Lithium battery diaphragm containing aminated polybenzimidazole (at) halloysite nanotube complex (PyPBI (at) HNTs), preparation method of lithium battery diaphragm and lithium battery

Abstract

The invention relates to the technical field of lithium batteries, in particular to a lithium battery diaphragm containing aminated polybenzimidazole (at) halloysite nanotube composites (PyPBI (at) HNTs), a preparation method of the lithium battery diaphragm and a lithium battery, and the preparation method comprises four steps which are shown in Figure 1 in Figure 1 in Figure 1 in the specification. According to the invention, aminated polybenzimidazole (Py-NH2-PBI) and a halloysite nanotube (HNTs-Cl) with a halogen atom (Cl) on the surface are synthesized, and the Py-NH2-PBI is wrapped on the HNTs through a chemical reaction to form an organic-inorganic complex (PyPBI-HNTs) with a core-shell structure. The PyPBI-coated HNTs are uniformly dispersed in an OPBI matrix through a non-solvent phase transfer method (NIPS) to obtain the OPBI-coated Py-H composite diaphragm disclosed by the invention, and the problem that the compatibility of the HNTs and the diaphragm matrix OPBI is poor is solved. The diaphragm is rich in nitrogen element and has high affinity with electrolyte; compared with an OPBI coated HNTs diaphragm, the OPBI coated Py-H composite diaphragm has the advantages that the tensile strength (TS) and the ionic conductivity (sigma) are respectively improved by 30.96% and 21.82%, and the lithium dendrite inhibition effect is good; and the assembled lithium battery has high specific capacity and can safely and stably operate at 90 DEG C.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), a preparation method thereof, and a lithium battery. Background Art

[0002] The separator is one of the core components of lithium batteries (LIBs). Its function is to separate the positive electrode from the negative electrode to prevent the battery from short-circuiting and causing safety accidents such as fire and explosion. At the same time, it ensures that lithium ions can pass through the internal microporous channels during the charge and discharge cycles to ensure the normal operation of the battery. The quality of its performance directly affects the safety, capacity, rate, life and other performances of the battery during service.

[0003] Polyolefin separators, such as polyethylene (PE) separators, polypropylene (PP) separators, and PE / PP composite membranes, are the separator products commonly used in the production of commercial lithium batteries at present. Their production processes mainly include dry process and wet process. Due to the limitations of material properties and production processes, polyolefin separators still face relatively difficult problems in application: First, the melting point of polyolefin materials is low, which is an inherent property, so polyolefins have poor heat resistance, resulting in the fact that such separators are prone to thermal shrinkage at high temperatures, thus causing battery short-circuiting, and further triggering dangerous events such as fire and explosion of lithium batteries; Second, the conductivity, electrolyte wettability, flame retardancy, electrochemical stability window, etc. of polyolefin separators are not ideal; Third, the growth of lithium dendrites is serious during the service of the battery assembled with polyolefin separators. Lithium dendrites are easy to pierce the separator, causing micro-short circuits inside the lithium battery and posing potential safety hazards to the lithium battery; Fourth, the cycle stability of the battery assembled with polyolefin separators at high temperatures (such as 50°C, 90°C) is very poor; Fifth, the electrode polarization of the lithium battery assembled with polyolefin separators is relatively large.

[0004] To improve the use safety and electrochemical performance of lithium batteries, some materials are coated on the surface of polyolefin separators through different coating processes to form coated polyolefin separators; currently, the coated separators on the market mainly include inorganic coated separators, organic coated separators, and organic + inorganic coated separators. Coating heat-resistant materials (inorganic, organic, inorganic / organic mixture) on the surface of polyolefin separators improves the heat resistance of the separators to a certain extent. However, there is still a risk that the matrix material - polyolefin under the coating will undergo thermal shrinkage and cause the collapse of the overall structure of the separator at a sufficiently high temperature and for a sufficiently long time. Therefore, this modification scheme based on polyolefin separators cannot fundamentally solve the heat resistance problem of the separators and cannot completely solve the use safety of lithium batteries. In addition, the growth of anode lithium dendrites is still relatively serious during the charge and discharge cycles of the lithium battery assembled with this kind of coated polyolefin separator. As is well known, coating will also produce a series of negative effects, such as an increase in separator thickness and bulk resistance (Rb ) There are problems such as increase and decrease in charge / discharge efficiency. In addition to modified polyolefin separators, some scholars have developed high-temperature resistant composite lithium battery separators. For example, high-temperature resistant polymer materials (such as polyvinylidene fluoride (PVDF), polyimide (PI), polybenzimidazole (PBI), polyether ether ketone (PEEK), etc.) are used as the matrix, and high-temperature resistant inorganic nano-fillers (such as halloysite, silica, boron nitride, etc.) are introduced. However, the prominent problems of this separator preparation scheme are the uniform dispersion of inorganic nano-fillers in the polymer matrix and the compatibility with the polymer matrix.

[0005] Therefore, the existing separator technology still needs to be improved and developed. Summary of the Invention

[0006] In view of the above deficiencies of the existing separator technology, the purpose of the present invention is to provide a lithium battery separator containing amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), its preparation method, and a lithium battery, aiming to solve the following problems: a. Existing polyolefin separators are prone to thermal shrinkage at high temperatures; b. The lithium dendrites on the anode surface of lithium batteries assembled with existing polyolefin separators grow disorderly seriously; c. The high-temperature cycle stability of lithium batteries assembled with existing polyolefin separators is poor; d. The electrode polarization of lithium batteries assembled with existing polyolefin separators is relatively large; e. The conductivity, electrolyte wettability, flame retardancy, electrochemical stability window, etc. of polyolefin separators are not very ideal; f. The compatibility between inorganic nano-fillers and polymer matrix in organic-inorganic high-temperature resistant composite separators and the uniform dispersion of inorganic nano-fillers in the polymer matrix.

[0007] The technical solution of the present invention is as follows:

[0008] A preparation method of a lithium battery separator containing amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) includes the steps:

[0009] Provide a solution of OPBI solution, amino-functionalized polybenzimidazole (Py-NH2-PBI) and halloysite nanotube (HNTs) composite (PyPBI@HNTs);

[0010] Mix the OPBI solution and the solution of amino-functionalized polybenzimidazole (Py-NH2-PBI) and halloysite nanotube (HNTs) composite (PyPBI@HNTs) to obtain a mixed solution (PyPBI@HNTs-OPBI solution);

[0011] Coat the mixed solution (PyPBI@HNTs-OPBI solution) on a substrate, and remove the solvent in the mixed solution (PyPBI@HNTs-OPBI solution) to obtain a lithium battery composite separator (OPBI@Py-H) in which the PyPBI@HNTs composite is uniformly dispersed in a polyarylether benzimidazole (OPBI) matrix.

[0012] The preparation method of a lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), characterized in that the PyPBI@HNTs composite is an organic-inorganic composite with a core-shell structure formed by chemically wrapping aminated polybenzimidazole (Py-NH2-PBI) onto the outer surface of halloysite nanotubes (HNTs).

[0013] The preparation method of a lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), wherein the solvents of the PyPBI@HNTs composite solution and the OPBI solution are jointly selected from one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0014] The preparation method of a lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), wherein in the PyPBI@HNTs-OPBI mixed solution, the total mass of the PyPBI@HNTs composite is 5%-30% of the mass of OPBI.

