Preparation method of lithium battery with high stability

Abstract

The application provides a lithium battery preparation method with high stability. The carbon source and mesocarbon microbeads obtained by treating natural plants are used as negative electrode materials, so that the stability is ensured, the battery capacity is improved, and the mechanical performance and high charge carrier mobility are excellent. The effective components in the binder can enhance the binding force of the binder due to the heat generated in the battery charging and discharging process, improve the binding force of the active material on the current collector, have the ion conducting effect, have excellent electrochemical performance, and avoid the environmental pollution of the binder such as polyvinylidene fluoride. The heat released by the negative electrode additive during the battery operation preferentially causes the crosslinking polymerization reaction of the modifier and the binder, improves the binding force of the negative electrode active material on the substrate, reduces the shedding of the active material, reduces the reaction of the modifier and the binder under the action of the electrolyte, and prevents the generation of a too thick SEI film.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and specifically to a method for preparing a lithium battery with high stability. Background Technology

[0002] With the development trend of the new energy industry, lithium batteries have become the main power source for mobile power supplies and portable electronic devices due to their advantages such as high energy density, green safety, and low self-discharge. In recent years, lithium batteries have been widely used, but they also face many problems, such as insufficient stability, high manufacturing costs, and environmental pollution. In particular, the safety of lithium batteries has received close attention in recent years. Reports of lithium battery fires in electric vehicles are frequent, causing countless losses. Ensuring the safety of lithium batteries is paramount, and improving battery stability while increasing capacity is currently a major research focus.

[0003] The stability of lithium batteries is determined by the composition of their positive and negative electrodes and the electrolyte. Lithium iron phosphate is commonly used as the positive electrode material in lithium batteries, but the negative electrode material is composed of both non-carbon and carbon materials. The negative electrode materials actually used in lithium-ion batteries are generally carbon materials, such as graphite, soft carbon (e.g., coke), and hard carbon. Negative electrode materials under investigation include nitrides, PAS, tin-based oxides, tin alloys, nanomaterials, and other intermetallic compounds. However, using non-carbon materials as negative electrode materials can lead to structural instability during lithium battery charging. To ensure the stability of the lithium battery, this invention selects carbon materials as the negative electrode material. Although carbon materials are stable as negative electrode materials, their specific capacity is lower than that of other non-carbon materials, resulting in a lower initial discharge specific capacity. To address these issues, this invention provides a method for preparing a stable negative electrode material with high specific capacity and a method for preparing a stable lithium battery. Summary of the Invention

[0004] The main objective of this invention is to provide a method for preparing a lithium battery with high stability.

[0005] The second objective of this invention is to provide a method for preparing a lithium battery electrode with high stability.

[0006] A third objective of this invention is to provide a method for preparing a binder in a lithium battery electrode with high stability.

[0007] The specific preparation method is as follows:

[0008] A method for preparing a lithium battery with high stability.

[0009] The adhesive is prepared as follows:

[0010] a. Take 3-5 parts of polypropylene glycol and 2-4 parts of 4,4'-dicyclohexylmethane diisocyanate, add ethyl acetate, mix well, and place in a reaction vessel. Control the temperature at 220-225℃, keep warm for 4-5 hours, and then cool to room temperature for later use.

[0011] b. Take 1-2 parts of isophorone diisocyanate and 2-4 parts of trifluoromethanesulfonate, add them to ethyl acetate solvent, mix and heat to 175-180℃ at a rate of 1-2℃ / min, keep warm for 2-4h, then add dropwise to step a at a rate of 20-25 drops / min, control the solution temperature at 110-115℃, keep warm for 1-2h, then add 4-5 parts of polymethyl methacrylate, heat to 140-145℃, keep warm for 3-4h to obtain the final product.

[0012] The preparation method of the modifier is as follows:

[0013] ① Take 4-5 parts of octylphenoxy polyethoxyethyl phosphate and 4-5 parts of 3-sulfopropylhexadecyl dimethylammonium and put them into DNM solution. Put them into a reaction vessel and heat them to 180-190℃ at a rate of 2-4℃ / min. Keep them at this temperature for 3-4 hours and then cool them to room temperature for later use.

[0014] ② Take 1-2 parts of alkylphenol polyoxyethylene ether and 1-2 parts of medium-chain triglycerides, add them to ethyl acetate solvent, heat to 150-160℃ and stir for 2-3 hours, then add them dropwise to step ① at a rate of 30 drops / min, control the solution temperature to 110-130℃, and stir for 4-5 hours to obtain the final product.

[0015] The conductive agent is obtained by mixing 1-2 parts acetylene black, 4-5 parts mesophase carbon microspheres, and 3-5 parts graphite evenly.

[0016] The preparation method of the negative electrode material is as follows:

[0017] i. Clean the biochar source with water and dry it in an oven at 70-75℃ for 5-7 hours. Crush the dried biochar source to 400-500 mesh and mix it evenly. Place it in a tube furnace and calcine it under nitrogen protection. Increase the temperature at 2-3℃ / min to 550-560℃ and calcine for 4-5 hours. After that, take it out and grind it into 5-10μm powder for later use.

[0018] ii. Grind the dried biocarbon source into powder, add mesophase carbon microspheres with a particle size of 5-10μm and grind them together until uniform, wherein the mass ratio of biocarbon source to mesophase carbon microspheres is 4:1.

[0019] iii. Activation: Take a 10-12 wt% hydrogen chloride solution, immerse the above powder in the solution at 60°C for 30-45 minutes, remove it, rinse it with clean water, then immerse it again in a 5-10 wt% HF solution at 50°C for 20-40 minutes, remove it, rinse it with water, then immerse it in a modifier at 70°C for 2-4 hours, remove it and dry it in an oven at 80-90°C to obtain the final product.

[0020] The biocarbon source is one or both of rice husks and coconut shells, preferably 10-15 parts rice husks and 5-10 parts coconut shells.

[0021] The preparation method of the negative electrode additive is as follows:

[0022] (1) Take 4-6 parts of ethyl cellulose and 1-3 parts of 2,2-dimethylolpropionic acid, add ethyl acetate and mix. Then heat the mixture to 150-160℃ at a rate of 3-4℃ / min and keep it at that temperature for 3-4h. Then add 4-5 parts of gum arabic and control the temperature between 170-175℃. Keep it at that temperature for 5-7h and set it aside for later use.

[0023] (2) Add 1-2 parts of perfluorooctanoic acid glycol and 1-2 parts of polyphenylimidazolium to dimethylacetamide and mix evenly. Then heat to 130-140℃ and keep warm for 3-4 hours. Mix with the solution prepared in step (1), control the temperature to 200-220℃, and keep warm for 2-4 hours to obtain the solution.

[0024] Methods for preparing the negative electrode:

[0025] Cleaning of the current collector: Immerse copper foil in a 0.3-0.5wt% sodium hydroxide solution, vibrate it with microwave, and then dry it at 40-50℃ for 2-4 hours for later use;

[0026] Mixed granulation: Take the negative electrode material, binder, and negative electrode additive in a mass ratio of (80-84):(8-10):(11-15), granulate using spray granulation method, control the particle size to be 20-30μm, and dry in an oven at 80-85℃ for 4-5 hours for later use;

[0027] Preparation of electrode sheet: Mix the negative electrode material and conductive agent from the above steps in a mass ratio of (90-92):(8-10), add NMP and stir to form a uniform slurry, coat it evenly on the surface of copper foil, roll it after drying, and dry it at 40-50℃ for 5-6 hours; then slice it according to the required size to obtain the electrode sheet.

