Preparation method of cross-linked gel polymer electrolyte, electrolyte and application thereof

Abstract

The present invention discloses a method for preparing a cross-linked gel polymer electrolyte, comprising the following steps: S1: synthesizing a vinyl ether having a bromine initiation site by an esterification reaction; S2: mixing a lithium salt, the vinyl ether having a bromine initiation site and polyethylene glycol (meth) acrylate to form a mixed solution, and then mixing it with a deep eutectic solvent to obtain a precursor solution; S3: under an inert atmosphere, infiltrating the precursor solution obtained in S2 onto a diaphragm, and assembling it into a battery with a battery positive electrode material and a negative electrode material, heating to induce free radical polymerization, and obtaining the cross-linked gel polymer electrolyte. The present invention also discloses corresponding products and applications. The present invention prepares a cross-linked gel polymer electrolyte by simultaneously catalyzing cationic polymerization and free radical polymerization by lithium salt, thereby reducing the introduction of non-electrolyte components, and the addition of multiple bromine sites can stabilize the electrode-electrolyte interface, form a strong artificial solid electrolyte interface layer, and improve the cycle stability of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer electrolytes, and in particular relates to a preparation method of a cross-linked gel polymer electrolyte, the electrolyte and applications thereof. Background Art

[0002] Lithium batteries are widely used in energy storage devices due to their high energy density and long cycle life. To meet the public's demand for high-energy-density batteries, lithium metal batteries using lithium metal with a higher specific capacity as the negative electrode have attracted widespread attention. However, traditional organic liquid electrolytes have defects such as volatility, flammability, and even explosion, posing safety risks during use. Polymer electrolytes have the advantages of flexibility and easy processing. Compared with traditional liquid electrolytes, they have excellent properties such as no leakage and low vapor pressure, which can effectively solve the safety issues of lithium metal batteries. However, the slow transmission of lithium ions in polymers and the low ionic conductivity make them unfavorable for their commercial application.

[0003] Gel polymer electrolytes combine the advantages of polymer electrolytes and liquid electrolytes, offering superior electrochemical performance while avoiding the drawbacks of liquid electrolytes, such as leakage and volatility. However, gel electrolytes require a large amount of solvent during preparation, and some in-situ preparation methods also require the introduction of additional initiators, which can affect the battery's electrochemical performance. Furthermore, the uneven deposition of lithium ions and the high reactivity of lithium metal can cause uncontrolled lithium dendrite growth and persistent interfacial reactions, compromising the battery's cycling performance.

[0004] Patent CN110350243A discloses an in-situ preparation method for a polymer electrolyte, in which monomers, lithium salts, and initiators are added to a diaphragm and heated for in-situ polymerization to obtain a polymer electrolyte. This patent obtains a linear polymer electrolyte material by initiating free radical polymerization with lithium salts, solving the electrolyte-electrode contact problem. However, it cannot form a stable electrode-electrolyte interface, and problems such as interfacial reactions still exist. Summary of the Invention

[0005] In response to one or more of the above-mentioned defects or improvement needs in the prior art, the present invention provides a method for preparing a cross-linked gel polymer electrolyte, an electrolyte, and its application. The cross-linked gel polymer electrolyte is prepared by simultaneously catalyzing cationic polymerization and free radical polymerization by lithium salts, which reduces the introduction of non-electrolyte components, reduces the electrolyte cost, and simplifies the preparation method of lithium-ion batteries. In addition, the addition of polybrominated sites can stabilize the electrode-electrolyte interface, form a strong artificial solid electrolyte interface layer, and improve the cycle stability of the battery.

[0006] According to a first aspect of the present invention, a method for preparing a cross-linked gel polymer electrolyte is provided, wherein the cross-linked gel polymer electrolyte is prepared by lithium salt-catalyzed cationic polymerization and free radical polymerization, and the preparation method comprises the following steps:

[0007] S1: Synthesis of vinyl ether with bromine initiation sites via esterification reaction;

[0008] S2: mixing the lithium salt, the vinyl ether having a bromine initiation site obtained in S1, and at least one of polyethylene glycol acrylate or polyethylene glycol methacrylate to form a mixed solution, and then mixing it with a deep eutectic solvent to obtain a precursor solution;

[0009] S3: Under an inert atmosphere, the precursor solution obtained in S2 is infiltrated onto a separator, and assembled into a battery with a positive electrode material and a negative electrode material, and heated to induce free radical polymerization to obtain a cross-linked gel polymer electrolyte.

