High-energy-density lithium battery temperature-resistant safe composite diaphragm and preparation method thereof

Abstract

The invention belongs to the technical field of lithium battery diaphragms, and particularly relates to a high-energy-density lithium battery temperature-resistant safe composite diaphragm and a preparation method thereof. According to the preparation method, aluminum chloride hexahydrate is taken as an aluminum source, a sol-gel method is combined with carbon dioxide supercritical drying to prepare an aluminum oxide composite material with an aerogel structure, and the aluminum oxide composite material is matched with nano cellulose, a polyacrylate binder and a dispersing agent to prepare coating slurry; the polypropylene base material is coated with the coating slurry to form the composite diaphragm, so that the thermal shrinkage performance of the diaphragm is reduced while the safety is ensured by using a relatively large coating thickness, and meanwhile, the high energy density is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery diaphragms, and in particular relates to a high-energy-density, heat-resistant and safe composite diaphragm for lithium batteries and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are composed of a positive electrode, a negative electrode, a separator, and an electrolyte. The separator does not directly participate in the chemical reactions that occur during the charge and discharge process, but its presence physically separates the anode and cathode, while providing an ion transmission channel between the cathode and the anode. The separator ensures the realization of related functions such as battery charge and discharge, and reduces safety hazards when the battery is used. The separator needs to have the following properties to ensure safe use: (1) Electronic insulation. Insulation is a property that the separator must have. The separator needs to prevent electrons from flowing through it to both sides. This requires the separator to have very high resistance and good electronic insulation. (2) Maintaining physical shape and size stability under high temperature conditions. Thermal stability is the property of the separator to remain stable at high temperatures, which is an important property for maintaining safe battery operation. (3) Not reacting with the substances inside the battery and not intervening in the reactions inside the battery. The separator is in an environment where the electrolyte and electrochemical reactions are constantly occurring for a long time, which requires the separator to maintain stable chemical properties and not interfere with the reactions between the electrodes.

[0003] A Chinese patent (publication number CN116565456A) discloses a lithium battery separator, its preparation method, and application. The coating of the lithium battery separator prepared by this invention is thin and light, and the coating has high heat resistance. The thermal shrinkage of the coating after baking at 180°C for 1 hour is less than 2%, which can meet the requirements of isolating the positive and negative electrodes of the lithium battery and transmitting lithium ions, while improving the thermal stability and adhesion of the lithium battery separator; when the temperature inside the battery rises abnormally, it effectively avoids the melting and rupture of the battery cell causing thermal runaway, thereby improving the energy density and dynamic performance of the lithium battery cell. However, the coating thickness prepared by this patented technology is too small, and the coating accuracy requirements are high. At the same time, the thin coating is easily affected by the environment, resulting in insufficient product safety.

[0004] Therefore, how to modify the battery separator coating material to reduce the thermal shrinkage of the separator while ensuring safety using a larger coating thickness and obtaining high energy density has become a key area that needs to be tackled. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a high-energy-density, heat-resistant and safe composite diaphragm for lithium batteries and a preparation method thereof. The present invention uses aluminum chloride hexahydrate as an aluminum source, and prepares an alumina composite material with an aerogel structure through a sol-gel method combined with carbon dioxide supercritical drying. A coating slurry is prepared by combining nanocellulose, a polyacrylate binder and a dispersant, and the coating slurry is coated on a polypropylene substrate to form a composite diaphragm. While using a larger coating thickness to ensure safety, the thermal shrinkage performance of the diaphragm is reduced, and a high energy density is obtained at the same time.

[0006] A first aspect of the present invention provides a method for preparing a heat-resistant and safe composite diaphragm for a high-energy-density lithium battery, comprising the following steps:

[0007] In parts by weight, 16 to 20 parts of alumina composite material, 10 to 16 parts of nanocellulose, 4 to 6 parts of polyacrylate binder and 0.2 to 0.4 parts of dispersant are added to 400 to 500 parts of deionized water and ultrasonically dispersed for 50 to 60 minutes to obtain a coating slurry. The coating slurry is applied on a polypropylene substrate and dried to form a coating to obtain a high-energy-density, heat-resistant and safe composite diaphragm for lithium batteries.

