Multifunctional negative electrode binder, silicon-carbon negative electrode plate and lithium ion battery

Abstract

A preparation method of the multifunctional negative electrode binder with flame-retardant and self-repairing performance comprises the following steps: preparing an emulsion, and adding a mixed solution of an acrylic monomer and a phosphorus-based flame-retardant monomer into the emulsion to prepare a pre-emulsion; uniformly mixing part of the pre-emulsion with an initiator to obtain a water-based flame-retardant emulsion; adding an emulsifier SR-10 into the rest of the pre-emulsion, and then adding an initiator to obtain an acrylate emulsion; dropwise adding an acrylate emulsion into the water-based flame-retardant emulsion, adding a hydrazide compound aqueous solution after dropwise adding, stirring, and adjusting to be neutral, so as to obtain the multifunctional negative electrode binder with flame-retardant and self-repairing properties. By introducing the flame-retardant emulsifier and the phosphorus-based flame-retardant monomer, the flame-retardant property of the binder is improved, the safety performance of a battery is improved on the basis of keeping cycle stability, and when the binder is applied to a silicon-carbon negative pole piece, the flame-retardant property is given to the pole piece while expansion of a silicon system pole piece is inhibited; and the lithium battery has higher capacity retention ratio and safety after circulation.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and particularly relates to a preparation method and application of a negative electrode binder. Background Art

[0002] Silicon has a high theoretical lithium storage capacity (3579 mAh / g), making it a negative electrode material for high specific capacity lithium ion batteries. Currently, domestic and foreign production enterprises have developed silicon-carbon negative electrode materials with a silicon content of 1%-10% to a certain extent. However, silicon-carbon negative electrodes have obvious shortcomings: there is a serious volume expansion effect during charge and discharge, resulting in a short battery cycle life; an unstable solid electrolyte interface will cause battery thermal runaway, posing a safety hazard. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a multifunctional negative electrode binder with flame retardant and self-healing properties for silicon-carbon negative electrodes, to solve the problems of volume expansion of silicon-carbon negative electrodes and battery thermal runaway, and to improve the cycle reversibility and safety performance of lithium batteries.

[0004] To achieve the above purpose, the technical solution of the present invention is realized as follows: A multifunctional negative electrode binder, the polymerization monomers of the multifunctional negative electrode binder are acrylic acid-based and phosphorus-based flame retardant types, and are prepared by emulsion polymerization. Specifically, it is prepared by the following method (the following dosages are in parts by weight unless otherwise specified):

[0005] Step 1: Prepare an emulsion; add a mixture of 1400-2000 parts by mass of acrylate monomer mixture and 1-500 parts by mass of phosphorus-based flame retardant monomer to 30-1200 parts of the emulsion to obtain a pre-emulsion;

[0006] Step 2: Mix 1 / 20~1 / 15 of the pre-emulsion with 4-6 parts by mass of an initiator, and react under the first reaction conditions to obtain an aqueous flame retardant emulsion;

[0007] Step 3: Add 0.5~2 parts by mass of emulsifier SR-10 to the remaining pre-emulsion, then add 4-6 parts by mass of the initiator, add 400~600 parts by mass of deionized water and stir for 5~10 min to obtain an acrylate emulsion;

[0008] Step 4: Dropwise add the acrylate emulsion to the aqueous flame retardant emulsion. During the dropping process, the temperature is controlled at 80~90°C. After the dropping is completed, react under the second reaction conditions, cool down to below 50°C, add a 50wt% aqueous solution of hydrazide compound and stir for 5-15 min, then adjust to neutral to obtain a multifunctional negative electrode binder with flame retardant and self-healing properties.

[0009] The first reaction conditions are: heating to 80 - 90 °C and stirring for 1 - 3 h; the second reaction conditions are: heating to 90 °C and stirring for 1.5 - 3 h.

[0010] The preparation of the emulsion in Step 1 includes the following steps: adding 5 - 10 parts by mass of an emulsifier mixture to 400 - 600 parts by mass of deionized water and stirring well to form an emulsion; the emulsifier mixture includes a non-ionic acrylic acid phosphate monomer emulsifier FM30, an anionic Solvay phosphate emulsifier RS-610, and a reactive emulsifier SR-10 with a mass ratio of 0.8 - 1:0.8 - 1:3.5 - 4.

[0011] The acrylate monomer mixture in Step 1 includes components in parts by mass: 65 - 85 parts of soft monomers, 10 - 30 parts of hard monomers, and 0.5 - 3 parts of functional self-crosslinking monomers.

[0012] The soft monomers are one or more of butyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate.

[0013] The hard monomers are one or more of isobornyl acrylate, ethyl methacrylate, methyl acrylate, butyl methacrylate, methyl methacrylate, acrylic acid, and styrene.

[0014] The functional self-crosslinking monomer is a 50 wt% aqueous solution of diacetone acrylamide, and the mass ratio of diacetone acrylamide to adipic dihydrazide in the aqueous solution of diacetone acrylamide is (2 - 5):1.

[0015] The phosphorus-based flame retardant monomer is one or more of dimethyl vinyl phosphate, diethyl vinyl phosphate, and triallyl phosphate.

[0016] In Step 2 and Step 3, the initiator is one or both of potassium persulfate and ammonium persulfate.

