Lithium ion battery, battery diaphragm and preparation method thereof

Abstract

The invention discloses a lithium ion battery, a battery diaphragm and a preparation method of the battery diaphragm. The diaphragm comprises a base membrane and a coating layer, the coating layer comprises a PAN (at) C (at) LATP composite material. According to the technical scheme, the PAN and carbon material coated titanium aluminum phosphate composite material is prepared, the carbon material can provide a good conductive network, lithium ion transmission is facilitated, the requirement of a battery for ion conduction during normal work can be met, and it is ensured that the battery has good charge and discharge performance; pAN has certain viscosity, after PAN is compounded with a carbon material, the carbon material enhances the overall structure and mechanical performance of the composite material, and the bonding performance can be improved; meanwhile, the PAN and the carbon material have relatively good thermal stability and can bear heat generated in the working process of the battery to a certain extent, so that the problems of diaphragm deformation, damage and the like caused by temperature rise can be reduced, and the safety of the battery is favorably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a lithium ion battery, a battery separator and a preparation method thereof. Background Art

[0002] The separator is an important component of a single battery, and its main function is to separate the positive electrode material and the negative electrode material.

[0003] In the prior art, the diaphragm is usually a polymer diaphragm, such as a polyethylene or polypropylene porous polyolefin membrane. The polymer material has a low melting point. When the temperature is increased, the polymer diaphragm will shrink and melt, causing the electrode to short-circuit under conditions such as overcharging, thereby causing thermal runaway.

[0004] To this end, the Chinese invention patent application with application publication number CN116826313A discloses a flame-retardant diaphragm for lithium-ion batteries and a preparation method thereof, wherein the flame-retardant diaphragm includes a base film and a coating layer; the coating layer includes a Mg(OH)2@LATP composite material, which contains LATP and has good low flammability and high temperature resistance; and contains a Mg(OH)2 component, which has excellent flame retardancy. However, the ionic conductivity of Mg(OH)2 itself is relatively low, which affects the ion transmission efficiency of the entire composite material to a certain extent, especially in high-power application scenarios, and cannot meet the needs of fast charging and discharging. In addition, Mg(OH)2 itself is a flaky crystal or powder with weak bonding performance, and is easy to peel off from the electrode. At the same time, under high temperature conditions, Mg(OH)2 is prone to decomposition reaction, which affects the performance of the diaphragm and the safety of the battery.

[0005] Therefore, there is an urgent need to study a battery separator that can maintain good lithium ion conductivity and high adhesion, improve the thermal stability of the separator, and ensure high safety, so as to improve the shortcomings of the above-mentioned existing composite materials and further improve the safety of lithium-ion batteries. Summary of the invention

[0006] The main purpose of the present invention is to provide a lithium-ion battery, a battery separator and a preparation method thereof, aiming to solve the technical problem that the existing composite materials used for separators cannot further improve the thermal stability of the separator while maintaining good lithium ion conductivity and adhesion.

[0007] In order to achieve the above-mentioned object, the first aspect of the present invention provides a battery separator, comprising a base film and a coating layer; the coating layer comprises a PAN@C@LATP composite material.

[0008] Furthermore, the coating layer also includes a dispersant, a thickener, a binder and a wetting agent.

[0009] Furthermore, the dispersant is any one of hydrolyzed polymaleic anhydride, lauramide, polyethylene wax, and ethyl acetate; the thickener is any one of sodium hydroxymethyl cellulose, hydroxyethyl cellulose, and methyl cellulose; and the binder is any one of polyacrylic acid, polyacrylamide, and polyvinyl alcohol.

[0010] Furthermore, the wetting agent is a silanol nonionic surfactant.

[0011] Furthermore, the base film is a porous structure film.

[0012] Furthermore, the carbon base in the PAN@C@LATP composite material is polymer-derived porous carbon.

[0013] A second aspect of the present invention provides a method for preparing a battery separator, which is used to prepare any of the above-mentioned battery separators, comprising the following steps:

[0014] Adding the PAN@C@LATP composite material and the dispersant into the first solvent and mixing them evenly;

[0015] Add thickener, binder and wetting agent, mix well, and obtain coating slurry of PAN@C@LATP composite material;

[0016] The coating slurry is uniformly coated on a base film and dried to obtain the battery separator.

[0017] Furthermore, the components of the coating slurry are calculated by weight: PAN@C@LATP composite material is 18% to 38%, thickener is 0.2% to 1.0%, binder is 0.3% to 1.7%, wetting agent is 0.05% to 0.55%, dispersant is 0.1% to 1.0%, and the rest is the first solvent.

[0018] Furthermore, the step of adding the PAN@C@LATP composite material and the dispersant into the solvent and mixing them evenly may further include the following steps:

[0019] Adding an organic base and an acidic solution into a second solvent and reacting them sufficiently to obtain a buffer solution;

[0020] Adding LATP powder and a carbon source to the buffer solution for sufficient reaction to obtain a polymer-modified LATP material;

[0021] The polymer-modified LATP material is carbonized to obtain a C@LATP composite material.

[0022] Furthermore, after the step of carbonizing the polymer-modified LATP material to obtain the C@LATP composite material, the following steps are also included:

[0023] The C@LATP composite material is placed in a mixed gas of argon and oxygen for heating treatment.

[0024] Furthermore, after the step of placing the C@LATP composite material in a mixed gas of argon and oxygen for heating, the method further comprises the following steps:

[0025] Dispersing the C@LATP composite material in a third solvent to obtain a dispersion of the C@LATP composite material;

[0026] dissolving PAN powder in a fourth solvent in a sealed environment to obtain a PAN solution;

[0027] The PAN solution is added to the dispersion and mixed thoroughly to obtain a PAN@C@LATP composite material.

[0028] A third aspect of the present invention provides a lithium-ion battery, such as the separator described in any one of the above items.

[0029] Beneficial effects:

[0030] A battery separator of the present invention comprises a base film and a coating layer; the coating layer comprises a PAN@C@LATP composite material. In this technical solution, a titanium aluminum phosphate composite material coated with PAN and carbon material is prepared, wherein the carbon material can provide a good conductive network, which is conducive to the transmission of lithium ions, can meet the battery's demand for ion conduction during normal operation, and ensure that the battery has good charge and discharge performance; PAN itself has a certain viscosity, and when compounded with carbon material, the carbon material enhances the overall structure and mechanical properties of the composite material, which helps to improve the bonding performance; at the same time, PAN and carbon material have good thermal stability, can withstand the heat generated during the operation of the battery to a certain extent, can reduce the deformation and damage of the separator caused by the increase in temperature, and is conducive to improving the safety of the battery.

