Nanometer lithium aluminum titanium phosphate coated diaphragm for lithium battery and preparation method and application of nanometer lithium aluminum titanium phosphate coated diaphragm

Abstract

The invention discloses a nanometer lithium aluminum titanium phosphate coated diaphragm for a lithium battery and a preparation method and application thereof, and mainly relates to the technical field of secondary battery diaphragms.The diaphragm comprises a base diaphragm and a nanometer lithium aluminum titanium phosphate coating attached to the surface of the base diaphragm, lithium aluminum titanium phosphate in the coating material is uniform in particle size and good in dispersity, and the nanometer lithium aluminum titanium phosphate is coated with the nanometer lithium aluminum titanium phosphate coating. The problem of non-uniform surface electric field distribution of the negative electrode caused by contact between titanium aluminum lithium phosphate particles and a lithium metal interface can be effectively inhibited, so that the phenomenon of lithium surface unevenness caused by Li < + > segregation in the lithium deposition process is relieved, and the growth of lithium dendrites is inhibited; the coating diaphragm has excellent heat resistance, high ionic conductivity, good cycling stability and the like at the same time, and the application range of the lithium titanium aluminum phosphate coating diaphragm is widened.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary battery separators, and specifically relates to a nano-lithium titanium aluminum phosphate coated separator for lithium batteries, and a preparation method and application thereof. Background Art

[0002] As fossil energy is facing increasingly severe problems of energy depletion and environmental pollution, efficient storage and utilization of energy is particularly important. Lithium batteries have gradually become a research hotspot due to their advantages such as high energy density, long cycle life, and no memory effect. However, although the polyolefin separators (such as polyethylene and polypropylene) currently used in lithium batteries have good mechanical and electrochemical properties, their electrolyte wettability is poor, resulting in uneven distribution of lithium flux, which in turn triggers the growth of lithium dendrites. In addition, polyolefin separators are prone to shrinkage after heating, which may cause direct contact between the positive and negative electrodes, thereby causing internal short circuits in the battery, posing serious safety hazards.

[0003] To solve these problems, many studies have tried to introduce oxide coatings with good heat resistance (such as alumina, halloysite, boehmite, titanium dioxide, etc.) on the separator base film. However, the oxide material itself cannot directly transport lithium ions, which usually leads to a decrease in battery ion conductivity and rate performance. In contrast, lithium aluminum titanium phosphate (LiATP) 1+x Al x Ti 2-x (PO 4 ) 3 , where 0.3≤x≤0.5) the solid electrolyte not only has good mechanical strength, but its high ionic conductivity enables it to effectively replace the oxide coating and improve the electrochemical performance of the battery.

[0004] At present, the preparation process of lithium aluminum titanium phosphate mainly includes high-temperature solid phase method, sol-gel method and liquid phase precipitation method. Although the above methods have been widely used, there are still some problems. For example, during the solid phase reaction, due to the occurrence of pyrophosphating reaction, the product is easy to melt and adhere to the reactor wall, resulting in a low yield of the product. Secondly, the particles of lithium aluminum titanium phosphate prepared by the solid phase method are of different sizes, and the subsequent mechanical crushing may cause the distortion of the crystal lattice, thereby affecting its performance. The sol-gel method often uses titanium tetrachloride as a titanium source, but this substance reacts with moisture in the air to form HCl acid mist, which is harmful to humans and the environment; or nitric acid solution is used to inhibit the hydrolysis of tetrabutyl titanate, and corrosion-resistant production equipment increases the cost of industrial production. The liquid phase precipitation method involves cumbersome steps such as precipitant mixing, heating, filtering, washing and drying, and the product is not easy to collect, resulting in great waste, reducing production efficiency and increasing costs.

[0005] In addition, due to the uneven size and poor dispersion of LATP particles, the coated LATP coating may contact the lithium anode interface, resulting in uneven electric field distribution on the anode surface. Uneven lithium deposition may lead to Li + Segregation and uneven lithium surface induce tip charge effect, which further promotes the growth of dendritic lithium dendrites, aggravates interfacial side reactions and affects its electrochemical performance.

