaction of each monomer and copolymer electrolyte in each step of this example is shown in FIG. Figure 2 As shown:

[0087] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer A)

[0088] Dissolve 10 g of 1-vinylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill the mixture at 60°C for 40 minutes. Wash the mixture three times with 20 ml of n-hexane (separation), and rotary distill the mixture at 60°C for 40 minutes to yield 23.12 g (75.72%) of the product.

[0089] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 31.50g (93%) of a reddish-brown, transparent liquid.

[0090] (2) Preparation of unsaturated acrylate monomer containing cyclic boroxane (monomer B)

[0091] Under argon atmosphere, 10 ml of trimethyl borate and 6 ml of 1,2-propylene glycol were dissolved in 40 ml of anhydrous acetonitrile, stirred at 65 °C for 2 h, 6.5 ml of hydroxyethyl methacrylate was added, and stirring was continued at 70 °C for 4 h to obtain a pink liquid.

[0092] (3) Composition of polymer electrolyte precursor solution: the mass ratio of monomer A to monomer B is 9:1, lithium salt: lithium bis(trifluoromethanesulfonyl imide): 40 wt% of the total mass of monomer A and monomer B, thermal initiator: azobisisobutyronitrile (5% of the total mass of monomer A and monomer B).

[0093] (4) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A thermal initiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was dropped onto a glass fiber membrane and heated at 80°C in a vacuum for 12 hours to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 5.2×10 -7 S cm -1 .

[0094] Example 4: The schematic diagram of the preparation reaction of each monomer and copolymer electrolyte in each step of this example is shown in FIG. Figure 2 As shown:

[0095] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer A)

[0096] Dissolve 10 g of 1-vinylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill the mixture at 60°C for 40 minutes. Wash the mixture three times with 20 ml of n-hexane (separation), and rotary distill the mixture at 60°C for 40 minutes to yield 23.12 g (75.72%) of the product.

[0097] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 31.50g (93%) of a reddish-brown, transparent liquid.

[0098] (2) Preparation of unsaturated acrylate monomer containing cyclic boroxane (monomer B)

[0099] Under argon atmosphere, 10 ml of trimethyl borate and 6 ml of 1,2-propylene glycol were dissolved in 40 ml of anhydrous acetonitrile, stirred at 65 °C for 2 h, 6.5 ml of hydroxyethyl methacrylate was added, and stirring was continued at 70 °C for 4 h to obtain a pink liquid.

[0100] (3) Composition of polymer electrolyte precursor solution: the mass ratio of monomer A to monomer B is 3:1, lithium salt: lithium bis(trifluoromethanesulfonyl imide): 30 wt% of the total mass of monomer A and monomer B, thermal initiator: dibenzoyl peroxide (1% of the total mass of monomer A and monomer B).

[0101] (4) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A thermal initiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was dropped onto a glass fiber membrane and heated at 60°C in a vacuum for 9 hours to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 5.2×10 -4 S cm -1 .

[0102] Example 5: The schematic diagram of the preparation reaction of each monomer and copolymer electrolyte in each step of this example is shown in FIG. Figure 2 As shown:

[0103] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer A)

[0104] Dissolve 10 g of 1-vinylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill the mixture at 60°C for 40 minutes. Wash the mixture three times with 20 ml of n-hexane (separation), and rotary distill the mixture at 60°C for 40 minutes to yield 23.12 g (75.72%) of the product.

[0105] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 31.50g (93%) of a reddish-brown, transparent liquid.

[0106] (2) Preparation of unsaturated acrylate monomer containing cyclic boroxane (monomer B)

[0107] Under argon atmosphere, 10 ml of trimethyl borate and 6 ml of 1,2-propylene glycol were dissolved in 40 ml of anhydrous acetonitrile, stirred at 65 °C for 2 h, 6.5 ml of hydroxyethyl methacrylate was added, and stirring was continued at 70 °C for 4 h to obtain a pink liquid.

[0108] (3) Composition of polymer electrolyte precursor solution: the mass ratio of monomer A to monomer B is 1:1, lithium salt: lithium bis(trifluoromethanesulfonyl imide): 5 wt% of the total mass of monomer A and monomer B, thermal initiator: dibenzoyl peroxide (0.1% of the total mass of monomer A and monomer B).