[0031] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments. DETAILED DESCRIPTION

[0032] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0033] In this application, some industry terms are explained as follows:

[0034] PAN: Polyacrylonitrile; LATP: Lithium Aluminum Titanium Phosphate; Heat shrinkage: The degree of dimensional shrinkage of a material after being heated, evaluated by the ratio of dimensional change to original size, where MD% (Machine Direction) represents longitudinal shrinkage and TD% (Transverse Direction) represents transverse shrinkage; Air permeability: The time required for a certain volume of air to pass through a certain area of ​​material under a specific pressure, measured in seconds / 100 milliliters (s / 10mls), reflecting the pore structure and pore size distribution of the membrane; Coating surface density: The ratio of the mass of the coating material applied on the surface of a specific material to the area covered by the coating, measured in grams per square meter (g / m 2 ) as a unit; Anode-thermal stripping: Under specific temperature conditions, the battery separator bonded to the electrode is heated and the battery separator is stripped from the electrode.

[0035] An embodiment of the present invention provides a battery separator, comprising a base film and a coating layer; the coating layer comprises a PAN@C@LATP composite material.

[0036] In the above embodiments, the carbon material can provide a good conductive network, which is beneficial to the transmission of lithium ions, can meet the battery's demand for ion conduction during normal operation, and ensure that the battery has good charge and discharge performance; PAN itself has a certain viscosity. When compounded with the carbon material, the carbon material enhances the overall structure and mechanical properties of the composite material, which helps to improve the bonding performance; at the same time, PAN and carbon materials have good thermal stability, can withstand the heat generated during the operation of the battery to a certain extent, can reduce the deformation and damage of the diaphragm caused by the increase in temperature, and is beneficial to improving the safety of the battery.

[0037] In one embodiment, the dispersant is any one of hydrolyzed polymaleic anhydride, lauramide, polyethylene wax, and ethyl acetate; the thickener is any one of sodium hydroxymethyl cellulose, hydroxyethyl cellulose, and methyl cellulose; the binder is any one of polyacrylic acid, polyvinylidene fluoride, styrene-butadiene rubber, epoxy resin, and phenolic resin.

[0038] In this embodiment, the dispersant is a substance that can promote the uniform dispersion of solid particles in a liquid. Any one of hydrolyzed polymaleic anhydride, lauramide, polyethylene wax, ethyl acetate, and sodium polyacrylate as a dispersant can make the PAN@C@LATP composite material uniformly dispersed in the solvent to avoid agglomeration. This helps to ensure that the components of the coating layer are evenly distributed, thereby ensuring the consistency of the performance of the entire diaphragm. When the composite material is evenly dispersed, the carbon material therein can better construct a conductive network and improve the transmission efficiency of lithium ions. The thickener is a substance that can increase the viscosity of the liquid. For example, sodium hydroxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, etc. can increase the viscosity of the coating slurry. Suitable viscosity can make the coating slurry better adhere to the base film, prevent problems such as sagging and dripping during the preparation process, and ensure the uniformity of the thickness of the coating layer. Moreover, the thickened slurry is easier to control during the coating process, which helps to improve production efficiency and product quality. In addition, the thickener can also enhance the mechanical strength of the coating layer to a certain extent and improve the durability of the diaphragm. A binder is a substance with bonding properties that can bond different materials together. The binder is selected from any one of polyacrylic acid, polyvinylidene fluoride, styrene-butadiene rubber, epoxy resin, and phenolic resin, and its main function is to enhance the bonding force between the coating layer and the base film. Good bonding performance can ensure that the coating layer is firmly attached to the base film, and will not fall off during the use of the battery due to volume changes, mechanical stress, and other factors during the charging and discharging process. This is crucial to maintaining the structural integrity and stability of the diaphragm, ensuring long-term stable operation of the battery, and also helping to improve the safety of the battery. A wetting agent is a substance that can reduce the surface tension of a liquid and improve the wettability of the liquid to a solid surface. As a wetting agent, a silanol nonionic surfactant can improve the wettability of the coating slurry to the base film. Good wettability can make the coating slurry more fully infiltrate the surface of the base film, reduce the generation of pores and defects, and make the coating more uniform. A uniform coating layer can provide a more stable ion transmission channel and better thermal stability, reducing the battery performance degradation and safety risks caused by local performance differences. At the same time, the wetting agent can also improve the fluidity of the coating slurry, making it easier to spread on the base film, further improving the convenience of the production process and product quality.

[0039] In the above embodiments, the dry molecular structure of hydrolyzed polymaleic acid contains a large number of carboxyl groups, which can prevent particle aggregation through electrostatic repulsion or steric hindrance effect, so that the particles are evenly dispersed in the solution, and its polyelectrolyte properties are stable. Under harsh conditions such as high temperature and high pH, ​​the chemical structure is not easily destroyed and can maintain good performance; the amide group in lauryl amide has a certain polarity and non-polar structure, so that it can interact with the particle surface and be well compatible with the solvent, thereby playing a dispersing role. Its long-chain alkyl part (non-polar part) can interact with the organic solvent, and the amide group (polar part) can be adsorbed on the surface of PAN@C@LATP composite material particles, and the particle aggregation is prevented through steric hindrance. However, compared with hydrolyzed polymaleic anhydride, its electrostatic repulsion is weaker and the dispersion effect is relatively limited; polyethylene wax can form a waxy film on the surface of PAN@C@LATP composite material particles. When preparing battery separator coating slurry, it can reduce the friction between particles and make the particles evenly dispersed, but in strong polar solvents or high-temperature aerobic environments, oxidation and decomposition will occur, thereby affecting its dispersion effect; ethyl acetate has an ester bond and can have a good adsorption effect on PAN@C@LATP composite material particles, and the alkyl group in its molecular structure can interact with organic solvents to improve the dispersibility of particles in solvents, but compared with hydrolyzed polymaleic anhydride, ester dispersants are prone to hydrolysis in acidic and alkaline environments; therefore, in this embodiment, the dispersant preferably uses hydrolyzed polymaleic anhydride.

