Glued diaphragm and lithium ion battery

Abstract

The invention discloses a glued diaphragm and a lithium ion battery, which are used for solving the technical problems in the prior art that the structural strength of the diaphragm is poor, and the compatibility, the bonding strength and the thermal stability of a binder, an electrolyte and a pole piece material are poor. The method comprises the following steps: adding polyvinylidene fluoride powder and N-methyl pyrrolidone into a closed reaction kettle, stirring, raising the temperature of the reaction kettle to 50-70 DEG C, adding hydrogen peroxide and ferrous sulfate, regulating the pH value of a system to 4 by using diluted hydrochloric acid, carrying out oxidation reaction for 2-3 hours, and carrying out post-treatment to obtain an active intermediate; through the synergistic effect of multiple enhancement mechanisms between the acrylic acid modified polypropylene base membrane and the modified polyvinylidene fluoride binder coated on the diaphragm base material, the mechanical property of the diaphragm is remarkably improved, and the thermal stability and bonding strength of the binder in the charge-discharge cycle process are also improved; and the safety of the battery and the overall performance of the battery are effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of nanofiltration membrane processing, and in particular to a glue-coated diaphragm and a lithium-ion battery. Background Art

[0002] The separator is one of the four main materials used in the manufacture of lithium-ion batteries. Its main function is to isolate the positive and negative electrodes, completely isolate the electronic contact between the positive and negative electrodes to prevent short circuits, and allow lithium ions to shuttle freely between the positive and negative electrodes during charging and discharging. Therefore, the performance of the separator determines the overall performance and safety of the battery and is one of the key bottlenecks in the development of lithium-ion battery technology.

[0003] At present, most lithium batteries use dry-process diaphragms made of polypropylene as the diaphragm substrate. The manufacturing process of dry-process diaphragms is usually a unidirectional stretching process. Its transverse tensile strength is dozens of times lower than its longitudinal tensile strength. In addition, the battery cell will produce shrinkage wrinkles during the vacuum drying process. After the battery cell is stacked, the positive and negative electrodes are in a relatively loose state. During transportation, there are problems such as movement of the positive and negative electrodes and damage to the diaphragm, which reduces the safety performance of lithium batteries.

[0004] In addition, when lithium batteries are used for a long time, the binder (such as polymer binder, such as polyvinylidene fluoride PVDF) will decompose, and the decomposition products will form deposits on the surface of the negative electrode, resulting in the appearance of black spots, or will dissolve or migrate to the negative electrode interface during the use of the lithium battery, resulting in local chemical reactions or deposition and the appearance of black spots, resulting in a shorter cycle life and an uneven appearance of the lithium battery;

[0005] Therefore, there are still certain technical challenges in terms of the mechanical properties of damage and wrinkles of lithium battery separators, as well as the compatibility of adhesives with electrolytes and electrode materials, bonding strength and thermal stability. Summary of the invention

[0006] The purpose of the present invention is to provide a glue-coated diaphragm and a lithium-ion battery, which are used to solve the technical problems of mechanical properties of battery diaphragms being damaged and wrinkled in the prior art, and compatibility, stability and bonding strength of adhesives with electrolytes and pole piece materials.

[0007] The object of the present invention can be achieved by the following technical solution: a glue-coated diaphragm, wherein the glue-coated diaphragm is processed by the following steps:

[0008] S1. Add polyvinylidene fluoride powder and N-methylpyrrolidone into a closed reactor and stir. Raise the temperature of the reactor to 50-70°C, add hydrogen peroxide and ferrous sulfate, add dilute hydrochloric acid dropwise to adjust the pH of the system to 4, perform oxidation reaction for 2-3h, and perform post-treatment to obtain an active intermediate.

[0009] S2, adding active intermediate, modified nano-silica, dispersant, binder, thickener, and N-methylpyrrolidone into a reaction kettle and stirring for 1-2 hours, raising the temperature of the reaction kettle to 40-50° C., and post-treating to obtain a modified coating;

[0010] The synthetic principle of modified rubber coating is:

[0011] Under acidic conditions, divalent iron ions act as catalysts and react with hydrogen peroxide to generate hydroxyl radicals and trivalent iron ions. The trivalent iron ions continue to react with hydrogen peroxide to generate (·OOH) free radicals. The generated (·OOH) free radicals then react with divalent iron ions to generate hydroxyl free radicals. After ·OH comes into contact with the PVDF surface, it will capture the hydrogen atoms on the PVDF molecule, resulting in the breakage of the CH bond and the generation of new free radical sites, which modify the amine groups (-NH 2 ) reacts with the active groups (such as hydroxyl, carbonyl, etc.) on the surface of PVDF treated with hydroxyl free radicals to form graft polymerization.

