A polyimide fiber-based composite gel electrolyte, its preparation method and application

Abstract

This invention provides a polyimide fiber-based composite gel electrolyte, its preparation method, and its application, relating to the field of composite electrolyte technology. The invention provides a polyimide fiber-based composite gel electrolyte, chemically comprising a polyimide fiber-based composite membrane and an electrolyte; the polyimide fiber-based composite membrane comprises a polyimide fiber membrane and a poly(dimethylsiloxane)-boronic acid hybrid network doped in the polyimide fiber membrane; the mass content of the polyimide fiber-based composite membrane in the polyimide fiber-based composite gel electrolyte is 30-70%; the electrolyte comprises a lithium salt and an organic solvent. The polyimide fiber-based composite gel electrolyte provided by this invention has self-healing properties, combines mechanical and electrochemical properties, has low interfacial impedance with the electrode, long service life, and excellent high-temperature stability and fire resistance.

Description

Technical Field

[0001] This invention relates to the field of composite electrolyte technology, specifically to a polyimide fiber-based composite gel electrolyte, its preparation method, and its application. Background Technology

[0002] With the popularization and application of new energy vehicles, battery safety has attracted widespread attention. During charging and discharging, internal battery malfunctions or overheating can lead to accidents such as combustion and explosion. Therefore, developing electrolyte materials with fire-resistant properties has become a research hotspot and a challenge.

[0003] In recent years, researchers have proposed numerous strategies to improve the thermal stability and flame retardancy of electrolytes, focusing on flame retardant addition and gel electrolyte design. Regarding flame retardants, inexpensive phosphorus-containing flame retardants, such as triphenyl phosphate (TPP), trimethyl phosphate (TMP), triethyl phosphate (TEP), and diphenyl acrylamide phosphate (DPM), can suppress flame spread and reduce the severity of fires in the event of internal battery failures. However, these flame retardant additives are generally unstable, easily degraded on the negative electrode surface, and pose a risk of leakage, leading to battery component corrosion and ultimately, a decline in battery performance.

[0004] The related technology discloses a method for preparing a high flame-retardant polyimide fiber / aerogel composite membrane, including the following steps: (1) dissolving a diamine monomer in a reaction solvent, introducing nitrogen gas, and adding a dianhydride monomer under ice-water bath stirring conditions to prepare a polyamic acid solution; (2) adding a silane crosslinking agent to the polyamic acid solution for chemical crosslinking, then adding a flame-retardant crosslinking agent, and then adding an imidizing agent to obtain a polyimide solution; (3) coating the polyimide solution onto a polyimide fiber membrane to obtain a polyimide wet gel composite membrane, and then aging it; (4) placing the aged polyimide wet gel composite membrane in an organic solvent for solvent exchange, and then drying it to obtain a high flame-retardant polyimide fiber / aerogel composite membrane. The composite membrane has an average pore size of 50~150nm, high porosity, good mechanical properties, and good flame retardancy; at the same time, the contact angle of the composite membrane is less than 13°, and it has good electrolyte affinity. However, the aforementioned high flame-retardant polyimide fiber / aerogel composite membrane does not have self-healing properties. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a polyimide fiber-based composite gel electrolyte, its preparation method, and its application. The polyimide fiber-based composite gel electrolyte provided by this invention has good self-healing properties and combines structural support and ion conduction functions.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a polyimide fiber-based composite gel electrolyte, the chemical composition of which includes a polyimide fiber-based composite membrane and an electrolyte;

[0008] The polyimide fiber-based composite membrane comprises a polyimide fiber membrane and a poly(dimethylsiloxane)-boronic acid hybrid network doped in the polyimide fiber membrane; the mass content of the polyimide fiber-based composite gel electrolyte in the polyimide fiber-based composite membrane is 30-70%.

[0009] The electrolyte includes inorganic salts and organic solvents.