[0040] Thickeners such as hydroxyethyl cellulose, carboxymethyl cellulose and sodium hydroxymethyl cellulose can improve the viscosity of the solution by interacting with the solvent. Among them, the main raw material of sodium hydroxymethyl cellulose is natural cellulose, which is widely available and relatively low in cost. Therefore, sodium hydroxymethyl cellulose is preferably used as the thickener in this embodiment. Polymers such as binders such as polyacrylic acid, polyacrylamide, and polyvinyl alcohol have similar carboxyl functional groups and can form chemical bonds or hydrogen bonds with the components in the base film and the coating layer to play a bonding effect. Because polyacrylic acid has excellent water solubility, it can be easily mixed with other water-soluble substances when preparing electrode materials to form a uniform slurry, which is conducive to the uniform dispersion of active substances, conductive agents, etc., thereby improving the electrochemical properties of the electrode. Therefore, in this embodiment, the binder is preferably polyacrylic acid. Silicon alcohol nonionic surfactants are used as wetting agents, which have the effect of reducing surface tension and improving the wettability of liquid to solid. For example, polyoxyethylene ethers, polyol ester surfactants, etc., can improve wetting properties by changing the interfacial properties of liquid and solid surfaces.

[0041] In one embodiment, the base film is a porous structure film.

[0042] In this embodiment, the porous structure film serves as a base film, providing basic physical support for the entire battery separator. It has certain strength and toughness, and can withstand various mechanical stresses inside the battery, such as expansion and contraction of electrode materials, pressure during assembly, etc. This physical support ensures the stability and reliability of the separator during battery use, prevents the separator from rupturing or damage, and thus ensures the normal operation of the battery. It can also prevent the positive and negative electrodes from directly contacting each other and prevent short circuits from occurring. At the same time, due to its porosity, lithium ions are allowed to shuttle freely between the positive and negative electrodes, realizing the charging and discharging process of the battery.

[0043] Specifically, the porous structure film is a polyolefin diaphragm. In the working environment of the battery, the polyolefin diaphragm can remain stable and is not easy to react chemically with the electrolyte, electrode materials, etc. in the battery, ensuring the stable performance of the battery. The polyolefin diaphragm has high mechanical performance indicators such as tensile strength and puncture resistance, and can withstand various mechanical stresses during battery assembly and use. For example, in the production and assembly process of the battery, the diaphragm needs to go through process steps such as winding and packaging. The high strength of the polyolefin diaphragm can ensure that it will not be easily broken or damaged during these processes; in the use of the battery, the expansion and contraction of the electrode material will also produce a certain amount of mechanical pressure on the diaphragm. The polyolefin diaphragm can withstand this pressure and maintain the integrity of the battery structure.

[0044] In one embodiment, the carbon matrix in the PAN@C@LATP composite material is polymer-derived porous carbon.

[0045] In this embodiment, polymer-derived porous carbon is a carbon material with a porous structure obtained by a polymer carbonization process. As a carbon base, polymer-derived porous carbon has a rich pore structure and a high specific surface area. These characteristics enable it to provide a good conductive network for the transmission of lithium ions. Lithium ions can move quickly in the pores of porous carbon, thereby improving the charge and discharge performance of the battery. Compared with traditional carbon materials, the pore structure of polymer-derived porous carbon is more uniform and controllable, and can better meet the transmission needs of lithium ions. The high specific surface area and pore structure of porous carbon enable it to fully contact and combine with materials such as PAN and LATP. This combination can enhance the overall structural stability of the composite material and improve its mechanical properties. During the use of the battery, the composite material needs to withstand various stresses such as expansion and contraction of the electrode material and erosion of the electrolyte. The presence of polymer-derived porous carbon can effectively disperse these stresses and prevent the composite material from breaking and damaging. The performance of polymer-derived porous carbon can be regulated by controlling its preparation process and parameters. For example, the pore structure, specific surface area and conductivity of porous carbon can be controlled by adjusting parameters such as polymer type, carbonization temperature and time. This controllability allows us to design and prepare PAN@C@LATP composite materials with specific properties according to different battery application requirements, thereby improving the performance and adaptability of batteries.

[0046] Specifically, the polymer-derived porous carbon of the present application includes polydopamine-derived porous carbon, phenolic resin-derived porous carbon, polypyrrole-derived porous carbon, and polyaniline-derived porous carbon; wherein dopamine contains abundant active groups and can undergo polymerization reaction under certain conditions to form polydopamine. Polydopamine has strong adhesion and modifiability, and can form a uniform coating on the surface of various materials. After high-temperature carbonization treatment of polydopamine, a polydopamine-derived porous carbon material can be obtained. By regulating the carbonization conditions of polydopamine, pore structures with different pore sizes and distributions can be formed, including micropores, mesopores, and macropores. The rich pore structure provides a large number of channels and active sites for ion transport, gas adsorption, and storage.

[0047] Another embodiment of the present invention provides a method for preparing a battery separator, which is used to prepare any of the above-mentioned battery separators, comprising the following steps:

[0048] Add the PAN@C@LATP composite material and the dispersant into the first solvent and mix them thoroughly;

[0049] Add thickener, binder and wetting agent in sequence and mix them evenly to obtain coating slurry of PAN@C@LATP composite material;

[0050] The coating slurry is uniformly coated on a base film and dried to obtain the battery separator.

[0051] In this embodiment, the dispersant is hydrolyzed polymaleic anhydride. The first solvent can be ultrapure water, or an organic solvent such as ethanol or acetone, so that the dispersant can be evenly dispersed in the system, so as to better play its role in dispersing the PAN@C@LATP composite material; at the same time, it provides a uniformly mixed environment for the PAN@C@LATP composite material and the thickener, binder, wetting agent, etc. added subsequently, promoting the interaction and uniform dispersion of the components.

[0052] In one embodiment, the components of the coating slurry are calculated by weight: PAN@C@LATP composite material is 18% to 38%, thickener is 0.2% to 1.0%, binder is 0.3% to 1.7%, wetting agent is 0.05% to 0.55%, dispersant is 0.1% to 1.0%, and the rest is the first solvent.

