A composite solid electrolyte membrane for lithium batteries and a method for preparing the same

Abstract

The application belongs to the technical field of lithium ion batteries, and particularly relates to a composite solid electrolyte membrane for lithium batteries and a preparation method thereof. The polyimidazole salt and modified mesoporous molecular sieve are used as additives of the solid electrolyte membrane. The polyimidazole salt is synthesized by using a Debus-Radziszewski reaction, and the polyimidazole salt has alkyl chains with different carbon atom numbers in the main chain. The appropriate carbon chain length can effectively enhance the ion conductivity and flexibility of the electrolyte membrane. The modified mesoporous molecular sieve has an ordered pore structure, a large specific surface area and good dispersibility, and can enhance the mechanical strength of the solid polymer electrolyte, improve the ion conductivity and cycle stability of the lithium ion battery. The two synergize, greatly improving the ion conductivity and flexibility of the electrolyte membrane.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically a composite solid electrolyte membrane for lithium batteries and its preparation method. Background Technology

[0002] Lithium-ion batteries are an important rechargeable battery technology widely used in electric vehicles, portable devices, and energy storage systems. Traditional lithium-ion batteries use liquid electrolytes, but liquid electrolytes present a series of safety and stability issues, such as battery combustion, leakage, and evaporation. Therefore, in recent years, researchers have focused on developing safer, more stable, and higher-performing electrolyte materials, among which composite solid electrolyte membranes have attracted considerable attention as a potential alternative.

[0003] Traditional liquid electrolytes, such as organic solvents and salt solutions, pose safety hazards due to their flammability, high volatility, and tendency to generate gases at high temperatures. Furthermore, liquid electrolytes are highly sensitive to temperature and external pressure, which can lead to fluctuations and degradation in battery performance.

[0004] The composite solid-state electrolyte membrane, composed of a polymer matrix and ceramic particles, exhibits excellent ionic conductivity and chemical stability, effectively addressing the problems of traditional liquid electrolytes. Simultaneously, the composite solid-state electrolyte can suppress lithium dendrite formation, thereby improving battery cycle life.

[0005] The polymer matrix is ​​the main component of the composite solid electrolyte, commonly including polyethylene oxide (PEO) and polyacrylonitrile (PAN). These polymers possess high molecular chain flexibility, providing sufficient mechanical strength and flexibility while maintaining high lithium-ion conductivity. Introducing ceramic particles, such as lithium oxide (Li₂O), helps improve the ionic conductivity of the composite solid electrolyte. The ceramic particles form a network structure within the polymer matrix, facilitating the passage of lithium ions and thus enhancing the battery's conductivity.

[0006] The technology for preparing composite solid electrolytes is constantly developing. Electrolyte membranes with a certain thickness and uniformity can be prepared using methods such as casting, solution impregnation, and stretching. The influence of controlling conditions such as temperature, humidity, and pressure during the preparation process on the performance of electrolyte membranes is being increasingly studied.

[0007] Composite solid-state electrolyte membranes, as a key component of lithium-ion batteries, offer enhanced safety and stability, and are expected to find widespread application in electric vehicles, wearable devices, and energy storage systems. Continuous improvements in their performance will drive the development of lithium-ion battery technology, leading to higher energy density, longer lifespan, and safer, more reliable battery systems.

[0008] Overall, composite solid electrolyte membranes have great potential in the field of lithium battery technology, and their research and development will provide strong support for the advancement of future energy storage technology. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention discloses a composite solid electrolyte membrane for lithium batteries and its preparation method.

[0010] A composite solid electrolyte membrane for lithium batteries comprises the following components: a polymer matrix, a lithium salt, a polyimide salt, and a modified mesoporous molecular sieve.

[0011] Preferably, the composite solid electrolyte membrane for lithium batteries is composed of the following components by mass: 90-110 parts polymer matrix, 1-20 parts lithium salt, 10-20 parts polyimide salt, and 10-15 parts modified mesoporous molecular sieve.

[0012] The polymer matrix is ​​a polymer electrolyte commonly used in the art, and can be selected from at least one of polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polycarbonate, and polyacrylate; preferably, the present invention uses polyvinylidene fluoride as the polymer matrix.

[0013] Polyvinylidene fluoride (PVDF) exhibits excellent chemical stability, resisting the attack of many chemicals. This allows it to maintain stability in electrolyte membranes for extended periods and resist chemical degradation. As a polar polymer, it possesses high polarizability and dielectric constant, which contributes to improving the ionic conductivity of solid electrolyte membranes. PVDF also demonstrates good thermal stability, maintaining its physical and electrical properties over a wide temperature range, making it suitable for various operating conditions. Furthermore, PVDF exhibits good solubility in some solvents, which facilitates the control of its structure and properties during film preparation. However, while PVDF is flexible, its crystallinity in the polymer chain can lead to relatively poor processability. This may pose challenges to membrane preparation and molding. Compared to some other solid electrolyte materials, PVDF may have lower ionic conductivity. This could be a disadvantage in applications requiring high ionic conductivity.

