High-stability protective coating for lithium battery positive electrode and preparation method thereof

Abstract

The application discloses a high-stability protective coating for a lithium battery positive electrode and a preparation method thereof, relates to the technical field of lithium batteries, and relates to the technical field of lithium batteries. The coating comprises an inner layer coating, a transition layer coating and an outer layer coating. The inner layer coating raw material comprises polyvinylidene fluoride, a solvent and a polyaniline-coated sulfur / carbon nanotube composite material, and the mass ratio is 1:5-6:0.3-0.6. The transition layer coating raw material comprises polyvinylidene fluoride, a solvent, a polyaniline-coated sulfur / carbon nanotube composite material and modified nano zirconium phosphate, and the mass ratio is 1:5-6:0.2-0.3:0.2-0.3. The outer layer coating raw material comprises polyvinylidene fluoride, a solvent and modified nano zirconium phosphate, and the mass ratio is 1:5-6:0.4-0.7. The lithium battery positive electrode protective coating provided by the application has excellent heat resistance and chemical resistance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium batteries, in particular to a high-stability protective coating for a lithium battery positive electrode and a preparation method thereof. BACKGROUND

[0002] Lithium batteries are a high-performance and environmentally friendly battery technology that is favored for its high energy density, long cycle life and stable power output. Compared with traditional alkaline batteries and nickel-hydrogen batteries, lithium batteries not only provide more durable and stable power support, but also have a lighter volume and weight, greatly improving portability and use convenience. The core components of lithium batteries include positive electrode materials, negative electrode materials, electrolytes, separators and housings. The positive electrode material is a key component of lithium batteries, and its performance directly affects the energy density, cycle life and safety of the battery. Common positive electrode materials include lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), lithium manganate (LiMn2O4) and ternary materials (such as lithium nickel cobalt manganate).

[0003] With the popularity of electric vehicles and portable electronic devices, lithium ion batteries have become the main choice in the energy storage field. Among them, the performance of the positive electrode material plays a crucial role in the performance and cycle life of the battery. During the battery manufacturing process, adding a protective coating layer to the surface of the positive electrode sheet is an effective method to improve safety performance. However, in actual applications, common positive electrode protective coatings have some problems, such as poor dispersion effect, insufficient adhesion, and easy peeling after long-term soaking in electrolyte. These problems seriously affect the improvement effect of the positive electrode protective coating on the safety performance of the battery. SUMMARY

[0004] In order to provide a high-stability protective coating for a lithium battery positive electrode, the application provides a high-stability protective coating for a lithium battery positive electrode and a preparation method thereof.

[0005] The application provides a high-stability protective coating for a lithium battery positive electrode, which adopts the following technical scheme:

[0006] A high-stability protective coating for a lithium battery positive electrode, the coating includes an inner layer coating, a transition layer coating and an outer layer coating; the inner layer coating raw materials include polyvinylidene fluoride, solvent, polyphenylamine coated sulfur / carbon nanotube composite material, with a mass ratio of 1:5-6:0.3-0.6; the transition layer coating raw materials include polyvinylidene fluoride, solvent, polyphenylamine coated sulfur / carbon nanotube composite material, modified nano zirconium phosphate, with a mass ratio of 1:5-6:0.2-0.3:0.2-0.3; the outer layer coating raw materials include polyvinylidene fluoride, solvent, modified nano zirconium phosphate, with a mass ratio of 1:5-6:0.4-0.7.

[0007] Preferably, the polyaniline-coated sulfur / carbon nanotube composite is prepared from the following raw materials by weight: 2-3 parts of sulfur / carbon nanotube composite, 0.3-0.6 parts of 5-sulfosalicylic acid doped polyaniline, 95-190 parts of N,N-dimethylformamide.

[0008] Preferably, the sulfur / carbon nanotube composite is prepared from the following raw materials by weight: 16-24 parts of sulfur, 4-6 parts of carbon nanotube, 40-60 parts of anhydrous ethanol.

[0009] Preferably, the 5-sulfosalicylic acid doped polyaniline is prepared from the following raw materials by weight: 1.02-2.04 parts of 5-sulfosalicylic acid, 200-400 parts of water, 0.042-0.084 parts of aniline, 0.15-0.3 parts of ammonium persulfate.