[0012] S3, adding the diaphragm substrate and modified coating into the reactor and stirring, raising the temperature of the reactor to 180-210°C, keeping the temperature for 6-8h, degassing and scraping the film, and post-processing to obtain the coated diaphragm.

[0013] Furthermore, in step S1, the polyvinylidene fluoride powder, N-methylpyrrolidone, 30wt% hydrogen peroxide, and ferrous sulfate are used in a ratio of 10-20g:100-200mL:150-200mL:2-5g, and the post-treatment includes: after the reaction is completed, washing the reaction mixture with deionized water until it is neutral, placing it in a drying oven at 100°C, and drying it to constant weight to obtain an intermediate.

[0014] Furthermore, in step S2, the amount ratio of the intermediate, modified nano-silica, dispersant, binder, thickener, and N-methylpyrrolidone is 10-20g:5-8g:1-2g:8-10g:2-4g:200-300mL, the dispersant is polyethylene glycol, the binder is an acrylic polymer, and the thickener is carboxymethyl cellulose. The post-treatment includes: after the reaction is completed, filtering to remove insoluble matter and unstable particles, washing with anhydrous ethanol 5 times, filtering, placing in a vacuum drying oven at 80°C, and drying to constant weight to obtain a modified coating.

[0015] Furthermore, the modified nano-silicon dioxide is obtained by processing the following steps:

[0016] A1. Add sodium hydroxide solution and nano-silicon dioxide into a high-speed centrifugal mixer, raise the mixer temperature to 50-60°C, disperse and stir for 30 minutes, centrifuge for 20 minutes, and post-treat to obtain activated nano-silicon dioxide;

[0017] A2. Add activated nano-silica, 3-aminopropyltriethoxysilane and hydrochloric acid solution into a reaction kettle and stir. Increase the temperature of the stirrer to 50-60° C. and stir for 3-4 hours to obtain modified nano-silica.

[0018] The reaction equation for preparing modified nano-silicon dioxide is:

[0019]

[0020] The synthesis principle of modified nano-silica is:

[0021] The ethoxy group of 3-aminopropyltriethoxysilane undergoes a hydrolysis reaction in the presence of water under acidic conditions to generate silanol groups and ethanol. The silanol groups undergo a condensation reaction with the silanol groups on the surface of silica, losing a water molecule to form a Si-O-Si bond.

[0022] Further, in step A1, the 1 mol / L sodium hydroxide solution and the nano-silica are used in a ratio of 400-500 mL:15-20 g, and the nano-silica particle size is 400-500 nm. The post-treatment includes: after the reaction is completed, washing with a 20 wt% ethanol aqueous solution for 5 times and centrifuging to obtain activated nano-silica. In step A2, the activated nano-silica, 3-aminopropyltriethoxysilane, and hydrochloric acid solution are used in a ratio of 10-12 g:30-35 g:200-300 mL, and the hydrochloric acid concentration is 0.1 mol / L. The post-treatment includes: after the coupling agent is fully grafted onto the surface of the silica, washing with a 20 wt% ethanol aqueous solution for 5 times, centrifuging, and placing the product in a 120° C. drying oven and drying to constant weight to obtain modified nano-silica.

[0023] Furthermore, the diaphragm substrate is processed by the following steps:

[0024] B1. Add polypropylene particles and acetone into a reactor and stir, raise the temperature of the reactor to 60-80° C., stir for 2-3 hours, and perform post-treatment to obtain a polypropylene non-woven fabric;

[0025] B2. Add polypropylene non-woven fabric, acrylic acid aqueous solution and benzophenone solution into a reaction kettle, move to a UV cross-linking instrument, perform UV grafting reaction, and post-treat to obtain a diaphragm substrate.

[0026] The reaction equation for preparing the diaphragm substrate is:

[0027]

[0028] The synthesis principle of the diaphragm substrate is:

[0029] During the reaction, benzophenone absorbs ultraviolet light energy, causes intramolecular or intermolecular electron transfer, forms free radicals, and captures hydrogen atoms from polypropylene chains or acrylic acid molecules. The generated polypropylene free radicals are activated and react with acrylic acid to form free radicals with acrylic acid monomers. These free radicals continue to react with more acrylic acid monomers, causing the acrylic acid chain to continue to grow, forming polyacrylic acid chain segments. Acrylic acid monomers are continuously grafted onto the main chain of polypropylene to generate a polypropylene-based diaphragm substrate.