[0006] Therefore, there is an urgent need to develop a new type of LATP coated diaphragm material that can overcome the problems in the existing technology and thus improve its application effect in batteries and other related fields. Summary of the invention

[0007] Based on this, the purpose of the present invention is to provide a nano-lithium aluminum titanium phosphate coated diaphragm for lithium batteries and its preparation method and application, aiming to solve or improve the above-mentioned problems.

[0008] In a first aspect, the present invention provides a nano-lithium aluminum titanium phosphate coated diaphragm for a lithium battery, the diaphragm comprising a porous polymer base film and a nano-lithium aluminum titanium phosphate coating attached to one or both sides of the base film; the nano-lithium aluminum titanium phosphate coating is composed of nano-lithium aluminum titanium phosphate powder and additives, in terms of mass: 70%≤nano-lithium aluminum titanium phosphate powder<100%, 0%<additive≤30%; the additives are composed of a binder and a solvent.

[0009] In some embodiments, the porous polymer base film material is one or more of PP, PE, and PI; the thickness of the base film material is 1 μm-30 μm, and the porosity of the base film is 40%-70%.

[0010] In certain embodiments, the coating thickness on one side is 1 μm-5 μm.

[0011] In certain embodiments, the mass ratio of nano-lithium aluminum titanium phosphate powder, binder, and solvent ranges from: (5-30): (1-10): (60-94).

[0012] In some embodiments, the binder is one or more of PVDF, PVDF-HFP, PTFE, and PAA.

[0013] In some embodiments, the solvent is one or more of N,N-dimethylformamide, N-methylpyrrolidone, and acetone.

[0014] In some embodiments, the nano-lithium aluminum titanium phosphate powder has the following chemical formula: Li 1+x Al x Ti 2-x (PO 4 ) 3, wherein 0.3≤x≤0.5, and the particle size range of the nano-lithium aluminum titanium phosphate powder is 200-500 nm.

[0015] In some embodiments, the nano-lithium aluminum titanium phosphate powder is evenly dispersed without agglomeration, and the ionic conductivity after secondary tableting and sintering is greater than 1.2×10 -4 S / cm, electronic conductivity <5.0×10 -9 S / cm.

[0016] In a second aspect, the present invention provides a method for preparing a nano-lithium aluminum titanium phosphate coated diaphragm for a lithium battery, comprising the following steps: S1: Preparation of nano-lithium aluminum titanium phosphate powder; S11: dispersing tetrabutyl titanate in ethanol according to a molar ratio to form a first mixed solution; S12: dispersing ammonium dihydrogen phosphate, aluminum nitrate, and lithium nitrate in deionized water according to a molar ratio to form a second mixed solution; In certain embodiments, the amount of the Li source is 1.05 times the molar stoichiometric coefficient to compensate for heat loss under high temperature conditions; the volume ratio of deionized water to ethanol is 8:2; S13: adding the second mixed solution to the first mixed solution to form a nano-lithium aluminum titanium phosphate precursor solution; In certain embodiments, the second mixed solution is added dropwise into the first mixed solution at a stirring speed of 300-500 rpm.

[0017] In certain embodiments, the second mixed solution is added dropwise into the first mixed solution with a stirring speed of 400 rpm through a constant pressure dropping funnel to achieve atomic-level liquid phase mixing of each element to form a nano-lithium aluminum titanium phosphate precursor solution; S14: heating and keeping the nano-lithium aluminum titanium phosphate precursor solution in a pressurized container, drying after crystallization, and sintering to obtain nano-lithium aluminum titanium phosphate powder; In some embodiments, the precursor solution is heated and kept at 160° C. in a pressurized container to form crystal nuclei, which are then dried and placed in a muffle furnace for solid-phase sintering at 850° C. to obtain nano-lithium aluminum titanium phosphate solid powder.

