Cross-linked sulfonated cation exchange polymer, diaphragm and preparation method thereof

Abstract

The invention provides a cross-linked sulfonated cation exchange polymer, a diaphragm and a preparation method thereof, and relates to the technical field of lithium batteries. According to the cross-linked sulfonated cation exchange polymer provided by the invention, a large number of microphase partitions are formed in the polymer due to polarity difference of molecular chain segments of the polymer, and meanwhile, a main chain is provided with a three-dimensional structure unit which provides a large number of transmission channels for migration of lithium ions; and moreover, a large number of negatively charged ions exist in the channel, so that lithium ion dissociation is promoted, the transmission rate of lithium ions is improved, free growth of lithium dendrites is reduced, the possibility of short circuit caused by the fact that the lithium dendrites penetrate through the diaphragm to be in contact with a positive electrode is greatly reduced, the coulombic efficiency of the battery is improved, the cycle life of the battery is prolonged, and capacity fading of the battery is reduced.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to cross-linked sulfonated cation exchange polymers, separators, and their preparation methods. Background Technology

[0002] Currently, lithium-ion batteries using graphite as the anode are already very close to their theoretical capacity, with little room for further improvement. Replacing graphite with lithium metal as the anode material could increase the specific capacity by more than tenfold; however, the widespread use of high-capacity lithium metal anodes still faces several challenges. One key issue is the dendritic growth of lithium. During lithium deposition / deposition, irregular lithium dendrites form on the lithium metal anode. This dendritic growth pattern leads to several significant problems: lithium dendrites, when grown to a certain extent, can puncture the separator, causing a short circuit and posing a serious safety hazard; simultaneously, as lithium metal continues to deposit, the solid electrolyte interface film on the anode material surface repeatedly breaks and reforms, continuously consuming active lithium and reducing its coulombic efficiency.

[0003] Patent CN117638402A discloses a composite separator for solid-state lithium metal batteries and its preparation method. This battery has a first metal-organic framework (MOF) coating of oxidizing metal ions on the separator surface and a second MOF coating on the lithium metal electrode surface. The spatial confinement of the MOF material suppresses the cycling volume fluctuation of the lithium anode, while the regular pore structure induces uniform lithium ion distribution, mitigating dendrite penetration at high current densities. Patent CN114335898B discloses a separator for lithium metal batteries. The separator surface is coated with a functional coating that can undergo in-situ electrochemical or chemical reactions with metallic lithium to generate a lithiophilic metal. The lithiophilic metal generated after the reaction serves as a lithium deposition site, suppressing lithium dendrite formation. Patent CN111969162A discloses a separator based on alloy element modification. By co-sputtering and depositing two elements simultaneously on the surface of the separator substrate, namely lithium and an element with a certain solid solubility with lithium, the deposition direction of lithium is controlled by space, so that the growth direction of lithium changes from negative electrode to separator to separator to negative electrode, thus eliminating the possibility of lithium dendrite growth penetrating the separator.

[0004] Currently, there are four promising strategies to address the growth of lithium metal dendrites: 1) Preparing ceramic coatings with high Young's modulus, which suppress dendrite growth through physical inhibition without considering the lithium dendrite nucleation process. However, due to the non-uniform electric field and lithium-ion flux in liquid electrolyte systems, nucleation is usually non-uniform. Under abuse conditions, lithium dendrites can still form along the membrane gaps to reach the positive electrode, creating internal short circuits and causing irreversible capacity loss; 2) Preparing two-dimensional material coatings with regular pore structures, including boron nitride nanosheets, nitrogen-sulfur co-doped graphene nanosheets, metal-organic frameworks, graphene oxide molecular brushes, etc. However, the raw material synthesis conditions are demanding, resulting in low yields and high prices, making large-scale industrial production difficult; 3) Preparing functional coatings with lithium-affinity properties, such as Au, Cu, Mg, Zn, MnO, MnCO3, SnO2, and TiO2. 2-x Alternatively, lithium metal deposition can be induced by the lithium metal's own lithiophilic properties or by its reaction with lithium metal to reduce it to a lithiophilic metal. However, the resulting heterogeneous nucleation sites are not reversible, and the coating loses its functional properties after being covered by lithium metal. 4) Prepare a separator coating modified with alloying elements to form a lithium metal passivation layer on the negative electrode surface and the separator surface. Considering the overall cost, lithiophilicity and nucleation ability, as well as the diffusion rate of lithium ions, the number of elements that can be used to react and generate the alloy layer is relatively small, and the dissolution of functional particles usually uses polar solvents, which is poorly compatible with existing aqueous coating processes. Summary of the Invention

