Preparation method and application of high ionic conductivity composite electrolyte

Abstract

The application discloses a preparation method and application of a high-ionic-conductivity composite electrolyte, and comprises the following specific steps: first, sulfonated polyetherimide is prepared; then, the sulfonated polyetherimide is soaked in a lithium hydroxide aqueous solution; hydroxyl ions nucleophilically attack carbonyl of the imide to initiate hydrolytic ring-opening, meanwhile, lithium ions replace hydrogen ions in sulfonic acid groups and carboxylic acid groups through ion exchange, and under the synergistic effect, lithium sulfonate / carboxylic acid lithium functionalized polyetheramide is obtained. The lithium sulfonate / carboxylic acid lithium functionalized polyetheramide is blended with polyvinylidene hexafluoropropylene to prepare a composite polymer film, the composite polymer film is swelled in an electrolyte containing lithium salt, and a composite electrolyte is obtained. According to the method, ring-opening modification of the sulfonated polyetherimide is induced through ion exchange under alkaline conditions, an ion conductor polymer which is synergistically functionalized by lithium sulfonate, lithium carboxylate and amide groups is formed, lithium ion migration in the electrolyte is promoted, and stable circulation of a lithium metal battery in a high-ionic-conductivity and wide temperature range is realized.

Description

Technical Field

[0001] This invention relates to the field of lithium metal battery technology, specifically to a method for preparing and applying a composite electrolyte with high ionic conductivity. Background Technology

[0002] Ion conductivity is a crucial indicator for evaluating electrolyte performance, playing a decisive role in the power density, cycle life, and interfacial stability of lithium metal batteries. In all-solid-state polymer electrolytes, ion transport relies on the chain segment movement of the polymer matrix, resulting in low ionic conductivity at room temperature. In contrast, gel polymer electrolytes introduce a small amount of solvent into the three-dimensional network structure of the polymer matrix, combining the high safety of solid-state electrolytes with the good ionic conductivity of liquid electrolytes. In gel electrolytes, the polymer matrix not only acts as the mechanical framework supporting the electrolyte membrane but also serves as an important ion transport medium. Therefore, to further improve the ionic conductivity of electrolytes, this study focuses on the interactions between the polymer matrix, lithium salt, and solvent, optimizing the molecular structure design of the polymer matrix, and introducing functionalized groups to construct composite electrolytes, thereby enhancing the overall ionic conductivity. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a high ionic conductivity composite electrolyte and its application. The composite electrolyte prepared by this method has excellent ionic conductivity, high lithium-ion transference number, and good compatibility with the positive and negative electrodes of lithium batteries. When applied to lithium metal batteries, it exhibits excellent electrochemical performance under a wide temperature range.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a high ionic conductivity composite electrolyte, comprising the following steps:

[0005] (1) Preparation of sulfonated polyetherimide: Polyetherimide was dissolved in ultra-dry dichloroethane to obtain solution A; sulfonating reagent and ultra-dry dichloroethane were stirred evenly to obtain solution B; solution B was added dropwise to solution A, and the mixture was heated and stirred at 50-70°C for 1-5 h under an argon atmosphere. The solid product was collected, washed with isopropanol, and dried in a vacuum drying oven at 50-70°C to obtain sulfonated polyetherimide.

[0006] (2) Preparation of lithium sulfonate / lithium carboxylate functionalized polyether amide: The sulfonated polyether imide prepared in step (1) is dissolved in an organic solvent and stirred for 1-2 hours to obtain solution C; solution C is uniformly coated on a polytetrafluoroethylene plate and dried in a vacuum oven at 40-80°C. After the solvent evaporates, a sulfonated polyether imide film is formed; the sulfonated polyether imide film is immersed in a lithium hydroxide aqueous solution and stirred for 2-6 hours. Then the film is taken out and dried in a vacuum oven at 60-70°C to obtain lithium sulfonate / lithium carboxylate functionalized polyether amide.

[0007] (3) Preparation of composite electrolyte: Disperse the lithium sulfonate / lithium carboxylate functionalized polyether amide prepared in step (2) in an organic solvent and stir until uniform to obtain solution D; dissolve polyvinylidene fluoride cohexafluoropropylene in acetone to obtain solution E; mix solution D and solution E evenly, coat it on a polytetrafluoroethylene vinyl plate, and heat and dry it in a vacuum oven at 60-80℃ to obtain a composite polymer film; immerse the composite polymer film in an ester-based electrolyte containing 0.5-2 mol / L lithium salt until it swells to obtain the composite electrolyte.