[0017] The aqueous solution of hydrazide compound in Step 4 is a solution prepared by completely dissolving 1 part by mass of solid powder of hydrazide compound in 1 part by mass of deionized water, and the hydrazide compound is one of adipic dihydrazide, carbohydrazide, malonic dihydrazide, succinic dihydrazide, and glutaric dihydrazide. According to the experimental results, adipic dihydrazide has the best effect.

[0018] On the other hand, the present invention provides a silicon-carbon negative electrode sheet, which is prepared using the above multifunctional negative electrode binder, and the preparation method includes the following steps:

[0019] Step 1: Mix the negative electrode silicon-carbon material, the negative electrode graphite material, and the first conductive agent at a rotation speed of 1500 - 2500 rpm / min and stir and disperse for 0.5 - 2 h to obtain a mixed solid powder.

[0020] Step 2: Add a second conductive agent, a multifunctional anode binder, a second binder, and water to the mixed solid powder, stir at a speed of 1500 - 2500 rpm for 0.5 - 2 h to obtain a silicon-carbon anode slurry;

[0021] Step 3: Coat the silicon-carbon anode slurry on the surface of the copper foil at a speed of 1 - 8 m / min, and dry it in a vacuum environment at 50 - 150 °C for 1 - 12 h to obtain a silicon-carbon anode sheet.

[0022] The mass ratio of the anode silicon-carbon material: anode graphite material: first conductive agent: second conductive agent: multifunctional anode binder: second binder: water is 3 - 4: 33 - 34: 1 - 2: 9 - 11: 6 - 8: 44 - 46: 2 - 20;

[0023] The anode silicon-carbon material is a composite material of nano-silicon and graphite;

[0024] The anode graphite material is any one or more of artificial graphite, modified natural graphite, hard carbon, and mesophase carbon microsphere materials;

[0025] The first conductive agent is conductive carbon black; the second conductive agent is an aqueous solution of carbon nanotubes with a solid content of 1%;

[0026] The second binder is an aqueous solution of sodium carboxymethyl cellulose with a solid content of 1.2%.

[0027] On the other hand, the present invention provides a lithium-ion battery containing the above-mentioned silicon-carbon anode sheet.

[0028] Compared with the prior art, the present invention has the following beneficial effects: (1) The emulsifier used in the present invention is flame-retardant, which can improve the flame-retardant performance of the binder, thereby improving the safety performance of the battery. (2) The present invention uses a phosphorus-based flame-retardant monomer to improve the flame-retardant performance of the binder while retaining the self-healing function of polyacrylic acid. The phosphorus-based compound can evaporate into the gas phase to form phosphorus free radicals such as PO2 and PO. The phosphorus free radicals can capture free radicals for combustion, thereby reducing or even stopping the combustion reaction, and can effectively improve the safety performance of the lithium-ion battery, and improve the safety performance of the battery on the basis of maintaining cycle stability. (3) The present invention is applied to the silicon-carbon anode sheet, using a flame-retardant and self-healing multifunctional binder, which can inhibit the expansion of the silicon-based anode sheet while giving the anode sheet flame-retardant performance, so that the lithium battery has a higher capacity retention rate and safety after cycling, providing the possibility for the commercialization of silicon-carbon anodes in lithium batteries. Specific embodiments

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually illustrative only and in no way limits the present invention and its application or use. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0030] Techniques, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the techniques, methods, and devices should be regarded as part of the authorization specification.

[0031] In the following embodiments, the test methods or testing methods, unless otherwise specified, are all conventional methods; the reagents and materials, unless otherwise specified, are all obtained from conventional commercial channels or prepared by conventional methods.

[0032] Example 1

[0033] This embodiment provides a preparation method of a flame-retardant and self-healing multifunctional negative electrode binder and a preparation method of a silicon-carbon negative electrode sheet:

[0034] The preparation method of a flame-retardant and self-healing multifunctional negative electrode binder:

[0035] Step 1: Mix 1 g of non-ionic emulsifier acrylate phosphate monomer (FM30), 1 g of anionic Solvay phosphate emulsifier (RS-610), and 4 g of reactive emulsifier SR-10, add them to 600 g of deionized water and stir well to form an emulsion. Then add 700 g of butyl acrylate, 350 g of 2-ethylhexyl acrylate, 50 g of 2-hydroxyethyl acrylate, 100 g of isobornyl acrylate, 115 g of methyl acrylate, 70 g of butyl methacrylate, 15 g of acrylic acid, 15 g of 50 wt% diacetone acrylamide aqueous solution (mass ratio of diacetone acrylamide to adipic dihydrazide is 5:1), and 15 g of phosphorus-based flame-retardant monomer dimethyl vinyl phosphate to the emulsion to obtain a pre-emulsion.

[0036] Step 2: Mix 1 / 20 of the pre-emulsion with 5 g of potassium persulfate, heat it to 80 - 85 °C, and stir for reaction to obtain an aqueous flame-retardant emulsion.

[0037] Step 3: Add 2 g of emulsifier SR-10 to the remaining pre-emulsion, then add 4 g of potassium persulfate and 500 g of deionized water, and stir for 5 minutes to obtain an acrylate emulsion.

