A lithium battery separator prepared by coaxial parallel electrospinning, method and application

Abstract

The application discloses a lithium battery diaphragm prepared by coaxial parallel electrospinning, a method and application. The method comprises the following steps: S1, dissolving a fiber skeleton polymer and a fiber functional polymer in organic solutions respectively to form uniform core layer parallel solutions A and B; S2, dissolving a metal salt in a water solution containing a hydrophilic polymer to form a uniform shell layer spinning solution; S3, coaxial parallel electrospinning the core layer parallel solutions A and B and the shell layer spinning solution, and preparing a composite nanofiber membrane with metal salt nano-aggregates by means of interface effect; and S4, immersing the prepared composite nanofiber membrane in an alkali salt solution to cause an anion exchange reaction, then drying into a film, and then immersing the film in an acetonitrile solution containing TAPB and DHTP to react at room temperature. The prepared lithium battery diaphragm can eliminate resource waste and safety problems caused by thermal runaway of lithium batteries, and has important significance for development and application of lithium battery diaphragms.

Description

Technical Field

[0001] This invention relates to the field of lithium battery materials technology. More specifically, it relates to a lithium battery separator, a method for preparing it using coaxial parallel electrospinning, and its applications. Background Technology

[0002] In recent years, with the rapid application and popularization of electronic products, mobile phones, energy storage devices, and electric vehicles, the requirements for batteries have become increasingly systematic and stringent. Lithium-ion batteries, due to their high energy density, long cycle life, and lightweight convenience, are gradually replacing lead-acid, nickel-metal hydride, and nickel-cadmium batteries, attracting increasing attention. Lithium-ion batteries mainly consist of four parts: positive and negative electrode materials, electrolyte, separator, and battery casing. The lithium-ion battery separator, as one of the most important components, has a direct impact on battery safety and cost. Its main functions are: 1) preventing direct contact between the positive and negative electrodes, thus preventing short circuits; 2) providing a transport channel for lithium ions; and 3) providing pore protection in the event of thermal runaway, thereby preventing short circuits.

[0003] Currently, the most commonly used lithium battery separators on the market are polyolefin separator materials prepared by dry or chemical processes. These separators have good electrochemical stability and suitable mechanical strength, as well as certain thermal shut-off performance. However, with the widespread application of lithium-ion batteries, they also face increasing challenges. Some shortcomings of traditional lithium-ion battery separator materials are no longer sufficient to meet the high safety performance requirements of modern society. For example, 1) poor thermal stability: whether it is the widely used polyolefin separator material or the polymer separator material such as PET and PI with high mechanical strength and temperature resistance, these separator materials may exhibit thermal shrinkage or failure to close ion channels when the battery experiences thermal runaway, leading to short circuits and uncontrollable fires and explosions, posing a great hidden danger to the application of lithium batteries; 2) poor self-recovery function: although some researchers have conducted experiments on separator pore closure under lithium battery thermal runaway and applied them, these attempts to close the separator pores are only one-time events. Although they avoid damage and danger caused by current short circuits to a certain extent, the battery has completely lost the transport capacity of ion channels and cannot be used again, which undoubtedly results in a great waste of resources.

[0004] Therefore, it is necessary to develop a new method for preparing lithium battery separators to overcome the resource waste and safety issues caused by thermal runaway in lithium batteries. Summary of the Invention

[0005] To address the aforementioned problems, the first objective of this invention is to provide a method for preparing lithium-ion battery separators using coaxial parallel electrospinning. This invention utilizes coaxial parallel electrospinning technology to prepare parallel core fibers and then wraps these core fibers with shell fibers, resulting in core-shell structured composite nanofibers. Metal oxide-COF composite nanoparticles, serving as the protective structure of the lithium-ion battery separator, are uniformly distributed on the surface of the parallel core fibers. The precursor for this protective structure is formed by the hydrophilic and hydrophobic properties and interfacial effects of the shell and core materials, resulting in metal salt nanoaggregates formed during the contraction of a local finite element region at the moment of nanofiber synthesis. These aggregates are then further processed through anion exchange reactions and interfacial self-assembly to ultimately obtain the metal oxide-COF composite nanoparticles.

[0006] The second objective of this invention is to provide a lithium battery separator prepared using the method described above. By selecting the raw materials and controlling the conditions of the preparation method, a lithium battery separator with high mechanical strength, good chemical stability, good solvent stability, and temperature response is finally obtained. This lithium battery separator can effectively eliminate the adverse consequences caused by thermal runaway of lithium batteries. That is, when the temperature is abnormal, the nanofibers partially expand without causing damage to the fiber structure, and the pores close. When the temperature returns to normal, the nanofibers recover, and the transport capacity of the ion channels is restored.

[0007] A third objective of this invention is to provide an application of the lithium battery separator described above in the field of energy storage batteries.

[0008] In this invention, the entire surface of a single fiber is decomposed, and each tiny region capable of undergoing the same deformation is considered a simple part, which can be called a finite element region.

[0009] To achieve the first objective mentioned above, the present invention adopts the following technical solution:

[0010] This invention discloses a method for preparing lithium battery separators using coaxial parallel electrospinning, characterized by comprising the following steps:

[0011] S1. The fiber skeleton polymer and the fiber functional polymer are dissolved in an organic solution to form a homogeneous core layer parallel solution A and a core layer parallel solution B, wherein the concentration of the core layer parallel solution A is 8-25 wt% and the concentration of the core layer parallel solution B is 8-25 wt%.

[0012] S2. Dissolve the metal salt in an aqueous solution of a hydrophilic polymer to form a uniform shell spinning solution, wherein the concentration of the metal salt is 0.5-30 wt% and the concentration of the hydrophilic polymer is 3-15 wt%.

