Lithium battery diaphragm, preparation method thereof and lithium battery

Abstract

The invention provides a lithium battery diaphragm, a preparation method thereof and a lithium battery, and belongs to the field of lithium batteries. The method comprises the following steps: carrying out gradient stirring on a blended solution of an inorganic nanoparticle dispersion solution and a polyvinylidene fluoride solution to obtain a composite spinning solution; performing electrostatic spinning on the composite spinning solution to obtain a nanofiber membrane; and carrying out hot pressing treatment on the nanofiber membrane to obtain the lithium battery diaphragm. Through a three-in-one technical path of two-component synergistic modification, electrostatic spinning parameter optimization and hot-pressing process innovation, four core defects of thermal stability, porosity regulation and control, electrochemical stability and interface bonding force in the prior art are specifically solved, and the comprehensive performance of the lithium battery diaphragm is comprehensively improved.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a lithium battery separator and its preparation method, and a lithium battery. Background Technology

[0002] Lithium-ion batteries are widely used in electronic devices, electric vehicles, and other fields as important energy storage devices. The separator, as a key component of lithium-ion batteries, plays a decisive role in the battery's safety, stability, and performance.

[0003] As lithium batteries develop towards higher energy densities, the requirements for the overall performance of separators are becoming increasingly stringent, such as requiring higher thermal stability, more precisely controlled porosity and pore size distribution, and excellent electrochemical stability. Therefore, developing a lithium battery separator with high thermal stability, ideal porosity and pore size distribution, and high electrochemical stability is of significant practical importance for improving the safety, stability, and performance of lithium batteries and meeting the development needs of high-energy-density lithium batteries. Summary of the Invention

[0004] This application provides a lithium battery separator and its preparation method, as well as a lithium battery, to solve the following technical problem: how to improve the overall performance of the lithium battery separator.

[0005] In a first aspect, embodiments of this application provide a method for preparing a lithium battery separator, the method comprising: A composite spinning solution was obtained by gradient stirring of a mixture of inorganic nanoparticle dispersion and polyvinylidene fluoride solution. The composite spinning solution was electrospun to obtain a nanofiber membrane. The nanofiber membrane is subjected to hot pressing treatment to obtain a lithium battery separator; The inorganic nanoparticle dispersion includes one or more of the following: titanium dioxide dispersion, alumina dispersion, zirconium dioxide dispersion, magnesium oxide dispersion, and silica dispersion. The electrospinning includes the following parameters: spinning voltage of 15kV to 25kV, flow rate of 0.5mL / h to 1mL / h, and receiving distance of 15cm to 25cm.

[0006] Optionally, the inorganic nanoparticle dispersion is composed of a titanium dioxide dispersion and an alumina dispersion, wherein the mass concentration of the titanium dioxide dispersion is 0.5% to 1.5%, and the mass concentration of the alumina dispersion is 0.3% to 1.0%. The mass concentration of the polyvinylidene fluoride solution is 12% to 18%.

[0007] Optionally, the volume ratio of the titanium dioxide dispersion to the polyvinylidene fluoride solution is 1:(5-10); The volume ratio of the alumina dispersion to the polyvinylidene fluoride solution is 1:(8-12); The titanium dioxide particle size in the titanium dioxide dispersion is 50 nm to 100 nm. The alumina in the alumina dispersion has a particle size of 30 nm to 80 nm.

[0008] Optionally, the viscosity of the composite spinning solution is 30 mPa·s to 50 mPa·s; The nanofibers in the nanofiber membrane have a diameter of 100nm to 300nm and a fiber spacing of 50nm to 200nm. The thickness of the nanofiber membrane is 30 μm to 50 μm.

[0009] Optionally, the hot pressing treatment includes the following parameters: temperature of 120℃~150℃, pressure of 5MPa~10MPa, and holding time of 10min~20min.

[0010] In a second aspect, embodiments of this application provide a lithium battery separator prepared by the method described in any one of the first aspects, wherein the lithium battery separator is composed of polyvinylidene fluoride body and inorganic nanoparticles dispersed in the polyvinylidene fluoride body; The thickness of the lithium battery separator is 12μm to 20μm.

[0011] Optionally, the lithium battery separator has a three-dimensional through-pore structure, with an average pore size of 50nm to 100nm, a porosity of 40% to 50%, and a coefficient of variation of pore size distribution of <10%.

[0012] Optionally, a micro-fusion layer is formed between the polyvinylidene fluoride body and the inorganic nanoparticles, and the thickness of the micro-fusion layer is 50 nm to 100 nm.

[0013] Optionally, the lithium battery separator meets the following performance requirements: thermal shrinkage rate <5% after being kept at 180°C for 1 hour, tensile strength of 18MPa~21MPa, and ionic conductivity ≥2.9×10⁻⁶. -3 S / cm, liquid absorption rate ≥430%.

[0014] Thirdly, embodiments of this application provide a lithium battery, which includes a positive electrode, a negative electrode, an electrolyte, and a separator located between the positive and negative electrodes, wherein the separator is the lithium battery separator described in any one of the second aspects.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing a lithium battery separator. Through a three-pronged approach of two-component synergistic modification, electrospinning parameter optimization, and innovative hot-pressing process, it specifically addresses four core deficiencies in existing technologies: thermal stability, porosity control, electrochemical stability, and interfacial adhesion. This comprehensively improves the overall performance of the lithium battery separator, as detailed below: To address the deficiency of insufficient thermal stability, this application constructs a high-temperature resistant structure through two-component synergistic modification. High-temperature resistant and electrochemically stable inorganic nanoparticle dispersions, such as titanium dioxide dispersions and alumina dispersions, are selected and combined in one or more ways to form a two-component inorganic system. These inorganic nanoparticles possess high melting point characteristics and, after being composited with polyvinylidene fluoride (PVDF) matrix, form a high-temperature resistant network framework. Combined with the interfacial fusion between the matrix and particles during hot pressing, this effectively suppresses structural shrinkage at high temperatures, significantly improves the thermal stability of the separator, and avoids battery safety hazards caused by separator deformation under high-temperature conditions.