[0015] The preparation method of a lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), wherein the preparation of the organic-inorganic composite with a core-shell structure (PyPBI@HNTs) is to first synthesize modified halloysite nanotubes (HNTs-Cl) with halogen atoms (Cl) on the surface through a chemical reaction, then synthesize aminated polybenzimidazole (Py-NH2-PBI) through a chemical reaction, and finally react HNTs-Cl with Py-NH2-PBI to obtain PyPBI@HNTs.

[0016] The preparation method of a lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), wherein the preparation process of the OPBI solution: add 0.3 g of OPBI powder into a solvent, and vigorously stir at 60 - 100 °C for 18 - 24 hours; the preparation process of the PyPBI@HNTs composite solution: disperse the PyPBI@HNTs composite into a solvent, and perform ultrasonic treatment for 0.5 - 2 hours; the preparation process of the PyPBI@HNTs-OPBI mixed solution: slowly drop the PyPBI@HNTs composite solution into the OPBI solution, and stir at a low speed for 18 - 30 hours.

[0017] The preparation method of a lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), wherein the method for removing the solvent in the PyPBI@HNTs-OPBI mixed solution is: place the substrate coated with the PyPBI@HNTs-OPBI mixed solution in anhydrous methanol for soaking treatment, and the soaking treatment is to stand still at room temperature for 8 - 15 minutes.

[0018] A lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), the composite separator is prepared by the nonsolvent induced phase separation (NIPS) method, and the microscopic pores of the separator are composed of regular, uniform and dense finger-like pores and sponge-like pores.

[0019] The lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), wherein the thickness of the composite separator is 20 - 40 microns.

[0020] A lithium battery, including a positive electrode sheet, a negative electrode sheet and a lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), that is, a composite separator (OPBI@Py-H); the lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), that is, the composite separator (OPBI@Py-H), is located between the positive electrode sheet and the negative electrode sheet of the lithium battery.

[0021] Beneficial effects: The present invention provides a lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), a preparation method thereof, and a lithium battery. The preparation method includes the steps of: providing a solution of OPBI, a composite (PyPBI@HNTs) of amino-functionalized polybenzimidazole (Py-NH2-PBI) and halloysite nanotubes (HNTs); mixing the OPBI solution and the solution of the composite (PyPBI@HNTs) of amino-functionalized polybenzimidazole (Py-NH2-PBI) and halloysite nanotubes (HNTs) to obtain a mixed solution (PyPBI@HNTs-OPBI solution); coating the mixed solution (PyPBI@HNTs-OPBI solution) on a substrate and removing the solvent in the mixed solution (PyPBI@HNTs-OPBI solution) to obtain a lithium battery composite separator (OPBI@Py-H) in which the PyPBI@HNTs composite is uniformly dispersed in a polyarylether benzimidazole (OPBI) matrix; and assembling a lithium battery using the composite separator (OPBI@Py-H). By introducing the composite (PyPBI@HNTs) into the OPBI-based separator, the present invention has the following advantages: (1) It solves the problem of poor compatibility between HNTs and the separator matrix OPBI, realizes the uniform dispersion of HNTs in the separator matrix OPBI, and the tensile strength (TS) of the OPBI@Py-H composite separator is increased by 30.96% compared with the OPBI@HNTs separator; (2) The OPBI@Py-H composite separator is rich in nitrogen elements, has a large affinity with the electrolyte, and the separator has regular, uniform, and dense finger-like pores and sponge-like pores, which provide more sites and microscopic channels for the transport of lithium ions, is conducive to inducing lithium ions to pass through the separator more quickly and uniformly deposit on the surface of the lithium metal anode. These characteristics in terms of performance and structure make the ionic conductivity (σ) of the OPBI@Py-H composite separator increase by 21.82% compared with the OPBI@HNTs separator, and it has a good effect of inhibiting lithium dendrites; (3) The lithium battery assembled using the OPBI@Py-H composite separator has a large specific capacity, good cycle stability and rate performance, and a low degree of battery electrode polarization; (4) The OPBI@Py-H composite separator has excellent high-temperature resistance, and the battery assembled using this composite separator can operate safely and stably at 90°C. Description of the Drawings

[0022] Figure 1 It is a schematic diagram of the process for preparing a lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) and assembling a lithium battery according to the present invention.

[0023] Figure 2Schematic diagrams of the preparation principles and processes of modified halloysite nanotubes with halogen atoms (Cl) on the surface (HNTs-Cl), aminated polybenzimidazole (Py-NH2-PBI), organic-inorganic composite (PyPBI@HNTs), and composite separator (OPBI@Py-H).

[0024] Figure 3 For (a) TEM image and EDS spectrum of HNTs-Cl, (b-d) TEM images of HNTs-Cl, Py-NH2-PBI, and PyPBI@HNTs, (e) TEM image and EDS spectrum of PyPBI@HNTs, (f) XRD patterns of HNTs-Cl, PyPBI@HNTs, and Py-NH2-PBI, (g) FT-IR spectra of HNTs-Cl, PyPBI@HNTs, and Py-NH2-PBI.

[0025] Figure 4 SEM images of the surface and cross-section of PP, OPBI, OPBI@HNT20, and OPBI@Py-H20 separators.

[0026] Figure 5 For (a) structural characterization diagrams of HNTs unit cell, OPBI chain segment, and Py-NH2-PBI chain segment, (b) diagram of the interfacial structure evolution before and after the incorporation of Py-NH2-PBI.

[0027] Figure 6 For (a) AC impedance curves of double-steel plate symmetric cells assembled with PP, OPBI, OPBI@HNT20, and OPBI@Py-H20 separators respectively, (b) Nyquist plots of double-lithium electrode symmetric cells assembled with PP, OPBI, OPBI@HNT20, and OPBI@Py-H20 separators respectively, (c) LSV curves of cells assembled with PP, OPBI, and OPBI@Py-H20 separators respectively; (d) plating / stripping cycling curves of symmetric cells, (e) Figure 4 Magnified view of (d), (f) charge-discharge curves of LiFePO4 half-cells assembled with PP, OPBI, OPBI@HNT20, and OPBI@Py-H20 separators for 300 cycles, (g-h) charge-discharge voltage curves of LiFePO4 half-cells assembled with PP and OPBI@Py-H20 separators respectively, (i) rate curves of LiFePO4 half-cells assembled with PP, OPBI, OPBI@HNT20, and OPBI@Py-H20 separators respectively.

[0028] Figure 7SEM images of the lithium anode after 300 cycles of the LiFePO4 half-cells assembled with (a) PP, OPBI, and OPBI@Py-H20 separators respectively, and (b) a schematic diagram of lithium dendrite growth on the lithium anode of the battery.

[0029] Figure 8 Discharge specific capacities of the LiFePO4 half-cells assembled with PP and OPBI@Py-H20 separators at 50 °C and 90 °C.

[0030] Figure 9 1H NMR spectrum of Py-NH2-PBI.

[0031] Figure 10 Infrared spectra of (a) PyPBI@HNTs, OPBI separator, and OPBI@Py-H20 separator, and (b) XRD patterns of PyPBI@HNTs, OPBI separator, and OPBI@Py-H20 separator.

[0032] Figure 11 SEM images of the pore distribution on the separator surface drawn using Image-J software, (b) digital photos of the electrolyte-wetted separator, (c) contact angle between the electrolyte and the separator, (d) percentage of pore volume on the separator surface, and (e) porosity and electrolyte absorption rate of the separator.

[0033] Figure 12 Images of (a) folding, bending, and recovery of the OPBI@Py-H20 separator, and (b) stress-strain curves of the OPBI@HNT20 separator and OPBI@Py-H20 separator.