[0005] This application provides a cross-linked sulfonated cation exchange polymer, a separator, and a method for preparing the same. The cross-linked sulfonated cation exchange polymer has a rigid three-dimensional molecular structure and does not contain ether groups, which endows the cation exchange membrane with superior mechanical properties, chemical stability, and ionic conductivity. At the same time, the polarity difference between chain segments results in a large number of microphase partitions within the polymer, promoting the formation of ion transport channels and further improving the lithium-ion transport capacity of the separator. In addition, the three-dimensional structural units on the main chain provide a large number of transport channels for lithium-ion migration, and the presence of a large number of negatively charged ions within the channels is conducive to promoting lithium-ion dissociation, increasing the lithium-ion transport rate, and thus reducing the free growth of lithium dendrites. This significantly reduces the possibility of lithium dendrites penetrating the separator and contacting the positive electrode, causing a short circuit. The separator polymerized using this polymer can improve the coulombic efficiency and cycle life of the battery, and reduce the capacity decay of the battery.

[0006] In a first aspect, this application provides a cross-linked sulfonated cation exchange polymer, the characteristic structure of which is as shown in Formula 1;

[0007] Formula 1:

[0008]

[0009] Wherein, Ar-SO3H is a sulfonated aromatic group, B-CF3 is a group with a certain three-dimensional spatial structure containing a trifluoromethyl group; the value of x ranges from 0.6 to 0.9, the value of y ranges from 0.1 to 0.4, x+y=1, and n≥100.

[0010] Furthermore, the Ar-SO3H can be any one of the following structures, where n ranges from 2 to 10:

[0011] .

[0012] Furthermore, the B-CF3 can be any of the following structures:

[0013] , ,

[0014] , .

[0015] Preferably, the cross-linked sulfonated cation exchange polymer has a weight-average molecular weight of 300,000-500,000 and a molecular weight distribution of 1.9-2.1.

[0016] Secondly, this application provides a method for preparing a cross-linked sulfonated cation exchange polymer, comprising the following preparation steps:

[0017] In an inert gas environment, sulfonated diamine monomer and triethylamine are dissolved in an organic solvent, and 1,4,5,8-naphthalenetetracarboxylic dianhydride, benzoic acid and alkynyl-containing fluorinated diamine are added and stirred. The mixture is heated to 80-140℃ and reacted for 6-10 h, and then heated to 180-220℃ and reacted for 12-24 h to obtain a cross-linked sulfonated cation exchange polymer.

[0018] Optionally, under an inert gas environment, sulfonated diamine monomer and triethylamine are dissolved in an organic solvent, and 1,4,5,8-naphthalenetetracarboxylic dianhydride, benzoic acid and alkynyl-containing fluorinated diamine are added and stirred. The mixture is then heated to 80-140℃ and reacted for 6-10 h, and then heated to 180-220℃ and reacted for 12-24 h to obtain a cross-linked sulfonated cation exchange polymer.

[0019] After cooling to 60-100℃, add an organic solvent to dilute the polymer solution concentration to 5-10% of the original concentration to obtain a polymer solution; 2) Pour the polymer solution into acetone, and after acetone extraction and drying, obtain a cation exchange polymer.

[0020] Furthermore, the sulfonated diamine monomer is any one of the following structures:

[0021] , , .

[0022] Furthermore, the alkynyl-containing fluorinated diamine monomer is any one of the following structures:

[0023] , ,

[0024] , .

[0025] Furthermore, the molar ratio of the sulfonated diamine monomer, 1,4,5,8-naphthalenetetracarboxylic dianhydride, benzoic acid, fluorinated diamine, and triethylamine is 0.6-0.9:1:1.0-1.6:0.1-0.4:1.2-2.0.

[0026] Furthermore, the organic solvent is dimethylformamide; the inert gas is nitrogen or argon.