[0016] To address the shortcomings of insufficient precision in controlling porosity and pore size distribution, this application achieves precise control through optimization of electrospinning parameters. A combination of parameters—15kV–25kV spinning voltage, 0.5mL / h–1mL / h flow rate, and 15cm–25cm receiving distance—allows the composite spinning solution to form uniformly sized nanofibers under the influence of an electric field. These fibers naturally interweave to form the initial pore structure. This parameter combination, through the coordinated matching of electric field strength, fluid supply, and receiving distance, ensures the regularity of fiber spacing and arrangement, thereby achieving precise control of porosity and pore size distribution. This constructs three-dimensional, interconnected, uniform channels, providing an optimized pathway for lithium-ion transport and electrolyte storage.

[0017] To address the shortcomings of insufficient electrochemical stability, this application leverages the synergistic effect of two-component inorganic nanoparticles to achieve improvement. The selected inorganic nanoparticles, such as titanium dioxide and alumina, possess electrochemical stability characteristics such as wide bandgap or high insulation. The composite system formed by the two components can suppress the oxidative decomposition of the electrolyte under high voltage, reduce ion migration resistance, and broaden the electrochemical window of the separator. This allows the separator to be adapted to high-voltage cathode materials, solving the problem of easy oxidation and decomposition of traditional separators under high voltage and ensuring battery cycle stability.

[0018] To address the deficiency of insufficient interfacial bonding, this application innovatively enhances the interfacial function through a hot-pressing process. Hot-pressing activates the polyvinylidene fluoride (PVDF) molecular chains, giving them fluidity, and forces the matrix and inorganic nanoparticles into close contact through pressure. This promotes interfacial molecular diffusion and fusion, forming a stable interfacial bonding layer, significantly improving interfacial shear strength, preventing inorganic particle detachment or interlayer delamination, and balancing mechanical strength and ion conductivity.

[0019] The three technologies mentioned above work together to optimize the material composition, structure construction and interface strengthening in all aspects, and ultimately achieve a breakthrough in the overall performance of lithium battery separators by simultaneously improving thermal stability, porosity control precision, electrochemical stability and interfacial bonding. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic flowchart illustrating a method for preparing a lithium battery separator according to an embodiment of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1 to 6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0025] Figure 1This is a schematic flowchart illustrating a method for preparing a lithium battery separator according to an embodiment of this application.

[0026] like Figure 1 As shown in the figure, this application provides a method for preparing a lithium battery separator, the method comprising: S1. The mixture of inorganic nanoparticle dispersion and polyvinylidene fluoride solution is subjected to gradient stirring to obtain composite spinning solution. S2. Electrospin the composite spinning solution to obtain a nanofiber membrane; S3. The nanofiber membrane is subjected to hot pressing treatment to obtain a lithium battery separator; Among them, the inorganic nanoparticle dispersion includes one or more of the following: titanium dioxide dispersion, alumina dispersion, zirconium dioxide dispersion, magnesium oxide dispersion, and silica dispersion.

[0027] It should be noted that the core function of the composite spinning solution preparation step (S1) is to lay the foundation for the formation of a synergistic structure of 'high-temperature resistant skeleton + electrochemically stable layer' in the final separator by constructing a precursor system with uniformly dispersed inorganic particles. Through the uniform fusion of bicomponent inorganic nanoparticles and the polyvinylidene fluoride (PVDF) matrix, a composite spinning solution with uniform dispersion and suitable viscosity is prepared. Essentially, by optimizing the material ratio and dispersion process, the aggregation of inorganic particles is eliminated, allowing titanium dioxide (TiO2) and alumina (Al2O3) to form a continuously distributed three-dimensional network in the PVDF matrix. This lays the material foundation for subsequent electrospinning to form a fiber membrane with a specific structure and for interfacial fusion through hot pressing, ensuring that the final separator simultaneously possesses high temperature resistance, high electrochemical stability, and good interfacial compatibility.

[0028] The core function of the electrospinning step (S2) is to transform the composite spinning solution into a nanofiber membrane with a three-dimensional interconnected pore structure. Through the stretching effect of an electric field, the composite spinning solution forms continuous nanofibers, and the naturally interwoven pores between the fibers provide natural channels for lithium-ion transport and electrolyte storage. Simultaneously, by precisely controlling the spinning parameters—including fiber diameter, spacing, and membrane thickness—initial control of porosity and pore size distribution is achieved. This provides a good precursor structure for further optimization of the structural performance in the subsequent hot-pressing process, ensuring the membrane possesses highly efficient ion transport capabilities.

[0029] The core function of the hot-pressing step (S3) is to achieve the dual goals of interface strengthening and precise structural control. Through the synergistic effect of temperature and pressure, PVDF molecular chain segments are activated, enabling the PVDF matrix and inorganic nanoparticles to form a micro-fusion layer at the interface, significantly improving interfacial bonding and mechanical strength. Simultaneously, without destroying the three-dimensional interconnected pore structure, the fiber membrane is further densified, precisely controlling the final thickness, porosity, and pore size distribution of the membrane, balancing mechanical strength and ion transport efficiency, and ultimately ensuring that the membrane meets the comprehensive performance requirements of thermal stability, electrochemical stability, and ion conduction efficiency.

[0030] In some embodiments, the inorganic nanoparticle dispersion is composed of a titanium dioxide dispersion and an alumina dispersion, wherein the mass concentration of the titanium dioxide dispersion is 0.5% to 1.5% and the mass concentration of the alumina dispersion is 0.3% to 1.0%. The mass concentration of the polyvinylidene fluoride solution is 12% to 18%.

[0031] A composite filler composed of nano-titanium dioxide and nano-alumina is used. Nano-titanium dioxide, with its high melting point (1840℃), primarily constructs a high-temperature resistant framework within the separator, effectively inhibiting the shrinkage of the polymer matrix at high temperatures. Nano-alumina, due to its excellent electrochemical inertness and high insulation, forms an electrochemically stable layer at the separator-electrolyte interface, significantly suppressing the oxidative decomposition of the electrolyte under high voltage. The two components complement each other, forming a synergistic protective effect.

[0032] In some embodiments, the volume ratio of titanium dioxide dispersion to polyvinylidene fluoride solution is 1:(5-10); The volume ratio of alumina dispersion to polyvinylidene fluoride solution is 1:(8-12).