[0010] Preferably, the method for preparing the polyaniline-coated sulfur / carbon nanotube composite comprises the following steps:

[0011] By weight, 16-24 parts of sulfur and 4-6 parts of carbon nanotube are added to a ball mill tank, 40-60 parts of anhydrous ethanol is added at the same time, then ball milling is carried out at a ball milling speed of 350-450 rpm for 5-6 h to obtain a mixture of sulfur and carbon nanotube; the mixture is dried in a constant temperature air drying oven at 55-65 ℃ and ground, then transferred to a hydrothermal reaction kettle, and heated at 155-165 ℃ for 12-14 h under inert gas protection, cooled to room temperature after the reaction is completed, and ground to obtain a sulfur / carbon nanotube composite.

[0012] Preferably, the method for preparing the 5-sulfosalicylic acid doped polyaniline comprises the following steps:

[0013] By weight, 1.02-2.04 parts of 5-sulfosalicylic acid is added to 150-300 parts of water, stirred until completely dissolved to obtain a 5-sulfosalicylic acid solution, then 0.042-0.084 parts of aniline is added and mixed uniformly, and deoxygenated by nitrogen at 20-30 ℃ for 15-20 min; 0.15-0.3 parts of ammonium persulfate is added to 50-100 parts of water, stirred until completely dissolved, then slowly added to the system, and reacted for 6-8 h; the obtained product is filtered, washed with methanol to remove residual impurities, washed with water until neutral, and vacuum dried at 70-80 ℃ for 24-30 h to obtain 5-sulfosalicylic acid doped polyaniline.

[0014] Preferably, the method for preparing the polyaniline-coated sulfur / carbon nanotube composite comprises the following steps:

[0015] 0.3-0.6 parts of 5-sulfosalicylic acid doped polyaniline and 20-40 parts of N,N-dimethylformamide are added to 2-3 parts of sulfur / carbon nanotube composite by weight, and ball milling is carried out in a ball mill at a rotating speed of 200-300 rpm for 1-2 h; 70-150 parts of N,N-dimethylformamide are added to the obtained mixture, which is uniformly dispersed by stirring, to obtain a suspension, and the suspension is subjected to spray drying treatment to obtain a polyaniline-coated sulfur / carbon nanotube composite.

[0016] The spray drying treatment is carried out under the following conditions: atomization pressure 0.14-16 MPa, needle pressure 0.2-0.3 MPa, air inlet temperature 155-165℃, and feeding speed 13-17 mL / min.

[0017] Preferably, the modified nanometer zirconium phosphate is prepared from the following raw materials by weight: 9-18 parts of phosphoric acid, 13-26 parts of water, 2-3 parts of graphene oxide, and 1-2 parts of zirconium oxychloride octahydrate.

[0018] Preferably, the preparation method of the modified nanometer zirconium phosphate comprises the following steps:

[0019] Preferably, the preparation method of the modified nanometer zirconium phosphate comprises the following steps:

[0020] The application provides a preparation method of a high-stability protective coating for a lithium battery positive electrode.

[0021] The preparation method of a high-stability protective coating for a lithium battery positive electrode comprises the following steps:

[0022] The raw materials of each layer are weighed according to the mass ratio;

[0023] The polyvinylidene fluoride is added to the solvent, and after stirring until the polyvinylidene fluoride is fully dissolved, the polyaniline-coated sulfur / carbon nanotube composite is added, and stirring is performed at a dispersion speed of 400-600 rpm for 2-10 min to obtain the inner layer coating.

[0024] Polyvinylidene fluoride is added to the solvent, and after stirring until the polyvinylidene fluoride is fully dissolved, the polyaniline-coated sulfur / carbon nanotube composite material is added, and stirred at a dispersion speed of 400-600 rpm for 2-10 min; then modified nano-zirconium phosphate is added, and stirred at a dispersion speed of 400-600 rpm for 2-10 min, to obtain the transition layer coating;

[0025] Polyvinylidene fluoride is added to the solvent, and after stirring until the polyvinylidene fluoride is fully dissolved, the modified nano-zirconium phosphate is added, and stirred at a dispersion speed of 400-600 rpm for 2-10 min, to obtain the outer layer coating.

[0026] In summary, the present application includes at least one of the following beneficial technical effects:

[0027] 1. The high-stability protective coating for the positive electrode of a lithium battery provided by the present application has a multi-layer structure. The polyaniline-coated sulfur / carbon nanotube composite material in the inner layer coating provides good electronic conductivity, helps to quickly conduct electrons, reduces the accumulation of electric charges inside the battery, and thus reduces the risk of thermal runaway. The addition of modified nano-zirconium phosphate in the transition layer coating enhances the chemical stability and mechanical strength of the coating, effectively inhibits the shuttle effect of polysulfides, reduces the side reactions between the electrolyte and the positive electrode material, and further improves the safety of the battery. The modified nano-zirconium phosphate in the outer layer coating serves as the main component, providing excellent chemical stability and mechanical protection, preventing the erosion of the electrolyte, and reducing the performance degradation of the battery in high-temperature or harsh environments. The transition layer between the inner and outer layers smoothly transitions the conductivity and insulation, avoiding stress concentration and performance mutation at the interface. DETAILED DESCRIPTION

[0028] The present application is further described below in conjunction with examples.