[0038] Step 4: Dropwise add acrylate emulsion into the waterborne flame retardant emulsion. During the dropping process, control the temperature at 80 - 90 °C. After the dropping is completed, raise the temperature to 90 °C, react for 1.5 h, then cool down to below 50 °C, add an aqueous solution of adipic dihydrazide prepared with 1.5 g of adipic dihydrazide and 1.5 g of deionized water, stir for 15 min, and then adjust to neutral with lithium carbonate solution to obtain a multifunctional anode binder with flame retardancy and self - healing properties.

[0039] The preparation method of the silicon - carbon anode electrode sheet is as follows:

[0040] Step 1: Mix 4.6 g of anode silicon - carbon material, 41.4 g of anode graphite material and 1.45 g of the first conductive agent carbon black, with a rotation speed of 1500 - 2500 rpm / min, and stir and disperse for 0.5 - 2 h to obtain a mixed solid powder;

[0041] Step 2: Add 12.5 g of the second conductive agent carbon nanotubes, 8.75 g of the multifunctional binder, 56.2 g of an aqueous solution of sodium carboxymethyl cellulose with a solid content of 1.2% and 3 - 20 g of water to the mixed solid powder, with a rotation speed of 1500 - 2500 rpm / min, and stir and disperse for 0.5 - 2 h to obtain a silicon - carbon anode slurry;

[0042] Step 3: Coat the silicon - carbon anode slurry on the surface of the copper foil at a speed of 1 - 8 m / min, and dry it in a vacuum environment at 50 - 150 °C for 1 - 12 h to obtain the silicon - carbon anode electrode sheet;

[0043] Step 4: Assemble the Li||silicon - carbon half - cell with the silicon - carbon anode electrode sheet to obtain the initial Coulombic efficiency and capacity of the silicon - carbon electrode sheet.

[0044] Example 2

[0045] This example provides a preparation method of a multifunctional anode binder with flame retardancy and self - healing properties and a preparation method of a silicon - carbon anode electrode sheet:

[0046] The preparation method of the multifunctional anode binder with flame retardancy and self - healing properties:

[0047] Step 1: Mix 120 g of non-ionic emulsifier acrylic acid phosphate monomer (FM30), 120 g of anionic Solvay phosphate emulsifier (RS-610), and 600 g of reactive emulsifier SR-10, add them to 40 kg of deionized water, and stir well to form an emulsion. Then add 114 kg of butyl acrylate, 24 kg of 2-ethylhexyl acrylate, 4 kg of 2-hydroxyethyl acrylate, 4 kg of isobornyl acrylate, 4 kg of methyl acrylate, 9 kg of butyl methacrylate, 1.5 kg of acrylic acid, 3.2 kg of 50 wt% diacetone acrylamide aqueous solution (the mass ratio of diacetone acrylamide to adipic dihydrazide is 4:1), and 2 kg of phosphorus-based flame retardant monomer dimethyl vinyl phosphate into the emulsion to obtain a pre-emulsion;

[0048] Step 2: Mix 1 / 15 of the pre-emulsion with 400 g of ammonium persulfate, heat it up to 80 - 85 °C, and stir for reaction to obtain an aqueous flame retardant emulsion;

[0049] Step 3: Add 120 g of emulsifier SR-10 to the remaining pre-emulsion, then add 480 g of ammonium persulfate and 4.4 kg of deionized water, and stir for 5 minutes to obtain an acrylate emulsion;

[0050] Step 4: Dropwise add the acrylate emulsion into the aqueous flame retardant emulsion. During the dropping process, control the temperature at 80 - 90 °C. After the dropping is completed, heat it up to 90 °C, react for 1.5 h, then cool it down to below 50 °C, add an aqueous solution of adipic dihydrazide prepared by mixing 400 g of adipic dihydrazide and 400 g of deionized water, stir for 15 min, and then adjust it to neutral with lithium carbonate solution to obtain a multifunctional anode binder with flame retardant and self-healing properties.

[0051] The preparation method of the silicon-carbon anode electrode is as follows:

[0052] Step 1: Mix 4.6 g of anode silicon-carbon material, 41.4 g of anode graphite material, and 1.45 g of the first conductive agent carbon black, stir and disperse at a rotation speed of 1500 - 2500 rpm / min for 0.5 - 2 h to obtain a mixed solid powder;

[0053] Step 2: Add 12.5 g of the second conductive agent carbon nanotubes, 8.75 g of the multifunctional binder, 56.2 g of an aqueous solution of sodium carboxymethyl cellulose with a solid content of 1.2%, and 3 - 20 g of water to the mixed solid powder, stir and disperse at a rotation speed of 1500 - 2500 rpm / min for 0.5 - 2 h to obtain a silicon-carbon anode slurry;

[0054] Step 3: Coat the silicon-carbon anode slurry on the surface of the copper foil at a speed of 1 - 8 m / min, and dry it in a vacuum environment at 50 - 150 °C for 1 - 12 h to obtain the silicon-carbon anode electrode;

[0055] Step 4: Assemble the silicon-carbon negative electrode sheet into a Li||silicon-carbon half-cell to obtain the initial Coulombic efficiency and capacity of the silicon-carbon electrode sheet.