[0033] The mass concentration of the titanium dioxide dispersion is controlled between 0.5% and 1.5%, and the mass concentration of the alumina dispersion is controlled between 0.3% and 1.0%. The volume ratio of the titanium dioxide dispersion to the polyvinylidene fluoride solution is 1:5 to 1:10, and the volume ratio of the alumina dispersion to the polyvinylidene fluoride solution is 1:8 to 1:12. This ratio range ensures the effective content of inorganic functional components in the membrane, which can significantly improve thermal and electrochemical stability, while avoiding particle agglomeration or instability in the spinning process due to excessive addition.

[0034] Polyvinylidene fluoride (PVDF) solution concentration: The mass concentration of the PVDF solution is set between 12% and 18%. This concentration range ensures that the spinning solution has a suitable viscosity, which is crucial for forming continuous, uniform nanofibers rather than droplets. If the concentration is too low, the fibers will easily break; if the concentration is too high, the spinning resistance will increase, and the nozzle will easily become clogged.

[0035] In some embodiments, the particle size of titanium dioxide in the titanium dioxide dispersion is 50 nm to 100 nm; The alumina particle size in the alumina dispersion is 30 nm to 80 nm.

[0036] The particle size of nano-titanium dioxide is controlled between 50 nm and 100 nm, and the particle size of nano-alumina is controlled between 30 nm and 80 nm. This particle size range is beneficial for the stable dispersion of particles in polymer solutions, avoiding sedimentation, while ensuring that they have sufficient specific surface area in the final fiber to perform their function, and will not puncture the diaphragm or affect fiber formation due to excessive particle size.

[0037] In some embodiments, the mixture of inorganic nanoparticle dispersion and polyvinylidene fluoride solution is subjected to gradient stirring, specifically including: First, perform low-speed pre-stirring at 150 rpm to 250 rpm for 0.5 h to 1.5 h; Then, disperse at high speed for 1.5 to 2.5 hours at a speed of 450 to 550 rpm.

[0038] A gradient stirring strategy of low-speed premixing followed by high-speed dispersion was adopted. First, premixing was performed at a low speed of 150 rpm to 250 rpm for 0.5 to 1.5 hours to allow initial wetting and mixing of the components, preventing eddies or entrained air bubbles due to excessively high initial speed. Then, high-speed dispersion was performed at 450 rpm to 550 rpm for 1.5 to 2.5 hours. Sufficient shear force was applied to thoroughly break up the agglomerates of nanoparticles, achieving molecular-level uniform encapsulation and dispersion in the polyvinylidene fluoride solution.

[0039] In some embodiments, electrospinning includes the following parameters: spinning voltage of 15kV to 25kV, flow rate of 0.5mL / h to 1mL / h, and receiving distance of 15cm to 25cm.

[0040] This application utilizes a high-voltage electrostatic field to prepare nanoscale fibers from a composite spinning solution and construct the initial three-dimensional porous structure of a membrane. The spinning voltage parameter is set to 15kV to 25kV. Within this voltage range, the electrostatic force is sufficient to overcome the surface tension of the spinning solution, forming a stable Taylor cone and sufficiently accelerating and stretching the jet, which is a prerequisite for obtaining fine and uniform nanofibers. The spinning flow rate is controlled at 0.5mL / h to 1mL / h. The lower flow rate, matched with the above voltage parameter, ensures that the jet has sufficient time to be sufficiently stretched, refined, and solidified in the electric field, thereby forming fibers with uniform diameter. Excessive flow rate can easily lead to increased or uneven fiber diameter, or even beading defects. The receiving distance is set to 15cm to 25cm. This distance provides sufficient flight path for the jet, allowing the solvent to evaporate fully. The fibers are completely solidified when deposited into the receiving device, avoiding adhesion between fibers due to residual solvent, and contributing to the formation of a loose and porous three-dimensional network structure.

[0041] In some embodiments, the viscosity of the composite spinning solution is 30 mPa·s to 50 mPa·s; The nanofibers in the nanofiber membrane have a diameter of 100 nm to 300 nm and a fiber spacing of 50 nm to 200 nm. The thickness of the nanofiber membrane is 30μm to 50μm.

[0042] By employing the aforementioned component formulation and stirring process, the viscosity of the final composite spinning solution is precisely controlled within the range of 30 mPa·s to 50 mPa·s. This viscosity range is an ideal window for electrospinning, ensuring that the spinning solution has sufficient chain entanglement to form a stable jet, while also possessing appropriate fluidity to ensure a continuous and smooth spinning process, preventing nozzle clogging.

[0043] This application successfully prepared a nanofiber membrane composed of nanofibers with diameters ranging from 100 nm to 300 nm. A spacing of 50 nm to 200 nm was formed between the fibers, directly constituting the prototype of the membrane's three-dimensional interconnected pore structure. At this stage, the thickness of the nanofiber membrane was controlled between 30 μm and 50 μm, reserving space for subsequent hot-pressing processes.

[0044] In some embodiments, the hot pressing process includes the following parameters: temperature of 120°C to 150°C, pressure of 5 MPa to 10 MPa, and holding time of 10 min to 20 min.

[0045] Hot pressing is a key finishing step in this preparation method, aiming to achieve the curing, strengthening, and precise control of the diaphragm structure and its pore structure. The hot pressing temperature is controlled between 120°C and 150°C. This temperature range is higher than the glass transition temperature of polyvinylidene fluoride (approximately -40°C to -30°C, but its microscopic chain segment movement is activated at higher temperatures), but much lower than its melting point (approximately 170°C). At this temperature, the molecular chain segment movement of polyvinylidene fluoride is enhanced, exhibiting a certain degree of thermoplasticity, allowing it to deform and fuse under pressure, but without completely melting and flowing, thus strengthening the structure while retaining its porous characteristics. The hot pressing pressure is limited to 5 MPa to 10 MPa, and the holding time is 10 min to 20 min. Under these conditions, the polyvinylidene fluoride fibers undergo thermal fusion bonding at the contact points, forming strong "weld points," which greatly improves the mechanical strength of the diaphragm (tensile strength can reach 18 MPa to 21 MPa). More importantly, under these thermodynamic conditions, the interface between polyvinylidene fluoride matrix and nano-titanium dioxide and nano-alumina particles forms a dense micro-fusion layer with a thickness of approximately 50 nm to 100 nm. This achieves a strong bond between rigid inorganic particles and a flexible polymer matrix, effectively preventing particle shedding and significantly reducing interfacial stress at high temperatures. As a result, the thermal shrinkage rate of the diaphragm is less than 5% after being kept at 180°C for 1 hour.