[0014] The lithium salt is at least one of lithium perchlorate, lithium hexafluorophosphate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium dioxalate borate, and lithium nitrate; preferably, lithium tetrafluoroborate is used as the lithium salt of the present invention, which has high electrical conductivity and good chemical stability.

[0015] The polyimidazolium salt is a main-chain alkylated polyimidazolium salt, the main chain of which is composed of alternating imidazole groups and alkyl groups.

[0016] The preparation method of the polyimide salt includes the following steps:

[0017] 90-110 mmol of diamine and 20-30 mL of water were mixed and cooled in an ice-water bath to obtain a mixture. 20-30 mL of 37 wt% hydrochloric acid aqueous solution was added to the mixture to obtain an acidic diamine solution. A mixture of 8-9 g of formaldehyde and 14-15 g of glyoxal was added dropwise to the acidic diamine solution, and then refluxed at 75-85 °C for 4-5 h. The solvent and unreacted monomers were removed by rotary evaporation to obtain the polyimide salt.

[0018] The diamine is one of 1,4-diaminobutane, 1,6-diaminohexane, 1,8-diaminooctane, 1,10-diaminodecane, and 1,12-diaminododecane; preferably, the diamine is 1,8-diaminooctane.

[0019] This invention synthesizes polyimidazolium salts with alkyl chains having different numbers of carbon atoms in the main chain using the Debus-Radziszewski reaction. The invention reveals that the length of the carbon chain significantly affects the performance of polyimidazolium salts. By adding polyimidazolium salts with different carbon chain lengths to electrolyte membranes, it was found that longer carbon chains significantly enhance the flexibility, high-temperature resistance, and corrosion resistance of the electrolyte membrane. However, longer carbon chains hinder ion transport, reducing the ionic conductivity of the electrolyte membrane. Conversely, shorter carbon chains reduce the toughness of the electrolyte membrane, exhibiting significant brittleness, making it prone to cracking or breakage during practical use. This may affect the mechanical stability and lifespan of the electrolyte membrane. Therefore, this invention preferably uses polyimidazolium salts with eight carbon atoms synthesized from 1,8-diaminooctane, which exhibits excellent flexibility, high-temperature resistance, and corrosion resistance, while having a relatively small impact on the ionic conductivity of the electrolyte membrane.

[0020] The reaction process for synthesizing polyimidazolium salt from 1,8-diaminooctane is as follows:

[0021]

[0022] The preparation method of the modified mesoporous molecular sieve includes the following steps:

[0023] S1. Mesoporous molecular sieves were added to a 9-11 mmol / L Tris buffer solution and ultrasonically dispersed to obtain a mesoporous molecular sieve suspension.

[0024] S2. Add dopamine to the mesoporous molecular sieve suspension obtained in step S1 to obtain a precursor suspension. Stir at 40-50℃ for 6-8 hours, and then filter, wash and dry to obtain the modified mesoporous molecular sieve.

[0025] The ultrasonic power is 600-800W and the frequency is 40-80kHz.

[0026] The concentration of dopamine in the precursor suspension is 10-30 mmol / L, and the mass-to-volume ratio of the amount of mesoporous molecular sieve added to the Tris buffer solution is 1 g: (5-20) L.

[0027] Mesoporous molecular sieves possess an ordered pore structure, a large specific surface area, and nanoscale particle size. The surface voids formed during stacking and their unique mesoporous channels facilitate ion entry and passage. Furthermore, as an inorganic particle, mesoporous molecular sieves can improve the mechanical properties of polymer electrolyte membranes while simultaneously enhancing their ionic conductivity. However, like most inorganic particles, they exhibit poor dispersibility in polymers. Therefore, this invention employs polydopamine coating to anchor the mesoporous molecular sieves within the polymer cross-linking network. This enhances the mechanical strength of the solid polymer electrolyte, improves its dispersibility in the polymer matrix, facilitates the suppression of lithium dendrites, and ultimately improves the ionic conductivity and cycle stability of lithium-ion batteries.

[0028] A composite solid electrolyte membrane for lithium batteries and its preparation method, comprising the following steps:

[0029] Polyvinylidene fluoride (PVDF) and acetone solution are mixed and stirred at 50-60°C until PVDF dissolves in acetone to form a transparent sol. After 0.5-1 h, lithium salt, polyimidazolium salt, and modified mesoporous molecular sieve are added to the PVDF sol, and stirring and sonication are continued for 0.5-1 h. Then, a certain amount of pore-forming agent dimethyl carbonate is added, and after mixing evenly, the reaction is continued at a constant temperature and stirred for 4-8 h to obtain a uniform and transparent casting solution. After cooling to room temperature, the solution is coated onto a film, the film is peeled off, and dried at 80-90°C for 24-36 h to obtain the composite solid electrolyte membrane for lithium batteries.