[0056] Example 3

[0057] This example provides a preparation method of a multifunctional negative electrode binder with flame retardancy and self-healing properties, and a preparation method of a silicon-carbon negative electrode sheet:

[0058] The preparation method of the multifunctional negative electrode binder with flame retardancy and self-healing properties:

[0059] Step 1: Mix 1.5 g of non-ionic emulsifier acrylic acid phosphate monomer (FM30), 1.5 g of anionic Solvay phosphate emulsifier (RS-610), and 6 g of reactive emulsifier SR-10, add them to 550 g of deionized water and stir well to prepare an emulsion. Then add 525 g of butyl acrylate, 367 g of 2-ethylhexyl acrylate, 42 g of 2-hydroxyethyl acrylate, 228 g of styrene, 140 g of methyl methacrylate, 84 g of ethyl methacrylate, 20 g of acrylic acid, 62 g of 50 wt% diacetone acrylamide aqueous solution (the mass ratio of diacetone acrylamide to adipic dihydrazide is 3:1), and 80 g of phosphorus-based flame retardant monomer diethyl vinyl phosphate to the emulsion to obtain a pre-emulsion;

[0060] Step 2: Mix 1 / 20 of the pre-emulsion with 4 g of potassium persulfate, heat it to 80 - 85 °C, and stir for reaction to obtain an aqueous flame retardant emulsion;

[0061] Step 3: Add 1.5 g of emulsifier SR-10 to the remaining pre-emulsion, then add 4 g of potassium persulfate and 600 g of deionized water, and stir for 5 minutes to obtain an acrylate emulsion;

[0062] Step 4: Dropwise add the acrylate emulsion to the aqueous flame retardant emulsion, control the temperature at 80 - 90 °C during the dropping process. After the dropping is completed, heat it to 90 °C, react for 1.5 h, then cool it to below 50 °C, add an aqueous solution of adipic dihydrazide prepared by mixing 10 g of adipic dihydrazide and 10 g of deionized water, stir for 15 min, and then adjust it to neutral with lithium carbonate solution to obtain a multifunctional negative electrode binder with flame retardancy and self-healing properties.

[0063] The preparation method of the silicon-carbon negative electrode sheet is as follows:

[0064] Step 1: Mix 4.6 g of negative electrode silicon-carbon material, 41.4 g of negative electrode graphite material, and 1.45 g of first conductive agent carbon black, rotate at 1500 - 2500 rpm / min, and stir and disperse for 0.5 - 2 h to obtain a mixed solid powder;

[0065] Step 2: Add 12.5 g of the second conductive agent, carbon nanotubes, 8.75 g of the multifunctional binder, 56.2 g of an aqueous solution of sodium carboxymethylcellulose with a solid content of 1.2%, and 3 - 20 g of water to the mixed solid powder. Stir and disperse at a rotation speed of 1500 - 2500 rpm / min for 0.5 - 2 h to obtain the silicon-carbon negative electrode slurry;

[0066] Step 3: Coating the silicon-carbon negative electrode slurry on the surface of the copper foil at a speed of 1 - 8 m / min, and drying it in a vacuum environment at 50 - 150 °C for 1 - 12 h to obtain the silicon-carbon negative electrode sheet;

[0067] Step 4: Assemble the Li||silicon-carbon half-cell with the silicon-carbon negative electrode sheet to obtain the initial Coulomb efficiency and capacity of the silicon-carbon electrode sheet.

[0068] Example 4

[0069] This example provides a preparation method of a multifunctional negative electrode binder with flame retardancy and self-healing properties and a preparation method of a silicon-carbon negative electrode sheet:

[0070] The preparation method of the multifunctional negative electrode binder with flame retardancy and self-healing properties:

[0071] Step 1: Mix 5 kg of non-ionic emulsifier acrylate phosphate monomer (FM30), 5 kg of anionic Solvay phosphate emulsifier (RS-610), and 20 kg of reactive emulsifier SR-10, add them to 3000 kg of deionized water and stir well to prepare an emulsion. Add 525 kg of butyl acrylate, 2450 kg of 2-ethylhexyl acrylate, 700 kg of isobornyl acrylate, 425 kg of methyl methacrylate, 825 kg of butyl methacrylate, 145 kg of acrylic acid, 105 kg of 50% aqueous solution of diacetone acrylamide (the mass ratio of diacetone acrylamide to adipic dihydrazide is 2.5:1), and 145 kg of phosphorus-based flame retardant monomer diethyl vinyl phosphate to the emulsion to obtain a pre-emulsion;

[0072] Step 2: Mix 1 / 15 of the pre-emulsion with 25 kg of potassium persulfate, heat it up to 80 - 85 °C, and stir for reaction to obtain an aqueous flame retardant emulsion;

[0073] Step 3: Add 10 kg of emulsifier SR-10 to the remaining pre-emulsion, then add 10 kg of potassium persulfate and 2000 kg of deionized water, and stir for 5 minutes to obtain an acrylate emulsion;

[0074] Step 4: Drop acrylate emulsion into the aqueous flame retardant emulsion. During the dropping process, control the temperature at 80 - 90 °C. After the dropping is completed, raise the temperature to 90 °C. After reacting for 1.5 h, cool down to below 50 °C. Add an aqueous solution of adipic dihydrazide prepared with 20 kg of adipic dihydrazide and 20 kg of deionized water. After stirring for 8 min, adjust to neutral with lithium carbonate solution to obtain a multifunctional anode binder with flame retardant and self - repair functions.