[0046] Based on a general inventive concept, embodiments of this application provide a lithium battery separator prepared by any of the above methods, wherein the lithium battery separator is composed of polyvinylidene fluoride body and inorganic nanoparticles dispersed in polyvinylidene fluoride body. The thickness of the lithium battery separator is 12μm to 20μm.

[0047] In some embodiments, the lithium battery separator has a three-dimensional through-pore structure with an average pore size of 50 nm to 100 nm, a porosity of 40% to 50%, and a coefficient of variation of pore size distribution of <10%.

[0048] The three-dimensional interconnected channels have an average pore size of 50–100 nm, a porosity of 40–50%, and a pore size distribution variation coefficient of <10%. These structural parameters ensure uniformity and good connectivity of the channels, enabling them to store sufficient electrolyte (ensuring a liquid absorption rate of ≥430%) and provide efficient lithium-ion transport channels (achieving an ionic conductivity of ≥2.9 × 10⁻⁶). -3 (S / cm) to improve battery charge and discharge performance and consistency.

[0049] It should be noted that the formation of the three-dimensional through-hole structure in this embodiment is the result of the synergistic effect of three steps: composite spinning solution preparation, electrospinning, and hot pressing. Through a progressive design of material dispersion uniformity control, precise fiber structure construction, and pore optimization and control, the target structural features are finally achieved. The specific formation process is as follows: A uniform dispersion system in the composite spinning solution lays the foundation for the uniformity of the pore structure. A process combining gradient stirring and ultrasonic dispersion is employed. First, titanium dioxide (50-100 nm) and alumina (30-80 nm) dispersions are ultrasonically treated for 3-5 hours to achieve monodispersion. Then, they are blended with a 12-18% (w / w) polyvinylidene fluoride (PVDF) solution at a specific volume ratio. A gradient stirring mode of "pre-stirring at 150-250 rpm for 0.5-1.5 hours + high-speed dispersion at 450-550 rpm for 1.5-2.5 hours" ensures the uniform distribution of inorganic particles in the PVDF matrix, avoiding uneven fiber structure caused by localized agglomeration. Simultaneously, the viscosity of the composite spinning solution is adjusted to 30-50 mPa. The viscosity s ensures the fluidity of the spinning solution and enables the formation of continuous, unbroken fibers under the action of an electric field, providing a material basis for the regularity of the subsequent channel structure.

[0050] The electrospinning process constructs an initial three-dimensional interconnected channel structure through parameter synergy. A parameter combination of "high voltage, low current, and close-range reception" is employed. A spinning voltage of 15 to 25 kV provides sufficient electric field stretching force, enabling rapid refinement of the composite spinning solution after it is ejected from the nozzle. A low flow rate of 0.5 to 1 mL / h ensures uniform spraying of the spinning solution, preventing fiber adhesion or beading. A close-range reception of 15 to 25 cm shortens the fiber flight path, reduces environmental interference, and allows the fibers to be arranged in an orderly, interwoven pattern. Under the synergistic effect of these three parameters, nanofibers with diameters of 100 to 300 nm and spacings of 50 to 200 nm are formed. The gaps formed by the natural interweaving of the fibers constitute the initial channels. Before hot pressing, the nanofiber membrane thickness is controlled at 30 to 50 μm. At this point, a preliminary three-dimensional interconnected channel structure has been formed, and the uniformity of fiber diameter and spacing provides a foundation for subsequent precise control of the pore size.

[0051] Hot pressing optimizes the structure through densification and homogenization, ultimately forming the target pore structure. The hot pressing process utilizes temperatures of 120-150°C, pressures of 5-10 MPa, and holding times of 10-20 minutes. This activates the PVDF molecular chains, giving them fluidity and allowing them to fill some of the gaps between fibers under pressure, while preventing complete fiber melting and pore blockage. The synergistic effect of pressure and holding time allows for appropriate fusion between fibers, improving structural stability and precisely controlling porosity to 40-50%. Furthermore, during hot pressing, the PVDF matrix and inorganic particles form a 50-100 nm micro-fusion layer, further standardizing the pore boundaries. Combined with the uniform fiber structure formed during electrospinning, this ultimately stabilizes the average pore size at 50-100 nm with a pore size distribution variation coefficient of <10%, while preserving the three-dimensional interconnected structural characteristics, achieving a precise match between porosity, pore size, and distribution uniformity.

[0052] In some embodiments, a micro-fusion layer is formed between the polyvinylidene fluoride body and the inorganic nanoparticles, and the thickness of the micro-fusion layer is 50 nm to 100 nm.

[0053] It should be noted that the formation of the micro-fusion layer is the result of the synergistic effect of the uniform dispersion system of the composite spinning solution and the hot pressing process. Through the interfacial interaction between inorganic nanoparticles and the polyvinylidene fluoride (PVDF) matrix, a stable interfacial layer with a thickness of 50 to 100 nm is finally formed. The specific formation process is as follows: The uniform dispersion system of the composite spinning solution lays the core foundation for the formation of the micro-fusion layer. In the preparation process, titanium dioxide (50-100 nm) and alumina (30-80 nm) are first ultrasonically treated for 3-5 hours to break the interparticle aggregation forces and achieve monodispersion. Then, they are blended with a PVDF solution of 12-18% by mass at a specific volume ratio. A gradient stirring process of "pre-stirring at 150-250 rpm for 0.5-1.5 hours + high-speed dispersion at 450-550 rpm for 1.5-2.5 hours" ensures that the inorganic nanoparticles are uniformly distributed in the PVDF matrix, guaranteeing that each particle surface can fully contact the PVDF molecular chains, eliminating local voids and concentration differences at the interface, and creating conditions for interfacial molecular diffusion and fusion during subsequent hot pressing. Simultaneously, the viscosity of the composite spinning solution is controlled at 30-50 mPa. The viscosity ensures that the inorganic particles in the nanofibers formed after spinning remain in a tightly bound initial state with the PVDF matrix, avoiding interfacial defects caused by the separation of particles from the matrix.