[0053] In this embodiment, the ratio of PAN@C@LATP composite material is within the range of 18% to 38% to ensure good ion conductivity, thermal stability and mechanical properties. The ratio cannot be too low, otherwise it cannot fully play its role in enhancing battery performance, such as providing a conductive network, improving bonding performance and thermal stability. If the ratio is too high, the coating slurry will be too thick and difficult to be evenly coated on the base film, and the performance will be reduced. The ratio of thickener is 0.2% to 1.0% to make it better attached to the base film. When the ratio is too low, the required viscosity cannot be achieved, and the coating layer will have problems such as sagging and uneven thickness; if the ratio is too high, the slurry will be too viscous and difficult to operate, and it will affect the dispersibility and ion transmission performance of other components. The binder ratio is 0.3% to 1.7%, ensuring that the coating layer will not fall off during the use of the battery. When the ratio is too low, the bonding force is insufficient, which easily causes the coating layer to separate from the base film; if the ratio is too high, the fluidity of the coating slurry may be affected. The proportion of wetting agent is 0.05% to 0.55%, which enables the slurry to spread better on the surface of the base film and reduce the generation of pores and defects. When the proportion is too low, the wetting effect is not obvious, resulting in uneven coating; too high a proportion increases the cost. The proportion of dispersant is 0.1% to 1.0%. When the proportion is too low, the dispersion effect is not good, resulting in agglomeration of the composite material and affecting the performance of the coating slurry; too high a proportion may increase the cost.

[0054] In one embodiment, the step of adding the PAN@C@LATP composite material and the dispersant to the solvent and mixing them thoroughly further comprises the following steps:

[0055] Adding an organic base and an acidic solution into a second solvent and reacting them sufficiently to obtain a buffer solution;

[0056] Adding LATP powder and a carbon source to the buffer solution for sufficient reaction to obtain a polymer-modified LATP material;

[0057] The polymer-modified LATP material is carbonized to obtain a C@LATP composite material.

[0058] In the present embodiment, an organic base and an acidic solution are added to the second solvent to fully react to obtain a buffer solution, which is used to provide a stable pH environment for subsequent reactions. The buffer solution can resist the influence of external acid and alkali to a certain extent, and keep the pH value of the solution relatively stable. This ensures that the subsequent LATP powder and carbon source react under suitable pH conditions to avoid excessive pH fluctuations affecting the reaction and the quality of the product. LATP powder, as the main reactant, reacts with the carbon source under the specific environment of the buffer solution. The introduction of the carbon source is to form a porous carbon structure in the subsequent carbonization process. Through the reaction, the carbon source will self-polymerize on the surface of the LATP powder, thereby polymer-modifying the LATP. During the carbonization process, the polymer-modified layer undergoes pyrolysis and structural transformation under conditions such as high temperature to form a polymer-derived porous carbon structure.

[0059] Specifically, in the buffer solution, the organic base and the acidic solution can be tris(hydroxymethyl)aminomethane and hydrochloric acid solution, ethylenediamine and acetic acid solution, or diethanolamine and phosphoric acid solution. The present application uses tris(hydroxymethyl)aminomethane and hydrochloric acid solution, and the second solvent is ultrapure water. The carbon source can be dopamine, pyrrole, aniline and phenolic compounds. The present application preferably uses dopamine. It can be understood that dopamine contains abundant functional groups, such as hydroxyl (-OH) and amino (-NH-), etc. These functional groups can form hydrogen bonds, ionic bonds or covalent bonds with the surfaces of various materials, so that dopamine can be firmly attached to various substrate materials. In the preparation of battery separators, dopamine can adhere well to the surface of the base film, ensure the stability of the coating layer, prevent the coating layer from falling off the base film during use, and ensure the structural integrity and performance stability of the battery separator.

[0060] In one embodiment, after the step of carbonizing the polymer-modified LATP material to obtain the C@LATP composite material, the following steps are further included:

[0061] The C@LATP composite material is placed in a mixed gas of argon and oxygen for heating treatment.

[0062] In this embodiment, the above steps are used to optimize the carbon structure. Under the heating environment of the mixed gas, argon, as an inert gas, can provide a relatively stable atmosphere to prevent the C@LATP composite material from being over-oxidized or reacting unnecessarily with other impurities at high temperatures. At the same time, the presence of oxygen can moderately oxidize the carbon structure in the composite material. This oxidation can introduce some specific functional groups, such as hydroxyl, carboxyl, etc., on the surface of the carbon material, thereby improving the surface chemical properties of the carbon material. These functional groups can increase the interaction between the carbon material and other components (such as PAN, electrolyte, etc.) and improve the overall performance of the composite material. Heat treatment can promote the further growth and improvement of the crystal structure in the C@LATP composite material and improve the crystallinity of the material. Higher crystallinity usually means better physical and chemical stability, as well as better electrical properties. In the application of battery separators, this helps to improve the ion conductivity, thermal stability and mechanical strength of the separator, thereby extending the service life of the battery and improving safety. By adjusting the ratio of argon and oxygen in the mixed gas and parameters such as the heating temperature and time, the performance of the C@LATP composite material can be precisely regulated. For example, different oxygen contents can lead to different degrees of carbon oxidation, thus affecting the conductivity, hydrophilicity and pore structure of the material. In this way, composite materials with optimal performance can be customized according to specific application requirements.

[0063] In one embodiment, after the step of placing the C@LATP composite material in a mixed gas of argon and oxygen for heating, the method further includes the following steps:

[0064] Dispersing the C@LATP composite material in a third solvent to obtain a dispersion of the C@LATP composite material;

[0065] dissolving PAN powder in a fourth solvent in a sealed environment to obtain a PAN solution;

[0066] The PAN solution is added to the dispersion and mixed thoroughly to obtain a PAN@C@LATP composite material.

[0067] In this embodiment, the third solvent disperses the C@LATP composite material uniformly therein to form a stable dispersion system. The third solvent is ultrapure water, and the fourth solvent disperses the PAN powder uniformly therein. The fourth solvent includes toluene, dimethyl sulfoxide (DMSO), and N,N-dimethylformamide (DMF). In this application, N,N-dimethylacetamide is preferably used.

[0068] Another embodiment of the present invention provides a lithium-ion battery, comprising any of the above-mentioned separators.

[0069] The preparation process and performance of the present invention are described below with reference to some specific embodiments.

[0070] Embodiment 1:

[0071] Diaphragm preparation:

[0072] (1) Preparation of C@LATP composites

[0073] Take 230 mg of tris(hydroxymethyl)aminomethane, add it into a reactor filled with 110 ml of ultrapure water, and add 0.1 mol / l dilute hydrochloric acid dropwise to adjust the pH to 8.5, then stop adding, and stir the reaction for 40 min;

[0074] S1: Take LATP powder and 176 mg of dopamine hydrochloride and add them into the reactor in sequence, stir and react at room temperature for 12 hours to obtain polydopamine-modified LATP;

[0075] S2: In an environment with nitrogen as the protective gas, the polydopamine-modified LATP was carbonized at 800 degrees Celsius for 180 minutes. After cooling to room temperature, it was placed in a tubular furnace with argon and oxygen in a volume ratio of 97.5:2.5, and reacted at 450 degrees Celsius for 1.5 hours. After cooling to room temperature, the C@LATP composite material was obtained.