[0027] Thirdly, this application provides a method for preparing a diaphragm, comprising the following preparation process;

[0028] The cross-linked sulfonated cation exchange polymer described in this application or the cross-linked sulfonated cation exchange polymer obtained by the method described in this application and dimethyl sulfoxide are prepared into a polymer solution with a concentration of 0.05-0.2 g / mL; then the temperature is raised to 100-120℃ and the reaction is carried out for 2-10 h to obtain a sulfonated polymer electrolyte membrane.

[0029] After the sulfonated polymer electrolyte membrane is heat-treated at 250~300℃ for 2~8h, the cross-linked membrane is acidified with dilute sulfuric acid or dilute hydrochloric acid solution to finally obtain the cation exchange polymer electrolyte membrane.

[0030] Preferably, the concentration of the dilute sulfuric acid or dilute hydrochloric acid solution is 0.5-2 mol / L.

[0031] Fourthly, this application provides a diaphragm obtained by a preparation method.

[0032] Beneficial effects: 1. This invention provides a cross-linked sulfonated cation exchange polymer. Due to the polarity difference of the polymer molecular chain segments, a large number of microphase partitions are formed inside the polymer. At the same time, the main chain has three-dimensional structural units that provide a large number of transport channels for lithium ion migration. Moreover, the presence of a large number of negatively charged ions inside the channels is conducive to promoting lithium ion dissociation, increasing the lithium ion transport rate, thereby reducing the free growth of lithium dendrites, significantly reducing the possibility of lithium dendrites penetrating the separator and contacting the positive electrode to cause a short circuit, thereby improving the battery coulombic efficiency and cycle life, and reducing the battery capacity decay. Detailed Implementation

[0033] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0034] Example 1, a method for preparing a cross-linked sulfonated cation exchange polymer electrolyte membrane, includes the following preparation steps:

[0035] 1) Preparation of 3,5,5'-tristrifluoromethyl-4,6'-diamino-6'ethynyl-3,3,3',3'-tetramethyl-1,1-spirobisindane:

[0036] Bisphenol A and methanesulfonic acid were mixed under an inert gas atmosphere and stirred at room temperature for 4 days, with the mass percentage of bisphenol A to methanesulfonic acid controlled at 3:5. After the reaction was completed, the mixture was poured into ice water, filtered, washed, and dried. It was then purified by recrystallization with anhydrous ethanol to obtain 3,3,3',3'-tetramethyl-1,1-spirobisinden-6,6'-diol with a purity of over 90%.

[0037] The obtained diol was dissolved in DMF, and anhydrous potassium carbonate and 2-chloro-5-nitrotrifluorotoluene were added. The mixture was heated to 140°C and reacted for 16 hours under nitrogen protection, with a molar ratio of diol to trifluorotoluene of 1:1.3. After the reaction was completed, the mixture was cooled to room temperature, filtered through deionized water, dried, and then washed with methanol to obtain trifluoromethyl-substituted nitrobisindenium.

[0038] Trifluoromethyl-substituted nitrobisindane intermediate was added to anhydrous ethanol, followed by 2.4% (by weight) of Pd / C catalyst. The mixture was heated to 80°C and then slowly added dropwise with hydrazine hydrate. After stirring continuously for 16 hours, the catalyst was removed by hot filtration, washed with deionized water, dried by vacuum filtration, and purified by hot washing with dichloromethane to obtain 3,5,5'-tritrifluoromethyl-4,6'-diamino-3,3,3',3'-tetramethyl-1,1-spirobisindane.

[0039] The diaminotrifluoromethyl intermediate was dissolved in a mixed solvent of triethylamine and tetrahydrofuran. Pd(PPh3)2Cl2 and CuI were added as a composite catalyst, followed by the addition of trimethylsilylacetylene. The mixture was heated to 60°C and reacted for 10 hours. After the reaction was completed, dilute hydrochloric acid was added to remove the trimethylsilyl protecting group. The product was purified by column chromatography to obtain 3,5,5'-tritrifluoromethyl-4,6'-diamino-6'acetyleno-3,3,3',3'-tetramethyl-1,1-spirobisinden.