[0028] Methods for preparing the positive electrode of a lithium battery:

[0029] Cleaning the current collector: Soak the aluminum foil in a 0.01-0.03wt% hydrogen chloride solution for 20-30 minutes, rinse with clean water, and dry in a 40-45℃ oven for 1-2 hours for later use;

[0030] Preparation: Lithium iron phosphate, conductive agent, and binder are mixed evenly in a mass ratio of (90-94):(3-5):(3-5), and NMP solvent is added to form a uniform slurry;

[0031] Electrode sheet preparation: The slurry is evenly coated onto the surface of aluminum foil, dried at 90-100℃ for 4-5 hours, rolled and cut into slices according to the required size to obtain the electrode sheet.

[0032] Methods for preparing highly stable lithium batteries:

[0033] S1: Winding: The positive electrode, separator, and negative electrode of the battery are welded using an ultrasonic welding machine in that order, and then wound. After winding, under the combined action of static pressure, it is pressed into the required shape and placed into the middle cavity of the outer packaging for top sealing.

[0034] S2: Assembly: After top sealing, inject electrolyte into the battery, immerse it at 100-110℃ for 2-4 minutes, then inject electrolyte again in a low humidity environment, remove air bubbles in a vacuum environment and reseal.

[0035] S3: Inspection: Inspect the prepared batteries to ensure they are intact, leak-free, and do not bulge. Also, inspect the aluminum casing for inkjet printing.

[0036] Advantages of this invention:

[0037] Carbon materials have a significant advantage as anode materials for lithium batteries: they are stable. However, the theoretical energy density of carbon materials is lower than that of other materials; for example, the theoretical energy density of graphite is only 372 mAh·g. -1 To address the aforementioned issues, this invention selects carbon sources obtained from processed natural plants as the negative electrode material. The unique porosity and pore structure of natural plants allows lithium ions to freely intercalate and deintercalate. Combined with chemically derived carbon materials, this serves as the negative electrode material for lithium batteries, improving both battery capacity and stability. Modified and activated rice husks and coconut shells, along with mesophase carbon microspheres, are selected from natural plants to form the carbon negative electrode. This carbon negative electrode not only exhibits stable properties and high initial discharge specific capacity but also possesses excellent mechanical properties and high charge carrier mobility. Furthermore, NMP can form a stable slurry, allowing the positive and negative electrode materials to be uniformly and stably suspended in the solution, facilitating coating and resulting in more uniform and stable battery performance during subsequent preparation.

[0038] Lithium-ion battery electrodes are composed of active materials, binders, current collectors, and other components. The binder acts like a neural network connecting the various parts of the electrode system, bonding the active materials and the electrode substrate together and establishing electronic and ion conduction pathways. This influences the initial discharge specific capacity, stability, and cycle performance of the positive and negative electrode materials, as well as the battery's capacity.

[0039] Currently, the most common binder is polyvinylidene fluoride (PVDF), which can bond and fix mesophase carbon microspheres onto the substrate. However, the aforementioned carbon anode materials contain bio-carbon sources. After processing, the microstructure of the bio-carbon sources is not as regular as that of the mesophase carbon microspheres, which are spherical or near-spherical, but rather exhibits an irregular microstructure. PVDF cannot effectively bond and mix the bio-carbon sources and mesophase carbon microspheres together. Furthermore, due to the low bonding strength of PVDF, the compaction density of the electrode is low after electrode rolling, making it impossible to effectively bond and fix the bio-carbon sources onto the current collector. During long-term charge and discharge of the battery, the active material will fall off the copper foil of the current collector, resulting in a deterioration in the battery's cycle performance and charge / discharge performance. Therefore, this invention provides a binder that can effectively improve the bonding and fixation of bio-carbon sources and mesophase carbon microspheres onto the current collector. The binder provided by this invention can enhance its adhesive strength by utilizing the heat generated during battery charging and discharging. In the preparation of the negative electrode material, the negative electrode material and binder are first granulated into spheres using a spray granulation method, improving the tap density of the negative electrode material and the mixing uniformity of the bio-carbon source and mesophase carbon microspheres, which is beneficial for subsequent operations. The effective components in the binder also have ion-conducting properties, exhibiting excellent electrochemical performance and avoiding the environmental pollution caused by conventional binders such as polyvinylidene fluoride.

[0040] During battery operation, a stable solid electrolyte interphase (SEI) film forms on the surface of the active material on the negative electrode. The SEI film effectively prevents contact between the active material and the electrolyte, preventing electrolyte decomposition and failure. Because lithium-ion batteries primarily use modified and activated bio-carbon sources as the negative electrode material, along with a special binder, an SEI film forms at the negative electrode under the influence of the electrolyte. However, under the presence of charge and heat, the thickness of the SEI film, which is meant to protect the negative electrode, increases. This thickened SEI film passivates the negative electrode. Furthermore, since the SEI film is formed by the deposition of lithium elements from the battery, an excessively thick SEI film also consumes lithium ions, leading to a decrease in battery capacity and an increase in internal resistance. To address these issues, negative electrode additives are added to the negative electrode material. The active components in these additives preferentially undergo cross-linking polymerization reactions with the modifiers and binders under the heat released during battery operation. This improves the adhesion of the negative electrode active material to the substrate, reduces active material shedding, and minimizes the reaction of the modifiers and binders under the influence of the electrolyte, preventing the formation of an excessively thick SEI film. Specific implementation methods

[0041] Example 1

[0042] A method for preparing a lithium battery with high stability.

[0043] The adhesive is prepared as follows:

[0044] a. Take 4 parts of polypropylene glycol and 3 parts of 4,4'-dicyclohexylmethane diisocyanate, add them to ethyl acetate, mix them evenly, and put them into a reaction vessel. Control the temperature at 223℃, keep it at this temperature for 4.5 hours, and then cool it to room temperature for later use.

[0045] b. Take 1.5 parts of isophorone diisocyanate and 3 parts of trifluoromethanesulfonate, add them to ethyl acetate solvent, mix and heat to 178°C at a rate of 1.5°C / min, keep at this temperature for 3 hours, then add to step a dropwise at a rate of 23 drops / min, control the solution temperature at 113°C, keep at this temperature for 1.5 hours, then add 4.5 parts of polymethyl methacrylate, heat to 143°C, and keep at this temperature for 3.5 hours to obtain the final product.

[0046] The preparation method of the modifier is as follows:

[0047] ① Take 4.5 parts of octylphenoxy polyethoxyethyl phosphate and 4.5 parts of 3-sulfopropylhexadecyl dimethylammonium and put them into DNM solution. Put them into a reaction vessel and heat them to 185℃ at a rate of 3℃ / min. Keep them at this temperature for 3.5h and then cool them to room temperature for later use.

[0048] ② Take 1.5 parts of alkylphenol polyoxyethylene ether and 1.5 parts of medium-chain triglycerides, add them to ethyl acetate solvent, heat to 155℃ and stir for 2.5h, then add them dropwise to step ① at a rate of 30 drops / min, control the solution temperature at 120℃, and stir for 4.5h to obtain the final product.