[0076] (2) Preparation of PAN@C@LATP composite materials:

[0077] S1: 5.8 g of C@LATP composite material and 250 ml of ultrapure water were added to a three-necked flask, mixed under mechanical stirring at 1000 rpm for 6 h, and ultrasonically treated at 45 KHZ and 450 W power for 12 h to obtain a C@LATP composite material dispersion;

[0078] S2: 1.65 g of PAN powder was added into a reactor containing 12.5 g of N,N-dimethylacetamide, and the mixture was stirred at 750 rpm for 6 h in a sealed environment to obtain a PAN solution;

[0079] S3: Under the conditions of mechanical stirring speed of 1500rpm, 50KHZ and 450w power ultrasonic vibration, the PAN solution was added to the C@LATP composite dispersion at a flow rate of 0.5ml / min through a three-necked flask;

[0080] S4: After the PAN solution is completely added to the C@LATP composite dispersion, the stirring speed is reduced to 500 rpm, stirring is continued for 4 h, and then ultrasonic vibration is performed at 45 KHZ and 450 W power for 5 h to obtain a mixed solution;

[0081] S5: The mixed solution was centrifuged at 12000 rpm for 20 min, filtered, washed and dried at 0.08 MPa vacuum and 60 degrees Celsius for 48 h to obtain the PAN@C@LATP composite material.

[0082] (3) Preparation of PAN@C@LATP composite coating slurry:

[0083] S1: Add 18% PAN@C@LATP composite material by mass and 0.85% hydrolyzed polymaleic anhydride by mass into ultrapure water and premix at 1600 rpm for 180 min; add 0.8% sodium carboxymethyl cellulose by mass and continue stirring at 1000 rpm for 120 min; add 1.35% polyacrylic acid by mass and continue stirring at 800 rpm for 150 min; add 0.7% silanol nonionic surfactant by mass and continue stirring at 750 rpm for 90 min. Filter the above slurry and remove iron to obtain PAN@C@LATP composite material coating slurry.

[0084] (4) Preparation of battery separator modified with PAN@C@LATP composite material:

[0085] S1: Using a micro-gravure roller coating process, the PAN@C@LATP composite material coating slurry is evenly rolled onto the substrate by a coater, and then rolled up for use after being baked in a 75°C oven, thereby obtaining a battery separator modified with the PAN@C@LATP composite material for lithium-ion batteries to be prepared.

[0086] Embodiment 2:

[0087] The only difference between this embodiment and embodiment 1 is that the mass proportion of the PAN@C@LATP composite material added is 28%.

[0088] Embodiment 3:

[0089] The only difference between this embodiment and embodiment 1 is that the mass proportion of the PAN@C@LATP composite material added is 38%.

[0090] Embodiment 4:

[0091] Diaphragm preparation:

[0092] (1) Preparation of C@LATP composites

[0093] Take 230 mg of tris(hydroxymethyl)aminomethane, add it into a reactor filled with 110 ml of ultrapure water, and add 0.1 mol / l dilute hydrochloric acid dropwise to adjust the pH to 8.5, then stop adding, and stir the reaction for 40 min;

[0094] S1: Take LATP powder and 176 mg of dopamine hydrochloride and add them into the reactor in sequence, stir and react at room temperature for 12 hours to obtain polydopamine-modified LATP;

[0095] S2: In an environment with nitrogen as the protective gas, the polydopamine-modified LATP was carbonized at 800 degrees Celsius for 180 minutes. After cooling to room temperature, it was placed in a tubular furnace with argon and oxygen in a volume ratio of 97.5:2.5, and reacted at 450 degrees Celsius for 1.5 hours. After cooling to room temperature, the C@LATP composite material was obtained.

[0096] (2) Preparation of PAN@C@LATP composite materials:

[0097] S1: 5.8 g of C@LATP composite material and 250 ml of ultrapure water were added to a three-necked flask, mixed under mechanical stirring at 1000 rpm for 6 h, and ultrasonically treated at 45 KHZ and 450 W power for 12 h to obtain a C@LATP composite material dispersion;

[0098] S2: 1.65 g of PAN powder was added into a reactor containing 12.5 g of N,N-dimethylacetamide, and the mixture was stirred at 750 rpm for 6 h in a sealed environment to obtain a PAN solution;

[0099] S3: Under the conditions of mechanical stirring speed of 1500rpm, 50KHZ and 450w power ultrasonic vibration, the PAN solution was added to the C@LATP composite dispersion at a flow rate of 0.5ml / min through a three-necked flask;

[0100] S4: After the PAN solution is completely added to the C@LATP composite dispersion, the stirring speed is reduced to 500 rpm, stirring is continued for 4 h, and then ultrasonic vibration is performed at 45 KHZ and 450 W power for 5 h to obtain a mixed solution;

[0101] S5: The mixed solution was centrifuged at 12000 rpm for 20 min, filtered, washed and dried at 0.08 MPa vacuum and 60 degrees Celsius for 48 h to obtain the PAN@C@LATP composite material.

[0102] (3) Preparation of PAN@C@LATP composite coating slurry:

[0103] S31: Add 38% by mass of PAN@C@LATP composite material and 0.5% by mass of hydrolyzed polymaleic anhydride into ultrapure water, and premix at 1600 rpm for 180 min; add 0.2% by mass of sodium carboxymethyl cellulose, and continue stirring at 1000 rpm for 120 min; add 5% by mass of polyacrylic acid, and continue stirring at 800 rpm for 150 min; add 0.1% by mass of silanol nonionic surfactant, and continue stirring at 750 rpm for 90 min. Filter the above slurry and remove iron to obtain PAN@C@LATP composite material coating slurry.

[0104] (4) Preparation of battery separator modified with PAN@C@LATP composite material:

[0105] S1: Using a micro-gravure roller coating process, the PAN@C@LATP composite material coating slurry is evenly rolled onto the substrate by a coater, and then rolled up for use after being baked in a 75°C oven, thereby obtaining a battery separator modified with the PAN@C@LATP composite material for lithium-ion batteries to be prepared.

