Preparation method of polymer microspheres

Abstract

The invention provides a preparation method of polymer microspheres, an electric negative electrode coating prepared from the polymer microspheres and a battery electric negative electrode. According to the method, polyvinyl alcohol is grafted and modified through carbon nanofibers, so that the elongation at break of the coating is improved, and the high-capacity retention rate of a battery negative electrode is improved; coating electrolyte swelling is inhibited through the carboxylated styrene-butadiene copolymer, and the peeling strength of the coating is improved; through the synergistic effect of polyallylamine hydrochloride and phytic acid, the crack density of the coating is reduced, and the capacity retention ratio of the negative electrode of the battery is improved; the elasticity modulus of the coating is improved through glyoxal polyacrylamide, the crack density of the coating is reduced, and the capacity retention rate of the battery negative electrode is improved; and the peel strength of the coating is improved through fluorinated polyvinyl alcohol, and the capacity retention rate of the battery negative electrode is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer materials, and particularly relates to a preparation method of high polymer microspheres. BACKGROUND

[0002] With the rapid development of electric vehicles and large-scale energy storage systems, higher requirements are put forward for the energy density, cycle life and safety of lithium ion batteries. Silicon-based materials are considered as the core candidate materials for the next generation of high-energy-density anodes due to their ultra-high theoretical specific capacity. However, silicon materials have a huge volume change during lithium ion intercalation / deintercalation, which leads to mechanical stress concentration of electrode structure, active material powdering and falling off, repeated rupture and reconstruction of solid-state electrolyte interface film, and finally causes rapid capacity decay and short cycle life.

[0003] Traditional polyvinylidene fluoride (PVDF) based polymer materials as electrode coating face great challenges:

[0004] (1) Insufficient mechanical adaptability: PVDF has low elastic modulus and limited ductility, which cannot effectively buffer the volume expansion stress of silicon particles, leading to micro-cracks in the electrode and gradual expansion, which destroys the integrity of the conductive network.

[0005] (2) Poor interface stability: The adhesion of PVDF to silicon particles and current collectors (such as copper foil) mainly depends on van der Waals force, which is prone to active material falling off, interface peeling and current collector separation under repeated volume changes, leading to rapid cycle capacity decay.

[0006] (3) Limited electrochemical window: PVDF is prone to electrochemical oxidation and decomposition at high potentials, and has a high swelling rate in electrolyte, especially in carbonate solvents, which exacerbates side reactions and reduces interface stability.

[0007] (4) High temperature performance defects: PVDF has limited thermal stability and may promote heat diffusion in thermal runaway scenarios, posing a safety hazard.

[0008] (5) Not resistant to electrolyte swelling: Swelling will directly cause the relaxation of the binder, weaken its binding force to the active particles, and cause particle separation and falling off; at the same time, swelling will also reduce the adhesion of the binder to the current collector, and may induce cracks in the electrode, reducing the effective porosity and ion transport efficiency of the electrode.

[0009] To solve the above problems, researchers have tried alternative solutions such as water-based polymer microsphere materials (such as carboxymethyl cellulose / styrene-butadiene rubber system), polyacrylic acid, and polyimide, but still have the following limitations:

[0010] (1) Water-based polymer microsphere materials as electrode coating are prone to metal ion leaching and interface side reactions in high voltage applications.

[0011] (2) Most high polymer materials are difficult to balance high adhesive strength, moderate elastic modulus and electrochemical inertness.

[0012] (3) Single component water-based polymer microsphere material cannot meet the multiple requirements of silicon negative electrode (stress buffering, interface bonding, electrolyte stability) simultaneously.

[0013] Therefore, it is of great significance to develop a new type of multifunctional and high polymer microsphere material by molecular design, component cooperation to adapt to silicon-based negative electrode material. SUMMARY

[0014] In order to solve the above problems, the first aspect of the present application provides a preparation method of polymer microspheres, comprising the following steps:

[0015] Step S1, carboxylated modified carbon nanofiber: carbon nanofiber is added to a mixed acid solution for oxidation reaction, the filter cake is collected by filtration, and the filter cake is washed and dried to obtain carboxylated carbon nanofiber A;

[0016] Step S2, acyl chloride modified carbon nanofiber: carboxylated carbon nanofiber A is dispersed in a thionyl chloride solution, and an acyl chloride reaction is carried out under nitrogen protection, the filter cake is collected by filtration, and the filter cake is washed and dried to obtain carbon nanofiber B;

[0017] Step S3, grafting modified fluorinated polyvinyl alcohol: fluorinated polyvinyl alcohol is dissolved in N,N-dimethylacetamide to prepare solution C; carbon nanofiber B and triethylamine are added to solution C to carry out grafting reaction, and reaction liquid D is obtained; reaction liquid D is added to ethanol, and the precipitate is collected and dried to prepare modified fluorinated polyvinyl alcohol E; modified fluorinated polyvinyl alcohol E is dispersed in water to prepare solution F;

[0018] Step S4, add glyoxalated polyacrylamide: glyoxalated polyacrylamide is dispersed in solution F to prepare solution G;

[0019] Step S5, add carboxylated styrene-butadiene copolymer: carboxylated styrene-butadiene copolymer is dispersed in solution G to prepare solution H;

[0020] Step S6, add polyacrylic acid: polyacrylic acid is dispersed in solution H to prepare solution I;

[0021] Step S7, add hydrochloric acid polyallylamine and phytic acid: hydrochloric acid polyallylamine and phytic acid are dispersed in solution I, and the pH value is adjusted to prepare hydrogel J;

[0022] Step S8, prepare microspheres: graphene and silicon-containing negative electrode material are added to hydrogel J, uniformly dispersed to prepare slurry K, and slurry K is dried and ground to prepare microspheres.

[0023] As a preferred technical solution, the mass ratio of the carbon nanofiber and the mixed acid solution in step S1 is 1:(180-220); the diameter of the carbon nanofiber is 20-30 nm, and the length is 10-30 μm; the mixed acid solution is a mixture of H2SO4 and HNO3, and the volume ratio of H2SO4 to HNO3 is 3:1; the oxidation reaction temperature is 65-75 °C, and the oxidation reaction time is 5-6 h; the washing solution is purified water; the drying temperature is 75-85 °C, and the drying time is 24-30 h.

[0024] As a preferred technical solution, the mass ratio of the carbon nanofiber A and the thionyl chloride solution in step S2 is 1:(380-420); the solvent of the thionyl chloride solution is tetrahydrofuran, and the mass ratio of thionyl chloride to tetrahydrofuran is 1:(18-22); the acyl chloride reaction temperature is 65-70 °C, and the acyl chloride reaction time is 10-12 h; the washing solution is tetrahydrofuran; and the drying temperature is 75-85 °C, and the drying time is 24-30 h.