[0018] S2: preparing nano-lithium aluminum titanium phosphate powder and an auxiliary agent according to a mass ratio; adding the nano-lithium aluminum titanium phosphate powder to a solvent for ultrasonic dispersion to form a solute dispersion A; S3: adding the binder to the solvent and stirring and dispersing the mixture to form a binder dispersion B; S4: compounding and homogenizing the solute dispersion A and the binder dispersion B in proportion to form a lithium aluminum titanium phosphate coating slurry C; S5: After the lithium aluminum titanium phosphate coating slurry C is subjected to vacuum defoaming treatment at 0.01 - 0.1 MPa for 1 - 60 min, it is coated on the surface of the base film, and the temperature is maintained at 40°C -80°C and dried for 2 h-18 h to neutralize the electrons on the surface of the diaphragm to form a nano lithium aluminum titanium phosphate coated diaphragm for lithium batteries.

[0019] In a third aspect, the present invention provides an application of a nano-lithium aluminum titanium phosphate coated diaphragm for a lithium battery, characterized in that the nano-lithium aluminum titanium phosphate coated diaphragm as described in the first aspect is applied to a lithium ion battery.

[0020] In a fourth aspect, the present invention provides a lithium-ion battery, wherein the lithium-ion battery adopts the nano-lithium aluminum titanium phosphate coated diaphragm for the lithium battery as described in the first aspect.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The nano-lithium aluminum titanium phosphate coated diaphragm prepared by the present invention has the characteristics of strong heat resistance, high ion conductivity, high cycle stability, etc. The nano-lithium aluminum titanium phosphate particles in the coating layer are uniform in size and dispersed evenly, which inhibits the uneven electric field distribution on the negative electrode surface caused by the contact between the lithium aluminum titanium phosphate particles and the lithium metal interface, and alleviates the Li deposition process. + Segregation forms an uneven lithium surface, thereby inhibiting the growth of lithium dendrites, which can help expand the application range of lithium aluminum titanium phosphate coated diaphragms.

[0022] In addition, the method of the present invention requires less equipment, has a simple process and is easy to control, can effectively save energy and reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 is the XRD diagram of the nano-lithium aluminum titanium phosphate solid powder precursor after sintering in Example 8 of the present invention; Figure 2 is a SEM image of the nano-lithium aluminum titanium phosphate solid powder precursor after sintering in Example 8 of the present invention; Figure 3 The charge and discharge performance from the 1st to the 400th cycle at a current density of 5 C is the charge and discharge performance of the lithium aluminum titanium phosphate coated diaphragm assembled lithium metal battery in Example 13 of the present invention and the nano lithium aluminum titanium phosphate coated diaphragm assembled lithium metal battery provided in Comparative Example 3.

[0025] Figure 4 The charge and discharge performance from the 1st to the 400th cycle at a current density of 5C is the charge and discharge performance of the lithium aluminum titanium phosphate coated diaphragm assembled lithium metal battery in Example 13 of the present invention and the PE diaphragm assembled lithium metal battery provided in Comparative Example 4. DETAILED DESCRIPTION

[0026] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below in conjunction with specific examples. The raw materials, reagents, etc. used without indicating the manufacturer are all conventional products that can be purchased commercially, and this detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention.

[0027] In addition, for the numerical ranges in the present invention, it is understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the range.

[0028] Unless otherwise specified, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which the invention relates. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of a conflict with any incorporated document, the contents of this specification shall prevail.

[0029] The words "include", "including", "have", "contain", etc. used in this article are open-ended terms, meaning including but not limited to. Example 1

[0030] This embodiment provides a nano-lithium aluminum titanium phosphate solid powder (Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 ) Coating the diaphragm, the specific steps are as follows: S1: dispersing 6.9425 g of tetrabutyl titanate in 40 mL of ethanol to form a first mixed solution; S2: 4.1410 g of ammonium dihydrogen phosphate, 1.1350 g of aluminum nitrate, and 1.1294 g of lithium nitrate were dispersed in deionized water according to a molar stoichiometric ratio to form a second mixed solution; the ratio of deionized water to ethanol was 8:2.