[0010] As a further improvement of the present invention, the vinyl ether having a bromine initiation site is obtained by reacting a hydroxyl-containing vinyl ether with a bromine-containing reagent.

[0011] More preferably, the hydroxyl-containing vinyl ether has a structure as shown in formula (1):

[0012]

[0013] In formula (1), n ​​is an integer of 1 to 10.

[0014] Further preferably, the bromine-containing reagent is selected from:

[0015]

[0016] In formula (II), formula (III) and formula (IV), X is Br, Cl or OH.

[0017] As a further improvement of the present invention, in step S2, the lithium salt is at least one of lithium perchlorate, lithium iodide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalatoborate;

[0018] The mass ratio of the vinyl ether having a bromine initiation site to the polyethylene glycol acrylate and / or polyethylene glycol methacrylate is 1:1 to 1:1000; the mass ratio of the polyethylene glycol acrylate and / or polyethylene glycol methacrylate to the lithium salt is 5:1 to 20:1.

[0019] As a further improvement of the present invention, in step S2, the deep eutectic solvent is in liquid form and is obtained by mixing a lithium salt and a Lewis base in a certain proportion;

[0020] The lithium salt is at least one of lithium hexafluorophosphate, lithium difluorooxalatoborate, and lithium tetrafluoroborate;

[0021] The Lewis base is at least one of sulfolane, N-methylacetamide, N-methyltrifluoroacetamide, succinonitrile, 18-crown-6 ether, and 15-crown-5 ether;

[0022] The molar ratio of the lithium salt to the Lewis base is 1:3 to 1:80.

[0023] As a further improvement of the present invention, in step S2, the mass ratio of the mixed solution to the deep eutectic solvent is 1:0.2 to 1:5.

[0024] As a further improvement of the present invention, the relative molecular weight of the polyethylene glycol acrylate or polyethylene glycol methacrylate is 300 to 4000.

[0025] Further preferably, polyethylene glycol methacrylate has a structure as shown in formula (V):

[0026]

[0027] Here, m is an integer from 4 to 89.

[0028] Further preferably, the polyethylene glycol acrylate has a structure as shown in formula (VI):

[0029]

[0030] Here, m is an integer from 4 to 89.

[0031] As a further improvement of the present invention, in step S3, the separator is a porous cellulose separator or a polyolefin separator with a thickness of 20 microns to 300 microns.

[0032] As a further improvement of the present invention, in step S3, when heating to initiate free radical polymerization, the heating temperature is 70° C. to 90° C., and the polymerization reaction time is 24 hours to 72 hours.

[0033] According to a second aspect of the present invention, a cross-linked gel polymer electrolyte is provided, which is prepared according to the preparation method of the cross-linked gel polymer electrolyte.

[0034] According to a third aspect of the present invention, there is provided an application of a cross-linked gel polymer electrolyte in a lithium ion battery, using the cross-linked gel polymer electrolyte, and the cross-linked gel polymer electrolyte is obtained by the preparation method.

[0035] The present invention first chemically modifies hydroxyl-containing vinyl ether by an acyl bromide reagent to obtain vinyl ether with bromine initiation sites; secondly, a deep eutectic solvent is formed by mixing a lithium salt and a Lewis base, and the mixture is mixed with a bromine-containing initiation site vinyl ether and a polyethylene glycol (meth) acrylate mixture in a certain proportion, slowly added to a porous diaphragm, assembled into a battery with the negative electrode and positive electrode materials of a lithium battery, and thermally initiated in situ polymerization is performed to prepare a cross-linked gel polymer electrolyte. The lithium salt can simultaneously catalyze the cationic polymerization of the vinyl ether and the free radical polymerization of the polyethylene glycol (meth) acrylate initiated by the bromine-containing initiation sites; and the addition of polyethylene glycol (meth) acrylate can slow down the reaction rate of the cationic polymerization to obtain a more uniform cross-linked gel polymer electrolyte membrane. When the polymer electrolyte is applied to a lithium battery, the introduction of the deep eutectic solvent can improve the electrochemical performance of the battery; and the addition of multiple bromine sites can stabilize the electrode-electrolyte interface, form a solid artificial solid electrolyte interface layer, and improve the cycle stability of the battery.

[0036] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0037] (1) In the preparation method of the cross-linked gel polymer electrolyte of the present invention, lithium salt can simultaneously catalyze cationic polymerization and free radical polymerization to prepare the cross-linked gel polymer electrolyte, thereby reducing the introduction of non-electrolyte components, lowering the electrolyte cost and simplifying the preparation method of the lithium-ion battery.