[0025] As a preferred technical solution, the mass ratio of the fluorinated polyvinyl alcohol and N,N-dimethylacetamide in step S3 is 1:(9-11); the mass ratio of the carbon nanofiber B, triethylamine, and fluorinated polyvinyl alcohol is 1:(0.4-0.6):(15-17); the grafting reaction temperature is 57-62 °C, and the grafting reaction time is 24-29 h; the mass ratio of the reaction liquid D to ethanol is 1:(70-75); the drying temperature is 75-85 °C, and the drying time is 24-30 h; the weight average molecular weight of the fluorinated polyvinyl alcohol is 85,000-95,000 Da, and the substitution degree of the hydroxyl group in the fluorinated polyvinyl alcohol is 15-25% (molar ratio); the mass concentration of the modified fluorinated polyvinyl alcohol E in the solution F is 5-5.5%; and the dispersion temperature is 65-75 °C, and the dispersion time is 24-28 h.

[0026] As a preferred technical solution, the preparation method of the fluorinated polyvinyl alcohol in step S3 is as follows: using high-purity (≥98%) 1H,1H,2H,2H-perfluorooctyl iodine as a fluorination reagent, and reacting with polyvinyl alcohol (molecular weight 85,000-95,000 Da) previously dissolved in anhydrous DMSO under nitrogen protection; first, the polyvinyl alcohol is prepared into a clear solution with a mass concentration of 10%, and after being warmed to 70±2 °C, a NaOH catalyst is added, and then the fluorination reagent is slowly added dropwise, and the molar ratio of the polyvinyl alcohol structural unit to the fluorination reagent is controlled to be 1:(0.15-0.25), and the reaction is carried out for 24 hours; and then, the -O-CH2-CH2-C8F 17The radicals are covalently grafted to the polyvinyl alcohol chain, and the target fluorination degree is controlled at 15% to 25%; after the reaction is completed, the mixture is cooled, poured into a mixed solution of acetone and ethanol, and precipitated, the volume ratio of acetone to ethanol is 1:1, and the by-products NaI and unreacted reagents are completely removed through Soxhlet extraction, and finally a white fibrous solid product is obtained through 80°C vacuum drying for 24 hours.

[0027] As a preferred technical solution, the mass concentration of the glyoxalated polyacrylamide in the solution G in the step S4 is 1.0% to 1.5%; the dispersion temperature is 60°C to 70°C, and the dispersion time is 24h to 28h.

[0028] As a preferred technical solution, the preparation process of the glyoxalated polyacrylamide in the step S4 is as follows: polyacrylamide with a molecular weight of 5000000Da to 6000000Da is dissolved in water to prepare a solution with a mass concentration of 2%, a 40% glyoxal aqueous solution is added, the molar ratio of glyoxal to amide group is about 1:8, acetic acid is used to adjust the pH value to 4.0±0.2, and reaction is carried out at 60°C to 70°C for 4 hours to 6 hours; during the reaction process, mechanical stirring (300rpm) is used to ensure uniform mixing; and finally, the product is purified through dialysis and freeze-dried to obtain a white solid.

[0029] As a preferred technical solution, the mass concentration of the carboxylated styrene-butadiene copolymer in the solution H in the step S5 is 1.2% to 1.8%; the dispersion temperature is 65°C to 75°C, and the dispersion time is 24h to 28h; the styrene-butadiene in the carboxylated styrene-butadiene copolymer is a random copolymer, the molecular weight is 200000Da to 300000Da; the molar ratio of styrene to butadiene is 1:3; the molar ratio of 1,4-structure in the butadiene segment is 70%; the carboxyl group (-COOH) is introduced on the double bond of the butadiene segment through a free radical grafting reaction, and the carboxyl group density is 0.8mmol / g to 1.2mmol / g.

[0030] As a preferred technical solution, the mass concentration of the polyacrylic acid in the solution I in the step S6 is 1.5% to 2.0%; the dispersion temperature is 65°C to 75°C, and the dispersion time is 24h to 28h; and the molecular weight of the polyacrylic acid is 50000Da to 100000Da.

[0031] As a preferred technical solution, the pH value of the hydrogel J in the step S7 is 6.8 to 7.2; the molecular weight of the polyallylamine hydrochloride is 11000Da to 15000Da; the mass ratio of the polyallylamine hydrochloride, phytic acid, and the solution I is 1:(0.5 to 0.7):(150 to 160); the molecular weight of the polyallylamine hydrochloride is 11000Da to 15000Da; and the mass fraction of chloride ions in the polyallylamine hydrochloride is 17.0% to 18.0%.

[0032] As a preferred technical solution, the mass ratio of the hydrogel J, graphene and silicon-containing negative electrode material in step S8 is 1:(0.01-0.02):(0.2-0.3); the silicon-containing negative electrode material is Si-Ti-Ni alloy; the drying temperature is 85-95 DEG C, and the drying time is 4-10 h; and the particle size D50 of the microspheres is 3-5 μm.

[0033] As a preferred technical solution, the grinding process in step S8 adopts an air flow crushing system, and fine grinding is carried out in a nitrogen protection environment (oxygen content <5%). In operation, the dried raw material is first passed through an 80-mesh sieve, the classification wheel rotation speed is set to 4500±50 rpm, the main / auxiliary nozzle pressure is controlled to 0.75±0.02 MPa and 0.55±0.02 MPa respectively, and the feeding rate is stabilized at 7.5±0.3 kg / h. The whole process is maintained by a water cooling system to keep the grinding cavity temperature <45 DEG C, and the vibration value (<4.5 mm / s) and pressure fluctuation (<5%) are monitored in real time. Sampling is carried out every 30 minutes to detect the particle size distribution (D10 is 1-2 μm, D50 is 3-5 μm, and D90 <7 μm).

[0034] In a second aspect of the present application, a high polymer microsphere is provided, which is prepared by any of the above preparation methods.

[0035] In a third aspect of the present application, an electric negative electrode slurry is provided, which is a dispersion liquid of the above high polymer microsphere and water. The high polymer microsphere and water are mixed uniformly at a mass ratio of 1:1, and can be used as the electric negative electrode slurry.

[0036] In a fourth aspect of the present application, an electric negative electrode coating is provided, which is prepared by coating the electric negative electrode slurry on a current collector and drying. The electric negative electrode slurry is a dispersion liquid of the above high polymer microsphere and water. The high polymer microsphere and water are mixed uniformly at a mass ratio of 1:1, and can be used as the electric negative electrode slurry.

[0037] In a fifth aspect of the present application, a method for improving the elongation at break of an electric negative electrode coating is provided, which adopts the above electric negative electrode slurry to prepare the coating.

[0038] In a sixth aspect of the present application, a method for improving the peeling strength of an electric negative electrode coating is provided, which adopts the above electric negative electrode slurry to prepare the coating.