[0013] S3. The core layer parallel solution A and core layer parallel solution B described in step S1 are coaxially parallel electrospun with the shell spinning solution described in step S2, and a composite nanofiber membrane with metal salt nanoaggregates is obtained by means of the interface effect.

[0014] S4. The composite nanofiber membrane prepared in step S3 is immersed in an alkaline salt solution with a concentration of 0.02-0.6wt% to undergo anion exchange reaction. After drying, it is immersed in an acetonitrile solution containing TAPB and DHTP and reacted at room temperature for 24-48 hours. After rinsing, drying and rolling, a lithium battery separator with a metal oxide-COF fiber protective structure is obtained.

[0015] This invention starts with the fine structure of nanofibers constructed by electrospinning. A fiber-backbone polymer with good chemical stability, thermal stability, hydrophilicity, and dielectric properties is selected as one pole of the core layer parallel spinning solution, and a fiber-functional polymer with good chemical stability, thermal sensitivity, and hydrophilicity is selected as the other pole. A hydrophilic polymer solution containing soluble metal salts is used as the shell layer spinning solution. Using coaxial parallel electrospinning technology and leveraging interfacial effects, a composite nanofiber membrane with metal salt nanoaggregates is prepared. Through anion exchange reaction and interfacial self-assembly, a lithium battery separator with a metal oxide-COF fiber protective structure is obtained. This lithium battery separator exhibits high mechanical strength, good chemical stability, good solvent stability, and temperature responsiveness. More importantly, this lithium battery separator can effectively eliminate the adverse consequences of thermal runaway in lithium batteries, avoid damage and danger caused by short circuits, and the ion channel transport capacity can recover as the temperature returns to normal.

[0016] Furthermore, when the temperature of a lithium battery rises, the fibers on one side, formed by the fibrous backbone polymer, essentially maintain their original shape, thus preserving their independent existence. Meanwhile, the fibers on the other side, composed of thermosensitive functional polymers, expand, causing the pores between the fibers to shrink or even close. This effectively reduces or even prevents metal ions from passing through the separator and reaching the negative electrode. This automatically reduces the power output of the lithium battery, preventing temperature runaway and short circuits caused by lithium ion transport under thermal runaway. When the temperature returns to normal, the thermosensitive polymers return to their original state, and the newly formed channels maintain efficient metal ion passage. Additionally, when the thermosensitive polymers expand due to heat, the parallel core layer causes them to expand freely to one side, while the side with a smaller expansion rate only bends, without damaging the fiber structure. This effectively ensures the integrity of the fiber structure and maintains high mechanical strength and liquid absorption. Simultaneously, the parallel core layer solutions A and B can intermingle during fiber formation, ensuring that the fiber structure does not disintegrate and detach during the expansion of the thermosensitive polymers. Meanwhile, the fiber-protected structure of the metal oxide / COF composite nanoparticles ensures the independence of the interfaces between each fiber during the aforementioned thermal expansion, preventing the fusion of fiber shells at high temperatures that could lead to battery failure. Furthermore, the COF-modified metal oxide nanoparticles not only prevent redox reactions within the metal particles themselves from damaging the battery structure but also enhance the strength and liquid absorption of the fibers, thus significantly promoting battery performance. By combining the properties of the raw materials, controlling the preparation conditions, and utilizing the unique structure, the lithium-ion battery separator possesses excellent resistance to thermal runaway, ensuring battery life and safety.

[0017] During the experimental exploration, the inventors discovered that if the core layer parallel solution A and the core layer parallel solution B are mixed as the core layer spinning solution for spinning, the two polymers will jointly form a nanofiber with uniform composition in each region, and there will be no layered structure between the two polymers. In terms of physical properties, due to the mixing and spinning of polymers with different properties, the thermal stability of the fiber will be worse (compared to the fiber formed by a polymer with good thermal stability alone), and the thermal expansion and recovery performance will be worse (compared to the fiber formed by a polymer with good temperature sensitivity and thermal resilience alone); and if a three-layer structure is formed, consisting of a core layer parallel solution, another core layer parallel solution, and a shell layer, its performance is also difficult to meet the requirements. The following is an explanation of the different situations: (1) If the innermost core layer is a polymer with good temperature sensitivity and thermal resilience, and the middle layer is a polymer with good thermal stability, when the temperature rises, two situations will occur: 1) The binding force of the middle layer polymer is very large, restricting 1) If the innermost core polymer layer deforms, this composite structure cannot expand and block ion channels when the ambient temperature rises, which can cause short circuits or even explosions in the battery. 2) The middle layer polymer layer is stable in shape when heated, but its binding force is not strong. In this case, the innermost core polymer layer will be broken by the heat, which will reduce or even block the gaps between the fibers, thus protecting the lithium battery. However, this deformation is destructive. When the temperature returns to normal, the innermost core polymer layer will gradually return to its original shape, while the middle polymer layer structure, due to the violent damage, cannot achieve self-healing after tearing. This will have a certain impact on the mechanical and electrical properties of the separator. Repeated damage in this process may even damage the battery separator. (2) If the innermost core layer is a polymer with good thermal stability, while the middle layer is a polymer with good thermosensitivity and thermal resilience, when the ambient temperature rises, the innermost core layer polymer, due to its good thermal stability, will basically maintain its original state; however, the thermosensitivity and thermal resilience polymer in the middle layer will expand due to heat, and the interface that was originally closely fused with the central polymer will separate due to the large-scale expansion. Although the thermosensitivity polymer will return to a state similar to its original state after the temperature recovers, the interface that was originally fused into one will be divided into two independent interface morphologies. This has a significant impact on the electrical and mechanical properties of the material, especially the mechanical properties, and thus affects the performance of the lithium battery.