[0038] (2) The preparation method of the cross-linked gel polymer electrolyte of the present invention is to prepare the cross-linked gel polymer electrolyte by in-situ catalytic cationic polymerization and free radical polymerization of lithium salt, thereby increasing the contact between the electrolyte and the electrode, reducing the interfacial charge transfer impedance and interfacial mass transfer impedance, and improving the rate performance of the battery.

[0039] (3) In the preparation method of the cross-linked gel polymer electrolyte of the present invention, lithium salt first catalyzes the cationic polymerization of vinyl ether to obtain polyvinyl ether containing bromine initiation sites, and further lithium salt catalyzes free radical polymerization to obtain a gel polymer electrolyte containing a cross-linked network; the step-by-step polymerization method adjusts the structure of the polymer network, reduces the crystallization of polyethylene glycol, and improves the conductivity of the electrolyte.

[0040] (4) The preparation method of the cross-linked gel polymer electrolyte of the present invention introduces a large amount of bromine element to form a stable electrode-electrolyte interface layer at the lithium negative electrode interface, which can stabilize the negative electrode and reduce the generation and growth of lithium dendrites.

[0041] (5) The preparation method of the cross-linked gel polymer electrolyte of the present invention can effectively fix the deep eutectic solvent, reduce the contact between the lithium salt and the incompletely coordinated Lewis base and the electrode, reduce the interfacial side reactions, and improve the cycle stability of the battery.

[0042] (6) The preparation method of the cross-linked gel polymer electrolyte of the present invention, the deep eutectic solvent contained in the prepared cross-linked gel polymer electrolyte improves the conductivity of the electrolyte; at the same time, when the electrolyte material prepared by this method is applied to a battery, the deep eutectic solvent with the advantages of low vapor pressure and non-flammability can improve the safety of the battery; and the deep eutectic solvent acts as a catalyst and solvent, thereby reducing the use of organic solvents in the electrolyte preparation process and reducing pollution to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Flow chart of the preparation method of the cross-linked gel polymer electrolyte in an embodiment of the present invention;

[0044] Figure 2 is a curve showing the change of ionic conductivity with temperature of the cross-linked gel polymer electrolyte membrane prepared in Example 1 of the present invention;

[0045] Figure 3 This is a cycle performance diagram of the lithium battery prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0046] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0047] The present invention provides a method for preparing a cross-linked gel polymer electrolyte by lithium salt-catalyzed cationic polymerization and free radical polymerization, comprising the following steps:

[0048] (1) Synthesis of vinyl ethers with bromine initiation sites by esterification;

[0049] (2) mixing a lithium salt, a vinyl ether having a bromine initiation site, and polyethylene glycol (meth)acrylate to form a mixed solution, and then mixing it with a deep eutectic solvent to obtain a precursor solution;

[0050] (3) Under an inert atmosphere, the precursor solution is soaked on the separator, assembled into a battery with the positive electrode material and the negative electrode material, and heated to induce free radical polymerization to obtain a cross-linked gel polymer electrolyte.

[0051] In some embodiments, the vinyl ether in step (1) is obtained by reacting a hydroxyl-containing vinyl ether with a bromine-containing reagent;

[0052] Preferably, the hydroxyl-containing vinyl ether has a structure as shown in formula (1):

[0053]

[0054] In formula (1), n ​​is an integer from 1 to 10;

[0055] Preferably, the structural formula of the bromine-containing reagent is selected from:

[0056]

[0057] In formula (II), formula (III) and formula (IV), X is Br, Cl or OH.

[0058] In some specific embodiments, a hydroxyl-containing vinyl ether undergoes an esterification reaction with an acyl bromide or acyl chloride in Formula (II), Formula (III), or Formula (IV) in the presence of an acid binding agent to obtain a vinyl ether containing a bromine initiation site. The acid binding agent is preferably one or more of triethylamine, diethylamine, trimethylamine, pyridine, and bipyridine. The reaction conditions are preferably: adding the acyl chloride or acyl bromide to a solution containing the vinyl ether and the acid binding agent in an ice bath, reacting for 0.5 to 1.5 hours, then heating to 20 to 30° C. and reacting for 5 to 20 hours.