[0109] (4) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A thermal initiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was dropped onto a glass fiber membrane and heated in a vacuum at 40°C for 6 hours to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 1.8×10 -5 S cm -1 .

[0110] Example 6 For the schematic diagram of the preparation reaction of each reaction monomer and copolymer electrolyte in each step of this example, please refer to Figure 2 As shown:

[0111] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer A)

[0112] Dissolve 10 g of 1-vinylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill the mixture at 60°C for 40 minutes. Wash the mixture three times with 20 ml of n-hexane (separation), and rotary distill the mixture at 60°C for 40 minutes to yield 23.12 g (75.72%) of the product.

[0113] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 31.50g (93%) of a reddish-brown, transparent liquid.

[0114] (2) Preparation of unsaturated acrylate monomer containing cyclic boroxane (monomer B)

[0115] Under argon atmosphere, 10 ml of trimethyl borate and 6 ml of 1,2-propylene glycol were dissolved in 40 ml of anhydrous acetonitrile, stirred at 65 °C for 2 h, 6.5 ml of hydroxyethyl methacrylate was added, and stirring was continued at 70 °C for 4 h to obtain a pink liquid.

[0116] (3) Composition of polymer electrolyte precursor solution: the mass ratio of monomer A to monomer B is 9:1, lithium salt: lithium bis(trifluoromethanesulfonyl imide): 40 wt% of the total mass of monomer A and monomer B, thermal initiator: dibenzoyl peroxide (5% of the total mass of monomer A and monomer B).

[0117] (4) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A thermal initiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was dropped onto a glass fiber membrane and heated at 80°C in a vacuum for 12 hours to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 4.2×10 6 S cm -1 .

[0118] Example 7 For the schematic diagram of the preparation reaction of each monomer and copolymer electrolyte in each step of this example, please refer to Figure 2 As shown:

[0119] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer A)

[0120] Dissolve 10 g of 1-vinylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill the mixture at 60°C for 40 minutes. Wash the mixture three times with 20 ml of n-hexane (separation), and rotary distill the mixture at 60°C for 40 minutes to yield 23.12 g (75.72%) of the product.

[0121] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 31.50g (93%) of a reddish-brown, transparent liquid.

[0122] (2) Preparation of unsaturated acrylate monomer containing cyclic boroxane (monomer B)

[0123] Under argon atmosphere, 10 ml of trimethyl borate and 6 ml of 1,2-propylene glycol were dissolved in 40 ml of anhydrous acetonitrile, stirred at 65 °C for 2 h, 6.5 ml of hydroxyethyl methacrylate was added, and stirring was continued at 70 °C for 4 h to obtain a pink liquid.

[0124] (3) Composition of polymer electrolyte precursor solution: the mass ratio of monomer A to monomer B is 3:1, lithium salt: lithium bis(trifluoromethanesulfonyl imide): 30 wt% of the total mass of monomer A and monomer B, photoinitiator: 2-hydroxy-methylphenylpropane-1-one (1% of the total mass of monomer A and monomer B).

[0125] (4) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A photoinitiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was applied to a glass plate and irradiated with 365 nm ultraviolet light for 5 minutes to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 5.4×10 -4 S cm -1 .

[0126] Example 8 For the schematic diagram of the preparation reaction of each reaction monomer and copolymer electrolyte in each step of this example, please refer to Figure 2 As shown:

[0127] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer A)

[0128] Dissolve 10 g of 1-vinylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill the mixture at 60°C for 40 minutes. Wash the mixture three times with 20 ml of n-hexane (separation), and rotary distill the mixture at 60°C for 40 minutes to yield 23.12 g (75.72%) of the product.

[0129] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 31.50g (93%) of a reddish-brown, transparent liquid.

[0130] (2) Preparation of unsaturated acrylate monomer containing cyclic boroxane (monomer B)

[0131] Under argon atmosphere, 10 ml of trimethyl borate and 6 ml of 1,2-propylene glycol were dissolved in 40 ml of anhydrous acetonitrile, stirred at 65 °C for 2 h, 6.5 ml of hydroxyethyl methacrylate was added, and stirring was continued at 70 °C for 4 h to obtain a pink liquid.

