A high-temperature-resistant polybenzimidazole diaphragm rich in imidazole groups and a preparation method thereof, and a lithium ion battery

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a high-temperature-resistant polybenzimidazole diaphragm with an imidazole group-rich semi-interpenetrating structure, a preparation method of the diaphragm and a lithium ion battery. The diaphragm is rich in imidazole groups, acyloxy groups or amide groups, has strong affinity to electrolyte, and has good electrolyte wettability and liquid retention; the above groups can promote lithium salt dissociation, and the lithium ion Li + coordinating; the semi-interpenetrating network structure has a large number of uniformly distributed mesopores, improves porosity, expands lithium ion Li + transport channels; the polybenzimidazole OPBI and polyvinylimidazole PVIm have good heat resistance, and the crosslinked structure further enhances the heat resistance and mechanical strength of the diaphragm. The diaphragm has regular finger-shaped pores and sponge-shaped pores, has high conductivity, good electrochemical stability, and can effectively inhibit the disorderly growth of lithium dendrites. The battery assembled by the diaphragm has excellent safety, discharge specific capacity, cycle stability (at normal temperature and high temperature), rate performance, and low electrode polarization.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a high-temperature resistant polybenzimidazole separator with a semi-interpenetrating structure rich in imidazole groups, its preparation method, and a lithium-ion battery thereof. Background Technology

[0002] The separator is one of the core components of lithium-ion batteries (LIBs). Its function is to separate the positive and negative electrodes to prevent short circuits and safety accidents, while ensuring that lithium ions can pass through the micropores normally during charging and discharging to ensure normal battery operation. Its performance directly affects the battery's safety, capacity, rate capability, lifespan, and other performance characteristics during service.

[0003] Polyolefin separators, such as polyethylene (PE) separators, polypropylene (PP) separators, and PE / PP composite membranes, are currently the separator products commonly used in the production of commercial lithium-ion batteries. Their production processes mainly include dry and wet processes. Due to limitations in material properties and manufacturing processes, polyolefin separators still face several challenging issues in their application: First, polyolefin materials have a low melting point, an inherent property, resulting in poor heat resistance in polyolefin separators. At high temperatures, they are prone to thermal shrinkage, which can cause short circuits and lead to dangerous events such as lithium battery fires and explosions. Second, the conductivity, electrolyte wettability, flame retardancy, and electrochemical stability window of polyolefin separators are not ideal. Third, batteries assembled with polyolefin separators experience severe lithium dendrite growth during service. These dendrites can easily pierce the separator, causing micro-short circuits inside the lithium battery and posing safety hazards. Fourth, batteries assembled with polyolefin separators exhibit poor cycle stability at high temperatures (e.g., 90°C). Fifth, batteries assembled with polyolefin separators exhibit significant electrode polarization.

[0004] To improve the safety and electrochemical performance of lithium-ion batteries, various materials are coated onto the surface of polyolefin separators using different coating processes to form coated polyolefin separators. Currently, the main types of coated separators on the market are inorganic coated separators, organic coated separators, and organic + inorganic coated separators. This method of coating heat-resistant materials (inorganic, organic, or a mixture of inorganic and organic) onto the surface of the polyolefin separator improves the separator's heat resistance to some extent. However, the substrate material under the coating—polyolefin—still faces the risk of thermal shrinkage leading to the collapse of the entire separator structure under sufficiently high temperatures and long enough times. Therefore, this modification scheme based on polyolefin separators cannot fundamentally solve the problem of separator heat resistance and cannot completely solve the safety issues of lithium-ion batteries. Furthermore, lithium-ion batteries assembled with this type of coated polyolefin separator still exhibit significant anode lithium dendrite growth during charge-discharge cycles. As is well known, coating also produces a series of negative effects, such as increased separator thickness and increased bulk resistance (Ro). bIncreased saturation and decreased charge / discharge efficiency are some of the drawbacks. Therefore, existing diaphragm technology still needs improvement and development. Summary of the Invention

[0005] In view of the shortcomings of existing membrane technologies, the present invention aims to provide a high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups, a method for its preparation, and a lithium-ion battery, in order to solve the following problems: a. Existing polyolefin membranes are prone to thermal shrinkage at high temperatures; b. Lithium dendrites on the anode surface of lithium-ion batteries assembled with existing polyolefin membranes exhibit severe disordered growth; c. Lithium-ion batteries assembled with existing polyolefin membranes have poor high-temperature cycle stability; d. Lithium-ion batteries assembled with existing polyolefin membranes exhibit significant electrode polarization; e. The conductivity, electrolyte wettability, flame retardancy, and electrochemical stability window of polyolefin membranes are not ideal.

[0006] The technical solution of the present invention is as follows: A high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups and its preparation method, comprising the following steps: 1. Provide a mixed solution of polybenzimidazole OPBI, N-vinylimidazole VIM, initiator, and crosslinking agent; 2. The mixed solution is heated under inert gas protection to carry out a chemical reaction. The mixed solution after the chemical reaction is completed is coated on a substrate, and the solvent in the mixed solution is removed to obtain a high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups.

[0007] The method for preparing the high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups is characterized in that the initiator is azobisisobutyronitrile (AIBN), and the crosslinking agent is N,N'-methylenebisacrylamide (NMBA) or ethyl dimethacrylate (EDMA).

[0008] The method for preparing the high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups is characterized by the following steps in the preparation of the mixed solution: 0.3 g of polybenzimidazole OPBI powder is added to a solvent and stirred vigorously at 60-100°C for 10-15 hours; then 0.05-0.20 g of N-vinylimidazolium VIm is added to the solution; next, azobisisobutyronitrile (AIBN) initiator is added to the solution at 1 wt.% relative to the N-vinylimidazolium VIm monomer; finally, N,N'-methylenebisacrylamide (NMBA) or ethyl dimethacrylate (EDMA) crosslinking agent is added to the solution, with a mass ratio of crosslinking agent to monomer of 0.3:1, and a corresponding molar ratio of nNMBA:nVIm of 1:5.5 or nEDMA:nVIm of 1:7.

[0009] The method for preparing the high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups is characterized in that the inert gas is nitrogen (N2) or argon (Ar).

[0010] The method for preparing the high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups is characterized in that the chemical reaction conditions are heating the mixed solution to 60-80°C and stirring continuously for 10-15 hours.

[0011] The method for preparing the high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups is characterized in that the solvent removal method in the mixed solution after the chemical reaction is performed is as follows: the substrate coated with the mixed solution after the chemical reaction is performed is immersed in anhydrous methanol for immersion treatment, wherein the immersion treatment is performed by standing at room temperature for 8-15 minutes.

[0012] The micropores of the high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups are composed of finger-like pores and sponge-like pores, and the molecular-level microstructure is a semi-interpenetrating structure.

[0013] The thickness of the high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups is 20-40 micrometers.