[0008] Preferably, in step (1), the concentrations of both solution A and solution B are 0.1 to 0.5 g / mL, and the mass ratio between polyetherimide and sulfonating agent is (1 to 5): 1.

[0009] Preferably, in step (1), the molecular weight of the polyetherimide is 40,000 to 50,000; and the sulfonating agent is one or more of chlorosulfonic acid, camphor sulfonic acid, sulfur trioxide, and aminosulfonic acid.

[0010] Preferably, in step (2), the concentration of solution C is 0.1 to 0.5 g / mL, and the concentration of the lithium hydroxide aqueous solution is 0.01 to 1 mol / L.

[0011] Preferably, in step (3), the concentration of solution D is 0.005-0.02 g / mL, the concentration of solution E is 0.01-0.05 g / mL, and the mass ratio between lithium sulfonate / lithium carboxylate functionalized polyether amide and polyvinylidene fluoride cohexafluoropropylene is 1:(1-10).

[0012] Preferably, in steps (2) and (3), the organic solvent is one or more of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0013] Preferably, in step (3), the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalate borate; and the ester-based electrolyte is one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0014] Preferably, in step (3), the molecular weight of the polyvinylidene fluoride cohexafluoropropylene is 200,000 to 600,000.

[0015] The present invention also provides an application of the composite electrolyte prepared by the above-mentioned method for preparing high ionic conductivity composite electrolyte in lithium metal batteries.

[0016] Preferably, the lithium metal battery includes a positive electrode, a negative electrode, and a composite electrolyte between the positive and negative electrodes; the positive electrode active material is one or more of lithium iron phosphate, lithium cobalt oxide, and iodine-carbon composite material, and the negative electrode material is lithium metal or lithium alloy.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) In this invention, sulfonated polyetherimide is ring-opened and lithiated to obtain lithium sulfonate / lithium carboxylate functionalized polyether amide. By optimizing the molecular structure of the electrolyte matrix, the interaction between ions and functional groups of the polymer matrix is ​​regulated, and the lithium ion solvation structure is optimized, thereby achieving a simultaneous increase in lithium ion concentration and lithium ion mobility in the composite electrolyte, which significantly improves the ionic conductivity and lithium ion transference number of the electrolyte.

[0019] (2) The composite electrolyte of the present invention has excellent interfacial compatibility with the positive and negative electrodes of the lithium metal battery, enabling the lithium metal battery to achieve good electrochemical performance over a wide temperature range. Attached Figure Description

[0020] Figure 1 The lithium-ion transference number and ionic conductivity test graphs of the composite electrolytes prepared in Comparative Example 1 and Example 1, and Comparative Example 2, respectively; (a) Ionic conductivity test graphs of the composite electrolytes prepared in Comparative Example 1 and Example 1, and Comparative Example 2, respectively; (b) Lithium-ion transference number test graph of the composite electrolyte prepared in Example 1; (c) Lithium-ion transference number test graph of the composite electrolyte prepared in Comparative Example 1; (d) Lithium-ion transference number test graph of Comparative Example 2.

[0021] Figure 2 Electrochemical performance test diagrams of the composite electrolytes prepared in Comparative Example 1 and Example 1, and the lithium metal battery assembled in Comparative Example 2; (a) lithium iron phosphate battery, (b) lithium cobalt oxide battery, (c) lithium iodine battery.

[0022] Figure 3 The electrochemical performance of the composite electrolytes prepared for Comparative Example 1 and Example 1, and the lithium iron phosphate battery assembled for Comparative Example 2, was tested at test temperatures of 80°C and -20°C, respectively; (a) Cycling performance of the battery at 80°C and 2C rate; (b) Charge-discharge curve of the battery at -20°C and 0.1C rate. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0024] Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available products with a purity of analytical grade or higher.