[0029] The chemical reagents used in the preparation examples, examples, and comparative examples provided by the present application are all commercially available.

[0030] Preparation Example 1: Preparation of polyaniline-coated sulfur / carbon nanotube composite material

[0031] Preparation Example 1.1

[0032] S1. Add 16 g of sulfur and 4 g of carbon nanotubes to a ball mill tank, and at the same time, add 40 g of anhydrous ethanol, then ball mill at a speed of 350 rpm for 5 h to obtain a mixture of sulfur and carbon nanotubes; transfer the mixture to a hydrothermal reaction kettle after drying in a constant temperature air drying oven at 55℃ and grinding, and heat at 155℃ under inert gas protection for 12 h. After the reaction is completed, cool to room temperature, and grind to obtain a sulfur / carbon nanotube composite material with a core-shell structure;

[0033] S2. 1.02 g of 5-sulfosalicylic acid was added to 150 g of deionized water, stirred until completely dissolved to obtain a 5-sulfosalicylic acid solution, then 0.042 g of aniline was mixed uniformly, and then deoxygenated by nitrogen at 20°C for 15 min; 0.15 g of ammonium persulfate was added to 50 g of deionized water, stirred until completely dissolved, then slowly added to the system, and reacted for 6 h; the product was filtered, washed with methanol to remove residual impurities, washed with deionized water until neutral, and vacuum dried at 70°C for 30 h to obtain 5-sulfosalicylic acid doped polyaniline;

[0034] S3. 0.3 g of 5-sulfosalicylic acid doped polyaniline prepared in S2 was added to 2 g of sulfur / carbon nanotube composite prepared in S1, and 20 g of N,N-dimethylformamide was added, and then ball-milled at a speed of 200 rpm for 1 h; 70 g of N,N-dimethylformamide was added to the obtained mixture, stirred and dispersed uniformly to obtain a suspension, and then the suspension was subjected to spray drying treatment under the following conditions: atomization pressure 0.14 MPa, needle pressure 0.2 MPa, inlet air temperature 155°C, and feeding speed 13 mL / min, to obtain a polyaniline-coated sulfur / carbon nanotube composite.

[0035] Preparation Example 1.2

[0036] S1. 20 g of sulfur and 5 g of carbon nanotubes were added to a ball mill tank, 50 g of anhydrous ethanol was added, and then ball-milled at a speed of 400 rpm for 5.5 h to obtain a mixture of sulfur and carbon nanotubes; the mixture was dried in a constant temperature air drying oven at 60°C and ground, then transferred to a hydrothermal reaction kettle, and heated at 160°C for 13 h under inert gas protection, cooled to room temperature after the reaction was completed, and then ground to obtain a sulfur / carbon nanotube composite with a core-shell structure;

[0037] S2. 1.53 g of 5-sulfosalicylic acid was added to 225 g of deionized water, stirred until completely dissolved to obtain a 5-sulfosalicylic acid solution, then 0.063 g of aniline was mixed uniformly, and then deoxygenated by nitrogen at 25°C for 18 min; 0.225 g of ammonium persulfate was added to 75 g of deionized water, stirred until completely dissolved, then slowly added to the system, and reacted for 7 h; the product was filtered, washed with methanol to remove residual impurities, washed with deionized water until neutral, and vacuum dried at 75°C for 27 h to obtain 5-sulfosalicylic acid doped polyaniline;

[0038] S3. To 2.5 g of the sulfur / carbon nanotube composite material prepared in S1, 0.45 g of the 5-sulfosalicylic acid doped polyaniline prepared in S2 and 30 g of N,N-dimethylformamide were added, and ball-milling was performed at a rotation speed of 250 rpm for 1.5 h; 110 g of N,N-dimethylformamide was added to the obtained mixture, and the mixture was stirred and dispersed uniformly to obtain a suspension, and the suspension was subjected to spray drying treatment under the conditions that the atomization pressure was 0.15 MPa, the needle pressure was 0.25 MPa, the air inlet temperature was 160 ℃, and the feeding speed was 15 mL / min, thereby obtaining the polyaniline-coated sulfur / carbon nanotube composite material.