[0030] Further, in step B1, the amount ratio of the polypropylene particles and the acetone solution is 20-30g:100-120mL, and the post-treatment includes: adding the mixed slurry of the polypropylene particles and acetone after stirring evenly to an electrospinning device for electrospinning, the spinning high voltage static is 20-23kV, the injection speed is 10mL·h-1, and the distance between the collector and the needle is 1-5cm, so as to obtain a polypropylene non-woven fabric; in step B2, the amount ratio of the polypropylene non-woven fabric, the acrylic acid aqueous solution, and the benzophenone solution is 5-10g:20-30mL:50-80mL, the acrylic acid aqueous solution is composed of acrylic acid and deionized water in a ratio of 20g:100mL, the benzophenone solution is composed of benzophenone and acetone solution in a ratio of 4g:110mL, the ultraviolet light wavelength is 254nm, and the energy is 500mJ / cm 2 , the oxygen content is 0.2%, and the post-treatment includes: after the reaction is completed, soaking in 95% ethanol aqueous solution, filtering, placing the solid in a vacuum drying oven at a temperature of 30°C, and drying to constant weight to obtain a diaphragm substrate.

[0031] Furthermore, in step S3, the ratio of the membrane substrate and the modified coating is 180-200g:1000-1500mL, and the post-treatment includes: quenching the membrane in a water bath until the membrane is completely solidified, adding an ethanol solution with a concentration of 50% and soaking for 35-45h, the water bath quenching temperature is 15-25°C, and drying at room temperature to obtain a coated membrane.

[0032] The present invention also provides a lithium-ion battery, comprising an electrode body and an electrolyte consisting of a positive electrode plate, a negative electrode plate, a glue-coated diaphragm, and the electrode body is prepared by alternately arranging a plurality of positive electrode plates and a plurality of negative electrode plates, and then arranging a glue-coated diaphragm between two adjacent positive electrode plates and negative electrode plates to obtain an electrode body blank; placing the electrode body blank under a press, setting the pressure to 2.5-4.5MPa and the temperature to 20-30°C, and cold pressing and laminating to obtain the electrode body.

[0033] The present invention has the following beneficial effects:

[0034] 1. Hydrogen peroxide generates highly active hydroxyl radicals under the catalysis of divalent iron ions, which attack the CH and CF bonds on the surface of polyvinylidene fluoride to introduce hydroxyl groups, and then use 3-aminopropyltriethoxysilane as a bridge to build a strong chemical bond connection between polyvinylidene fluoride and materials such as silicon dioxide. By introducing a siloxy network structure, the surface of polyvinylidene fluoride is made more stable, the glass transition temperature is increased, and the production of easily decomposed products is reduced under long-term battery charging and discharging. In addition, the polar groups introduced on the surface of the modified polyvinylidene fluoride also significantly improve the compatibility with the electrolyte and the electrode material, reduce the decomposition of the electrolyte and the occurrence of side reactions, and further enhance the adhesion between the binder and the electrode material. This enhanced bonding force can effectively avoid the electrode falling off and poor contact during the battery cycle, which not only improves the thermal stability and bonding strength of the polyvinylidene fluoride binder, but also improves the cycle life of the battery.

[0035] 2. The acrylic acid-modified polyacrylate-based membrane introduces carboxyl active groups. These carboxyl groups can react with the amino groups on the surface of aminosilane-modified silica to form stable amide bonds, which significantly improves its tensile strength and puncture resistance, effectively reducing the damage and wrinkles that occur during battery manufacturing and use. At the same time, the acrylic acid-modified polyacrylate-based membrane produces stronger hydrogen bonds or dipole interactions with the modified polyvinylidene fluoride surface, thereby more firmly fixing the electrode material on the diaphragm. Therefore, this multiple reinforcement mechanism works synergistically to construct a functionally gradient interface structure, which not only significantly improves the mechanical properties of the diaphragm, making it less prone to damage and wrinkles, but also has many positive effects on the performance of the binder. At the same time, the enhanced bonding strength also improves the thermal stability of the binder during the charge and discharge cycle, reduces the possibility of black spots on the electrode material, and ultimately effectively improves the cycle stability of the electrode material, the safety of the battery, and the overall performance of the battery.