[0039] In a seventh aspect of the present application, a method for improving the elastic modulus of an electric negative electrode coating is provided, which adopts the above electric negative electrode slurry to prepare the coating.

[0040] In an eighth aspect of the present application, a method for inhibiting the swelling of an electric negative electrode coating is provided, which adopts the above electric negative electrode slurry to prepare the coating.

[0041] In a ninth aspect, the present application provides a method for reducing the crack density of an electrode coating, which uses the electrode slurry described above to prepare the coating.

[0042] In a tenth aspect, the present application provides a battery electrode, which comprises a current collector and an electrode coating adhered to the current collector. In use, the polymer microspheres are mixed with water in a mass ratio of 1:1, and then coated on a copper foil current collector. The coating is dried at 80°C for 24 hours in a vacuum, and the thickness of the coating is 50 μm. The coating is used as a battery electrode material.

[0043] In an eleventh aspect, the present application provides a method for improving the capacity retention rate of a battery electrode, which uses the electrode coating described above to prepare the battery electrode.

[0044] Through the above technical solutions, the present application has the following technical effects:

[0045] (1) The carbon nanofiber grafted polyvinyl alcohol improves the elongation at break of the coating, and improves the high capacity retention rate of the battery electrode;

[0046] (2) The carboxylated styrene-butadiene copolymer inhibits the electrolyte swelling of the coating, and improves the peel strength of the coating;

[0047] (3) The synergistic effect of the polyallylamine hydrochloride and phytic acid reduces the crack density of the coating, and improves the capacity retention rate of the battery electrode;

[0048] (4) The glyoxalated polyacrylamide improves the elastic modulus of the coating, reduces the crack density of the coating, and improves the capacity retention rate of the battery electrode;

[0049] (5) The fluorinated polyvinyl alcohol improves the peel strength of the coating, and improves the capacity retention rate of the battery electrode. DETAILED DESCRIPTION

[0050] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the applicant describes and analyzes the present application through specific examples and comparative examples.

[0051] Example 1

[0052] Step S1, carboxylated modified carbon nanofiber: carbon nanofiber is added into mixed acid solution for oxidation reaction, filter cake is collected, and after washing and drying, carboxylated carbon nanofiber A is obtained; the mass ratio of the carbon nanofiber to the mixed acid solution is 1:180; the diameter of the carbon nanofiber is 20 nm, and the length is 10 μm; the mixed acid solution is a mixture of H2SO4 and HNO3, and the volume ratio of H2SO4 to HNO3 is 3:1; the oxidation reaction temperature is 65 ℃, and the oxidation reaction time is 5 h; the washing solution is purified water; the drying temperature is 75 ℃, and the drying time is 24 h;

[0053] Step S2, acyl chloride modified carbon nanofiber: carboxylated carbon nanofiber A is dispersed in a solution of thionyl chloride, and under the protection of nitrogen, acyl chloride reaction is carried out, filter cake is collected, and after washing and drying, carbon nanofiber B is obtained; the mass ratio of the carbon nanofiber A to the solution of thionyl chloride is 1:380; the solvent of the solution of thionyl chloride is tetrahydrofuran, and the mass ratio of thionyl chloride to tetrahydrofuran is 1:18; the acyl chloride reaction temperature is 65 ℃, and the acyl chloride reaction time is 10 h; the washing solution is tetrahydrofuran; the drying temperature is 75 ℃, and the drying time is 24 h;

[0054] Step S3, grafted modified fluorinated polyvinyl alcohol: fluorinated polyvinyl alcohol is dissolved in N,N-dimethylacetamide to prepare solution C; carbon nanofiber B and triethylamine are added into solution C for grafting reaction to obtain reaction liquid D; reaction liquid D is added into ethanol, and the precipitate is collected and dried to prepare modified fluorinated polyvinyl alcohol E; the mass ratio of the fluorinated polyvinyl alcohol to N,N-dimethylacetamide is 1:9; the mass ratio of the carbon nanofiber B, triethylamine and fluorinated polyvinyl alcohol is 1:0.4:15; the grafting reaction temperature is 57 ℃, and the grafting reaction time is 24 h; the mass ratio of the reaction liquid D to ethanol is 1:70; the drying temperature is 75 ℃, and the drying time is 24 h; the weight average molecular weight of the fluorinated polyvinyl alcohol is 85000 Da, and the substitution degree of the hydroxyl group in the fluorinated polyvinyl alcohol is 15% (molar ratio) ;

[0055] Modified fluorinated polyvinyl alcohol E is dispersed in water to prepare solution F; the mass concentration of the modified fluorinated polyvinyl alcohol E in solution F is 5%; the dispersion temperature is 65 ℃, and the dispersion time is 24 h;

[0056] The preparation method of the fluorinated polyvinyl alcohol is as follows: using high purity (≥98%) 1H, 1H, 2H, 2H-perfluorooctyl iodine as a fluorination reagent, and polyvinyl alcohol (molecular weight 85000) previously dissolved in anhydrous DMSO is reacted under nitrogen protection; first, the polyvinyl alcohol is prepared into a clear solution with a mass concentration of 10%, after warming to 70±2℃, NaOH catalyst is added, then the fluorination reagent is slowly added dropwise, the molar ratio of polyvinyl alcohol structure unit to fluorination agent is controlled to be 1:0.15, the reaction is carried out for 24 hours, and -O-CH2-CH2-C8F 17 group is covalently grafted onto the polyvinyl alcohol chain, and the target fluorination degree is controlled at 15%; after the reaction is completed, the mixture is cooled, poured into a mixture of acetone and ethanol to precipitate, the volume ratio of acetone to ethanol is 1:1, and the by-products NaI and unreacted reagents are completely removed by Soxhlet extraction, and finally a white fibrous solid product is obtained by vacuum drying at 80℃ for 24 hours;

[0057] Step S4, adding glyoxalated polyacrylamide: dispersing glyoxalated polyacrylamide in solution F to prepare solution G; the mass concentration of the glyoxalated polyacrylamide in solution G is 1.0%; the dispersion temperature is 60℃, and the dispersion time is 24h;

[0058] The preparation process of the glyoxalated polyacrylamide is as follows: polyacrylamide with a molecular weight of 5000000 Da is dissolved in water to prepare a solution with a mass concentration of 2%, a 40% glyoxal aqueous solution is added so that the molar ratio of glyoxal to amide group is about 1:8, the pH value is adjusted to 4.0±0.2 by acetic acid, and the reaction is carried out at 60℃ for 4 hours; during the reaction process, mechanical stirring (300rpm) is used to ensure uniform mixing; finally, the product is purified by dialysis and freeze-dried to obtain a white solid;