[0010] Preferably, the thickness of the polyimide fiber membrane is 100~500μm;

[0011] The polyimide fiber membrane has a pore size of 0.5~5μm, a porosity of 50~90%, and a fiber diameter of 0.2~1μm.

[0012] Preferably, the inorganic salt includes lithium salt, sodium salt, or zinc salt;

[0013] The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium fluorosulfonylimide, and lithium bis(oxalato)borate; the concentration of inorganic salt in the electrolyte is 1-3 mol / L.

[0014] Preferably, the organic solvent includes one or more of triethyl phosphate, fluoroethylene carbonate, dimethyl carbonate, and diethyl carbonate.

[0015] Preferably, the electrolyte further includes an ionic liquid and / or additives;

[0016] The ionic liquid comprises 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt;

[0017] The additives include vinylene carbonate and / or LiPO2F2.

[0018] This invention also provides a method for preparing the polyimide fiber-based composite gel electrolyte described in the above technical solution, comprising the following steps:

[0019] The polyamic acid solution was electrospun, and the resulting electrospun membrane was subjected to imidization and annealing treatments to obtain a polyimide fiber membrane.

[0020] A poly(dimethylsiloxane)-boric acid-isopropanol mixed solution was placed on a polyimide fiber membrane and then cured to obtain a polyimide fiber-based composite membrane.

[0021] The polyimide fiber-based composite membrane was immersed in an electrolyte to obtain a polyimide fiber-based composite gel electrolyte.

[0022] Preferably, the mass concentration of the polyamic acid solution is 15-25%;

[0023] The electrospinning operating parameters include: voltage of 10~30kV; receiving distance of 10~20cm; and solution propulsion rate of 3~5mL / h.

[0024] The imidization is a programmed imidization, which includes sequentially performing a first heating, a first holding, a second heating, and a second holding; the heating rates of the first heating and the second heating are independently 5~10℃ / min; the temperature of the first holding is 130~160℃ and the time is 20~60min; the temperature of the second holding is 230~260℃ and the time is 30~90min.

[0025] The annealing process is performed at a temperature of 350~450℃ for a time of 30~90 minutes.

[0026] Preferably, the poly(dimethylsiloxane)-boric acid-isopropanol mixed solution contains 15-25% poly(dimethylsiloxane) by mass and 0.1-0.5% boric acid by mass.

[0027] The curing temperature is 100~120℃ and the time is 30~90min.

[0028] Preferably, the soaking temperature is 20~60℃ and the soaking time is 2~24h.

[0029] The present invention also provides the application of the polyimide fiber-based composite gel electrolyte described in the above technical solution or the polyimide fiber-based composite gel electrolyte prepared by the preparation method described in the above technical solution in batteries.

[0030] The polyimide fiber-based composite gel electrolyte provided by this invention has a three-dimensional network structure. The polyimide fiber-based composite membrane can effectively fix the liquid components in the electrolyte, effectively reduce the fluidity of the electrolyte, and improve the electrochemical performance of the composite gel electrolyte.

[0031] The polyimide fiber-based composite membrane and the electrolyte form a gel-like whole, giving the polyimide fiber-based composite gel electrolyte both structural support and ion conduction functions.

[0032] Existing technologies rely on chemical cross-linking to form rigid structures, lacking a dynamic bonding mechanism. This invention addresses this by adding a poly(dimethylsiloxane)-boronic acid hybrid network. An organic-inorganic hybrid membrane formed by the reaction of poly(dimethylsiloxane) (PDMS) and boric acid is filled into a polyimide fiber membrane, forming a composite structure. The PDMS hydroxyl groups react with boric acid to form dynamic coordination bonds, which can recombine after material damage, endowing the material with self-healing properties, viscoelasticity, and an optimized pore structure. After mechanical damage (such as shearing or compression), the material can autonomously repair itself, restoring structural integrity and ion transport capabilities.