[0014] A lithium-ion battery includes a positive electrode, a negative electrode, and a high-temperature resistant polybenzimidazole separator with a semi-interpenetrating structure rich in imidazole groups; the high-temperature resistant polybenzimidazole separator with a semi-interpenetrating structure rich in imidazole groups is located between the positive electrode and the negative electrode.

[0015] Beneficial Effects: This invention provides a high-temperature resistant polybenzimidazole separator with a semi-interpenetrating structure rich in imidazole groups, its preparation method, and a lithium-ion battery. The preparation method includes the following steps: providing a mixed solution of polybenzimidazole OPBI, N-vinylimidazolium VIM, an initiator, and a crosslinking agent; heating the mixed solution under inert gas protection to carry out a chemical reaction; coating the chemically reacted mixed solution onto a substrate; and removing the solvent from the mixed solution to obtain a high-temperature resistant polybenzimidazole separator with a semi-interpenetrating structure rich in imidazole groups; and assembling a lithium-ion battery using the high-temperature resistant polybenzimidazole separator with a semi-interpenetrating structure rich in imidazole groups. This invention constructs a semi-interpenetrating network structure in a battery separator through an in-situ crosslinking reaction, which has the following advantages: (1) The molecular chains in the semi-interpenetrating network structure are rich in imidazole groups, acyloxy groups, or amide groups. These groups have a strong affinity for the electrolyte, improving the electrolyte wettability and liquid retention of the separator; (2) The molecular chains in the semi-interpenetrating network structure are rich in imidazole groups, acyloxy groups, or amide groups, promoting the dissociation of lithium salts and facilitating the dissociation of lithium ions (Li). + Provides coordination; (3) The semi-interpenetrating network structure has a large number of uniformly distributed mesopores, which improves porosity and expands the lithium-ion Li +(4) The diaphragm is a homogeneous organic material, and there is no phase interface problem; (5) Polybenzimidazole OPBI and polyvinylimidazole PVIm have good heat resistance, and the cross-linked structure further enhances the heat resistance and mechanical strength of the diaphragm. Therefore, the diaphragm prepared by this invention has a high affinity with the electrolyte and can also be used for lithium ions. + This membrane provides more sites and microchannels for lithium ion transport; a non-solvent phase inversion method is used to construct microchannels composed of regular finger-like pores and sponge-like pores in the separator. In terms of performance, this separator exhibits good electrolyte wettability, high conductivity, and good electrochemical stability. Furthermore, its unique pore structure, ion coordination structure, and uniform mesopores of a semi-interpenetrating network induce lithium ions to pass through the separator more rapidly and deposit uniformly on the lithium metal anode surface, effectively suppressing the disordered growth of lithium dendrites and improving the safety and electrochemical performance of lithium-ion batteries. Batteries assembled using this separator exhibit excellent discharge specific capacity, cycle stability, and rate performance, especially outstanding charge-discharge stability at high temperatures; in addition, the battery electrode polarization is low. Attached Figure Description

[0016] Figure 1 and Figure 2 This invention relates to a method, process, and lithium-ion battery preparation method for a high-temperature resistant polybenzimidazole membrane rich in imidazole groups. + Transportation diagram.

[0017] Figure 3 (a) is the Fourier transform infrared spectrum, (b) is the X-ray diffraction pattern, (c) is the thermogravimetric analysis curve, (d) is the solubility test result, and (e) is the flexibility of the OPBI-VED-20 membrane.

[0018] Figure 4 (a) is a schematic diagram of the solubility test during the pore formation process of the OPBI-VED-20 membrane, and (b) is a schematic diagram of the multipore formation mechanism.

[0019] Figure 5 (a) shows the affinity between the membranes prepared with different crosslinking agents and the liquid electrolyte; (b) shows the contact angle between the membranes prepared with different crosslinking agents and the electrolyte; (c) shows the surface pore distribution and percentage of the membranes prepared with different crosslinking agents; and (d) shows the scanning electron microscope images of the cross-sections of the membranes prepared with different crosslinking agents.

[0020] Figure 6 (a) shows the affinity between the membranes prepared with different crosslinking agents and different amounts and the liquid electrolyte, and (b) shows the contact angle between the membranes prepared with different crosslinking agents and different amounts and the electrolyte.

[0021] Figure 7 The thermogravimetric analysis curve of the diaphragm is shown.

[0022] Figure 8 (a) shows the flame retardancy test of the diaphragm, and (b) shows the heat resistance of the PP, OPBI, OPBI-VED-20 and OPBI-VMBA-20 diaphragms.

[0023] Figure 9 The heat resistance of PP, OPBI, OPBI-VED-5 / 10 / 15 and OPBI-VMBA-5 / 10 / 15 separators.

[0024] Figure 10 Scanning electron microscope images of PP, OPBI, OPBI-VED-20 and OPBI-VMBA-20 membranes.

[0025] Figure 11 Scanning electron microscope images of PP, OPBI, OPBI-VED-5 / 10 / 15 and OPBI-VMBA-5 / 10 / 15 membranes.

[0026] Figure 12 (a) Nyquist plot of SS / SS symmetric cell assembled with PP, OPBI, OPBI-VED-20, and OPBI-VMBA-20 separators; (b) AC impedance curve of half cell; (c) Potential change of Li / Li symmetric cell assembled with PP and OPBI-VED-20 separators during long cycle; (d) LSV curve; (e) Cycling performance of LiFePO4 / separator / Li cell assembled with PP, OPBI, and OPBI-VED-20 separators at 25℃; (f) Rate performance of LiFePO4 / separator / Li cell assembled with PP, OPBI, OPBI-VED-20, and OPBI-VMBA-20 separators; (g) Physicochemical properties of PP, OPBI, OPBI-VED-20, and OPBI-VMBA-20 separators (P = porosity, EU = electrolyte absorption rate, σ = ionic conductivity).

[0027] Figure 13 Nyquist plot of SS / SS symmetric cells assembled using PP, OPBI, OPBI-VED-5 / 10 / 15 and OPBI-VMBA-5 / 10 / 15 separators.

[0028] Figure 14 Rate performance of LiFePO4 / separator / Li cells assembled using PP, OPBI, OPBI-VED-5 / 10 / 15 and OPBI-VMBA-5 / 10 / 15 separators.

[0029] Figure 15Cycling performance of LiFePO4 / separator / Li batteries assembled using PP, OPBI, OPBI-VED-5 / 10 / 15 and OPBI-VMBA-5 / 10 / 15 separators at 25°C.

[0030] Figure 16 (a) shows the cycle performance of LiFePO4 / membrane / Li batteries assembled with PP and OPBI-VED-20 membranes at 0.5C rate and 90 °C; (b) shows the cycle performance of LiFePO4 / membrane / Li batteries assembled with OPBI-VED-20 membranes at different high temperatures; and (c) shows the performance of LiFePO4 / membrane / Li batteries assembled with different membranes at high temperatures. Detailed Implementation

[0031] This invention provides a high-temperature resistant polybenzimidazole separator with a semi-interpenetrating structure rich in imidazole groups, a method for preparing the same, and a lithium-ion battery. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0032] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0033] like Figure 1 As shown, this invention provides a method for preparing a high-temperature resistant polybenzimidazole separator with a semi-interpenetrating structure rich in imidazole groups, and a lithium-ion battery, comprising the following steps: Step S10: Provide a mixed solution of polybenzimidazole OPBI, N-vinylimidazole VIM, initiator, and crosslinking agent; Step S20: The mixed solution is heated under inert gas protection to carry out a chemical reaction. The mixed solution after the chemical reaction is completed is coated on the substrate, and the solvent in the mixed solution is removed to obtain a high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups. Step S30: Assemble a lithium-ion battery using the high-temperature resistant polybenzimidazole separator with a semi-interpenetrating structure rich in imidazole groups.