[0025] Example 1

[0026] A method for preparing a composite electrolyte with high ionic conductivity includes the following steps:

[0027] (1) Dissolve 10g of polyetherimide (molecular weight: 40000) in 50mL of ultra-dry dichloroethane to obtain solution A; take 4g of chlorosulfonic acid and 40mL of ultra-dry dichloroethane and stir evenly to obtain solution B; add solution B dropwise to solution A, heat and stir at 60℃ for 2h under argon atmosphere, collect the solid product, wash the product with isopropanol, and dry the product at 60℃ in a vacuum drying oven to obtain sulfonated polyetherimide;

[0028] (2) Take 5g of the sulfonated polyetherimide prepared in step (1) and dissolve it in 15mL of N,N-dimethylacetamide. Stir for 2h to obtain solution C. Coat solution C evenly on a polytetrafluoroethylene board and heat it in a vacuum oven at 40°C to dry it. After the solvent evaporates, a sulfonated polyetherimide film is formed. Immerse the sulfonated polyetherimide film in a 0.05mol / L lithium hydroxide aqueous solution and stir for 6h. Heat the resulting film in a vacuum oven at 70°C to dry it to obtain lithium sulfonate / lithium carboxylate functionalized polyether amide.

[0029] (3) Take 0.3g of lithium sulfonate / lithium carboxylate functionalized polyether amide prepared in step (2) and disperse it in 20mL of N,N-dimethylacetamide and stir it evenly to obtain solution D; take 0.5g of polyvinylidene fluoride cohexafluoropropylene (molecular weight: 400000) and dissolve it in 10mL of acetone to obtain solution E; mix solution D and solution E evenly, coat it on polytetrafluoroethylene board, and heat and dry it in a vacuum oven at 60℃ to obtain a composite polymer film; immerse the polymer film in an electrolyte containing 1mol / L lithium hexafluorophosphate in ethylene carbonate / methyl ethyl carbonate (volume ratio of ethylene carbonate to methyl ethyl carbonate is 1:1) until it swells to obtain a composite electrolyte.

[0030] Comparative Example 1

[0031] As a control experiment for Example 1, unlike Example 1, Comparative Example 1 did not use lithium hydroxide aqueous solution to treat the sulfonated polyetherimide film. The specific steps are as follows:

[0032] (1) Dissolve 10g of polyetherimide (molecular weight: 40000) in 50mL of ultra-dry dichloroethane to obtain solution A; take 4g of chlorosulfonic acid and 40mL of ultra-dry dichloroethane and stir evenly to obtain solution B; add solution B dropwise to solution A, heat and stir at 60℃ for 2h under argon atmosphere, collect the solid product, wash the product with isopropanol, and dry the product at 60℃ in a vacuum drying oven to obtain sulfonated polyetherimide;

[0033] (2) Take 0.3g of the sulfonated polyetherimide prepared in step (1) and disperse it in 20mL of N,N-dimethylacetamide and stir it evenly to obtain solution C; take 0.5g of polyvinylidene fluoride cohexafluoropropylene (molecular weight: 400000) and dissolve it in 10mL of acetone to obtain solution D; mix solution C and solution D evenly, coat it on a polytetrafluoroethylene plate, and heat and dry it in a vacuum oven at 60℃ to obtain a composite polymer film; immerse the polymer film in an electrolyte containing 1mol / L lithium hexafluorophosphate in ethylene carbonate / methyl ethyl carbonate (volume ratio of ethylene carbonate to methyl ethyl carbonate 1:1) until it swells to obtain a composite electrolyte.

[0034] Comparative Example 2

[0035] As a control experiment for Example 1, Comparative Example 2 used a commercial polyolefin separator, model Celgard2300, and the electrolyte used to assemble the lithium battery was ethylene carbonate / ethyl methyl carbonate with 1 mol / L lithium hexafluorophosphate (volume ratio 1:1).

[0036] The composite electrolytes prepared in Example 1 and Comparative Example 1, as well as Comparative Example 2, were tested for ionic conductivity and lithium-ion transference number on a CHI604E testing system, with the test temperature maintained at a constant 25°C.

[0037] The results of the ionic conductivity test are as follows: Figure 1 As shown in Figure a, the room temperature ionic conductivity of the composite electrolyte in Example 1 is 8.78 mS / cm, the room temperature ionic conductivity of the composite electrolyte in Comparative Example 1 is 2.76 mS / cm, and the room temperature ionic conductivity of Comparative Example 2 is 2.63 mS / cm. This demonstrates that the composite electrolyte prepared in this example exhibits high ionic conductivity. After ring-opening induced under alkaline conditions, sulfonated polyetherimide introduces more polar functional groups. These polar functional groups form a high density of active sites on the polymer chain. The interaction between these sites and the lithium salt and solvent facilitates the establishment of efficient and continuous ion transport channels. Therefore, the ionic conductivity of this example is significantly improved compared to the comparative examples.