[0054] The synergistic effect of hot-pressing parameters directly drives the formation and thickness control of the micro-fusion layer. The hot-pressing temperature is controlled between 120 and 150°C, a range higher than the glass transition temperature of PVDF (115°C), allowing the PVDF molecular chains to acquire sufficient activity, transforming from a rigid state to a fluid viscoelastic state. The hot-pressing pressure of 5 to 10 MPa propels the PVDF viscoelastic molecular chains to diffuse towards the surface of the inorganic nanoparticles, filling the microscopic gaps between the particles and the matrix, forming a close molecular-level contact. A holding time of 10 to 20 minutes ensures that the PVDF molecular chains can fully penetrate the surface of the inorganic particles, forming a stable bond with the particles through intermolecular forces, avoiding insufficient interfacial bonding caused by short processing times. Under the synergistic effect of temperature, pressure, and holding time, a continuous transition layer, namely the micro-fusion layer, is gradually formed at the interface between the PVDF matrix and the inorganic nanoparticles. The hot-pressing temperature is lower than the melting point of PVDF (170℃), which avoids excessive particle encapsulation or structural collapse caused by the complete melting of PVDF. Ultimately, the thickness of the micro-fusion layer is precisely controlled between 50 and 100 nm, which ensures the interfacial bonding strength without affecting the transport of lithium ions at the interface.

[0055] Therefore, the micro-fusion layer is not a simple physical mixing interface, but a reinforced interface phase with gradient transition characteristics formed through thermal pressing. Its formation effectively eliminates the inherent interface defects between polyvinylidene fluoride and inorganic nanoparticles caused by differences in thermal expansion coefficients, which is the fundamental reason for realizing the "rigid particle reinforcement - flexible matrix toughening" composite structure and simultaneously improving the interfacial shear strength, mechanical strength and thermal stability of the diaphragm.

[0056] In some embodiments, the lithium battery separator meets the following properties: thermal shrinkage rate <5% after being kept at 180°C for 1 hour, tensile strength of 18MPa~21MPa, and ionic conductivity ≥2.9×10⁻⁶. -3 S / cm, liquid absorption rate ≥430%.

[0057] The heat shrinkage rate is less than 5% after maintaining the temperature at 180℃ for 1 hour. This performance parameter is jointly guaranteed by the high-temperature resistant skeleton formed by the two-component inorganic particles and the interface fusion structure, which significantly improves the safety of the battery in high-temperature environments and avoids short circuits between the positive and negative electrodes.

[0058] The tensile strength is 18MPa to 21MPa. This strength range is achieved through a composite structure of "rigid particle reinforcement - flexible matrix toughening", which ensures that the separator can withstand mechanical stress during battery assembly and cycle use and avoids damage.

[0059] Based on a general inventive concept, embodiments of this application provide a lithium battery, which includes a positive electrode, a negative electrode, an electrolyte, and a separator located between the positive and negative electrodes. The separator is any of the lithium battery separators described above.

[0060] In some implementations, the positive electrode active material is LiNi. 0.8 Co 0.1 Mn 0.1 One of O2 (NCM811) and LiCoO2; the negative electrode uses one of graphite and silicon-carbon composite materials; the electrolyte is a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, with 1-3 wt% of lithium salt LiPF6 added. The lithium battery is prepared by first assembling the positive electrode, negative electrode, and prepared separator into a cell in sequence, then injecting the electrolyte, sealing it, and performing formation and aging treatments to obtain a complete lithium battery.

[0061] The lithium battery separator provided in this application possesses comprehensive advantages in thermal stability, electrochemical compatibility, ion transport efficiency, structural stability, and mechanical strength when used in lithium batteries. These advantages are based on the synergistic effect of the separator's core structure and performance characteristics, as detailed below: Thermal stability provides crucial safety assurance for lithium batteries. The separator utilizes a high-temperature resistant framework formed by titanium dioxide and aluminum oxide dual-component inorganic nanoparticles, combined with a micro-fused layer created through hot pressing. It maintains a thermal shrinkage rate of less than 5% after 1 hour at 180°C, significantly outperforming traditional polyolefin separators and existing comparative technologies. This characteristic effectively prevents short circuits between the positive and negative electrodes caused by separator shrinkage and deformation during charging and discharging, especially at high temperatures, reducing the risk of battery thermal runaway. This lays the foundation for the safe use of lithium batteries and makes them suitable for applications with stringent safety requirements, such as electric vehicles and electronic devices.

[0062] The electrochemical stability advantage aligns with the development needs of high-energy-density lithium batteries. The wide bandgap (3.2 eV) of titanium dioxide in the separator suppresses the oxidative decomposition of the electrolyte under high voltage, while the high insulation of alumina reduces ion migration resistance. The synergistic electrochemical stabilizing layer formed by these two materials allows the separator to be compatible with high-voltage cathode materials (such as NCM811) above 4.2V. When paired with this type of cathode material, the lithium battery retains >90% capacity after 100 cycles, exhibiting a stable voltage plateau. This overcomes the shortcomings of existing separators with narrow electrochemical windows and inability to adapt to high-voltage cathode materials, facilitating the design of higher energy densities in lithium batteries.

[0063] The superior ion transport efficiency enhances the charge / discharge performance and rate capability of lithium batteries. The separator possesses a three-dimensional interconnected pore structure with an average pore size of 50–100 nm, a porosity of 40–50%, and a pore size distribution variation coefficient <10%. This uniform pore structure provides efficient channels for lithium-ion transport. Simultaneously, the synergistic effect of the hydroxyl groups on the alumina surface and the polar groups of polyvinylidene fluoride results in a separator liquid absorption rate ≥430% and an electrolyte wetting time <5 s, significantly improving the compatibility between the electrolyte and the separator. These characteristics collectively contribute to a separator ionic conductivity ≥2.9 × 10⁻⁶. -3 With an increase in S / cm and a 15% improvement in lithium-ion migration number, it supports 5C fast charging of lithium batteries and maintains a capacity retention rate of >85% during fast charging, meeting users' needs for rapid replenishment of lithium batteries.