[0008] As a preferred solution, the weight proportion of the alumina composite material in the present invention can be 16 parts, 17 parts, 18 parts, 19 parts or 20 parts.

[0009] As a preferred solution, the weight proportion of the nanocellulose in the present invention can be 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts or 16 parts.

[0010] As a preferred solution, the weight proportion of the polyacrylate binder in the present invention can be 4 parts, 4.5 parts, 5 parts, 5.5 parts or 6 parts.

[0011] As a preferred solution, the weight proportion of the dispersant in the present invention can be 0.2 parts, 0.25 parts, 0.3 parts, 0.35 parts or 0.4 parts, etc.

[0012] As a preferred technical solution of the present invention, the preparation method of the alumina composite material includes: adding halloysite nanoclay loaded with titanium dioxide to aluminum chloride hexahydrate to form a precursor solution, and then gelling the precursor solution to obtain the alumina composite material.

[0013] The alumina composite material of the invention uses aluminum chloride hexahydrate as an aluminum source and halloysite nanoclay loaded with titanium dioxide as a reinforcing phase, and is prepared by a sol-gel method combined with carbon dioxide supercritical drying to obtain an alumina composite material with an aerogel structure.

[0014] As a preferred technical solution of the present invention, the preparation method of halloysite nanoclay-loaded titanium dioxide includes: dispersing 2.4 to 2.8 parts of halloysite nanoclay in 100 to 120 parts of anhydrous ethanol, then adding 1.2 to 1.6 parts of titanium tetrachloride and ultrasonicating for 30 to 40 minutes, adding 0.012 to 0.016 parts of sodium hydroxide after stirring for 80 to 90 minutes, heat treating at 170 to 180° C. for 20 to 24 hours, centrifuging, washing with water, and drying to obtain halloysite nanoclay-loaded titanium dioxide.

[0015] As a preferred technical solution of the present invention, the preparation method of the precursor solution includes: adding 2 to 4 parts of aluminum chloride hexahydrate to a mixture of 30 to 40 parts of deionized water and 20 to 30 parts of anhydrous ethanol, and then adding 1.6 to 2.4 parts of halloysite nanoclay loaded titanium dioxide and stirring for 50 to 60 minutes to obtain a precursor solution.

[0016] As a preferred technical solution of the present invention, the gelation treatment step includes: adding 0.2 to 0.4 parts of hydroxyethyl cellulose to 50 to 70 parts of the precursor solution and stirring for 160 to 180 minutes, then adding 0.6 to 0.8 parts of 1,2-propylene oxide and gelling at room temperature for 4 to 6 hours, using anhydrous ethanol for solvent replacement, supercritical carbon dioxide drying, and crushing to obtain an alumina composite material.

[0017] As a preferred technical solution of the present invention, the conditions for supercritical carbon dioxide drying are: temperature of 40-44° C. and pressure of 12-13 MPa.

[0018] As a preferred technical solution of the present invention, the nanocellulose is modified nanocellulose;

[0019] The preparation method of the modified nanocellulose comprises: firstly subjecting commercially available nanocellulose to acetylation to obtain acetylated nanocellulose; and subjecting the acetylated nanocellulose to modification with cobalt nitrate hexahydrate and 2-methylimidazole to obtain modified nanocellulose.

[0020] The modified nanocellulose of the present invention uses nanocellulose as raw material, is first acetylated to obtain acetylated nanocellulose, and then modified using cobalt nitrate hexahydrate and 2-methylimidazole, and organic metal skeleton particles are in situ grown on the surface of the nanocellulose, thereby preparing the modified nanocellulose.

[0021] As a preferred technical solution of the present invention, the acetylation treatment step includes: dispersing 4 to 6 parts of commercially available nanocellulose in 400 to 500 parts of N,N-dimethylacetamide, then adding 1.8 to 2.4 parts of pyridine and 0.6 to 0.8 parts of acetyl chloride, and stirring the reaction at 70 to 80°C for 50 to 60 minutes.

[0022] As a preferred technical solution of the present invention, the modification treatment step includes: dispersing 1.5 to 1.7 parts of acetylated nanocellulose in 140 to 160 parts of methanol, adding 1.6 to 1.8 parts of cobalt nitrate hexahydrate and stirring for 6 to 8 hours, then adding 1.9 to 2.1 parts of 2-methylimidazole and 140 to 160 parts of methanol and stirring for 22 to 24 hours, centrifuging, washing with ethanol, and drying to obtain modified nanocellulose.