[0106] Embodiment 5:

[0107] Diaphragm preparation:

[0108] (1) Preparation of C@LATP composites

[0109] Take 230 mg of tris(hydroxymethyl)aminomethane, add it into a reactor filled with 110 ml of ultrapure water, and add 0.1 mol / l dilute hydrochloric acid dropwise to adjust the pH to 8.5, then stop adding, and stir the reaction for 40 min;

[0110] S1: Take LATP powder and 176 mg of dopamine hydrochloride and add them into the reactor in sequence, stir and react at room temperature for 12 hours to obtain polydopamine-modified LATP;

[0111] S2: In an environment with nitrogen as the protective gas, the polydopamine-modified LATP was carbonized at 800 degrees Celsius for 180 minutes. After cooling to room temperature, it was placed in a tubular furnace with argon and oxygen in a volume ratio of 97.5:2.5, and reacted at 450 degrees Celsius for 1.5 hours. After cooling to room temperature, the C@LATP composite material was obtained.

[0112] (2) Preparation of PAN@C@LATP composite materials:

[0113] S1: 5.8 g of C@LATP composite material and 250 ml of ultrapure water were added to a three-necked flask, mixed under mechanical stirring at 1000 rpm for 6 h, and ultrasonically treated at 45 KHZ and 450 W power for 12 h to obtain a C@LATP composite material dispersion;

[0114] S2: 1.65 g of PAN powder was added into a reactor containing 12.5 g of N,N-dimethylacetamide, and the mixture was stirred at 750 rpm for 6 h in a sealed environment to obtain a PAN solution;

[0115] S3: Under the conditions of mechanical stirring speed of 1500rpm, 50KHZ and 450w power ultrasonic vibration, the PAN solution was added to the C@LATP composite dispersion at a flow rate of 0.5ml / min through a three-necked flask;

[0116] S4: After the PAN solution is completely added to the C@LATP composite dispersion, the stirring speed is reduced to 500 rpm, stirring is continued for 4 h, and then ultrasonic vibration is performed at 45 KHZ and 450 W power for 5 h to obtain a mixed solution;

[0117] S5: The mixed solution was centrifuged at 12000 rpm for 20 min, filtered, washed and dried at 0.08 MPa vacuum and 60 degrees Celsius for 48 h to obtain the PAN@C@LATP composite material.

[0118] (3) Preparation of PAN@C@LATP composite coating slurry:

[0119] S31: Add 38% by mass of PAN@C@LATP composite material and 1.0% by mass of hydrolyzed polymaleic anhydride into ultrapure water, and premix at 1600 rpm for 180 min; add 0.55% by mass of sodium carboxymethyl cellulose, and continue stirring at 1000 rpm for 120 min; add 10% by mass of polyacrylic acid, and continue stirring at 800 rpm for 150 min; add 0.4% by mass of silanol nonionic surfactant, and continue stirring at 750 rpm for 90 min. Filter the above slurry and remove iron to obtain PAN@C@LATP composite material coating slurry.

[0120] (4) Preparation of battery separator modified with PAN@C@LATP composite material:

[0121] S1: Using a micro-gravure roller coating process, the PAN@C@LATP composite material coating slurry is evenly rolled onto the substrate by a coater, and then rolled up for use after being baked in a 75°C oven, thereby obtaining a battery separator modified with the PAN@C@LATP composite material for lithium-ion batteries to be prepared.

[0122] Embodiment 6:

[0123] Diaphragm preparation:

[0124] (1) Preparation of C@LATP composites

[0125] Take 230 mg of tris(hydroxymethyl)aminomethane, add it into a reactor filled with 110 ml of ultrapure water, and add 0.1 mol / l dilute hydrochloric acid dropwise to adjust the pH to 8.5, then stop adding, and stir the reaction for 40 min;

[0126] S1: Take LATP powder and 176 mg of dopamine hydrochloride and add them into the reactor in sequence, stir and react at room temperature for 12 hours to obtain polydopamine-modified LATP;

[0127] S2: In an environment with nitrogen as the protective gas, the polydopamine-modified LATP was carbonized at 800 degrees Celsius for 180 minutes. After cooling to room temperature, it was placed in a tubular furnace with argon and oxygen in a volume ratio of 97.5:2.5, and reacted at 450 degrees Celsius for 1.5 hours. After cooling to room temperature, the C@LATP composite material was obtained.

[0128] (2) Preparation of PAN@C@LATP composite materials:

[0129] S1: 5.8 g of C@LATP composite material and 250 ml of ultrapure water were added to a three-necked flask, mixed under mechanical stirring at 1000 rpm for 6 h, and ultrasonically treated at 45 KHZ and 450 W power for 12 h to obtain a C@LATP composite material dispersion;

[0130] S2: 1.65 g of PAN powder was added into a reactor containing 12.5 g of N,N-dimethylacetamide, and the mixture was stirred at 750 rpm for 6 h in a sealed environment to obtain a PAN solution;

[0131] S3: Under the conditions of mechanical stirring speed of 1500rpm, 50KHZ and 450w power ultrasonic vibration, the PAN solution was added to the C@LATP composite dispersion at a flow rate of 0.5ml / min through a three-necked flask;

[0132] S4: After the PAN solution is completely added to the C@LATP composite dispersion, the stirring speed is reduced to 500 rpm, stirring is continued for 4 h, and then ultrasonic vibration is performed at 45 KHZ and 450 W power for 5 h to obtain a mixed solution;

[0133] S5: The mixed solution was centrifuged at 12000 rpm for 20 min, filtered, washed and dried at 0.08 MPa vacuum and 60 degrees Celsius for 48 h to obtain the PAN@C@LATP composite material.

[0134] (3) Preparation of PAN@C@LATP composite coating slurry:

[0135] S31: Add 38% by mass of PAN@C@LATP composite material and 1.5% by mass of hydrolyzed polymaleic anhydride into ultrapure water, and premix at 1600 rpm for 180 min; add 0.9% by mass of sodium carboxymethyl cellulose, and continue stirring at 1000 rpm for 120 min; add 15% by mass of polyacrylic acid, and continue stirring at 800 rpm for 150 min; add 0.7% by mass of silanol nonionic surfactant, and continue stirring at 750 rpm for 90 min. Filter the above slurry and remove iron to obtain PAN@C@LATP composite material coating slurry.

[0136] (4) Preparation of battery separator modified with PAN@C@LATP composite material:

[0137] S1: Using a micro-gravure roller coating process, the PAN@C@LATP composite material coating slurry is evenly rolled onto the substrate by a coater, and then rolled up for use after being baked in a 75°C oven, thereby obtaining a battery separator modified with the PAN@C@LATP composite material for lithium-ion batteries to be prepared.