[0039] Preparation Example 1.3

[0040] S1. 24 g of sulfur and 6 g of carbon nanotubes were added to a ball mill tank, 60 g of anhydrous ethanol was added at the same time, and then ball-milling was performed at a ball-milling speed of 450 rpm for 6 h to obtain a mixture of sulfur and carbon nanotubes; the mixture was dried in a constant-temperature air-drying oven at 65 ℃ and ground, and then transferred to a hydrothermal reaction kettle and heated at 165 ℃ for 14 h under inert gas protection, cooled to room temperature after the reaction was completed, and ground to obtain a sulfur / carbon nanotube composite material with a core-shell structure;

[0041] S2. 2.045 g of 5-sulfosalicylic acid was added to 300 g of deionized water, stirred until completely dissolved to obtain a 5-sulfosalicylic acid solution, and then 0.084 g of aniline was added and mixed uniformly, and nitrogen was introduced to remove oxygen at 30 ℃ for 20 min; 0.3 g of ammonium persulfate was added to 100 g of deionized water, stirred until completely dissolved, and then slowly added to the system, and reacted for 8 h; the obtained product was filtered, washed with methanol to remove residual impurities, washed with deionized water until neutral, and vacuum dried at 80 ℃ for 24 h, thereby obtaining 5-sulfosalicylic acid doped polyaniline;

[0042] S3. To 3 g of the sulfur / carbon nanotube composite material prepared in S1, 0.6 g of the 5-sulfosalicylic acid doped polyaniline prepared in S2 and 40 g of N,N-dimethylformamide were added, and ball-milling was performed at a rotation speed of 300 rpm for 2 h; 150 g of N,N-dimethylformamide was added to the obtained mixture, and the mixture was stirred and dispersed uniformly to obtain a suspension, and the suspension was subjected to spray drying treatment under the conditions that the atomization pressure was 0.16 MPa, the needle pressure was 0.3 MPa, the air inlet temperature was 165 ℃, and the feeding speed was 17 mL / min, thereby obtaining the polyaniline-coated sulfur / carbon nanotube composite material.

[0043] Preparation Example 2 Preparation of modified nano-zirconium phosphate

[0044] Preparation Example 2.1

[0045] Mixing 9 g of phosphoric acid, 13 g of deionized water, and 2 g of graphene oxide, ultrasonic dispersion for 40 min, then add 1 g of zirconium oxychloride octahydrate, stir uniformly and place in a hydrothermal reaction kettle, heat at 180℃ in an oven for 5h; after the reaction is completed, cool to room temperature, centrifugal collection of the product, and resuspended with deionized water, repeat 3 times, then wash the sample with ethanol, then dry the product in an oven at 60℃ for 30h, after grinding, modified nano zirconium phosphate is obtained.

[0046] Preparation Example 2.2

[0047] Mixing 13.5 g of phosphoric acid, 20.5 g of deionized water, and 2.5 g of graphene oxide, ultrasonic dispersion for 50 min, then add 1.5 g of zirconium oxychloride octahydrate, stir uniformly and place in a hydrothermal reaction kettle, heat at 200℃ in an oven for 6h; after the reaction is completed, cool to room temperature, centrifugal collection of the product, and resuspended with deionized water, repeat 4 times, then wash the sample with ethanol, then dry the product in an oven at 65℃ for 27h, after grinding, modified nano zirconium phosphate is obtained.

[0048] Preparation Example 2.3

[0049] Mixing 18 g of phosphoric acid, 26 g of deionized water, and 3 g of graphene oxide, ultrasonic dispersion for 60 min, then add 2 g of zirconium oxychloride octahydrate, stir uniformly and place in a hydrothermal reaction kettle, heat at 220℃ in an oven for 7h; after the reaction is completed, cool to room temperature, centrifugal collection of the product, and resuspended with deionized water, repeat 5 times, then wash the sample with ethanol, then dry the product in an oven at 70℃ for 24h, after grinding, modified nano zirconium phosphate is obtained.