[0040] 2) Preparation of cross-linked sulfonated polymers:

[0041] Under an inert gas environment, 2.064 g of 2,2'-benzidine disulfonic acid and 1.417 g of triethylamine were dissolved in 30 mL of DMF. Then, 2.52 g of 3,5,5'-tristrifluoromethyl-4,6'-diamino-6'ethynyl-3,3,3',3'-tetramethyl-1,1-spirobisindane, 3.228 g of 1,4,5,8-naphthalenetetracarboxylic dianhydride, and 2.017 g of benzoic acid (end-capped) were added and stirred until homogeneous. The mixture was heated to 100 °C and reacted for 10 h, then heated to 220 °C and reacted for 12 h. The mixture was then cooled to 60 °C and diluted with 70 mL of DMF to obtain a polymer solution. The polymer solution was poured into 500 mL of acetone, and after acetone extraction and drying, a cross-linked sulfonated polymer was obtained. The average weight-average molecular weight of the polymer was 400,000, and the molecular weight distribution was 2.1 ± 0.12.

[0042] .

[0043] 3) Film formation:

[0044] A sulfonated polymer and dimethyl sulfoxide were prepared into a polymer solution with a concentration of 0.1 g / mL. The filtered filtrate was poured onto a clean glass plate and dried at 80℃ for 2 h, 100℃ for 2 h, 120℃ for 2 h, and then at 120℃ under vacuum for 10 h to remove the solvent, thus obtaining a sulfonated polymer electrolyte membrane. The sulfonated polymer electrolyte membrane was placed in a high-temperature oven and heat-treated at 250℃ for 5 h, then cooled to room temperature. The cross-linked membrane was then acidified with 1.5 mol / L dilute sulfuric acid for 24 h, finally yielding a cross-linked sulfonated cation exchange polymer electrolyte membrane.

[0045] Example 2, the preparation method of the crosslinked sulfonated cation exchange polymer electrolyte membrane, differs from Example 1 in that: the step of "dissolving 2.064g of 2,2'-benzidine disulfonic acid and 1.417g of triethylamine in 30mL of DMF, adding 2.52g of 3,5,5'-tristrifluoromethyl-4,6'-diamino-6'ethynyl-3,3,3',3'-tetramethyl-1,1-spirobisindane, 3.228g of 1,4,5,8-naphthalenetetracarboxylic dianhydride and 2.017g of benzoic acid and stirring until homogeneous" is replaced with "dissolving 2.904g of 3-amino-2-decaneaminobenzenesulfonic acid-1-benzenesulfonic acid and 1.417g of triethylamine in 30mL of DMF, adding 2.52g of..." 3,5,5'-tris(trifluoromethyl)-4,6'-diamino-6'-ethynyl-3,3,3',3'-tetramethyl-1,1-spirobisindane, 3.418 g of 1,4,5,8-naphthalenetetracarboxylic dianhydride and 2.017 g of benzoic acid were stirred until homogeneous.

[0046] After extraction with acetone and drying, a cross-linked sulfonated polymer was obtained. The average weight-average molecular weight of the polymer was 400,000, and the molecular weight distribution was 2.0 ± 0.1.

[0047] .

[0048] Example 3, the preparation method of crosslinked sulfonated cation exchange polymer electrolyte membrane, differs from Example 2 in that: "2.904 g of 3-amino-2-decaneaminobenzenesulfonic acid-1-benzenesulfonic acid and 1.417 g of triethylamine were dissolved in 30 mL of LDMF, and 2.52 g of 3,5,5'-tristrifluoromethyl-4,6'-diamino-6'ethynyl-3,3,3',3'-tetramethyl-1,1-spirobisindane, 3.418 g of 1,4,5,8-naphthalenetetracarboxylic dianhydride and 2.017 g of benzoic acid were added and stirred until homogeneous." Replace with "Dissolve 2.904g of 3-amino-2-decaneaminobenzenesulfonic acid-1-benzenesulfonic acid and 1.417g of triethylamine in 30mL of DMF, add 3.168g of 9,9-bis(3-trifluoromethyl-5-amino-5-ethynyl)fluorene, 3.378g of 1,4,5,8-naphthalenetetracarboxylic dianhydride and 2.017g of benzoic acid and stir until homogeneous".

[0049] After extraction with acetone and drying, a cross-linked sulfonated polymer was obtained. The average weight-average molecular weight of the polymer was 400,000, and the molecular weight distribution was 2.0 ± 0.1.

[0050] .