[0138] Comparative Example 1:

[0139] (1) Preparation of C@LATP composites

[0140] S1: Take 230 mg of tris(hydroxymethyl)aminomethane, add it into a reactor filled with 110 ml of ultrapure water, and add 0.1 mol / l dilute hydrochloric acid dropwise to adjust the pH to 8.5, then stop adding dropwise, and stir the reaction for 40 min;

[0141] S2: LATP powder and 176 mg of dopamine hydrochloride were added to the reactor in sequence, and stirred at room temperature for 12 h to obtain polydopamine-modified LATP;

[0142] S3: In an environment with nitrogen as the protective gas, the polydopamine-modified LATP was carbonized at 800 degrees Celsius for 180 minutes. After cooling to room temperature, it was placed in a tubular furnace with argon and oxygen in a volume ratio of 97.5:2.5, and reacted at 450 degrees Celsius for 1.5 hours. After cooling to room temperature, the C@LATP composite material was obtained.

[0143] (2) Preparation of C@LATP composite coating slurry:

[0144] S1: Add 38% by mass of C@LATP composite material and 0.85% by mass of hydrolyzed polymaleic anhydride into ultrapure water, and premix at 1600 rpm for 180 min; add 0.8% by mass of sodium carboxymethyl cellulose, and continue stirring at 1000 rpm for 120 min; add 1.35% by mass of polyacrylic acid, and continue stirring at 800 rpm for 150 min; add 0.7% by mass of silanol nonionic surfactant, and continue stirring at 750 rpm for 90 min. Filter the above slurry and remove iron to obtain C@LATP composite material coating slurry.

[0145] (3) Preparation of battery separator modified with C@LATP composite material:

[0146] S1: Using a micro-gravure roller coating process, the C@LATP composite material coating slurry is evenly rolled onto the substrate by a coater, and then rolled up for use after being baked in a 75°C oven, thereby obtaining a battery separator modified with the C@LATP composite material for the lithium-ion battery to be prepared.

[0147] Comparative Example 2:

[0148] (1) Preparation of PAN@LATP composite materials:

[0149] S1: 5.8 g of LATP material and 250 ml of ultrapure water were added to a three-necked flask, mixed under mechanical stirring at 1000 rpm for 6 h, and ultrasonically treated at 45 KHZ and 450 W power for 12 h to obtain a LATP material dispersion;

[0150] S2: 1.65 g of PAN powder was added into a reactor containing 12.5 g of N,N-dimethylacetamide, and the mixture was stirred at 750 rpm for 6 h in a sealed environment to obtain a PAN solution;

[0151] S3: Under the conditions of mechanical stirring speed of 1500rpm, 50KHZ and 450w ultrasonic vibration power, the PAN solution was added to the LATP dispersion at a flow rate of 0.5ml / min through a three-necked flask;

[0152] S4: Add the PAN solution completely into the LATP dispersion, reduce the stirring speed to 500 rpm, continue stirring for 4 h, and then perform ultrasonic vibration at 45 KHZ and 450 W power for 5 h to obtain a mixed solution;

[0153] S5: The mixed solution was centrifuged at a speed of 12000 rpm for 20 min, filtered, washed and dried at a vacuum degree of 0.08 MPa and 60 degrees Celsius for 48 h to obtain a PAN@LATP composite material.

[0154] (2) Preparation of PAN@LATP composite coating slurry:

[0155] S1: Add 38% PAN@LATP composite material by mass and 0.85% hydrolyzed polymaleic anhydride by mass into ultrapure water and premix at 1600 rpm for 180 min; add 0.8% sodium carboxymethyl cellulose by mass and continue stirring at 1000 rpm for 120 min; add 1.35% polyacrylic acid by mass and continue stirring at 800 rpm for 150 min; add 0.7% silanol nonionic surfactant by mass and continue stirring at 750 rpm for 90 min, filter the above slurry and remove iron to obtain PAN@LATP composite material coating slurry.

[0156] (3) Preparation of battery separator modified with PAN@LATP composite material:

[0157] S1: The PAN@LATP composite material coating slurry is evenly rolled onto the substrate by a coating machine using a micro-gravure roller coating process, and then rolled up for use after being baked in an oven at 75°C, thereby obtaining a battery separator modified with the PAN@LATP composite material for lithium-ion batteries to be prepared.

[0158] Comparative Example 3:

[0159] The only difference between this comparative example and Example 1 is that this comparative example has only a base film, and the above-mentioned polyolefin separator is used for comparison, and no coating layer is provided.

[0160] Comparative Example 4: No PAN@C@LATP composite material was prepared or added, and the rest was the same as Example 1. The details are as follows:

[0161] (3) Preparation of coating slurry:

[0162] S1: Add 1.5% by mass of hydrolyzed polymaleic anhydride into ultrapure water and premix at 1600 rpm for 180 min; add 0.9% by mass of sodium carboxymethyl cellulose and continue stirring at 1000 rpm for 120 min; add 15% by mass of polyacrylic acid and continue stirring at 800 rpm for 150 min; add 0.7% by mass of a silanol nonionic surfactant and continue stirring at 750 rpm for 90 min, filter the above slurry and remove iron to obtain a coating slurry.

[0163] (4) Preparation of battery separator:

[0164] S1: The coating slurry is uniformly rolled onto the substrate by a coating machine using a micro-gravure roller coating process, and then rolled up for use after being baked in an oven at 75°C, thereby obtaining the battery separator for the lithium-ion battery to be prepared.

[0165] Test: The diaphragms prepared in the above examples and comparative examples were subjected to performance tests according to the GB / T36363-2018 testing standard, and the peel strength was tested by a universal testing machine, and the air permeability was tested by a Gurley air permeability tester. The obtained data are shown in the following table:

[0166] Table 1 Diaphragm air permeability, peel strength and thermal shrinkage test results

[0167]

[0168] The following conclusions can be drawn from Table 1:

[0169] Compared with Comparative Examples 1 to 4, the permeability test results of Examples 1 to 6 show that the permeability values ​​of Examples 1 to 6 are lower than those of Comparative Examples 1 and 2, and higher than those of Comparative Examples 3 and 4, indicating that in the embodiments, the membrane structure formed by the PAN@C@LATP composite material is relatively compact and uniform, and the interaction between its particles and with other additives makes the diffusion path of gas molecules in the membrane relatively complex, so the permeability is lower than that of Comparative Examples 1 and 2, and the permeability is better; the membrane of only the C@LATP composite material in Comparative Example 1 and the membrane of the PAN@LATP composite material in Comparative Example 2 have a structure relative to the PAN@C@LATP composite material It is looser or has more pores, making it easier for gas molecules to pass through, resulting in a higher permeability value and relatively poor permeability performance. Comparative Example 3 has no coating layer, and the porous structure of its base film is not conducive to gas barrier, so the permeability value is very low. Comparative Example 4 lacks a core-shell structure but still has a coating layer, so the permeability value is higher than that of Comparative Example 3, and higher than that of Examples 1 to 6; and it can be seen from Examples 1 to 3 that when the mass ratio of the core-shell structure PAN@C@LATP in the slurry increases from 18% to 38%, the permeability value increases successively, and the permeability performance deteriorates. It can be seen from Examples 3 to 6 that the mass proportion of PAN@C@LATP in the slurry is the main factor affecting the permeability value of the membrane.