[0059] Taking diethylene glycol monovinyl ether and bromoisobutyryl bromide as an example, the esterification reaction formula is:

[0060]

[0061] In other specific embodiments, the hydroxyl-containing vinyl ether can also undergo an esterification reaction with the carboxylic acid of Formula (II), Formula (III), or Formula (IV) in the presence of a catalyst and a dehydrating agent to obtain a vinyl ether containing a bromine-initiating site. The catalyst is preferably N,N-dimethylaminopyridine; the dehydrating agent is preferably one or more of N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride. The reaction conditions are preferably: add the hydroxyl-containing vinyl ether to a solution containing the bromine-containing carboxylic acid, catalyst, and dehydrating agent in an ice bath, react for 0.5 to 1.5 hours, then raise the temperature to 20 to 30°C and react for 15 to 30 hours.

[0062] Taking diethylene glycol monovinyl ether and bromoisobutyric acid as an example, the esterification reaction formula is:

[0063]

[0064] Furthermore, in step (2), it should be noted that polyethylene glycol (meth)acrylate means at least one of polyethylene glycol acrylate or polyethylene glycol methacrylate. In some embodiments, the relative molecular weight of polyethylene glycol acrylate or polyethylene glycol methacrylate is 300 to 4000.

[0065] Preferably, polyethylene glycol methacrylate has a structure as shown in formula (V):

[0066]

[0067] Wherein, m is an integer from 4 to 89;

[0068] Preferably, polyethylene glycol acrylate has a structure as shown in formula (VI):

[0069]

[0070] Here, m is an integer from 4 to 89.

[0071] Preferably, in step (2), the lithium salt is at least one of lithium perchlorate, lithium iodide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalatoborate;

[0072] Further preferably, the mass ratio of the vinyl ether containing bromine initiation sites to polyethylene glycol (meth)acrylate is 1:1 to 1:1000; and the mass ratio of the polyethylene glycol (meth)acrylate to the lithium salt is 5:1 to 20:1.

[0073] In some embodiments, the deep eutectic solvent in step (2) is liquid and is obtained by mixing a lithium salt and a Lewis base in a certain proportion; wherein the lithium salt is preferably at least one of lithium hexafluorophosphate, lithium difluorooxalatoborate, and lithium tetrafluoroborate; and the Lewis base is preferably at least one of cyclopentane sulfone, N-methylacetamide, N-methyltrifluoroacetamide, succinonitrile, 18-crown-6 ether, and 15-crown-5 ether.

[0074] More preferably, the molar ratio of the lithium salt to the Lewis base is 1:3 to 1:80.

[0075] In some embodiments, in step (2), the mass ratio of the mixed solution to the deep eutectic solvent is 1:0.2 to 1:5.

[0076] In some embodiments, in step (3), the membrane is a porous cellulose membrane or a polyolefin membrane with a thickness of 20 μm to 300 μm.

[0077] In some embodiments, in step (3), when heating to initiate the polymerization reaction, the heating temperature is 70° C. to 90° C.; and the polymerization reaction time is 24 hours to 72 hours.

[0078] The present invention also provides a cross-linked gel polymer electrolyte prepared by the preparation method.

[0079] The present invention also provides application of the cross-linked gel polymer electrolyte in lithium ion batteries.

[0080] The present invention prepares a cross-linked gel polymer electrolyte by simultaneously catalyzing the cationic polymerization of vinyl ether and the polymerization of acrylate using lithium salts. The bromine-containing initiator can be catalyzed by the lithium salt to initiate free radical polymerization. The introduction of a large amount of bromine stabilizes the negative electrode of the lithium battery, inhibiting the formation and growth of lithium dendrites and extending the battery life. Furthermore, the introduction of a deep eutectic solvent effectively increases the ionic conductivity of the cross-linked gel polymer electrolyte, effectively enhancing the electrochemical performance of the lithium battery.

[0081] The following are specific embodiments:

[0082] Example 1

[0083] This embodiment provides a method for preparing a cross-linked gel polymer electrolyte membrane, and the preparation method is as follows:

[0084] 5.0 g of diethylene glycol monovinyl ether (n=2) and 4.4 g of triethylamine were added to a flask containing 20 mL of dichloromethane. Bromoisobutyryl bromide (9.2 g) dissolved in 10 mL of dichloromethane was added dropwise to the diethylene glycol monovinyl ether mixture under an ice bath. The mixture was reacted at 0°C for 1 h and then gradually heated to room temperature. After reacting overnight, the insoluble salt was filtered out, 50 mL of dichloromethane was added, and the organic phase was washed with saturated NaHCO3 and distilled water, dried over anhydrous sodium sulfate, and purified by column chromatography to obtain bromine-containing diethylene glycol monovinyl ether.