[0018] Furthermore, the electrospinning used in this invention is needleless coaxial parallel electrospinning. Coaxial parallel electrospinning technology is a combination of coaxial electrospinning and parallel electrospinning. It is based on the advantage of parallel electrospinning in stress deformation (when subjected to internal stress, deformation is used to offset the structural damage caused by stress). At the same time, the instantaneous aggregation caused by the hydrophilic and hydrophobic effects at the interface during coaxial electrospinning can controllably realize the construction of the microporous structure of the separator while greatly improving the production efficiency of electrospinning. This effectively reduces the cost of electrospinning preparation and has important positive significance for the development and application of electrospinning in lithium battery separators.

[0019] Furthermore, the fiber backbone polymer includes, but is not limited to, one or more of PVDF, PVDF-HFP, PMMA, PAN, PPSU, or PSU; preferably, the fiber functional polymer is hydrophobic polyacrylamide.

[0020] At the initial stage of the dynamic jet being drawn out by the electric field, the shell solution encapsulates the parallel core polymer solution. The characteristics of the entire jet are: firstly, due to the relatively small proportion of the shell solution, only a thin coating film can be formed at the point of jet formation; secondly, due to the difference in hydrophilicity and hydrophobicity between the core and shell solutions, a hydrophilic-hydrophobic interface is formed between them. As the solvent evaporates and the jet is elongated, the hydrophilic-hydrophobic effect between the core and shell becomes more pronounced. When the shell solution is insufficient to cover the entire core layer, with further solvent evaporation, the core polymer forms fine nanofibers, while the shell solution covering it shrinks within the finite element region in a very short time due to the interfacial effect, thus forming metal salt nanoaggregates attached to the core nanofibers.

[0021] Furthermore, the metal salt includes, but is not limited to, one or more of aluminum salts, zirconium salts, or titanium salts; preferably, the metal salt includes, but is not limited to, one or more of aluminum nitrate, aluminum sulfate, aluminum chloride, zirconium nitrate, zirconium sulfate, zirconium chloride, titanium nitrate, titanium sulfate, and titanium chloride; preferably, the hydrophilic polymer includes, but is not limited to, one or more of gelatin, polyvinyl alcohol, and polyvinylpyrrolidone; preferably, the solute in the alkaline salt solution includes, but is not limited to, one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia, and hexamethylenetetramine. When the composite nanofiber membrane is immersed in the alkaline salt solution, an anion exchange reaction will occur. This anion exchange reaction can be referenced to precipitation-dissolution equilibrium, that is, the highly soluble metal salt nanoaggregates will be transformed into less soluble metal hydroxide nanoaggregates.

[0022] Furthermore, the concentration of the core layer parallel solution A is 8-25 wt%; exemplaryly, the concentration of the core layer parallel solution A can also be 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, etc.; the concentration of the core layer parallel solution B is 8-25 wt%; exemplaryly, the concentration of the core layer parallel solution B can also be 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, etc.

[0023] Furthermore, the concentration of the metal salt is 0.5-30 wt%; exemplarily, the concentration of the metal salt can also be 0.5 wt%, 1 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 23 wt%, 25 wt%, 27 wt%, 30 wt%, etc.; the concentration of the hydrophilic polymer is 3-15 wt%; exemplarily, the concentration of the hydrophilic polymer can also be 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, etc.

[0024] Furthermore, the concentration of the alkaline salt solution is 0.02-0.6 wt%; exemplaryly, the concentration of the alkaline salt solution can be 0.02 wt%, 0.04 wt%, 0.06 wt%, 0.08 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.55 wt%, 0.6 wt%, etc.

[0025] Furthermore, during coaxial electrospinning, the flow rate of the core layer parallel solution A is 1.5-7.5 ml / h, the flow rate of the core layer parallel solution B is 1.5-7.5 ml / h, the flow rate of the shell layer spinning solution is 1-5 ml / h, the temperature is 18-25℃, the humidity is 20-40%, the roller speed is 200 r / min, the spinning voltage is 3-100 KV, and the receiving distance is 12-30 cm.

[0026] Furthermore, the flow rates of the core layer parallel solution A and the core layer parallel solution B can be the same or different. For example, the flow rates of the core layer parallel solution A and the core layer parallel solution B are 1.5 ml / h, 2 ml / h, 2.5 ml / h, 3 ml / h, 3.5 ml / h, 4 ml / h, 4.5 ml / h, 5 ml / h, 5.5 ml / h, 6 ml / h, 6.5 ml / h, 7 ml / h, 7.5 ml / h, etc.; the flow rate of the shell spinning solution can be 1 ml / h, 2 ml / h, 3 ml / h, 4 ml / h, 5 ml / h, etc. In order to obtain high-performance composite nanofibers, it is necessary to control the total flow rate of the core layer parallel solution A and the core layer parallel solution B to be greater than the flow rate of the shell spinning solution. Preferably, the spinning effect is best when the flow rate ratio of the core layer parallel solution A, the core layer parallel solution B and the shell spinning solution is 1.5-2:1.5-2:1.1-1.2.

[0027] Furthermore, the total solute concentration of the acetonitrile solution containing TAPB and DHTP is 5-10 wt%; exemplaryly, the total solute concentration can be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, etc.; the mass ratio of TAPB to DHTP is 1:1.5.

[0028] Furthermore, in step S4, the anion exchange reaction takes 10-60 minutes.

[0029] Furthermore, rolling can increase the density of the fiber membrane. Its main function is to eliminate the electrostatic force on the membrane surface to facilitate battery assembly, while avoiding the connection of holes and preventing the battery from short-circuiting. In step S4, the rolling pressure is 10-50 MPa; for example, the rolling pressure can be 10 MPa, 20 MPa, 30 MPa, 40 MPa, 50 MPa, etc.

[0030] Furthermore, the organic solution includes, but is not limited to, one or more of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, tetrahydrofuran, dimethyl sulfoxide, dichloromethane, and acetone.