[0036] 3. The glue-coated diaphragm prepared in the present invention has adhesive layers on both sides of the base film, and each positive and negative electrode sheet is bonded to the surface of the diaphragm using cold pressing pressure, thereby reducing the number of diaphragm damage during the core stacking and transportation process, and can keep the positive and negative electrode sheets in a good position and a highly consistent spacing, reduce diaphragm wrinkles, and reduce the defects of uneven battery appearance, effectively reduce the safety performance risks caused by the overlap of the positive and negative electrode sheets, improve the interface state of the negative electrode and improve the cycle performance of the battery. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Example 1

[0039] This embodiment provides a method for preparing a lithium ion battery containing a glue-coated separator, comprising the following steps:

[0040] S1. Preparation of modified rubber coating

[0041] Weigh: 100 g of polyvinylidene fluoride powder and 1000 mL of N-methylpyrrolidone are added into a closed reactor and stirred. The temperature of the reactor is raised to 50° C., 1500 mL of hydrogen peroxide and 2 g of ferrous sulfate are added, and dilute hydrochloric acid is added dropwise to adjust the pH of the system to 4. The oxidation reaction is carried out for 2 hours. After the reaction is completed, the reaction mixture is washed with deionized water until it is neutral, placed in a drying oven at 100° C., and dried to constant weight to obtain an intermediate and an active intermediate;

[0042] Weigh: 100g of active intermediate, 50g of modified nano-silica, 10g of dispersant, 80g of binder, 20g of thickener, and 2000mL of N-methylpyrrolidone, add into the reactor and stir for 1h. Raise the temperature of the reactor to 40°C. After the reaction is completed, remove insoluble matter and unstable particles by suction, wash with anhydrous ethanol 5 times, filter, place in a vacuum drying oven at 80°C, and dry to constant weight to obtain the modified coating.

[0043] S2. Preparation of modified nano-silica

[0044] Weigh: 4000mL of sodium hydroxide solution and 150g of nano-silicon dioxide are added to a high-speed centrifugal mixer, the temperature of the mixer is increased to 50°C, dispersed and stirred for 30min, centrifuged for 20min, and after the reaction is completed, washed 5 times with a 20wt% ethanol aqueous solution and centrifuged to obtain activated nano-silicon dioxide;

[0045] Weigh: 100g of activated nano-silica, 300g of 3-aminopropyltriethoxysilane, and 2000mL of hydrochloric acid solution, add them into a reactor and stir, raise the temperature of the stirrer to 50°C, stir for 3h, the concentration of hydrochloric acid is 0.1mol / L, after the coupling agent is fully grafted onto the surface of silica, wash it 5 times with 20wt% ethanol aqueous solution, centrifuge it, place the product in a drying oven at 120°C, dry it to constant weight, and obtain modified nano-silica. Post-treatment obtains modified nano-silica.

[0046] S3. Preparation of diaphragm substrate

[0047] Weigh: 200g of polypropylene particles and 1000mL of acetone were added to the reactor and stirred. The temperature of the reactor was raised to 60℃ and stirred for 2h. The mixed slurry after stirring was added to the electrospinning equipment for electrospinning. The high voltage electrostatic of spinning was 20kV and the injection speed was 10mL·h -1, the distance between the collector and the needle is 1 cm, and a polypropylene nonwoven fabric is obtained;

[0048] Weigh: 50g of polypropylene non-woven fabric, 200mL of acrylic acid aqueous solution, and 500mL of benzophenone solution, add them into a reactor, move them into a UV cross-linking instrument, and perform UV grafting reaction. The acrylic acid aqueous solution is composed of a mixture of acrylic acid and deionized water in a ratio of 20g:100mL, and the benzophenone solution is composed of a mixture of benzophenone and acetone solution in a ratio of 4g:110mL. The wavelength of the UV light is 254nm, and the energy is 500mJ / cm 2 , the oxygen content is 0.2%. After the reaction is completed, it is placed in a 95% ethanol aqueous solution for soaking, filtered, and the solid is placed in a vacuum drying oven at a temperature of 30°C and dried to constant weight to obtain a diaphragm substrate.

[0049] S4. Preparation of glue-coated diaphragm

[0050] Weigh: 180g of diaphragm substrate and 1000mL of modified coating glue are added into the reactor and stirred. The temperature of the reactor is raised to 180°C. The reaction is kept warm for 6 hours. Degassing and film scraping are carried out. The film is quenched in a water bath until the film is completely solidified. An ethanol solution with a concentration of 50% is added and soaked for 35 hours. The water bath quenching temperature is 15°C. Dry at room temperature to obtain a coated diaphragm.

