A crosslinked cellulose-based gel polymer electrolyte and its preparation method

Abstract

The present invention discloses a cross-linked cellulose-based gel polymer electrolyte and a preparation method thereof. The method comprises the following steps: a preparation method of water-soluble allyl cellulose with different degrees of substitution and a preparation method of a cross-linked cellulose-based gel polymer electrolyte. A polymer film is obtained by cross-linking allyl cellulose polyethylene glycol dimethacrylate / polyethylene glycol diacrylate and 1,4-butanediol bis(thioglycolate) with double bonds under ultraviolet irradiation through a thiol-ene click reaction; the polymer film is immersed in a carbonate electrolyte to obtain a cross-linked cellulose-based gel polymer electrolyte. The ionic conductivity and interfacial impedance of the gel polymer electrolyte can be adjusted by changing the degree of substitution of allyl cellulose and the content of polyethylene glycol dimethacrylate / polyethylene glycol diacrylate. The cross-linked cellulose-based gel polymer electrolyte has high ionic conductivity, high interfacial compatibility, high thermal stability and cycling performance.

Description

Technical Field

[0001] The invention belongs to the field of modified cellulose composite membranes and electrolytes for lithium ion batteries, and particularly relates to a cross-linked cellulose-based gel polymer electrolyte and a preparation method thereof. Background Art

[0002] Since the 1990s, the widespread use of lithium-ion batteries has driven in-depth research on separators, gel electrolytes, and solid electrolytes. Commercial separators primarily use polyolefin separators and liquid electrolytes. These polyolefin separators are prone to liquid electrolyte leakage and have poor thermal stability, which can further lead to safety issues. Researchers have turned their attention to new electrolytes such as gel electrolytes and solid electrolytes. Gel polymer electrolytes combine some of the advantages of solid electrolytes and liquid electrolytes, possessing higher ionic conductivity than solid electrolytes at room temperature and better ability to prevent electrolyte leakage than liquid electrolytes.

[0003] However, the substrates widely used in gel polymer electrolytes are mainly polyethylene oxide (PEO) and its derivatives. The rich ether bonds contained in PEO can complex with lithium ions and can transport lithium ions through the movement of chain segments. However, these polymers mainly come from the petroleum industry, and the synthesis process usually involves many organic solvents. With people's increasing attention to environmental pollution and resource shortages, finding environmentally friendly and renewable resources has become an important way to overcome the non-biodegradability of traditional polymers. In nature, cellulose, which is extremely abundant in nature, not only has ether bonds similar to those in PEO, but also has the advantages of good degradability and low cost. At the same time, cellulose contains a large number of hydroxyl polar groups, which can promote the dissociation of lithium salts, adsorb solvent molecules, and promote lithium ion transport.

[0004] However, in practical applications, cellulose is still difficult to gel with commercial ester electrolytes, which limits the further application of natural materials such as cellulose in lithium-ion batteries. Zhi Du et al. used dimethyl sulfoxide (DMSO) containing lithium salts as the electrolyte to gel pure cellulose cross-linked membranes. This is still far from the commonly used commercial carbonate electrolytes, and its high interfacial impedance with lithium metal electrodes limits its further application (A mechanically robust, biodegradable and high-performance cellulose gel membrane as gel polymer electrode of lithium-ion battery, Electrochimica Acta, 299 (2019), 19–26.). However, through certain chemical modifications and blending, it is possible to effectively increase the affinity with commercial electrolytes. Summary of the Invention

[0005] To overcome the shortcomings of the existing technology, the present invention provides a cross-linked cellulose-based gel polymer electrolyte with high ionic conductivity and high interfacial compatibility, and a method for its preparation. By chemically modifying commercial cellulose powder to a certain extent and introducing high-dielectric-constant oligomers, the flexible segments of the oligomers serve as cross-linkers. The resulting polymer electrolyte reacts rapidly under ultraviolet light, yielding a gel polymer electrolyte for lithium-ion batteries with high ionic conductivity and excellent interfacial compatibility.

[0006] The present invention aims to address the incompatibility of natural macromolecules with commercial ester electrolytes in lithium-ion batteries, thereby improving ionic conductivity and interfacial compatibility, and thus enhancing the electrochemical performance of lithium-ion batteries. Furthermore, the present invention discloses a method for preparing a cellulose-based gel polymer electrolyte. This method utilizes ultraviolet light curing, is simple, rapid, and easy to operate, and has great potential for application in lithium-ion batteries.