[0031] To achieve the second objective mentioned above, the present invention uses a lithium battery separator prepared by the method described above; the lithium battery separator has a thickness of 20-1000 μm, a porosity of 25-65%, an electrolyte absorption rate of 200-1000%, and a mechanical tensile strength of 15-55 MPa.

[0032] To achieve the third objective mentioned above, this invention discloses an application of the lithium battery separator described above in the field of energy storage batteries, for example, it can be applied to the preparation of lithium-ion batteries, lithium metal batteries, and lithium-ion power batteries.

[0033] The beneficial effects of this invention are as follows:

[0034] This invention discloses a method for preparing lithium battery separators using coaxial parallel electrospinning and its application, which has the following advantages:

[0035] 1. This patent starts with the fine structure of nanofibers constructed by electrospinning. It selects a fiber skeleton polymer with good chemical stability, thermal stability, hydrophilicity and dielectric properties as one pole of the core layer parallel spinning solution, and selects a fiber functional polymer with good chemical stability, thermal sensitivity and hydrophilicity as the other pole of the core layer parallel spinning solution. It uses a hydrophilic polymer solution containing soluble metal salts as the shell layer spinning solution. Using coaxial parallel electrospinning technology and with the help of interface effect, a composite nanofiber membrane with metal salt nanoaggregates is prepared. Through anion exchange reaction and interface self-assembly process, a lithium battery separator with a metal oxide-COF fiber protective structure is obtained. The lithium battery separator possesses high mechanical strength, good chemical stability, good solvent stability, and temperature responsiveness. More importantly, it can effectively eliminate the adverse consequences of thermal runaway in lithium batteries, avoid damage and danger caused by short circuits, and allow the ion channel's transport capacity to recover as the temperature returns to normal. By combining the properties of various raw materials, controlling the preparation conditions, and its special structure, the lithium battery separator is endowed with excellent resistance to battery thermal runaway, ensuring battery life and safety.

[0036] 2. The lithium battery separator of the present invention uses polymer and metal oxide / COF composite nanoparticles, both of which have good chemical and thermal stability. This not only endows the battery separator with high chemical and thermal stability, but also greatly enhances the strength of the fiber membrane material, which has important practical significance for the specific application of lithium battery separators.

[0037] 3. The electrospinning method used in this invention is needleless coaxial parallel electrospinning, which can controllably realize the construction of the micro-porous structure of the separator while greatly improving the production efficiency of electrospinning. This effectively reduces the cost of electrospinning preparation and has important positive significance for the development and application of electrospinning in lithium battery separators. Attached Figure Description

[0038] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0039] Figure 1 This is a schematic diagram of the core fiber morphology and deformation process in an embodiment of the present invention.

[0040] Figure 2 This is a schematic diagram of the needleless coaxial parallel electrospinning method used in an embodiment of the present invention.

[0041] Figure 3 The image shows the SEM morphology of the lithium battery separator prepared in Example 1. Detailed Implementation

[0042] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0043] Unless otherwise specified, all raw materials used in this invention are commercially available. Any range described in this invention includes end values, any values ​​between end values, and any sub-ranges formed by end values ​​or any values ​​between end values. Unless otherwise specified, all percentages are mass percentages.

[0044] Figure 1 This diagram illustrates the morphology and deformation process of the core fiber in this embodiment. Part A represents one side of the fiber composed of thermosensitive functional polymers, and part B represents the other side of the fiber composed of thermally stable fibrous skeleton polymers. The particles are metal oxide-COF composite nanoparticles attached to the fiber surface. When the ambient temperature rises, the side of the fiber composed of thermosensitive functional polymers expands towards the fiber pores. The thermally stable fibrous skeleton polymers simply twist and deform to offset the stress changes caused by the expansion of the functional polymers. Therefore, the interface between the two polymers does not peel off due to forced force. When the ambient temperature drops to normal, the side of the fiber composed of functional polymers recovers its original shape, and the fibrous skeleton polymers simply return to their initial state from twisting. This offsets the stress changes caused by the recovery of the functional polymer morphology. Again, the interface between the two polymers does not peel off due to forced force. Therefore, the fiber, and even the lithium battery separator itself, can maintain good performance. The lithium battery separator prepared from this material can perfectly solve the problem of temperature runaway in lithium batteries.

[0045] Example 1

[0046] The method for preparing lithium battery separators using coaxial parallel electrospinning described in this embodiment can be referred to... Figure 2 A schematic diagram of needleless coaxial parallel electrospinning, with the following specific steps:

[0047] (1) Dissolve the fiber skeleton polymer PVDF in N,N-dimethylacetamide to form a homogeneous core layer parallel solution A with a concentration of 25wt%.

[0048] (2) Dissolve the fiber functional polymer hydrophobic polyacrylamide in N,N-dimethylformamide to form a uniform core layer parallel solution B with a concentration of 15wt%.

[0049] (3) Dissolve soluble aluminum nitrate in an aqueous solution of gelatin to form a uniform shell spinning solution. The concentration of aluminum nitrate is 5 wt% and the concentration of gelatin is 5 wt%.

[0050] (4) Using PVDF solution as one pole of the core layer parallel solution (A); hydrophobic polyacrylamide as the other pole of the core layer parallel solution (B); and a solution composed of aluminum nitrate and gelatin as the shell layer solution, coaxial parallel electrospinning was performed, and a composite nanofiber membrane with aluminum nitrate nano-aggregates was prepared by means of interfacial effect. The flow rate of the core layer parallel solution A was controlled at 7.5 ml / h, the flow rate of the core layer parallel solution B was controlled at 7.5 ml / h, and the flow rate of the shell layer spinning solution was controlled at 5 ml / h; the spinning conditions were: temperature 25℃, humidity 35%, roller speed 200 r / min, spinning voltage 70 KV, and receiving distance 18 cm.