[0051] S5. Preparation of lithium-ion batteries

[0052] Alternately arrange lithium iron phosphate positive plates and graphite negative plates, and then arrange a glue-coated separator between two adjacent positive plates and negative plates to obtain an electrode body; place the electrode body under a press, set the pressure to 2.5 MPa, the temperature to 20° C., and cold press to obtain an electrode body;

[0053] The electrode body is placed in an ethylene carbonate electrolyte and packaged to obtain a lithium-ion battery.

[0054] Example 2

[0055] This embodiment provides a method for preparing a lithium ion battery containing a glue-coated separator, comprising the following steps:

[0056] S1. Preparation of modified rubber coating

[0057] Weigh: 150g of polyvinylidene fluoride powder and 1500mL of N-methylpyrrolidone are added into a closed reactor and stirred. The temperature of the reactor is raised to 60°C. 1800mL of hydrogen peroxide and 3g of ferrous sulfate are added. Dilute hydrochloric acid is added dropwise to adjust the pH of the system to 4. The oxidation reaction is carried out for 2.5h. After the reaction is completed, the reaction mixture is washed with deionized water until it is neutral, placed in a drying oven at 100°C, and dried to constant weight to obtain an intermediate and an active intermediate;

[0058] Weigh: 180g of active intermediate, 70g of modified nano-silica, 15g of dispersant, 90g of binder, 30g of thickener, and 2500mL of N-methylpyrrolidone, add into the reactor and stir for 1.5h. The temperature of the reactor is raised to 45°C. After the reaction is completed, filter out insoluble matter and unstable particles, wash with anhydrous ethanol 5 times, filter, place in a vacuum drying oven at 80°C, and dry to constant weight to obtain modified coating.

[0059] S2. Preparation of modified nano-silica

[0060] Weigh: 4500mL of sodium hydroxide solution and 170g of nano-silicon dioxide are added to a high-speed centrifugal mixer, the temperature of the mixer is increased to 55°C, dispersed and stirred for 30min, centrifuged for 20min, and after the reaction is completed, washed 5 times with a 20wt% ethanol aqueous solution and centrifuged to obtain activated nano-silicon dioxide;

[0061] Weigh: 110g of activated nano-silica, 320g of 3-aminopropyltriethoxysilane, and 2500mL of hydrochloric acid solution, add them into the reactor and stir, raise the temperature of the stirrer to 55°C, stir for 3.5h, the concentration of hydrochloric acid is 0.1mol / L, after the coupling agent is fully grafted to the surface of silica, wash it with 20wt% ethanol aqueous solution 5 times, centrifuge it, place the product in a drying oven at 120°C, dry it to constant weight, and obtain modified nano-silica. Post-treatment obtains modified nano-silica.

[0062] S3. Preparation of diaphragm substrate

[0063] Weigh: 250g of polypropylene particles and 1100mL of acetone were added to the reactor and stirred. The temperature of the reactor was raised to 70℃ and stirred for 2.5h. The mixed slurry after stirring was added to the electrospinning equipment for electrospinning. The spinning high voltage static was 21kV and the injection speed was 10mL·h -1 , the distance between the collector and the needle is 3 cm, and a polypropylene nonwoven fabric is obtained;

[0064] Weigh: 80g of polypropylene non-woven fabric, 250mL of acrylic acid aqueous solution, and 700mL of benzophenone solution, add them into a reactor, move them into a UV cross-linking instrument, and perform UV grafting reaction. The acrylic acid aqueous solution is composed of a mixture of acrylic acid and deionized water in a ratio of 20g:100mL, and the benzophenone solution is composed of a mixture of benzophenone and acetone solution in a ratio of 4g:110mL. The wavelength of the UV light is 254nm, and the energy is 500mJ / cm 2 , the oxygen content is 0.2%, and the post-treatment includes: after the reaction is completed, soaking in 95% ethanol aqueous solution, filtering, placing the solid in a vacuum drying oven at a temperature of 30°C, and drying to constant weight to obtain a diaphragm substrate.

[0065] S4. Preparation of glue-coated diaphragm

[0066] Weigh: 190g of diaphragm substrate and 1300mL of modified coating glue are added into the reactor and stirred. The temperature of the reactor is increased to 200℃, and the reaction is kept warm for 7h. Degassing and film scraping are carried out, and the film is quenched in a water bath until the film is completely solidified. Add 50% ethanol solution and soak for 40h. The water bath quenching temperature is 20℃, and dry at room temperature to obtain a coated diaphragm.