[0034] Figure 13 Images of (a) the separator after being placed at different temperatures for 1 h, (b) experimental phenomena of the separator combustion, and (c) TGA curve of the separator. Detailed implementation manners

[0035] The present invention provides a lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), a preparation method thereof, and a lithium battery. To make the objectives, technical solutions, and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] Those skilled in the art of the present technology can understand that, unless otherwise defined, all terms used herein (including technical terms and scientific terms) have the same meaning as the general understanding of those of ordinary skill in the art to which the present invention pertains. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with the meaning in the context of the prior art, and will not be interpreted with an idealized or overly formal meaning unless specifically defined as here.

[0037] As Figure 1 shown, the present invention provides a lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), a preparation method thereof, and a lithium battery, including the steps of:

[0038] Step S10: Provide a solution of OPBI solution, aminated polybenzimidazole (Py-NH2-PBI), and a composite (PyPBI@HNTs) of halloysite nanotubes (HNTs);

[0039] Step S20: Mix the OPBI solution and the solution of the composite (PyPBI@HNTs) of aminated polybenzimidazole (Py-NH2-PBI) and halloysite nanotubes (HNTs) to obtain a mixed solution (PyPBI@HNTs-OPBI solution);

[0040] Step S30: Coat the mixed solution (PyPBI@HNTs-OPBI solution) on a substrate and remove the solvent in the mixed solution (PyPBI@HNTs-OPBI solution) to obtain a lithium battery composite separator (OPBI@Py-H) in which the PyPBI@HNTs composite is uniformly dispersed in a polyarylether benzimidazole (OPBI) matrix;

[0041] Step S40: Assemble a lithium battery using the composite separator (OPBI@Py-H).

[0042] In this embodiment, poly(aryl ether benzimidazole) (OPBI) is a polymer with excellent thermal stability and mechanical properties. Since the OPBI molecular chain contains polar ether bonds and pyridine structures, it can enhance the affinity with the electrolyte. Therefore, when it is prepared into a polymer separator for use in lithium batteries, the safety and electrochemical performance of the battery can be improved. Halloysite nanotubes (HNTs) are an inorganic nanomaterial with good chemical stability, a unique tubular structure, and abundant surface hydroxyl groups. The HNTs can be modified through chemical reactions to synthesize modified halloysite nanotubes (HNTs-Cl) with halogen atoms (Cl) on the surface. The PyPBI@HNTs composite is obtained by chemically wrapping amino-functionalized polybenzimidazole (Py-NH2-PBI) on the surface of HNTs. For the specific preparation process, please refer to the attached Figure 2 .

[0043] Specifically, in view of the characteristics of OPBI, HNTs, Py-NH2-PBI, and the PyPBI@HNTs composite, the composite separator (OPBI@Py-H) prepared by the technical solution of the present invention has the following advantages: (1) It solves the problem of poor compatibility between HNTs and the separator matrix OPBI, realizes the uniform dispersion of HNTs in the separator matrix OPBI, and the tensile strength (TS) of the OPBI@Py-H composite separator is increased by 30.96% compared with the OPBI@HNTs separator; (2) The OPBI@Py-H composite separator is rich in nitrogen elements and has a large affinity with the electrolyte. Moreover, the separator has regular, uniform, and dense finger-shaped pores and sponge-like pores, which provide more sites and microscopic channels for the transport of lithium ions, facilitating the induction of lithium ions to pass through the separator more quickly and deposit uniformly on the surface of the lithium metal anode. These performance and structural characteristics make the ionic conductivity (σ) of the OPBI@Py-H composite separator increased by 21.82% compared with the OPBI@HNTs separator, and it has a good effect on inhibiting lithium dendrite growth; (3) The lithium battery assembled with the OPBI@Py-H composite separator has a large specific capacity, good cycle stability and rate performance, and a low degree of battery electrode polarization; (4) The OPBI@Py-H composite separator has excellent high-temperature resistance, and the battery assembled with this composite separator can operate safely and stably at 90°C.

[0044] In some embodiments, the solvents of the solution of the complex (PyPBI@HNTs) of the aminated polybenzimidazole (Py-NH2-PBI) and halloysite nanotubes (HNTs) and the solvent of the OPBI solution are jointly selected from, but not limited to, one or more of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and N,N-dimethylacetamide; ensuring that the solvents of the solution of the complex (PyPBI@HNTs) of the aminated polybenzimidazole (Py-NH2-PBI) and halloysite nanotubes (HNTs) and the OPBI solution are consistent is conducive to the subsequent use of the non-solvent induced phase separation process.

[0045] In some embodiments, in the PyPBI@HNTs-OPBI mixed solution, the total mass of the PyPBI@HNTs complex is 5%-30% of the mass of OPBI; this can make the lithium battery separator contain an appropriate amount of PyPBI@HNTs, so as to utilize PyPBI@HNTs to improve the diffusion force in the non-solvent phase inversion process and obtain a high-temperature resistant lithium battery composite separator (OPBI@Py-H) with a microstructure composed of regular finger-like pores and sponge-like pores. This composite separator is rich in nitrogen elements, has good electrolyte wettability, high conductivity, and good electrochemical stability. Moreover, through the unique pore structure and ion coordination structure, it induces lithium ions to pass through the separator more quickly and deposit uniformly on the surface of the lithium metal anode, effectively suppressing the disordered growth of lithium dendrites and improving the safety and electrochemical performance of lithium batteries. The battery assembled with this separator exhibits excellent discharge specific capacity, cycle stability, and rate performance, especially being able to operate safely and stably at 90 °C; in addition, the degree of electrode polarization of the battery is relatively low.

[0046] In a preferred embodiment, the complex (PyPBI@HNTs) is obtained by chemically reacting amino-functionalized polybenzimidazole (Py-NH2-PBI) to coat the surface of HNTs; the solution of the complex (PyPBI@HNTs) is a solution using N-methylpyrrolidone as the solvent; the solvent of the OPBI solution is N-methylpyrrolidone; polyarylether benzimidazole has excellent thermal stability, mechanical properties, flame retardancy, etc., and the molecular chain contains polar ether bonds and pyridine structures. Halloysite nanotubes (HNTs) are an inorganic nanomaterial with good chemical stability, a unique tubular structure, and abundant surface hydroxyl groups, and can be modified by chemical reactions to synthesize modified halloysite nanotubes (HNTs-Cl) with halogen atoms (Cl) on the surface. The PyPBI@HNTs complex is obtained by chemically reacting amino-functionalized polybenzimidazole (Py-NH2-PBI) to coat the surface of HNTs. The separator prepared by introducing the nitrogen-rich PyPBI@HNTs complex into the OPBI matrix not only solves the compatibility problem between the inorganic nanomaterial HNTs and the OPBI matrix and the problem of uniform dispersion in the separator matrix OPBI, but also improves the affinity between the separator and the electrolyte and the high-temperature resistance of the separator; the introduction of the PyPBI@HNTs complex changes the diffusion force in the non-solvent phase inversion process, resulting in the formation of a microscopic pore structure composed of regular finger-like pores and sponge-like pores in the separator. The good compatibility of the PyPBI@HNTs complex with the OPBI matrix and its uniform dispersion in the OPBI matrix result in a 30.96% increase in the tensile strength (TS) of the OPBI@Py-H composite separator compared to the OPBI@HNTs separator; the OPBI@Py-H composite separator is rich in nitrogen elements, has a large affinity with the electrolyte, and has regular, uniform, and dense finger-like pores and sponge-like pores, providing more sites and microscopic channels for the transport of lithium ions, which is conducive to inducing lithium ions to pass through the separator more quickly and deposit uniformly on the surface of the lithium metal anode. These performance and structural characteristics result in a 21.82% increase in the ionic conductivity (σ) of the OPBI@Py-H composite separator compared to the OPBI@HNTs separator, and it has a good effect on inhibiting lithium dendrites; the OPBI@Py-H composite separator has excellent high-temperature resistance, and the battery assembled with this composite separator can operate safely and stably at 90°C; the lithium battery assembled with the OPBI@Py-H composite separator has a large specific capacity, good cycle stability and rate performance, and a low degree of battery electrode polarization. Applying the OPBI@Py-H composite separator to lithium batteries helps to solve the safety problems of lithium batteries caused by the heat resistance, flammability of the separator and the disordered growth of lithium dendrites, and improves the safety performance and electrochemical performance of lithium batteries from the perspective of the separator.