[0132] (3) Composition of polymer electrolyte precursor solution: the mass ratio of monomer A to monomer B is 1:1, lithium salt: lithium bis(trifluoromethanesulfonyl imide): 5 wt% of the total mass of monomer A and monomer B, photoinitiator: 2-hydroxy-methylphenylpropane-1-one (0.1% of the total mass of monomer A and monomer B).

[0133] (4) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A photoinitiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was then coated on a glass plate and irradiated with 365 nm ultraviolet light for 2 minutes to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 6.9×10 -5 S cm -1 .

[0134] Example 9: The schematic diagram of the preparation reaction of each monomer and copolymer electrolyte in each step of this example is shown in FIG. Figure 2 As shown:

[0135] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer A)

[0136] Dissolve 10 g of 1-vinylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill the mixture at 60°C for 40 minutes. Wash the mixture three times with 20 ml of n-hexane (separation), and rotary distill the mixture at 60°C for 40 minutes to yield 23.12 g (75.72%) of the product.

[0137] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 31.50g (93%) of a reddish-brown, transparent liquid.

[0138] (2) Preparation of unsaturated acrylate monomer containing cyclic boroxane (monomer B)

[0139] Under argon atmosphere, 10 ml of trimethyl borate and 6 ml of 1,2-propylene glycol were dissolved in 40 ml of anhydrous acetonitrile, stirred at 65 °C for 2 h, 6.5 ml of hydroxyethyl methacrylate was added, and stirring was continued at 70 °C for 4 h to obtain a pink liquid.

[0140] (3) Composition of polymer electrolyte precursor solution: the mass ratio of monomer A to monomer B is 9:1, lithium salt: lithium bis(trifluoromethanesulfonyl imide): 40 wt% of the total mass of monomer A and monomer B, photoinitiator: 2-hydroxy-methylphenylpropane-1-one (5% of the total mass of monomer A and monomer B).

[0141] (4) Preparation of polymer electrolyte: cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A photoinitiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was applied to a glass plate and irradiated with 365 nm ultraviolet light for 10 minutes to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 1.5×10 -6 S cm -1 .

[0142] Example 10 For the schematic diagram of the preparation reaction of each monomer and copolymer electrolyte in each step of this example, please refer to Figure 2 As shown:

[0143] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer A)

[0144] Dissolve 10 g of 1-vinylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill the mixture at 60°C for 40 minutes. Wash the mixture three times with 20 ml of n-hexane (separation), and rotary distill the mixture at 60°C for 40 minutes to yield 23.12 g (75.72%) of the product.

[0145] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 31.50g (93%) of a reddish-brown, transparent liquid.

[0146] (2) Preparation of unsaturated acrylate monomer containing cyclic boroxane (monomer B)

[0147] Under argon atmosphere, 10 ml of trimethyl borate and 6 ml of 1,2-propylene glycol were dissolved in 40 ml of anhydrous acetonitrile, stirred at 65 °C for 2 h, 6.5 ml of hydroxyethyl methacrylate was added, and stirring was continued at 70 °C for 4 h to obtain a pink liquid.

[0148] (3) Composition of polymer electrolyte precursor solution: the mass ratio of monomer A to monomer B is 3:1, lithium salt: lithium bis(trifluoromethanesulfonyl)imide: 30 wt% of the total mass of monomer A and monomer B), photoinitiator: 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone (1% of the total mass of monomer A and monomer B).

[0149] (4) Preparation of polymer electrolyte: cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A photoinitiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was coated on a glass plate and irradiated with 365 nm ultraviolet light for 5 minutes to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 1.1×10 -4 S cm -1 .

[0150] Example 11: The schematic diagram of the preparation reaction of each monomer and copolymer electrolyte in each step of this example is shown in FIG. Figure 2 As shown:

[0151] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer A)

[0152] Dissolve 10 g of 1-vinylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill the mixture at 60°C for 40 minutes. Wash the mixture three times with 20 ml of n-hexane (separation), and rotary distill the mixture at 60°C for 40 minutes to yield 23.12 g (75.72%) of the product.