[0067] S5. Preparation of lithium-ion batteries

[0068] Alternately arrange lithium iron phosphate positive plates and graphite negative plates, and then arrange a glue-coated separator between two adjacent positive plates and negative plates to obtain an electrode body; place the electrode body under a press, set the pressure to 3.5 MPa, the temperature to 25° C., and cold press to obtain an electrode body;

[0069] The electrode body is placed in an ethylene carbonate electrolyte and packaged to obtain a lithium-ion battery.

[0070] Example 3

[0071] This embodiment provides a method for preparing a lithium ion battery containing a glue-coated separator, comprising the following steps:

[0072] S1. Preparation of modified rubber coating

[0073] Weigh: 200g of polyvinylidene fluoride powder and 2000mL of N-methylpyrrolidone are added into a closed reactor and stirred. The temperature of the reactor is raised to 70°C. 2000mL of hydrogen peroxide and 5g of ferrous sulfate are added. Dilute hydrochloric acid is added dropwise to adjust the pH of the system to 4. The oxidation reaction is carried out for 3h. After the reaction is completed, the mixture after the reaction is washed with deionized water until it is neutral, placed in a drying oven at 100°C, and dried to constant weight to obtain an intermediate and an active intermediate;

[0074] Weigh: 200g of active intermediate, 80g of modified nano-silica, 20g of dispersant, 100g of binder, 40g of thickener, and 3000mL of N-methylpyrrolidone, add into the reactor and stir for 2h. The temperature of the reactor is raised to 50°C. After the reaction is completed, filter out insoluble matter and unstable particles, wash with anhydrous ethanol 5 times, filter, place in a vacuum drying oven at 80°C, and dry to constant weight to obtain modified coating.

[0075] S2. Preparation of modified nano-silica

[0076] Weigh: 4000mL of sodium hydroxide solution and 150g of nano-silicon dioxide are added to a high-speed centrifugal mixer, the temperature of the mixer is increased to 60°C, dispersed and stirred for 30min, centrifuged for 20min, and after the reaction is completed, washed 5 times with a 20wt% ethanol aqueous solution and centrifuged to obtain activated nano-silicon dioxide;

[0077] Weigh: 120g of activated nano-silica, 350g of 3-aminopropyltriethoxysilane, and 3000mL of hydrochloric acid solution, add them into a reactor and stir, raise the temperature of the stirrer to 60°C, stir for 4h, the concentration of hydrochloric acid is 0.1mol / L, after the coupling agent is fully grafted onto the surface of silica, wash it 5 times with 20wt% ethanol aqueous solution, centrifuge it, place the product in a drying oven at 120°C, dry it to constant weight, and obtain modified nano-silica. Post-treatment obtains modified nano-silica.

[0078] S3. Preparation of diaphragm substrate

[0079] Weigh: 300g of polypropylene particles and 1200mL of acetone were added to the reactor and stirred. The temperature of the reactor was raised to 80℃ and stirred for 3h. The mixed slurry after stirring was added to the electrospinning equipment for electrospinning. The high voltage electrostatic of spinning was 23kV and the injection speed was 10mL·h -1 , the distance between the collector and the needle is 5 cm, and a polypropylene nonwoven fabric is obtained;

[0080] Weigh: 100 g of polypropylene non-woven fabric, 300 mL of acrylic acid aqueous solution, and 800 mL of benzophenone solution, add them into a reactor, and move them into a UV cross-linking instrument to perform UV grafting reaction. The acrylic acid aqueous solution is composed of a mixture of acrylic acid and deionized water in a ratio of 20 g:100 mL, and the benzophenone solution is composed of a mixture of benzophenone and acetone solution in a ratio of 4 g:110 mL. The wavelength of the UV light is 254 nm, and the energy is 500 mJ / cm 2 , the oxygen content is 0.2%, and the post-treatment includes: after the reaction is completed, soaking in 95% ethanol aqueous solution, filtering, placing the solid in a vacuum drying oven at a temperature of 30°C, and drying to constant weight to obtain a diaphragm substrate.

[0081] S4. Preparation of glue-coated diaphragm

[0082] Weigh: 200 g of diaphragm substrate and 1500 mL of modified coating glue, add into the reactor and stir, raise the temperature of the reactor to 210°C, keep warm for 8 hours, degas and scrape the film, quench the film in a water bath until the film is completely solidified, add 50% ethanol solution and soak for 45 hours, the water bath quenching temperature is 25°C, dry at room temperature to obtain the coated diaphragm.