[0064] The structural stability and mechanical strength advantages ensure the long-term cycle reliability of lithium batteries. The separator, formed through hot pressing with a 50-100nm micro-fusion layer, achieves an interfacial shear strength ≥1.56N / cm between the polyvinylidene fluoride matrix and inorganic nanoparticles, avoiding the risk of inorganic particle detachment or interlayer delamination and improving the structural integrity of the separator. Simultaneously, the composite structure of "rigid particle reinforcement - flexible matrix toughening" enables the separator to achieve a tensile strength of 18-21MPa, capable of withstanding mechanical stress during lithium battery assembly and volume changes during cycle use. This prevents battery performance degradation or safety hazards caused by separator damage, extending the lifespan of the lithium battery.

[0065] In summary, the core advantages of this application lie in three dimensions: collaborative material design, innovative structural optimization, and process adaptability. These advantages support each other to form a comprehensive technological barrier, as detailed below: The synergistic design of materials constructs a functionally complementary composite system, laying the foundation for improved overall performance. This application uses titanium dioxide and alumina bicomponent inorganic nanoparticles to modify polyvinylidene fluoride (PVDF) substrates, forming a "high-temperature resistant framework + electrochemically stable layer" structure through their synergistic function. Titanium dioxide provides rigid support for the membrane to resist structural deformation under high-temperature conditions, while alumina optimizes the compatibility between the membrane and the electrolyte and inhibits oxidation reactions under high voltage due to its surface hydrophilicity and electrochemical stability. The synergistic effect of these two materials overcomes the limitations of single-material modification in performance improvement, enabling the membrane to possess both high thermal stability and excellent electrochemical compatibility.

[0066] Structural innovation and optimization achieve a balance between performance and enhanced functionality, resolving the contradiction between structure and performance in existing technologies. The three-dimensional through-pore structure provides a smooth path for lithium-ion transport while ensuring sufficient electrolyte storage and rapid wetting, avoiding ion transport obstruction caused by unreasonable pore structure. The micro-fusion layer formed between polyvinylidene fluoride matrix and inorganic nanoparticles not only enhances interfacial bonding and prevents inorganic particles from detaching or delaminating, but also improves the mechanical strength of the separator through the composite effect of "rigid particle reinforcement - flexible matrix toughening," achieving simultaneous optimization of structural stability and mechanical performance, ensuring that the separator maintains structural integrity during battery assembly and long-term cycling.

[0067] The advantages of process adaptability lower the industrialization threshold and have broad application prospects. The preparation process of this application is based on the mature technology route of electrospinning and hot pressing. The core process parameters can be optimized and adjusted on existing production equipment without relying on special customized equipment. The gradient dispersion process of the composite spinning solution and the electrospinning parameter design of "high pressure, low flow and close-range reception" take into account both product uniformity and production efficiency, avoiding the production difficulty and cost increase caused by complex processes. This enables the technical solution to be quickly adapted to the needs of industrial production and promotes the large-scale application of high-performance lithium battery separators.

[0068] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0069] Example 1: Two-component synergistic modification of the separator (basic solution) Raw material ratio (mass fraction): Polyvinylidene fluoride (PVDF) solution: 15wt% (dissolved in N,N-dimethylformamide (DMF), 50mL); Nano titanium dioxide (TiO2) dispersion: 1wt% (dispersed in DMF, particle size 80nm, 10mL); Nano alumina (Al2O3) dispersion: 0.5wt% (dispersed in DMF, particle size 60nm, 10mL); Mass ratio: TiO2 dispersion:PVDF solution = 1:5, Al2O3 dispersion:PVDF solution = 1:10.

[0070] Preparation steps: S1, Dispersion preparation: The TiO2 and Al2O3 dispersions were ultrasonically treated for 3 hours each, mixed with PVDF solution, premixed at 200 rpm for 1 hour, and then dispersed at 500 rpm for 2 hours to form a uniform spinning solution; S2, Electrospinning: The spinning solution was injected into an electrospinning machine, the spinning voltage was set to 20 kV, the flow rate to 0.8 mL / h, and the receiving distance to 20 cm, to form a nanofiber membrane on the receiving plate (thickness before hot pressing: 40 μm, fiber diameter: 200 ± 50 nm, fiber spacing: 100 ± 30 nm); S3, Hot pressing: The fiber membrane was placed in a hot press and held at 130℃ and 8 MPa for 15 minutes to form a diaphragm containing a 50-100 nm micro-fusion layer, with a thickness of 15 μm after hot pressing.

[0071] Diaphragm performance: Heat shrinkage rate (180℃, 1h): 4.5%; Tensile strength: 19MPa (GB / T36363-2018); Porosity: 45% (n-butanol immersion method), pore size distribution variation coefficient: 8%; Liquid absorption rate: 460% (n-butanol immersion for 12h), electrolyte wetting time: 4s; Ionic conductivity: 3.0×10⁻⁶ -3 S / cm (electrochemical impedance spectroscopy, 25℃); Cyclic capacity retention (NCM811 cathode, 1C charge-discharge, 100 cycles): 92%.

[0072] Example 2: High TiO2 ratio modified membrane (enhanced thermal stability) This embodiment is based on the disclosure in Embodiment 1, with the following modifications: Raw material ratio: PVDF solution: 15wt% (DMF, 50mL); TiO2 dispersion: 1.5wt% (DMF, particle size 70nm, 15mL); Al2O3 dispersion: 0.5wt% (DMF, 10mL); mass ratio: TiO2 dispersion:PVDF solution = 1:3.3, Al2O3 dispersion:PVDF solution = 1:10.

[0073] Key process parameters: Electrospinning: voltage 25kV, flow rate 0.5mL / h, fiber diameter 150±30nm, thickness before hot pressing 30μm; Hot pressing treatment: 140℃, 10MPa, holding pressure for 10min, thickness after hot pressing 12μm.

[0074] Diaphragm performance: Heat shrinkage rate (180℃, 1h): 3.8% (15.6% lower than Example 1); Tensile strength: 21MPa (rigid particle reinforcement effect); Ionic conductivity: 2.9×10⁻⁶ -3 S / cm (porosity 42%, excellent uniformity).