[0153] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 31.50g (93%) of a reddish-brown, transparent liquid.

[0154] (2) Preparation of unsaturated acrylate monomer containing cyclic boroxane (monomer B)

[0155] Under argon atmosphere, 10 ml of trimethyl borate and 6 ml of 1,2-propylene glycol were dissolved in 40 ml of anhydrous acetonitrile, stirred at 65 °C for 2 h, 6.5 ml of hydroxyethyl methacrylate was added, and stirring was continued at 70 °C for 4 h to obtain a pink liquid.

[0156] (3) Composition of polymer electrolyte precursor solution: the mass ratio of monomer A to monomer B is 1:1, lithium salt: lithium bis(trifluoromethanesulfonyl)imide: 5 wt% of the total mass of monomer A and monomer B), photoinitiator: 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone (0.1% of the total mass of monomer A and monomer B).

[0157] (4) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A photoinitiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was applied to a glass plate and irradiated with 365 nm ultraviolet light for 2 minutes to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 7.3×10 -5 S cm -1 .

[0158] Example 12: For the schematic diagram of the preparation reaction of each monomer and copolymer electrolyte in each step of this example, please refer to Figure 2 As shown:

[0159] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer A)

[0160] Dissolve 10 g of 1-vinylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill the mixture at 60°C for 40 minutes. Wash the mixture three times with 20 ml of n-hexane (separation), and rotary distill the mixture at 60°C for 40 minutes to yield 23.12 g (75.72%) of the product.

[0161] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 31.50g (93%) of a reddish-brown, transparent liquid.

[0162] (2) Preparation of unsaturated acrylate monomer containing cyclic boroxane (monomer B)

[0163] Under argon atmosphere, 10 ml of trimethyl borate and 6 ml of 1,2-propylene glycol were dissolved in 40 ml of anhydrous acetonitrile, stirred at 65 °C for 2 h, 6.5 ml of hydroxyethyl methacrylate was added, and stirring was continued at 70 °C for 4 h to obtain a pink liquid.

[0164] (3) Composition of polymer electrolyte precursor solution: the mass ratio of monomer A to monomer B is 9:1, lithium salt: lithium bis(trifluoromethanesulfonyl)imide: 40 wt% of the total mass of monomer A and monomer B), photoinitiator: 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone (5% of the total mass of monomer A and monomer B).

[0165] (4) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A photoinitiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was applied to a glass plate and irradiated with 365 nm ultraviolet light for 10 minutes to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 5.1×10 -5 S cm -1 .

[0166] Example 13: The schematic diagram of the preparation reaction of each monomer and copolymer electrolyte in each step of this example is shown in FIG. Figure 3 As shown:

[0167] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer C)

[0168] Dissolve 10 g of 1-allylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill at 60°C for 40 minutes. Wash three times with 20 ml of n-hexane (separation), then rotary distill at 60°C for 40 minutes to yield 20.12 g (72.2%) of product.

[0169] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 29.50g (88.6%) of a reddish-brown, transparent liquid.

[0170] (2) Composition of polymer electrolyte precursor solution: the mass ratio of monomer C to 3-(trimethoxysilyl)propyl methacrylate (monomer D) is 3:1, lithium salt: lithium bis(trifluoromethanesulfonyl imide): 30 wt% of the total mass of monomer A and monomer B, thermal initiator: azobis(isoheptylcarbonitrile) (1% of the total mass of monomer C and monomer D).

[0171] (3) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A thermal initiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was dropped onto a glass fiber membrane and heated at 60°C in a vacuum for 9 hours to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 5.7×10 -4 S cm-1 .

[0172] Example 14: The schematic diagram of the preparation reaction of each monomer and copolymer electrolyte in each step of this example is shown in FIG. Figure 3 As shown:

[0173] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer C)

[0174] Dissolve 10 g of 1-allylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill at 60°C for 40 minutes. Wash three times with 20 ml of n-hexane (separation), then rotary distill at 60°C for 40 minutes to yield 20.12 g (72.2%) of product.