[0050] Example 1

[0051] S1. In a stirring tank, 10 g of β-crystal polyvinylidene fluoride with a molecular weight of 400-500 million is added to 50 g of solvent N-methyl pyrrolidone, after stirring until the polyvinylidene fluoride is fully dissolved, 3 g of polyaniline coated sulfur / carbon nanotube composite material prepared by preparation example 1.1 is added, and stirred at a dispersion speed of 400 rpm for 10 min; control the vacuum degree inside the stirring tank ≤-90 kPa, the temperature inside the stirring tank ≤60℃; the inner layer coating is obtained;

[0052] S2. In a stirring tank, 10g of β crystal form polyvinylidene fluoride with a molecular weight of 400-500 million was added to 50g of solvent N-methyl pyrrolidone, after stirring until the polyvinylidene fluoride was fully dissolved, 2g of the polyamine coated sulfur / carbon nanotube composite material prepared in Preparation Example 1.1 was added, and stirred at a dispersion speed of 400rpm for 10min; then 2g of the modified nano-zirconium phosphate prepared in Preparation Example 2.1 was added, and stirred at a dispersion speed of 400rpm for 10min, the vacuum degree inside the stirring tank was controlled to be ≤-90kPa, and the temperature inside the stirring tank was controlled to be ≤60℃; thus a transition layer coating was obtained;

[0053] S3. In a stirring tank, 10g of β crystal form polyvinylidene fluoride with a molecular weight of 400-500 million was added to 50g of solvent N-methyl pyrrolidone, after stirring until the polyvinylidene fluoride was fully dissolved, 4g of the modified nano-zirconium phosphate prepared in Preparation Example 2.1 was added, and stirred at a dispersion speed of 400rpm for 10min, the vacuum degree inside the stirring tank was controlled to be ≤-90kPa, and the temperature inside the stirring tank was controlled to be ≤60℃; thus an outer layer coating was obtained.

[0054] Example 2

[0055] S1. In a stirring tank, 10g of β crystal form polyvinylidene fluoride with a molecular weight of 400-500 million was added to 50g of solvent N-methyl pyrrolidone, after stirring until the polyvinylidene fluoride was fully dissolved, 3g of the polyamine coated sulfur / carbon nanotube composite material prepared in Preparation Example 1.2 was added, and stirred at a dispersion speed of 500rpm for 6min; the vacuum degree inside the stirring tank was controlled to be ≤-90kPa, and the temperature inside the stirring tank was controlled to be ≤60℃; thus an inner layer coating was obtained;

[0056] S2. In a stirring tank, 10g of β crystal form polyvinylidene fluoride with a molecular weight of 400-500 million was added to 50g of solvent N-methyl pyrrolidone, after stirring until the polyvinylidene fluoride was fully dissolved, 2g of the polyamine coated sulfur / carbon nanotube composite material prepared in Preparation Example 1.2 was added, and stirred at a dispersion speed of 500rpm for 6min; then 2g of the modified nano-zirconium phosphate prepared in Preparation Example 2.2 was added, and stirred at a dispersion speed of 500rpm for 6min, the vacuum degree inside the stirring tank was controlled to be ≤-90kPa, and the temperature inside the stirring tank was controlled to be ≤60℃; thus a transition layer coating was obtained;

[0057] S3. In a stirring tank, 10g of β crystal form polyvinylidene fluoride with a molecular weight of 400-500 million was added to 50g of solvent N-methyl pyrrolidone, after stirring until the polyvinylidene fluoride was fully dissolved, 4g of the modified nano-zirconium phosphate prepared in Preparation Example 2.2 was added, and stirred at a dispersion speed of 500rpm for 6min, the vacuum degree inside the stirring tank was controlled to be ≤-90kPa, and the temperature inside the stirring tank was controlled to be ≤60℃; thus an outer layer coating was obtained.

[0058] Example 3

[0059] S1. In a stirring tank, 10 g of β crystal form polyvinylidene fluoride with a molecular weight of 400-500 million was added to 50 g of solvent N-methyl pyrrolidone, and after stirring until the polyvinylidene fluoride was fully dissolved, 3 g of the polyaniline-coated sulfur / carbon nanotube composite material prepared in Preparation Example 1.3 was added, and stirred at a dispersion speed of 600 rpm for 2 min; the vacuum degree inside the stirring tank was controlled to be ≤-90 kPa, and the temperature inside the stirring tank was controlled to be ≤60℃; thus an inner layer coating was obtained;

[0060] S2. In a stirring tank, 10 g of β crystal form polyvinylidene fluoride with a molecular weight of 400-500 million was added to 50 g of solvent N-methyl pyrrolidone, and after stirring until the polyvinylidene fluoride was fully dissolved, 2 g of the polyaniline-coated sulfur / carbon nanotube composite material prepared in Preparation Example 1.3 was added, and stirred at a dispersion speed of 600 rpm for 2 min; then 2 g of the modified nano-zirconium phosphate prepared in Preparation Example 2.3 was added, and stirred at a dispersion speed of 600 rpm for 2 min, and the vacuum degree inside the stirring tank was controlled to be ≤-90 kPa, and the temperature inside the stirring tank was controlled to be ≤60℃; thus a transition layer coating was obtained;