[0023] As a preferred technical solution of the present invention, the polyacrylate adhesive is Sanrui High-Tech LIB-S101 adhesive and Sanrui High-Tech LIB-S106P5 adhesive.

[0024] As a preferred technical solution of the present invention, the viscosity of the LIB-S101 adhesive at 25°C is 10 to 100 mPa·s, and the viscosity of the LIB-S106P5 adhesive at 25°C is 50 to 1000 mPa·s.

[0025] As a preferred technical solution of the present invention, the mass ratio of the LIB-S101 binder to the LIB-S106P5 binder is (1-2):1.

[0026] The polyacrylate binder is compounded using Sanrui Gaocai's LIB-S101 binder and LIB-S106P5 binder. The LIB-S101 binder has good wetting and dispersing properties on alumina particles, and has excellent dispersibility and adhesion, which can ensure good adhesion of alumina composite materials to achieve high energy density. The LIB-S106P5 binder has a high glass transition temperature and excellent heat shrinkage resistance, which can reduce the thermal shrinkage of the diaphragm under high temperature conditions. The comprehensive performance of the composite diaphragm is improved by compounding the binder.

[0027] As a preferred technical solution of the present invention, the thickness of the coating is 2 μm.

[0028] As a preferred technical solution of the present invention, the dispersant is selected from BYK-LPC20992 or BASF AA4140.

[0029] The second aspect of the present invention provides a high energy density, heat-resistant and safe composite diaphragm for lithium batteries prepared by the method described in the first aspect.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention realizes the effective compounding of alumina composite material and modified nanocellulose on a polypropylene substrate by compounding a polyacrylate binder, forming a "multi-level pore channel of alumina composite material + organic metal rigid skeleton" structure in the coating. While using a larger coating thickness to ensure safety, it effectively reduces the thermal shrinkage rate of the composite material and obtains high energy density.

[0032] (2) The aerogel-structured alumina in the composite material of the present invention can provide more ion transmission channels, enhance the wettability of the electrolyte, and promote the rapid migration of lithium ions. At the same time, titanium dioxide can absorb some impurity electrolytes, which helps to reduce the interfacial impedance between the diaphragm and the electrode, and has good compatibility with the electrolyte, which can promote the transport of lithium ions and improve the ionic conductivity of the diaphragm, thereby achieving high energy density; halloysite nanotubes are a natural nanotubular clay material with excellent high temperature resistance. Combined with the porous network and high specific surface area of ​​the gel-structured alumina, they effectively block heat conduction and inhibit thermal shrinkage under high temperature conditions.

[0033] (3) The modified nanocellulose-loaded organic metal framework particles of the present invention have a high specific surface area, providing more pathways for lithium ion migration. At the same time, the hydroxyl groups of nanocellulose can enhance the wettability of the electrolyte and improve the ionic conductivity, thereby obtaining a high energy density. In addition, the organic metal framework has a high thermal decomposition temperature and can form a stable lattice structure at high temperatures, thereby inhibiting the thermal shrinkage and melting of the diaphragm. Nanocellulose can provide flexibility, which, combined with the rigidity of the organic metal framework, makes the diaphragm resistant to shrinkage at high temperatures. DETAILED DESCRIPTION

[0034] For the convenience of understanding the present invention, the present invention is given below with examples. It should be understood by those skilled in the art that the examples are only for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0035] The sources of some components in the Examples and Comparative Examples are as follows:

[0036] Aluminum chloride hexahydrate, CAS No. 7784-13-6, was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0037] Halloysite nanoclay, product number H431905, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0038] Titanium tetrachloride, CAS No. 7550-45-0, was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.;

[0039] Hydroxyethyl cellulose, CAS No. 9004-62-0, was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.;

[0040] 1,2-Propylene oxide, CAS No. 75-56-9, was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0041] Ceramic powder was purchased from Jiangsu Jingshengyuan New Material Technology Co., Ltd.