[0051] (5) The prepared composite nanofiber membrane was immersed in a 0.6 wt% sodium hydroxide solution (ethanol and water volume ratio of 8:2) for 10 min, then rinsed with ethanol and dried; the dried composite nanofiber was immersed in an acetonitrile solution with 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 2,5,dihydroxyterephthalaldehyde (DHTP) as monomers, the mass ratio of 1,3,5-tris(4-aminophenyl)benzene (TAPB) to 2,5,dihydroxyterephthalaldehyde (DHTP) was 1:1.5, the total concentration was 10 wt%, and the reaction was carried out at room temperature for 24 hours, then rinsed with anhydrous ethanol solution and dried;

[0052] (6) The composite nanofibers prepared in step (5) are extruded by roller extrusion to compress the loosely and irregularly stacked nanofibers into a dense nanofiber membrane. The extrusion pressure is 10 MPa, and a dense lithium battery separator with a thickness of 0.20 mm can be obtained.

[0053] The lithium battery separator was placed in an aqueous solution, and the temperature was raised from room temperature (25°C) to 130°C and then lowered back to 25°C. After drying, the changes in its conductivity and tensile strength were monitored. The tensile strength test was performed using a universal tensile testing machine, referring to the thin film tensile properties test method in GB / T1040.3-2006.

[0054] Porosity measurement: The lithium battery separator was cut into 4cm*4cm pieces and dried under vacuum at 60℃ for 4 hours. The density was calculated from mass and volume, denoted as pb. The absorbent used was n-butanol, with a density pb of 0.809 g / cm³. 3Weigh the sample membrane and record it as mp. Immerse the fiber membrane to be tested fully in n-butanol liquid for 2 hours. At this time, it can be considered that the absorption is complete. Remove the sample membrane from the n-butanol. Wipe off the excess n-butanol on the surface of the sample membrane with paper. Weigh the wet weight and take the difference between the wet weight and the dry weight. The mass obtained is the mass of absorbed n-butanol, recorded as mb. Calculate the porosity using the following formula: Porosity = (mb / pb) / (mb / pb+mp / pp)*100%.

[0055] Specific surface area and pore diameter were determined according to the gas adsorption BET method in GB / T 19587-2004, and the samples were tested using a specific surface adsorption instrument.

[0056] Conductivity testing method: After thoroughly immersing the fiber membrane in an electrolyte solution of 1 mol / L LiPF6 / EC-DEC (volume ratio 1:1), the membrane was sandwiched between two stainless steel blocking electrodes in a glove box. Measurements were performed at room temperature using a Solartron 1280Z electrochemical workstation (frequency range: 1-20000; sine wave amplitude: 5 mV).

[0057] The air permeability test refers to the test methods for textiles and nonwovens in GB / T 24218.15-2018, and the air permeability of the material is measured using a fabric air permeability meter.

[0058] The liquid absorption rate test should refer to the liquid absorption rate determination method in QB / T 2303.11-2008 Test Methods for Pulp Paper for Batteries.

[0059] The relevant performance parameters of the lithium battery separator prepared in Example 1 are shown in Table 1 after testing.

[0060] Table 1. Relevant performance parameters of lithium battery separators

[0061]

[0062]

[0063] As shown in Table 1, the lithium battery separator prepared by this invention has moderate porosity, pore diameter, and specific surface area; excellent air permeability and liquid absorption; and its tensile strength and conductivity remain essentially unchanged after exposure to high temperatures, maintaining stable performance. Therefore, it is reusable and possesses the good performance required for a separator.

[0064] Figure 3The SEM image of the lithium battery separator prepared in Example 1 is shown. The fiber body is composed of two parallel polymers: one side is a hydrophobic polyacrylamide part and the other side is a PVDF part. The fusion of the interface leads to the two being combined into one to form a complete fiber body. The numerous small particles attached to the surface are Al2O3-COF composite nanoparticles.

[0065] Example 2

[0066] The method for preparing lithium battery separators using coaxial parallel electrospinning described in this embodiment can be referred to... Figure 2 A schematic diagram of needleless coaxial parallel electrospinning, with the following specific steps:

[0067] (1) Dissolve the fiber skeleton polymer PVDF-HFP in N-methylpyrrolidone to form a homogeneous core layer parallel solution A with a concentration of 10wt%.

[0068] (2) Dissolve the fiber functional polymer hydrophobic polyacrylamide in tetrahydrofuran to form a uniform core layer parallel solution B with a concentration of 25wt%.

[0069] (3) Dissolve soluble zirconium nitrate in an aqueous solution of polyvinyl alcohol to form a uniform shell spinning solution. The concentration of zirconium nitrate is 20 wt% and the concentration of polyvinyl alcohol is 3 wt%.

[0070] (4) Using PVDF-HFP solution as one pole of the core layer parallel solution (A); hydrophobic polyacrylamide as the other pole of the core layer parallel solution (B); and a solution composed of zirconium nitrate and polyvinyl alcohol as the shell layer solution, coaxial parallel electrospinning was performed, and a composite nanofiber membrane with aluminum nitrate nanoaggregates was prepared by means of interfacial effect. The flow rate of the core layer parallel solution A was controlled at 6 ml / h, the flow rate of the core layer parallel solution B was controlled at 6 ml / h, and the flow rate of the shell spinning solution was controlled at 4 ml / h; the spinning conditions were: temperature 20℃, humidity 25%, roller speed 200 r / min, spinning voltage 60 KV, and receiving distance 15 cm.