[0030] The ultrasonic power is 600-800W and the frequency is 40-80kHz.

[0031] The beneficial effects of this invention are:

[0032] This invention uses polyimidazolium salts and modified mesoporous molecular sieves as additives for solid electrolyte membranes. The polyimidazolium salts used are synthesized via the Debus-Radziszewski reaction, employing alkyl chains with varying carbon atom numbers in their main chains. Appropriate carbon chain lengths effectively enhance the ionic conductivity and flexibility of the electrolyte membrane. The modified mesoporous molecular sieves, with their ordered pore structure, large specific surface area, and good dispersibility, enhance the mechanical strength of the solid polymer electrolyte and improve the ionic conductivity and cycle stability of lithium-ion batteries. The synergistic effect of these two additives significantly improves the ionic conductivity and flexibility of the electrolyte membrane. Detailed Implementation

[0033] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0034] Polyvinylidene fluoride, item number: FR904 W, Shanghai Sanaifu New Materials Co., Ltd.

[0035] Mesoporous molecular sieve, product number: DM-2, Shandong Dengzhuo Chemical Co., Ltd.

[0036] Example 1

[0037] A composite solid electrolyte membrane for lithium batteries, comprising, by mass, the following components: 100 parts polymer matrix, 12 parts lithium salt, 16 parts polyimide salt, and 14 parts modified mesoporous molecular sieve.

[0038] The polymer matrix is ​​polyvinylidene fluoride.

[0039] The lithium salt is lithium tetrafluoroborate.

[0040] The preparation method of the polyimide salt includes the following steps:

[0041] 100 mmol of 1,4-diaminobutane and 25 mL of water were mixed and cooled in an ice-water bath to obtain a mixture. 25 mL of 37 wt% hydrochloric acid aqueous solution was added to the mixture to obtain an acidic diamine solution. A mixture of 8.12 g of formaldehyde and 14.51 g of glyoxal was added dropwise to the acidic diamine solution, and then refluxed at 80 °C for 4 h. The solvent and unreacted monomers were removed by rotary evaporation to obtain the polyimide salt.

[0042] The preparation method of the modified mesoporous molecular sieve includes the following steps:

[0043] S1. Mesoporous molecular sieves were added to a 10 mmol / L Tris buffer solution and ultrasonically dispersed to obtain a mesoporous molecular sieve suspension.

[0044] S2. Add dopamine to the mesoporous molecular sieve suspension obtained in step S1 to obtain a precursor suspension. Stir at 45°C for 7 hours, and then filter, wash and dry to obtain the modified mesoporous molecular sieve.

[0045] The ultrasonic power is 600W and the frequency is 60kHz.

[0046] The concentration of dopamine in the precursor suspension is 20 mmol / L, and the mass-to-volume ratio of the added mesoporous molecular sieve to the Tris buffer solution is 1 g: 10 L.

[0047] A composite solid electrolyte membrane for lithium batteries and its preparation method, comprising the following steps:

[0048] By weight, 100 parts of polyvinylidene fluoride (PVDF) and 600 parts of acetone solution were mixed and stirred at 55°C until PVDF dissolved in acetone to form a transparent sol. After 0.5 h, 12 parts of lithium salt, 16 parts of polyimidezazole salt, and 14 parts of modified mesoporous molecular sieve were added to the PVDF sol, and the mixture was stirred and sonicated for another 0.5 h. Then, a certain amount of pore-forming agent dimethyl carbonate was added, and the mixture was mixed evenly. The mixture was stirred and reacted at a constant temperature for another 6 h to obtain a uniform and transparent casting solution. After cooling to room temperature, the solution was coated onto a film, the film was peeled off, and dried at 90°C for 36 h to obtain the composite solid electrolyte membrane for lithium batteries.

[0049] The ultrasonic power is 600W and the frequency is 60kHz.

[0050] Example 2

[0051] A composite solid electrolyte membrane for lithium batteries, comprising, by mass, the following components: 100 parts polymer matrix, 12 parts lithium salt, 16 parts polyimide salt, and 14 parts modified mesoporous molecular sieve.

[0052] The polymer matrix is ​​polyvinylidene fluoride.

[0053] The lithium salt is lithium tetrafluoroborate.

[0054] The preparation method of the polyimide salt includes the following steps:

[0055] 100 mmol of 1,6-diaminohexane and 25 mL of water were mixed and cooled in an ice-water bath to obtain a mixture. 25 mL of 37 wt% hydrochloric acid aqueous solution was added to the mixture to obtain an acidic diamine solution. A mixture of 8.12 g of formaldehyde and 14.51 g of glyoxal was added dropwise to the acidic diamine solution, and then the mixture was refluxed at 80 °C for 4 h. The solvent and unreacted monomers were removed by rotary evaporation to obtain the polyimide salt.