[0031] S3: adding the second mixed solution dropwise into the first mixed solution with a stirring speed of 400 rpm through a constant pressure dropping funnel to achieve atomic-level liquid phase mixing of each element to form a nano-lithium aluminum titanium phosphate precursor solution; S4: using a pressurized container to heat the precursor solution at 160° C. to form crystal nuclei, and after the crystal nuclei are generated, drying is performed and then placing the solution in a muffle furnace for solid-phase sintering at 850° C. to obtain nano-lithium aluminum titanium phosphate solid powder.

[0032] S5: adding 0.3200 g of the nano-lithium aluminum titanium phosphate powder to 1.0000 g of N,N-dimethylformamide for ultrasonic dispersion to form a solute dispersion A; S6: adding 0.0800 g of a binder PVDF into 0.6000 g of a N,N-dimethylformamide solvent and stirring and dispersing the mixture to form a binder dispersion B; S7: Compounding the solute dispersion A and the binder dispersion B and then homogenizing them to form a lithium aluminum titanium phosphate coating slurry; S8: After the lithium titanium aluminum phosphate coating slurry is defoamed at 0.35 MPa in vacuum for 10 min, it is scraped on the surface of a 9 μm PE diaphragm to a coating thickness of 3 μm. After drying at 50 °C for 4 h, the electrons on the surface of the diaphragm are neutralized to form a lithium titanium aluminum phosphate coated diaphragm for lithium batteries. Example 2

[0033] The amount of nano-lithium aluminum titanium phosphate powder different from that in Example 1 is 0.1000 g, the binder PVDF is 0.0200 g, 1.0000 g of N,N-dimethylformamide is added in step 5, and 0.8800 g is added in step 6. Other than this, the other operating steps and conditions are the same as those in Example 1. Example 3

[0034] The amount of nano-lithium aluminum titanium phosphate powder different from that in Example 1 is 0.2000 g, the binder PVDF is 0.0600 g, 1.0000 g of N,N-dimethylformamide is added in step 5, and 0.7400 g is added in step 6. Other than this, the other operating steps and conditions are the same as those in Example 1. Example 4

[0035] The amount of nano-lithium aluminum titanium phosphate powder different from that in Example 1 is 0.4000 g, the binder PVDF is 0.1000 g, 1.0000 g of N,N-dimethylformamide is added in step 5, and 0.5000 g is added in step 6. Other than this, the other operating steps and conditions are the same as those in Example 1. Example 5

[0036] The amount of nano-lithium aluminum titanium phosphate powder different from that in Example 1 is 0.6000 g, the binder PVDF is 0.2000 g, 1.0000 g of N,N-dimethylformamide is added in step 5, and 0.2000 g is added in step 6. Other than this, the other operating steps and conditions are the same as those in Example 1. Example 6

[0037] The difference from Example 1 is that the binder in step 5 is replaced with PVDF-HFP. Other than this, the other operating steps and conditions are the same as those in Example 1. Example 7

[0038] The difference from Example 1 is that the solvent in steps 5 and 6 is replaced with N-methylpyrrolidone. Other than this, the other operating steps and conditions are the same as those in Example 1. Example 8

[0039] The difference from Example 1 is that the coating thickness in step 8 is changed to 1 μm. Other than this, the other operating steps and conditions are the same as those in Example 1. Example 9

[0040] The difference from Example 1 is that the coating thickness in step 8 is changed to 5 μm. Other than this, the other operating steps and conditions are the same as those in Example 1. Example 10

[0041] The difference from Example 1 is that the base film thickness in step 8 is changed to 7 μm. Other operating steps and conditions are the same as those in Example 1. Embodiment 11

[0042] The difference from Example 1 is that the vacuum defoaming time in step 8 is changed to 60 min. Other than this, the other operating steps and conditions are the same as those in Example 1. Example 12