[0049] The conductive agent is obtained by mixing 1.5 parts acetylene black, 4.5 parts mesophase carbon microspheres, and 4 parts graphite evenly.

[0050] The preparation method of the negative electrode material is as follows:

[0051] i. Take the biochar source, wash it with clean water, put it in a 73℃ oven and dry it for 6 hours. Crush the dried biochar source to 450 mesh, mix it evenly and put it into a tube furnace for calcination under nitrogen protection. The temperature is increased to 555℃ at 2.5℃ / min and calcined for 4.5 hours. After that, take it out and grind it into 8μm powder for later use.

[0052] ii. Grind the dried biocarbon source into powder, add mesophase carbon microspheres with a particle size of 8μm and grind them together until uniform, wherein the mass ratio of biocarbon source to mesophase carbon microspheres is 4:1.

[0053] iii. Activation: Take an 11 wt% hydrogen chloride solution, immerse the above powder in the solution at 60°C for 38 minutes, remove it, rinse it with clean water, then immerse it again in an 8 wt% HF solution at 50°C for 30 minutes, remove it, rinse it with water, then immerse it in a modifier at 70°C for 3 hours, remove it and dry it in an 85°C oven to obtain the final product.

[0054] The biocarbon sources included 13 parts rice husks and 8 parts coconut shells.

[0055] The preparation method of the negative electrode additive is as follows:

[0056] (1) Take 5 parts of ethyl cellulose and 2 parts of 2,2-dimethylolpropionic acid, add ethyl acetate and mix. Then heat the mixture to 155℃ at a rate of 3.5℃ / min and keep it at that temperature for 3.5h. Then add 4.5 parts of gum arabic and control the temperature at 173℃. Keep it at that temperature for 6h and set it aside for later use.

[0057] (2) 1.5 parts of perfluorooctanoic acid glycol and 1.5 parts of polyphenylene imidazole are added to dimethylacetamide and mixed evenly. The mixture is heated to 135°C and kept at this temperature for 3.5 hours. Then it is mixed with the solution prepared in step (1). The temperature is controlled at 210°C and kept at this temperature for 3 hours to obtain the final product.

[0058] Methods for preparing the negative electrode:

[0059] Cleaning of the current collector: Immerse copper foil in a 0.4wt% sodium hydroxide solution, vibrate it with microwave, and then dry it at 45℃ for 3 hours for later use;

[0060] Mixed granulation: Take the negative electrode material, binder, and negative electrode additive in a mass ratio of 82:9:13, granulate using spray granulation method, control the particle size to 25μm, and dry in an 83℃ oven for 4.5h for later use;

[0061] Electrode preparation: The negative electrode material and conductive agent from the above steps are mixed evenly in a mass ratio of 91:9. NMP is added and stirred into a uniform slurry. The slurry is evenly coated on the surface of copper foil, dried, rolled, and dried at 45°C for 5.5 hours. The slab is then sliced ​​according to the required size to obtain the electrode sheet.

[0062] Methods for preparing the positive electrode of a lithium battery:

[0063] Cleaning the current collector: Soak the aluminum foil in a 0.02wt% hydrogen chloride solution for 25 minutes, rinse with water, and dry in a 43℃ oven for 1.5 hours for later use;

[0064] Preparation: Lithium iron phosphate, conductive agent, and binder are mixed evenly in a mass ratio of 92:4:4, and NMP solvent is added to form a uniform slurry;

[0065] Electrode sheet preparation: The slurry is evenly coated onto the surface of aluminum foil, dried at 95°C for 4.5 hours, rolled, and sliced ​​according to the required size to obtain the electrode sheet.

[0066] Methods for preparing highly stable lithium batteries:

[0067] S1: Winding: The positive electrode, separator, and negative electrode of the battery are welded using an ultrasonic welding machine in that order, and then wound. After winding, under the combined action of static pressure, it is pressed into the required shape and placed into the middle cavity of the outer packaging for top sealing.

[0068] S2: Assembly: After top sealing, electrolyte is injected into the battery. After being immersed at 105°C for 3 minutes, electrolyte is injected again under low humidity. Air bubbles are removed under vacuum and the battery is sealed again.

[0069] S3: Inspection: Inspect the prepared batteries to ensure they are intact, leak-free, and do not bulge. Also, inspect the aluminum casing for inkjet printing.

[0070] Example 2

[0071] A method for preparing a lithium battery with high stability.

[0072] The adhesive is prepared as follows:

[0073] a. Take 3 parts of polypropylene glycol and 4 parts of 4,4'-dicyclohexylmethane diisocyanate, add them to ethyl acetate, mix them evenly, and put them into a reaction vessel. Control the temperature at 220℃, keep it at this temperature for 5 hours, and then cool it to room temperature for later use.

[0074] b. Take 1 part of isophorone diisocyanate and 4 parts of trifluoromethanesulfonate, add them to ethyl acetate solvent, mix and heat to 180°C at a rate of 1°C / min, keep warm for 2 hours, then add to step a at a rate of 25 drops / min, control the solution temperature at 110°C, keep warm for 2 hours, then add 4 parts of polymethyl methacrylate, heat to 145°C, keep warm for 3 hours to obtain the final product.

[0075] The preparation method of the modifier is as follows:

[0076] ① Take 4 parts of octylphenoxy polyethoxyethyl phosphate and 5 parts of 3-sulfopropylhexadecyl dimethylammonium and put them into DNM solution. Put them into a reaction vessel and heat them to 190℃ at a rate of 2℃ / min. Keep them at this temperature for 3 hours and then cool them to room temperature for later use.

[0077] ② Take 2 parts of alkylphenol polyoxyethylene ether and 1 part of medium-chain triglyceride, add them to ethyl acetate solvent, heat to 160℃ and stir for 2 hours, then add them dropwise to step ① at a rate of 30 drops / min, control the solution temperature at 130℃, and stir for 4 hours to obtain the final product.

[0078] The conductive agent is prepared by mixing 2 parts acetylene black, 4 parts mesophase carbon microspheres, and 5 parts graphite evenly.

[0079] The preparation method of the negative electrode material is as follows:

[0080] i. Take the biochar source, wash it with clean water, put it in a 75℃ oven and dry it for 5 hours. Crush the dried biochar source to 500 mesh, mix it evenly and put it into a tube furnace for calcination under nitrogen protection. Heat the furnace to 560℃ at 2℃ / min and calcinate for 4 hours. After taking it out, grind it into 10μm powder for later use.

[0081] ii. Grind the dried biocarbon source into powder, add mesophase carbon microspheres with a particle size of 5μm and grind them together until uniform, wherein the mass ratio of biocarbon source to mesophase carbon microspheres is 4:1.

[0082] iii. Activation: Take a 12wt% hydrogen chloride solution, immerse the above powder in the solution at 60℃ for 30 minutes, remove it, rinse it with clean water, then immerse it again in a 10wt% HF solution at 50℃ for 20 minutes, remove it, rinse it with water, then immerse it in a modifier at 70℃ for 4 hours, remove it and dry it in an 80℃ oven to obtain the final product.

[0083] Of these, 21 samples were derived from rice husks as the biocarbon source.