[0075] The preparation method of the silicon - carbon anode sheet is as follows:

[0076] Step 1: Mix 4.6 g of anode silicon - carbon material, 41.4 g of anode graphite material, and 1.45 g of the first conductive agent carbon black at a rotation speed of 1500 - 2500 rpm / min, and stir and disperse for 0.5 - 2 h to obtain a mixed solid powder;

[0077] Step 2: Add 12.5 g of the second conductive agent carbon nanotubes, 8.75 g of the multifunctional binder, 56.2 g of an aqueous solution of sodium carboxymethyl cellulose with a solid content of 1.2%, and 3 - 20 g of water to the mixed solid powder. Stir and disperse at a rotation speed of 1500 - 2500 rpm / min for 0.5 - 2 h to obtain a silicon - carbon anode slurry;

[0078] Step 3: Coat the silicon - carbon anode slurry on the surface of the copper foil at a speed of 1 - 8 m / min, and dry it in a vacuum environment at 50 - 150 °C for 1 - 12 h to obtain the silicon - carbon anode sheet;

[0079] Step 4: Assemble the Li||silicon - carbon half - cell with the silicon - carbon anode sheet to obtain the initial Coulombic efficiency and capacity of the silicon - carbon anode sheet.

[0080] Example 5

[0081] This example provides a preparation method of a multifunctional anode binder with flame retardant and self - repair functions and a preparation method of a silicon - carbon anode sheet:

[0082] The preparation method of the multifunctional anode binder with flame retardant and self - repair functions:

[0083] Step 1: Mix 1 g of non-ionic emulsifier acrylic acid phosphate monomer (FM30), 1 g of anionic Solvay phosphate emulsifier (RS-610), and 4 g of reactive emulsifier SR-10, add them to 600 g of deionized water, stir well to form an emulsion. Then add 700 g of butyl acrylate, 350 g of 2-ethylhexyl acrylate, 50 g of 2-hydroxyethyl acrylate, 100 g of isobornyl acrylate, 115 g of methyl acrylate, 70 g of butyl methacrylate, 15 g of acrylic acid, 15 g of 50 wt% diacetone acrylamide aqueous solution (mass ratio of diacetone acrylamide to adipic dihydrazide is 5:1), 15 g of phosphorus-based flame retardant monomer diethyl vinyl phosphate, and 15 g of phosphorus-based flame retardant monomer dimethyl vinyl phosphate into the emulsion to obtain a pre-emulsion;

[0084] Step 2: Mix 1 / 20 of the pre-emulsion with 5 g of potassium persulfate, heat up to 80 - 85 °C, stir and react to obtain an aqueous flame retardant emulsion;

[0085] Step 3: Add 2 g of emulsifier SR-10 to the remaining pre-emulsion, then add 4 g of potassium persulfate and 500 g of deionized water, stir for 5 minutes to obtain an acrylate emulsion;

[0086] Step 4: Dropwise add the acrylate emulsion into the aqueous flame retardant emulsion, control the temperature at 80 - 90 °C during the dropping process. After the dropping is completed, heat up to 90 °C, react for 1.5 h, then cool down to below 50 °C, add an aqueous solution of adipic dihydrazide prepared by mixing 1.5 g of adipic dihydrazide and 1.5 g of deionized water, stir for 15 min, and adjust to neutral with lithium carbonate solution to obtain a multifunctional anode binder with flame retardancy and self-healing properties.

[0087] The preparation method of the silicon-carbon anode plate is as follows:

[0088] Step 1: Mix 4.6 g of anode silicon-carbon material, 41.4 g of anode graphite material, and 1.45 g of the first conductive agent carbon black, stir and disperse at a rotation speed of 1500 - 2500 rpm / min for 0.5 - 2 h to obtain a mixed solid powder;

[0089] Step 2: Add 12.5 g of the second conductive agent carbon nanotubes, 8.75 g of the multifunctional binder, 56.2 g of an aqueous solution of sodium carboxymethyl cellulose with a solid content of 1.2%, and 3 - 20 g of water to the mixed solid powder, stir and disperse at a rotation speed of 1500 - 2500 rpm / min for 0.5 - 2 h to obtain a silicon-carbon anode slurry;

[0090] Step 3: Coat the silicon-carbon anode slurry on the surface of the copper foil at a speed of 1 - 8 m / min, and dry it in a vacuum environment at 50 - 150 °C for 1 - 12 h to obtain the silicon-carbon anode plate;

[0091] Step 4: Assemble the silicon-carbon negative electrode sheet into a Li||silicon-carbon half-cell to obtain the initial Coulombic efficiency and capacity of the silicon-carbon electrode sheet.