[0051] Example 4, the preparation method of crosslinked sulfonated cation exchange polymer electrolyte membrane, differs from Example 2 in that the method of "dissolving 2.904 g of 3-amino-2-decaneaminobenzenesulfonic acid-1-benzenesulfonic acid and 1.417 g of triethylamine in 30 mL of LMF, adding 2.52 g of 3,5,5'-tristrifluoromethyl-4,6'-diamino-6'ethynyl-3,3,3',3'-tetramethyl-1,1-spirobisindane, 3.418 g of 1,4,5,8-naphthalenetetracarboxylic dianhydride and 2.017 g of benzoic acid and stirring until homogeneous" is replaced with "dissolving 2.904 g of 3-amino-2-decaneaminobenzenesulfonic acid-1-benzenesulfonic acid and 1.417 g of triethylamine in 30 mL of LMF". In DMF, 2.652 g of 4-ethynyl-bis(4-trifluoromethyl-3-amino)pterene, 3.338 g of 1,4,5,8-naphthalenetetracarboxylic dianhydride, and 2.017 g of benzoic acid were added and stirred until homogeneous. After extraction with acetone and drying, a cross-linked sulfonated polymer was obtained with a weight-average molecular weight of 300,000-500,000 and a molecular weight distribution of 1.9-2.1. Preparation of 4-ethynyl-bis(4-trifluoromethyl-3-amino)pterene: In anhydrous acetonitrile, cesium fluoride, 1,8-dialkoxyanthracene, and 4-trifluoromethyl-3-nitrobenzyne were added and subjected to a cycloaddition reaction at 80-100 °C in a molar ratio of 0.1:1:2.2. The cycloaddition was removed by reflux with hydrochloric acid and methanol solution to generate a triptterene intermediate containing hydroxyl, trifluoromethyl, and nitro groups. The intermediate was dissolved in ethanol, and a palladium catalyst on carbon was added at a molar ratio of 1:0.05. The mixture was stirred at room temperature under nitrogen for 8-12 h to obtain bis(4-trifluoromethyl-3-amino)triptene. Bis(4-trifluoromethyl-3-amino)triptene was then dissolved in dichloromethane, and N-bromosuccinimide was added at a molar ratio of 1:1.07. The mixture was stirred at 0 °C for 2-4 h to obtain 4-bromo-bis(4-trifluoromethyl-3-amino)triptene. 4-Bromo-bis(4-trifluoromethyl-3-amino)triptene and trimethylsilylacetylene were dissolved in a mixed solvent of triethylamine and tetrahydrofuran. Pd(PPh3)2Cl2 and CuI were added as composite catalysts. The molar ratio of 4-bromo intermediate:trimethylsilylacetylene:Pd(PPh3)2Cl2:CuI:triacetylene was 1:1.5:0.05:0.1:3. The mixture was refluxed for 6-8 h to obtain 4-acetylenyl-bis(4-trifluoromethyl-3-amino)triptene.

[0052] .

[0053] Comparative Example 1, the preparation method of the cross-linked sulfonated cation exchange polymer electrolyte membrane differs from that of Example 1 in that "2.064 g of 2,2'-benzidine disulfonic acid and 1.417 g of triethylamine are dissolved in 30 mL of DMF, and 2.52 g of 3,5,5'-tristrifluoromethyl-4,6'-diamino-6'ethynyl-3,3,3',3'-tetramethyl-1,1-spirobisindane, 3.228 g of 1,4,5,8-naphthalenetetracarboxylic dianhydride and 2.017 g of benzoic acid are added and stirred until homogeneous." The solution was changed to: "Dissolve 2.064 g of 2,2'-benzidine disulfonic acid and 1.417 g of triethylamine in 30 mL of DMF, add 1.819 g of 2,7-diamino-6-trifluoromethyl-acetylenenaphthalene, 3.228 g of 1,4,5,8-naphthalenetetracarboxylic dianhydride and 2.017 g of benzoic acid, and stir until homogeneous." After acetone extraction and drying, a cross-linked sulfonated polymer was obtained. The polymer had a weight-average molecular weight of 400,000 and a molecular weight distribution of 2.0 ± 0.1.