[0033] The viscoelasticity of PDMS allows the composite film to adhere tightly to the electrode surface, significantly reducing the interfacial impedance between the polyimide fiber-based composite gel electrolyte and the electrode; simultaneously, boric acid and lithium salts (e.g., TFSI) - The formation of coordination bonds (e.g., boron-nitrogen coordination bonds) inhibits anion migration and reduces interfacial side reactions, resulting in excellent interfacial stability of the polyimide fiber-based composite gel electrolyte provided by this invention during long-term cycling, significantly reducing capacity decay and improving the service life of the polyimide fiber-based composite gel electrolyte.

[0034] The porous structure of the polyimide fiber membrane synergistically with the flexible network of PDMS provides Li + It provides a continuous transport channel; and calculations using the Arrhenius equation show that it has a lower activation energy (lower resistance to ion transport), more stable conductivity over a wide temperature range, and well-optimized ion transport.

[0035] The present invention utilizes a polyimide fiber-based composite membrane with excellent high-temperature stability and fire resistance, which can effectively suppress the occurrence and spread of fire, thereby fully meeting the needs of practical applications.

[0036] In the preparation of polyimide fiber-based composite membranes, this invention eliminates the need for complex steps such as silane crosslinking, flame retardant crosslinking agent addition, and solvent exchange. Instead, it adopts a two-step method of "electrospinning + in-situ curing" to achieve batch preparation. The preparation process is simple, efficient, has a short preparation cycle, low cost, and is suitable for industrial production. Detailed Implementation

[0037] This invention provides a polyimide fiber-based composite gel electrolyte, the chemical composition of which includes a polyimide fiber-based composite membrane and an electrolyte;

[0038] The polyimide fiber-based composite gel electrolyte provided by this invention has a three-dimensional network structure. The polyimide fiber-based composite membrane can effectively fix the liquid components in the electrolyte, effectively reduce the fluidity of the electrolyte, and improve the electrochemical performance of the composite gel electrolyte. The polyimide fiber-based composite membrane and the electrolyte form a gel-like whole, giving the polyimide fiber-based composite gel electrolyte both structural support and ion conduction functions.

[0039] In this invention, the mass content of the polyimide fiber-based composite membrane in the polyimide fiber-based composite gel electrolyte is 30-70%, specifically 30%, 40%, 50%, 60%, or 70%. In this invention, too low a content of the polyimide fiber-based composite membrane will reduce the structural support capacity, while too high a content may reduce the electrolyte loading and affect ionic conductivity. This invention controls the content of the polyimide fiber-based composite membrane within the above-mentioned range, thereby optimizing the balance between mechanical and electrochemical properties. The polyimide fiber-based composite membrane used in this invention exhibits excellent high-temperature stability and fire resistance, effectively suppressing the occurrence and spread of fire, thus fully meeting the needs of practical applications.

[0040] In this invention, the thickness of the polyimide fiber membrane is preferably 100-500 μm, specifically 100 μm, 200 μm, 300 μm, 400 μm, or 500 μm. In this invention, if the thickness of the polyimide fiber-based composite membrane is too large, the internal resistance will increase, the ionic conductivity will decrease, and the energy density will decrease; if the thickness is too small, the mechanical strength will be insufficient, making it prone to short circuits and insufficient electrolyte retention. This invention controls the thickness of the polyimide fiber-based composite membrane within the above-mentioned range, which contributes to the synergy of high battery safety and high energy density. The porous structure of the polyimide fiber membrane, in conjunction with the flexible network of PDMS, provides a high-quality battery for Li... + It provides a continuous transport channel; and calculations using the Arrhenius equation show that it has a lower activation energy (lower resistance to ion transport), more stable conductivity over a wide temperature range, and well-optimized ion transport.

[0041] In this invention, the polyimide fiber-based composite membrane comprises a polyimide fiber membrane and a poly(dimethylsiloxane)-boronic acid hybrid network doped in the polyimide fiber membrane. In this invention, the mass concentration of the poly(dimethylsiloxane)-boronic acid hybrid network in the polyimide fiber-based composite membrane is preferably 5-30%, more preferably 10-20%, and may specifically be 5%, 10%, 15%, 20%, 25%, or 30%.