[0084] The preparation method of the negative electrode additive is as follows:

[0085] (1) Take 4 parts of ethyl cellulose and 3 parts of 2,2-dimethylolpropionic acid, add ethyl acetate and mix. Then heat the mixture to 160℃ at a rate of 3℃ / min and keep it at that temperature for 3 hours. Then add 5 parts of gum arabic and control the temperature at 170℃. Keep it at that temperature for 7 hours and set it aside for later use.

[0086] (2) Add 1 part of perfluorooctanoic acid glycol and 2 parts of polyphenylimidazolium to dimethylacetamide and mix evenly. Then heat to 130°C and keep warm for 4 hours. Mix with the solution prepared in step (1), control the temperature at 200°C and keep warm for 4 hours to obtain the final product.

[0087] Methods for preparing the negative electrode:

[0088] Cleaning of the current collector: Immerse copper foil in a 0.3wt% sodium hydroxide solution, vibrate it with microwave, and then dry it at 50℃ for 2 hours for later use;

[0089] Mixed granulation: Take the negative electrode material, binder, and negative electrode additive in a mass ratio of 84:8:15, granulate using spray granulation method, control the particle size to 20μm, and dry in an 85℃ oven for 4 hours for later use.

[0090] Electrode preparation: Mix the negative electrode material and conductive agent from the above steps in a mass ratio of 92:8, add NMP and stir to form a uniform slurry, coat it evenly on the surface of copper foil, dry it and roll it, and dry it at 50°C for 5 hours; then slice it according to the required size to obtain the electrode sheet.

[0091] Methods for preparing the positive electrode of a lithium battery:

[0092] Cleaning the current collector: Soak the aluminum foil in a 0.03wt% hydrogen chloride solution for 20 minutes, rinse with water, and dry in a 45℃ oven for 1 hour for later use;

[0093] Preparation: Lithium iron phosphate, conductive agent, and binder are mixed evenly in a mass ratio of 94:3:5, and NMP solvent is added to form a uniform slurry;

[0094] Electrode sheet preparation: The slurry is evenly coated onto the surface of aluminum foil, dried at 90°C for 5 hours, rolled and cut into slices according to the required size to obtain the electrode sheet.

[0095] Methods for preparing highly stable lithium batteries:

[0096] S1: Winding: The positive electrode, separator, and negative electrode of the battery are welded using an ultrasonic welding machine in that order, and then wound. After winding, under the combined action of static pressure, it is pressed into the required shape and placed into the middle cavity of the outer packaging for top sealing.

[0097] S2: Assembly: After top sealing, electrolyte is injected into the battery. After being immersed at 110°C for 2 minutes, electrolyte is injected again under low humidity. Air bubbles are removed under vacuum and the battery is sealed again.

[0098] S3: Inspection: Inspect the prepared batteries to ensure they are intact, leak-free, and do not bulge. Also, inspect the aluminum casing for inkjet printing.

[0099] Example 3

[0100] A method for preparing a lithium battery with high stability.

[0101] The adhesive is prepared as follows:

[0102] a. Take 5 parts of polypropylene glycol and 2 parts of 4,4'-dicyclohexylmethane diisocyanate, add them to ethyl acetate, mix them evenly, and put them into a reaction vessel. Control the temperature at 225℃, keep it at this temperature for 4 hours, and then cool it to room temperature for later use.

[0103] b. Take 2 parts of isophorone diisocyanate and 2 parts of trifluoromethanesulfonate, add them to ethyl acetate solvent, mix and heat to 175°C at a rate of 2°C / min, keep warm for 4 hours, then add to step a at a rate of 20 drops / min, control the solution temperature at 115°C, keep warm for 1 hour, then add 5 parts of polymethyl methacrylate, heat to 140°C, keep warm for 4 hours to obtain the final product.

[0104] The preparation method of the modifier is as follows:

[0105] ① Take 5 parts of octylphenoxy polyethoxyethyl phosphate and 4 parts of 3-sulfopropylhexadecyl dimethylammonium and put them into DNM solution. Put them into a reaction vessel and heat them to 180℃ at a rate of 4℃ / min. Keep them at this temperature for 4 hours and then cool them to room temperature for later use.

[0106] ② Take 1 part of alkylphenol polyoxyethylene ether and 2 parts of medium-chain triglyceride, add them to ethyl acetate solvent, heat to 150℃ and stir for 3 hours, then add them dropwise to step ① at a rate of 30 drops / min, control the solution temperature at 110℃, and stir for 5 hours to obtain the final product.

[0107] The conductive agent is prepared by mixing 1 part acetylene black, 5 parts mesophase carbon microspheres, and 3 parts graphite evenly.

[0108] The preparation method of the negative electrode material is as follows:

[0109] i. Take the biochar source, wash it with clean water, put it in a 70℃ oven and dry it for 7 hours. Crush the dried biochar source to 400 mesh, mix it evenly and put it into a tube furnace for calcination under nitrogen protection. Heat it to 550℃ at 3℃ / min and calcinate for 5 hours. After that, take it out and grind it into 5μm powder for later use.

[0110] ii. Grind the dried biocarbon source into powder, add mesophase carbon microspheres with a particle size of 10μm and grind them together until uniform, wherein the mass ratio of biocarbon source to mesophase carbon microspheres is 4:1.

[0111] iii. Activation: Take a 10wt% hydrogen chloride solution, immerse the above powder in the solution at 60℃ for 45 minutes, remove it, rinse it with clean water, then immerse it again in a 5wt% HF solution at 50℃ for 40 minutes, remove it, rinse it with water, then immerse it in a modifier at 70℃ for 2 hours, remove it and dry it in a 90℃ oven to obtain the final product.

[0112] The biocarbon source was coconut shells in 21 samples.

[0113] The preparation method of the negative electrode additive is as follows:

[0114] (1) Take 6 parts of ethyl cellulose and 1 part of 2,2-dimethylolpropionic acid, add ethyl acetate and mix. Then heat to 150℃ at a rate of 4℃ / min and keep warm for 4h. Add 4 parts of gum arabic and control the temperature at 175℃. Keep warm for 5h and set aside.

[0115] (2) Add 2 parts of perfluorooctanoic acid glycol and 1 part of polyphenylimidazolium to dimethylacetamide and mix evenly. Then heat to 140°C and keep warm for 3 hours. Mix with the solution prepared in step (1), control the temperature at 220°C and keep warm for 2 hours to obtain the final product.

[0116] Methods for preparing the negative electrode:

[0117] Cleaning of the current collector: Immerse copper foil in a 0.5wt% sodium hydroxide solution, vibrate it with microwave, and then dry it at 40℃ for 4 hours for later use;

[0118] Mixed granulation: Take the negative electrode material, binder, and negative electrode additive in a mass ratio of 80:10:11, granulate using spray granulation method, control the particle size to 30μm, and dry in an 80℃ oven for 5 hours for later use.

[0119] Electrode preparation: Mix the negative electrode material and conductive agent from the above steps in a mass ratio of 90:10, add NMP and stir to form a uniform slurry, coat it evenly on the surface of copper foil, dry it and roll it, and dry it at 40°C for 6 hours; then slice it according to the required size to obtain the electrode sheet.