[0056] The preparation method of the modified mesoporous molecular sieve includes the following steps:

[0057] S1. Mesoporous molecular sieves were added to a 10 mmol / L Tris buffer solution and ultrasonically dispersed to obtain a mesoporous molecular sieve suspension.

[0058] S2. Add dopamine to the mesoporous molecular sieve suspension obtained in step S1 to obtain a precursor suspension. Stir at 45°C for 7 hours, and then filter, wash and dry to obtain the modified mesoporous molecular sieve.

[0059] The ultrasonic power is 600W and the frequency is 60kHz.

[0060] The concentration of dopamine in the precursor suspension is 20 mmol / L, and the mass-to-volume ratio of the added mesoporous molecular sieve to the Tris buffer solution is 1 g: 10 L.

[0061] A composite solid electrolyte membrane for lithium batteries and its preparation method, comprising the following steps:

[0062] By weight, 100 parts of polyvinylidene fluoride (PVDF) and 600 parts of acetone solution were mixed and stirred at 55°C until PVDF dissolved in acetone to form a transparent sol. After 0.5 h, 12 parts of lithium salt, 16 parts of polyimidezazole salt, and 14 parts of modified mesoporous molecular sieve were added to the PVDF sol, and the mixture was stirred and sonicated for another 0.5 h. Then, a certain amount of pore-forming agent dimethyl carbonate was added, and the mixture was mixed evenly. The mixture was stirred and reacted at a constant temperature for another 6 h to obtain a uniform and transparent casting solution. After cooling to room temperature, the solution was coated onto a film, the film was peeled off, and dried at 90°C for 36 h to obtain the composite solid electrolyte membrane for lithium batteries.

[0063] The ultrasonic power is 600W and the frequency is 60kHz.

[0064] Example 3

[0065] A composite solid electrolyte membrane for lithium batteries, comprising, by mass, the following components: 100 parts polymer matrix, 12 parts lithium salt, 16 parts polyimide salt, and 14 parts modified mesoporous molecular sieve.

[0066] The polymer matrix is ​​polyvinylidene fluoride.

[0067] The lithium salt is lithium tetrafluoroborate.

[0068] The preparation method of the polyimide salt includes the following steps:

[0069] 100 mmol of 1,8-diaminooctane and 25 mL of water were mixed and cooled in an ice-water bath to obtain a mixture. 25 mL of 37 wt% hydrochloric acid aqueous solution was added to the mixture to obtain an acidic diamine solution. A mixture of 8.12 g of formaldehyde and 14.51 g of glyoxal was added dropwise to the acidic diamine solution, and then refluxed at 80 °C for 4 h. The solvent and unreacted monomers were removed by rotary evaporation to obtain the polyimide salt.

[0070] The preparation method of the modified mesoporous molecular sieve includes the following steps:

[0071] S1. Mesoporous molecular sieves were added to a 10 mmol / L Tris buffer solution and ultrasonically dispersed to obtain a mesoporous molecular sieve suspension.

[0072] S2. Add dopamine to the mesoporous molecular sieve suspension obtained in step S1 to obtain a precursor suspension. Stir at 45°C for 7 hours, and then filter, wash and dry to obtain the modified mesoporous molecular sieve.

[0073] The ultrasonic power is 600W and the frequency is 60kHz.

[0074] The concentration of dopamine in the precursor suspension is 20 mmol / L, and the mass-to-volume ratio of the added mesoporous molecular sieve to the Tris buffer solution is 1 g: 10 L.

[0075] A composite solid electrolyte membrane for lithium batteries and its preparation method, comprising the following steps:

[0076] By weight, 100 parts of polyvinylidene fluoride (PVDF) and 600 parts of acetone solution were mixed and stirred at 55°C until PVDF dissolved in acetone to form a transparent sol. After 0.5 h, 12 parts of lithium salt, 16 parts of polyimidezazole salt, and 14 parts of modified mesoporous molecular sieve were added to the PVDF sol, and the mixture was stirred and sonicated for another 0.5 h. Then, a certain amount of pore-forming agent dimethyl carbonate was added, and the mixture was mixed evenly. The mixture was stirred and reacted at a constant temperature for another 6 h to obtain a uniform and transparent casting solution. After cooling to room temperature, the solution was coated onto a film, the film was peeled off, and dried at 90°C for 36 h to obtain the composite solid electrolyte membrane for lithium batteries.

[0077] The ultrasonic power is 600W and the frequency is 60kHz.

[0078] Example 4

[0079] A composite solid electrolyte membrane for lithium batteries, comprising, by mass, the following components: 100 parts polymer matrix, 12 parts lithium salt, 16 parts polyimide salt, and 14 parts modified mesoporous molecular sieve.

[0080] The polymer matrix is ​​polyvinylidene fluoride.

[0081] The lithium salt is lithium tetrafluoroborate.