[0059] Step S5, adding carboxylated styrene-butadiene copolymer: dispersing carboxylated styrene-butadiene copolymer in solution G to prepare solution H; the mass concentration of the carboxylated styrene-butadiene copolymer in solution H is 1.2%; the dispersion temperature is 65℃, and the dispersion time is 24h;

[0060] The styrene-butadiene in the carboxylated styrene-butadiene copolymer is a random copolymer, the molecular weight is 200000 Da, the molar ratio of styrene to butadiene is 1:3, and the molar ratio of 1,4-structure in the butadiene segment is 70%; carboxyl groups (-COOH) are introduced on the double bonds of the butadiene segment by free radical grafting reaction, and the carboxyl group density is 0.8mmol / g;

[0061] Step S6, adding polyacrylic acid: dispersing polyacrylic acid in solution H to prepare solution I; the mass concentration of the polyacrylic acid in solution I is 1.5%; the dispersion temperature is 65℃, and the dispersion time is 24h; the molecular weight of the polyacrylic acid is 50000Da;

[0062] Step S7, adding polyallylamine hydrochloride and phytic acid: dispersing polyallylamine hydrochloride and phytic acid in solution I to prepare hydrogel J by adjusting the pH value; the pH value of the hydrogel J is 6.8; the molecular weight of the polyallylamine hydrochloride is 11000Da; the mass ratio of the polyallylamine hydrochloride, the phytic acid and solution I is 1:0.5:150; the molecular weight of the polyallylamine hydrochloride is 11000Da; the mass fraction of chloride ions in the polyallylamine hydrochloride is 17.0%;

[0063] Step S8, preparing microspheres: adding graphene and silicon-containing negative electrode material into the hydrogel J to uniformly disperse to prepare slurry K, and then drying and grinding the slurry K to prepare microspheres; the mass ratio of the hydrogel J, the graphene and the silicon-containing negative electrode material is 1:0.01:0.2; the silicon-containing negative electrode material is Si-Ti-Ni alloy; the drying temperature is 85℃, and the drying time is 4h; the particle size D50 of the microspheres is 3μm;

[0064] The grinding process adopts an airflow crushing system, and fine grinding is carried out in a nitrogen protection environment (oxygen content <5%). When operating, first, dry raw materials are passed through an 80-mesh sieve, the classification wheel rotation speed is set to 4500±50rpm, the main / auxiliary nozzle pressure is controlled to 0.75±0.02MPa and 0.55±0.02MPa respectively, and the feeding rate is stabilized at 7.5±0.3kg / h. The whole process is maintained by a water cooling system to keep the grinding cavity temperature <45℃, and the vibration value (<4.5mm / s) and pressure fluctuation (<5%) are monitored in real time. Every 30 minutes, sample detection is carried out on the particle size distribution (D10 is 1μm-2μm, D50 is 3μm-5μm, and D90<7μm).

[0065] Example 2

[0066] Step S1, carboxylated modified carbon nanofiber: adding carbon nanofiber into a mixed acid solution to carry out oxidation reaction, collecting the filter cake by filtration, and then washing and drying to obtain carboxylated carbon nanofiber A; the mass ratio of the carbon nanofiber to the mixed acid solution is 1:200; the diameter of the carbon nanofiber is 25nm, and the length is 20μm; the mixed acid solution is a mixture of H2SO4 and HNO3, and the volume ratio of H2SO4 to HNO3 is 3:1; the oxidation reaction temperature is 70℃, and the oxidation reaction time is 5.5h; the washing solution is purified water; the drying temperature is 80℃, and the drying time is 25h;

[0067] Step S2, acyl chloride modification of carbon nanofiber: carboxylated carbon nanofiber A is dispersed in a solution of thionyl chloride, and an acyl chloride reaction is carried out under nitrogen protection. The filter cake is collected by filtration, washed, and dried to obtain carbon nanofiber B. The mass ratio of the carbon nanofiber A to the solution of thionyl chloride is 1:400. The solvent of the solution of thionyl chloride is tetrahydrofuran, and the mass ratio of the thionyl chloride to the tetrahydrofuran is 1:20. The acyl chloride reaction temperature is 68°C, and the acyl chloride reaction time is 11 hours. The solution used for washing is tetrahydrofuran. The drying temperature is 80°C, and the drying time is 28 hours.

[0068] Step S3, graft modification of fluorinated polyvinyl alcohol: fluorinated polyvinyl alcohol is dissolved in N,N-dimethylacetamide to prepare solution C. Carbon nanofiber B and triethylamine are added to solution C to perform a graft reaction to obtain reaction liquid D. Reaction liquid D is added to ethanol to collect the precipitate, which is dried to prepare modified fluorinated polyvinyl alcohol E. The mass ratio of the fluorinated polyvinyl alcohol to N,N-dimethylacetamide is 1:10. The mass ratio of the carbon nanofiber B, triethylamine, and fluorinated polyvinyl alcohol is 1:0.5:16. The graft reaction temperature is 60°C, and the graft reaction time is 27 hours. The mass ratio of the reaction liquid D to ethanol is 1:72. The drying temperature is 80°C, and the drying time is 26 hours. The weight average molecular weight of the fluorinated polyvinyl alcohol is 90,000 Da, and the degree of substitution of the hydroxyl groups in the fluorinated polyvinyl alcohol is 20% (molar ratio).

[0069] Modified fluorinated polyvinyl alcohol E is dispersed in water to prepare solution F. The mass concentration of the modified fluorinated polyvinyl alcohol E in solution F is 5.2%. The dispersion temperature is 70°C, and the dispersion time is 26 hours.

[0070] The preparation method of the fluorinated polyvinyl alcohol is as follows: high-purity (≥98%) 1H,1H,2H,2H-perfluorooctyl iodine is used as a fluorination reagent, and polyvinyl alcohol (molecular weight 90,000 Da) previously dissolved in anhydrous DMSO is reacted under nitrogen protection. First, the polyvinyl alcohol is prepared into a clear solution with a mass concentration of 10%, and after being heated to 70±2°C, a NaOH catalyst is added, and the fluorination reagent is slowly added dropwise. The molar ratio of the polyvinyl alcohol structural unit to the fluorination reagent is controlled to be 1:0.2, and the reaction is carried out for 24 hours. The -O-CH2-CH2-C8F 17 group is covalently grafted onto the polyvinyl alcohol chain through a Williamson etherification reaction, and the target fluorination degree is controlled to be 20%. After the reaction is completed, the mixture is cooled, precipitated into a mixture of acetone and ethanol with a volume ratio of 1:1, and the by-products NaI and unreacted reagents are completely removed through a Soxhlet extraction. Finally, a white fibrous solid product is obtained through 80°C vacuum drying for 24 hours.