[0071] (5) The prepared composite nanofiber membrane was immersed in a 0.02 wt% sodium hydroxide solution (ethanol and water volume ratio of 8:2) for 60 min, then rinsed with ethanol and dried; the dried composite nanofiber was immersed in an acetonitrile solution with 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 2,5,dihydroxyterephthalaldehyde (DHTP) as monomers, the mass ratio of 1,3,5-tris(4-aminophenyl)benzene (TAPB) to 2,5,dihydroxyterephthalaldehyde (DHTP) was 1:1.5, the total concentration was 5 wt%, and the reaction was carried out at room temperature for 48 hours, then rinsed with anhydrous ethanol solution and dried;

[0072] (6) The composite nanofibers prepared in step (5) are extruded by roller extrusion to compress the loosely and irregularly stacked nanofibers into a dense nanofiber membrane. The extrusion pressure is 40 MPa, and a dense lithium battery separator with a thickness of 0.17 mm can be obtained.

[0073] The lithium battery separator prepared in Example 2 was tested under the same conditions as in Example 1. The relevant performance parameters are shown in Table 2.

[0074] Table 2 Relevant performance parameters of lithium battery separators

[0075]

[0076] As shown in Table 2, the lithium battery separator prepared by this invention has moderate porosity, pore diameter, and specific surface area; excellent air permeability and liquid absorption; and its tensile strength and conductivity remain essentially unchanged after exposure to high temperatures, maintaining stable performance. Therefore, it is reusable and possesses the good performance required for a separator.

[0077] Example 3

[0078] The method for preparing lithium battery separators using coaxial parallel electrospinning described in this embodiment can be referred to... Figure 2 A schematic diagram of needleless coaxial parallel electrospinning, with the following specific steps:

[0079] (1) Dissolve the fiber skeleton polymer PAN in dimethyl sulfoxide to form a homogeneous core layer parallel solution A with a concentration of 8 wt%.

[0080] (2) Dissolve the fiber functional polymer hydrophobic polyacrylamide in dichloromethane to form a homogeneous core layer parallel solution B with a concentration of 8wt%.

[0081] (3) Dissolve soluble titanium chloride in an aqueous solution of polyvinylpyrrolidone to form a uniform shell spinning solution. The concentration of titanium chloride is 5 wt% and the concentration of polyvinylpyrrolidone is 8 wt%.

[0082] (4) Coaxial parallel electrospinning was performed using PAN solution as one pole of the core layer parallel solution (A); hydrophobic polyacrylamide as the other pole of the core layer parallel solution (B); and a solution composed of titanium chloride and polyvinylpyrrolidone as the shell layer solution. The flow rate of the core layer parallel solution A was controlled at 1.5 ml / h, the flow rate of the core layer parallel solution B was controlled at 1.5 ml / h, and the flow rate of the shell layer spinning solution was controlled at 1 ml / h. Spinning conditions: temperature 18℃, humidity 28%, roller speed 200 r / min, spinning voltage 50 KV, and receiving distance 25 cm.

[0083] (5) The prepared composite nanofiber membrane was immersed in a 0.10 wt% sodium hydroxide solution (ethanol:water volume ratio of 8:2) for 20 min, then rinsed with ethanol and dried. The dried composite nanofiber was then immersed in an acetonitrile solution containing 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 2,5,dihydroxyterephthalaldehyde (DHTP) monomers, with a mass ratio of 1:1.5 and a total concentration of 8 wt%. The reaction was carried out at room temperature for 30 hours. Afterward, it was rinsed with anhydrous ethanol solution and dried.

[0084] (6) The composite nanofibers prepared in step (5) are compressed into a dense nanofiber membrane using a roller extrusion method. The extrusion pressure is 45 MPa. A dense lithium battery separator with a thickness of 0.15 mm can then be obtained.

[0085] The lithium battery separator prepared in Example 3 was tested under the same conditions as in Example 1. The relevant performance parameters are shown in Table 3.

[0086] Table 3 Relevant performance parameters of lithium battery separators

[0087]

[0088] As shown in Table 3, the lithium battery separator prepared by this invention has moderate porosity, pore diameter, and specific surface area; excellent air permeability and liquid absorption; and its tensile strength and conductivity remain essentially unchanged after exposure to high temperatures, maintaining stable performance. Therefore, it is reusable and possesses the good performance required for a separator.

[0089] Comparative Example 1

[0090] The method for preparing lithium battery separators using coaxial parallel electrospinning described in this comparative example can be referred to... Figure 2 A schematic diagram of needleless coaxial parallel electrospinning, with the following specific steps:

[0091] (1) Dissolve the fiber skeleton polymer PVDF in N,N-dimethylacetamide to form a homogeneous core layer parallel solution A with a concentration of 25wt%.

[0092] (2) Dissolve the fiber functional polymer hydrophobic polyacrylamide in N,N-dimethylformamide to form a uniform core layer parallel solution B with a concentration of 15wt%.

[0093] (3) Dissolve soluble zirconium chloride in an aqueous solution of gelatin to form a homogeneous shell spinning solution. The concentration of zirconium chloride is 5 wt% and the concentration of gelatin is 5 wt%.

[0094] (4) Using PVDF solution as one pole of the core layer parallel solution (A); hydrophobic polyacrylamide as the other pole of the core layer parallel solution (B); and a solution composed of zirconium chloride and gelatin as the shell layer solution, coaxial parallel electrospinning was performed, and a composite nanofiber membrane with zirconium chloride nano-aggregates was obtained by means of interfacial effect. The flow rate of the core layer parallel solution A was controlled at 8 ml / h, the flow rate of the core layer parallel solution B was controlled at 6 ml / h, and the flow rate of the shell layer spinning solution was controlled at 3.5 ml / h; the spinning conditions were: temperature 25℃, humidity 42%, roller speed 200 r / min, spinning voltage 75 KV, and receiving distance 18 cm.