[0042] Commercially available nanocellulose, product number TL-011, was purchased from Nanjing Tianlu Nanotechnology Co., Ltd.;

[0043] Pyridine, CAS No. 110-86-1, was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.;

[0044] Acetyl chloride, CAS No. 75-36-5, was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0045] Cobalt nitrate hexahydrate, CAS No. 10026-22-9, was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.;

[0046] 2-Methylimidazole, CAS No. 693-98-1, was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.;

[0047] LIB-S101 adhesive, with a viscosity of 10–100 mPa·s at 25°C, was purchased from Shanghai Sanrui Polymer Materials Co., Ltd.

[0048] LIB-S106P5 adhesive, with a viscosity of 50–1000 mPa·s at 25°C, was purchased from Shanghai Sanrui Polymer Materials Co., Ltd.

[0049] Dispersant: BYK-LPC20992, BASF AA4140.

[0050] Example 1

[0051] This embodiment provides a method for preparing a heat-resistant and safe composite diaphragm for a high-energy-density lithium battery, comprising the following steps:

[0052] In parts by weight, 20 parts of alumina composite material, 16 parts of modified nanocellulose, 6 parts of polyacrylate binder (4 parts of LIB-S101 binder and 2 parts of LIB-S106P5 binder) and 0.4 parts of dispersant (BYK-LPC20992) were added to 500 parts of deionized water and ultrasonically dispersed for 60 minutes to obtain a coating slurry. The coating slurry was applied to a polypropylene substrate and dried to form a coating with a thickness of 2 μm to obtain a high-energy-density, heat-resistant and safe composite diaphragm for lithium batteries.

[0053] Preparation of the alumina composite material: (1) by weight, 2.8 parts of halloysite nanoclay are dispersed in 120 parts of anhydrous ethanol, and then 1.6 parts of titanium tetrachloride are added and ultrasonicated for 40 minutes, and after stirring for 90 minutes, 0.016 parts of sodium hydroxide are added, and the mixture is heat-treated at 180° C. for 20 hours, centrifuged, washed with water, and dried to obtain halloysite nanoclay-loaded titanium dioxide; (2) 4 parts of aluminum chloride hexahydrate are added to a mixture of 40 parts of deionized water and 30 parts of anhydrous ethanol, and then 2.4 parts of halloysite nanoclay-loaded titanium dioxide are added and stirred for 60 minutes to obtain a precursor solution; 0.4 parts of hydroxyethyl cellulose are added to 70 parts of the precursor solution and stirred for 180 minutes, and then 0.8 parts of 1,2-propylene oxide are added and gelled at room temperature for 6 hours, and anhydrous ethanol is used for solvent replacement, supercritical carbon dioxide drying (temperature is 44° C., pressure is 12 MPa), and crushing is obtained to obtain an alumina composite material.

[0054] The modified nanocellulose is prepared as follows: 6 parts by weight of commercially available nanocellulose are dispersed in 500 parts of N,N-dimethylacetamide, 2.4 parts of pyridine and 0.8 parts of acetyl chloride are then added, and the mixture is stirred at 80°C for 50 minutes; 1.7 parts of acetylated nanocellulose are dispersed in 160 parts of methanol, 1.8 parts of cobalt nitrate hexahydrate are added, and the mixture is stirred for 8 hours, followed by the addition of 2.1 parts of 2-methylimidazole and 160 parts of methanol, and the mixture is stirred for 24 hours. The mixture is then centrifuged, washed with ethanol, and dried to obtain the modified nanocellulose.

[0055] Example 2

[0056] This embodiment provides a method for preparing a heat-resistant and safe composite diaphragm for a high-energy-density lithium battery, comprising the following steps:

[0057] In parts by weight, 16 parts of alumina composite material, 10 parts of modified nanocellulose, 4 parts of polyacrylate binder (2 parts of LIB-S101 binder and 2 parts of LIB-S106P5 binder) and 0.2 parts of dispersant BASF AA4140 were added to 400 parts of deionized water and ultrasonically dispersed for 50 minutes to obtain a coating slurry. The coating slurry was applied to a polypropylene substrate and dried to form a coating with a thickness of 2 μm to obtain a high-energy-density, heat-resistant and safe composite diaphragm for lithium batteries.