[0034] In this embodiment, polybenzimidazole (OPBI) is a polymer with excellent thermal stability and mechanical properties. Because the OPBI molecular chain contains polar imidazole groups, it can enhance the affinity with the electrolyte. Therefore, using it to prepare a polymer separator for lithium-ion batteries can improve battery safety and electrochemical performance. Polyvinyl imidazole (PVIm) is also rich in polar imidazole groups and has good heat resistance. It can undergo a cross-linking reaction under the action of a cross-linking agent to form a network structure. The cross-linked network structure can enhance the heat resistance and mechanical strength of the separator. The cross-linking agent contains acyloxy or amide groups. These groups, in addition to enhancing the affinity between the separator and the electrolyte, can also promote the dissociation of lithium salts, thus facilitating the dissociation of lithium ions (Li). + The transport provides coordination sites.

[0035] Specifically, given the characteristics of polybenzimidazole OPBI, polyvinylimidazole PVIm, crosslinking agent, and semi-interpenetrating crosslinked network structure, the application of high-temperature resistant polybenzimidazole membranes with a semi-interpenetrating structure rich in imidazole groups has the following advantages: (1) The molecular chains in the semi-interpenetrating network structure are rich in imidazole groups, acyloxy groups, or amide groups. These groups have a strong affinity for the electrolyte, improving the electrolyte wettability and liquid retention of the membrane; (2) The molecular chains in the semi-interpenetrating network structure are rich in imidazole groups, acyloxy groups, or amide groups, promoting the dissociation of lithium salts and facilitating the dissociation of lithium ions (Li). + Provides coordination, facilitating lithium-ion Li + (3) The semi-interpenetrating network structure has a large number of uniformly distributed mesopores, which improves porosity and expands the lithium-ion Li + Lithium-ion Li+ is realized through the channels of the diaphragm. + (4) The membrane is a homogeneous organic material and there is no phase interface problem. (5) Polybenzimidazole OPBI and polyvinylimidazole PVIm have good heat resistance and the cross-linked structure further enhances the heat resistance and mechanical strength of the membrane.

[0036] This invention utilizes a solvent-free phase inversion method to obtain a high-temperature resistant lithium-ion battery separator with a microporous structure composed of regular finger-like pores and sponge-like pores. This separator exhibits excellent thermal stability, showing no significant shrinkage at 200°C, which supports its application in high-temperature lithium-ion batteries. The presence of polar imidazole groups and polar groups in the crosslinking agent increases the compatibility between the separator and the electrolyte, enabling better absorption and storage of the electrolyte (electrolyte absorption rate 676.79%), while also providing numerous coordination sites for lithium-ion transport. The semi-interpenetrating network structure has a large number of uniformly distributed mesopores, increasing the porosity (89.4%) and expanding the lithium-ion transport capacity. + Lithium-ion Li+ is realized through the channels of the diaphragm. +The OPBI-VED-20 separator exhibits uniform and efficient transport. Therefore, its ionic conductivity is 109.5% higher than that of the PP separator, and it can effectively suppress the disordered growth of lithium dendrites (3500h lithium plating / stripping test), improving the safety of lithium-ion batteries. Batteries assembled using this separator demonstrate excellent discharge specific capacity, cycle stability, and rate performance, especially outstanding charge-discharge stability at high temperatures. Batteries assembled using the OPBI-VED-20 separator exhibit a capacity of 168.7 mAh g⁻¹ at 90℃. -1 Its high discharge specific capacity is close to the theoretical capacity of LiFePO4 batteries (170 mAh g). -1 It can still operate safely at 100℃.

[0037] In some embodiments, the solvents of the solution and the mixed solution are selected from, but not limited to, one or more of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and N,N-dimethylacetamide.

[0038] In some embodiments, the initiator is azobisisobutyronitrile (AIBN), and the crosslinking agent is N,N'-methylenebisacrylamide (NMBA) or ethyl dimethacrylate (EDMA).

[0039] In some embodiments, the amount of N-vinylimidazolium VIM added is 0.05-0.20 g, which allows for the construction of a more suitable semi-interpenetrating network structure in the lithium-ion battery separator. This separator exhibits good electrolyte wettability, high conductivity, high porosity, and good electrochemical stability. Furthermore, its unique pore structure and ion coordination structure induce lithium ions to pass through the separator more rapidly and deposit uniformly on the lithium metal anode surface, effectively suppressing the disordered growth of lithium dendrites and improving the safety and electrochemical performance of the lithium-ion battery. Batteries assembled using this separator exhibit excellent discharge specific capacity, cycle stability, and rate performance, especially outstanding charge-discharge stability at high temperatures; in addition, the battery electrode polarization is low.

[0040] In a preferred embodiment, the solvent of the solution is N-methylpyrrolidone, the amount of the initiator azobisisobutyronitrile (AIBN) is 1 wt.% relative to the N-vinylimidazolium VIm monomer, and the amount of the crosslinking agent ethyl dimethacrylate (EDMA) is 0.3 times the mass of the VIm monomer. Polybenzimidazole (OPBI) has excellent thermal stability, mechanical properties, and flame retardancy, and its molecular chain contains polar ether bonds and imidazole groups, which can enhance the affinity with the electrolyte. Therefore, preparing it into a polymer separator for use in lithium-ion batteries can improve the safety and electrochemical performance of the battery. Polyvinylimidazolium (PVIm) is also rich in polar imidazole groups, has good heat resistance, and can undergo a crosslinking reaction under the action of a crosslinking agent to form a network structure. The crosslinked network structure can further enhance the heat resistance and mechanical strength of the separator. The crosslinking agent ethyl dimethacrylate (EDMA) molecule contains acyl groups. In addition to enhancing the affinity between the separator and the electrolyte, these polar groups can also promote the dissociation of lithium salts, leading to lithium ionization (Li). + The polybenzimidazole OPBI molecular chains and cross-linked polyvinylimidazole PVIm molecular chains intertwine to form a semi-interpenetrating network structure, providing coordination sites for lithium ion transport. + The rapid transport of lithium ions (Li) provides uniform microchannels, which is beneficial for the rapid transport of Li-ion ions. + Uniform deposition at the negative electrode effectively suppresses the disordered growth of lithium dendrites. A high-temperature resistant lithium-ion battery separator with a microporous structure composed of regular finger-like pores and sponge-like pores was obtained using a solvent-free phase inversion method. Therefore, considering the molecular chain structure and semi-interpenetrating network structure of polybenzimidazole (OPBI), polyvinylimidazole (PVIm), and crosslinking agent, as well as the finger-like and sponge-like pores, the separator exhibits excellent ionic conductivity, heat resistance, flame retardancy, and suppression of disordered lithium dendrite growth. Consequently, the assembled battery exhibits excellent discharge specific capacity, cycle stability, and rate performance, especially outstanding charge-discharge stability at high temperatures, showing a capacity of 168.7 mAh g⁻¹ at 90℃. -1 Its high discharge specific capacity is close to the theoretical capacity of LiFePO4 batteries (170 mAh g). -1 It can still operate safely at 100℃.