[0092] Example 6

[0093] This example provides a preparation method of a flame-retardant and self-healing multifunctional negative electrode binder and a preparation method of a silicon-carbon negative electrode sheet:

[0094] The preparation method of the flame-retardant and self-healing multifunctional negative electrode binder:

[0095] Step 1: Mix 1 g of non-ionic emulsifier acrylic acid phosphate monomer (FM30), 1 g of anionic Solvay phosphate emulsifier (RS-610), and 4 g of reactive emulsifier SR-10, add them to 600 g of deionized water and stir well to prepare an emulsion. Then add 700 g of butyl acrylate, 350 g of 2-ethylhexyl acrylate, 50 g of 2-hydroxyethyl acrylate, 100 g of isobornyl acrylate, 115 g of methyl acrylate, 70 g of butyl methacrylate, 15 g of acrylic acid, 15 g of 50 wt% diacetone acrylamide aqueous solution (mass ratio of diacetone acrylamide to adipic dihydrazide is 5:1), 15 g of phosphorus-based flame retardant monomer diethyl vinyl phosphate, 15 g of phosphorus-based flame retardant monomer dimethyl vinyl phosphate, and 15 g of phosphorus-based flame retardant monomer triallyl phosphate to the emulsion to obtain a pre-emulsion;

[0096] Step 2: Mix 1 / 20 of the pre-emulsion with 5 g of potassium persulfate, heat it to 80-85 °C, stir and react to obtain an aqueous flame-retardant emulsion;

[0097] Step 3: Add 2 g of emulsifier SR-10 to the remaining pre-emulsion, then add 4 g of potassium persulfate and 500 g of deionized water, stir for 5 minutes to obtain an acrylate emulsion;

[0098] Step 4: Dropwise add the acrylate emulsion to the aqueous flame-retardant emulsion. During the dropping process, control the temperature at 80-90 °C. After the dropping is completed, raise the temperature to 90 °C, react for 1.5 h, then cool it to below 50 °C. Add an aqueous solution of adipic dihydrazide prepared from 1.5 g of adipic dihydrazide and 1.5 g of deionized water, stir for 15 min, and then adjust it to neutral with lithium carbonate solution to obtain a flame-retardant and self-healing multifunctional negative electrode binder.

[0099] The preparation method of the silicon-carbon negative electrode sheet is as follows:

[0100] Step 1: Mix 4.6 g of negative electrode silicon-carbon material, 41.4 g of negative electrode graphite material, and 1.45 g of first conductive agent carbon black, rotate at 1500-2500 rpm / min, and stir and disperse for 0.5-2 h to obtain a mixed solid powder;

[0101] Step 2: Add 12.5 g of the second conductive agent carbon nanotubes, 8.75 g of the multifunctional binder, 56.2 g of an aqueous solution of sodium carboxymethyl cellulose with a solid content of 1.2%, and 3 - 20 g of water to the mixed solid powder, and stir and disperse at a rotation speed of 1500 - 2500 rpm for 0.5 - 2 h to obtain the silicon-carbon negative electrode slurry;

[0102] Step 3: Coat the silicon-carbon negative electrode slurry on the surface of the copper foil at a speed of 1 - 8 m / min, and dry it in a vacuum environment at 50 - 150 °C for 1 - 12 h to obtain the silicon-carbon negative electrode sheet;

[0103] Step 4: Assemble the Li||silicon-carbon half-cell with the silicon-carbon negative electrode sheet to obtain the initial Coulombic efficiency and capacity of the silicon-carbon electrode sheet.

[0104] Example 7

[0105] This example provides a preparation method of a multifunctional negative electrode binder with flame retardancy and self-healing function and a preparation method of a silicon-carbon negative electrode sheet:

[0106] The preparation method of the multifunctional negative electrode binder with flame retardancy and self-healing function:

[0107] Step 1: Mix 1 g of non-ionic emulsifier polyoxyethylene nonylphenol ether (NP-10), 1 g of anionic emulsifier polyoxyethylene ether ammonium sulfate (CO-436), and 4 g of reactive emulsifier SR-10, add them to 600 g of deionized water and stir well to prepare an emulsion. Add 700 g of butyl acrylate, 350 g of 2-ethylhexyl acrylate, 50 g of 2-hydroxyethyl acrylate, 100 g of isobornyl acrylate, 115 g of methyl acrylate, 70 g of butyl methacrylate, 15 g of acrylic acid, and 15 g of a 50 wt% aqueous solution of diacetone acrylamide (the mass ratio of diacetone acrylamide to adipic dihydrazide is 5:1) to the emulsion to obtain a pre-emulsion;

[0108] Step 2: Mix 1 / 20 of the pre-emulsion with 5 g of potassium persulfate, heat it to 80 - 85 °C, and stir for reaction to obtain an aqueous flame-retardant emulsion;

[0109] Step 3: Add 2 g of emulsifier SR-10 to the remaining pre-emulsion, then add 4 g of potassium persulfate and 500 g of deionized water, and stir for 5 minutes to obtain an acrylate emulsion;

[0110] Step 4: Dropwise add the acrylate emulsion to the aqueous flame-retardant emulsion. During the dropping process, control the temperature at 80 - 90 °C. After the dropping is completed, raise the temperature to 90 °C, react for 1.5 h, then cool it to below 50 °C, add an aqueous solution of adipic dihydrazide prepared from 1.5 g of adipic dihydrazide and 1.5 g of deionized water, stir for 15 min, and adjust it to neutral with a lithium carbonate solution to obtain the negative electrode binder.