[0120] Methods for preparing the positive electrode of a lithium battery:

[0121] Cleaning the current collector: Soak the aluminum foil in a 0.01wt% hydrogen chloride solution for 30 minutes, rinse with water, and dry in a 40℃ oven for 2 hours for later use;

[0122] Preparation: Lithium iron phosphate, conductive agent, and binder are mixed evenly in a mass ratio of 90:5:3, and NMP solvent is added to form a uniform slurry;

[0123] Electrode sheet preparation: The slurry is evenly coated onto the surface of aluminum foil, dried at 100℃ for 4 hours, rolled and pressed, and sliced ​​according to the required size to obtain the electrode sheet.

[0124] Methods for preparing highly stable lithium batteries:

[0125] S1: Winding: The positive electrode, separator, and negative electrode of the battery are welded using an ultrasonic welding machine in that order, and then wound. After winding, under the combined action of static pressure, it is pressed into the required shape and placed into the middle cavity of the outer packaging for top sealing.

[0126] S2: Assembly: After top sealing, inject electrolyte into the battery, immerse it at 100°C for 4 minutes, then inject electrolyte again in a low humidity environment, remove air bubbles in a vacuum environment and reseal.

[0127] S3: Inspection: Inspect the prepared batteries to ensure they are intact, leak-free, and do not bulge. Also, inspect the aluminum casing for inkjet printing.

[0128] Comparative Example 1

[0129] A method for preparing a lithium battery with high stability.

[0130] The method for preparing the adhesive is as follows:

[0131] a. Take 8 parts of polypropylene glycol and 3 parts of 4,4'-dicyclohexylmethane diisocyanate, add them to ethyl acetate, mix them evenly, and put them into a reaction vessel. Control the temperature at 223℃, keep it at this temperature for 4.5 hours, and then cool it to room temperature for later use.

[0132] b. Take 1.5 parts of isophorone diisocyanate and 3 parts of trifluoromethanesulfonate, add them to ethyl acetate solvent, mix and heat to 178°C at a rate of 1.5°C / min, keep at this temperature for 3 hours, then add to step a dropwise at a rate of 23 drops / min, control the solution temperature at 113°C, keep at this temperature for 1.5 hours, then add 4.5 parts of polymethyl methacrylate, heat to 143°C, and keep at this temperature for 3.5 hours to obtain the final product.

[0133] The rest is the same as in Example 1.

[0134] Comparative Example 2

[0135] A method for preparing a lithium battery with high stability.

[0136] The method for preparing the adhesive is as follows:

[0137] a. Take 4 parts of polypropylene glycol and 3 parts of 4,4'-dicyclohexylmethane diisocyanate, add them to ethyl acetate, mix them evenly, and put them into a reaction vessel. Control the temperature at 223℃, keep it at this temperature for 4.5 hours, and then cool it to room temperature for later use.

[0138] b. Take 1.5 parts of isophorone diisocyanate, 3 parts of trifluoromethanesulfonate, and 4.5 parts of polymethyl methacrylate, add them to ethyl acetate solvent, mix and heat to 178°C at a rate of 1.5°C / min, keep warm for 3 hours, then add dropwise to step a at a rate of 23 drops / min, control the solution temperature at 113°C, and keep warm for 3.5 hours to obtain the final product.

[0139] The rest is the same as in Example 1.

[0140] Comparative Example 3

[0141] A method for preparing a lithium battery with high stability.

[0142] The method for preparing the adhesive is as follows:

[0143] a. Take 4 parts of polypropylene glycol and 3 parts of 4,4'-dicyclohexylmethane diisocyanate, add them to ethyl acetate, mix them evenly, and put them into a reaction vessel. Control the temperature at 223℃, keep it at this temperature for 4.5 hours, and then cool it to room temperature for later use.

[0144] b. Take 1.5 parts of isophorone diisocyanate and 3 parts of trifluoromethanesulfonate, add them to ethyl acetate solvent, mix and heat to 178°C at a rate of 1.5°C / min, keep at this temperature for 3 hours, then add to step a at a rate of 23 drops / min, control the solution temperature at 113°C, keep at this temperature for 1.5 hours, add 1 part of polymethyl methacrylate, heat to 143°C, keep at this temperature for 3.5 hours to obtain the final product.

[0145] The rest is the same as in Example 1.

[0146] Comparative Example 4

[0147] A method for preparing a lithium battery with high stability.

[0148] The method for preparing the adhesive is as follows:

[0149] Take 4 parts of polypropylene glycol, 3 parts of 4,4'-dicyclohexylmethane diisocyanate, 1.5 parts of isophorone diisocyanate, 3 parts of trifluoromethanesulfonate, and 4.5 parts of polymethyl methacrylate, add ethyl acetate and mix well. Then put the mixture into a reaction vessel, control the temperature at 223℃, keep it at this temperature for 10 hours, and then cool it to room temperature to obtain the final product.

[0150] The rest is the same as in Example 1.

[0151] Comparative Example 5

[0152] A method for preparing a lithium battery with high stability.

[0153] The binder is polyvinylidene fluoride.

[0154] The rest is the same as in Example 1.

[0155] Comparative Example 6

[0156] A method for preparing a lithium battery with high stability.

[0157] The preparation method of the modifier is as follows:

[0158] ① Take 4.5 parts of octylphenoxy polyethoxyethyl phosphate and 7 parts of 3-sulfopropylhexadecyl dimethylammonium and put them into DNM solution. Put them into a reaction vessel and heat them to 185℃ at a rate of 3℃ / min. Keep them at this temperature for 3.5h and then cool them to room temperature for later use.

[0159] ② Take 1.5 parts of alkylphenol polyoxyethylene ether and 1.5 parts of medium-chain triglycerides, add them to ethyl acetate solvent, heat to 155℃ and stir for 2.5h, then add them dropwise to step ① at a rate of 30 drops / min, control the solution temperature at 120℃, and stir for 4.5h to obtain the final product.

[0160] The rest is the same as in Example 1.

[0161] Comparative Example 7

[0162] A method for preparing a lithium battery with high stability.

[0163] The preparation method of the modifier is as follows:

[0164] ① Take 4.5 parts of octylphenoxy polyethoxyethyl phosphate and 4.5 parts of 3-sulfopropylhexadecyl dimethylammonium and put them into DNM solution. Put them into a reaction vessel and heat them to 185℃ at a rate of 3℃ / min. Keep them at this temperature for 3.5h and then cool them to room temperature for later use.

[0165] ② Take 1.5 parts of alkylphenol polyoxyethylene ether, add it to ethyl acetate solvent, heat to 155℃ and stir for 2.5h, then add it dropwise to step ① at a rate of 30 drops / min, control the solution temperature at 120℃, and stir for 4.5h to obtain the final product.

[0166] The rest is the same as in Example 1.

[0167] Comparative Example 8

[0168] A method for preparing a lithium battery with high stability.

[0169] The preparation method of the modifier is as follows:

[0170] ① Take 4.5 parts of octylphenoxy polyethoxyethyl phosphate, 4.5 parts of 3-sulfopropyl hexadecyl dimethyl ammonium, 1.5 parts of alkylphenol polyoxyethylene ether, and 1.5 parts of medium-chain triglycerides and put them into DNM solution. Place them in a reaction vessel and heat to 185℃ at a rate of 3℃ / min. Keep at this temperature for 10 hours and then cool to room temperature to obtain the final product.

[0171] The rest is the same as in Example 1.

[0172] Comparative Example 9

[0173] A method for preparing a lithium battery with high stability.