[0083] S5. Preparation of lithium-ion batteries

[0084] Alternately arrange lithium iron phosphate positive plates and graphite negative plates, and then arrange a glue-coated separator between two adjacent positive plates and negative plates to obtain an electrode body; place the electrode body under a press, set the pressure to 4.5 MPa, the temperature to 30° C., and cold press to obtain an electrode body;

[0085] The electrode body is placed in an ethylene carbonate electrolyte and packaged to obtain a lithium-ion battery.

[0086] Comparative Example 1

[0087] The difference between this comparative example and Example 3 is that in step S1, no hydrogen peroxide and ferrous sulfate are added.

[0088] Comparative Example 2

[0089] The difference between this comparative example and Example 3 is that in step S2, no modified nano-silicon dioxide is added.

[0090] Comparative Example 3

[0091] The difference between this comparative example and Example 3 is that in step S3, no acrylic acid aqueous solution is added.

[0092] Comparative Example 4

[0093] The difference between this comparative example and Example 3 is that in step S5, the electrode body is replaced by the electrode blank to prepare the lithium ion battery.

[0094] Performance Test:

[0095] The performance of the coated diaphragms and lithium-ion batteries prepared in Examples 1-3 and Comparative Examples 1-4 was tested, wherein the capacity efficiency retention rate of the test sample after 500 charge and discharge cycles was tested according to the standard GB / T 43695-2024 "Requirements and measurement methods for energy conversion efficiency of lithium-ion batteries and battery packs", the tensile strength of the sample was measured according to the standard GB / T1040.1-2018 "Determination of tensile properties of plastics Part 1: General", and the peel strength of the sample was measured according to the standard JC / T 2781-2023 "Test method for peel strength of surface layer and substrate layer of PE co-extruded wood-plastic composite materials" to prove the bonding strength of the adhesive of the diaphragm. The specific test results are shown in Table 1:

[0096] Table 1-Performance test data of the sample

[0097]

[0098] It can be seen from the relevant data in Table 1 that, compared with the comparative example, the glue-coated diaphragm provided by the present invention constructs a functionally gradient interface structure through the synergistic effect of multiple reinforcement mechanisms between the polypropylene base film modified with acrylic acid and the modified polyvinylidene fluoride binder coated on the diaphragm substrate, which not only significantly improves the mechanical properties of the diaphragm, making it less prone to breakage and wrinkling, but also improves the thermal stability of the binder during the charge and discharge cycle, reduces the possibility of black spots on the electrode material, and ultimately effectively improves the cycle stability of the electrode material, the safety of the battery and the overall performance of the battery.

[0099] Compared with Examples 1-4, the peel strength and shrinkage rate of Comparative Example 1 are reduced, indicating that hydrogen peroxide generates highly active hydroxyl radicals under the catalysis of divalent iron ions, introduces hydroxyl groups on the surface of polyvinylidene fluoride, increases active sites, and serves as a bridge for subsequent monomers to generate more free radicals, thereby enhancing the adhesion between the binder and the electrode material and the diaphragm.

[0100] Compared with Examples 1-4, the shrinkage rate of Comparative Example 2 is reduced, indicating that by introducing a siloxy network structure between polyvinylidene fluoride and materials such as silicon dioxide, a strong chemical bond connection is constructed, so that the cross-linking degree between polyvinylidene fluoride and the base film material is enhanced, the glass transition temperature of the adhesive is increased, and then the thermal stability and bonding strength of the diaphragm are improved.

[0101] Compared with Examples 1-4, the breaking strength and elongation at break of Comparative Example 3 are significantly reduced, indicating that the polar carboxyl groups introduced by the acrylic acid grafted modified polypropylene form stable amide bonds through amination reaction with the amino groups on the surface of aminosilane-modified silica, further enhancing the interaction with the modified adhesive layer and significantly improving the mechanical properties of the polypropylene-based film.

[0102] Compared with Examples 1-4, the capacity retention rate of Comparative Example 4 is significantly reduced, indicating that the electrode body replacing the traditional electrode body has poor conductivity, which affects electron transmission; the electrode stability is poor and the structure is loose; the interface stability is poor, and the electrode is prone to fall off or poor contact, so the battery capacity retention rate is significantly reduced.