[0111] The preparation method of the silicon-carbon negative electrode sheet is as follows:

[0112] Step 1: Mix 4.6 g of negative electrode silicon-carbon material, 41.4 g of negative electrode graphite material, and 1.45 g of the first conductive agent carbon black at a rotation speed of 1500 - 2500 rpm / min, and stir and disperse for 0.5 - 2 h to obtain a mixed solid powder;

[0113] Step 2: Add 12.5 g of the second conductive agent carbon nanotubes, 8.75 g of the multifunctional binder, 56.2 g of an aqueous solution of sodium carboxymethyl cellulose with a solid content of 1.2%, and 3 - 20 g of water to the mixed solid powder, and stir and disperse at a rotation speed of 1500 - 2500 rpm / min for 0.5 - 2 h to obtain the silicon-carbon negative electrode slurry;

[0114] Step 3: Coat the silicon-carbon negative electrode slurry on the surface of the copper foil at a speed of 1 - 8 m / min, and dry it in a vacuum environment at 50 - 150 °C for 1 - 12 h to obtain the silicon-carbon negative electrode sheet;

[0115] Step 4: Assemble the silicon-carbon negative electrode sheet into a Li||silicon-carbon half-cell to obtain the initial Coulombic efficiency and capacity of the silicon-carbon electrode sheet.

[0116] Comparative Example 1

[0117] This example provides a preparation method of a silicon-carbon negative electrode sheet:

[0118] Step 1: Mix 4.6 g of negative electrode silicon-carbon material, 41.4 g of negative electrode graphite material, and 1.45 g of the first conductive agent carbon black at a rotation speed of 1500 - 2500 rpm / min, and stir and disperse for 0.5 - 2 h to obtain a mixed solid powder;

[0119] Step 2: Add 12.5 g of the second conductive agent carbon nanotubes, 8.75 g of the first binder Suzhou Derby DA-208, 56.2 g of an aqueous solution of sodium carboxymethyl cellulose with a solid content of 1.2%, and 3 - 20 g of water to the mixed solid powder, and stir and disperse at a rotation speed of 1500 - 2500 rpm / min for 0.5 - 2 h to obtain the silicon-carbon negative electrode slurry;

[0120] Step 3: Coat the silicon-carbon negative electrode slurry on the surface of the copper foil at a speed of 1 - 8 m / min, and dry it in a vacuum environment at 50 - 150 °C for 1 - 12 h to obtain the silicon-carbon negative electrode sheet;

[0121] Step 4: Assemble the silicon-carbon negative electrode sheet into a Li||silicon-carbon half-cell to obtain the initial Coulombic efficiency and capacity of the silicon-carbon electrode sheet.

[0122] The flame retardant grades of the binders in Examples 1 - 7 and the Suzhou Derby DA-208 binder in Comparative Example 1 were tested, and the results are shown in Table 1.

[0123] Flame retardant grade test: Tested according to the vertical burning test of thin materials in the flammability test of equipment and appliance component materials in UL94

[0124] Table 1 Combustion grade of binder

[0125] Sample Number Flame Retardant Grade Example 1 VTM-0 Example 2 VTM-0 Example 3 VTM-0 Example 4 VTM-0 Example 5 VTM-0 Example 6 VTM-0 Example 7 Complete Combustion Comparative Example 1 Complete Combustion

[0126] In Example 1-6 of the present invention, the multifunctional binder has a flame retardant grade of VTM-0. In Example 7, the binder loses the introduction of the flame retardant emulsifier and the flame retardant monomer and has no flame retardant performance and burns completely. Comparative Example 1 is the binder DA-208 of Suzhou Derby, which has no flame retardant performance and burns completely.

[0127] Prepare the silicon-carbon negative electrode sheet with the above binder, test the combustion performance of the electrode sheet, and assemble the Li||silicon-carbon half cell to test the initial Coulomb efficiency, capacity and 500-cycle capacity retention rate of the battery.

[0128] Table 2 Performance of silicon-carbon negative electrode sheet and lithium battery

[0129] Sample Number Combustion Grade of Silicon Carbon Anode Sheet Initial Coulombic Efficiency (%) Capacity (mAh / g) Capacity Retention Rate after 500 Cycles (%) Example 1 VTM-0 93.0 501 87.6 Example 2 VTM-0 92.8 499 87.3 Example 3 VTM-0 92.3 496 86.2 Example 4 VTM-0 92.6 492 86.8 Example 5 VTM-0 92.5 493 85.4 Example 6 VTM-0 92.6 496 86.5 Example 7 Complete Combustion 92.5 490 86.9 Comparative Example 1 Complete Combustion 92.5 498 75.3

[0130] As can be seen from Table 2, the binders in Examples 1-6 contain a flame retardant emulsifier and a flame retardant monomer, and the flame retardant grade of the silicon-carbon negative electrode sheet is VTM-0. The binder in Example 7 does not contain a flame retardant emulsifier and a flame retardant monomer, and the silicon-carbon negative electrode sheet burns completely. After preparing the silicon-carbon negative electrode sheets in Examples 1-7 and assembling the Li||silicon-carbon half cells, complete silicon-carbon negative electrode sheets can be made, which adhere to the copper foil without detachment, and the capacity retention rate exceeds 85% after 500 cycles.

[0131] In Comparative Example 1, the silicon-carbon negative electrode sheet burns completely, and the capacity retention rate after 500 cycles is only 75.3%.

[0132] In summary, the flame retardant and self-healing multifunctional negative electrode binder proposed by the present invention not only has flame retardant performance, but also is very excellent in cycle stability.