[0054] Preparation of 2,7-diamino-6-trifluoromethyl-acetylenenaphthalene: Concentrated sulfuric acid, concentrated nitric acid, and 1,6-dimethoxynaphthalene were slowly added to dichloromethane in a molar ratio of 2:2.2:1. The mixture was stirred at room temperature for 4-6 hours. The reaction solution was poured into ice water and extracted three times with dichloromethane. The solution was washed with saturated brine and dried over anhydrous magnesium sulfate to obtain 2,7-dinitro-1,6-dimethoxynaphthalene. Under nitrogen protection, 2,7-dinitro-1,6-dimethoxynaphthalene was dissolved in anhydrous dichloromethane. A dichloromethane solution of boron tribromide and trifluorotrimethylsilane were added dropwise. The mixture was stirred at room temperature for 12 hours in a molar ratio of boron tribromide:trifluorotrimethylsilane:1,6-dimethoxynaphthalene of 4:2:1. N-bromosuccinimide, trimethylsilylacetylene, Pd(PPh3)2Cl2 and CuI were added, and the mixture was refluxed for 7±1 h. The molar ratio of N-bromosuccinimide:trimethylsilylacetylene:1,6-dimethoxynaphthalene was 1:1.5:1 to obtain 2,7-diamino-6-trifluoromethyl-acetylenenaphthalene.

[0055]

[0056] Comparative Example 2, the preparation method of the crosslinked sulfonated cation exchange polymer electrolyte membrane differs from that of Example 1 in that: the method of "dissolving 2.064 g of 2,2'-benzidine disulfonic acid and 1.417 g of triethylamine in 30 mL of DMF, adding 2.52 g of 3,5,5'-tristrifluoromethyl-4,6'-diamino-6'ethynyl-3,3,3',3'-tetramethyl-1,1-spirobisindane, 3.228 g of 1,4,5,8-naphthalenetetracarboxylic dianhydride and 2.017 g of benzoic acid and stirring until homogeneous" is replaced with "dissolving 2.064 g of benzidine and 1.417 g of triethylamine in 30 mL of DMF, adding 2.33 g of 4,6'-diamino-6'ethynyl-3,3,3',3'-tetramethyl-1,1-spirobisindane, 3.228 g of..." "1,4,5,8-Naphthalenetetracarboxylic dianhydride and 2.017 g of benzoic acid were stirred evenly." After extraction with acetone and drying, a cross-linked sulfonated polymer was obtained. The polymer had an average weight-average molecular weight of 400,000 and a molecular weight distribution of 2.0 ± 0.1.

[0057] Preparation of 4,6'-diamino-6'-ethynyl-3,3,3',3'-tetramethyl-1,1-spirobis-indane: 2,2'-dimethylenebis(2-methylpropionitrile), isoprene, and p-toluenesulfonic acid were dissolved in anhydrous toluene at a molar ratio of 1:2.5:0.05. The mixture was refluxed at 110 °C for 16-20 h under nitrogen protection to obtain 3,3,3',3'-tetramethyl-1,1-spirobis-indane. The reaction solution was cooled to 0-5 °C in an ice-water bath, and fuming nitric acid and acetic anhydride were slowly added dropwise at a molar ratio of bis-indane:nitric acid:acetic anhydride of 1:2.2:5. The mixture was stirred at 0 °C for 2 h, then heated to room temperature and reacted for another 3 h to obtain 4,6'-diamino-3,3,3',3'-tetramethyl-1,1-spirobis-indane. The bis-indene intermediate was dissolved in anhydrous carbon tetrachloride, and bromosuccinimide and azobisisobutyronitrile were added in a molar ratio of 1:1.05:0.02. The mixture was refluxed at 80°C for 4-5 h under nitrogen protection to give 6-bromo-4,6'-diamino-3,3,3',3'-tetramethyl-1,1-spirobis-indene. The 6-bromo intermediate was dissolved in anhydrous tetrahydrofuran, and trimethylsilylacetylene, Pd(PPh3)2Cl2, CuI, and triethylamine were added in a molar ratio of 1:1.5:0.05:0.1:3. The mixture was refluxed at 60°C for 8-10 h under nitrogen protection. The solvent was removed by rotary evaporation, and the mixture was extracted with dichloromethane to give 4,6'-diamino-6'acetylene-3,3,3',3'-tetramethyl-1,1-spirobis-indene.