[0007] The purpose of the present invention is achieved by at least one of the following technical solutions:

[0008] A method for preparing a cross-linked cellulose-based gel polymer electrolyte comprises the following steps:

[0009] S1. Preparation of water-soluble allyl cellulose:

[0010] (1) preparing an alkali / urea solution by mixing sodium hydroxide, urea, and deionized water in a mass ratio of (4-8):(10-12):(75-85), adding cellulose powder at low temperature, and stirring at a speed of 1500-2000 r / min for 2-10 minutes to obtain a cellulose solution with a mass percentage of 3%-6%;

[0011] (2) adding allyl glycidyl ether dropwise to a cellulose solution at 25-35° C. under a nitrogen atmosphere, and reacting for 20-30 hours under a light-shielding condition with mechanical stirring or magnetic stirring; placing the reaction product in acetone 5-15 times the mass of the reaction solution, and then placing it in a dialysis bag for 3-7 days, and then freeze-drying it at -45--60° C. for 24-72 hours to obtain a white cellulose solid, i.e., allyl cellulose;

[0012] S2. Preparation of cross-linked cellulose-based gel polymer electrolyte:

[0013] (3) dissolving the allyl cellulose in a solvent to prepare a solution with a concentration of 1 wt% to 4 wt%, adding polyethylene glycol dimethacrylate or polyethylene glycol diacrylate, and then adding 1,4-butanediol bis(thioglycolate) and an initiator, stirring evenly, and centrifuging in a centrifuge at a speed of 6000 to 10000 r / min to form a casting solution;

[0014] (4) The casting solution is cast in a plastic culture dish, irradiated with ultraviolet light to form a gel, dried, cut into small discs, vacuum dried to completely remove water, and then soaked in an electrolyte in a glove box for 1 to 24 hours to obtain a cross-linked cellulose-based gel polymer electrolyte.

[0015] Furthermore, in step S1 (1), the dissolution temperature of the cellulose powder is -12°C to -16°C.

[0016] Furthermore, in step S1 (2), the molar ratio of allyl glycidyl ether to cellulose anhydrous glucose units is (3-12):1; preferably, the molar ratio of allyl glycidyl ether to cellulose anhydrous glucose units is (9-12):1.

[0017] Furthermore, in step S2 (3), the solvent is one of deionized water, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide. Preferably, the solvent is deionized water or dimethyl sulfoxide.

[0018] Furthermore, in step S2 (3), the molar ratio of polyethylene glycol dimethacrylate or polyethylene glycol diacrylate to allyl cellulose anhydrous glucose units is 0.35 to 0.75.

[0019] Furthermore, in step S2 (3), the amount of 1,4-butanediol bis(thioglycolate) added is half the amount of the double bond substance provided by polyethylene glycol dimethacrylate and allyl cellulose, or half the amount of the double bond substance provided by polyethylene glycol diacrylate and allyl cellulose.

[0020] Furthermore, in step S2 (3), the initiator is one of benzoin dimethyl ether and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone.

[0021] Furthermore, in step S2 (3), the amount of the initiator added is 7% to 14% of the amount of the 1,4-butanediol bis(thioglycolate) substance.

[0022] Furthermore, in step S2 (4), the ultraviolet light irradiation wavelength is 365 nm, and the irradiation time is 2 to 15 minutes.

[0023] Furthermore, in step S2 (4), the electrolyte is a carbonate electrolyte, including one of 1 mol / L lithium hexafluorophosphate in ethylene carbonate / dimethyl carbonate (volume ratio 1:1) electrolyte, 1 mol / L lithium hexafluorophosphate in ethylene carbonate / diethyl carbonate (volume ratio 1:2) electrolyte, and 1 mol / L lithium bis(trifluoromethylsulfonyl)amide in ethylene carbonate / dimethyl carbonate (volume ratio 1:1) electrolyte. Preferably, the electrolyte is 1 mol / L lithium hexafluorophosphate in ethylene carbonate / dimethyl carbonate (volume ratio 1:1) electrolyte.

[0024] The present invention also provides a cross-linked cellulose-based gel polymer electrolyte obtained by the above preparation method.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] (1) The raw materials used in the present invention are widely available and have high natural abundance. They are also biodegradable, low in cost, and environmentally friendly.