[0042] Existing technologies rely on chemical cross-linking to form rigid structures, lacking a dynamic bonding mechanism. This invention addresses this by adding a poly(dimethylsiloxane)-boronic acid hybrid network. An organic-inorganic hybrid membrane formed by the reaction of poly(dimethylsiloxane) (PDMS) and boric acid is filled into a polyimide fiber membrane, forming a composite structure. The PDMS hydroxyl groups react with boric acid to form dynamic coordination bonds, which can recombine after material damage, endowing the material with self-healing properties, viscoelasticity, and an optimized pore structure. After mechanical damage (such as shearing or compression), the material can autonomously repair itself, restoring structural integrity and ion transport capabilities.

[0043] The viscoelasticity of PDMS allows the composite film to adhere tightly to the electrode surface, significantly reducing the interfacial impedance between the polyimide fiber-based composite gel electrolyte and the electrode; simultaneously, boric acid and lithium salts (e.g., TFSI) - The formation of coordination bonds (e.g., boron-nitrogen coordination bonds) inhibits anion migration and reduces interfacial side reactions, resulting in excellent interfacial stability of the polyimide fiber-based composite gel electrolyte provided by this invention during long-term cycling, significantly reducing capacity decay and improving the service life of the polyimide fiber-based composite gel electrolyte.

[0044] In this invention, if the content of poly(dimethylsiloxane)-boronic acid hybrid network in the polyimide fiber-based composite membrane is too high, it will reduce ion transport efficiency and decrease thermal stability; if the content is too low, it will reduce the contact between the electrolyte membrane and the electrode interface. This invention controls the content of poly(dimethylsiloxane)-boronic acid hybrid network within the above range, which helps to optimize ion conductivity, electrolyte-electrode interface stability, and electrolyte membrane thermal stability.

[0045] In this invention, the pore size of the polyimide fiber membrane is preferably 0.5~5μm, specifically 0.5μm, 1μm, 2μm, 3μm, 4μm, or 5μm; the porosity of the polyimide fiber membrane is preferably 50~90%, specifically 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%; and the fiber diameter of the polyimide fiber membrane is preferably 0.2~1μm, specifically 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, or 1μm. This invention controls the pore size, porosity, and fiber diameter structural parameters of the polyimide fiber membrane within the above ranges, thereby achieving a synergistic effect on mechanical properties, thermal stability, and ionic conductivity.

[0046] In this invention, the electrolyte comprises an inorganic salt and an organic solvent. Preferably, the lithium salt comprises one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium fluorosulfonylimide (LiFSI), and lithium bis(oxalatoborate) (LiBOB); wherein, LiFSI has higher ionic conductivity and antioxidant properties, making it suitable for high-voltage cathodes. Preferably, the concentration of the inorganic salt in the electrolyte is 1-3 mol / L, specifically 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, or 3 mol / L.

[0047] In this invention, the organic solvent preferably includes one or more of triethyl phosphate (TEP), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), more preferably a mixed solvent of TEP-FEC, a mixed solvent of TEP-FEC-DMC, a mixed solvent of TEP-FEC-DEC, or a mixed solvent of TEP-FEC-DMC-DEC; the volume ratio of TEP to FEC in the mixed solvent is preferably 7~8:2~3, specifically 7:2, 7:2.5, 7:3, 8:2, 8:2.5, or 8:3.

[0048] In this invention, the electrolyte preferably further includes an ionic liquid and / or additives. The ionic liquid preferably comprises 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt; the concentration of the ionic liquid in the electrolyte is preferably 0-3 mol / L, specifically 0 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, or 3 mol / L. This invention improves the thermal stability and flame retardancy of the polyimide fiber-based composite gel electrolyte by adding an ionic liquid to the electrolyte.