[0058]

[0059] Comparative Example 3, the preparation method of the crosslinked sulfonated cation exchange polymer electrolyte membrane differs from that of Example 1 in that: "2.064 g of 2,2'-benzidine disulfonic acid and 1.417 g of triethylamine were dissolved in 30 mL of DMF, and 2.52 g of 3,5,5'-tristrifluoromethyl-4,6'-diamino-6'ethynyl-3,3,3',3'-tetramethyl-1,1-spirobisindane, 3.228 g of 1,4,5,8-naphthalenetetracarboxylic dianhydride and 2.017 g of benzoic acid were added and stirred until homogeneous." Replace with "Dissolve 2.064g benzidine and 1.417g triethylamine in 30mL DMF, add 2.52g 3,5,5'-tristrifluoromethyl-4,6'-diamino-6'ethynyl-3,3,3',3'-tetramethyl-1,1-spirobisindane, 3.228g 1,4,5,8-naphthalenetetracarboxylic dianhydride and 2.017g benzoic acid and stir until homogeneous."

[0060] After extraction with acetone and drying, a cross-linked sulfonated polymer was obtained. The average weight-average molecular weight of the polymer was 400,000, and the molecular weight distribution was 2.0 ± 0.1.

[0061] .

[0062] Physicochemical performance testing of the diaphragm:

[0063] The physicochemical properties of Examples 1-4, as well as the PE-based film and the PE / Al2O3 film, were characterized. The surface density, air permeability, and heat shrinkage were tested in accordance with BG / T36363-2018. The results are shown in Table 1.

[0064] Electrical performance testing:

[0065] 1) Ionic conductivity test:

[0066] The cross-linked sulfonated cation exchange polymer electrolyte membranes prepared in the examples and comparative examples were subjected to ionic conductivity testing according to the following steps: A resistance testing mold (stainless steel symmetrical electrode button mold: thickness 0.6 cm, cross-sectional area 1.267 cm²) was cut and prepared. 2 Four matching diaphragms were prepared and immersed in an electrolyte solution with a concentration of 1.0 mol / L lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a 1:1:1 volume ratio for 2 hours, keeping the solution sealed. The electrolyte solution was then injected into a resistance testing mold. One diaphragm was placed in the mold, and its AC impedance was measured. Another diaphragm was added, and the AC impedance was measured again, until all four diaphragms were used. The AC impedances R1, R2, R3, and R4 were measured. During the test, it was ensured that the electrolyte in the resistance testing mold completely submerged the placed diaphragms.

[0067] 2) 45℃ high-temperature cycling test:

[0068] The cross-linked sulfonated cation exchange polymer electrolyte membranes obtained in the examples and comparative examples were assembled into pouch batteries. A 45°C high-temperature cycling test was conducted according to the following steps: A pre-capacitated lithium-ion battery was placed in a 45°C constant-temperature chamber and left to stand for at least one hour to ensure the internal temperature of the battery was close to 45°C. Then, it was charged at a constant current and constant voltage of 1C, with a cutoff voltage of 3.65V and a cutoff current of 0.05C. Next, it was discharged at a constant current of 1C to 2.5V. The battery was cycled according to the above steps, and the discharge capacity retention rate after 300 cycles was recorded. The discharge capacity retention rate after 300 cycles was calculated by dividing the discharge capacity after the first cycle by the discharge capacity of the first cycle. Specific test data are shown in Table 1.

[0069] Table 1. Performance list of diaphragms in the examples and comparative examples.

[0070] sample Thickness / μm <![CDATA[Areal density / g / m 2 > Breathability sec / 100cc Heat shrinkage at 130℃ for 1 hour (%) (MD / TD) <![CDATA[Room temperature ionic conductivity (ms cm -1 ).]]> Capacity retention rate (%) after 300 cycles at 45℃ Example 1 12.6 4.1 92.1 1.1 / 0.7 0.62 84.3 Example 2 13.1 4.8 102.4 2.6 / 1.4 0.79 86.1 Example 3 13.7 4.4 84.2 1.8 / 0.4 0.84 87.7 Example 4 13.4 4.3 80.1 1.4 / 0.9 0.87 87.3 PE base film 9.1 5.2 145 4.1 / 3.9 <![CDATA[6*10 -4 ]]> 76.4 <![CDATA[PE / Al2O3 film]]> 12.2 8.1 152 0.8 / 0.6 0.41 81.2 Comparative Example 1 13.3 3.7 121.6 1.3 / 1.2 0.47 65.1 Comparative Example 2 13.4 4.0 101.5 1.2 / 1.2 0.56 77.6 Comparative Example 3 13.7 4.1 95.3 1.7 / 1.1 0.57 78.2

[0071] Compared with Comparative Example 2, Example 1 has a lower air permeability value and a higher ionic conductivity value, indicating that the polarity difference between polymer molecular chain segments can increase the microphase partitioning inside the membrane to a certain extent, providing corresponding ion transport channels for lithium ion migration.