[0027] (2) The preparation process of the present invention is mild. The modified allyl cellulose undergoes an efficient, precise, and rapid thiol-ene click reaction with an oligomer double bond crosslinker and a crosslinker with a thiol group. The thiol group reacts with the double bonds on the allyl cellulose and the double bonds on the polyethylene glycol dimethacrylate / polyethylene glycol diacrylate to form a three-dimensional network gel simply and quickly.

[0028] (3) The method provided by the present invention can regulate the interfacial compatibility and ionic conductivity of the gel polymer electrolyte by adjusting the content of polyethylene glycol dimethacrylate / polyethylene glycol diacrylate. At the same time, the introduced ester group ensures the compatibility of the electrolyte with commercial carbonate electrolytes, improves its swelling degree and thus improves the electrochemical performance of lithium-ion batteries.

[0029] (4) The cross-linked cellulose-based gel polymer electrolyte prepared by the present invention has high ionic conductivity, high interfacial compatibility, high thermal stability and cycling performance, and has good application prospects in the field of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a graph showing the relationship between the ionic conductivity of cellulose-based gel polymer electrolytes with different polyethylene glycol dimethacrylate contents and temperature.

[0031] Figure 2 Interfacial impedance spectra of cellulose-based gel polymer electrolytes with different polyethylene glycol dimethacrylate contents.

[0032] Figure 3Differential scanning calorimetry results of cellulose-based gel polymer electrolytes with different polyethylene glycol dimethacrylate contents and commercial polyolefin separator Celgard 2400.

[0033] Figure 4 This is a graph showing the discharge specific capacity of the cellulose-based gel polymer electrolyte prepared in Example 4 during the constant current cyclic charge-discharge test. DETAILED DESCRIPTION

[0034] The following examples further illustrate the specific implementation of the present invention, but the implementation and protection of the present invention are not limited thereto. It should be noted that if there are any processes not specifically described below, they can be implemented or understood by those skilled in the art with reference to the prior art. If the manufacturer of the reagents or instruments used is not indicated, they are deemed to be conventional products that can be purchased commercially.

[0035] Example 1

[0036] S1. Preparation of water-soluble allyl cellulose:

[0037] (1) An alkali / urea solution was prepared by mixing 20.37 g of sodium hydroxide, 34.92 g of urea, and 235.71 g of deionized water in a mass ratio of 7:12:81. 9 g of cellulose powder was added at -16°C and stirred at 1500 rpm for 2 min to obtain a 3% cellulose solution.

[0038] (2) In a nitrogen atmosphere at 25°C, allyl glycidyl ether is added dropwise to a cellulose solution, with the molar ratio of allyl glycidyl ether to the anhydrous glucose unit of cellulose being 3:1; the reaction is carried out under light-shielding conditions with mechanical or magnetic stirring for 20 hours, the reaction product is added to acetone with a mass 5 times that of the reaction solution and then placed in a dialysis bag for 3 days, followed by freeze-drying at -45°C for 48 hours to obtain a white cellulose solid, i.e., allyl cellulose;

[0039] S2. Preparation of cross-linked cellulose-based gel polymer electrolyte:

[0040] (3) 0.4 g of the above-mentioned allyl cellulose was dissolved in dimethyl sulfoxide to prepare a solution with a concentration of 1 wt%, and 0.5047 g of polyethylene glycol dimethacrylate (the molar ratio of polyethylene glycol dimethacrylate to allyl cellulose anhydrous glucose unit was 0.65) was added, followed by 0.3988 g of 1,4-butanediol bis(thioglycolate) and 0.02546 g of initiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone. After stirring evenly, the mixture was centrifuged at a speed of 10,000 r / min to form a casting solution;

[0041] (4) The casting solution was cast in a plastic culture dish and irradiated with 365 nm ultraviolet light for 15 min to form a gel. After drying, the discs were cut into small discs, vacuum dried to completely remove water, and then immersed in a 1 mol / L lithium hexafluorophosphate ethylene carbonate / dimethyl carbonate (volume ratio 1:1) electrolyte in a glove box for 10 h to obtain a cross-linked cellulose-based gel polymer electrolyte.

[0042] Example 2

[0043] S1. Preparation of water-soluble allyl cellulose:

[0044] (1) An alkali / urea solution was prepared by mixing 14.55 g of sodium hydroxide, 29.10 g of urea, and 247.35 g of deionized water in a mass ratio of 5:10:85. 9 g of cellulose powder was added at -16°C and stirred at 1500 rpm for 2 min to obtain a 3% cellulose solution.