[0049] In this invention, the additive preferably includes vinylene carbonate (VC) and / or LiPO2F2; the concentration of the additive in the electrolyte is preferably 0-5 mol / L, specifically 0 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, or 5 mol / L. This invention improves the cycling stability of the polyimide fiber-based composite gel electrolyte by forming a stable SEI film through the addition of vinylene carbonate to the electrolyte. This invention also improves the interfacial stability of the polyimide fiber-based composite gel electrolyte and enhances its compatibility with silicon-based anodes by adding LiPO2F2 to the electrolyte.

[0050] This invention also provides a method for preparing the polyimide fiber-based composite gel electrolyte described in the above technical solution, comprising the following steps:

[0051] The polyamic acid solution was electrospun, and the resulting electrospun membrane was subjected to imidization and annealing treatments to obtain a polyimide fiber membrane.

[0052] A poly(dimethylsiloxane)-boric acid-isopropanol mixed solution was placed on a polyimide fiber membrane and then cured to obtain a polyimide fiber-based composite membrane.

[0053] The polyimide fiber-based composite membrane was immersed in an electrolyte to obtain a polyimide fiber-based composite gel electrolyte.

[0054] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0055] In this invention, a polyamic acid solution is electrospun, and the resulting electrospun membrane is subjected to imidization and annealing treatments in sequence to obtain a polyimide fiber membrane.

[0056] In this invention, the mass concentration of the polyamic acid solution is preferably 15-25%, specifically 15%, 18%, 20%, 22%, or 25%. In this invention, the solvent in the polyamic acid solution preferably includes an amide solvent, more preferably N,N-dimethylacetamide and / or N,N-dimethylformamide.

[0057] In this invention, the preferred operating parameters for electrospinning include: a voltage of 10~30kV, specifically 10kV, 15kV, 20kV, 25kV or 30kV; a receiving distance of 10~20cm, specifically 10cm, 12cm, 14cm, 16cm, 18cm or 20cm; and a solution propulsion rate of 3~5mL / h, specifically 3mL / h, 3.5mL / h, 4mL / h, 4.5mL / h or 5mL / h.

[0058] Before imidization, the electrospun film is preferably dried. The drying temperature is preferably 30-40°C, more preferably 35°C. The drying time is preferably 1-3 hours, specifically 1 hour, 2 hours or 3 hours. The purpose of drying is to remove excess solvent.

[0059] In this invention, the imidization is preferably programmed imidization, which preferably includes sequentially performing a first heating, a first holding, a second heating, and a second holding; the heating rates of the first heating and the second heating are independently preferably 5~10℃ / min, specifically 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min; the temperature of the first holding is 130~160℃, specifically 130℃, 140℃, 150℃, or 160℃; the time of the first holding is preferably 20~60min, specifically 20min, 30min, 40min, 50min, or 60min; the temperature of the second holding is preferably 230~260℃, specifically 230℃, 240℃, 250℃, or 260℃; the time of the second holding is preferably 30~90min, specifically 30min, 40min, 50min, 60min, 70min, 80min, or 90min. In this invention, the imidization is preferably carried out under a protective atmosphere, which preferably includes nitrogen, argon or helium.

[0060] In this invention, the annealing temperature is preferably 350~450℃, specifically 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, or 450℃; the annealing time is preferably 30~90 min, specifically 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, or 90 min; the heating rate from the imidization temperature to the annealing temperature (denoted as the third heating) is preferably 5~10℃ / min, specifically 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min. In this invention, the annealing is preferably performed under a protective atmosphere, preferably including nitrogen, argon, or helium. This invention utilizes annealing to thoroughly remove residual solvents and low-molecular-weight volatiles, promoting further regular arrangement of molecular chains and enhancing the thermal stability, mechanical strength, and dimensional stability of the polyimide fiber membrane. This ensures that the structure remains intact during subsequent PDMS lamination. Annealing also reduces defects in the polyimide fiber membrane (such as micropores and cracks), optimizes the bonding force between fibers, ensures uniform pore filling during subsequent PDMS lamination, and avoids insufficient local electrolyte wetting.