[0170] Compared with Comparative Examples 1 to 4, the results of the anode-hot pressing stripping test of Examples 1 to 6 show that the stripping force values ​​of Examples 1 to 6 are significantly improved compared with Comparative Examples 1 to 4, and as the PAN@C@LATP composite material gradually increases from 18% to 38%, the higher the coating stripping strength of the corresponding diaphragm is; indicating that the PAN polymer chain in the PAN@C@LATP composite material can form a good physical and chemical interaction with the electrode material, such as van der Waals force, hydrogen bond, etc., so that the bonding force between the diaphragm and the electrode is enhanced, thereby improving the anode-hot pressing stripping force. In Comparative Example 1, the coating structure of PAN is lacking, and the bonding between the C@LATP composite material and the electrode is poor. The structure of the PAN@LATP composite material in Comparative Example 2 is not as effective as the PAN@C@LATP composite material in terms of interaction with the electrode. In Comparative Example 4, due to the lack of PAN@C@LATP composite material, the bonding force between other components in the slurry and the electrode is insufficient, resulting in a low stripping force.

[0171] The test results of thermal shrinkage of Examples 1 to 6 compared with Comparative Examples 1 to 4 show that the thermal shrinkage values ​​of Examples 1 to 6 are significantly lower than those of Comparative Examples 1 to 4, and as the PAN@C@LATP composite material gradually increases from 18% to 38%, the lower the thermal shrinkage rate of the coating of the corresponding diaphragm, the better the thermal shrinkage performance, indicating that the presence of the PAN@C@LATP composite material can improve the thermal stability of the diaphragm. In a high temperature environment, the carbon layer and other structures in the PAN polymer chain and the C@LATP composite material can support and stabilize the diaphragm structure and reduce thermal shrinkage; at the same time, Examples 3 to 6 are compared with Comparative Examples 1, 2 and 3. In comparison, it shows that the lack of effective PAN coating (Comparative Example 1) or the poor thermal stability of the structure itself (Comparative Example 2), or the absence of a coating layer (Comparative Example 3) will cause the diaphragm to easily shrink at high temperatures, further proving that PAN can reduce the thermal shrinkage rate; PAN@C@LATP composite material is compared with PAN@LATP composite material, and the carbon base has a synergistic effect with PAN and LATP, which can enhance the thermal stability of the composite material, confirming the effectiveness of the core-shell structure of PAN@C@LATP in improving the heat resistance, and that PAN, LATP and carbon base can work synergistically to improve the thermal shrinkage performance of the diaphragm.

[0172] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A battery separator, characterized in that: It comprises a base film and a coating layer; the coating layer comprises a PAN@C@LATP composite material.

2. The battery separator according to claim 1, characterized in that: The coating layer also includes a dispersant, a thickener, a binder and a wetting agent.

3. The battery separator according to claim 2, characterized in that: The dispersant is any one of hydrolyzed polymaleic anhydride, lauramide, polyethylene wax, and ethyl acetate; the thickener is any one of sodium hydroxymethyl cellulose, hydroxyethyl cellulose, and methyl cellulose; and the binder is any one of polyacrylic acid, polyacrylamide, and polyvinyl alcohol.

4. The battery separator according to claim 2, characterized in that: The wetting agent is a silanol nonionic surfactant.

5. The battery separator according to claim 1, characterized in that: The base film is a porous structure film.

6. The battery separator according to claim 1, characterized in that: The carbon matrix in the PAN@C@LATP composite material is polymer-derived porous carbon.

7. A method for preparing a battery separator, characterized in that: The method for preparing the battery separator according to any one of claims 1 to 6 comprises the following steps: Adding the PAN@C@LATP composite material and the dispersant into the first solvent and mixing them evenly; Add thickener, binder and wetting agent, mix well, and obtain coating slurry of PAN@C@LATP composite material; The coating slurry is uniformly coated on a base film and dried to obtain the battery separator.

8. The method for preparing a battery separator according to claim 7, characterized in that: The components of the coating slurry are calculated by weight: PAN@C@LATP composite material is 18% to 38%, thickener is 0.2% to 1.0%, binder is 0.3% to 1.7%, wetting agent is 0.05% to 0.55%, dispersant is 0.1% to 1.0%, and the rest is the first solvent.

9. The method for preparing a battery separator according to claim 7, characterized in that: The step of adding the PAN@C@LATP composite material and the dispersant into the solvent and mixing them thoroughly and uniformly also includes the following steps: Adding an organic base and an acidic solution into a second solvent and reacting them sufficiently to obtain a buffer solution; Adding LATP powder and a carbon source to the buffer solution for sufficient reaction to obtain a polymer-modified LATP material; The polymer-modified LATP material is carbonized to obtain a C@LATP composite material.

10. The method for preparing a battery separator according to claim 9, characterized in that: After the step of carbonizing the polymer-modified LATP material to obtain the C@LATP composite material, the following steps are also included: The C@LATP composite material is placed in a mixed gas of argon and oxygen for heating treatment.

11. The method for preparing a battery separator according to claim 10, characterized in that: After the step of placing the C@LATP composite material in a mixed gas of argon and oxygen for heating treatment, the following steps are also included: dispersing the C@LATP composite material in a third solvent to obtain a dispersion of the C@LATP composite material; dissolving PAN powder in a fourth solvent in a sealed environment to obtain a PAN solution; The PAN solution is added to the dispersion and mixed thoroughly to obtain a PAN@C@LATP composite material.

12. A lithium ion battery, characterized in that: The invention comprises the diaphragm according to any one of claims 1 to 6.

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