[0047] In some embodiments, the preparation process of the OPBI solution: Add 0.3 g of OPBI powder into a solvent, and vigorously stir at 60 - 100 °C for 18 - 24 hours; the preparation process of the PyPBI@HNTs composite solution: Disperse the PyPBI@HNTs composite into a solvent, and ultrasonically treat for 0.5 - 2 hours; the preparation process of the mixed solution (PyPBI@HNTs-OPBI solution): Slowly drip the PyPBI@HNTs composite solution into the OPBI solution, and stir at a low speed for 18 - 30 hours.

[0048] In some embodiments, in step S30, the method for removing the solvent in the mixed solution (PyPBI@HNTs-OPBI solution) is: Place the substrate coated with the mixed solution (PyPBI@HNTs-OPBI solution) in anhydrous methanol for soaking treatment. The soaking treatment is to let it stand at room temperature for 8 - 15 minutes. Use the nonsolvent-induced phase separation process to prepare a lithium battery separator. Since OPBI is insoluble in methanol, and the composite (PyPBI@HNTs) is also insoluble in methanol, while NMP or DMSO or DMAC is soluble in methanol, place the substrate coated with the mixed solution (PyPBI@HNTs-OPBI solution) at room temperature for 8 - 15 minutes. Use methanol to make the mixed solution (PyPBI@HNTs-OPBI solution) form a film quickly, and displace NMP or DMSO or DMAC to form pores, so that the prepared lithium battery separator has a microscopic pore structure composed of regular finger-like pores and sponge-like pores, which is beneficial to the rapid transmission of lithium ions and their uniform deposition on the anode surface, thereby inhibiting the disordered growth of lithium dendrites and improving the safety during the service process of the battery.

[0049] In some embodiments, in step S30, after the soaking treatment, a drying treatment is also performed to remove the methanol in the pores.

[0050] In some embodiments, the substrate is but not limited to a glass plate.

[0051] In addition, the present invention also provides two kinds of lithium battery separators, namely OPBI separator and OPBI@HNTs separator, which are prepared by the preparation method of the lithium battery separator containing the amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) (i.e., OPBI@Py-H).

[0052] In this embodiment, the preparation of the organic-inorganic composite (PyPBI@HNTs) with a core-shell structure is carried out by first synthesizing modified halloysite nanotubes (HNTs-Cl) with halogen atoms (Cl) on the surface through a chemical reaction, then synthesizing amino-functionalized polybenzimidazole (Py-NH2-PBI) through a chemical reaction, and finally reacting HNTs-Cl with Py-NH2-PBI to obtain the composite PyPBI@HNTs. The amino-functionalized Py-NH2-PBI serves as a shell to wrap around the surface of the core (HNTs). The purpose is to improve the compatibility between HNTs and the OPBI separator matrix, and introduce the composite PyPBI@HNTs into the OPBI separator matrix to enhance the mechanical strength and electrolyte affinity of the composite separator (OPBI@Py-H).

[0053] Introduce the composite PyPBI@HNTs into the OPBI separator matrix, and use the composite PyPBI@HNTs to change the diffusion force during the nonsolvent phase inversion process to obtain a lithium battery composite separator (OPBI@Py-H) with a microstructure composed of regular, uniform, and dense finger-like pores and sponge-like pores. The lithium battery composite separator (OPBI@Py-H) has excellent thermal stability and flame retardancy, without thermal shrinkage at 200 °C and no obvious combustion phenomenon when placed on a flame; the lithium battery composite separator (OPBI@Py-H) has good electrolyte wettability, a large electrolyte absorption rate (396%), and good electrochemical stability; the tensile strength (TS) and ionic conductivity (σ) of the lithium battery composite separator (OPBI@Py-H) are increased by 30.96% (from 8.30 MPa to 10.87 MPa) and 21.82% (from 1.65 mS·cm -1 to 2.01 mS·cm -1 ) compared with the separator (OPBI@HNTs), respectively, and has a good effect on suppressing lithium dendrites. The lithium battery composite separator (OPBI@Py-H) has diverse lithium ion transport modes, which can improve the transport efficiency of lithium ions between the positive and negative electrodes of the battery; the lithium battery composite separator (OPBI@Py-H) has a unique microstructure composed of regular finger-like pores and sponge-like pores and ion coordination sites, which can induce lithium ions to pass through the separator more quickly and deposit uniformly on the surface of the lithium metal anode, effectively suppressing the disordered growth of lithium dendrites and enhancing the use safety and electrochemical performance of lithium batteries. The battery assembled with this composite separator (OPBI@Py-H) exhibits excellent discharge specific capacity, cycle stability, and rate performance, especially being able to operate safely and stably at 90 °C; in addition, the degree of electrode polarization of the battery is relatively low.

[0054] In some embodiments, the thickness of the lithium battery composite separator (OPBI@Py-H) is 20 - 40 microns; the lithium battery composite separator (OPBI@Py-H) at this thickness has excellent thermal stability and can simultaneously inhibit the disordered growth of lithium dendrites.

[0055] In addition, the present invention also provides a lithium battery, comprising a positive electrode sheet, a negative electrode sheet, and a lithium battery composite separator (OPBI@Py-H); the composite separator (OPBI@Py-H) is located between the positive electrode sheet and the negative electrode sheet of the lithium battery.

[0056] In this embodiment, after 300 cycles at 0.5C, the capacity retention rate of the LiFePO4 / Li battery assembled with the lithium battery composite separator (OPBI@Py-H) is 87.59%. Moreover, the LiFePO4 / Li battery assembled with the lithium battery composite separator (OPBI@Py-H) operates safely at a temperature of 90°C and has a considerable capacity retention rate.

[0057] The following further gives examples to illustrate the present invention in detail. Similarly, it should be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the protection scope of the present invention.

[0058] Example 1

[0059] This example provides a lithium battery separator containing an amidated polybenzimidazole@halloysite nanotube complex (PyPBI@HNTs), its preparation method, and a lithium battery. The process schematic diagram is as Figure 1 shown, including the steps:

[0060] Step S1: Dissolve OPBI in NMP to form a uniform OPBI solution;

[0061] Dissolve the complex (PyPBI@HNTs) of amidated polybenzimidazole (Py-NH2-PBI) and halloysite nanotubes (HNTs) in NMP to form a PyPBI@HNTs complex solution with NMP as the solvent.