[0082] The preparation method of the polyimide salt includes the following steps:

[0083] 100 mmol of 1,10-diaminodecane and 25 mL of water were mixed and cooled in an ice-water bath to obtain a mixture. 25 mL of 37 wt% hydrochloric acid aqueous solution was added to the mixture to obtain an acidic diamine solution. A mixture of 8.12 g of formaldehyde and 14.51 g of glyoxal was added dropwise to the acidic diamine solution, and then the mixture was refluxed at 80 °C for 4 h. The solvent and unreacted monomers were removed by rotary evaporation to obtain the polyimide salt.

[0084] The preparation method of the modified mesoporous molecular sieve includes the following steps:

[0085] S1. Mesoporous molecular sieves were added to a 10 mmol / L Tris buffer solution and ultrasonically dispersed to obtain a mesoporous molecular sieve suspension.

[0086] S2. Add dopamine to the mesoporous molecular sieve suspension obtained in step S1 to obtain a precursor suspension. Stir at 45°C for 7 hours, and then filter, wash and dry to obtain the modified mesoporous molecular sieve.

[0087] The ultrasonic power is 600W and the frequency is 60kHz.

[0088] The concentration of dopamine in the precursor suspension is 20 mmol / L, and the mass-to-volume ratio of the added mesoporous molecular sieve to the Tris buffer solution is 1 g: 10 L.

[0089] A composite solid electrolyte membrane for lithium batteries and its preparation method, comprising the following steps:

[0090] By weight, 100 parts of polyvinylidene fluoride (PVDF) and 600 parts of acetone solution were mixed and stirred at 55°C until PVDF dissolved in acetone to form a transparent sol. After 0.5 h, 12 parts of lithium salt, 16 parts of polyimidezazole salt, and 14 parts of modified mesoporous molecular sieve were added to the PVDF sol, and the mixture was stirred and sonicated for another 0.5 h. Then, a certain amount of pore-forming agent dimethyl carbonate was added, and the mixture was mixed evenly. The mixture was stirred and reacted at a constant temperature for another 6 h to obtain a uniform and transparent casting solution. After cooling to room temperature, the solution was coated onto a film, the film was peeled off, and dried at 90°C for 36 h to obtain the composite solid electrolyte membrane for lithium batteries.

[0091] The ultrasonic power is 600W and the frequency is 60kHz.

[0092] Example 5

[0093] A composite solid electrolyte membrane for lithium batteries, comprising, by mass, the following components: 100 parts polymer matrix, 12 parts lithium salt, 16 parts polyimide salt, and 14 parts modified mesoporous molecular sieve.

[0094] The polymer matrix is ​​polyvinylidene fluoride.

[0095] The lithium salt is lithium tetrafluoroborate.

[0096] The preparation method of the polyimide salt includes the following steps:

[0097] 100 mmol of 1,12-diaminododecane and 25 mL of water were mixed and cooled in an ice-water bath to obtain a mixture. 25 mL of 37 wt% hydrochloric acid aqueous solution was added to the mixture to obtain an acidic diamine solution. A mixture of 8.12 g of formaldehyde and 14.51 g of glyoxal was added dropwise to the acidic diamine solution, and then refluxed at 80 °C for 4 h. The solvent and unreacted monomers were removed by rotary evaporation to obtain the polyimide salt.

[0098] The preparation method of the modified mesoporous molecular sieve includes the following steps:

[0099] S1. Mesoporous molecular sieves were added to a 10 mmol / L Tris buffer solution and ultrasonically dispersed to obtain a mesoporous molecular sieve suspension.

[0100] S2. Add dopamine to the mesoporous molecular sieve suspension obtained in step S1 to obtain a precursor suspension. Stir at 45°C for 7 hours, and then filter, wash and dry to obtain the modified mesoporous molecular sieve.

[0101] The ultrasonic power is 600W and the frequency is 60kHz.

[0102] The concentration of dopamine in the precursor suspension is 20 mmol / L, and the mass-to-volume ratio of the added mesoporous molecular sieve to the Tris buffer solution is 1 g: 10 L.

[0103] A composite solid electrolyte membrane for lithium batteries and its preparation method, comprising the following steps:

[0104] By weight, 100 parts of polyvinylidene fluoride (PVDF) and 600 parts of acetone solution were mixed and stirred at 55°C until PVDF dissolved in acetone to form a transparent sol. After 0.5 h, 12 parts of lithium salt, 16 parts of polyimidezazole salt, and 14 parts of modified mesoporous molecular sieve were added to the PVDF sol, and the mixture was stirred and sonicated for another 0.5 h. Then, a certain amount of pore-forming agent dimethyl carbonate was added, and the mixture was mixed evenly. The mixture was stirred and reacted at a constant temperature for another 6 h to obtain a uniform and transparent casting solution. After cooling to room temperature, the solution was coated onto a film, the film was peeled off, and dried at 90°C for 36 h to obtain the composite solid electrolyte membrane for lithium batteries.