[0071] Step S4, adding glyoxalated polyacrylamide: glyoxalated polyacrylamide is dispersed in solution F to prepare solution G; the mass concentration of the glyoxalated polyacrylamide in solution G is 1.3%; the dispersion temperature is 65°C, and the dispersion time is 26h;

[0072] The preparation process of the glyoxalated polyacrylamide is as follows: polyacrylamide with a molecular weight of 5500000 Da is dissolved in water to prepare a solution with a mass concentration of 2%, a 40% glyoxal aqueous solution is added to make the molar ratio of glyoxal to amide group about 1:8, acetic acid is added to adjust the pH value to 4.0±0.2, and the reaction is carried out at 65°C for 5 hours. During the reaction, mechanical stirring (300 rpm) is used to ensure uniform mixing. The final product is purified by dialysis and freeze-dried to obtain a white solid;

[0073] Step S5, adding carboxylated styrene-butadiene copolymer: the carboxylated styrene-butadiene copolymer is dispersed in solution G to prepare solution H; the mass concentration of the carboxylated styrene-butadiene copolymer in solution H is 1.4%; the dispersion temperature is 70°C, and the dispersion time is 26h;

[0074] The styrene-butadiene in the carboxylated styrene-butadiene copolymer is a random copolymer with a molecular weight of 250000 Da; the molar ratio of styrene to butadiene is 1:3; the molar ratio of 1,4-structure in the butadiene segment is 70%; carboxyl groups (-COOH) are introduced on the double bonds of the butadiene segment through a free radical grafting reaction, and the carboxyl group density is 1 mmol / g;

[0075] Step S6, adding polyacrylic acid: polyacrylic acid is dispersed in solution H to prepare solution I; the mass concentration of the polyacrylic acid in solution I is 1.7%; the dispersion temperature is 70°C, and the dispersion time is 26h; the molecular weight of the polyacrylic acid is 70000 Da;

[0076] Step S7, adding polyallylamine hydrochloride and phytic acid: polyallylamine hydrochloride and phytic acid are dispersed in solution I to adjust the pH value to prepare hydrogel J; the pH value of the hydrogel J is 7; the molecular weight of the polyallylamine hydrochloride is 13000 Da; the mass ratio of the polyallylamine hydrochloride, phytic acid, and solution I is 1:0.6:155; the molecular weight of the polyallylamine hydrochloride is 13000 Da; the mass fraction of chloride ions in the polyallylamine hydrochloride is 17.5%;

[0077] Step S8, preparing microspheres: adding graphene and silicon-containing negative electrode material into the hydrogel J to prepare slurry K, and then drying and grinding the slurry K to prepare microspheres; the mass ratio of the hydrogel J, graphene and silicon-containing negative electrode material is 1:0.015:0.25; the silicon-containing negative electrode material is Si-Ti-Ni alloy; the drying temperature is 90℃, and the drying time is 7h; the particle size D50 of the microspheres is 4μm;

[0078] The grinding process adopts an airflow crushing system, and fine grinding is carried out in a nitrogen protection environment (oxygen content <5%). When operating, first, dry raw materials are passed through an 80-mesh sieve, the classification wheel rotation speed is set to 4500±50 rpm, the main / auxiliary nozzle pressure is controlled to 0.75±0.02 MPa and 0.55±0.02 MPa respectively, and the feeding rate is stabilized at 7.5±0.3 kg / h. The whole process is maintained by a water cooling system to keep the grinding cavity temperature <45℃, and the vibration value (<4.5 mm / s) and pressure fluctuation (<5%) are monitored in real time. Sampling is taken every 30 minutes to detect the particle size distribution (D10 is 1μm~2μm, D50 is 3μm~5μm, and D90<7μm).

[0079] Example 3

[0080] Step S1, carboxylated modified carbon nanofiber: adding carbon nanofiber into a mixed acid solution to carry out oxidation reaction, collecting the filter cake by filtration, and then washing and drying to obtain carboxylated carbon nanofiber A; the mass ratio of the carbon nanofiber to the mixed acid solution is 1:220; the diameter of the carbon nanofiber is 30nm, and the length is 130μm; the mixed acid solution is a mixture of H2SO4 and HNO3, and the volume ratio of H2SO4 to HNO3 is 3:1; the oxidation reaction temperature is 75℃, and the oxidation reaction time is 6h; the washing solution is pure water; the drying temperature is 85℃, and the drying time is 30h;

[0081] Step S2, acyl chloride modified carbon nanofiber: dispersing carboxylated carbon nanofiber A in a thionyl chloride solution, and then carrying out acyl chloride reaction under nitrogen protection, collecting the filter cake by filtration, and then washing and drying to obtain carbon nanofiber B; the mass ratio of the carbon nanofiber A to the thionyl chloride solution is 1:420; the solvent of the thionyl chloride solution is tetrahydrofuran, and the mass ratio of the thionyl chloride to tetrahydrofuran is 1:22; the acyl chloride reaction temperature is 70℃, and the acyl chloride reaction time is 12h; the washing solution is tetrahydrofuran; the drying temperature is 85℃, and the drying time is 30h;

[0082] Step S3, graft modification of fluorinated polyvinyl alcohol: fluorinated polyvinyl alcohol is dissolved in N,N-dimethylacetamide to form solution C; carbon nanofiber B and triethylamine are added to solution C to perform a graft reaction to obtain reaction liquid D; reaction liquid D is added to ethanol, and the precipitate is collected and dried to form modified fluorinated polyvinyl alcohol E; the mass ratio of fluorinated polyvinyl alcohol to N,N-dimethylacetamide is 1:11; the mass ratio of carbon nanofiber B, triethylamine and fluorinated polyvinyl alcohol is 1:0.6:17; the graft reaction temperature is 62°C, and the graft reaction time is 29h; the mass ratio of reaction liquid D to ethanol is 1:75; the drying temperature is 85°C, and the drying time is 30h; the weight average molecular weight of the fluorinated polyvinyl alcohol is 95000 Da, and the degree of substitution of the hydroxyl group in the fluorinated polyvinyl alcohol is 25% by mole;

[0083] Modified fluorinated polyvinyl alcohol E is dispersed in water to form solution F; the mass concentration of modified fluorinated polyvinyl alcohol E in solution F is 5.5%; the dispersion temperature is 75°C, and the dispersion time is 28h;

[0084] The preparation method of the fluorinated polyvinyl alcohol is as follows: high-purity (≥98%) 1H, 1H, 2H, 2H-perfluorooctyl iodine is used as a fluorination reagent, and polyvinyl alcohol (molecular weight 95000 Da) previously dissolved in anhydrous DMSO is reacted under nitrogen protection; first, the polyvinyl alcohol is prepared into a clear solution with a mass concentration of 10%, and after being heated to 70±2°C, a NaOH catalyst is added, and then the fluorination reagent is slowly added dropwise, and the molar ratio of the polyvinyl alcohol structural unit to the fluorination reagent is controlled to be 1:0.25, and the reaction is carried out for 24 hours; the -O-CH2-CH2-C8F 17 group is covalently grafted onto the polyvinyl alcohol chain, and the target fluorination degree is controlled to be 25%; after the reaction is completed, the mixture is cooled, precipitated in a mixed solution of acetone and ethanol, the volume ratio of acetone to ethanol is 1:1, and the by-products NaI and unreacted reagents are completely removed by Soxhlet extraction, and finally a white fibrous solid product is obtained by vacuum drying at 80°C for 24 hours;