[0174] The preparation method of the negative electrode material is as follows:

[0175] i. Take the biochar source, wash it with clean water, put it in a 73℃ oven and dry it for 6 hours. Crush the dried biochar source to 450 mesh, mix it evenly and put it into a tube furnace for calcination under nitrogen protection. The temperature is increased to 555℃ at 2.5℃ / min and calcined for 4.5 hours. After that, take it out and grind it into 8μm powder for later use.

[0176] ii. Grind the dried biocarbon source into powder, add mesophase carbon microspheres with a particle size of 8μm and grind them together until uniform, wherein the mass ratio of biocarbon source to mesophase carbon microspheres is 2:1.

[0177] iii. Activation: Take an 11 wt% hydrogen chloride solution, immerse the above powder in the solution at 60°C for 38 minutes, remove it, rinse it with clean water, then immerse it again in an 8 wt% HF solution at 50°C for 30 minutes, remove it, rinse it with water, then immerse it in a modifier at 70°C for 3 hours, remove it and dry it in an 85°C oven to obtain the final product.

[0178] The rest is the same as in Example 1.

[0179] Comparative Example 10

[0180] A method for preparing a lithium battery with high stability.

[0181] The preparation method of the negative electrode material is as follows:

[0182] i. Take the biochar source, wash it with clean water, put it in a 73℃ oven and dry it for 6 hours. Crush the dried biochar source to 450 mesh, mix it evenly and put it into a tube furnace for calcination under nitrogen protection. The temperature is increased to 555℃ at 2.5℃ / min and calcined for 4.5 hours. After that, take it out and grind it into 8μm powder for later use.

[0183] ii. Grind the dried biocarbon source into powder, add mesophase carbon microspheres with a particle size of 8μm and grind them together until uniform, wherein the mass ratio of biocarbon source to mesophase carbon microspheres is 4:1.

[0184] iii. Activation: Take an 11 wt% hydrogen chloride solution, immerse the above powder in the solution at 60°C for 38 minutes, remove it, clean it with water, immerse it in the modifier at 70°C for 3 hours, remove it and dry it in an oven at 85°C to obtain the final product.

[0185] The rest is the same as in Example 1.

[0186] Comparative Example 11

[0187] A method for preparing a lithium battery with high stability.

[0188] The preparation method of the negative electrode material is as follows:

[0189] i. Take the biochar source, wash it with clean water, put it in a 73℃ oven and dry it for 6 hours. Crush the dried biochar source to 450 mesh, mix it evenly and put it into a tube furnace for calcination under nitrogen protection. The temperature is increased to 555℃ at 2.5℃ / min and calcined for 4.5 hours. After that, take it out and grind it into 8μm powder for later use.

[0190] ii. Grind the dried biocarbon source into powder, add mesophase carbon microspheres with a particle size of 8μm and grind them together until uniform, wherein the mass ratio of biocarbon source to mesophase carbon microspheres is 4:1.

[0191] iii. Activation: Take an 11 wt% hydrogen chloride solution, immerse the above powder in the solution at 60°C for 38 minutes, remove it, rinse it with clean water, then immerse it again in an 8 wt% HF solution at 50°C for 30 minutes, remove it, rinse it with water, and dry it in an 85°C oven to obtain the final product.

[0192] The rest is the same as in Example 1.

[0193] Comparative Example 12

[0194] A method for preparing a lithium battery with high stability.

[0195] The preparation method of the negative electrode material is as follows:

[0196] Activation: Immerse 8 μm mesophase carbon microspheres in an 11 wt% hydrogen chloride solution at 60°C for 38 min, then remove and rinse with water. Immerse again in an 8 wt% HF solution at 50°C for 30 min, rinse with water, and then immerse in a modifier at 70°C for 3 h. Finally, dry in an 85°C oven to obtain the final product.

[0197] The rest is the same as in Example 1.

[0198] Comparative Example 13

[0199] A method for preparing a lithium battery with high stability.

[0200] The negative electrode material is mesophase carbon microspheres.

[0201] The rest is the same as in Example 1.

[0202] Comparative Example 14

[0203] A method for preparing a lithium battery with high stability.

[0204] The preparation method of the negative electrode additive is as follows:

[0205] (1) Take 5 parts of ethyl cellulose and 5 parts of 2,2-dimethylolpropionic acid, add ethyl acetate and mix. Then heat to 155℃ at a rate of 3.5℃ / min and keep warm for 3.5h. Add 4.5 parts of gum arabic and control the temperature at 173℃. Keep warm for 6h and set aside.

[0206] (2) 1.5 parts of perfluorooctanoic acid glycol and 1.5 parts of polyphenylene imidazole are added to dimethylacetamide and mixed evenly. The mixture is heated to 135°C and kept at this temperature for 3.5 hours. Then it is mixed with the solution prepared in step (1). The temperature is controlled at 210°C and kept at this temperature for 3 hours to obtain the final product.

[0207] The mass ratio of the negative electrode additive to the negative electrode material is 13:88.

[0208] The rest is the same as in Example 1.

[0209] Comparative Example 15

[0210] A method for preparing a lithium battery with high stability.

[0211] The preparation method of the negative electrode additive is as follows:

[0212] (1) Take 5 parts of ethyl cellulose and 2 parts of 2,2-dihydroxymethylpropionic acid, add ethyl acetate and mix. Then heat to 155℃ at a rate of 3.5℃ / min and keep warm for 3.5h. Then control the temperature at 173℃ and keep warm for 6h. Then set aside for later use.

[0213] (2) 1.5 parts of perfluorooctanoic acid glycol and 1.5 parts of polyphenylene imidazole are added to dimethylacetamide and mixed evenly. The mixture is heated to 135°C and kept at this temperature for 3.5 hours. Then it is mixed with the solution prepared in step (1). The temperature is controlled at 210°C and kept at this temperature for 3 hours to obtain the final product.

[0214] The mass ratio of the negative electrode additive to the negative electrode material is 13:88.

[0215] The rest is the same as in Example 1.

[0216] Comparative Example 16

[0217] A method for preparing a lithium battery with high stability.

[0218] The preparation method of the negative electrode additive is as follows:

[0219] (1) Take 5 parts of ethyl cellulose, 2 parts of 2,2-dimethylolpropionic acid, 4.5 parts of gum arabic, 1.5 parts of perfluorooctanoic acid ethylene glycol, and 1.5 parts of polyphenylene imidazole and add them to ethyl acetate for mixing. Then, heat the mixture to 210℃ at a rate of 3.5℃ / min and keep it at that temperature for 15h to obtain the final product.

[0220] The mass ratio of the negative electrode additive to the negative electrode material is 13:88.

[0221] The rest is the same as in Example 1.

[0222] Comparative Example 17

[0223] A method for preparing a lithium battery with high stability.

[0224] The method for preparing the negative electrode is as follows:

[0225] Cleaning of the current collector: Immerse copper foil in a 0.4wt% sodium hydroxide solution, vibrate it with microwave, and then dry it at 45℃ for 3 hours for later use;

[0226] Mixed granulation: Take the negative electrode material and binder at a mass ratio of 82:9, granulate using spray granulation method, control the particle size to 25μm, and dry in an oven at 83℃ for 4.5h for later use;

[0227] Electrode preparation: The negative electrode material and conductive agent from the above steps are mixed evenly in a mass ratio of 91:9. NMP is added and stirred into a uniform slurry. The slurry is evenly coated on the surface of copper foil, dried, rolled, and dried at 45°C for 5.5 hours. The slab is then sliced ​​according to the required size to obtain the electrode sheet.