[0085] 0.4 g of lithium hexafluorophosphate and 1.5 g of sulfolane were weighed and stirred in a molar ratio of 1:5 to form a deep eutectic solvent, which was recorded as A1. 0.2 g of the above-mentioned bromine-containing vinyl ether, 0.2 g of lithium perchlorate and 2.0 g of polyethylene glycol methacrylate (M n =475) and stirred to form a mixed solution, designated A2. 1.0g of A1 and 1.0g of A2 were weighed and stirred to form a precursor solution. A cellulose separator was soaked in the precursor solution and assembled with the positive and negative electrode materials to form a battery. The battery was then oven-polymerized at 80°C for 48 hours to obtain a cross-linked polymer electrolyte.

[0086] like Figure 1 As shown, it first chemically modifies the hydroxyl-containing vinyl ether with an acyl bromide reagent to obtain a vinyl ether with a bromine-containing initiation site; secondly, a deep eutectic solvent is formed by mixing a lithium salt and a Lewis base, which is mixed with a mixed solution of bromine-containing vinyl ether and polyethylene glycol methacrylate in a certain proportion, and then dropped onto a commercial separator. The battery is assembled with the negative and positive electrode materials of a lithium battery, and a cross-linked gel polymer electrolyte is prepared by thermally inducing in situ polymerization.

[0087] Figure 2 The ionic conductivity of the cross-linked gel polymer electrolyte membrane prepared in Example 1 of the present invention changes with temperature. The results show that the electrolyte has a conductivity of 4.7×10-5 S cm -1 ionic conductivity.

[0088] Figure 3 This is a cycle performance diagram of the lithium battery prepared in Example 1 of the present invention. The results show that it can stably cycle 700 times at a 1C rate.

[0089] Example 2

[0090] This embodiment provides a method for preparing a cross-linked gel polymer electrolyte membrane, and the preparation method is as follows:

[0091] 4.1 g of ethylene glycol monovinyl ether (n=1) and 4.3 g of trimethylamine were added to a flask containing 20 mL of tetrahydrofuran. 2-bromopropionyl chloride (7.5 g) dissolved in 10 mL of tetrahydrofuran was added dropwise to the ethylene glycol monovinyl ether mixture under an ice bath. The mixture was reacted at 0°C for 0.5 h, then gradually heated to 20°C and reacted for 20 h. The insoluble salts were removed by filtration, and the solvent was removed by concentration. 50 mL of ethyl acetate was added, and the organic phase was washed with saturated NaHCO3 and distilled water, dried over anhydrous magnesium sulfate, and purified by column chromatography to obtain bromoethylene glycol monovinyl ether.

[0092] 0.6 g of lithium difluorooxalatoborate and 0.92 g of N-methylacetamide were weighed and stirred in a molar ratio of 1:3 to form a deep eutectic solvent, which was recorded as A1. 5 mg of the above-mentioned bromovinyl ether, 1.0 g of lithium perchlorate and 5 g of polyethylene glycol methacrylate (M n =4000) and stirred to form a mixture, designated A2. 1.0 g of A1 and 0.2 g of A2 were weighed and stirred to form a precursor solution. A cellulose membrane was immersed in the precursor solution and oven-polymerized at 70°C for 72 h to obtain a cross-linked polymer electrolyte. The ionic conductivity of the electrolyte membrane at room temperature was 4.2 × 10 -5 S cm -1 .

[0093] Example 3

[0094] This embodiment provides a method for preparing a cross-linked gel polymer electrolyte membrane, and the preparation method is as follows:

[0095] 10.0 g of polyethylene glycol monovinyl ether (n=10), 4.7 g of N,N'-dicyclohexylcarbodiimide, and 0.5 g of N,N-dimethylaminopyridine were added to a flask containing 20 mL of tetrahydrofuran. 2-bromophenylacetic acid (11.3 g) dissolved in 10 mL of tetrahydrofuran was added dropwise to the polyethylene glycol monovinyl ether mixture under an ice bath. The mixture was reacted at 0°C for 0.5 h, then gradually heated to 20°C and reacted for 30 h. The insoluble matter was removed by filtration, and the solvent was concentrated to remove it. 50 mL of ethyl acetate was added, and the organic phase was washed with saturated NaHCO3 and distilled water, dried over anhydrous magnesium sulfate, and purified by column chromatography to obtain bromine-containing polyethylene glycol monovinyl ether.