[0085] Step S4, addition of glyoxalated polyacrylamide: glyoxalated polyacrylamide is dispersed in solution F to form solution G; the mass concentration of glyoxalated polyacrylamide in solution G is 1.5%; the dispersion temperature is 70°C, and the dispersion time is 28h;

[0086] The preparation process of glyoxalated polyacrylamide is as follows: polyacrylamide with a molecular weight of 6000000 Da is dissolved in water to prepare a solution with a mass concentration of 2%, a 40% glyoxal aqueous solution is added, the molar ratio of glyoxal to amide group is about 1:8, the pH value is adjusted to 4.0±0.2 by acetic acid, the reaction is carried out at 70°C for 6 hours, and mechanical stirring (300 rpm) is used to ensure uniform mixing during the reaction. The final product is purified by dialysis and freeze-dried to obtain a white solid;

[0087] Step S5, adding carboxylated styrene-butadiene copolymer: dispersing the carboxylated styrene-butadiene copolymer in solution G to prepare solution H; the mass concentration of the carboxylated styrene-butadiene copolymer in solution H is 1.8%; the dispersion temperature is 75°C, and the dispersion time is 28h;

[0088] The styrene-butadiene in the carboxylated styrene-butadiene copolymer is a random copolymer with a molecular weight of 200000 Da-300000 Da; the molar ratio of styrene to butadiene is 1:3; the molar ratio of 1,4-structure in the butadiene segment is 70%; carboxyl groups (-COOH) are introduced on the double bonds of the butadiene segment through a free radical grafting reaction, and the carboxyl group density is 1.2 mmol / g;

[0089] Step S6, adding polyacrylic acid: dispersing polyacrylic acid in solution H to prepare solution I; the mass concentration of the polyacrylic acid in solution I is 2.0%; the dispersion temperature is 75°C, and the dispersion time is 28h; the molecular weight of the polyacrylic acid is 100000 Da;

[0090] Step S7, adding polyallylamine hydrochloride and phytic acid: dispersing polyallylamine hydrochloride and phytic acid in solution I to adjust the pH value to prepare hydrogel J; the pH value of the hydrogel J is 7.2; the molecular weight of the polyallylamine hydrochloride is 15000 Da; the mass ratio of the polyallylamine hydrochloride, phytic acid, and solution I is 1:0.7:160; the molecular weight of the polyallylamine hydrochloride is 15000 Da; the mass fraction of chloride ions in the polyallylamine hydrochloride is 18.0%;

[0091] Step S8, preparing microspheres: adding graphene and silicon-containing negative electrode material to the hydrogel J to disperse uniformly to prepare slurry K, and the slurry K is dried and ground to prepare microspheres; the mass ratio of the hydrogel J, graphene, and silicon-containing negative electrode material is 1:0.02:0.3; the silicon-containing negative electrode material is Si-Ti-Ni alloy; the drying temperature is 95°C, and the drying time is 4h-10h; the particle size D50 of the microspheres is 5μm;

[0092] The grinding process adopts a jet mill system, and fine grinding is performed in a nitrogen protection environment (oxygen content <5%). During operation, first, dry raw materials are passed through an 80-mesh sieve, the classification wheel rotation speed is set to 4500±50 rpm, the main / auxiliary nozzle pressure is controlled at 0.75±0.02 MPa and 0.55±0.02 MPa respectively, and the feeding rate is stabilized at 7.5±0.3 kg / h. The grinding cavity temperature is maintained at <45°C throughout the process by a water cooling system, and the vibration value (<4.5 mm / s) and pressure fluctuation (<5%) are monitored in real time. Sampling is performed every 30 minutes to detect the particle size distribution (D10 is 1 μm-2 μm, D50 is 3 μm-5 μm, and D90 is <7 μm).

[0093] Comparative Example 1

[0094] In step S3, unmodified carbon nanofibers and unmodified fluorinated polyvinyl alcohol mixture (only physical mixing) are used instead of modified fluorinated polyvinyl alcohol E, and other parameters are consistent with Example 1.

[0095] The elongation at break is determined according to ASTM-D638 "Standard Test Methods for Tensile Properties of Plastics". The microspheres are mixed with water at a mass ratio of 1:1, uniformly, cast into a film, vacuum dried at 80°C for 24 hours, and punched into standard samples (6 mm wide, 30 mm long), with a thickness of 100±5 μm. The elongation at break is determined. The difference in elongation at break reflects the stress buffering capacity of the material.

[0096] The capacity retention rate is tested according to GB / T 44027.1-2024 "Determination of Carbon Materials - Part 1: Determination of Initial Specific Discharge Capacity, Initial Coulombic Efficiency, and Capacity Retention Rate at Different Rates". When using, the microspheres are mixed with water at a mass ratio of 1:1, uniformly, coated on a copper foil current collector, vacuum dried at 80°C for 24 hours, with a coating thickness of 50 μm, and the capacity retention rate is measured. The temperature is 25±0.5°C, the current is 0.5C, and the voltage range is 0.005-1.5V; the electrolyte composition is: lithium hexafluorophosphate (LiPF6) 1M concentration, main solvent is ethylene carbonate (EC), co-solvent is diethyl carbonate (DEC), EC to DEC ratio is 1:1 (volume ratio); the capacity retention rate is measured after 100 cycles of charging and discharging.

[0097] The test results are shown in the table below. Carbon nanofiber grafted modified fluorinated polyvinyl alcohol can improve the elongation at break and improve the capacity retention rate. After modification of carbon nanofiber, it is covalently connected to polyvinyl alcohol through ester bond, forming a stable chemical bonding network. When the silicon negative electrode expands, the material can dissipate energy through reversible stretching of molecular chains, improving the elongation at break and improving the capacity retention rate. Unmodified carbon nanofiber and polyvinyl alcohol are only physically mixed, the interface is weakly bonded, stress is concentrated, leading to separation of carbon nanofiber from the polymer matrix during the expansion of the silicon negative electrode, and also damaging the conductive network.

[0098] Table 1: Effect of modified polyvinyl alcohol and modified carbon nanofiber on friction coefficient

[0099]

[0100] Comparative Example 2

[0101] In step S5, no carboxylated styrene-butadiene copolymer was added, and other parameters were consistent with Example 1.