[0095] (5) The prepared composite nanofiber membrane was immersed in a 0.6 wt% sodium hydroxide solution (ethanol and water volume ratio of 8:2) for 10 min, then rinsed with ethanol and dried; the dried composite nanofiber was immersed in an acetonitrile solution with 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 2,5,dihydroxyterephthalaldehyde (DHTP) as monomers, the mass ratio of 1,3,5-tris(4-aminophenyl)benzene (TAPB) to 2,5,dihydroxyterephthalaldehyde (DHTP) was 1:1.5, the total concentration was 10 wt%, and the reaction was carried out at room temperature for 24 hours, then rinsed with anhydrous ethanol solution and dried;

[0096] (6) The composite nanofibers prepared in step (5) are extruded by roller extrusion to compress the loose, irregularly stacked nanofibers into a dense nanofiber membrane. The extrusion pressure is 10 MPa, and a dense lithium battery separator with a thickness of 0.21 mm can be obtained.

[0097] The tests were conducted under the same conditions as in Example 1. The relevant performance parameters of the lithium battery separator prepared in Comparative Example 1 are shown in Table 4.

[0098] Table 4. Relevant performance parameters of lithium battery separators

[0099]

[0100] Table 4 shows that the prepared lithium battery separator has moderate porosity, pore diameter, and specific surface area, and excellent liquid absorption rate. However, after exposure to high temperatures, the tensile strength and conductivity decreased significantly. This is mainly due to the low liquid supply per unit time of the shell solution, which prevents uniform finite element region shrinkage at the core interface. This results in small and irregular particle sizes of the generated metal salt nanoaggregates, which in turn affects the final fiber structure. When the ambient temperature rises, the ZrO2 / COF composite nanoparticles generated by the shell solution cannot effectively protect the core fibers. High temperatures can damage the fiber structure, affecting the mechanical and electrical properties of the fibers, thus hindering the application of the fiber membrane in lithium batteries.

[0101] Comparative Example 2

[0102] The method for preparing lithium battery separators using coaxial parallel electrospinning described in this comparative example can be referred to... Figure 2 A schematic diagram of needleless coaxial parallel electrospinning, with the following specific steps:

[0103] (1) Dissolve the fiber skeleton polymer PVDF in N,N-dimethylacetamide to form a homogeneous core layer parallel solution A with a concentration of 25wt%.

[0104] (2) Dissolve the fiber functional polymer hydrophobic polyacrylamide in N,N-dimethylformamide to form a uniform core layer parallel solution B with a concentration of 15wt%.

[0105] (3) Dissolve soluble zirconium chloride in an aqueous solution of gelatin to form a homogeneous shell spinning solution. The concentration of zirconium chloride is 5 wt% and the concentration of gelatin is 5 wt%.

[0106] (4) Using PVDF solution as one pole of the core layer parallel solution (A); hydrophobic polyacrylamide as the other pole of the core layer parallel solution (B); and a solution composed of zirconium chloride and gelatin as the shell layer solution, coaxial parallel electrospinning was performed, and a composite nanofiber membrane with zirconium chloride nanoaggregates was prepared by means of the interfacial effect. The flow rate of the core layer parallel solution A was controlled at 8 ml / h, the flow rate of the core layer parallel solution B was controlled at 6 ml / h, and the flow rate of the shell spinning solution was controlled at 4.5 ml / h; the spinning conditions were: temperature 25℃, humidity 42%, roller speed 200 r / min, spinning voltage 75 KV, and receiving distance 18 cm.

[0107] (5) Immerse the prepared composite nanofiber membrane in a 0.6 wt% sodium hydroxide solution (ethanol and water volume ratio of 8:2) for 10 min, then rinse with ethanol and dry.

[0108] (6) The composite nanofibers prepared in step (5) are extruded by roller extrusion to compress the loosely and irregularly stacked nanofibers into a dense nanofiber membrane. The extrusion pressure is 10 MPa, and a dense lithium battery separator with a thickness of 0.20 mm can be obtained.

[0109] The lithium battery separator prepared in Comparative Example 2 was tested under the same conditions as in Example 1. The relevant performance parameters are shown in Table 5.

[0110] Table 5. Relevant performance parameters of lithium battery separators

[0111]

[0112] As can be seen from Table 5, the prepared lithium battery separator has moderate porosity, pore diameter and specific surface area; and excellent liquid absorption rate. However, after being subjected to high temperature, the tensile strength and conductivity decreased significantly. This is mainly due to the chemical reduction reaction of the zirconia nanoaggregates generated in the shell solution in the electrolyte after the application temperature increases, which damages the separator structure, thereby reducing its mechanical strength and conductivity, which is not conducive to its promotion in lithium battery applications.

[0113] Comparative Example 3

[0114] The method for preparing lithium battery separators using coaxial parallel electrospinning described in this comparative example can be referred to... Figure 2 A schematic diagram of needleless coaxial parallel electrospinning, with the following specific steps:

[0115] (1) Dissolve the fiber skeleton polymer PVDF in N,N-dimethylacetamide to form a homogeneous core layer parallel solution A with a concentration of 25wt%.

[0116] (2) Dissolve the fiber functional polymer hydrophobic polyacrylamide in N,N-dimethylformamide to form a uniform core layer parallel solution B with a concentration of 15wt%.

[0117] (3) Dissolve soluble zirconium chloride in an aqueous solution of gelatin to form a homogeneous shell spinning solution. The concentration of zirconium chloride is 5 wt% and the concentration of gelatin is 5 wt%.

[0118] (4) Using PVDF solution as one pole of the core layer parallel solution (A); hydrophobic polyacrylamide as the other pole of the core layer parallel solution (B); and a solution composed of zirconium chloride and gelatin as the shell layer solution, coaxial parallel electrospinning was performed, and a composite nanofiber membrane with zirconium chloride nanoaggregates was prepared by means of the interfacial effect. The flow rate of the core layer parallel solution A was controlled at 8 ml / h, the flow rate of the core layer parallel solution B was controlled at 6 ml / h, and the flow rate of the shell spinning solution was controlled at 14 ml / h; the spinning conditions were: temperature 25℃, humidity 42%, roller speed 200 r / min, spinning voltage 75 KV, and receiving distance 18 cm.