[0038] The lithium-ion transport number test results are as follows: Figure 1 As shown in b, 1c, and 1d, the lithium-ion transference number (LTN) of Example 1 is 0.69, that of Comparative Example 1 is 0.43, and that of Comparative Example 2 is 0.40. The lithium hydroxide solution causes a ring-opening reaction in the imide, forming an amide group that interacts with the lithium salt anion, restricting the free movement of the anion. Simultaneously, the highly delocalized negative charges of the sulfonate and carboxylate anions in the lithium sulfonate / lithium carboxylate functionalized polyether amide electrostatically repel the lithium salt anion, further inhibiting anion movement. This significantly increases the LTN of the examples. Therefore, the LTN of this example is significantly higher than that of the comparative examples.

[0039] Lithium metal batteries were assembled using the composite electrolytes prepared in Example 1 and Comparative Example 1, respectively, and Comparative Example 2, and the electrochemical performance of the lithium metal batteries was tested. Specifically, in an anhydrous and oxygen-free glove box, a lithium metal sheet was used as the negative electrode, and lithium iron phosphate electrode sheets, lithium cobalt oxide electrode sheets, and iodine-carbon composite materials were used as the positive electrodes, respectively. The electrolyte was placed between the positive and negative electrodes to assemble the lithium metal battery. The electrochemical performance of the assembled lithium metal battery was tested on a Newway battery testing system at a test temperature of 25°C.

[0040] Figure 2 These are the charge-discharge curves of the composite electrolytes prepared in Example 1 and Comparative Example 1, and the lithium metal battery assembled in Comparative Example 2, tested at 25°C. Figure 2 As shown in Figure a, at a 2C rate, the lithium iron phosphate battery assembled with the composite electrolyte prepared in Example 1 has a specific capacity of 156 mAh / g and a voltage polarization of 170 mV. The lithium iron phosphate battery assembled with the composite electrolyte prepared in Comparative Example 1 has a specific capacity of 122 mAh / g and a voltage polarization of 440 mV. The lithium iron phosphate battery assembled in Comparative Example 2 has a specific capacity of 110 mAh / g and a voltage polarization of 445 mV. Figure 2 As shown in b, at a 2C rate, the lithium cobalt oxide battery assembled with the composite electrolyte prepared in Example 1 has a specific capacity of 152 mAh / g and a voltage polarization of 120 mV. The lithium cobalt oxide battery assembled with the composite electrolyte prepared in Comparative Example 1 has a specific capacity of 120 mAh / g and a voltage polarization of 383 mV. The lithium cobalt oxide battery assembled in Comparative Example 2 has a specific capacity of 104 mAh / g and a voltage polarization of 570 mV. Figure 2 As shown in Figure c, at a 2C rate, the lithium-iodine battery assembled with the composite electrolyte prepared in Example 1 has a specific capacity of 204 mAh / g and a voltage polarization of 594 mV. In contrast, the lithium-iodine battery assembled with the composite electrolyte prepared in Comparative Example 1 has a specific capacity of 116 mAh / g and a voltage polarization of 655 mV. The lithium-iodine battery assembled in Comparative Example 2 has a specific capacity of 91 mAh / g and a voltage polarization of 770 mV. It is evident that the composite electrolyte prepared in this example exhibits excellent compatibility with both the positive and negative electrodes in lithium iron phosphate, lithium cobalt oxide, and lithium-iodine battery systems. Compared to Comparative Examples 1 and 2, the lithium metal battery assembled with the composite electrolyte prepared in this example has the advantages of higher specific capacity and lower voltage polarization. This indicates that the multifunctionalized groups in the lithium sulfonate / lithium carboxylate polyether amide polymer matrix can improve the electrode reaction rate at the interface and reduce interfacial impedance, thereby achieving high battery capacity.