[0043] The difference from Example 1 is that the drying time in step 8 is changed to 8 h. Otherwise, the other operating steps and conditions are the same as those in Example 1. Example 13

[0044] This embodiment provides a lithium metal battery assembled with a nano-titanium aluminum phosphate lithium coating diaphragm prepared in Example 1, and the specific operation steps are as follows: S1: stack the LFP positive electrode sheet, the above-mentioned diaphragm, lithium steel sheet, and spring sheet in order, and inject 1M LiPF 6 The button cells were assembled with electrolyte in EC / DEC=1:1 (v:v) and electrochemical tests were performed after standing and formation. Comparative Example 1

[0045] The lithium aluminum titanium phosphate material was synthesized with reference to Example 2 disclosed in Chinese patent CN117059919B. The specific operation steps are as follows: S1: weigh 0.555g of Li 2 CO 3 , 0.183g mass of Al 2 O 3 , 1.311 g of TiO 2 and 3.96 g of NH 4 H 2 PO 4 , put it into the ball mill, where the high temperature process will cause lithium loss, so Li 2 CO 3 The actual mass exceeds that of Li 2 CO 3 10% of the theoretical chemical ratio mass; S2: weigh 0.1×3.96 g of sucrose for later use; S3: placing the lithium source, aluminum source, titanium source and phosphorus source precursor compounds weighed in step S1 in a ball mill, adding isopropanol until the isopropanol covers the raw materials, and ball milling is performed. After the ball milling is completed, drying is performed, and the sintered product is separated; S4: placing the raw materials dried in step S3 into a crucible for sintering; S5: crushing the sintered product after sintering in step S4.

[0046] S6: adding 0.3200 g of the nano-lithium aluminum titanium phosphate powder to 1.0000 g of N,N-dimethylformamide for ultrasonic dispersion to form a solute dispersion A; S7: adding 0.0800 g of a binder PVDF into 0.6000 g of a N,N-dimethylformamide solvent and stirring and dispersing the mixture to form a binder dispersion B; S8: Compounding the solute dispersion A and the binder dispersion B and then slurrying them to form a lithium aluminum titanium phosphate coating slurry; S9: The lithium titanium aluminum phosphate coating slurry is subjected to vacuum defoaming at 0.35 MPa for 10 min, and then coated on the surface of a 9 μm PE diaphragm with a coating layer thickness of 3 μm. After drying at 50 °C for 4 h, the electrons on the surface of the diaphragm are neutralized to form a lithium titanium aluminum phosphate coated diaphragm for lithium batteries. Comparative Example 2

[0047] This comparative example provides a polyolefin PE diaphragm. Comparative Example 3

[0048] This embodiment provides a lithium metal battery assembled with a nano-titanium aluminum phosphate lithium coating diaphragm prepared in Comparative Example 1, and the specific operation steps are as follows: S1: stack the LFP positive electrode sheet, the above-mentioned diaphragm, lithium steel sheet, and spring sheet in order, and inject 1M LiPF 6 The button cells were assembled with electrolyte in EC / DEC=1:1 (v:v) and electrochemical tests were performed after standing and formation. Comparative Example 4

[0049] This embodiment provides a lithium metal battery assembled with the polyolefin PE diaphragm provided in Comparative Example 2, and the specific operation steps are as follows: S1: stack the LFP positive electrode sheet, the above-mentioned diaphragm, lithium steel sheet, and spring sheet in order, and inject 1M LiPF 6 The button cells were assembled with electrolyte in EC / DEC=1:1 (v:v) and electrochemical tests were performed after standing and formation.