[0058] Preparation of the alumina composite material: (1) in parts by weight, 2.4 parts of halloysite nanoclay are dispersed in 100 parts of anhydrous ethanol, and then 1.2 parts of titanium tetrachloride are added and ultrasonicated for 30 minutes. After stirring for 80 minutes, 0.012 parts of sodium hydroxide are added, and the mixture is heat-treated at 170°C for 24 hours, centrifuged, washed with water, and dried to obtain halloysite nanoclay-loaded titanium dioxide; (2) 2 parts of aluminum chloride hexahydrate are added to a mixture of 30 parts of deionized water and 20 parts of anhydrous ethanol, and then 1.6 parts of halloysite nanoclay-loaded titanium dioxide are added and stirred for 50 minutes to obtain a precursor solution; 0.2 parts of hydroxyethyl cellulose are added to 50 parts of the precursor solution and stirred for 160 minutes, and then 0.6 parts of 1,2-propylene oxide are added and gelled at room temperature for 4 hours, and anhydrous ethanol is used for solvent replacement, supercritical carbon dioxide drying (temperature is 40°C, pressure is 12MPa), and crushing to obtain an alumina composite material.

[0059] The modified nanocellulose is prepared as follows: 4 parts by weight of commercially available nanocellulose are dispersed in 400 parts of N,N-dimethylacetamide, 1.8 parts of pyridine and 0.6 parts of acetyl chloride are then added, and the mixture is stirred at 70° C. for 60 minutes; 1.5 parts of acetylated nanocellulose are dispersed in 140 parts of methanol, 1.6 parts of cobalt nitrate hexahydrate are added, and the mixture is stirred for 6 hours; 1.9 parts of 2-methylimidazole and 140 parts of methanol are then added, and the mixture is stirred for 22 hours. The mixture is then centrifuged, washed with ethanol, and dried to obtain the modified nanocellulose.

[0060] Example 3

[0061] This embodiment provides a method for preparing a heat-resistant and safe composite diaphragm for a high-energy-density lithium battery, comprising the following steps:

[0062] In parts by weight, 18 parts of alumina composite material, 12 parts of modified nanocellulose, 5 parts of polyacrylate binder (3 parts of LIB-S101 binder and 2 parts of LIB-S106P5 binder) and 0.3 parts of dispersant BYK-LPC20992 were added to 450 parts of deionized water and ultrasonically dispersed for 55 minutes to obtain a coating slurry. The coating slurry was applied to a polypropylene substrate and dried to form a coating with a thickness of 2 μm to obtain a high-energy-density, heat-resistant and safe composite diaphragm for lithium batteries.

[0063] Preparation of the alumina composite material: (1) by weight, 2.6 parts of halloysite nanoclay are dispersed in 110 parts of anhydrous ethanol, and then 1.4 parts of titanium tetrachloride are added and ultrasonicated for 35 minutes, and after stirring for 85 minutes, 0.014 parts of sodium hydroxide are added, and the mixture is heat-treated at 175° C. for 22 hours, centrifuged, washed with water, and dried to obtain halloysite nanoclay-loaded titanium dioxide; (2) 3 parts of aluminum chloride hexahydrate are added to a mixture of 35 parts of deionized water and 25 parts of anhydrous ethanol, and then 1.8 parts of halloysite nanoclay-loaded titanium dioxide are added and stirred for 55 minutes to obtain a precursor solution; 0.3 parts of hydroxyethyl cellulose are added to 60 parts of the precursor solution and stirred for 170 minutes, and then 0.6-0.8 parts of 1,2-propylene oxide are added and gelled at room temperature for 5 hours, and anhydrous ethanol is used for solvent replacement, supercritical carbon dioxide drying (temperature is 42° C., pressure is 12.5 MPa), and crushing is obtained to obtain an alumina composite material.

[0064] The modified nanocellulose is prepared as follows: 5 parts by weight of commercially available nanocellulose are dispersed in 450 parts of N,N-dimethylacetamide, 2.2 parts of pyridine and 0.7 parts of acetyl chloride are then added, and the mixture is stirred at 75° C. for 55 minutes; 1.6 parts of acetylated nanocellulose are dispersed in 150 parts of methanol, 1.7 parts of cobalt nitrate hexahydrate are added, and the mixture is stirred for 7 hours; 2.0 parts of 2-methylimidazole and 150 parts of methanol are then added, and the mixture is stirred for 23 hours. The mixture is then centrifuged, washed with ethanol, and dried to obtain the modified nanocellulose.