[0041] In some embodiments, the preparation process of the mixed solution is as follows: 0.3 g of polybenzimidazole OPBI powder is added to a solvent and stirred vigorously at 60-100°C for 10-15 hours; then 0.05-0.20 g of N-vinylimidazolium Vim is added to the solution; next, 1 wt.% of the initiator azobisisobutyronitrile (AIBN) relative to the N-vinylimidazolium Vim monomer is added to the solution; finally, N,N'-methylenebisacrylamide (NMBA) or ethyl dimethacrylate (EDMA) crosslinking agent is added to the solution, with a mass ratio of crosslinking agent to monomer of 0.3:1, and a corresponding molar ratio of nNMBA:nVIm of 1:5.5 or nEDMA:nVIm of 1:7.

[0042] In some embodiments, the method for removing the solvent from the mixed solution in step S20 is as follows: the mixed solution is heated under inert gas protection to carry out a chemical reaction; the mixed solution after the chemical reaction is completed is coated onto a substrate; and the substrate coated with the mixed solution is immersed in anhydrous methanol for immersion treatment. The immersion treatment is left to stand at room temperature for 8-15 minutes. A lithium-ion battery separator is prepared using a non-solvent-induced phase separation process. Since OPBI is insoluble in methanol, and cross-linked polyvinyl imidazole PVIm is also insoluble in methanol at room temperature, while NMP, DMSO, or DMAC are soluble in methanol, the substrate coated with the mixed solution is left to stand at room temperature for 8-15 minutes. Methanol is used to make the mixed solution form a film quickly and replace NMP, DMSO, or DMAC to form pores. This results in a lithium-ion battery separator with a micro-channel structure composed of regular finger-like pores and sponge-like pores, which is beneficial for the uniform deposition of lithium ions on the anode surface, thereby inhibiting the disorderly growth of lithium dendrites and improving the safety of the battery during service.

[0043] In some embodiments, in step S20, after the soaking treatment, a drying treatment is also performed to remove methanol from the channels.

[0044] In some embodiments, the substrate is, but is not limited to, a glass plate.

[0045] In addition, the present invention also provides several types of lithium-ion battery separators, which are prepared using the method for preparing high-temperature resistant polybenzimidazole separators with a semi-interpenetrating structure rich in imidazole groups.

[0046] In this embodiment, a semi-interpenetrating network structure is introduced into the lithium-ion battery separator. A high-temperature resistant lithium-ion battery separator rich in imidazole groups, with micropores composed of regular finger-like and sponge-like pores, is obtained using a non-solvent phase inversion method. The lithium-ion battery separator exhibits excellent thermal stability and flame retardancy, showing no thermal shrinkage at 200°C and no obvious combustion when placed in a flame. The lithium-ion battery separator also demonstrates good electrolyte wettability, high electrolyte absorption rate (676.79%), and high conductivity (1.32 mS / cm). -1 It exhibits good electrochemical stability; the lithium-ion battery separator possesses diverse lithium-ion transport mechanisms, which can improve lithium-ion efficiency. + The lithium-ion battery separator exhibits excellent transport efficiency between the positive and negative electrodes. It possesses a unique microporous structure composed of regular finger-like and sponge-like pores, as well as a semi-interpenetrating network structure. This structure induces lithium ions to pass through the separator more rapidly and deposit uniformly on the lithium metal anode surface, effectively suppressing the disordered growth of lithium dendrites and improving the safety and electrochemical performance of the lithium-ion battery. Batteries assembled using this separator demonstrate excellent discharge specific capacity, cycle stability, and rate performance, especially outstanding charge-discharge stability at high temperatures. Furthermore, the battery electrode polarization is low.

[0047] In some embodiments, the thickness of the high-temperature resistant polybenzimidazole separator with a semi-interpenetrating network structure rich in imidazole groups is 20-40 micrometers; the lithium-ion battery separator at this thickness has excellent thermal stability and can suppress the disordered growth of lithium dendrites.

[0048] In addition, the present invention also provides a lithium-ion battery, including a positive electrode, a negative electrode, and a semi-interpenetrating lithium-ion battery separator containing imidazole groups; the high-temperature resistant polybenzimidazole lithium-ion battery separator with a semi-interpenetrating network structure rich in imidazole groups is located between the positive electrode and the negative electrode.

[0049] In this embodiment, the LiFePO4 / Li battery assembled using the high-temperature resistant polybenzimidazole separator with a semi-interpenetrating network structure rich in imidazole groups exhibits a peak discharge specific capacity of 156.6 mAh g⁻¹ at 0.5C. -1 After 200 cycles, the battery retains 94.1% of its capacity. Furthermore, the battery assembled using the high-temperature resistant polybenzimidazole separator with a semi-interpenetrating network structure rich in imidazole groups can operate stably and safely at high temperatures (such as 80°C, 90°C, and 100°C).

[0050] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. Example

[0051] This embodiment provides a method for preparing a high-temperature resistant polybenzimidazole separator with a semi-interpenetrating network structure rich in imidazole groups, and a lithium-ion battery. The process flow diagram is shown in the attached figure of the specification. Figure 1 As shown, the steps include: Step S1: Dissolve polybenzimidazole OPBI, N-vinylimidazole VIM, initiator, and crosslinking agent in NMP to form a homogeneous mixed solution; Step S2: Stir the mixed solution continuously at 70°C under inert gas protection for 12 hours to obtain the mixed solution; Step S3: The obtained mixed solution is coated onto a glass plate with a scraper and transferred to anhydrous methanol (MeOH) and left to stand for 10 minutes to obtain a porous membrane. The porous membrane is then dried at room temperature to obtain a high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating network structure rich in imidazole groups. Step S4: Assemble a lithium-ion battery using the high-temperature resistant polybenzimidazole separator with the semi-interpenetrating network structure rich in imidazole groups.

[0052] The amounts of N-vinylimidazolium VIm monomer added were 0.05, 0.10, 0.15 and 0.20 g, respectively; the amount of initiator azobisisobutyronitrile (AIBN) was 1 wt.% of the N-vinylimidazolium VIm monomer; the crosslinking agent was N,N'-methylenebisacrylamide (NMBA) or ethyl dimethacrylate (EDMA); the mass ratio of crosslinking agent to N-vinylimidazolium VIm monomer was 0.3:1; and the corresponding molar ratios nNMBA:nVIm was 1:5.5 or nEDMA:nVIm was 1:7.