[0045] (2) Under nitrogen atmosphere and at 25°C, allyl glycidyl ether was added dropwise to the cellulose solution, with the molar ratio of allyl glycidyl ether to the anhydroglucose unit of cellulose being 6:1; the reaction was carried out under light-shielding conditions with mechanical or magnetic stirring for 30 hours. The reaction product was added to acetone (5 times the mass of the reaction solution) and then placed in a dialysis bag for 3 days, followed by freeze-drying at -50°C for 48 hours to obtain a white cellulose solid, i.e., allyl cellulose;

[0046] S2. Preparation of cross-linked cellulose-based gel polymer electrolyte:

[0047] (3) 0.4 g of the above-mentioned allyl cellulose was dissolved in dimethyl sulfoxide to prepare a solution with a concentration of 1 wt%, and 0.5047 g of polyethylene glycol dimethacrylate (the molar ratio of polyethylene glycol dimethacrylate to allyl cellulose anhydrous glucose unit was 0.65) was added, followed by 0.3988 g of 1,4-butanediol bis(thioglycolate) and 0.02546 g of initiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone. After stirring evenly, the mixture was centrifuged at a speed of 10,000 r / min to form a casting solution;

[0048] (4) The casting solution was cast in a plastic culture dish and irradiated with 365 nm ultraviolet light for 15 min to form a gel. After drying, the discs were cut into small discs, vacuum dried to completely remove water, and then immersed in a 1 mol / L lithium hexafluorophosphate ethylene carbonate / dimethyl carbonate (volume ratio 1:1) electrolyte in a glove box for 10 h to obtain a cross-linked cellulose-based gel polymer electrolyte.

[0049] Example 3

[0050] S1. Preparation of water-soluble allyl cellulose:

[0051] (1) An alkali / urea solution was prepared by mixing 19.95 g of sodium hydroxide, 34.20 g of urea, and 230.85 g of deionized water in a mass ratio of 7:12:81. 15 g of cellulose powder was added at -12°C and stirred at 1900 rpm for 5 min to obtain a 5% cellulose solution.

[0052] (2) In a nitrogen atmosphere at 30°C, allyl glycidyl ether is added dropwise to a cellulose solution, with the molar ratio of allyl glycidyl ether to the anhydrous glucose unit of cellulose being 12:1; the reaction is carried out under light-shielding conditions with mechanical or magnetic stirring for 24 hours, the reaction product is added to acetone with a mass 10 times that of the reaction solution, placed in a dialysis bag, dialyzed for 7 days, and then freeze-dried at -55°C for 72 hours to obtain a white cellulose solid, i.e., allyl cellulose;

[0053] S2. Preparation of cross-linked cellulose-based gel polymer electrolyte:

[0054] (3) 0.2 g of the above-mentioned allyl cellulose was dissolved in dimethyl sulfoxide to prepare a solution with a concentration of 2 wt%, and 0.1315 g of polyethylene glycol dimethacrylate (the molar ratio of polyethylene glycol dimethacrylate to allyl cellulose anhydrous glucose unit was 0.35) was added, followed by 0.2002 g of 1,4-butanediol bis(thioglycolate) and 0.02864 g of initiator benzoin dimethyl ether. After stirring evenly, the mixture was centrifuged at 6000 r / min to form a casting solution;

[0055] (4) The casting solution was cast in a plastic culture dish and irradiated with 365 nm ultraviolet light for 5 min to form a gel. After drying, the discs were cut into small discs, vacuum dried to completely remove water, and then immersed in a 1 mol / L lithium hexafluorophosphate ethylene carbonate / dimethyl carbonate (volume ratio 1:1) electrolyte in a glove box for 20 h to obtain a cross-linked cellulose-based gel polymer electrolyte.

[0056] Example 4

[0057] S1. Preparation of water-soluble allyl cellulose:

[0058] (1) An alkali / urea solution was prepared by mixing 19.95 g of sodium hydroxide, 34.20 g of urea, and 230.85 g of deionized water in a mass ratio of 7:12:81. 15 g of cellulose powder was added at -12°C and stirred at 1900 rpm for 5 min to obtain a 5% cellulose solution.