[0061] After obtaining the polyimide fiber membrane, the present invention places a poly(dimethylsiloxane)-boric acid-isopropanol mixed solution on the polyimide fiber membrane and then cures it to obtain a polyimide fiber-based composite membrane.

[0062] In this invention, the mass concentration of poly(dimethylsiloxane) (PDMS) in the poly(dimethylsiloxane)-boric acid-isopropanol mixed solution is preferably 15-25%, specifically 15%, 18%, 20%, 22%, or 25%; the mass concentration of boric acid in the poly(dimethylsiloxane)-boric acid-isopropanol mixed solution is preferably 0.1-0.5%, specifically 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%.

[0063] In this invention, the curing temperature is 100~120℃, specifically 100℃, 105℃, 110℃, 115℃, or 120℃; the curing time is preferably 30~90min, specifically 30min, 40min, 50min, 60min, 70min, 80min, or 90min. In this invention, the organic-inorganic hybrid membrane formed by the reaction of poly(dimethylsiloxane) (PDMS) and boric acid is filled into a polyimide fiber membrane to form a composite structure, endowing the material with self-healing properties, viscoelasticity, and optimized pore structure.

[0064] After obtaining the polyimide fiber-based composite membrane, the present invention places the polyimide fiber-based composite membrane in an electrolyte and immerses it to obtain a polyimide fiber-based composite gel electrolyte.

[0065] In this invention, the soaking temperature is preferably 20~60℃, specifically 20℃, 25℃, 30℃, 40℃, 50℃, or 60℃; the soaking time is preferably 2~24h, more preferably 2~8h or 12~24h, specifically 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, or 24h. Preferably, the soaking time is determined based on the thickness of the polyimide fiber-based composite film. When the thickness of the polyimide fiber-based composite film is 100~300μm, the soaking time is 2~8h; when the thickness of the polyimide fiber-based composite film is 400~500μm, the soaking time is 12~24h. In this invention, the purpose of soaking is to ensure that the electrolyte fully wets the pores of the polyimide fiber-based composite membrane, forming a gel-like electrolyte. After removal, the membrane can be used for subsequent battery assembly or performance testing, avoiding the influence of excess free electrolyte on battery performance. Under the aforementioned conditions, this invention ensures that the polyimide fiber-based composite membrane is fully wetted with the electrolyte. Soaking at room temperature is simple and avoids solvent evaporation. Appropriate heating (30~60℃) can accelerate electrolyte wetting and shorten the soaking time.

[0066] In the preparation of polyimide fiber-based composite membranes, this invention eliminates the need for complex steps such as silane crosslinking, flame retardant crosslinking agent addition, and solvent exchange. Instead, it adopts a two-step method of "electrospinning + in-situ curing" to achieve batch preparation. The preparation process is simple, efficient, has a short preparation cycle, low cost, and is suitable for industrial production.

[0067] The present invention also provides the application of the polyimide fiber-based composite gel electrolyte described in the above technical solution or the polyimide fiber-based composite gel electrolyte prepared by the preparation method described in the above technical solution in batteries.

[0068] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, of the polyimide fiber-based composite gel electrolyte, its preparation method, and its application, should not be construed as limiting the scope of protection of the present invention.

[0069] Example 1

[0070] A polyamic acid (PAA) solution (20 wt% concentration, N,N-dimethylacetamide solvent) was loaded into a syringe and electrospun at room temperature. The resulting electrospun membrane was dried in air at 30–40 °C for 2 hours, and then subjected to imidization and annealing in a tube furnace under nitrogen protection to obtain a polyimide fiber membrane. The electrospinning parameters were: a syringe distance of 18 cm from the aluminum foil, a voltage of 20 kV, and a flow rate of 3 mL / h. Imidization and annealing treatment: The temperature is increased from room temperature to 150℃ at a heating rate of 10℃ / min and held for 30 min for imidization. Then, the temperature is increased to 250℃ at a heating rate of 10℃ / min and held for 60 min for imidization. Finally, the temperature is increased to 400℃ at a heating rate of 5℃ / min and annealed for 60 min to obtain a polyimide fiber membrane (thickness of 150μm, pore size of 1.5μm, porosity of 85%, and fiber diameter of 0.5μm).