[0062] Step S2: Slowly drop the PyPBI@HNTs complex solution into the OPBI solution and stir at a low speed for 24 hours to obtain a mixed solution (PyPBI@HNTs-OPBI solution). The total mass of the PyPBI@HNTs complex in the mixed solution (PyPBI@HNTs-OPBI solution) is 20% of the mass of OPBI.

[0063] Step S3: Coat the obtained mixed solution (PyPBI@HNTs-OPBI solution) on a glass plate with a spatula, transfer it to anhydrous methanol (MeOH), and let it stand for 10 minutes to obtain a porous membrane. Then dry the porous membrane at room temperature to obtain a composite separator (OPBI@Py-H).

[0064] Step S4: Assemble a lithium battery using the composite separator (OPBI@Py-H).

[0065] Among them, the preparation process of the OPBI solution: Add 0.3 g of OPBI powder to 3 mL of NMP, and stir vigorously at 80 °C for 24 hours.

[0066] The preparation process of the PyPBI@HNTs composite solution: Disperse 0.06 g of the PyPBI@HNTs composite into 1 mL of NMP solvent and sonicate for 0.5 hours.

[0067] The preparation process of the organic-inorganic composite (PyPBI@HNTs) with a core-shell structure: Dissolve 1.1 mmol (0.39 g) of Py-NH2-PBI powder in 16 mL of dimethyl sulfoxide (DMSO), and then stir at 60 °C until a homogeneous solution is obtained. Then, add 1 mmol (0.36 g) of the reactant HNTs-Cl, and then add 1.2 mmol (0.15 g) of the organic base 4-dimethylaminopyridine (DMAP) to create an alkaline environment. Stir the reactants and react at 60 °C for 48 hours to obtain the final product PyPBI@HNTs. By centrifugation, wash PyPBI@HNTs with dimethyl sulfoxide multiple times until no characteristic peak of polybenzimidazole (PBI) is observed in the 1H-nuclear magnetic resonance spectrum (1H-NMR). Then dry the washed product at 80 °C for 24 hours.

[0068] Preparation process of the amino-functionalized polybenzimidazole (Py-NH2-PBI): Initially, in a 100 mL flask, 40 g of polyphosphoric acid (PPA) solvent was preheated to 140 °C and continuously stirred using a magnetic stirrer to achieve the solvent state required for the synthesis reaction. Subsequently, 2 mmol (0.43 g) of 3,3'-diaminobenzidine (DAB) was added to the polyphosphoric acid, and the mixture was heated and stirred for 2 hours until a homogeneous solution was obtained. Then, 2 mmol (0.36 g) of 5-aminoisophthalic acid (5-AIPA) was added to the flask, and the reaction was continued with stirring until a state where continuous drawing was possible was reached, indicating that the reaction was complete. Next, another 2 mmol of 3,3'-diaminobenzidine (DAB) was added and stirred for 2 hours until homogeneous. After adding 2 mmol (0.49 g) of 4,4'-biphenyldicarboxylic acid (BPDC), the reaction continued for about 24 hours until a drawable state of the polymer was successfully formed. After the above reaction was completed, the final product was cured in deionized water (DI water), and then washed five times with sodium bicarbonate (NaHCO3) to remove the polyphosphoric acid. Then, it was washed with deionized water until the pH value of the solution reached 7. Finally, the product was dried in an oven at 80 °C for 12 hours to obtain the product Py-NH2-PBI for subsequent use.

[0069] Preparation process of the modified halloysite nanotubes (HNTs-Cl) with halogen atoms (Cl) on the surface: 1 g of halloysite nanotubes (HNTs) was dispersed in a three-necked flask containing 20 mL of toluene, and 5 mL of (3-chloropropyl)trimethoxysilane (CPTMS) was added. The mixture was stirred and refluxed at 115 °C for 8 hours. Subsequently, the resulting product was centrifugally washed three times with toluene. Then, the final product, chloropropyl-functionalized halloysite nanotubes (HNTs-Cl), was dried in an oven at 60 °C for 8 hours.

[0070] For comparison, this example also provides PP (polypropylene) membranes, OPBI membranes, and OPBI@HNTs membranes. Among them, the preparation methods of the OPBI membranes and OPBI@HNTs membranes are the same as that of the composite membrane (OPBI@Py-H), and the non-solvent phase transfer method is used.

[0071] The OPBI@HNT20 membrane means that the total mass of HNTs is 20% of the mass of OPBI.

[0072] The OPBI@Py-H20 membrane means that the mass of the PyPBI@HNTs complex is 20% of the mass of OPBI.

[0073] Figure 1Schematic diagram of the preparation method of a lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) and the process of assembling a lithium battery.

[0074] Figure 2 Schematic diagram of the preparation principle and process of modified halloysite nanotubes (HNTs-Cl) with halogen atoms (Cl) on the surface, amino-functionalized polybenzimidazole (Py-NH2-PBI), organic-inorganic composite (PyPBI@HNTs), and composite separator (OPBI@Py-H).

[0075] Figure 3 For (a) TEM image and EDS spectrum of HNTs-Cl, (b-d) TEM images of HNTs-Cl, Py-NH2-PBI, and PyPBI@HNTs, (e) TEM image and EDS spectrum of PyPBI@HNTs, (f) XRD patterns of HNTs-Cl, PyPBI@HNTs, and Py-NH2-PBI, and (g) FT-IR spectra of HNTs-Cl, PyPBI@HNTs, and Py-NH2-PBI. Transmission electron microscopy (TEM) analysis ( Figure 3 b-d) shows that flocculent Py-NH2-PBI is uniformly coated on the surface of chloropropyl-functionalized halloysite nanotubes (HNTs-Cl), while energy-dispersive X-ray spectroscopy (EDS) area scan analysis ( Figure 3 e) indicates that compared with the original halloysite nanotubes (HNTs), the nitrogen element content in the PyPBI@HNTs composite increases. These results together verify that Py-NH2-PBI has been successfully grafted and polymerized onto HNTs-Cl, and this conclusion is further confirmed by the presence of chlorine elements in the modified halloysite nanotubes and the distribution of nitrogen elements in the nanocomposite. The crystal structure was verified by X-ray diffraction (XRD) analysis. As Figure 3 shown in f, PyPBI@HNTs exhibits characteristic peaks consistent with crystalline HNTs-Cl, although the peak intensity is reduced, which may be due to the attenuation effect of the amorphous polymer coating on the signal. Fourier transform infrared spectroscopy (FT-IR) analysis ( Figure 3 g) confirms that the composite material retains the key absorption characteristics of both HNTs-Cl and Py-NH2-PBI, specifically including: a) HNTs-Cl: vibrations of Si-O (1031 cm -1 ) and Al-O (534 cm -1 ) ; b) Py-NH2-PBI: stretching vibration of C=N (1640 cm -1 ) and out-of-plane bending vibration of aromatic C-H (764 cm -1)。In addition, characteristic peaks such as the -OH vibration of HNTs-Cl (3694 / 3621 cm -1 ) and the N-H bending vibration of Py-NH2-PBI (1530 cm -1 ) also provide further support for the formation of the composite material. Combining with the XRD data, these results indicate that the two components have been successfully integrated without damaging their respective structures.