[0053] The inert gas is nitrogen (N2).

[0054] The solvent for the mixed solution is N-methylpyrrolidone (NMP).

[0055] The prepared membranes were named OPBI-VED-20, OPBI-VMBA-20, OPBI-VED-15, OPBI-VMBA-15, OPBI-VED-10, OPBI-VMBA-10, OPBI-VED-5, and OPBI-VMBA-5, respectively.

[0056] In comparison, this embodiment also provides PP (polypropylene) membranes, OPBI membranes, and OPBI-V-5 / 10 / 15 / 20 membranes (uncrosslinked). The preparation methods of OPBI membranes and OPBI-V-5 / 10 / 15 / 20 membranes (uncrosslinked) are the same as those of OPBI-VED-5 / 10 / 15 / 20 membranes and OPBI-VMBA-5 / 10 / 15 / 20 membranes, all of which use a solvent-free phase transfer method.

[0057] Figure 2 Preparation method, process, and lithium-ion lithium-ion battery of a high-temperature resistant polybenzimidazole separator with a semi-interpenetrating network structure rich in imidazole groups. + Transportation diagram.

[0058] Figure 3 (a) is the Fourier transform infrared spectrum, (b) is the X-ray diffraction pattern, (c) is the thermogravimetric analysis curve, (d) is the solubility test result, and (e) is the flexibility of the OPBI-VED-20 membrane. Figure 3 This paper presents the FT-IR spectra of OPBI, OPBI-VED-20, and OPBI-VMBA-20 membranes. Both OPBI-VED-20 and OPBI-VMBA-20 membranes show an FT-IR spectrum at 1602 cm⁻¹. -1 (C=N), 1400 cm -1 (benzimidazole structure) and 1169 cm -1 The characteristic peak of OPBI is observed at the (ether bond) position. Furthermore, the OPBI-VED-20 and OPBI-VMBA-20 membranes exhibit a peak at 1725 cm⁻¹. -1 The appearance of a new peak (C=O) confirms the existence of the PVIm and N,N'-methylenebisacrylamide NMBA crosslinking systems crosslinked with ethyl dimethacrylate (EDMA). Figure 3 b shows the XRD patterns of OPBI, OPBI-VED-20, and OPBI-VMBA-20 membranes. The diffraction peak shift of the OPBI-VMBA-20 membrane is more significant, and a noticeable shift is also observed in the OPBI-VED-20 membrane. This is because the cross-linked structure of the membrane leads to a decrease in interplanar spacing, and the degree of cross-linking using NMBA as the cross-linking agent is higher than that of the EDMA system. Figure 3 As shown in Figure d, by immersing the membranes in NMP solvent for solubility testing, the uncrosslinked membranes completely dissolved, while the crosslinked OPBI-VED-20 membranes exhibited a flocculent morphology, and the OPBI-VMBA-20 membranes maintained a clear thin-film structure. These results collectively confirm the presence of the PVIm crosslinked structure in the OPBI-VED-20 and OPBI-VMBA-20 membranes. The TGA curves of the membranes are shown below. Figure 3As shown in Figure c, compared to OPBI-based membranes, commercial PP membranes begin to lose weight around 350°C, and their weight retention is almost zero at ~480°C, indicating complete thermal decomposition and highlighting their poor thermal stability. OPBI-VED-20 and OPBI-VMBA-20 membranes exhibit initial weight loss around 300-350°C, which is attributed to the decomposition of PVIm. Figure 3 e showcased the flexibility test results of the OPBI-VED-20 separator, which showed no damage or cracking after bending and folding operations. This demonstrates its good flexibility, meeting the basic requirements for battery assembly and operation.

[0059] Figure 4 (a) is a schematic diagram of the solubility test during the pore formation process of the OPBI-VED-20 membrane, and (b) is a schematic diagram of the multipore formation mechanism. To further investigate the multipore formation mechanism of high-temperature resistant polybenzimidazole membranes with a semi-interpenetrating structure rich in imidazole groups (e.g., Figure 4 (a) An OPBI-VED-20 solution was coated onto a clean glass plate and dried in a 120°C oven for 24 hours to remove NMP, forming a dense diaphragm. The diaphragm was then cut into 2×2 cm samples, weighed, and immersed in methanol for 10 minutes. After drying, it was weighed again. Next, the diaphragm was immersed in deionized water for 12 hours, dried, and weighed. The dense diaphragm weighed 5.13 mg, 4.64 mg after methanol immersion, and 4.29 mg after deionized water immersion, indicating the existence of the aforementioned pore-forming mechanism. Figure 4 b elucidates a multiple pore-forming mechanism. During the pore-forming process of the high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups, both solvent and non-solvent diffusion occur simultaneously. Furthermore, unreacted VIM, short-chain PVIm, and uncrosslinked PVIm dissolve in methanol during the non-solvent phase transfer NIPS process. Additionally, uncrosslinked PVIm also dissolves during immersion in deionized water to remove unreacted VIM, short-chain PVIm, and impurities.

[0060] Figure 5(a) shows the affinity of the membranes prepared with different crosslinking agents to the liquid electrolyte; (b) shows the contact angle between the membranes prepared with different crosslinking agents and the electrolyte; (c) shows the surface pore distribution and percentage of the membranes prepared with different crosslinking agents; and (d) shows the scanning electron microscope images of the cross-sections of the membranes prepared with different crosslinking agents. The wettability of the OPBI-based membranes is significantly better than that of the PP membranes, with the OPBI-VED-20 membrane exhibiting superior wettability. The contact angle between the OPBI membrane and the electrolyte is 25.9°, much smaller than the 53.1° of the PP membrane, further confirming the excellent wettability of the OPBI membrane. This is attributed to the NH bonds and ether bonds present in the imidazole ring of OPBI, which endow the material with high polarity. These polar groups can form hydrogen bonds and van der Waals forces with the polar solvents in the electrolyte, thereby significantly reducing the surface energy. By constructing a semi-interpenetrating network to introduce PVIm into the OPBI-VED-20 and OPBI-VMBA-20 membranes, their electrolyte wettability was significantly better than that of OPBI and PP membranes, with the OPBI-VED-20 membrane exhibiting the best electrolyte wettability (contact angle of 14.8°). This improvement is due to the lone pair electrons possessed by the nitrogen atoms in the imidazole ring of PVIm and the polar groups in the crosslinking agent, which can also form hydrogen bonds and van der Waals interactions with the polar solvent in the electrolyte, thereby further reducing the electrolyte contact angle. Figure 5 As shown in Figure c, analysis of the pore distribution on the membrane surface further confirmed these observations: the porosity of the OPBI membrane was 18.76%, significantly higher than that of the PP membrane (8.09%), while the porosity of the OPBI-VED-20 membrane reached 26.94%. After introducing PVIm into the OPBI matrix through a semi-interpenetrating network, the OPBI-VED-20 membrane exhibited a more uniform surface pore distribution. Figure 5 Image d is a cross-sectional image of the diaphragm, showing that the pore structure of the OPBI-based diaphragm consists of prominent finger-like macropores and a small number of sponge-like pores. Notably, the finger-like pores in the OPBI-VED-20 diaphragm are more regular and exhibit better permeability.