[0059] (2) In a nitrogen atmosphere at 30°C, allyl glycidyl ether is added dropwise to a cellulose solution, with the molar ratio of allyl glycidyl ether to the anhydrous glucose unit of cellulose being 12:1; the reaction is carried out under light-shielding conditions with mechanical or magnetic stirring for 24 hours, the reaction product is added to acetone with a mass 10 times that of the reaction solution, and then placed in a dialysis bag for 7 days, followed by freeze-drying at -55°C for 48 hours to obtain a white cellulose solid, i.e., allyl cellulose;

[0060] S2. Preparation of cross-linked cellulose-based gel polymer electrolyte:

[0061] (3) 0.2 g of the above-mentioned allyl cellulose was dissolved in dimethyl sulfoxide to prepare a solution with a concentration of 2 wt%, and 0.1878 g of polyethylene glycol dimethacrylate (the molar ratio of polyethylene glycol dimethacrylate to allyl cellulose anhydrous glucose unit was 0.50) was added, followed by 0.2356 g of 1,4-butanediol bis(thioglycolate) and 0.03369 g of initiator benzoin dimethyl ether. After stirring evenly, the mixture was centrifuged at 6000 r / min to form a casting solution;

[0062] (4) The casting solution was cast in a plastic culture dish and irradiated with 365 nm ultraviolet light for 2 min to form a gel. After drying, the resulting discs were cut into small discs. After complete dehydration by vacuum drying, the discs were immersed in a 1 mol / L lithium hexafluorophosphate ethylene carbonate / dimethyl carbonate (volume ratio 1:1) electrolyte in a glove box for 20 h to obtain a cross-linked cellulose-based gel polymer electrolyte.

[0063] Example 5

[0064] S1. Preparation of water-soluble allyl cellulose:

[0065] (1) An alkali / urea solution was prepared by mixing 19.74 g of sodium hydroxide, 33.84 g of urea, and 228.42 g of deionized water in a mass ratio of 7:12:81. 18 g of cellulose powder was added at -12°C and stirred at 2000 rpm for 7 min to obtain a 6% cellulose solution.

[0066] (2) In a nitrogen atmosphere at 30°C, allyl glycidyl ether is added dropwise to a cellulose solution, with the molar ratio of allyl glycidyl ether to the anhydrous glucose unit of cellulose being 12:1; the reaction is carried out under light-shielding conditions with mechanical or magnetic stirring for 24 hours, the reaction product is added to acetone with a mass 10 times that of the reaction solution, and then placed in a dialysis bag for 7 days, followed by freeze-drying at -55°C for 48 hours to obtain a white cellulose solid, i.e., allyl cellulose;

[0067] S2. Preparation of cross-linked cellulose-based gel polymer electrolyte:

[0068] (3) Dissolve 0.2 g of the above-mentioned allyl cellulose in dimethyl sulfoxide to prepare a solution with a concentration of 2 wt%. Add 0.2441 g of polyethylene glycol dimethacrylate (the molar ratio of polyethylene glycol dimethacrylate to allyl cellulose anhydrous glucose unit is 0.65), then add 0.2709 g of 1,4-butanediol bis(thioglycolate), and 0.03874 g of initiator benzoin dimethyl ether. After stirring evenly, centrifuge at 6000 r / min to form a casting solution;

[0069] (4) The casting solution was cast in a plastic culture dish and irradiated with 365 nm ultraviolet light for 2 min to form a gel. After drying, the resulting pieces were cut into small discs. After complete dehydration by vacuum drying, the pieces were immersed in a 1 mol / L lithium hexafluorophosphate ethylene carbonate / dimethyl carbonate (volume ratio 1:1) electrolyte in a glove box for 24 h to obtain a cross-linked cellulose-based gel polymer electrolyte.

[0070] Example 6

[0071] S1. Preparation of water-soluble allyl cellulose:

[0072] (1) Prepare an alkali / urea solution by mixing 22.80 g of sodium hydroxide, 31.35 g of urea, and 230.85 g of deionized water in a mass ratio of 8:11:81. Add 15 g of cellulose powder at -12°C and stir at 2000 rpm for 5 min to obtain a 5% cellulose solution.