[0102] Comparative Example 3

[0103] In step S5, polystyrene was used instead of carboxylated styrene-butadiene copolymer, and other parameters were consistent with Example 1.

[0104] Comparative Example 4

[0105] In step S5, polybutadiene was used instead of carboxylated styrene-butadiene copolymer, and other parameters were consistent with Example 1.

[0106] The microspheres were mixed with water at a mass ratio of 1:1, coated on a copper foil current collector, and vacuum dried at 80°C for 24 hours. The coating thickness was 50 μm. The peel strength and thickness expansion rate were measured.

[0107] The peel strength was determined according to ASTM D903 "Standard Test Methods for Peel Resistance of Adhesives". The 90° peel test was performed at a speed of 50 mm / min and an ambient temperature of 23±2°C.

[0108] Thickness expansion rate test method:

[0109] A 25 mm x 25 mm electrode sample (including the current collector) was taken, and the thickness was measured. The average value of five points (center + four corners) was taken as the reference thickness. The T0 thickness value was recorded. The sample was placed in an electrolyte (1M LiPF6 in EC / DMC (1:1)) and soaked in a sealed container at 25°C for 48 hours, with the liquid level 10 mm above the sample. The sample was taken out, the surface electrolyte was cleaned, and the thickness was measured at the same measurement point and under the same measurement conditions. The T1 thickness value was recorded. The thickness expansion rate = (T1-T0)T0 / x 100%.

[0110] The test results are shown in the table below. The carboxylated styrene-butadiene copolymer can significantly improve the peel strength. Possible reasons include the following: (1) the carboxylate group (-COO-) forms a coordination bond with the surface of the metal current collector, improving the bonding strength; (2) the negative carboxyl group interacts with the positive current collector by electrostatic interaction; (3) the butadiene rubber phase penetrates into the surface pores of the current collector, forming a mechanical interlocking structure, improving the bonding strength.

[0111] Carboxylated styrene-butadiene copolymer can inhibit electrolyte swelling. Possible reasons include the following: (1) styrene rigid chain segment produces a molecular sieve pore size of 0.5-0.8 nm (smaller than the size of EC / DMC solvent molecules but larger than Li + diameter), selectively preventing solvent molecules from penetrating; (2) carboxylate groups (-COO-) produce electrostatic repulsion with electrolyte solvent molecules, further preventing solvent molecules from penetrating.

[0112] Table 2: Effect of carboxylated styrene-butadiene copolymer on performance

[0113]

[0114] Comparative Example 5

[0115] In step S7, no polyallylamine hydrochloride and phytic acid were added, and the other parameters were consistent with Example 1.

[0116] Comparative Example 6

[0117] In step S7, only polyallylamine hydrochloride was added, and no phytic acid was added, and the other parameters were consistent with Example 1.

[0118] Comparative Example 7

[0119] In step S7, only phytic acid was added, and no polyallylamine hydrochloride was added, and the other parameters were consistent with Example 1.

[0120] In use, the microspheres were mixed with water at a mass ratio of 1:1, coated on a copper foil current collector, and vacuum dried at 80°C for 24 hours. The coating thickness was 50 μm, and the capacity retention rate and crack density were measured.

[0121] The capacity retention rate determination method was consistent with the foregoing.

[0122] Crack density determination method:

[0123] 1. Core detection instrument

[0124] Main equipment: Hitachi S-4800 field emission scanning electron microscope (FESEM)

[0125] Auxiliary system: JEOL JEM100CXII transmission electron microscope (TEM)

[0126] Analysis software: Image-Pro Plus 6.0 image analysis system

[0127] 2. Parameter settings

[0128] Acceleration voltage 5 kV; working distance 8 mm; magnification 10,000X

[0129] 3. Sample preparation

[0130] Post-cycling sampling: disassembly of the battery in an argon glovebox

[0131] Electrolyte washing: 3 times of dimethyl carbonate immersion (5 min each time)

[0132] Vacuum drying: temperature 60 °C, time 12 h

[0133] Cross-section preparation: ultramicrotome (slice thickness 100 nm)

[0134] 4. Image acquisition

[0135] Field of view selection: 5 non-overlapping areas were randomly selected

[0136] Resolution: 2048 x 1536 pixels (300 dpi)

[0137] Gray contrast: black-white difference ≥ 60% (software calibration)

[0138] 5. Crack quantification

[0139] Crack definition: width > 50 nm and length > 1 pm

[0140] Crack density calculation: total length of cracks / area of field of view (pm / pm 2 )

[0141] The test results are shown in the following table. The synergistic effect of polyallylamine hydrochloride and phytic acid reduces the crack density and improves the capacity retention rate. The electrostatic interaction between the -NH3 + of polyallylamine hydrochloride and the phytate hexaphosphate ion can reversibly crosslink to form a three-dimensional network, a dynamic self-repairing network mechanism, which can dissipate energy through reversible bond breaking / recombination during the expansion of the silicon negative electrode, effectively buffer the volume change of the silicon negative electrode, disperse the internal stress generated by the expansion of the silicon negative electrode, and reduce the crack density; it can also reduce the shedding of active materials and maintain the integrity of the electrode structure. The above aspects can improve the capacity retention rate. The absence of polyallylamine hydrochloride and phytic acid reduces the dynamic crosslinking ability of the binder network; only polyallylamine hydrochloride without phytic acid cannot form a complete ionic crosslinking network; only phytic acid without polyallylamine hydrochloride lacks sufficient cation crosslinking sites.

[0142] Table 3: Effect of polyallylamine hydrochloride and phytic acid on performance

[0143]

[0144] Comparative Example 8

[0145] In step S4, polyacrylamide was used instead of glyoxalated polyacrylamide, and other parameters were consistent with Example 1.

[0146] Elastic modulus was tested according to ASTM D 4065-06 "Standard Practice for Plastics: Dynamic Mechanical Properties - Modulus of Elasticity". The microspheres were mixed with water at a mass ratio of 1:1, cast into a film, dried at 80°C under vacuum for 24 hours, punched into standard sample bars, and the elastic modulus was measured.

[0147] The crack density was measured according to the method described above.

[0148] The test results are shown in the table below. Compared with polyacrylamide, glyoxalated polyacrylamide can significantly improve the elastic modulus. Possible reasons include the following: (1) the aldehyde group of glyoxal reacts with the amide group on the polyacrylamide chain through nucleophilic addition, first forming an unstable hydroxymethyl intermediate, and then forming an imine crosslinking point through intermolecular condensation. During the crosslinking process, a single glyoxal molecule can connect two polyacrylamide chains, forming a three-dimensional network structure that changes polyacrylamide from linear to network structure, providing mechanical support; (2) the residual aldehyde group of glyoxalated polyacrylamide reacts with the amine group (-NH3 + ) of the hydrochloride polyallylamine through Schiff base reaction, and the imine bond further strengthens the network structure. The parallel molecular chains of polyacrylamide are maintained only by intermolecular forces, resulting in lower elastic modulus.