[0061] Figure 6 (a) shows the affinity between the membranes prepared with different crosslinking agents and different amounts and the liquid electrolyte, and (b) shows the contact angle between the membranes prepared with different crosslinking agents and different amounts and the electrolyte. Figure 5Figures a and 5b clearly show that the membranes incorporating PVIm through the construction of a semi-interpenetrating network exhibit significantly better electrolyte wettability compared to OPBI and PP membranes, with the OPBI-VED-20 membrane demonstrating the best electrolyte wettability (contact angle of 14.8°). This performance improvement is attributed to the nitrogen atoms in the imidazole rings of PVIm and the polar groups in the crosslinking agent—these structural units, containing lone pairs of electrons, can form hydrogen bonds and van der Waals interactions with the polar solvents in the electrolyte, thereby further reducing the contact angle of the electrolyte. Figure 6 The test results were used as the preferred comparison.

[0062] Figure 7 The thermogravimetric analysis curves for the diaphragm are shown. Figure 3 The results for C were similar; other ratios of OPBI-VED and OPBI-VMBA membranes also showed mass loss within the same temperature range, confirming the successful introduction of PVIm. All OPBI-based membranes began to lose weight at approximately 550°C and maintained a high mass residue at 700°C, exhibiting excellent thermal stability. Notably, the OPBI-V-20 membrane did not show significant weight loss in the 300-350°C range, indicating that it failed to successfully construct a semi-interpenetrating network—this is due to the dissolution of uncrosslinked PVIm in methanol during membrane preparation (in the NIPS method, unpolymerized VIM monomers ultimately dissolve in methanol).

[0063] Figure 8 (a) shows the flame retardancy test of the separator, and (b) shows the heat resistance of PP, OPBI, OPBI-VED-20, and OPBI-VMBA-20 separators. Excellent flame retardant properties of lithium-ion battery separators are crucial for improving battery safety. Separators with good flame retardancy can effectively suppress flame spread and reduce the destructive impact of thermal runaway events, thereby significantly improving battery safety. Furthermore, flame-retardant separators can prevent the release of harmful gases during battery combustion, protecting both the environment and user safety. Figure 8 As shown in Figure a, the PP separator shrinks rapidly upon contact with a flame, ignites upon contact, and continues to burn even after the flame is removed. In contrast, the OPBI-based separator rapidly carbonizes without burning upon contact with a flame, attributed to the high thermal stability and high decomposition temperature inherent in OPBI's inherent rigid aromatic heterocyclic structure. The OPBI-VED-20 separator exhibits slight combustion upon contact with a flame, but rapidly carbonizes and ceases burning after the flame is removed—this phenomenon stems from the flammability of cross-linked PVIm; however, as an OPBI-based separator, it still maintains good flame-retardant properties. Therefore, sIPN separators can improve the safety of lithium-ion batteries during high-temperature operation to some extent. The thermal stability of the separator is crucial for ensuring the safety and performance of lithium-ion batteries at high temperatures. Figure 8As shown in b, the membranes were treated at different temperatures for 1 hour, and their thermal stability was evaluated by observing their shrinkage. The PP membranes showed no significant dimensional changes below 100°C, but exhibited significant shrinkage at 150°C and melting at 200°C; while the OPBI-based membranes did not show significant dimensional changes below 200°C.

[0064] Figure 9 The heat resistance of PP, OPBI, OPBI-VED-5 / 10 / 15, and OPBI-VMBA-5 / 10 / 15 separators was evaluated. Other OPBI-based separators also showed no dimensional changes below 200°C, exhibiting excellent thermal and dimensional stability. This characteristic stems from the alternating connections of benzimidazole rings and aromatic ether units in the OPBI backbone, forming a highly rigid conjugated structure. This rigid framework effectively restricts the rotation and thermal motion of the molecular chains, allowing the material to maintain structural integrity at high temperatures. Therefore, OPBI-based separators possess excellent thermal stability, meeting the basic requirements for battery operation in high-temperature environments.

[0065] Figure 10 Scanning electron microscope (SEM) images of PP, OPBI, OPBI-VED-20, and OPBI-VMBA-20 membranes are shown. Compared to PP membranes, OPBI-based membranes have larger pore sizes. This is because OPBI-based membranes are prepared using the NIPS method, whose pore formation mechanism relies on the diffusion exchange process between solvent and non-solvent, resulting in larger pore sizes compared to commercial PP membranes. Compared to OPBI membranes, high-temperature resistant polybenzimidazole membranes with a semi-interpenetrating structure rich in imidazole groups exhibit a denser and more uniform surface pore structure. Among them, the OPBI-VED-20 membrane, using EDMA as a crosslinking agent, exhibits a dense and uniform surface pore structure due to its moderate degree of crosslinking. However, when NMBA is used as a crosslinking agent, the OPBI-VMBA-20 membrane has a higher crosslinking density, resulting in a denser structure and lower porosity than the OPBI-VED-20 membrane.

[0066] Figure 11 Scanning electron microscope (SEM) images of PP, OPBI, OPBI-VED-5 / 10 / 15, and OPBI-VMBA-5 / 10 / 15 membranes. (Compared to...) Figure 10 Similar to the representation in [the previous section], the representation results are used to [comparison / representation]. Figure 10 The results are compared with those in the previous section for reference when making the best selection.