[0175] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 29.50g (88.6%) of a reddish-brown, transparent liquid.

[0176] (2) Composition of polymer electrolyte precursor solution: the mass ratio of monomer C to 3-(trimethoxysilyl)propyl methacrylate (monomer D) is 1:1, lithium salt: lithium bis(fluorosulfonyl)imide: 5 wt% of the total mass of monomer A and monomer B), thermal initiator: azobis(isoheptyl)carbonitrile (0.1% of the total mass of monomer C and monomer D).

[0177] (3) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A thermal initiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was dropped onto a glass fiber membrane and heated in a vacuum at 40°C for 6 hours to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 2.8×10 -4 S cm -1 .

[0178] Example 15 For the schematic diagram of the preparation reaction of each monomer and copolymer electrolyte in each step of this example, please refer to Figure 3 As shown:

[0179] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer C)

[0180] Dissolve 10 g of 1-allylimidazole and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill at 60°C for 40 minutes. Wash three times with 20 ml of n-hexane (separation), then rotary distill at 60°C for 40 minutes to yield 20.12 g (72.2%) of product.

[0181] Dissolve 20g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 29.50g (88.6%) of a reddish-brown, transparent liquid.

[0182] (2) Composition of polymer electrolyte precursor solution: monomer A and 3-(trimethoxysilyl)propyl methacrylate (monomer D) in a mass ratio of 9:1, lithium salt: lithium hexafluorophosphate: 40 wt% of the total mass of monomer A and monomer B), thermal initiator: azobisisoheptonitrile (5% of the total mass of monomer C and monomer D).

[0183] (3) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A thermal initiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was dropped onto a glass fiber membrane and heated at 80°C in a vacuum for 12 hours to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 3.4×10 -6 S cm -1 .

[0184] Example 16 For the schematic diagram of the preparation reaction of each monomer and copolymer electrolyte in each step of this example, please refer to Figure 4 As shown:

[0185] (1) Preparation of cationic ionic liquid monomers containing unsaturated bonds and branched substituent groups (monomer E)

[0186] Dissolve 10 g of 4-vinylpyridine and 24.64 g of 2-ethylhexyl bromide in 40 ml of ethyl acetate and react at 65°C for 24 hours. Rotary distill at 60°C for 40 minutes. Wash three times with 20 ml of n-hexane (separation), then rotary distill at 60°C for 40 minutes to yield 16.20 g (57.1%) of product.

[0187] Dissolve 10g of the product from the previous step in 80ml of chloroform. Dissolve 40g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 80ml of deionized water and slowly add dropwise at 40°C. Continue stirring at 40°C for 24 hours. After the reaction, rinse three times with copious amounts of water. Test the rinse water with AgNO3 solution to ensure it is free of bromide ions. Rotary evaporate at 70°C for 40 minutes, then dry in a vacuum oven at 70°C for 12 hours to yield 13.2g (79.0%) of a reddish-brown, transparent liquid.

[0188] (2) Composition of polymer electrolyte precursor solution: the mass ratio of monomer E to 3-(trimethoxysilyl)propyl methacrylate (monomer D) is 9:1, lithium salt: lithium bis(oxalatoborate): 40 wt% of the total mass of monomer A and monomer B), thermal initiator: azobis(isoheptylcarbonitrile) (5% of the total mass of monomer C and monomer D).

[0189] (3) Preparation of polymer electrolyte: Cationic ionic liquid monomers containing unsaturated bonds and branched substituents, unsaturated acrylate monomers containing cyclic boroxane, and lithium salts were uniformly mixed in different proportions. A thermal initiator was then added and magnetically stirred for 2 hours to obtain a uniform solution. The solution was dropped onto a glass fiber membrane and heated at 80°C in a vacuum for 12 hours to obtain a polymer electrolyte membrane. SS|polymer electrolyte|SS battery was assembled and the ionic conductivity was tested to be 5.2×10 -6 S cm -1 .

[0190] Comparative Example 1

[0191] The difference between this comparative example and Example 1 is that the unsaturated acrylate monomer B containing cyclic boroxine is not added to the precursor solution.