[0096] 0.02 g of lithium hexafluorophosphate and 1.3 g of N-methyltrifluoroacetamide were weighed and stirred at a molar ratio of 1:80 to form a deep eutectic solvent, which was recorded as A1. 2.0 g of the above-mentioned bromine-containing vinyl ether, 0.1 g of lithium perchlorate and 2.0 g of polyethylene glycol methacrylate (M n =300) and stirred to form a mixture, designated A2. 0.2g of A1 and 1.0g of A2 were weighed and stirred to form a precursor solution. The cellulose membrane was immersed in the precursor solution and oven-polymerized at 90°C for 24h to obtain a cross-linked polymer electrolyte. The ionic conductivity of the electrolyte membrane at room temperature was 1.5×10 -5 S cm -1 .

[0097] Example 4

[0098] This embodiment provides a method for preparing a cross-linked gel polymer electrolyte membrane, and the preparation method is as follows:

[0099] 5.0 g of diethylene glycol monovinyl ether (n=2) and 3.6 g of diethylamine were added to a flask containing 20 mL of dichloromethane. Bromoisobutyryl bromide (9.2 g) dissolved in 10 mL of dichloromethane was added dropwise to the diethylene glycol monovinyl ether mixture under an ice bath. The mixture was reacted at 0°C for 1.5 h, then gradually heated to 30°C and reacted for 5 h. The insoluble salt was removed by filtration, and the organic phase was washed with saturated NaHCO3 and distilled water, dried over anhydrous sodium sulfate, and purified by column chromatography to obtain bromine-containing diethylene glycol monovinyl ether.

[0100] 0.4 g of lithium hexafluorophosphate and 4.2 g of succinonitrile were weighed and stirred in a molar ratio of 1:20 to form a deep eutectic solvent, which was recorded as A1. 0.2 g of the above-mentioned bromine-containing vinyl ether, 0.2 g of lithium perchlorate and 2.0 g of polyethylene glycol methacrylate (M n=475) and stirred to form a mixed solution, designated A2. 1.0g of A1 and 1.0g of A2 were weighed and stirred to form a precursor solution. A cellulose separator was immersed in the precursor solution and assembled with the positive and negative electrode materials to form a battery. The battery was then oven-polymerized at 80°C for 54 hours to obtain a cross-linked polymer electrolyte. The ionic conductivity of the electrolyte membrane at room temperature was 3.1×10 -5 S cm -1 .

[0101] Example 5

[0102] This embodiment provides a method for preparing a cross-linked gel polymer electrolyte membrane, and the preparation method is as follows:

[0103] 5.0 g of diethylene glycol monovinyl ether (n=2) and 4.1 g of pyridine were added to a flask containing 20 mL of dichloromethane. Bromoisobutyryl bromide (9.2 g) dissolved in 10 mL of dichloromethane was added dropwise to the diethylene glycol monovinyl ether mixture under an ice bath. The mixture was reacted at 0°C for 1 h, then gradually heated to 25°C and reacted for 15 h. The insoluble salt was removed by filtration, and the organic phase was washed with saturated NaHCO3 and distilled water, dried over anhydrous sodium sulfate, and purified by column chromatography to obtain bromine-containing diethylene glycol monovinyl ether.

[0104] 0.05 g of lithium tetrafluoroborate and 1.4 g of 18-crown-6 ether were weighed and stirred in a molar ratio of 1:10 to form a deep eutectic solvent, which was recorded as A1. 0.02 g of the above-mentioned bromine-containing vinyl ether, 0.2 g of lithium perchlorate and 2.0 g of polyethylene glycol acrylate (M n =480) and stirred to form a mixed solution, designated A2. 1.0g of A1 and 1.0g of A2 were weighed and stirred to form a precursor solution. A cellulose separator was immersed in the precursor solution and assembled with the positive and negative electrode materials to form a battery. The battery was then oven-polymerized at 80°C for 54 hours to obtain a cross-linked polymer electrolyte. The ionic conductivity of the electrolyte membrane at room temperature was 2.1×10 -5 S cm -1 .