[0075] Example 3: High Al2O3 ratio modified membrane (enhanced electrochemical stability) This embodiment is based on the disclosure in Embodiment 1, with the following modifications: Raw material ratio: PVDF solution: 15wt% (DMF, 50mL); TiO2 dispersion: 1.0wt% (DMF, 10mL); Al2O3 dispersion: 1.0wt% (DMF, particle size 50nm, 20mL); mass ratio: Al2O3 dispersion: PVDF solution = 1:5.

[0076] Key process parameters: Electrospinning: voltage 15kV, flow rate 1mL / h, fiber diameter 300±80nm, spacing 150±50nm, thickness before hot pressing 50μm; Hot pressing treatment: 120℃, 5MPa, holding pressure for 20min (to retain more inter-fiber pores, thickness after hot pressing 20μm).

[0077] Membrane performance: Electrochemical window: 5.2V (vs. Li) + / Li, linear sweep voltammetry); Cyclic capacity retention (NCM811 cathode, 4.3V high voltage cycling, 100 cycles): 93%; Liquid uptake: 480% (Al2O3 surface hydroxyl groups enhance hydrophilicity); Porosity: 48%.

[0078] Example 4: PVDF Concentration Optimized Membrane (Balancing Strength and Porosity) This embodiment is based on the disclosure in Embodiment 1, with the following modifications: Raw material ratio: PVDF solution: 18wt% (DMF, 50mL, high concentration to improve matrix toughness); TiO2 dispersion: 1.0wt% (DMF, 10mL); Al2O3 dispersion: 0.5wt% (DMF, 10mL); Spinning solution viscosity: 45mPa s (measured by Ubbelohde viscometer).

[0079] Key process parameters: Hot pressing: 130℃, 8MPa, holding pressure for 15min (improves the uniformity of the micro-melt layer, with thicknesses of 45μm and 18μm before and after hot pressing, respectively).

[0080] Performance comparison: Tensile strength: 20MPa (5.2% improvement over 15wt%PVDF); Porosity: 42%, with 92% of pores having a diameter of 50-100nm; Interfacial shear strength: 1.58N / cm (interlayer peel test, 1.3% improvement over Example 1).

[0081] Example 5: Hot-pressing temperature gradient optimization of diaphragm (controlling pore structure) This embodiment is based on the disclosure in Embodiment 1, with the following modifications: Key process parameters: Hot pressing conditions: Temperature gradient: 120℃→150℃ (2℃ / min); Pressure pulse: 5MPa→10MPa (alternating once every 2min); Other raw materials and spinning parameters are the same as in Example 1; The thicknesses before and after hot pressing are 42μm and 16μm, respectively.

[0082] Membrane performance: Pore size distribution: coefficient of variation 7% (ultra-uniform pore structure); Ionic conductivity: 3.1 × 10⁻⁶ -3 S / cm (85% of the pores are through-holes); Porosity: 43%; Liquid absorption rate: 470%.

[0083] Lithium-ion battery separator performance in Examples 1-5

[0084] As shown in Table 1, the lithium battery separator of this application exhibits excellent performance in all core aspects and can be precisely controlled, fully meeting the usage requirements of high energy density lithium batteries.

[0085] Regarding the heat shrinkage rate, the heat shrinkage rate of each embodiment after maintaining at 180°C for 1 hour was less than 5%, with the lowest heat shrinkage rate of Embodiment 2 (high TiO2 ratio) at 3.8%, highlighting the strengthening effect of increasing the TiO2 ratio on thermal stability. The heat shrinkage rates of the other embodiments were between 4.2% and 4.8%, all showing excellent high-temperature structural stability.

[0086] In terms of tensile strength, all embodiments are in the range of 18 to 21 MPa. Embodiment 2 reaches 21 MPa due to the rigid particle reinforcement effect, Embodiment 4 increases to 20 MPa by optimizing the PVDF concentration, Embodiments 1 and 5 are both 20 MPa, and Embodiment 3 is 18 MPa. Overall, they exhibit good mechanical strength and can withstand the mechanical stress during battery assembly and cyclic use.

[0087] Regarding porosity and liquid absorption rate, the porosity was stably controlled within the ideal range of 42% to 48%, and the liquid absorption rate was ≥430%. Among them, Example 3 (high Al2O3 ratio) had the highest liquid absorption rate of 480%, which reflects the effect of the hydroxyl groups on the surface of Al2O3 on the wettability of the electrolyte. The liquid absorption rates of the other examples were between 430% and 470%, which can meet the requirements of sufficient electrolyte storage and rapid wetting.

[0088] Regarding ionic conductivity, all examples were ≥2.9×10⁻⁶. -3 In Example 5, through optimization using hot-pressing temperature gradients and pressure pulses, the ionic conductivity reached 3.1 × 10⁻⁶ S / cm. -3 The conductivity of the sample with a ratio of S / cm exhibits the best ion transport efficiency, while the conductivity of the other embodiments is around 2.9 × 10⁻⁶. -3 Up to 3.0×10 -3 The ratio between S / cm ensures efficient lithium-ion migration.

[0089] Regarding the retention rate of the cycling capacity, all examples showed ≥91% after 100 cycles, with Example 5 reaching the highest at 94%. Example 3 (high Al2O3 ratio) still reached 93% under high voltage cycling conditions of 4.3V, which fully verified the significant improvement of electrochemical stability brought about by the synergistic modification of the two-component inorganic particles and process optimization.

[0090] In summary, by adjusting the ratio of inorganic particles in the two-component mixture, the concentration of PVDF, and the hot-pressing process parameters, this application can specifically enhance the thermal stability, mechanical strength, ion transport efficiency, or electrochemical stability of the separator, and all performance characteristics can meet the stringent requirements of high-energy-density lithium batteries, achieving precise control and comprehensive improvement of overall performance.

[0091] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: Excellent thermal stability: TiO2 (melting point 1840℃) and Al2O3 (melting point 2054℃) form a high-temperature resistant network skeleton, which, combined with the PVDF matrix, allows the separator to maintain a thermal shrinkage rate of <5% for 1 hour at 180℃, which is significantly better than traditional polyolefin separators (thermal shrinkage rate >15% at 150℃). This effectively avoids short circuits between the positive and negative electrodes caused by separator shrinkage and deformation under high-temperature conditions, providing reliable safety protection for lithium batteries.