[0076] Figure 4 are SEM images of the surface and cross-section of PP, OPBI, OPBI@HNT20, and OPBI@Py-H20 membranes. Scanning electron microscope (SEM) images show that the OPBI-based membrane has a highly porous top / bottom surface and macroscopic finger-like pores in the cross-section, which is in sharp contrast to the commercially available polypropylene (PP) membrane with lower porosity. It is worth noting that compared with the pure OPBI membrane, the composite membrane exhibits larger surface pores ( Figure 4 b-d, f-h) and more obvious finger-like pores ( Figure 4 j-l). We propose that under the action of the solvent-nonsolvent diffusion force, the dispersion of halloysite nanotubes (HNTs) in the OPBI matrix forms vertical channels. The PyPBI@HNTs nanofiller with an aminated polybenzimidazole (Py-NH2-PBI) coating further enhances the dispersion effect through molecular compatibility, thus forming a fibrous surface texture and enlarged cross-sectional pores ( Figure 4 h, l). These structural characteristics of the OPBI@Py-H membrane enable it to efficiently absorb the electrolyte, thereby improving the ionic conductivity and the overall performance of the battery.

[0077] Figure 5 are the structural characterization diagrams of (a) the HNTs unit cell, OPBI chain segment, and Py-NH2-PBI chain segment, and (b) the interfacial structure evolution diagram before and after the incorporation of Py-NH2-PBI. Using VASP, the interfacial binding characteristics between halloysite nanotubes (HNTs, chemical formula Al2Si2H4O9) and OPBI were systematically studied by density functional theory (DFT) calculations. Under the framework of the generalized gradient approximation (GGA), the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional was used to model the electron interaction, and the projector-augmented wave (PAW) method was used to handle the electron-ion core interaction. To consider the weak interfacial force, the DFT-D3 dispersion correction was adopted, and The vacuum layer is used to mitigate the influence of periodic boundary effects. The OPBI@HNTs system exhibits an interfacial binding energy of -0.554 eV, indicating a weak interfacial interaction, mainly physical adsorption. This adsorption is mainly limited by the dipole-dipole interaction between the hydroxyl groups on the surface of halloysite nanotubes and the benzimidazole rings of OPBI, as well as the conformational mismatch between the rigid halloysite nanotube structure and the flexible OPBI chains. This insufficient binding force highlights the challenge of achieving a mechanically robust organic-inorganic interface in nanocomposites. To address this issue, Py-NH2-PBI was introduced as an interface modifier. In the modified OPBI@Py-H system, the binding energy was significantly increased to -1.366 eV, a 146.6% increase compared to the original system. This improvement stems from the strong electronic coupling between the extended π-conjugated bipyridine unit in Py-NH2-PBI and the aromatic rings of OPBI, which stabilizes the interface through π-π stacking interactions. The calculation results show that the functionalization of Py-NH2-PBI can effectively enhance the interfacial binding force, solve the compatibility problem, and provide a feasible strategy for designing high-performance composite separators with optimized organic-inorganic synergistic effects.

[0078] Figure 6 AC impedance curves of double-steel plate symmetric cells assembled with PP, OPBI, OPBI@HNT20, and OPBI@Py-H20 separators, respectively, (b) Nyquist plots of double-lithium electrode symmetric cells assembled with PP, OPBI, OPBI@HNT20, and OPBI@Py-H20 separators, respectively, (c) LSV curves of cells assembled with PP, OPBI, and OPBI@Py-H20 separators, respectively; (d) plating / stripping cycling curves of symmetric cells, (e) Figure 4 Magnified view of (d), (f) Charge-discharge curves of LiFePO4 half-cells assembled with PP, OPBI, OPBI@HNT20, and OPBI@Py-H20 separators for 300 cycles, (g-h) Charge-discharge voltage curves of LiFePO4 half-cells assembled with PP and OPBI@Py-H20 separators, respectively, (i) Rate curves of LiFePO4 half-cells assembled with PP, OPBI, OPBI@HNT20, and OPBI@Py-H20 separators, respectively.

[0079] In the EIS spectra ( Figure 6 a), the OPBI@Py-H separator exhibits the smallest bulk resistance (R b ), corresponding to 2.01 mS·cm -1The conductivity is 3.19 times that of the polypropylene (PP) separator. This performance improvement stems from the hydrophilic imidazole domains in the OPBI matrix and the wetting behavior of the Py-NH2-PBI / halloysite nanotube (HNTs) nanofillers, which together promote the absorption of the electrolyte and the migration of lithium ions (Li + ).

[0080] The interfacial resistance (R i ) has a significant impact on the kinetic characteristics and efficiency of the battery. The EIS analysis of the symmetric lithium metal battery ( Figure 6 b) shows that among all the tested separators, the OPBI@Py-H separator has the lowest interfacial resistance. This improvement is attributed to its uniform finger-like pore structure, which promotes the orderly transport of lithium ions and inhibits the accumulation of electrolyte decomposition products on the lithium electrode. The OPBI@Py-H separator reduces the bulk resistance (R b ) and the interfacial resistance (R i ), thus achieving excellent ionic conductivity and energy conversion efficiency. These findings highlight its potential as a high-performance separator for next-generation lithium-ion batteries (LIBs).

[0081] The electrochemical stability analysis ( Figure 6 c) conducted through linear sweep voltammetry (LSV) curves reveals different polarization onset voltages: 4.2 V for the polypropylene (PP) separator, 4.7 V for the OPBI separator, and 5.2 V for the OPBI@Py-H separator. The electrochemical window of the OPBI-based system is increased by 0.5 V, which is related to the hydrophilic imidazole functional groups they contain, and these functional groups enhance the electrolyte absorption capacity (the absorption rate is increased to 396% compared with the polypropylene separator (132%)). This creates a uniformly wetted electrode / separator interface (contact angle of 7.7° vs. 52.2° for the polypropylene separator), thus improving the interfacial compatibility ( Figure 11 ).

[0082] The OPBI@Py-H separator exhibits excellent performance, with an electrochemical window of 5.2 V and minimal polarization, which benefits from its hierarchical pore structure ( Figure 4 ). Specifically, the interconnected finger-like mesopores provide efficient electrolyte storage space, while the sub-nanometer channels promote the orderly migration of lithium ions. This structural feature not only increases the ionic conductivity by 3.19 times compared with the polypropylene separator but also inhibits the formation of lithium dendrites through the tortuous ion transport path, thus enhancing the electrochemical stability between the separator and the electrode.

[0083] To study the interfacial stability between the lithium electrode and the electrolyte, lithium / lithium symmetric cells were constructed using polypropylene (PP) separators and OPBI@Py-H separators, respectively, and a lithium stripping / plating cycle test was carried out for up to 3000 hours ( Figure 6 d). The cells using the polypropylene separator showed significantly larger polarization voltage fluctuations, with a maximum fluctuation amplitude reaching 40 mV ( Figure 6 e), while the cells based on the OPBI@Py-H separator maintained a narrow and stable polarization range throughout the cycle. This difference indicates that the composite separator OPBI@Py-H can effectively stabilize the lithium stripping / plating process. The dense finger-like pore channels in the composite separator OPBI@Py-H not only enhance the electrolyte retention ability but also provide an efficient ion transport path. Therefore, the bulk resistance (R b ) and the electrode-electrolyte interface resistance (R i ) of this separator are both reduced, thus improving the interfacial stability. These structural and electrochemical advantages together promote the improvement of the cycle life and safety of the cells using the OPBI@Py-H separator.

[0084] Figure 6 Figure f shows the change in discharge specific capacity of cells using different separators during 300 cycles at a rate of 0.5C. The capacity change trend is as follows: PP < OPBI < OPBI@HNT < OPBI@Py-H. The initial capacities of the cells assembled with polypropylene (PP) separators and OPBI separators are relatively low, which may be due to incomplete activation of the active materials. In subsequent cycles, the increase in capacity supports this hypothesis and indicates that the composite separator helps to promote the rapid charge and discharge of the cells. After 300 cycles, the capacity retention rate of the cells assembled with the PP separator is only 48.72%, while the cells assembled with the OPBI@Py-H separator show higher Coulomb efficiency and capacity retention rate.