[0061] S3. In a stirring tank, 10 g of β crystal form polyvinylidene fluoride with a molecular weight of 400-500 million was added to 50 g of solvent N-methyl pyrrolidone, and after stirring until the polyvinylidene fluoride was fully dissolved, 4 g of the modified nano-zirconium phosphate prepared in Preparation Example 2.3 was added, and stirred at a dispersion speed of 600 rpm for 2 min, and the vacuum degree inside the stirring tank was controlled to be ≤-90 kPa, and the temperature inside the stirring tank was controlled to be ≤60℃; thus an outer layer coating was obtained.

[0062] Example 4

[0063] Example 4 differs from Example 1 in that the mass of N-methyl pyrrolidone used in S1 in Example 4 is 55 g; and the mass of the polyaniline-coated sulfur / carbon nanotube composite material prepared in Preparation Example 1.1 is 4.5 g.

[0064] Example 5

[0065] Example 5 differs from Example 1 in that the mass of N-methyl pyrrolidone used in S1 in Example 5 is 60 g; and the mass of the polyaniline-coated sulfur / carbon nanotube composite material prepared in Preparation Example 1.1 is 6 g.

[0066] Example 6

[0067] Example 6 differs from Example 1 in that the mass of N-methylpyrrolidone employed in S2 in Example 6 is 55 g; the mass of the polyaniline-coated sulfur / carbon nanotube composite prepared from Preparation Example 1.1 is 2.5 g; and the mass of the modified nano-zirconium phosphate prepared from Preparation Example 2.1 is 2.5 g.

[0068] Example 7

[0069] Example 7 differs from Example 1 in that the mass of N-methylpyrrolidone employed in S2 in Example 7 is 60 g; the mass of the polyaniline-coated sulfur / carbon nanotube composite prepared from Preparation Example 1.1 is 3 g; and the mass of the modified nano-zirconium phosphate prepared from Preparation Example 2.1 is 3 g.

[0070] Example 8

[0071] Example 8 differs from Example 1 in that the mass of N-methylpyrrolidone employed in S3 in Example 8 is 55 g; and the mass of the modified nano-zirconium phosphate prepared from Preparation Example 2.1 is 5.5 g.

[0072] Example 9

[0073] Example 9 differs from Example 1 in that the mass of N-methylpyrrolidone employed in S3 in Example 9 is 60 g; and the mass of the modified nano-zirconium phosphate prepared from Preparation Example 2.1 is 7 g.

[0074] Comparative Example 1

[0075] Comparative Example 1 differs from Example 1 in that the mass of N-methylpyrrolidone employed in S1 in Comparative Example 1 is 40 g; and the mass of the polyaniline-coated sulfur / carbon nanotube composite prepared from Preparation Example 1.1 is 1.5 g.

[0076] Comparative Example 2

[0077] Comparative Example 2 differs from Example 1 in that the mass of N-methylpyrrolidone employed in S1 in Comparative Example 2 is 70 g; and the mass of the polyaniline-coated sulfur / carbon nanotube composite prepared from Preparation Example 1.1 is 7.5 g.

[0078] Comparative Example 3

[0079] Comparative Example 3 differs from Example 1 in that the mass of N-methylpyrrolidone employed in S2 in Comparative Example 3 is 40 g; the mass of the polyaniline-coated sulfur / carbon nanotube composite prepared from Preparation Example 1.1 is 1 g; and the mass of the modified nano-zirconium phosphate prepared from Preparation Example 2.1 is 1 g.

[0080] Comparative Example 4

[0081] Comparative Example 4 differs from Example 1 in that the mass of N-methylpyrrolidone used in S2 in Comparative Example 4 is 70 g; the mass of the polyaniline-coated sulfur / carbon nanotube composite prepared from Preparation Example 1.1 is 4 g; and the mass of the modified nano-zirconium phosphate prepared from Preparation Example 2.1 is 4 g.

[0082] Comparative Example 5

[0083] Comparative Example 5 differs from Example 1 in that the mass of N-methylpyrrolidone used in S3 in Comparative Example 5 is 40 g; and the mass of the modified nano-zirconium phosphate prepared from Preparation Example 2.1 is 2.5 g.

[0084] Comparative Example 6

[0085] Comparative Example 6 differs from Example 1 in that the mass of N-methylpyrrolidone used in S3 in Comparative Example 6 is 70 g; and the mass of the modified nano-zirconium phosphate prepared from Preparation Example 2.1 is 8.5 g.