[0105] The ultrasonic power is 600W and the frequency is 60kHz.

[0106] Comparative Example 1

[0107] A composite solid electrolyte membrane for lithium batteries, comprising, by mass, the following components: 100 parts polymer matrix and 12 parts lithium salt.

[0108] The polymer matrix is ​​polyvinylidene fluoride.

[0109] The lithium salt is lithium tetrafluoroborate.

[0110] A composite solid electrolyte membrane for lithium batteries and its preparation method, comprising the following steps:

[0111] By weight, 100 parts of polyvinylidene fluoride (PVDF) and 600 parts of acetone solution were mixed and stirred at 55°C until PVDF dissolved in acetone to form a transparent sol. After 0.5 h, 12 parts of lithium salt were added to the PVDF sol, and stirring and sonication were continued for another 0.5 h. Then, a certain amount of pore-forming agent dimethyl carbonate was added, and the mixture was stirred and reacted at a constant temperature for another 6 h to obtain a uniform and transparent casting solution. After cooling to room temperature, the solution was coated onto a film, the film was peeled off, and dried at 90°C for 36 h to obtain the composite solid electrolyte membrane for lithium batteries.

[0112] The ultrasonic power is 600W and the frequency is 60kHz.

[0113] Comparative Example 2

[0114] A composite solid electrolyte membrane for lithium batteries, comprising, by weight, the following components: 100 parts polymer matrix, 12 parts lithium salt, and 16 parts polyimide salt.

[0115] The polymer matrix is ​​polyvinylidene fluoride.

[0116] The lithium salt is lithium tetrafluoroborate.

[0117] The preparation method of the polyimide salt includes the following steps:

[0118] 100 mmol of 1,8-diaminooctane and 25 mL of water were mixed and cooled in an ice-water bath to obtain a mixture. 25 mL of 37 wt% hydrochloric acid aqueous solution was added to the mixture to obtain an acidic diamine solution. A mixture of 8.12 g of formaldehyde and 14.51 g of glyoxal was added dropwise to the acidic diamine solution, and then refluxed at 80 °C for 4 h. The solvent and unreacted monomers were removed by rotary evaporation to obtain the polyimide salt.

[0119] A composite solid electrolyte membrane for lithium batteries and its preparation method, comprising the following steps:

[0120] By weight, 100 parts of polyvinylidene fluoride (PVDF) and 600 parts of acetone solution were mixed and stirred at 55°C until PVDF dissolved in acetone to form a transparent sol. After 0.5 h, 12 parts of lithium salt and 30 parts of polyimidezide salt were added to the PVDF sol, and stirring and sonication were continued for another 0.5 h. Then, a certain amount of pore-forming agent dimethyl carbonate was added, and after mixing evenly, the mixture was stirred and reacted at a constant temperature for another 6 h to obtain a uniform and transparent casting solution. After cooling to room temperature, the solution was coated onto a film, the film was peeled off, and dried at 90°C for 36 h to obtain the composite solid electrolyte membrane for lithium batteries.

[0121] The ultrasonic power is 600W and the frequency is 60kHz.

[0122] Comparative Example 3

[0123] A composite solid electrolyte membrane for lithium batteries, comprising, by mass, the following components: 100 parts polymer matrix, 12 parts lithium salt, and 14 parts modified mesoporous molecular sieve.

[0124] The polymer matrix is ​​polyvinylidene fluoride.

[0125] The lithium salt is lithium tetrafluoroborate.

[0126] The preparation method of the modified mesoporous molecular sieve includes the following steps:

[0127] S1. Mesoporous molecular sieves were added to a 10 mmol / L Tris buffer solution and ultrasonically dispersed to obtain a mesoporous molecular sieve suspension.

[0128] S2. Add dopamine to the mesoporous molecular sieve suspension obtained in step S1 to obtain a precursor suspension. Stir at 45°C for 7 hours, and then filter, wash and dry to obtain the modified mesoporous molecular sieve.

[0129] The ultrasonic power is 600W and the frequency is 60kHz.

[0130] The concentration of dopamine in the precursor suspension is 20 mmol / L, and the mass-to-volume ratio of the added mesoporous molecular sieve to the Tris buffer solution is 1 g: 10 L.

[0131] A composite solid electrolyte membrane for lithium batteries and its preparation method, comprising the following steps:

[0132] By weight, 100 parts of polyvinylidene fluoride (PVDF) and 600 parts of acetone solution were mixed and stirred at 55°C until PVDF dissolved in acetone to form a transparent sol. After 0.5 h, 12 parts of lithium salt and 30 parts of modified mesoporous molecular sieve were added to the PVDF sol, and stirring and sonication were continued for another 0.5 h. Then, a certain amount of pore-forming agent dimethyl carbonate was added, and after mixing evenly, the mixture was stirred and reacted at a constant temperature for another 6 h to obtain a uniform and transparent casting solution. After cooling to room temperature, the solution was coated onto a film, the film was peeled off, and dried at 90°C for 36 h to obtain the composite solid electrolyte membrane for lithium batteries.