[0228] The rest is the same as in Example 1.

[0229] Comparative Example 18

[0230] A method for preparing a lithium battery with high stability.

[0231] In the preparation method of the positive electrode material: lithium iron phosphate, conductive agent and binder are mixed evenly in a mass ratio of 85:4:4, and NMP solvent is added to form a uniform slurry;

[0232] The rest is the same as in Example 1.

[0233] Comparative Example 19

[0234] A method for preparing a lithium battery with high stability.

[0235] The preparation method of the positive electrode material is as follows: the slurry is uniformly coated onto the surface of aluminum foil, dried at 80°C for 4.5 hours, rolled and pressed, and sliced ​​according to the required size to obtain the lithium battery positive electrode for later use.

[0236] The rest is the same as in Example 1.

[0237] Comparative Example 20

[0238] A method for preparing a lithium battery with high stability.

[0239] The preparation method of the negative electrode material is as follows:

[0240] Methods for preparing the negative electrode:

[0241] Cleaning of the current collector: Immerse copper foil in a 0.4wt% sodium hydroxide solution, vibrate it with microwave, and then dry it at 45℃ for 3 hours for later use;

[0242] The negative electrode material, binder, negative electrode additive and conductive agent are mixed evenly in a mass ratio of 82:9:13:9. NMP is added and stirred into a uniform slurry. The slurry is evenly coated on the surface of copper foil, dried and rolled to obtain the lithium battery negative electrode. After drying at 45°C for 5.5 hours, it is sliced ​​according to the required size to obtain the lithium battery negative electrode.

[0243] The rest is the same as in Example 1.

[0244] Comparative Example 21

[0245] A method for preparing a lithium battery with high stability.

[0246] Methods for preparing the negative electrode:

[0247] Cleaning of the current collector: Immerse copper foil in a 0.4wt% sodium hydroxide solution, vibrate it with microwave, and then dry it at 45℃ for 3 hours for later use;

[0248] Mixed granulation: Take the negative electrode material, binder and negative electrode additive in a mass ratio of 90:9:13, granulate using spray granulation method, control the particle size to 25μm, and dry in an oven at 83℃ for 4.5h for later use;

[0249] Electrode preparation: The negative electrode material and conductive agent from the above steps are mixed evenly in a mass ratio of 91:9. NMP is added and stirred into a uniform slurry. The slurry is evenly coated on the surface of copper foil, dried, rolled, and dried at 45°C for 5.5 hours. The slab is then sliced ​​according to the required size to obtain the electrode sheet.

[0250] The rest is the same as in Example 1.

[0251] Comparative Example 22

[0252] A method for preparing a lithium battery with high stability.

[0253] Methods for preparing the negative electrode:

[0254] Cleaning of the current collector: Immerse copper foil in a 0.4wt% sodium hydroxide solution, vibrate it with microwave, and then dry it at 45℃ for 3 hours for later use;

[0255] Mixed granulation: Take the negative electrode material, binder, and negative electrode additive in a mass ratio of 82:9:13, granulate using spray granulation method, control the particle size to 25μm, and dry in an 83℃ oven for 4.5h for later use;

[0256] Electrode preparation: The negative electrode material and conductive agent from the above steps are mixed evenly in a mass ratio of 80:9. NMP is added and stirred into a uniform slurry. The slurry is evenly coated on the surface of copper foil, dried, rolled, and dried at 45°C for 5.5 hours. The slab is then sliced ​​according to the required size to obtain the electrode sheet.

[0257] The rest is the same as in Example 1.

[0258] Comparative Example 23

[0259] The lithium battery is a commercially available carbon anode lithium battery.

[0260] Experimental Example 1: First Discharge Specific Capacity of Lithium-ion Batteries

[0261] According to the national standard GB / T24533-2019 "Graphite Anode Materials for Lithium-ion Batteries", the first discharge specific capacity of lithium batteries was tested, and the specific data are recorded in Table 1.

[0262] Table 1. Specific capacity of lithium batteries during initial discharge

[0263]

[0264] Note: Tests were conducted at a charge / discharge current density of 100 mA / g, and the unit of specific capacity is mAh·g. -1

[0265] As can be seen from the data in Table 1, the lithium battery prepared in the example has a much higher specific capacity during the first discharge than other comparative examples, with the specific capacity during the first discharge ranging from 1201.1 to 1210.7 mAh·g. -1 The first-discharge specific capacity of the lithium-ion battery obtained in Examples 1-4 was significantly higher than that of other comparative examples. Comparative Examples 1-4 adjusted the raw material ratio and preparation process of the binder, resulting in changes to the composition and structure of the binder. The final lithium-ion battery with this modified binder had a lower first-discharge specific capacity than Examples 1-3, but better than Comparative Example 23. Comparative Example 5 used a conventional binder, but because the negative electrode material was a treated bio-carbon source, the first-discharge specific capacity of the resulting lithium-ion battery was slightly higher than that of Comparative Example 25. Comparative Examples 6-8 modified the composition and preparation process of the modifier in the lithium-ion battery, but after testing, the highest first-discharge specific capacity of the resulting lithium-ion battery was only 789.4 mAh·g. -1 Comparative Examples 9-13 involved adjusting parameters in the anode material preparation process, but the highest initial discharge specific capacity of the resulting anode material was 897.8 mAh·g. -1 The lowest capacity is 387.4 mAh·g -1 Comparative Examples 14-17 adjusted the preparation process and raw material parameters of the negative electrode additives, resulting in lithium batteries with an initial discharge specific capacity of 978.5-1058.9 mAh·g.-1 Between; Comparative Examples 18-22 adjusted the relevant parameters in the lithium battery manufacturing process, and the resulting lithium batteries had a higher initial discharge specific capacity than Comparative Example 23.

[0266] Experimental Example 2: Compacted Density of Lithium-ion Battery Anode Sheet

[0267] The negative electrode was tested according to the compaction density of the negative electrode sheet in the national standard GB / T24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". The specific data of the compaction density of the negative electrode sheet are recorded in Table 2.

[0268] Table 2 Compacted density of negative electrode sheet

[0269]

[0270] The compaction density of lithium battery anode sheets is closely related to the morphology, tap density, specific surface area, and particle size distribution of carbon anode materials. As can be seen from the data in Table 2, the compaction density of the anode sheets prepared in Examples 1-3 is 3.60 g / cm³. 3 Above this, the compaction density far exceeds that of the other comparative examples. Comparative Examples 1-4 adjusted the binder formulation and process, altering the binder's composition and structure. Therefore, the microstructure of the anode material prepared after mixing with the binder also had defects, with a compaction density ranging from 2.24 to 2.51 g / cm³. 3 Between; Comparative Examples 6-8 adjusted the raw material formulation and preparation process of the modifier, and the compaction density of the negative electrode was much lower than that of Examples 1-3.

[0271] Experimental Example 3: Stability of Lithium-ion Batteries

[0272] The lithium batteries prepared in the examples and comparative examples were subjected to 800 cycles, and the capacity retention rate of the lithium batteries was tested. The specific data are recorded in Table 3.