[0072] Comparing the air permeability values, room temperature ionic conductivity, and high temperature cycling capacity retention data of Example 1, Comparative Example 1, Example 3, and Example 4, it can be found that the polymer backbone has three-dimensional structural units, and the greater the steric hindrance, the stronger the rigidity of the configuration, and the more ion transport channels inside the membrane, which is more conducive to the transport of lithium ions and the improvement of cycle life.

[0073] Comparing the ionic conductivity and cycle capacity retention data of Example 1 with those of Example 2 and Comparative Example 3, it can be found that increasing the negative charge density inside the separator is beneficial to promoting lithium ion dissociation, improving ion transport rate, reducing battery capacity decay, and thus improving battery cycle life.

[0074] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A cross-linked sulfonated cation exchange polymer, characterized in that, Its characteristic structure As shown in equation 1; Formula 1: Wherein, Ar-SO3H is a sulfonated aromatic group, B-CF3 is a group with a certain three-dimensional spatial structure containing a trifluoromethyl group; the value of x ranges from 0.6 to 0.9, the value of y ranges from 0.1 to 0.4, x+y=1, and n≥100.

2. The cross-linked sulfonated cation exchange polymer according to claim 1, characterized in that, The Ar-SO3H can be any one of the following structures, where n ranges from 2 to 10: 。 3. A cross-linked sulfonated cation exchange polymer according to claim 1 or 2, characterized in that, The B-CF3 is any one of the following structures: ， ， ， 。 4. A method for preparing the cross-linked sulfonated cation exchange polymer according to any one of claims 1-3, characterized in that, The preparation steps include the following: In an inert gas environment, sulfonated diamine monomer and triethylamine are dissolved in an organic solvent, and 1,4,5,8-naphthalenetetracarboxylic dianhydride, benzoic acid and alkynyl-containing fluorinated diamine are added and stirred. The mixture is heated to 80-140℃ and reacted for 6-10 h, and then heated to 180-220℃ and reacted for 12-24 h to obtain a cross-linked sulfonated cation exchange polymer.

5. The method for preparing a cross-linked sulfonated cation exchange polymer according to claim 4, characterized in that, The sulfonated diamine monomer is any one of the following structures: ， ， 。 6. A method for preparing a cross-linked sulfonated cation exchange polymer according to claim 4 or 5, characterized in that, The alkynyl-containing fluorinated diamine monomer is any one of the following structures: ， ， ， 。 7. The method for preparing a cross-linked sulfonated cation exchange polymer according to claim 6, characterized in that, The molar ratio of the sulfonated diamine monomer, 1,4,5,8-naphthalenetetracarboxylic dianhydride, benzoic acid, fluorinated diamine, and triethylamine is 0.6-0.9:1:1.0-1.6:0.1-0.4:1.2-2.

0.

8. The method for preparing a cross-linked sulfonated cation exchange polymer according to claim 4, characterized in that, The organic solvent is dimethylformamide; the inert gas is nitrogen or argon.

9. A method for preparing a diaphragm, characterized in that, The preparation process includes the following steps; The cross-linked sulfonated cation exchange polymer according to any one of claims 1-3 or the cross-linked sulfonated cation exchange polymer obtained by the method according to any one of claims 4-7 and dimethyl sulfoxide are prepared into a polymer solution with a concentration of 0.05-0.2 g / mL; then the temperature is raised to 100-120℃ and the reaction is carried out for 2-10 h to obtain a sulfonated polymer electrolyte membrane. After the sulfonated polymer electrolyte membrane is heat-treated at 250~300℃ for 2~8h, the cross-linked membrane is acidified with dilute sulfuric acid or dilute hydrochloric acid solution to finally obtain the cation exchange polymer electrolyte membrane.

10. A diaphragm, characterized in that, It is obtained by the preparation method described in claim 9.

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