[0149] Compared with polyacrylamide, glyoxalated polyacrylamide can significantly reduce the crack density. The possible reason is that the dynamic covalent crosslinking network formed by the imine bond (-N=CH-) of glyoxalated polyacrylamide can be reversibly reconstructed: the aldehyde group of glyoxal reacts with the amide group of polyacrylamide through nucleophilic addition to form an imine crosslinking point. This bond has (1) proton-catalyzed cleavage characteristics, H + promoting the hydrolysis of the imine bond into free amine and aldehyde group; (2) the active groups after cleavage can re-condense at new positions, self-adaptively balance and dynamically adjust, achieving micro-damage self-repair and reducing crack density.

[0150] Compared with polyacrylamide, glyoxalated polyacrylamide can significantly improve the capacity retention rate. Possible reasons include the following: (1) dissipating the volume change stress of the silicon negative electrode through reversible bond cleavage; (2) achieving micro-damage self-repair through bond recombination; (3) maintaining the overall stability of the three-dimensional network; thereby improving the capacity retention rate.

[0151] Table 4: Effect of glyoxalated polyacrylamide on performance

[0152]

[0153]

[0154] Comparative Example 9

[0155] In step S3, polyvinyl alcohol was used instead of fluorinated polyvinyl alcohol for the grafting reaction, and other parameters were consistent with Example 1.

[0156] The capacity retention rate measurement method refers to the aforementioned method, and the high-temperature high-voltage cycle stability is investigated. The test conditions are changed to harsh test conditions (55°C high temperature, 4.7V voltage), which can accelerate the oxidation and decomposition of the electrode slurry film and the electrolyte.

[0157] The peeling strength is consistent with the aforementioned measurement method.

[0158] The test results are shown in the following table. Compared with polyvinyl alcohol, fluorinated polyvinyl alcohol can significantly improve the peeling strength and improve the capacity retention rate.

[0159] The C-F bond is one of the strongest chemical bonds in nature, and is very firm and difficult to break. The fluorine-containing unit, especially the C-F bond, has extremely high bond energy, making it extremely stable in the high voltage (>4.2V) and strong reducing (lithium metal) environment of the battery, and it is not easy to be oxidized or decomposed. The fluorine-containing unit gives the electrode slurry film extremely strong electrochemical oxidation resistance, providing a wide electrochemical window for the electrode slurry film, effectively preventing the problems of active material powdering and falling off during long-term charge and discharge cycles, ensuring the integrity and stability of the electrode structure, and avoiding the sudden drop in capacity caused by the failure of the electrode slurry film.

[0160] At the interface level, the molecular chain of fluorinated polyvinyl alcohol can effectively infiltrate and spread on the surface of the electrode active material (especially the high-surface-energy oxide positive material) and the current collector. This excellent wettability ensures maximum contact and forms a firm interfacial adsorption through van der Waals forces, hydrogen bonds, and other interactions, thereby improving the peeling strength in macroscopic performance.

[0161] Table 5: Effect of fluorinated polyvinyl alcohol on performance

[0162] Test item Treatment condition Peeling strength (kgf / cm) Capacity retention rate (%) Example 1 / 18.5 92.5 Example 2 / 19.2 93.8 Example 3 / 20.1 94.5 Comparative Example 9 Use of polyvinyl alcohol instead of fluorinated polyvinyl alcohol 14.5 68.2

Claims

1. A method for preparing polymer microspheres, characterized in that, Includes the following steps: Step S1, carboxylation modified carbon nanofibers: Carbon nanofibers are added to a mixed acid solution for oxidation reaction, the filter cake is collected by filtration, and the filter cake is washed and dried to obtain carboxylation modified carbon nanofibers A. Step S2, Acyl chloride modified carbon nanofibers: Carboxylated carbon nanofibers A are dispersed in thionyl chloride solution and subjected to acyl chloride reaction under nitrogen protection. The filter cake is collected by filtration, and the filter cake is washed and dried to obtain carbon nanofibers B. Step S3, grafting modified fluorinated polyvinyl alcohol: Dissolve fluorinated polyvinyl alcohol in N,N-dimethylacetamide to prepare solution C; Carbon nanofibers B and triethylamine were added to solution C to carry out a grafting reaction, resulting in reaction solution D. Add reaction solution D to ethanol, collect the precipitate, and dry the precipitate to prepare modified fluorinated polyvinyl alcohol E; Modified fluorinated polyvinyl alcohol E was dispersed in water to prepare solution F; Step S4, Add glyoxalized polyacrylamide: Disperse glyoxalized polyacrylamide in solution F to prepare solution G; Step S5, adding carboxylated styrene-butadiene copolymer: Disperse the carboxylated styrene-butadiene copolymer in solution G to prepare solution H; Step S6, Add polyacrylic acid: Disperse polyacrylic acid in solution H to prepare solution I; Step S7, Add polyallylamine hydrochloride and phytic acid: Disperse polyallylamine hydrochloride and phytic acid in solution I, adjust the pH value to form hydrogel J; Step S8, Microsphere preparation: Graphene and silicon-containing negative electrode material are added to hydrogel J and dispersed evenly to form slurry K. Slurry K is dried and ground to form microspheres.

2. A polymer microsphere, characterized in that, The polymer microspheres are prepared by the preparation method described in claim 1.

3. A negative electrode slurry, characterized in that, The negative electrode slurry is a dispersion of the polymer microspheres described in claim 2 in water.

4. A negative electrode coating, characterized in that, The negative electrode coating is prepared by coating a negative electrode slurry onto a current collector and then drying it; the negative electrode slurry is a dispersion of polymer microspheres and water as described in claim 2.

5. A method for improving the elongation at break of an electrode coating, characterized in that, The method uses the negative electrode slurry as described in claim 3 to prepare the coating.

6. A method for improving the peel strength of an electrode coating, characterized in that, The method uses the negative electrode slurry as described in claim 3 to prepare the coating.

7. A method for improving the elastic modulus of an electrode coating, characterized in that, The method uses the negative electrode slurry as described in claim 3 to prepare the coating.

8. A method for suppressing swelling of a negative electrode coating, characterized in that, The method uses the negative electrode slurry as described in claim 3 to prepare the coating.

9. A method for reducing the crack density of an electrode coating, characterized in that, The method uses the negative electrode slurry as described in claim 3 to prepare the coating.

10. A method for improving the capacity retention rate of a battery negative electrode, characterized in that, The method uses the negative electrode coating as described in claim 4 to prepare the battery negative electrode, wherein the negative electrode coating is adhered to the current collector.

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