[0050] Table 1 Comparison of performance of nano-titanium aluminum phosphate lithium coating diaphragm materials in different embodiments <![CDATA[LATP surface loading g / m 2 > Heat resistance temperature ℃ Ionic conductivity S / cm Example 1 0.794 160 <![CDATA[5.8×10 -4 ]]> Example 2 0.774 160 <![CDATA[5.5×10 -4 ]]> Example 3 0.785 160 <![CDATA[5.7×10 -4 ]]> Example 4 0.811 170 <![CDATA[5.7×10 -4 > Example 5 0.893 180 <![CDATA[5.6×10 -4 ]]> Example 6 0.787 160 <![CDATA[5.6×10 -4 ]]> Example 7 0.800 160 <![CDATA[5.7×10 -4 ]]> Example 8 0.613 160 <![CDATA[5.2×10 -4 ]]> Example 9 1.056 180 <![CDATA[5.6×10 -4 ]]> Example 10 0.791 150 <![CDATA[5.9×10 -4 ]]> Embodiment 11 0.808 160 <![CDATA[5.8×10 -4 ]]> Example 12 0.788 160 <![CDATA[5.8×10 -4 ]]> Comparative Example 1 0.766 160 <![CDATA[5.3×10 -4 ]]> Comparative Example 2 0 140 <![CDATA[4.9×10 -4 ]]> As shown in Table 1, the nano-lithium aluminum titanium phosphate coated membranes of Examples 1-10 are compared with Comparative Examples 1-2. On the one hand, the addition of nano-lithium aluminum titanium phosphate improves the thermal stability of the membrane. On the other hand, due to the improvement of the wettability of the electrolyte and the effect of LATP on Li + The transmission effect greatly improves the ionic conductivity of the diaphragm. Different from the lithium titanium aluminum phosphate in comparative example 1, the lithium titanium aluminum phosphate in Examples 1-10 has a better improvement on the ionic conductivity of the diaphragm. The reason may be that the mechanical crushing process of the lithium titanium aluminum phosphate in comparative example 1 may cause the distortion of the crystal lattice, affecting its performance.

[0051] As shown in Table 2, compared with the above three examples, due to the Ti 4+ Will react with lithium metal to become Ti 3+ , resulting in a small amount of capacity loss, but compared with the long cycle performance, the nano-lithium aluminum titanium phosphate coated diaphragm enhances the long cycle performance of the diaphragm, which may be attributed to the reaction of lithium aluminum titanium phosphate to form a protective layer at the negative electrode interface, alleviating the Li deposition process. + Segregation forms an uneven lithium surface, which prevents the further growth of lithium dendrites, while the inner layer of lithium aluminum titanium phosphate plays the role of a solid electrolyte, accelerating the transmission of lithium ions at the interface.

[0052] Table 2 Comparison of performance of batteries assembled with nano-titanium aluminum phosphate coated diaphragms in different embodiments First cycle discharge capacity mAh / g 400-cycle discharge capacity mAh / g 100-cycle Coulomb efficiency Embodiment 13 108.1 114.3 99.79 Comparative Example 3 91.2 94 99.48 Comparative Example 4 125.6 Invalidation 96.98 In summary, after the diaphragm containing the nano-lithium titanium aluminum phosphate material prepared by the present invention is further assembled to form a battery, the thermal safety of the diaphragm assembly and the electrolyte retention rate can be improved, which is useful for improving the safety of battery use and electrochemical performance; at the same time, based on the uniform particle size and uniform dispersion of the nano-lithium titanium aluminum phosphate coating material, the uneven electric field distribution on the negative electrode surface caused by the contact between the lithium titanium aluminum phosphate particles and the lithium metal interface is suppressed, and the Li deposition process is alleviated. + Segregation forms an uneven lithium surface, thereby inhibiting the growth of lithium dendrites. At the same time, it has the characteristics of strong heat resistance, high ionic conductivity, and high cycle stability, which can help lithium titanium aluminum phosphate coated diaphragms expand their application range.

[0053] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0054] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A nano-lithium aluminum titanium phosphate coated diaphragm for lithium batteries, characterized in that: The diaphragm includes a porous polymer base film and a nano-lithium aluminum titanium phosphate coating attached to one side or both sides of the base film; the nano-lithium aluminum titanium phosphate coating is composed of nano-lithium aluminum titanium phosphate powder and additives, and the weight percentage is: 70%≤nano-lithium aluminum titanium phosphate powder<100%, 0%<additive≤30%; the additives are composed of a binder and a solvent.