[0085] The voltage-specific capacity curves ( Figure 6 g and 6h) show that, compared with the cells using the PP separator, the cells assembled with the OPBI@Py-H separator have a smaller electrode voltage difference during cycling, indicating that their charge and discharge processes are more stable and have great potential to become high-performance lithium-ion batteries (LIBs).

[0086] The rate performance evaluation ( Figure 6 i) was carried out within 7 cycle periods (from 0.1C back to 0.1C), and the change trend of the discharge specific capacity was also: PP < OPBI < OPBI@HNT < OPBI@Py-H. It is worth noting that the cells assembled with the OPBI@Py-H separator had a discharge specific capacity of 162.47 mAh·g -1 ) in the initial cycle and 159.10 mAh·g in the final cycle (-1 ) maintained a capacity retention rate of 97.93%, showing excellent cycle reversibility.

[0087] These performance advantages demonstrated by the battery assembled with the OPBI@Py-H separator are mainly attributed to its unique porous structure and the rich electrolyte in the separator. These characteristics enable efficient transport of lithium ions (Li + ), thus increasing the discharge capacity. In addition, its excellent cycle reversibility also helps to extend the service life of the battery, highlighting its broad application prospects in high-performance lithium-ion batteries.

[0088] Figure 7 SEM images of the lithium anode after 300 cycles of LiFePO4 half-cells assembled with (a) PP, OPBI, and OPBI@Py-H20 separators respectively, and (b) schematic diagram of lithium dendrite growth on the lithium anode of the battery. To evaluate the stability of the separator on the negative electrode side, the battery was disassembled after 300 cycles, and the lithium negative electrode was analyzed by scanning electron microscopy (SEM) ( Figure 7 a). Obviously, a large number of lithium dendrites formed on the surface of the lithium negative electrode in the battery assembled with the polypropylene (PP) separator; while in the battery assembled with the OPBI separator, fewer lithium dendrites formed on the surface of the lithium negative electrode. In contrast, in the battery assembled with the composite separator OPBI@Py-H, the obtained lithium negative electrode surface was almost smooth and uniform. This improvement benefits from the dense and uniform finger-like pore structure of the separator and its rich electrolyte retention ability, which promote the uniform transport of lithium ions (Li + ) and prevent the accumulation of local lithium ions. The potential mechanism is as Figure 7 shown in b. Overall, the OPBI@Py-H composite separator effectively inhibits the growth of dendrites and significantly improves the service life and safety of the battery.

[0089] Figure 8 Discharge specific capacities of LiFePO4 half-cells assembled with PP and OPBI@Py-H20 separators at 50 °C and 90 °C. To comprehensively evaluate the thermal performance of the separator, systematic charge-discharge cycle tests were conducted on lithium-ion batteries (LIBs) assembled with these separators under high-temperature conditions. Specifically, based on the electrochemical performance of the assembled lithium iron phosphate (LiFePO4) batteries during cycling, the practical application potential of these separators in high-temperature operation scenarios was evaluated. As Figure 8 shown in a, when tested at a cycling rate of 0.5C at 50 °C, the initial discharge capacity of the lithium iron phosphate battery assembled with the polypropylene (PP) separator was 147.80 mAh·g -1 . After 50 cycles, this capacity value decreased to 85.10 mAh·g -1, the corresponding capacity retention rate is 57.58%. In contrast, within the same cycle number, the lithium iron phosphate battery assembled with the OPBI@Py-H separator maintained 97.58% of its capacity (161.00 mAh·g -1 →157.10 mAh·g -1 ). At 90 °C, this performance difference is even more significant ( Figure 8 b). Under the same cycling conditions, the capacity of the lithium iron phosphate battery assembled with the PP separator decreased sharply from 141.10 mAh·g -1 to 6.90 mAh·g -1 (the capacity retention rate is only 4.89%). On the contrary, the lithium iron phosphate battery assembled with the OPBI@Py-H separator maintained 95.07% of its capacity (157.78 mAh·g -1 →150 mAh·g -1 ), demonstrating excellent thermal stability.

[0090] Obviously, the lithium-ion battery with the OPBI@Py-H separator exhibits more superior cycling stability at high temperatures. This indicates that this separator has great potential for realizing long-cycle-life batteries in high-temperature applications, which is a significant improvement compared to traditional separators.

[0091] Figure 9 is the 1H NMR spectrum of Py-NH2-PBI. Py-NH2-PBI was grafted onto chlorine-modified halloysite nanotubes (HNTs-Cl), enabling the nanotubes to be completely coated with polymer chains. The success of the synthesis reaction was confirmed by 1H nuclear magnetic resonance spectroscopy. In this spectrum, characteristic peaks 1 and 2 correspond to the hydrogen atoms on the bipyridine ring, characteristic peaks 3 and 5 correspond to the hydrogen atoms on the imidazole ring, and characteristic peak 4 corresponds to the hydrogen atoms on the -NH2 group. The ratio of the integral areas of peaks 1-3 to those of peaks 4-5 is 2:3, indicating that in the OPBI structure, the content of the bipyridine group is approximately 40%.

[0092] Figure 10 are the infrared spectra of (a) PyPBI@HNTs, OPBI separator, and OPBI@Py-H20 separator, and (b) the XRD patterns of PyPBI@HNTs, OPBI separator, and OPBI@Py-H20 separator. The chemical composition and crystallinity of the composite separators were analyzed by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). Fourier transform infrared spectroscopy ( Figure 10 a) shows that compared with the pure OPBI separator, the characteristic peak intensities of the OPBI@Py-H composite separator are enhanced, especially at 1600 cm -1 (C=N stretching vibration in the bipyridine or benzimidazole ring) and 1030 cm -1At (C-N stretching vibration in the heterocyclic skeleton). These enhanced peaks confirm the combination of the nitrogen-rich conjugated system and the amino functional group. X-ray diffraction pattern ( Figure 10 b) shows that the OPBI@Py-H composite separator is very similar to the pure OPBI separator, indicating that the content of PyPBI@HNTs is not sufficient to cause a detectable crystallographic phase change. This implies that a higher filler loading may be required to observe the X-ray diffraction peaks characteristic of the nanofiller.

[0093] Figure 11 For (a) SEM images of the pore distribution on the separator surface drawn using Image-J software, (b) digital photos of the electrolyte-wetted separator, (c) contact angle of the electrolyte with the separator, (d) percentage of pore volume on the separator surface, (e) porosity and electrolyte absorption rate of the separator. The OPBI@Py-H20 separator has a denser pore distribution, a larger pore volume, and a stronger ability to be wetted by the electrolyte.

[0094] Figure 12 For (a) images of the OPBI@Py-H20 separator being folded, bent, and restored, (b) stress-strain curves of the OPBI@HNT20 separator and the OPBI@Py-H20 separator. Figure 12 As shown in a, the composite separator OPBI@Py-H20 has good flexibility; Figure 12 As shown in b, introducing the composite (PyPBI@HNTs) into the OPBI-based separator solves the problem of poor compatibility between HNTs and the separator matrix OPBI, realizes the uniform dispersion of HNTs in the separator matrix OPBI, and makes the tensile strength (TS) of the OPBI@Py-H composite separator increase significantly (30.96%) compared with the OPBI@HNTs separator.