[0071] Poly(dimethylsiloxane) and boric acid-isopropanol mixed solution (boric acid:isopropanol mass ratio = 1:500) were mixed evenly at a mass ratio of 100:1. The resulting mixture (2 mL) was poured onto a polyimide fiber membrane and cured at 110℃ for 60 min to obtain a polyimide fiber-based composite membrane.

[0072] The polyimide fiber-based composite membrane was placed in an electrolyte (2M LiTFSI, with a solvent ratio of triethyl phosphate to fluorine of 8:2) and soaked at 30°C for 3 hours. After soaking, the membrane was removed to obtain the polyimide fiber-based composite gel electrolyte.

[0073] Comparative Example 1

[0074] The polyimide fiber-based composite gel electrolyte was prepared according to the method of Example 1, except that the boric acid-isopropanol mixed solution was replaced with trimethyl borate.

[0075] Trimethyl borate has low reactivity and insufficient cross-linking with PDMS, resulting in poor self-healing properties and uneven pore filling in the polyimide fiber-based composite membrane.

[0076] Comparative Example 2

[0077] The polyimide fiber-based composite gel electrolyte was prepared according to the method of Example 1, except that the annealing temperature was 300°C.

[0078] Insufficient annealing temperature leads to incomplete imidization of polyimide fibers, resulting in decreased thermal stability and mechanical properties.

[0079] Comparative Example 3

[0080] The polyimide fiber-based composite gel electrolyte was prepared according to the method of Example 1, with the only difference from Example 1 being that the curing temperature was 80°C.

[0081] Too low a curing temperature leads to incomplete reaction between PDMS and boric acid, resulting in a loose film structure.

[0082] Comparative Example 4

[0083] Polyimide fiber-based composite gel electrolytes were prepared according to the method of Example 1, with the only difference being that electrospinning was replaced by solution casting (pouring polyamic acid solution into a ceramic vessel); the resulting polyimide fiber membrane had a porosity of <20%.

[0084] The casting method cannot form a fibrous structure, resulting in extremely low porosity and uneven distribution.

[0085] Test Example 1

[0086] The testing method is as follows:

[0087] Porosity was obtained by gas adsorption (BET) test; mechanical properties were obtained by stress-strain curve test. The sample was cut into dumbbell shape with a width and length of 10 mm and 80 mm, respectively, and the stretching rate was 10 mm / min.

[0088] The self-healing rate was calculated by tensile testing using a universal testing machine. The sample was cut into a dumbbell shape with a width and length of 10 mm and 80 mm, respectively, and the tensile rate was 10 mm / min.

[0089] The electrolyte absorption rate was obtained by weighing the mass change of the polyimide fiber-based composite membrane before and after immersion in the electrolyte at room temperature. The electrolyte was a 2 mol / L LiTFSI electrolyte (the solvent was triethyl phosphate: ethylene fluorocarbonate in a volume ratio of 8:2).

[0090] Solution retention rate was obtained by testing the mass change of the polyimide fiber-based composite gel electrolyte after it was left at room temperature for 48 hours.

[0091] The total heat release was obtained by cone calorimetry, with a sample size of 100 mm × 100 mm and a thermal radiation intensity of 35 kW / m². 2 The exhaust system flow rate is 24L / s.

[0092] Ionic conductivity and interfacial resistance were obtained by AC impedance spectroscopy. A symmetrical cell with steel sheets as electrodes was used, with a low frequency of 0.01 Hz and a high frequency of 10 MHz.