[0105] Example 6

[0106] This embodiment provides a method for preparing a cross-linked gel polymer electrolyte membrane, and the preparation method is as follows:

[0107] 5.0 g of diethylene glycol monovinyl ether (n=2) and 4.1 g of bipyridine were added to a flask containing 20 mL of dichloromethane. Bromoisobutyryl bromide (9.2 g) dissolved in 10 mL of dichloromethane was added dropwise to the diethylene glycol monovinyl ether mixture under an ice bath. The mixture was reacted at 0°C for 1 h, then gradually heated to 25°C and reacted for 18 h. The insoluble salt was removed by filtration, 40 mL of dichloromethane was added, and the organic phase was washed with saturated NaHCO3 and distilled water, dried over anhydrous sodium sulfate, and purified by column chromatography to obtain bromine-containing diethylene glycol monovinyl ether.

[0108] 0.1 g of lithium tetrafluoroborate and 3.5 g of 15-crown-5 ether were weighed and stirred in a molar ratio of 1:15 to form a deep eutectic solvent, which was recorded as S1. 0.2 g of the above-mentioned bromine-containing vinyl ether, 0.2 g of lithium perchlorate and 2.0 g of polyethylene glycol acrylate (M n =480) and stirred to form a mixed solution, designated S2. 1.0g of S1 and 1.0g of S2 were weighed and stirred to form a precursor solution. A commercial polyethylene separator was immersed in the precursor solution and assembled with the positive and negative electrode materials to form a battery. The battery was then oven-polymerized at 80°C for 54 hours to obtain a cross-linked polymer electrolyte. The ionic conductivity of the electrolyte membrane at room temperature was 1.5×10 -5 S cm -1 .

[0109] Example 7

[0110] This embodiment provides a method for preparing a cross-linked gel polymer electrolyte membrane, and the preparation method is as follows:

[0111] 5.0 g of diethylene glycol monovinyl ether (n=2), 2.9 g of N,N'-diisopropylcarbodiimide, and 0.5 g of N,N-dimethylaminopyridine were added to a flask containing 20 mL of dichloromethane. 2-Bromopropionic acid (6.4 g) dissolved in 10 mL of dichloromethane was added dropwise to the polyethylene glycol monovinyl ether mixture under an ice bath. The mixture was reacted at 0°C for 1.5 h, then gradually heated to 30°C. After reacting for 15 h, the insoluble matter was removed by filtration, the solvent was removed by concentration, 50 mL of ethyl acetate was added, and the organic phase was washed with saturated NaHCO3 and distilled water, dried over anhydrous magnesium sulfate, and purified by column chromatography to obtain bromine-containing diethylene glycol monovinyl ether.

[0112] 0.2g of lithium hexafluorophosphate and 6.3g of sulfolane were weighed and stirred in a molar ratio of 1:40 to form a deep eutectic solvent, which was recorded as A1. 0.2g of the above-mentioned bromine-containing vinyl ether, 0.2g of lithium perchlorate and 2.0g of polyethylene glycol methacrylate (M n=1000) and stirred to form a mixed solution, designated A2. 1.2g of A1 and 0.8g of A2 were weighed and stirred to form a precursor solution. A cellulose separator was immersed in the precursor solution and assembled with the positive and negative electrode materials to form a battery. The battery was then oven-polymerized at 85°C for 54 hours to obtain a cross-linked polymer electrolyte. The ionic conductivity of the electrolyte membrane at room temperature was 2.3×10 -5 S cm -1 .

[0113] Example 8

[0114] This embodiment provides a method for preparing a cross-linked gel polymer electrolyte membrane, and the preparation method is as follows:

[0115] 5.0 g of diethylene glycol monovinyl ether (n=2), 2.9 g of N,N'-diisopropylcarbodiimide, and 0.5 g of N,N-dimethylaminopyridine were added to a flask containing 20 mL of dichloromethane. 2-Bromoisobutyric acid (7.0 g) dissolved in 10 mL of dichloromethane was added dropwise to the polyethylene glycol monovinyl ether mixture under an ice bath. The mixture was reacted at 0°C for 1 h, then gradually heated to 25°C. After reacting for 20 h, the insoluble matter was removed by filtration, the solvent was removed by concentration, 50 mL of ethyl acetate was added, and the organic phase was washed with saturated NaHCO3 and distilled water, dried over anhydrous magnesium sulfate, and purified by column chromatography to obtain bromine-containing diethylene glycol monovinyl ether.

[0116] 0.4 g of lithium hexafluorophosphate and 1.5 g of sulfolane were weighed and stirred in a molar ratio of 1:5 to form a deep eutectic solvent, which was recorded as A1. 0.2 g of the above-mentioned bromine-containing vinyl ether, 0.4 g of lithium perchlorate and 2.0 g of polyethylene glycol methacrylate (M n =2000) and stirred to form a mixed solution, designated A2. 1.5g of A1 and 0.5g of A2 were weighed and stirred to form a precursor solution. A cellulose separator was soaked in the precursor solution and assembled with the positive and negative electrode materials to form a battery. The battery was then oven-polymerized at 75°C for 72 hours to produce a cross-linked polymer electrolyte. The ionic conductivity of the electrolyte membrane at room temperature was 3.3×10 -5 S cm -1 .