[0041] Lithium iron phosphate batteries were assembled using the composite electrolyte prepared in Example 1, the composite electrolyte prepared in Comparative Example 1, and Comparative Example 2. The electrochemical performance of the batteries was tested at test temperatures of 80°C and -20°C. The test results are as follows: Figure 3 As shown. Figure 3 Figure a shows the cycle performance of the lithium iron phosphate batteries assembled in Example 1, Comparative Example 1, and Comparative Example 2 at 80°C and 2C rate. The lithium battery assembled in Example 1 has a discharge specific capacity of 167 mAh / g and maintains a capacity of 161 mAh / g after 800 stable cycles. The discharge specific capacity of Comparative Example 1 is 134 mAh / g, and the battery capacity significantly decreases after 400 cycles, eventually leading to battery damage. The discharge specific capacity of Comparative Example 2 is 122 mAh / g, and the battery capacity significantly decreases after 150 cycles, eventually leading to battery damage. Figure 3 b shows the charge-discharge curves of the lithium iron phosphate batteries assembled in Example 1 and Comparative Examples 1 and 2 at -20°C and a 0.1C rate. The lithium battery assembled in Example 1 has a discharge specific capacity of 145 mAh / g, which is higher than the discharge specific capacity of Comparative Example 1 (95 mAh / g) and Comparative Example 2 (82 mAh / g). Figure 3 The test results show that the composite electrolyte prepared in this embodiment has good electrochemical performance at both high and low temperatures and can be applied in wide-temperature-range lithium batteries.

[0042] Example 2

[0043] A method for preparing a composite electrolyte with high ionic conductivity includes the following steps:

[0044] (1) Dissolve 8g of polyetherimide (molecular weight: 40000) in 50mL of ultra-dry dichloroethane to obtain solution A; take 6g of chlorosulfonic acid and 40mL of ultra-dry dichloroethane and stir evenly to obtain solution B; add solution B dropwise to solution A, heat and stir at 50℃ for 1.5h under argon atmosphere, collect the solid product, wash the product with isopropanol, and dry the product at 50℃ in a vacuum drying oven to obtain sulfonated polyetherimide;

[0045] (2) Take 5g of the sulfonated polyetherimide prepared in step (1) and dissolve it in 20mL of N-methylpyrrolidone. Stir for 1h to obtain solution C. Coat solution C evenly on a polytetrafluoroethylene board and heat it in a vacuum oven at 60°C to dry it. After the solvent evaporates, a sulfonated polyetherimide film is formed. Immerse the sulfonated polyetherimide film in a 0.2mol / L lithium hydroxide aqueous solution and stir for 4h. Heat the resulting film in a vacuum oven at 60°C to dry it to obtain lithium sulfonate / lithium carboxylate functionalized polyether amide.

[0046] (3) Take 0.3g of lithium sulfonate / lithium carboxylate functionalized polyether amide prepared in step (2) and disperse it in 20mL of N-methylpyrrolidone and stir it evenly to obtain solution D; take 0.3g of polyvinylidene fluoride cohexafluoropropylene (molecular weight: 300000) and dissolve it in 10mL of acetone to obtain solution E; mix solution D and solution E evenly, coat it on polytetrafluoroethylene vinyl plate, and heat and dry it in a vacuum oven at 60℃ to obtain a composite polymer film; immerse the polymer film in an electrolyte containing 1.2mol / L lithium bis(trifluoromethanesulfonyl)imide in ethylene carbonate / dimethyl carbonate (the volume ratio between ethylene carbonate and dimethyl carbonate is 1:1) until it swells to obtain a composite electrolyte.

[0047] The composite electrolyte prepared in this embodiment was tested for ionic conductivity and lithium-ion transference number. A lithium metal battery was assembled using the composite electrolyte prepared in this embodiment, and the electrochemical performance of the lithium metal battery was tested. A lithium iron phosphate battery was assembled using the composite electrolyte prepared in this embodiment, and the electrochemical performance of the battery was tested at test temperatures of 80°C and -20°C. All the above test procedures were the same as in Example 1, and the test results are as follows:

[0048] The composite electrolyte in this embodiment has a room temperature ionic conductivity of 8.33 mS / cm and a lithium-ion transference number of 0.66, which shows that the composite electrolyte prepared in this embodiment has high ionic conductivity and lithium-ion transference number.

[0049] At 2C rate, the lithium iron phosphate battery assembled with the composite electrolyte prepared in this embodiment has a specific capacity of 150 mAh / g and a voltage polarization of 175 mV; at 2C rate, the lithium cobalt oxide battery assembled with the composite electrolyte prepared in this embodiment has a specific capacity of 149 mAh / g and a voltage polarization of 125 mV; at 2C rate, the lithium iodine battery assembled with the composite electrolyte prepared in this embodiment has a specific capacity of 196 mAh / g and a voltage polarization of 600 mV. It can be seen that the composite electrolyte prepared in this embodiment has the advantages of high specific capacity and low voltage polarization.