[0073] (2) In a nitrogen atmosphere at 30°C, allyl glycidyl ether is added dropwise to a cellulose solution, with the molar ratio of allyl glycidyl ether to the anhydrous glucose unit of cellulose being 12:1; the reaction is carried out under light-shielding conditions with mechanical or magnetic stirring for 24 hours, the reaction product is added to acetone with a mass 10 times that of the reaction solution, and then placed in a dialysis bag for 7 days, followed by freeze-drying at -55°C for 48 hours to obtain a white cellulose solid, i.e., allyl cellulose;

[0074] S2. Preparation of cross-linked cellulose-based gel polymer electrolyte:

[0075] (3) Dissolve 0.2 g of the above-mentioned allyl cellulose in dimethyl sulfoxide to prepare a solution with a concentration of 2 wt%. Add 0.2817 g of polyethylene glycol diacrylate (the molar ratio of polyethylene glycol diacrylate to allyl cellulose anhydrous glucose unit is 0.75), then add 0.3126 g of 1,4-butanediol bis(thioglycolate), and 0.0447 g of initiator benzoin dimethyl ether. After stirring evenly, centrifuge at 6000 r / min to form a casting solution;

[0076] (4) The casting solution was cast in a plastic culture dish and irradiated with 365 nm ultraviolet light for 2 min to form a gel. After drying, the resulting pieces were cut into small discs. After complete dehydration by vacuum drying, the pieces were immersed in a 1 mol / L lithium hexafluorophosphate ethylene carbonate / dimethyl carbonate (volume ratio 1:1) electrolyte in a glove box for 24 h to obtain a cross-linked cellulose-based gel polymer electrolyte.

[0077] Test Analysis

[0078] The gel polymer electrolyte obtained in Examples 1-5 was installed in the order of CR2032 positive electrode shell, stainless steel sheet or lithium sheet, gel polymer electrolyte, stainless steel sheet or lithium sheet, spring sheet, and negative electrode shell. After covering with tweezers, the shell was placed in a sealing machine for sealing at 50 kg / cm 2 The assembled lithium / gel polymer electrolyte / lithium battery and stainless steel / gel polymer electrolyte / stainless steel battery were used to test ionic conductivity and interfacial impedance.

[0079] Among them, the ionic conductivity is tested by the AC impedance method, using a battery with a stainless steel / gel polymer electrolyte / stainless steel structure. The ionic conductivity is given by the formula σ=d / (R b × S), where d represents the thickness of the gel polymer electrolyte and S represents the contact area between the stainless steel sheet and the polymer electrolyte film. In this test, d is taken as 1.96 cm 2 , R b The test data are shown in Table 1. For Examples 1, 2, and 5, the substitution degree of the allyl cellulose used is different. As the substitution degree increases, the ionic conductivity also increases. When the substitution degree of allyl cellulose is fixed, as shown in Table 1, the ionic conductivity of the allyl cellulose is increased. Figure 1 As shown, by adjusting the content of polyethylene glycol dimethacrylate (Examples 3, 4, and 5), it can be concluded that as the content of polyethylene glycol dimethacrylate increases, the ionic conductivity of the sample also increases, and the change of the ionic conductivity of Examples 3-5 with temperature conforms to the Arrhenius relationship, and the fitting has a relatively good determination coefficient.

[0080] Table 1

[0081] Thickness d (μm) <![CDATA[Body impedance R b (Ω)]]> Ionic conductivity σ (mS / cm) Example 1 268 11.95 1.13 Example 2 247 8.69 1.44 Example 3 193 7.04 1.39 Example 4 251 6.75 1.88 Example 5 250 4.35 2.90

[0082] The interfacial impedance is also measured using the AC impedance method, using a battery with a lithium / gel polymer electrolyte / lithium structure. Figure 2 As shown in the figure, with the increase of the content of polyethylene glycol dimethacrylate, the interface impedance between the gel polymer electrolyte and lithium metal gradually decreases, and the interface compatibility is significantly improved, which indicates that the wettability of the gel is also improved.

[0083] Thermal performance test was conducted on the polymer films obtained in Examples 3, 4 and 5 using a differential scanning calorimeter. The test conditions were room temperature to 300°C, a heating rate of 10°C / min, and a nitrogen atmosphere. Figure 3 As shown, the commercial Celgard 2400 separator exhibits a distinct endothermic peak at 163.8°C, corresponding to the melting behavior of the polypropylene used in the separator. However, Examples 3, 4, and 5 exhibit no distinct endothermic peak, with only a slight endothermic peak near 100°C, attributed to heat absorption by partially dried water within the system. The superior thermal stability of the examples is attributed to the high heat resistance of the cellulose substrate and the structural stability provided by its chemically cross-linked structure.