[0086] Comparative Example 7

[0087] Comparative Example 7 differs from Example 1 in that the polyaniline-coated sulfur / carbon nanotube composite in Comparative Example 7 is replaced with an equal amount of carbon nanotubes.

[0088] Comparative Example 8

[0089] Comparative Example 8 differs from Example 1 in that the modified nano-zirconium phosphate in Comparative Example 8 is replaced with an equal amount of nano-zirconium phosphate.

[0090] Performance detection test

[0091] The protective coatings obtained from Examples 1-9 and Comparative Examples 1-8 were coated on the surface of the positive electrode material, with an inner layer thickness of 10 μm; a transition layer thickness of 15 μm; and an outer layer thickness of 20 μm, and the following performance detection was carried out:

[0092] I. Peeling strength: The peeling strength was detected in accordance with the ASTM D3359-23 standard, and the results are shown in Table 1.

[0093] II. High temperature resistance performance detection: The positive electrode material coated with the protective coating was placed in a constant temperature drying oven at 85°C for storage for 48 h, and then the peeling strength was detected again, and the peeling strength reduction rate was recorded, and the results are shown in Table 1.

[0094] III. Chemical resistance performance detection: The positive electrode material coated with the protective coating was immersed in an electrolyte for 72 h, and then the peeling strength was detected again, and the peeling strength reduction rate was recorded, and the results are shown in Table 1.

[0095] The specific detection results are as follows:

[0096] Table 1 Performance test results

[0097] Peeling strength / (N / mm) 85°C, 48h, % of decrease in peeling strength % of decrease in peeling strength after immersion in electrolyte for 72h Example 1 1.92 3.5 0.91 Example 2 1.96 3.1 0.87 Example 3 1.87 3.7 0.89 Example 4 1.97 3.0 0.86 Example 5 1.94 3.2 0.90 Example 6 1.99 2.8 0.81 Example 7 1.95 3.0 0.87 Example 8 1.96 3.1 0.84 Example 9 1.93 3.3 0.92 Comparative Example 1 1.55 7.2 1.23 Comparative Example 2 1.65 6.9 1.45 Comparative Example 3 1.62 7.8 1.56 Comparative Example 4 1.54 8.1 1.77 Comparative Example 5 1.47 7.2 1.69 Comparative Example 6 1.50 6.6 1.81 Comparative Example 7 1.12 9.1 2.71 Comparative Example 8 1.33 12.3 2.95

[0098] As can be seen from the test results in Table 1, in the examples, the peeling strength of the protective coating for the positive electrode of the lithium battery provided by the application can reach 1.85 N / mm or more, and the peeling strength decrease rate is less than 4% after 48 h storage in a constant temperature drying oven at 85°C, indicating that the protective coating for the positive electrode of the lithium battery provided by the application has high thermal stability; the peeling strength decrease rate is less than 1% after 72 h immersion in the electrolyte, indicating that the protective coating for the positive electrode of the lithium battery provided by the application has high chemical stability.

[0099] The specific embodiments are only an explanation of the application, and are not a limitation of the application, and those skilled in the art can make modifications to the embodiments without creative contribution according to the needs after reading the specification, but as long as the modifications are within the scope of the claims of the application, they are protected by the Patent Law.

Claims

1. A high-stability protective coating for a lithium battery cathode, characterized by: The coating includes an inner layer coating, a transition layer coating and an outer layer coating; the inner layer coating raw material includes polyvinylidene fluoride, solvent, polyphenylamine coated sulfur / carbon nanotube composite material, and the mass ratio is 1:5-6:0.3-0.6; the transition layer coating raw material includes polyvinylidene fluoride, solvent, polyphenylamine coated sulfur / carbon nanotube composite material, modified nano zirconium phosphate, and the mass ratio is 1:5-6:0.2-0.3:0.2-0.3; the outer layer coating raw material includes polyvinylidene fluoride, solvent, modified nano zirconium phosphate, and the mass ratio is 1:5-6:0.4-0.7; The polyphenylamine coated sulfur / carbon nanotube composite material is prepared from the following raw materials by weight: 2-3 parts of sulfur / carbon nanotube composite material, 0.3-0.6 parts of 5-sulfosalicylic acid doped polyaniline, and 95-190 parts of N,N-dimethylformamide; The preparation method of the polyphenylamine coated sulfur / carbon nanotube composite material includes the following steps: The 5-sulfosalicylic acid doped polyaniline is prepared from the following raw materials by weight: 1.02-2.04 parts of 5-sulfosalicylic acid, 200-400 parts of water, 0.042-0.084 parts of aniline, and 0.15-0.3 parts of ammonium persulfate. The preparation method of the polyphenylamine coated sulfur / carbon nanotube composite material includes the following steps:

2. A high stability protective coating for lithium battery cathode as claimed in claim 1, wherein: The 5-sulfosalicylic acid doped polyaniline is prepared from the following raw materials by weight: 1.02-2.04 parts of 5-sulfosalicylic acid, 200-400 parts of water, 0.042-0.084 parts of aniline, and 0.15-0.3 parts of ammonium persulfate.