[0067] Figure 12(a) Nyquist plot of SS / SS symmetric cell assembled with PP, OPBI, OPBI-VED-20, and OPBI-VMBA-20 separators; (b) AC impedance curve of half cell; (c) Potential change of Li / Li symmetric cell assembled with PP and OPBI-VED-20 separators during long cycle; (d) LSV curve; (e) Cycling performance of LiFePO4 / separator / Li cell assembled with PP, OPBI, and OPBI-VED-20 separators at 25℃; (f) Rate performance of LiFePO4 / separator / Li cell assembled with PP, OPBI, OPBI-VED-20, and OPBI-VMBA-20 separators; (g) Physicochemical properties of PP, OPBI, OPBI-VED-20, and OPBI-VMBA-20 separators (P = porosity, EU = electrolyte absorption rate, σ = ionic conductivity). The ionic conductivity of the separator in a lithium-ion battery is a key parameter determining its electrochemical performance. Separators with high ionic conductivity can more effectively promote lithium-ion migration, thereby improving charge / discharge rates and energy conversion efficiency. The ionic conductivity of the separator was calculated by performing electrochemical impedance spectroscopy on assembled stainless steel / stainless steel symmetric cells. Figure 12 As shown in Figures a and g, the OPBI-based membrane exhibits significantly higher ionic conductivity than the PP membrane. This is attributed to its affinity for the electrolyte and its unique finger-like macropores and sponge-like channel structure, which collectively promote rapid lithium-ion conduction. Furthermore, as... Figure 13 As shown, the introduction of PVIm further enhances the ionic conductivity because the imidazole groups in PVIm increase the affinity between the membrane and the electrolyte. Specifically, the OPBI-VED-20 membrane exhibits a conductivity as high as 1.32 mS·cm. -1 The ionic conductivity of the OPBI-VMBA membrane is lower than that of the OPBI-VED membrane of the same proportion. This is because the higher degree of cross-linking resulting from the use of NMBA cross-linking agent reduces lithium-ion conductivity to some extent. It is worth noting that the higher conductivity of the high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups is also attributed to the nitrogen atoms in the imidazole rings. These nitrogen atoms, acting as Lewis bases, can coordinate with anions in the electrolyte, thereby promoting the dissociation of lithium salts. Figure 12 b illustrates the impedance performance of half-cells assembled using these separators, showing that the OPBI-VED-20 separator exhibits a lower interfacial resistance, further supporting the above conclusions. Lithium deposition / stripping experiments are crucial for evaluating the interfacial stability and electrochemical performance of battery materials during charge-discharge cycling. The lithium deposition / stripping process directly affects the energy density and safety of lithium-ion batteries. For example... Figure 12As shown in Figure c, during a 3500-hour cycle test, the battery using the OPBI-VED-20 separator exhibited a lower and more stable polarization voltage, significantly outperforming the battery using the PP separator. This result is likely related to the OPBI-VED-20 separator's stronger electrolyte affinity, higher electrolyte absorption rate, excellent ionic conductivity, lower interfacial resistance, and regular microporous structure. The electrochemical stability of the battery during charge and discharge was evaluated using a linear sweep voltammetry method. Figure 12 As shown in Figure d, the battery assembled with a PP separator exhibits voltage fluctuations around 3.2 V, while the battery with an OPBI-based separator demonstrates superior stability. In particular, the battery using the OPBI-VED-20 separator exhibits an electrochemical stability window of 4.0 V, exceeding that of other separators, demonstrating outstanding stability. This exceptional stability can be attributed to several factors: firstly, the OPBI-VED-20 separator possesses excellent absorption and retention capabilities for the electrolyte, effectively preventing interfacial reactions between the electrolyte and the negative electrode; secondly, the separator has a large finger-like pore structure, which facilitates rapid lithium-ion transport. In summary, the OPBI-VED-20 separator significantly improves battery performance while ensuring stable and safe operation. This also provides strong support for the safe operation and performance improvement of lithium-ion batteries at high temperatures. Battery cycle performance is a key indicator for evaluating lithium-ion batteries. Figure 12 As shown in Figure e, the battery's discharge capacity initially increases slightly during the first 10-20 cycles, then stabilizes, attributed to the slow processes of electrolyte wetting and battery activation. Peak discharge capacity is exhibited when the internal reactions reach equilibrium. The lithium-ion battery using a PP separator has an initial discharge capacity of 125.6 mAh g⁻¹. -1 The peak discharge capacity is 131.9 mAh g. -1 The lithium-ion batteries using OPBI, OPBI-V-20, OPBI-VMBA-20, and OPBI-VED-20 separators had initial discharge capacities of 138.6 mAh g⁻¹, respectively. -1 128.3 mAh g -1 136.4 mAh g -1 and 148.5 mAh g -1 The peak discharge capacity reached 140.9 mAh g. -1 138.5 mAh g -1 145.2 mAh g -1 and 156.6 mAh g -1The batteries assembled with OPBI-V-20 and OPBI separators exhibited similar discharge performance, further confirming that a semi-interpenetrating network did not form in the OPBI-V-20 separator due to the unsuccessful introduction of PVIm. Furthermore, the battery using the OPBI-VED-20 separator maintained a capacity retention of 94.1%, higher than the 91.1% of the OPBI separator, and its coulombic efficiency remained stable, indicating stable cycle performance. Figure 12 e and Figure 15 As shown, the introduction of PVIm significantly improves battery performance, partly due to its imidazole groups enhancing its affinity for the electrolyte and its coordination effect on lithium ions. Simultaneously, the solubility of unreacted VIM, short-chain PVIm, and uncrosslinked PVIm increases membrane porosity, ensuring efficient lithium-ion transport. In contrast, the high degree of crosslinking resulting from using VMBA as a crosslinking agent hinders lithium-ion migration. Therefore, OPBI-VED-20 is a better choice for lithium-ion batteries.

[0068] Figure 13 Nyquist plots of SS / SS symmetric cells assembled using PP, OPBI, OPBI-VED-5 / 10 / 15, and OPBI-VMBA-5 / 10 / 15 separators. The introduction of PVIm further improves ionic conductivity because the imidazole groups in PVIm improve the affinity between the separator and the electrolyte. Figure 12 In sample a, the OPBI-VED-20 membrane exhibited a filtration efficiency of 1.32 mS·cm. -1 The OPBI-VMBA membrane exhibits high ionic conductivity. However, its ionic conductivity is lower than that of the proportionally proportioned OPBI-VED membrane. This is because the higher cross-linking degree resulting from the use of NMBA reduces lithium-ion conductivity to some extent. Notably, the higher conductivity of the high-temperature resistant polybenzimidazole membrane with its imidazole-rich semi-interpenetrating structure is also attributed to the nitrogen atoms in the imidazole rings. These nitrogen atoms, acting as Lewis bases, can coordinate with anions in the electrolyte, thereby promoting the dissociation of lithium salts. Figure 12 b shows the impedance properties of half-cells assembled using these separators, where the OPBI-VED-20 separator exhibits a lower interface resistance, further supporting the above conclusions. Figure 13 As Figure 12 The comparison of 'a' is provided for reference during the selection process.

[0069] Figure 14 The rate performance of LiFePO4 / separator / Li batteries assembled using PP, OPBI, OPBI-VED-5 / 10 / 15, and OPBI-VMBA-5 / 10 / 15 separators was evaluated. Rate performance tests on the assembled batteries further validated their electrochemical performance at room temperature. Figure 12 f and Figure 14As shown, the discharge capacity decreases in a stepwise manner with increasing rate. It is noteworthy that the battery assembled using the OPBI-VED-20 separator can still provide 109.0 mAh g⁻¹ at a high rate of 5 C. -1 The discharge capacity is [value missing], and when the current rate recovers to the initial 0.1 C, its capacity can recover to a value close to the initial value of 161.1 mAhg. -1 This indicates that the battery assembled using the OPBI-VED-20 separator not only possesses excellent fast charge and discharge capabilities, but also exhibits good cycle stability and reversibility. Figure 14 As Figure 12 The comparison of f is provided for reference during the optimization process.