[0273] Table 3 Capacity retention rate of lithium batteries

[0274]

[0275] As can be seen from the data in Table 3, after 700 cycles, the capacity retention rate of Examples 1-3 was above 82.1%, and the cycle life far exceeded that of the other comparative examples, indicating that the stability of the lithium batteries was superior to that of the other comparative examples. Comparative Examples 1-4 adjusted the binder formulation, and Comparative Examples 6-8 adjusted the modifier formulation and process; the resulting lithium batteries, after 800 cycles, had a capacity retention rate between 60.5% and 68.7%. Comparative Examples 9-13 adjusted the preparation process parameters and raw material formulation of the negative electrode material; the highest capacity retention rate after 800 cycles was 73.5%. Comparative Examples 14-16 modified the formulation and process of the negative electrode additive; the final lithium-ion batteries obtained had a capacity retention rate between 54.9% and 57.6% after 800 cycles. Comparative Example 17 did not add any negative electrode additive; the cycle performance of the lithium battery was even lower than that of the commercially purchased lithium-ion battery in Comparative Example 23, with a capacity retention rate of only 41.9% after 800 cycles. Comparative Examples 18-22 adjusted some parameters in the lithium battery preparation process, but the final lithium batteries retained a capacity of 59.3-73.9% after 800 cycles.

Claims

1. A method for preparing a lithium battery with high stability, characterized in that: The method for preparing the negative electrode is as follows: Cleaning of the current collector: Immerse copper foil in a 0.3-0.5wt% sodium hydroxide solution, vibrate it with microwave, and then dry it at 40-50℃ for 2-4 hours for later use; Mixed granulation: Take the negative electrode material, binder, and negative electrode additive in a mass ratio of (80-84):(8-10):(11-15), granulate using spray granulation method, control the particle size to be 20-30μm, and dry in an oven at 80-85℃ for 4-5 hours for later use; Preparation of electrode sheet: Mix the above-mentioned mixed granulated negative electrode material and conductive agent in a mass ratio of (90-92):(8-10), add NMP and stir to form a uniform slurry, coat it evenly on the surface of copper foil, roll it after drying, and dry it at 40-50℃ for 5-6 hours; then slice it according to the required size to obtain the electrode sheet. The preparation method of the negative electrode material is as follows: i. Clean the biochar source with water and dry it in an oven at 70-75℃ for 5-7 hours. Crush the dried biochar source to 400-500 mesh and mix it evenly. Place it in a tube furnace and calcine it under nitrogen protection. Increase the temperature at 2-3℃ / min to 550-560℃ and calcine for 4-5 hours. After that, take it out and grind it into 5-10μm powder for later use. ii. Grind the dried biocarbon source into powder, add mesophase carbon microspheres with a particle size of 5-10μm and grind them together until uniform, wherein the mass ratio of biocarbon source to mesophase carbon microspheres is 4:

1. iii. Activation: Take a 10-12 wt% hydrogen chloride solution, immerse the powder obtained by the above co-grinding in the solution at 60°C for 30-45 minutes, remove it, wash it with clean water, then immerse it again in a 5-10 wt% HF solution at 50°C for 20-40 minutes, remove it, wash it with water, then immerse it in a modifier at 70°C for 2-4 hours, remove it and dry it in an oven at 80-90°C to obtain the final product. Among them, the biological carbon source is one or both of rice husks and coconut shells; The preparation method of the negative electrode additive is as follows: (1) Take 4-6 parts of ethyl cellulose and 1-3 parts of 2,2-dimethylolpropionic acid, add ethyl acetate and mix. Then, heat the mixture to 150-160℃ at a rate of 3-4℃ / min and keep it at that temperature for 3-4 hours. Then, add 4-5 parts of gum arabic and control the temperature between 170-175℃. Keep it at that temperature for 5-7 hours and set it aside. (2) Add 1-2 parts of perfluorooctanoic acid glycol and 1-2 parts of polyphenylimidazolium to dimethylacetamide and mix evenly. Then heat to 130-140℃ and keep warm for 3-4 hours. Then mix with the solution prepared in step (1), control the temperature at 200-220℃ and keep warm for 2-4 hours to obtain the solution. The method for preparing the modifier is as follows: ① Take 4-5 parts of octylphenoxy polyethoxyethyl phosphate and 4-5 parts of 3-sulfopropylhexadecyl dimethylammonium and put them into DNM solution. Put them into a reaction vessel and heat them to 180-190℃ at a rate of 2-4℃ / min. Keep them at this temperature for 3-4 hours and then cool them to room temperature for later use. ② Take 1-2 parts of alkylphenol polyoxyethylene ether and 1-2 parts of medium-chain triglycerides, add them to ethyl acetate solvent, heat to 150-160℃ and stir for 2-3 hours, then add them dropwise to step ① at a rate of 30 drops / min, control the solution temperature to 110-130℃, and stir for 4-5 hours to obtain the final product; The method for preparing the adhesive: a. Take 3-5 parts of polypropylene glycol and 2-4 parts of 4,4'-dicyclohexylmethane diisocyanate, add ethyl acetate and mix well. Then put the mixture into a reaction vessel, control the temperature at 220-225℃, keep it at this temperature for 4-5 hours, and then cool it to room temperature for later use. b. Take 1-2 parts of isophorone diisocyanate and 2-4 parts of trifluoromethanesulfonate, add them to ethyl acetate solvent, mix and heat to 175-180℃ at a rate of 1-2℃ / min, keep warm for 2-4h, then add dropwise to step a at a rate of 20-25 drops / min, control the solution temperature at 110-115℃, keep warm for 1-2h, then add 4-5 parts of polymethyl methacrylate, heat to 140-145℃, keep warm for 3-4h to obtain the final product.

2. The preparation method according to claim 1, characterized in that: The preparation method for lithium batteries with high stability is as follows: S1: Winding: The positive electrode, separator, and negative electrode of the battery are welded using an ultrasonic welding machine in that order, and then wound. After winding, under the combined action of static pressure, it is pressed into the required shape and placed into the middle cavity of the outer packaging for top sealing. S2: Assembly: After top sealing, inject electrolyte into the battery, immerse it at 100-110℃ for 2-4 minutes, then inject electrolyte again in a low humidity environment, remove air bubbles in a vacuum environment and reseal. S3: Inspection: Inspect the prepared batteries to ensure they are intact, leak-proof, and do not bulge. Also, inspect the aluminum casing for inkjet printing. Both the positive and negative electrodes contain conductive agents and binders.

3. The preparation method according to claim 2, characterized in that: The method for preparing the positive electrode of the lithium battery: Cleaning the current collector: Soak the aluminum foil in a 0.01-0.03wt% hydrogen chloride solution for 20-30 minutes, rinse with clean water, and dry in a 40-45℃ oven for 1-2 hours for later use; Preparation: Lithium iron phosphate, conductive agent, and binder are mixed evenly in a mass ratio of (90-94):(3-5):(3-5), and NMP solvent is added to form a uniform slurry; Electrode sheet preparation: The slurry is evenly coated onto the surface of aluminum foil, dried at 90-100℃ for 4-5 hours, rolled and cut into slices according to the required size to obtain the electrode sheet.

4. The preparation method according to any one of claims 1-3, characterized in that: The conductive agent is obtained by mixing 1-2 parts acetylene black, 4-5 parts mesophase carbon microspheres, and 3-5 parts graphite evenly.

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