[0133] The above are only exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A multifunctional negative electrode binder, characterized in that: The multifunctional negative electrode binder is prepared by the following method: Step 1: preparing an emulsion; adding 1400-2000 parts by mass of an acrylic acid ester monomer mixture and 1-500 parts by mass of a phosphorus-based flame retardant monomer to 30-1200 parts of the emulsion to obtain a pre-emulsion; Step 2: Mix 1 / 20 to 1 / 15 of the pre-emulsion with 4 to 6 parts by mass of an initiator, and react under the first reaction conditions to obtain an aqueous flame retardant emulsion; Step 3: Add 0.5-2 parts by weight of emulsifier SR-10 to the remaining pre-emulsion, then add 4-6 parts by weight of initiator, add 400-600 parts by weight of deionized water and stir for 5-10 minutes to obtain an acrylate emulsion; Step 4: Add acrylic emulsion to the aqueous flame retardant emulsion, and control the temperature at 80-90°C during the addition process. After the addition is completed, react under the second reaction condition, cool to below 50°C, add 50wt% aqueous solution of hydrazide compound, stir for 5-15 minutes, and adjust to neutral to obtain a multifunctional negative electrode binder with flame retardant and self-healing properties.

2. The multifunctional negative electrode binder according to claim 1, characterized in that: The first reaction condition is: heating to 80-90°C and stirring for 1-3 hours; the second reaction condition is: heating to 90°C and stirring for 1.5-3 hours.

3. The multifunctional negative electrode binder according to claim 1, characterized in that: The preparation of the emulsion in step 1 comprises the following steps: Take 5-10 parts by weight of the emulsifier mixture and add it to 400-600 parts by weight of deionized water and stir thoroughly to prepare an emulsion; The emulsifier mixture includes non-ionic acrylic phosphate monomer emulsifier FM30, anionic Solvay phosphate emulsifier RS-610, and reactive emulsifier SR-10 in a mass ratio of 0.8~1:0.8~1:3.5~4.

4. The multifunctional negative electrode binder according to claim 1, characterized in that: The acrylic ester monomer mixed solution in step 1 includes the following components in parts by mass: 65~85 parts of soft monomer, 10~30 parts of hard monomer, 0.5~3 parts of functional self-crosslinking monomer; The soft monomer is one or more of butyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate; The hard monomer is one or more of isobornyl acrylate, ethyl methacrylate, methyl acrylate, butyl methacrylate, methyl methacrylate, acrylic acid, and styrene; The functional self-crosslinking monomer is a 50wt% diacetone acrylamide aqueous solution, and the mass ratio of diacetone acrylamide to adipic acid dihydrazide in the diacetone acrylamide aqueous solution is (2-5):

1.

5. The multifunctional negative electrode binder according to claim 1, characterized in that: The phosphorus-based flame retardant monomer is one or more of vinyl dimethyl phosphate, vinyl diethyl phosphate, and triallyl phosphate.

6. The multifunctional negative electrode binder according to claim 1, characterized in that: In step 2 and step 3, the initiator is one or both of potassium persulfate and ammonium persulfate.

7. The method for preparing a flame retardant and self-repairing multifunctional adhesive according to claim 1, characterized in that: The hydrazide compound aqueous solution in step 4 is a solution prepared by completely dissolving 1 part of hydrazide compound solid powder by mass in 1 part of deionized water by mass, and the hydrazide compound is one of adipic acid dihydrazide, carbohydrazide, malonic acid dihydrazide, succinic acid dihydrazide, and glutaric acid dihydrazide.

8. A silicon-carbon negative electrode plate, characterized in that: The multifunctional negative electrode binder according to any one of claims 1 to 7 is used for preparation, and the preparation method comprises the following steps: Step 1: Mix the negative electrode silicon-carbon material, the negative electrode graphite material and the first conductive agent at a rotation speed of 1500-2500 rpm / min, and stir and disperse for 0.5-2h to obtain a mixed solid powder; Step 2: Add the second conductive agent, the multifunctional negative electrode binder, the second binder and water to the mixed solid powder, at a speed of 1500-2500 rpm / min, and stir and disperse for 0.5-2h to obtain a silicon-carbon negative electrode slurry; Step 3: Apply the silicon-carbon negative electrode slurry on the surface of the copper foil at a speed of 1-8 m / min, and dry it in a vacuum environment of 50-150°C for 1-12 hours to obtain a silicon-carbon negative electrode sheet.

9. The silicon-carbon negative electrode sheet according to claim 7, characterized in that: The mass ratio of the negative electrode silicon-carbon material: the negative electrode graphite material: the first conductive agent: the second conductive agent: the multifunctional negative electrode binder: the second binder: water is 3-4:33-34:1-2:9-11:6-8:44-46:2-20; The negative electrode silicon-carbon material is a composite material of nano-silicon and graphite; The negative electrode graphite material is any one or more of artificial graphite, modified natural graphite, hard carbon, and mesophase carbon microsphere material; The first conductive agent is conductive carbon black; the second conductive agent is a carbon nanotube aqueous solution with a solid content of 1%; The second binder is a sodium carboxymethyl cellulose aqueous solution with a solid content of 1.2%.

10. A lithium ion battery, characterized in that: A silicon-carbon negative electrode sheet comprising any one of claims 8 to 9.