[0133] The ultrasonic power is 600W and the frequency is 60kHz.

[0134] Comparative Example 4

[0135] A composite solid electrolyte membrane for lithium batteries, comprising, by mass, the following components: 100 parts polymer matrix, 12 parts lithium salt, 16 parts polyimide salt, and 14 parts mesoporous molecular sieve.

[0136] The polymer matrix is ​​polyvinylidene fluoride.

[0137] The lithium salt is lithium tetrafluoroborate.

[0138] The preparation method of the polyimide salt includes the following steps:

[0139] 100 mmol of 1,8-diaminooctane and 25 mL of water were mixed and cooled in an ice-water bath to obtain a mixture. 25 mL of 37 wt% hydrochloric acid aqueous solution was added to the mixture to obtain an acidic diamine solution. A mixture of 8.12 g of formaldehyde and 14.51 g of glyoxal was added dropwise to the acidic diamine solution, and then refluxed at 80 °C for 4 h. The solvent and unreacted monomers were removed by rotary evaporation to obtain the polyimide salt.

[0140] A composite solid electrolyte membrane for lithium batteries and its preparation method, comprising the following steps:

[0141] By weight, 100 parts of polyvinylidene fluoride (PVDF) and 600 parts of acetone solution were mixed and stirred at 55°C until PVDF dissolved in acetone to form a transparent sol. After 0.5 h, 12 parts of lithium salt, 16 parts of polyimidezide salt, and 14 parts of mesoporous molecular sieve were added to the PVDF sol, and the mixture was stirred and sonicated for another 0.5 h. Then, a certain amount of pore-forming agent dimethyl carbonate was added, and the mixture was mixed evenly. The mixture was stirred and reacted at a constant temperature for another 6 h to obtain a uniform and transparent casting solution. After cooling to room temperature, the solution was coated onto a film, the film was peeled off, and dried at 90°C for 36 h to obtain the composite solid electrolyte membrane for lithium batteries.

[0142] The ultrasonic power is 600W and the frequency is 60kHz.

[0143] Test Example 1

[0144] A composite solid electrolyte membrane for lithium batteries was placed between stainless steel electrodes. The ionic conductivity (δ) was then measured using a VMP3 measuring device and a 4294 sensor via AC impedance measurement in the 100MHz to 0.1Hz frequency band. The δ values ​​are: δ = l / (R×A), where δ is the ionic conductivity (mS / cm), l is the electrolyte thickness (cm), R is the measured resistance (mS), and A is the electrolyte area (cm²). 2 ))

[0145] Table 1: Results of Ion Conductivity Test

[0146] Ionic conductivity (mS / cm) Example 1 0.88 Example 2 0.86 Example 3 0.83 Example 4 0.71 Example 5 0.62 Comparative Example 1 0.34 Comparative Example 2 0.67 Comparative Example 3 0.64 Comparative Example 4 0.72

[0147] Test Example 2

[0148] The tensile properties of the composite solid electrolyte membrane for lithium batteries prepared in the examples were determined according to GB / T 1040.2-2006 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics". A universal tensile testing machine was used, and the test conditions were 25°C, tensile rate 15 mm / min, and each sample was tested at least five times. Before testing, the prepared samples were allowed to stand at room temperature (25°C) for at least 48 hours. The results are shown in Table 3.

[0149] Table 3: Results of Tensile Strength Tests

[0150] Tensile strength / MPa Example 1 7.3 Example 2 7.4 Example 3 8.9 Example 4 9.0 Example 5 9.1 Comparative Example 1 3.4 Comparative Example 2 5.1 Comparative Example 3 4.5 Comparative Example 4 8.1

[0151] As can be seen from Tables 1 and 2, the composite solid electrolyte membrane for lithium batteries prepared in Example 3 of the present invention has ions similar to those in Examples 2 and 3, and flexibility similar to those in Examples 4 and 5, thus possessing the advantages of both.

[0152] The comparison of Examples 1-5 shows that polyimidazolium salts in composite solid electrolyte membranes for lithium batteries have a significant impact on their ionic conductivity and flexibility, with the length of the main carbon chain being a key factor affecting both. Longer carbon chains can better enhance the flexibility, high-temperature resistance, and corrosion resistance of the electrolyte membrane; however, longer carbon chains hinder ion transport, reducing the ionic conductivity of the electrolyte membrane. Conversely, when the carbon chain is short, the addition of polyimidazolium salts reduces the toughness of the electrolyte membrane, resulting in significant brittleness and making it prone to cracking or breakage during practical use. This may affect the mechanical stability and lifespan of the electrolyte membrane. Polyimidazolium salts with eight carbon atoms, synthesized from 1,8-diaminooctane, exhibit excellent flexibility, high-temperature resistance, and corrosion resistance, while having a relatively small impact on the ionic conductivity of the electrolyte membrane.