[0084] The cycle performance is obtained by testing the gel polymer electrolyte obtained in Example 4 on a blue battery test system. The battery used is a lithium iron phosphate / gel polymer electrolyte / lithium structure. The voltage range of constant current charge and discharge is 2.5~3.65V. Figure 4 As shown in Figure 3, there is no obvious capacity drop after 70 cycles.

[0085] It should be understood that the above embodiments are only preferred implementation modes of the present invention and are only used to explain the present invention rather than to limit the present invention. Any changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a cross-linked cellulose-based gel polymer electrolyte, characterized in that: The steps include: S1. Preparation of water-soluble allyl cellulose: (1) Sodium hydroxide, urea, and water are mixed in a mass ratio to prepare an alkali / urea solution, and cellulose powder is added and stirred to dissolve at a low temperature of -12°C to -16°C to obtain a cellulose solution; (2) adding allyl glycidyl ether dropwise to the cellulose solution under a nitrogen atmosphere, and reacting under light-shielding conditions with mechanical stirring or magnetic stirring; adding the reaction product into acetone and then placing it into a dialysis bag for dialysis, and then freeze-drying to obtain allyl cellulose; S2. Preparation of cross-linked cellulose-based gel polymer electrolyte: (3) dissolving the allyl cellulose in a solvent to prepare a solution, adding polyethylene glycol dimethacrylate or polyethylene glycol diacrylate, and then adding 1,4-butanediol bis(thioglycolate) and an initiator, stirring evenly, and centrifuging to form a casting solution; (4) casting the casting solution into a plastic culture dish, irradiating it with ultraviolet light to form a gel, drying it, cutting it, vacuum drying it to completely remove water, and then soaking it in an electrolyte in a glove box to obtain a cross-linked cellulose-based gel polymer electrolyte; In step S1 (2), the molar ratio of allyl glycidyl ether to cellulose anhydroglucose unit is (3-12):1; In step S2 (3), the molar ratio of polyethylene glycol dimethacrylate or polyethylene glycol diacrylate to allyl cellulose anhydrous glucose units is 0.35 to 0.75; the amount of 1,4-butanediol bis(thioglycolate) added is half the amount of the double bond provided by polyethylene glycol dimethacrylate and allyl cellulose, or half the amount of the double bond provided by polyethylene glycol diacrylate and allyl cellulose; In step S2 (3), the initiator is one of benzoin dimethyl ether and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone; the amount of the initiator added is 7% to 14% of the amount of 1,4-butanediol bis(thioglycolate); In step S2 (4), the ultraviolet light irradiation wavelength is 365 nm, and the irradiation time is 2 to 15 minutes; The electrolyte is a carbonate electrolyte, including one of 1 mol / L lithium hexafluorophosphate ethylene carbonate / dimethyl carbonate electrolyte, 1 mol / L lithium hexafluorophosphate ethylene carbonate / diethyl carbonate electrolyte, and 1 mol / L lithium bis(trifluoromethylsulfonyl)amide ethylene carbonate / dimethyl carbonate electrolyte; the electrolyte immersion time is 1 to 24 hours.

2. The method for preparing a cross-linked cellulose-based gel polymer electrolyte according to claim 1, characterized in that: In step S1 (1), the mass ratio of sodium hydroxide, urea, and water is (4-8):(10-12):(75-85); the speed of stirring and dissolving is 1500-2000 r / min, and the stirring and dissolving time is 2-10 minutes; the mass percentage of the obtained cellulose solution is 3%-6%.

3. The method for preparing a cross-linked cellulose-based gel polymer electrolyte according to claim 1, characterized in that: In step S2 (3), the solvent is one of deionized water, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide; and the solvent is prepared into a solution with a concentration of 1 wt% to 4 wt%.

4. The method for preparing a cross-linked cellulose-based gel polymer electrolyte according to claim 1, wherein: In step S1 (2), the reaction time under mechanical stirring or magnetic stirring is 20 to 30 hours; the dialysis time in the dialysis bag is 3 to 7 days; the freeze-drying temperature is -45 to -60°C, and the freeze-drying time is 24 to 72 hours.

5. A cross-linked cellulose-based gel polymer electrolyte obtained by the preparation method according to any one of claims 1 to 4.

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