[0103] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A glue-coated diaphragm, characterized in that: The glue-coated diaphragm is processed by the following steps: S1. Add polyvinylidene fluoride powder and N-methylpyrrolidone into a closed reactor and stir. Raise the temperature of the reactor to 50-70°C, add hydrogen peroxide and ferrous sulfate, add dilute hydrochloric acid dropwise to adjust the pH of the system to 4, perform oxidation reaction for 2-3h, and perform post-treatment to obtain an active intermediate. S2, adding active intermediate, modified nano-silica, dispersant, binder, thickener, and N-methylpyrrolidone into a reaction kettle and stirring for 1-2 hours, raising the temperature of the reaction kettle to 40-50° C., and post-treating to obtain a modified coating; S3, adding the membrane substrate and modified coating into the reactor and stirring, raising the temperature of the reactor to 180-210°C, keeping the temperature for reaction for 6-8h, degassing and scraping the film, and post-processing to obtain the coated membrane.

2. A glue-coated diaphragm according to claim 1, characterized in that: In step S1, the amount ratio of the polyvinylidene fluoride powder, N-methylpyrrolidone, 30wt% hydrogen peroxide, and ferrous sulfate is 10-20g:100-200mL:150-200mL:2-5g.

3. The glue-coated diaphragm according to claim 1, characterized in that: In step S2, the amount ratio of the intermediate, modified nano-silica, dispersant, binder, thickener and N-methylpyrrolidone is 10-20g:5-8g:1-2g:8-10g:2-4g:200-300mL, the dispersant is polyethylene glycol, the binder is acrylic acid polymer, and the thickener is carboxymethyl cellulose.

4. The adhesive-coated diaphragm according to claim 1, characterized in that: The modified nano silicon dioxide is obtained by processing the following steps: A1. Add sodium hydroxide solution and nano-silicon dioxide into a high-speed centrifugal mixer, raise the mixer temperature to 50-60°C, disperse and stir for 30 minutes, centrifuge for 20 minutes, and post-treat to obtain activated nano-silicon dioxide; A2. Add activated nano-silica, 3-aminopropyltriethoxysilane and hydrochloric acid solution into a reaction kettle and stir. Increase the temperature of the stirrer to 50-60° C. and stir for 3-4 hours to obtain modified nano-silica.

5. A glue-coated diaphragm according to claim 4, characterized in that: In step A1, the 1 mol / L sodium hydroxide solution and the nano-silica are used in a ratio of 400-500 mL:15-20 g, and the nano-silica particle size is 400-500 nm. The post-treatment includes: after the reaction is completed, washing with a 20 wt% ethanol aqueous solution for 5 times and centrifuging to obtain activated nano-silica. In step A2, the activated nano-silica, 3-aminopropyltriethoxysilane, and hydrochloric acid solution are used in a ratio of 10-12 g:30-35 g:200-300 mL, and the hydrochloric acid concentration is 0.1 mol / L.

6. The glue-coated diaphragm according to claim 1, characterized in that: The diaphragm substrate is processed by the following steps: B1. Add polypropylene particles and acetone into a reactor and stir, raise the temperature of the reactor to 60-80° C., stir for 2-3 hours, and post-treat to obtain a polypropylene non-woven fabric; B2. Add polypropylene non-woven fabric, acrylic acid aqueous solution and benzophenone solution into a reaction kettle, move to a UV cross-linking instrument, perform UV grafting reaction, and post-treat to obtain a diaphragm substrate.

7. The adhesive-coated diaphragm according to claim 6, characterized in that: In step B1, the polypropylene particles and acetone solution are used in a ratio of 20-30 g: 100-120 mL; in step B2, the polypropylene non-woven fabric, acrylic acid aqueous solution, and benzophenone solution are used in a ratio of 5-10 g: 20-30 mL: 0.02-0.05 g, the acrylic acid aqueous solution is composed of acrylic acid and deionized water mixed in a ratio of 20 g: 100 mL, the benzophenone solution is composed of benzophenone and acetone solution mixed in a ratio of 4 g: 110 mL, the ultraviolet light wavelength is 254 nm, and the energy is 500 mJ / cm 2 , the oxygen content is 0.2%.

8. The adhesive-coated diaphragm according to claim 1, characterized in that: In step S3, the ratio of the diaphragm substrate to the modified coating is 180-200 g: 1000-1500 mL.

9. A lithium ion battery comprising the coated separator according to any one of claims 1 to 8, an electrode body consisting of a positive electrode plate, a negative electrode plate, a coated separator and an electrolyte, characterized in that: The preparation method of the electrode body is as follows: a plurality of positive plates and a plurality of negative plates are alternately arranged, and then a glue-coated separator is arranged between two adjacent positive plates and negative plates to obtain an electrode body blank; the electrode body blank is placed under a press, the pressure is set to 2.5-4.5MPa, the temperature is set to 20-30°C, and cold pressing is performed to obtain the electrode body.

Images