[0119] (5) The prepared composite nanofiber membrane was immersed in a 0.6 wt% sodium hydroxide solution (ethanol and water volume ratio of 8:2) for 10 min, then rinsed with ethanol and dried; the dried composite nanofiber was immersed in an acetonitrile solution with 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 2,5,dihydroxyterephthalaldehyde (DHTP) as monomers, the mass ratio of 1,3,5-tris(4-aminophenyl)benzene (TAPB) to 2,5,dihydroxyterephthalaldehyde (DHTP) was 1:1.5, the total concentration was 10 wt%, and the reaction was carried out at room temperature for 24 hours, then rinsed with anhydrous ethanol solution and dried;

[0120] (6) The composite nanofibers prepared in step (5) are extruded by roller extrusion to compress the loosely and irregularly stacked nanofibers into a dense nanofiber membrane. The extrusion pressure is 10 MPa, and a dense lithium battery separator with a thickness of 0.19 mm can be obtained.

[0121] The lithium battery separator prepared in Comparative Example 3 was tested under the same conditions as in Example 1. The relevant performance parameters are shown in Table 6.

[0122] Table 6. Relevant performance parameters of lithium battery separators

[0123]

[0124] As shown in Table 6, the prepared lithium battery separator exhibits moderate porosity, pore diameter, and specific surface area. However, after exposure to high temperatures, its tensile strength and conductivity, especially conductivity, decrease significantly. This is primarily due to the large volume of the shell solution supplied per unit time, leading to the formation of a coating layer at the core layer interface instead of metal salt aggregates. Subsequent post-processing also fails to produce ZrO2 / COF composite nanoparticles attached to the core layer fibers. Therefore, when the ambient temperature rises, the coating formed by the shell solution is first destroyed by the expanding core layer fibers. Subsequently, severe adhesion occurs between the fibers due to the lack of a protective interface, resulting in blockage of ion channels and a sharp decrease in the conductivity of the fiber membrane, failing to meet the preparation requirements of this application.

[0125] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing lithium battery separators using coaxial parallel electrospinning, characterized in that, Includes the following steps: S1. The fiber skeleton polymer and the fiber functional polymer are dissolved in an organic solution to form a homogeneous core layer parallel solution A and a core layer parallel solution B, wherein the concentration of the core layer parallel solution A is 8-25 wt% and the concentration of the core layer parallel solution B is 8-25 wt%. The functional polymer of the fiber is hydrophobic polyacrylamide; S2. Dissolve the metal salt in an aqueous solution of a hydrophilic polymer to form a homogeneous shell spinning solution, wherein the concentration of the metal salt is 0.5-30 wt% and the concentration of the hydrophilic polymer is 3-15 wt%. S3. The core layer parallel solution A and core layer parallel solution B described in step S1 are coaxially parallel electrospun with the shell spinning solution described in step S2, and a composite nanofiber membrane with metal salt nanoaggregates is obtained by means of the interface effect. S4. The composite nanofiber membrane prepared in step S3 is immersed in an alkaline salt solution with a concentration of 0.02-0.6wt% to undergo anion exchange reaction. After drying, it is immersed in an acetonitrile solution containing TAPB and DHTP and reacted at room temperature for 24-48 hours. After rinsing, drying and rolling, a lithium battery separator with a metal oxide-COF fiber protective structure is obtained.

2. The method according to claim 1, characterized in that, The fiber backbone polymer includes one or more of PVDF, PVDF-HFP, PMMA, PAN, PPSU, or PSU.

3. The method according to claim 1, characterized in that, The metal salt includes one or more of aluminum salts, zirconium salts, or titanium salts.

4. The method according to claim 1, characterized in that, The metal salt includes one or more of aluminum nitrate, aluminum sulfate, aluminum chloride, zirconium nitrate, zirconium sulfate, zirconium chloride, titanium nitrate, titanium sulfate, and titanium chloride.

5. The method according to claim 1, characterized in that, The hydrophilic polymer includes one or more of gelatin, polyvinyl alcohol, and polyvinylpyrrolidone.

6. The method according to claim 1, characterized in that, The solute in the alkaline salt solution includes one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia, and hexamethylenetetramine.

7. The method according to claim 1, characterized in that, During coaxial electrospinning, the flow rate of the core layer parallel solution A is 1.5-7.5 ml / h, the flow rate of the core layer parallel solution B is 1.5-7.5 ml / h, the flow rate of the shell layer spinning solution is 1-5 ml / h, the temperature is 18-25℃, the humidity is 20-40%, the drum speed is 200 r / min, the spinning voltage is 3-100 KV, and the receiving distance is 12-30 cm.

8. The method according to claim 7, characterized in that, The flow rate ratio of the core layer parallel solution A, the core layer parallel solution B, and the shell layer spinning solution is 1.5-2:1.5-2:1.1-1.

2.

9. The method according to claim 1, characterized in that, The total solute concentration of the acetonitrile solution containing TAPB and DHTP is 5-10 wt%; the mass ratio of TAPB to DHTP is 1:1.

5.

10. The method according to claim 1, characterized in that, In step S4, the anion exchange reaction takes 10-60 minutes.

11. The method according to claim 1, characterized in that, In step S4, the pressure of the roller is 10-50 MPa.

12. A lithium battery separator prepared by the method according to any one of claims 1-11.

13. The lithium battery separator according to claim 12, characterized in that, The lithium battery separator has a thickness of 20-1000 μm, a porosity of 25-65%, an electrolyte absorption rate of 200-1000%, and a mechanical tensile strength of 15-55 MPa.

14. The application of the lithium battery separator as described in claim 12 in the field of energy storage batteries.

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