[0153] The comparison between Comparative Examples 1-4 and Example 3 shows that both polyimidazolium salt and modified mesoporous molecular sieve have a significant impact on the ionic conductivity and flexibility of composite solid electrolyte membranes for lithium batteries. Without either addition, Comparative Example 1 exhibits extremely poor ionic conductivity and flexibility, which greatly limits the application range and service life of the electrolyte membrane. Adding either polyimidazolium salt or modified mesoporous molecular sieve alone results in significantly worse ionic conductivity and mechanical properties compared to adding both simultaneously. When the mass fraction of added mesoporous molecular sieve is too high, the polymer chains cannot form a dense network structure, failing to encapsulate the molecular sieve within the network structure. Furthermore, excessive addition of molecular sieve can easily lead to agglomeration, failing to provide reinforcement and resulting in a decrease in the mechanical strength of the film. Due to its inherent properties, polyimidazolium salt has limited effect on improving the toughness of polyvinylidene fluoride (PVDF). Excessive polyimidazolium salt content leads to disordered molecular arrangement, increasing brittleness and blocking ion transport channels, resulting in decreased conductivity. Therefore, when the two are combined and the appropriate amount is selected through experiments, they can have a synergistic effect, while enhancing the ionic conductivity and flexibility of the electrolyte membrane, and improving the service life and application range of the electrolyte membrane.

Claims

1. A composite solid electrolyte membrane for a lithium battery, characterized by, The composite solid-state electrolyte for lithium battery comprises the following components: a polymer matrix, a lithium salt, a polyimidazole salt, and a modified mesoporous molecular sieve. The polyimidazole salt is a main-chain alkylated polyimidazole salt, the main chain of which is composed of imidazole groups and alkyl groups alternately. The preparation method of the polyimidazole salt comprises the following steps: 90-110 mmol of a diamine and 20-30 mL of water are mixed and cooled in an ice water bath to obtain a mixed solution; 20-30 mL of a 37 wt% hydrochloric acid aqueous solution is added to the mixed solution to obtain an acidic diamine solution; a mixture of 8-9 g of formaldehyde and 14-15 g of glyoxal is added dropwise to the acidic diamine solution, and then the mixture is refluxed at 75-85°C for 4-5 h; the solvent and unreacted monomers are removed by rotary evaporation to obtain the polyimidazole salt; The preparation method of the modified mesoporous molecular sieve comprises the following steps: S1: adding mesoporous molecular sieve into a 9-11 mmol / L Tris buffer solution, and uniformly dispersing the mesoporous molecular sieve by ultrasonic treatment to obtain a mesoporous molecular sieve suspension; S2: adding dopamine into the mesoporous molecular sieve suspension obtained in step S1 to obtain a precursor suspension, stirring at 40-50°C for 6-8 h, and then filtering, washing, and drying to obtain the modified mesoporous molecular sieve.

2. The composite solid electrolyte membrane for a lithium battery according to claim 1, characterized by The polymer matrix is a polymer electrolyte commonly used in the art, and is at least one selected from polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polycarbonate, and polyacrylate.

3. The composite solid electrolytic membrane for a lithium battery according to claim 1, wherein The lithium salt is at least one selected from lithium perchlorate, lithium hexafluorophosphate, lithium difluoro(oxalato)borate, lithium trifluoromethylsulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium nitrate.

4. The composite solid electrolytic membrane for a lithium battery according to claim 1, wherein The diamine is one selected from 1,4-diaminobutane, 1,6-diaminohexane, 1,8-diaminooctane, 1,10-diaminodecane, and 1,12-diaminododecane.

5. The composite solid electrolytic membrane for a lithium battery according to claim 1, wherein The concentration of dopamine in the precursor suspension is 10-30 mmol / L, and the mass-volume ratio of the mesoporous molecular sieve to the Tris buffer solution is 1 g:(5-20) L.

6. A method for producing a composite solid electrolytic membrane for a lithium battery as claimed in any one of claims 1 to 5, characterized by, The preparation method comprises the following steps: polyvinylidene fluoride and an acetone solution are mixed, and the mixture is stirred at 50-60°C until the polyvinylidene fluoride is dissolved in the acetone to form a transparent sol; after 0.5-1 h, a lithium salt, a polyimidazole salt, and a modified mesoporous molecular sieve are added into the polyvinylidene fluoride sol, and the mixture is continuously stirred and ultrasonically treated for 0.5-1 h; then, a certain amount of a pore-forming agent dimethyl carbonate is added, and the mixture is uniformly mixed and continuously stirred at a constant temperature for 4-8 h to obtain a uniform and transparent casting solution; after being cooled to room temperature, the casting solution is scraped to form a film, the film is peeled off, and the film is dried at 80-90°C for 24-36 h to obtain the composite solid-state electrolyte film for lithium battery.

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