[0092] Widening of the electrochemical window: The wide bandgap of TiO2 (3.2eV) can suppress electrolyte oxidation under high voltage, and the high insulation properties of Al2O3 reduce ion migration resistance. The synergy of the two makes the separator suitable for high voltage cathode materials above 4.2V. When paired with NCM811 cathode, the capacity retention rate of lithium battery after 100 cycles is >90%, and the voltage platform is stable above 4.2V, which helps the research and development and application of high energy density lithium batteries.

[0093] Highly efficient lithium-ion transport: The membrane possesses a three-dimensional interconnected pore structure, achieving an ionic conductivity of 2.9 × 10⁻⁶. -3 With an increase in S / cm and a 15% improvement in lithium-ion migration number, it supports 5C fast charging of lithium batteries with a capacity retention rate of >85%, significantly improving battery charging and discharging efficiency and rate performance to meet the needs of rapid energy replenishment.

[0094] Excellent electrolyte compatibility: The synergistic effect of the hydroxyl groups on the Al2O3 surface and the polar groups of PVDF makes the membrane wettable to carbonate electrolytes for less than 5 seconds and the liquid absorption rate reach more than 450%, which is significantly better than traditional membranes (liquid absorption rate <200%), and can provide sufficient electrolyte guarantee for lithium-ion transport.

[0095] Strong interfacial bonding: Through hot-pressing induction process, a micro-fusion layer with a thickness of 50 to 100 nm is formed between the PVDF matrix and inorganic particles. The interfacial shear strength is increased by 30% compared with the traditional blending method, and the peeling force reaches 1.56 N / cm, which effectively avoids the detachment of inorganic particles or interlayer peeling and improves the stability of the membrane structure.

[0096] Precise porosity control: After hot pressing, the porosity of the diaphragm is controlled at 40% to 50%, with an average pore size of 50 to 100 nm and a pore size distribution variation coefficient of <10%. This ensures a liquid absorption rate of 450% to 480% while achieving a balance between mechanical strength and electrolyte wettability. The tensile strength of the diaphragm reaches 18 to 21 MPa.

[0097] Flexible material adaptability: Inorganic nanoparticles can be replaced with high-temperature resistant / electrochemically stable inorganic particles such as zirconium dioxide, magnesium oxide, and silicon dioxide. A single filler or other two-component combination can still form a "high-temperature resistant skeleton + electrochemically stable layer"; the solvent can be replaced with methylpyrrolidone, dimethyl sulfoxide, or tetrahydrofuran; and the electrolyte lithium salt can be replaced with lithium bis(fluorosulfonyl)imide, adapting to different application requirements.

[0098] Outstanding industrialization potential: The preparation process is based on mature electrospinning and hot pressing technology. The core process parameters can be optimized and adjusted on existing equipment without the need for special customized equipment. Furthermore, patents for integrated equipment for electrospinning and hot pressing processes can be considered to lower the industrialization threshold and facilitate large-scale production and widespread application.

[0099] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a lithium battery separator, characterized in that, The method includes: A composite spinning solution was obtained by gradient stirring of a mixture of inorganic nanoparticle dispersion and polyvinylidene fluoride solution. The composite spinning solution was electrospun to obtain a nanofiber membrane. The nanofiber membrane is subjected to hot pressing treatment to obtain a lithium battery separator; The inorganic nanoparticle dispersion includes one or more of the following: titanium dioxide dispersion, alumina dispersion, zirconium dioxide dispersion, magnesium oxide dispersion, and silica dispersion. The electrospinning includes the following parameters: spinning voltage of 15kV to 25kV, flow rate of 0.5mL / h to 1mL / h, and receiving distance of 15cm to 25cm.

2. The method according to claim 1, characterized in that, The inorganic nanoparticle dispersion is composed of titanium dioxide dispersion and alumina dispersion, wherein the mass concentration of titanium dioxide dispersion is 0.5% to 1.5% and the mass concentration of alumina dispersion is 0.3% to 1.0%. The mass concentration of the polyvinylidene fluoride solution is 12% to 18%.

3. The method according to claim 2, characterized in that, The volume ratio of the titanium dioxide dispersion to the polyvinylidene fluoride solution is 1:(5-10); The volume ratio of the alumina dispersion to the polyvinylidene fluoride solution is 1:(8-12); The titanium dioxide particle size in the titanium dioxide dispersion is 50 nm to 100 nm. The alumina in the alumina dispersion has a particle size of 30 nm to 80 nm.

4. The method according to claim 1, characterized in that, The viscosity of the composite spinning solution is 30 mPa·s to 50 mPa·s; The nanofibers in the nanofiber membrane have a diameter of 100nm to 300nm and a fiber spacing of 50nm to 200nm. The thickness of the nanofiber membrane is 30 μm to 50 μm.

5. The method according to claim 1, characterized in that, The hot pressing process includes the following parameters: temperature of 120℃~150℃, pressure of 5MPa~10MPa, and holding time of 10min~20min.

6. A lithium battery separator prepared by the method according to any one of claims 1 to 5, characterized in that, The lithium battery separator is composed of polyvinylidene fluoride body and inorganic nanoparticles dispersed in the polyvinylidene fluoride body; The thickness of the lithium battery separator is 12μm to 20μm.

7. The lithium battery separator according to claim 6, characterized in that, The lithium battery separator has a three-dimensional through-pore structure with an average pore size of 50nm to 100nm, a porosity of 40% to 50%, and a coefficient of variation of pore size distribution of <10%.

8. The lithium battery separator according to claim 6, characterized in that, A micro-fusion layer is formed between the polyvinylidene fluoride body and the inorganic nanoparticles, and the thickness of the micro-fusion layer is 50 nm to 100 nm.

9. The lithium battery separator according to claim 6, characterized in that, The lithium battery separator meets the following performance requirements: thermal shrinkage rate <5% after being kept at 180℃ for 1 hour, tensile strength of 18MPa~21MPa, and ionic conductivity ≥2.9×10⁻⁶. -3 S / cm, liquid absorption rate ≥430%.

10. A lithium battery, characterized in that, The lithium battery includes a positive electrode, a negative electrode, an electrolyte, and a separator located between the positive and negative electrodes, wherein the separator is the lithium battery separator according to any one of claims 6 to 9.

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