[0095] Figure 13 For (a) images of the separator after being placed at different temperatures for 1 h, (b) images of the separator combustion experiment, (c) TGA curves of the separator. Figure 13 As shown in a, after being exposed at 25 °C, 100 °C, 150 °C, and 200 °C for 2 hours, the polypropylene (PP) separator showed obvious dimensional deformation at 150 °C and collapsed into a linear shape at 200 °C. In contrast, the OPBI separator, the OPBI@HNTs separator, and the OPBI@Py-H separator maintained their original dimensions, highlighting the deficiency of the PP separator in terms of thermal dimensional stability. Figure 13 b further reveals the differences between these separators. The PP separator curled due to heat before contacting the alcohol lamp flame and burned completely in the open flame. On the contrary, the OPBI@Py-H separator did not change in size before contacting the flame and formed black carbide after burning, without flame spread, indicating its excellent flame retardant performance. Figure 13This trend was confirmed. Due to the decomposition of the polyolefin chain, the PP separator rapidly degrades at around 300 °C, while the OPBI-based separator maintains stability until approximately 550 °C. Notably, the OPBI@Py-H separator still retained 74.36% of its weight at 700 °C. Compared with the OPBI separator, both the OPBI@HNTs and OPBI@Py-H separators exhibited more excellent thermal decomposition resistance performance, which was attributed to the addition of inorganic nanofillers.

[0096] In summary, the present invention provides a lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), a preparation method thereof, and a lithium battery. The preparation method includes the steps of: providing a solution of a composite (PyPBI@HNTs) of an OPBI solution, aminated polybenzimidazole (Py-NH2-PBI), and halloysite nanotubes (HNTs); mixing the OPBI solution with the solution of the composite (PyPBI@HNTs) of aminated polybenzimidazole (Py-NH2-PBI) and halloysite nanotubes (HNTs) to obtain a mixed solution (PyPBI@HNTs-OPBI solution); coating the mixed solution (PyPBI@HNTs-OPBI solution) on a substrate and removing the solvent in the mixed solution (PyPBI@HNTs-OPBI solution) to obtain a lithium battery composite separator (OPBI@Py-H) in which the PyPBI@HNTs composite is uniformly dispersed in a polyarylether benzimidazole (OPBI) matrix; and assembling a lithium battery using the composite separator (OPBI@Py-H). By introducing the composite (PyPBI@HNTs) into the OPBI-based separator, the present invention has the following advantages: (1) It solves the problem of poor compatibility between HNTs and the separator matrix OPBI, realizes the uniform dispersion of HNTs in the separator matrix OPBI, and the tensile strength (TS) of the OPBI@Py-H composite separator is increased by 30.96% compared with the OPBI@HNTs separator; (2) The OPBI@Py-H composite separator is rich in nitrogen elements and has a large affinity with the electrolyte. Moreover, the separator has regular, uniform, and dense finger-shaped pores and sponge-like pores, which provide more sites and microscopic channels for the transport of lithium ions, facilitating the induction of lithium ions to pass through the separator more rapidly and deposit uniformly on the surface of the lithium metal anode. These characteristics in terms of performance and structure enable the ionic conductivity (σ) of the OPBI@Py-H composite separator to be increased by 21.82% compared with the OPBI@HNTs separator, and it has a good effect of inhibiting lithium dendrites; (3) The lithium battery assembled using the OPBI@Py-H composite separator has a large specific capacity, good cycle stability and rate performance, and a low degree of battery electrode polarization; (4) The OPBI@Py-H composite separator has excellent high-temperature resistance performance, and the battery assembled using this composite separator can operate safely and stably at 90 °C.

[0097] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), a preparation method thereof, and a lithium battery, characterized in that, Including the steps: Providing a solution of a complex (PyPBI@HNTs) of amino-functionalized polybenzimidazole (Py-NH2-PBI) and halloysite nanotubes (HNTs), and a polyarylether benzimidazole (OPBI) solution; Mixing the solution of the complex (PyPBI@HNTs) of amino-functionalized polybenzimidazole (Py-NH2-PBI) and halloysite nanotubes (HNTs) with the polyarylether benzimidazole (OPBI) solution to obtain a mixed solution (PyPBI@HNTs-OPBI solution); Coating the mixed solution (PyPBI@HNTs-OPBI solution) on a substrate and removing the solvent in the mixed solution (PyPBI@HNTs-OPBI solution) to obtain a lithium battery composite separator (OPBI@Py-H) in which the PyPBI@HNTs complex is uniformly dispersed in a polyarylether benzimidazole (OPBI) matrix; 2. A lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) according to claim 1 and its preparation method, characterized in that, The PyPBI@HNTs complex is an organic-inorganic complex with a core-shell structure formed by chemically reacting amino-functionalized polybenzimidazole (Py-NH2-PBI) to wrap the outer surface of halloysite nanotubes (HNTs); 3. A lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) according to claim 1 and a preparation method thereof, characterized in that, The solvent of the PyPBI@HNTs complex solution and the solvent of the OPBI solution are jointly selected from one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and dimethyl sulfoxide; 4. A lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) according to claim 1 and a preparation method thereof, characterized in that, In the PyPBI@HNTs-OPBI mixed solution, the total mass of the PyPBI@HNTs complex is 5%-30% of the mass of OPBI; 5. A lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) according to claim 2, and a preparation method thereof, characterized in that, The preparation of the organic-inorganic complex (PyPBI@HNTs) with a core-shell structure is to first synthesize modified halloysite nanotubes (HNTs-Cl) with halogen atoms (Cl) on the surface through a chemical reaction, then synthesize amino-functionalized polybenzimidazole (Py-NH2-PBI) through a chemical reaction, and finally react HNTs-Cl with Py-NH2-PBI to obtain PyPBI@HNTs; 6. A lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) according to claim 1 and a preparation method thereof, characterized in that, The preparation process of the OPBI solution: adding 0.3 g of OPBI powder into a solvent and vigorously stirring at 60-100 °C for 18-24 hours; the preparation process of the PyPBI@HNTs complex solution: dispersing the PyPBI@HNTs complex into a solvent and ultrasonically treating for 0.5-2 hours; the preparation process of the mixed solution (PyPBI@HNTs-OPBI solution): slowly dropping the PyPBI@HNTs complex solution into the OPBI solution and stirring at a low speed for 18-30 hours; 7. A lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) according to claim 1 and a preparation method thereof, characterized in that, The method for removing the solvent in the PyPBI@HNTs-OPBI mixed solution is: soaking the substrate coated with the PyPBI@HNTs-OPBI mixed solution in absolute methanol, and the soaking treatment is to stand at room temperature for 8-15 minutes.

8. A lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), characterized in that, Prepared by the method for preparing a lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) as described in any one of claims 1-7, the microchannels of the separator are composed of regular, uniform, and dense finger-like pores and sponge-like pores.

9. A lithium battery separator containing an aminated polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) according to claim 8, characterized in that, The thickness of the lithium battery separator containing the amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) is 20-40 microns.

10. A lithium battery, characterized in that, Comprising a positive electrode sheet, a negative electrode sheet, and a lithium battery separator containing an amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs) as described in any one of claims 8-9, namely a composite separator (OPBI@Py-H); the lithium battery separator containing the amino-functionalized polybenzimidazole@halloysite nanotube composite (PyPBI@HNTs), namely the composite separator (OPBI@Py-H), is located between the positive electrode sheet and the negative electrode sheet of the lithium battery.

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