[0117] The cross-linked gel polymer electrolyte membrane prepared by cationic polymerization and free radical polymerization catalyzed by lithium salts in the embodiment has higher ionic conductivity and better interface stability than traditional polymer electrolytes, and realizes long cycle of lithium batteries at 1C rate.

[0118] Since the polymer electrolyte in the present invention can be applied to lithium-ion batteries, the thickness of the cross-linked gel polymer electrolyte membrane prepared by lithium salt-catalyzed cationic polymerization and free radical polymerization can be flexibly adjusted according to actual needs. Of course, polymer electrolytes in non-thin film shapes can also be prepared according to actual application requirements.

[0119] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a cross-linked gel polymer electrolyte, characterized in that: The cross-linked gel polymer electrolyte is prepared by lithium salt-catalyzed cationic polymerization and free radical polymerization, and the preparation method comprises the following steps: S1: Synthesis of vinyl ether with bromine initiation sites via esterification reaction; S2: mixing the lithium salt, the vinyl ether having a bromine initiation site obtained in S1, and at least one of polyethylene glycol acrylate or polyethylene glycol methacrylate to form a mixed solution, and then mixing it with a deep eutectic solvent to obtain a precursor solution; S3: Under an inert atmosphere, the precursor solution obtained in S2 is infiltrated onto a separator, and assembled into a battery with a positive electrode material and a negative electrode material, and heated to induce free radical polymerization to obtain the cross-linked gel polymer electrolyte; In step S2, the deep eutectic solvent is in liquid form and is obtained by mixing a lithium salt and a Lewis base; the lithium salt is at least one of lithium hexafluorophosphate, lithium difluorooxalatoborate, and lithium tetrafluoroborate; and the Lewis base is at least one of cyclopentane sulfone, N-methylacetamide, N-methyltrifluoroacetamide, succinonitrile, 18-crown-6 ether, and 15-crown-5 ether.

2. The method for preparing a cross-linked gel polymer electrolyte according to claim 1, wherein: In step S1, the vinyl ether having a bromine initiation site is obtained by reacting a hydroxyl-containing vinyl ether with a bromine-containing reagent.

3. The method for preparing a cross-linked gel polymer electrolyte according to claim 1, wherein: In step S2, the lithium salt in the mixed solution is at least one of lithium perchlorate, lithium iodide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalatoborate; The mass ratio of the vinyl ether having a bromine initiation site to the polyethylene glycol acrylate and / or polyethylene glycol methacrylate is 1:1 to 1:1000; the mass ratio of the polyethylene glycol acrylate and / or polyethylene glycol methacrylate to the lithium salt in the mixed solution is 5:1 to 20:

1.

4. The method for preparing a cross-linked gel polymer electrolyte according to claim 1, wherein: In step S2, the molar ratio of the lithium salt to the Lewis base in the deep eutectic solvent is 1:3 to 1:

80.

5. The method for preparing a cross-linked gel polymer electrolyte according to claim 1, wherein: In step S2, the mass ratio of the mixed solution to the deep eutectic solvent is 1:0.2 to 1:

5.

6. The method for preparing a cross-linked gel polymer electrolyte according to claim 1, wherein: In step S2, the relative molecular weight of the polyethylene glycol acrylate or polyethylene glycol methacrylate is 300-4000.

7. The method for preparing a cross-linked gel polymer electrolyte according to claim 1, wherein: In step S3, the separator is a porous cellulose separator or a polyolefin separator with a thickness of 20 to 300 microns.

8. The method for preparing a cross-linked gel polymer electrolyte according to claim 1, wherein: The polymerization temperature is 70° C. to 90° C., and the polymerization reaction time is 24 hours to 72 hours.

9. A cross-linked gel polymer electrolyte prepared according to the method for preparing a cross-linked gel polymer electrolyte according to any one of claims 1 to 8.

10. Use of a cross-linked gel polymer electrolyte in a lithium ion battery, comprising the cross-linked gel polymer electrolyte according to claim 9, wherein the cross-linked gel polymer electrolyte is obtained by the preparation method according to any one of claims 1 to 8.

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