[0065] Comparative Example 1

[0066] The difference between this comparative example and Example 1 is that commercially available ceramic powder is used instead of the alumina composite material.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 1 is that commercially available nanocellulose (product number TL-011) is used instead of modified nanocellulose.

[0069] Comparative Example 3

[0070] The difference between this comparative example and Example 1 is that the amount of LIB-S101 adhesive in the polyacrylate adhesive is changed to 5 parts, and the amount of LIB-S106P5 adhesive is changed to 1 part.

[0071] Comparative Example 4

[0072] The difference between this comparative example and Example 1 is that the amount of LIB-S101 adhesive in the polyacrylate adhesive is changed to 2 parts, and the amount of LIB-S106P5 adhesive is changed to 4 parts.

[0073] The performance of the diaphragms provided in the above embodiments and comparative examples was tested using the following method:

[0074] (1) Air permeability test: refer to the requirements of GB / T 36363-2018 Polyolefin separators for lithium-ion batteries for testing.

[0075] (2) Thermal shrinkage performance test: Refer to the requirements of GB / T 36363-2018 Polyolefin separators for lithium-ion batteries for testing, and the temperature is 180°C.

[0076] (3) Energy density test: The battery separator samples were cut into 60 mm wide battery separators. Lithium cobalt oxide was used as the positive electrode active material, PVDF was used as the positive electrode binder, carbon nanotubes were used as the conductive agent, graphite was used as the negative electrode, styrene-butadiene rubber was used as the binder, and sodium carboxymethyl cellulose was used as the thickener to make soft-pack batteries. The battery capacity, the average output voltage of the battery during the charge and discharge process, and the battery weight were measured. The energy density was calculated using the following formula: Energy density = battery capacity × average voltage ÷ battery weight.

[0077] The above performance test data is shown in Table 1.

[0078] Table 1 Performance test results

[0079]

[0080] From the above content, it can be seen that the present invention realizes the effective compounding of alumina composite material and modified nanocellulose on a polypropylene substrate by compounding a polyacrylate binder, forming a "multi-level pore channel of alumina composite material + organic metal rigid skeleton" structure in the coating, thereby preparing a high-energy density lithium battery heat-resistant and safe composite diaphragm (Examples 1 to 3), which has the best comprehensive performance. While using a larger coating thickness to ensure safety, it effectively reduces the thermal shrinkage of the composite material and obtains high energy density.

[0081] Compared with Example 1, when commercially available ceramic powder is used instead of the alumina composite material, the thermal shrinkage performance deteriorates and the energy density decreases (Comparative Example 1); compared with Example 1, when commercially available nanocellulose (Article No. TL-011) is used instead of modified nanocellulose, the thermal shrinkage performance deteriorates and the energy density decreases (Comparative Example 2); compared with Example 1, the amount of LIB-S101 binder in the polyacrylate binder is changed to 5 parts, and the amount of LIB-S106P5 binder is changed to 1 part. Since the amount of LIB-S106P5 binder with good heat shrinkage resistance is too small, the compounding effect is poor, and the thermal shrinkage performance deteriorates (Comparative Example 3); compared with Example 1, the amount of LIB-S101 binder in the polyacrylate binder is changed to 2 parts, and the amount of LIB-S106P5 binder is changed to 4 parts. Since the amount of LIB-S101 binder with good wetting and dispersing properties for alumina particles is too small, the compounding effect is poor, and the energy density decreases (Comparative Example 4).

Claims

1. A method for preparing a heat-resistant and safe composite diaphragm for a high energy density lithium battery, characterized in that: The following steps are involved: In parts by weight, 16 to 20 parts of an aluminum oxide composite material, 10 to 16 parts of nanocellulose, 4 to 6 parts of a polyacrylate binder, and 0.2 to 0.4 parts of a dispersant are added to 400 to 500 parts of deionized water and ultrasonically dispersed for 50 to 60 minutes to obtain a coating slurry. The coating slurry is applied to a polypropylene substrate and dried to form a coating, thereby obtaining a heat-resistant and safe composite diaphragm for a high-energy-density lithium battery. The preparation method of the aluminum oxide composite material comprises: adding halloysite nano-clay loaded with titanium dioxide into aluminum chloride hexahydrate to form a precursor solution, and then performing gelation treatment on the precursor solution to obtain the aluminum oxide composite material.