3. A high stability protective coating for lithium battery cathode as claimed in claim 1, wherein: The preparation method of the polyphenylamine coated sulfur / carbon nanotube composite material includes the following steps:

4. A high stability protective coating for lithium battery cathode as claimed in claim 2, wherein: The 5-sulfosalicylic acid doped polyaniline is prepared from the following raw materials by weight: 1.02-2.04 parts of 5-sulfosalicylic acid, 200-400 parts of water, 0.042-0.084 parts of aniline, and 0.15-0.3 parts of ammonium persulfate. The preparation method of the polyphenylamine coated sulfur / carbon nanotube composite material includes the following steps:

5. A high stability protective coating for lithium battery cathodes according to claim 3, characterized in that: The 5-sulfosalicylic acid doped polyaniline is prepared from the following raw materials by weight: 1.02-2.04 parts of 5-sulfosalicylic acid, 200-400 parts of water, 0.042-0.084 parts of aniline, and 0.15-0.3 parts of ammonium persulfate. According to parts by weight, 1.02-2.04 parts of 5-sulfosalicylic acid is added to 150-300 parts of water, stirred to completely dissolved to obtain 5-sulfosalicylic acid solution, then 0.042-0.084 parts of aniline is mixed uniformly, and then oxygen is removed by nitrogen at 20-30 DEG C for 15-20 min; 0.15-0.3 parts of ammonium persulfate is added to 50-100 parts of water, stirred to completely dissolved, then slowly added to the system, and reacted for 6-8 h; the obtained product is filtered, washed with methanol to remove the remaining impurities, washed with water until neutral, and vacuum dried at 70-80 DEG C for 24-30 h to obtain 5-sulfosalicylic acid doped polyaniline.

6. A high stability protective coating for lithium battery cathodes according to claim 1, characterized in that: The modified nano zirconium phosphate is prepared from the following raw materials by weight: 9-18 parts of phosphoric acid, 13-26 parts of water, 2-3 parts of graphene oxide, and 1-2 parts of zirconium oxychloride octahydrate.

7. A high stability protective coating for lithium battery cathodes according to claim 6, characterized in that: The preparation method of the modified nano zirconium phosphate comprises the following steps: According to parts by weight, 9-18 parts of phosphoric acid, 13-26 parts of water, and 2-3 parts of graphene oxide are mixed, ultrasonic dispersion is carried out for 40-60 min, then 1-2 parts of zirconium oxychloride octahydrate is added, stirred uniformly, and then placed in a hydrothermal reaction kettle, and reacted at 180-220 DEG C in an oven for 5-7 h; after the reaction is completed, it is cooled to room temperature, the product is collected by centrifugation, resuspended with water, repeated for several times, the sample is washed with ethanol, then the product is dried in an oven at 60-70 DEG C for 24-30 h, and the modified nano zirconium phosphate is obtained after grinding.

8. The method for preparing a high-stability protective coating for a lithium battery positive electrode according to any one of claims 1-7, characterized in that: Comprise the following steps: The raw materials of each layer are weighed according to the mass ratio; Polyvinylidene fluoride is added to the solvent, stirred until the polyvinylidene fluoride is completely dissolved, then the polyaniline-coated sulfur / carbon nanotube composite material is added, and stirred at a dispersion speed of 400-600 rpm for 2-10 min; to obtain the inner layer coating; Polyvinylidene fluoride is added to the solvent, stirred until the polyvinylidene fluoride is completely dissolved, then the polyaniline-coated sulfur / carbon nanotube composite material is added, and stirred at a dispersion speed of 400-600 rpm for 2-10 min; then the modified nano zirconium phosphate is added, and stirred at a dispersion speed of 400-600 rpm for 2-10 min; to obtain the transition layer coating; Polyvinylidene fluoride is added to the solvent, stirred until the polyvinylidene fluoride is completely dissolved, then the modified nano zirconium phosphate is added, and stirred at a dispersion speed of 400-600 rpm for 2-10 min; to obtain the outer layer coating.