2. The nano-lithium aluminum titanium phosphate coated diaphragm for lithium battery according to claim 1, characterized in that: The porous polymer base film material is one or more of PP, PE, and PI; the thickness of the base film material is 1 μm-30 μm, and the porosity of the base film is 40%-70%.

3. The nano-lithium aluminum titanium phosphate coated diaphragm for lithium battery according to claim 1, characterized in that: The coating thickness on one side is 1 μm–5 μm.

4. The nano-lithium aluminum titanium phosphate coated diaphragm for lithium battery according to claim 1, characterized in that: The mass ratio range of nano-lithium aluminum titanium phosphate powder, binder and solvent is: 5-30: 1-10: 60-94.

5. A nano-lithium aluminum titanium phosphate coated diaphragm for a lithium battery according to any one of claims 1 to 4, characterized in that: The binder is one or more of PVDF, PVDF-HFP, PTFE and PAA.

6. A nano-lithium aluminum titanium phosphate coated diaphragm for a lithium battery according to any one of claims 1 to 4, characterized in that: The solvent is one or more of N,N-dimethylformamide, N-methylpyrrolidone and acetone.

7. A nano-lithium aluminum titanium phosphate coated diaphragm for a lithium battery according to any one of claims 1 to 4, characterized in that: The nano-lithium aluminum titanium phosphate powder has the following chemical formula: Li 1+x Al x Ti 2-x (PO4)3, wherein 0.3≤x≤0.5, and the particle size range of the nano-lithium aluminum titanium phosphate powder is 200-500 nm.

8. A method for preparing a nano-lithium aluminum titanium phosphate coated diaphragm for a lithium battery according to any one of claims 1 to 7, comprising the following steps: S1: Preparation of nano-lithium aluminum titanium phosphate powder; S11: dispersing tetrabutyl titanate in ethanol according to a molar ratio to form a first mixed solution; S12: dispersing ammonium dihydrogen phosphate, aluminum nitrate, and lithium nitrate in deionized water according to a molar ratio to form a second mixed solution; S13: adding the second mixed solution to the first mixed solution to form a nano-lithium aluminum titanium phosphate precursor solution; S14: heating and keeping the nano-lithium aluminum titanium phosphate precursor solution in a pressurized container, drying after crystallization, and sintering to obtain nano-lithium aluminum titanium phosphate powder; S2: preparing nano-lithium aluminum titanium phosphate powder and an auxiliary agent according to a mass ratio; adding the nano-lithium aluminum titanium phosphate powder to a solvent for ultrasonic dispersion to form a solute dispersion A; S3: adding the binder to the solvent and stirring and dispersing the mixture to form a binder dispersion B; S4: Compounding the solute dispersion A and the binder dispersion B in proportion and homogenizing them to form a lithium titanium aluminum phosphate coating slurry C; S5: After the lithium aluminum titanium phosphate coating slurry C is subjected to vacuum defoaming treatment at 0.01 - 0.1 MPa for 1 - 60 min, it is coated on the surface of the base film, and the temperature is maintained at 40°C -80°C and dried for 2 h-18 h to neutralize the electrons on the surface of the diaphragm to form a nano lithium aluminum titanium phosphate coated diaphragm for lithium batteries.

9. The method for preparing a nano-lithium aluminum titanium phosphate coated diaphragm for a lithium battery according to claim 8, characterized in that: The second mixed solution is added dropwise into the first mixed solution with a stirring speed of 300-500 rpm.

10. The use of a nano-lithium aluminum titanium phosphate coated diaphragm for lithium batteries according to any one of claims 1 to 7, characterized in that: The nano-lithium aluminum titanium phosphate coated diaphragm is applied to lithium ion batteries.

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