[0070] Figure 15 The cycle performance of LiFePO4 / separator / Li batteries assembled using PP, OPBI, OPBI-V-5 / 10 / 15 / 20, OPBI-VED-5 / 10 / 15 / 20 and OPBI-VMBA-5 / 10 / 15 / 20 separators at 25°C. Figure 15 As shown, the introduction of PVIm significantly improves battery performance. This is due, on the one hand, to its imidazole groups enhancing its affinity for the electrolyte and its coordination effect on lithium ions; on the other hand, the solubility of unreacted VIM, short-chain PVIm, and uncrosslinked PVIm increases the membrane porosity, ensuring efficient lithium-ion transport. In contrast, the high degree of crosslinking achieved by using VMBA as a crosslinking agent actually hinders lithium-ion migration. Therefore, OPBI-VED-20 is a better choice for lithium-ion batteries.

[0071] Figure 16 (a) shows the cycle performance of LiFePO4 / membrane / Li batteries assembled with PP and OPBI-VED-20 membranes at 0.5C rate and 90 °C; (b) shows the cycle performance of LiFePO4 / membrane / Li batteries assembled with OPBI-VED-20 membranes at different high temperatures; and (c) shows the performance of LiFePO4 / membrane / Li batteries assembled with different membranes at high temperatures. Figure 16 This section presents the results of charge-discharge cycle tests conducted at 90°C and a 0.5 C rate. The initial discharge capacity of all batteries was significantly higher than that tested at room temperature. This is primarily because the increased temperature promotes internal chemical reactions, increasing the reaction rate and thus releasing more charge. Notably, the battery assembled using the OPBI-VED-20 separator achieved a discharge capacity of 168.7 mAh g⁻¹. -1 The initial discharge capacity is close to its theoretical capacity (170 mAh g). -1The absence of significant performance degradation after 50 cycles indicates excellent high-temperature cycling stability. In contrast, batteries using PP separators exhibited significant performance degradation after the same number of cycles. Figure 16 As shown in Figure b, the battery assembled using the OPBI-VED-20 separator was tested at different high temperatures, with the highest operating temperature reaching 100℃. As the temperature increased, the discharge capacity first increased and then decreased. This is because, although high temperatures enhance reaction kinetics and reduce resistance, they also accelerate side reactions and solvent volatilization, thus weakening lithium-ion transport. Comparative analysis shows that the battery performs best at 90℃. Figure 16 As shown in Figure c, compared with other studies, the OPBI-VED-20 separator used in this work has certain advantages at high temperatures. Therefore, the battery assembled with the OPBI-VED-20 separator not only exhibits excellent electrochemical performance at room temperature, but also maintains excellent performance and stability at high temperatures.

[0072] In summary, this invention provides a high-temperature resistant polybenzimidazole separator with a semi-interpenetrating structure rich in imidazole groups, its preparation method, and a lithium-ion battery. The preparation method includes the following steps: providing a mixed solution of polybenzimidazole OPBI, N-vinylimidazolium VIM, an initiator, and a crosslinking agent; heating the mixed solution under inert gas protection to carry out a chemical reaction; coating the chemically reacted mixed solution onto a substrate; and removing the solvent from the mixed solution to obtain a high-temperature resistant polybenzimidazole separator with a semi-interpenetrating structure rich in imidazole groups; and assembling a lithium-ion battery using the high-temperature resistant polybenzimidazole separator with a semi-interpenetrating structure rich in imidazole groups. This invention introduces a semi-interpenetrating network structure into the lithium-ion battery separator and uses a solvent-free phase inversion method to obtain a high-temperature resistant lithium-ion battery separator rich in imidazole groups with micropores composed of regular finger-like pores and sponge-like pores. The separator prepared by this invention has a high affinity for the electrolyte and can simultaneously support lithium-ion batteries. + This membrane provides more sites and microchannels for lithium ion transport; a non-solvent phase inversion method is used to construct microchannels composed of regular finger-like pores and sponge-like pores in the separator. In terms of performance, the membrane exhibits good electrolyte wettability, high conductivity, and good electrochemical stability. Furthermore, its unique pore structure, ion coordination structure, and uniform mesopores of a semi-interpenetrating network induce lithium ions to pass through the separator more rapidly and deposit uniformly on the lithium metal anode surface, effectively suppressing the disordered growth of lithium dendrites and improving the safety and electrochemical performance of lithium-ion batteries. Batteries assembled using this membrane exhibit excellent discharge specific capacity, cycle stability, and rate performance, especially outstanding charge-discharge stability at high temperatures (80℃, 90℃, 100℃); in addition, the battery electrode polarization is low.

[0073] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups and its preparation method, characterized in that, Including the following steps: A mixed solution of polybenzimidazole OPBI, N-vinylimidazole VIM, initiator, and crosslinking agent is provided. The mixed solution is heated under inert gas protection to carry out a chemical reaction. The mixed solution after the chemical reaction is completed is coated on a substrate, and the solvent in the mixed solution is removed to obtain a high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups.

2. The method for preparing a high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups according to claim 1, characterized in that, The initiator is azobisisobutyronitrile (AIBN), and the crosslinking agent is N,N'-methylenebisacrylamide (NMBA) or ethyl dimethacrylate (EDMA).

3. The method for preparing a high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups according to claim 1, characterized in that, The solvent in the mixed solution is one or more of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and N,N-dimethylacetamide (DMAC).

4. The method for preparing a high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups according to claim 1, characterized in that, The preparation process of the mixed solution is as follows: 0.3g of polybenzimidazole OPBI powder is added to the solvent and stirred vigorously at 60-100℃ for 10-15 hours; then 0.05-0.20g of N-vinylimidazolium VIm is added to the solution; next, 1wt.% of the initiator azobisisobutyronitrile (AIBN) relative to the N-vinylimidazolium VIm monomer is added to the solution; finally, N,N'-methylenebisacrylamide (NMBA) or ethyl dimethacrylate (EDMA) crosslinking agent is added to the solution, with a mass ratio of crosslinking agent to monomer of 0.3:1, and the corresponding molar ratio nNMBA:nVIm is 1:5.5 or nEDMA:nVIm is 1:

7.

5. The method for preparing a high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups according to claim 1, characterized in that, The inert gas is either nitrogen (N2) or argon (Ar).

6. The method for preparing a high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups according to claim 1, characterized in that, The chemical reaction conditions are to heat the mixed solution to 60-100℃ and stir continuously for 10-15 hours.

7. The method for preparing a high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups according to claim 1, characterized in that, The method for removing the solvent from the mixed solution after the chemical reaction is completed is as follows: the substrate coated with the mixed solution after the chemical reaction is completed is immersed in anhydrous methanol for immersion treatment, wherein the immersion treatment is left to stand at room temperature for 8-15 minutes.

8. A high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups, characterized in that, The high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups, as described in any one of claims 1-7, is prepared by the method of preparation. The micropores of the membrane are composed of finger-like pores and sponge-like pores, and the molecular-level microstructure is a semi-interpenetrating structure.

9. The high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups according to claim 8, characterized in that, The thickness of the high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups is 20-40 micrometers.

10. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and a high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups as described in any one of claims 8-9; the high-temperature resistant polybenzimidazole membrane with a semi-interpenetrating structure rich in imidazole groups is located between the positive electrode and the negative electrode.

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