[0050] The lithium battery assembled in this embodiment has a discharge specific capacity of 160 mAh / g at 80°C and 2C rate, and retains a capacity of 150 mAh / g after 800 stable cycles. The lithium battery assembled in this embodiment has a discharge specific capacity of 132 mAh / g at -20°C and 0.1C rate. It can be seen that the composite electrolyte prepared in this embodiment has good electrochemical performance at both high and low temperatures and can be used in wide-temperature-range lithium batteries.

[0051] Example 3

[0052] A method for preparing a composite electrolyte with high ionic conductivity includes the following steps:

[0053] (1) Dissolve 10g of polyetherimide (molecular weight: 50000) in 50mL of ultra-dry dichloroethane to obtain solution A; take 2g of sulfur trioxide and 20mL of ultra-dry dichloroethane and stir evenly to obtain solution B; add solution B dropwise to solution A, heat and stir at 70℃ for 5h under argon atmosphere, collect the solid product, wash the product with isopropanol, and dry the product at 70℃ in a vacuum drying oven to obtain sulfonated polyetherimide;

[0054] (2) Take 5g of the sulfonated polyetherimide prepared in step (1) and dissolve it in 40mL of dimethyl sulfoxide. Stir for 1h to obtain solution C. Coat solution C evenly on a polytetrafluoroethylene plate and heat it in a vacuum oven at 80°C to dry it. After the solvent evaporates, a sulfonated polyetherimide film is formed. Immerse the sulfonated polyetherimide film in a 0.5mol / L lithium hydroxide aqueous solution and stir for 2h. Heat the resulting film in a vacuum oven at 70°C to dry it to obtain lithium sulfonate / lithium carboxylate functionalized polyether amide.

[0055] (3) Take 0.4g of lithium sulfonate / lithium carboxylate functionalized polyether amide prepared in step (2) and disperse it in 20mL of dimethyl sulfoxide and stir evenly to obtain solution D; take 0.6g of polyvinylidene fluoride cohexafluoropropylene (molecular weight: 500000) and dissolve it in 50mL of acetone to obtain solution E; mix solution D and solution E evenly, coat it on a polytetrafluoroethylene vinyl plate, and heat and dry it in a vacuum oven at 80℃ to obtain a composite polymer film; immerse the polymer film in an electrolyte containing 1.5mol / L lithium bis(trifluoromethanesulfonyl)imide in ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (the volume ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is 1:1:1) until it swells to obtain a composite electrolyte.

[0056] The composite electrolyte prepared in this embodiment was tested for ionic conductivity and lithium-ion transference number. A lithium metal battery was assembled using the composite electrolyte prepared in this embodiment, and the electrochemical performance of the lithium metal battery was tested. A lithium iron phosphate battery was assembled using the composite electrolyte prepared in this embodiment, and the electrochemical performance of the battery was tested at test temperatures of 80°C and -20°C. All the above test procedures were the same as in Example 1, and the test results are as follows:

[0057] The composite electrolyte in this embodiment has a room temperature ionic conductivity of 8.21 mS / cm and a lithium-ion transference number of 0.64, which shows that the composite electrolyte prepared in this embodiment has high ionic conductivity and lithium-ion transference number.

[0058] At 2C rate, the lithium iron phosphate battery assembled with the composite electrolyte prepared in this embodiment has a specific capacity of 151 mAh / g and a voltage polarization of 174 mV; at 2C rate, the lithium cobalt oxide battery assembled with the composite electrolyte prepared in this embodiment has a specific capacity of 155 mAh / g and a voltage polarization of 113 mV; at 2C rate, the lithium iodine battery assembled with the composite electrolyte prepared in this embodiment has a specific capacity of 194 mAh / g and a voltage polarization of 617 mV. It can be seen that the composite electrolyte prepared in this embodiment has the advantages of high specific capacity and low voltage polarization.

[0059] The lithium battery assembled in this embodiment has a discharge specific capacity of 165 mAh / g at 80℃ and 2C rate, and retains a capacity of 159 mAh / g after 800 stable cycles. The lithium battery assembled in this embodiment has a discharge specific capacity of 138 mAh / g at -20℃ and 0.1C rate. It can be seen that the composite electrolyte prepared in this embodiment has good electrochemical performance at both high and low temperatures and can be used in wide-temperature-range lithium batteries.