2. The method for preparing a heat-resistant and safe composite diaphragm for a high energy density lithium battery according to claim 1, characterized in that: The preparation method of the halloysite nanoclay-loaded titanium dioxide comprises: dispersing 2.4 to 2.8 parts of halloysite nanoclay in 100 to 120 parts of anhydrous ethanol, then adding 1.2 to 1.6 parts of titanium tetrachloride and ultrasonicating for 30 to 40 minutes, adding 0.012 to 0.016 parts of sodium hydroxide after stirring for 80 to 90 minutes, heat treating at 170 to 180° C. for 20 to 24 hours, centrifuging, washing with water, and drying to obtain the halloysite nanoclay-loaded titanium dioxide.

3. The method for preparing a heat-resistant and safe composite diaphragm for a high energy density lithium battery according to claim 1, characterized in that: The preparation method of the precursor solution comprises: adding 2 to 4 parts of aluminum chloride hexahydrate to a mixture of 30 to 40 parts of deionized water and 20 to 30 parts of anhydrous ethanol, and then adding 1.6 to 2.4 parts of halloysite nanoclay loaded titanium dioxide and stirring for 50 to 60 minutes to obtain the precursor solution.

4. The method for preparing a heat-resistant and safe composite diaphragm for a high energy density lithium battery according to claim 1, characterized in that: The gelling treatment step includes: adding 0.2 to 0.4 parts of hydroxyethyl cellulose to 50 to 70 parts of the precursor solution and stirring for 160 to 180 minutes, then adding 0.6 to 0.8 parts of 1,2-propylene oxide and gelling at room temperature for 4 to 6 hours, using anhydrous ethanol for solvent replacement, supercritical carbon dioxide drying, and crushing to obtain an aluminum oxide composite material.

5. The method for preparing a heat-resistant and safe composite diaphragm for a high energy density lithium battery according to claim 1, characterized in that: The nanocellulose is modified nanocellulose; The preparation method of the modified nanocellulose comprises: firstly subjecting commercially available nanocellulose to acetylation to obtain acetylated nanocellulose; and subjecting the acetylated nanocellulose to modification with cobalt nitrate hexahydrate and 2-methylimidazole to obtain modified nanocellulose.

6. The method for preparing a heat-resistant and safe composite diaphragm for a high energy density lithium battery according to claim 5, characterized in that: The acetylation treatment step includes: dispersing 4 to 6 parts of commercially available nanocellulose in 400 to 500 parts of N,N-dimethylacetamide, then adding 1.8 to 2.4 parts of pyridine and 0.6 to 0.8 parts of acetyl chloride, and stirring the reaction at 70 to 80° C. for 50 to 60 minutes.

7. The method for preparing a heat-resistant and safe composite diaphragm for a high energy density lithium battery according to claim 5, characterized in that: The modification treatment steps include: dispersing 1.5 to 1.7 parts of acetylated nanocellulose in 140 to 160 parts of methanol, adding 1.6 to 1.8 parts of cobalt nitrate hexahydrate and stirring for 6 to 8 hours, then adding 1.9 to 2.1 parts of 2-methylimidazole and 140 to 160 parts of methanol and stirring for 22 to 24 hours, centrifuging, washing with ethanol, and drying to obtain modified nanocellulose.

8. The method for preparing a heat-resistant and safe composite diaphragm for a high energy density lithium battery according to claim 1, characterized in that: The polyacrylate adhesives are Sanrui High-Tech LIB-S101 adhesive and Sanrui High-Tech LIB-S106P5 adhesive; The viscosity of the LIB-S101 adhesive at 25°C is 10-100 mPa·s, and the viscosity of the LIB-S106P5 adhesive at 25°C is 50-1000 mPa·s; The mass ratio of the LIB-S101 binder to the LIB-S106P5 binder is (1-2):

1.

9. The method for preparing a heat-resistant and safe composite diaphragm for a high energy density lithium battery according to claim 1, characterized in that: The thickness of the coating was 2 μm.

10. A high energy density lithium battery heat-resistant safety composite diaphragm, characterized in that: Prepared according to the method according to any one of claims 1 to 9.

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