[0192] The obtained polymer electrolyte was assembled into SS|polymer electrolyte|SS battery, and the ionic conductivity was tested to be 4.5×10 -6 S cm -1 .

[0193] Comparative Example 2

[0194] The difference between this comparative example and Example 1 is that the cationic ionic liquid monomer A containing unsaturated bonds and branched substituent groups is not added to the precursor solution.

[0195] The obtained polymer electrolyte was assembled into SS|polymer electrolyte|SS battery, and the ionic conductivity was tested to be 3.8×10 -5 S cm -1 .

[0196] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0197] It should be understood that the above embodiments are merely illustrative of the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent variations or modifications made in accordance with the spirit and substance of the present invention are intended to be encompassed within the scope of protection of the present invention.

Claims

1. A modified polyionic liquid-based copolymer solid electrolyte, characterized in that The invention comprises a lithium salt and a modified polyionic liquid-based copolymer, wherein the general structural formula of the modified polyionic liquid-based copolymer is as follows: ； Wherein, n=10-1000, m=10-1000, the content of lithium salt in the solid electrolyte is 5-40wt%, and the content of modified polyionic liquid-based copolymer is 60-95wt%; The modified polyionic liquid-based copolymer comprises an ionic liquid polymer segment and a boroxane-containing polymer segment, wherein the content of the ionic liquid polymer in the modified polyionic liquid-based copolymer is 50-90 wt %, and the content of the boroxane-containing polymer is 10-50 wt %.

2. The modified polyionic liquid-based copolymer solid electrolyte according to claim 1, characterized in that: The number average molecular weight of the modified polyionic liquid-based copolymer is 1,000 to 50,000.

3. The modified polyionic liquid-based copolymer solid electrolyte according to claim 2, characterized in that: The number average molecular weight of the modified polyionic liquid-based copolymer is 1,000 to 10,000.

4. The method for preparing a modified polyionic liquid-based copolymer solid electrolyte according to any one of claims 1 to 3, wherein include: Provided are a cationic ionic liquid monomer and a monomer having an active group and a boroxane. The structure of the cationic ionic liquid monomer is shown below: ； The structure of the monomer having an active group and boroxane is shown below: ； A polymer electrolyte precursor solution comprising the cationic ionic liquid monomer, a monomer having an active group and boroxane, a lithium salt and an initiator is subjected to a copolymerization reaction under heating or light irradiation conditions to obtain the modified polyionic liquid-based copolymer solid electrolyte; the mass ratio of the cationic ionic liquid monomer to the monomer having an active group and boroxane is 1:1-9:1, the polymerization temperature of the copolymerization reaction is 40-80°C, the polymerization time is 6-12 hours, and the illumination time under 365nm ultraviolet light is 2-10 minutes.

5. The preparation method according to claim 4, characterized in that: The initiator is selected from thermal initiators and / or photoinitiators.

6. The preparation method according to claim 5, characterized in that: The thermal initiator is selected from any one of azobisisobutyronitrile, azobisisoheptanenitrile, dibenzoyl peroxide, dialkyl peroxide, isopropylbenzene hydroperoxide, and tert-butyl hydroperoxide, or a combination of two or more thereof.

7. The preparation method according to claim 5, characterized in that: The photoinitiator is selected from any one or a combination of two or more of 2-hydroxy-methylphenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl-1-propanone, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

8. The preparation method according to claim 4, wherein: The mass ratio of the combination of the initiator, the cationic ionic liquid monomer, and the monomer having one active group and boroxane is 0.1-5:

100.

9. The preparation method according to claim 4, characterized in that: The lithium salt is selected from any one of lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), lithium hexafluorophosphate, and lithium bis(oxalatoborate), or a combination of two or more thereof.

10. The preparation method according to claim 4, characterized in that: The mass ratio of the combination of the lithium salt, the cationic ionic liquid monomer, and the monomer having one active group and boroxane is 5-40:

100.

11. A lithium secondary battery, characterized in that The invention relates to a modified polyionic liquid-based copolymer solid electrolyte comprising the modified polyionic liquid-based copolymer solid electrolyte according to any one of claims 1 to 3.

Images