[0093] Battery cycle performance was tested by charging and discharging the entire battery using a battery testing system, with a current density of 2A / g.

[0094] The test results are shown in Table 1.

[0095] Table 1. Performance test results of the polyimide fiber-based composite gel electrolytes prepared in the examples and comparative examples.

[0096]

[0097] As shown in Table 1, the polyimide fiber-based composite gel electrolyte prepared by this invention has high porosity and uniform pore structure; high fracture stress; high electrolyte absorption and retention rate; good self-healing performance; low total heat release; high ionic conductivity; low interfacial point resistance; and excellent battery cycling performance.

[0098] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A polyimide fiber-based composite gel electrolyte, characterized in that, The chemical composition includes a polyimide fiber-based composite membrane and an electrolyte; The polyimide fiber-based composite membrane comprises a polyimide fiber membrane and a poly(dimethylsiloxane)-boronic acid hybrid network doped in the polyimide fiber membrane; the mass content of the polyimide fiber-based composite gel electrolyte in the polyimide fiber-based composite membrane is 30-70%. The electrolyte comprises inorganic salts and organic solvents; The preparation method of the polyimide fiber-based composite gel electrolyte includes the following steps: The polyamic acid solution was electrospun, and the resulting electrospun membrane was subjected to imidization and annealing treatments to obtain a polyimide fiber membrane. A poly(dimethylsiloxane)-boric acid-isopropanol mixed solution was placed on a polyimide fiber membrane and then cured to obtain a polyimide fiber-based composite membrane. The polyimide fiber-based composite membrane was immersed in an electrolyte to obtain a polyimide fiber-based composite gel electrolyte. The mass concentration of the polyamic acid solution is 15-25%; The electrospinning operating parameters include: voltage of 10~30kV; receiving distance of 10~20cm; and solution propulsion rate of 3~5mL / h. The imidization is a programmed imidization, which includes sequentially performing a first heating, a first holding, a second heating, and a second holding; the heating rates of the first heating and the second heating are independently 5~10℃ / min; the temperature of the first holding is 130~160℃ and the time is 20~60min; the temperature of the second holding is 230~260℃ and the time is 30~90min. The annealing process is performed at a temperature of 350~450℃ for a time of 30~90 minutes.

2. The polyimide fiber-based composite gel electrolyte according to claim 1, characterized in that, The thickness of the polyimide fiber membrane is 100~500μm; The polyimide fiber membrane has a pore size of 0.5~5μm, a porosity of 50~90%, and a fiber diameter of 0.2~1μm.

3. The polyimide fiber-based composite gel electrolyte according to claim 1, characterized in that, The inorganic salts include lithium salts, sodium salts, or zinc salts; The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium fluorosulfonylimide, and lithium bis(oxalato)borate; the concentration of inorganic salt in the electrolyte is 1-3 mol / L.

4. The polyimide fiber-based composite gel electrolyte according to claim 1, characterized in that, The organic solvent includes one or more of triethyl phosphate, fluoroethylene carbonate, dimethyl carbonate, and diethyl carbonate.

5. The polyimide fiber-based composite gel electrolyte according to claim 1, 3, or 4, characterized in that, The electrolyte also includes ionic liquids and / or additives; The ionic liquid comprises 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt; The additives include vinylene carbonate and / or LiPO2F2.

6. The polyimide fiber-based composite gel electrolyte according to claim 1, characterized in that, The poly(dimethylsiloxane)-boric acid-isopropanol mixed solution contains 15-25% poly(dimethylsiloxane) by mass and 0.1-0.5% boric acid by mass. The curing temperature is 100~120℃ and the time is 30~90min.

7. The polyimide fiber-based composite gel electrolyte according to claim 1, characterized in that, The soaking temperature is 20~60℃, and the soaking time is 2~24h.

8. The application of the polyimide fiber-based composite gel electrolyte according to any one of claims 1 to 7 in a battery.

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