[0060] Although this application has been described in detail in this specification with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of this application are protected by this application.

Claims

1. A method for preparing a composite electrolyte with high ionic conductivity, characterized in that, Includes the following steps: (1) Preparation of sulfonated polyetherimide: Polyetherimide was dissolved in ultra-dry dichloroethane to obtain solution A; sulfonating reagent and ultra-dry dichloroethane were stirred evenly to obtain solution B; solution B was added dropwise to solution A, and the mixture was heated and stirred at 50-70°C for 1-5 h under an argon atmosphere. The solid product was collected, washed with isopropanol, and dried in a vacuum drying oven at 50-70°C to obtain sulfonated polyetherimide. (2) Preparation of lithium sulfonate / lithium carboxylate functionalized polyether amide: The sulfonated polyether imide prepared in step (1) is dissolved in an organic solvent and stirred for 1-2 hours to obtain solution C; solution C is uniformly coated on a polytetrafluoroethylene plate and dried in a vacuum oven at 40-80°C. After the solvent evaporates, a sulfonated polyether imide film is formed; the sulfonated polyether imide film is immersed in a lithium hydroxide aqueous solution and stirred for 2-6 hours. Then the film is taken out and dried in a vacuum oven at 60-70°C to obtain lithium sulfonate / lithium carboxylate functionalized polyether amide. (3) Preparation of composite electrolyte: Disperse the lithium sulfonate / lithium carboxylate functionalized polyether amide prepared in step (2) in an organic solvent and stir until uniform to obtain solution D; dissolve polyvinylidene fluoride cohexafluoropropylene in acetone to obtain solution E; mix solution D and solution E evenly, coat it on a polytetrafluoroethylene vinyl plate, and heat and dry it in a vacuum oven at 60-80℃ to obtain a composite polymer film; immerse the composite polymer film in an ester-based electrolyte containing 0.5-2 mol / L lithium salt until it swells to obtain the composite electrolyte.

2. The method for preparing a high ionic conductivity composite electrolyte according to claim 1, characterized in that, In step (1), the concentrations of both solution A and solution B are 0.1–0.5 g / mL; the mass ratio between polyetherimide and sulfonating agent is (1–5):

1.

3. The method for preparing a high ionic conductivity composite electrolyte according to claim 1 or 2, characterized in that, In step (1), the molecular weight of the polyetherimide is 40,000 to 50,000; the sulfonating agent is one or more of chlorosulfonic acid, camphor sulfonic acid, sulfur trioxide, and aminosulfonic acid.

4. The method for preparing a high ionic conductivity composite electrolyte according to claim 1 or 2, characterized in that, In step (2), the concentration of solution C is 0.1 to 0.5 g / mL, and the concentration of the lithium hydroxide aqueous solution is 0.01 to 1 mol / L.

5. A method for preparing a high ionic conductivity composite electrolyte according to claim 1 or 2, characterized in that, In step (3), the concentration of solution D is 0.005-0.02 g / mL, the concentration of solution E is 0.01-0.05 g / mL, and the mass ratio between lithium sulfonate / lithium carboxylate functionalized polyether amide and polyvinylidene fluoride cohexafluoropropylene is 1:(1-10).

6. A method for preparing a high ionic conductivity composite electrolyte according to claim 1 or 2, characterized in that, In steps (2) and (3), the organic solvent is one or more of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

7. The method for preparing a high ionic conductivity composite electrolyte according to claim 1 or 2, characterized in that, In step (3), the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalate borate; the ester-based electrolyte is one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate.

8. A method for preparing a high ionic conductivity composite electrolyte according to claim 1 or 2, characterized in that, In step (3), the molecular weight of the polyvinylidene fluoride cohexafluoropropylene is 200,000 to 600,000.

9. The application of a composite electrolyte prepared by the method of any one of claims 1-8 in lithium metal batteries.

10. The application of the composite electrolyte according to claim 9 in lithium metal batteries, characterized in that, The lithium metal battery includes a positive electrode, a negative electrode, and a composite electrolyte between the positive and negative electrodes; the positive electrode active material is one or more of lithium iron phosphate, lithium cobalt oxide, and iodine-carbon composite material, and the negative electrode material is lithium metal or lithium alloy.

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