An acrylate binder for silicon-based anodes, and a method of preparation and use thereof

Abstract

The application belongs to the technical field of binders, and particularly relates to an acrylic ester binder for a silicon-based negative electrode, a preparation method and application thereof; the acrylic ester binder for the silicon-based negative electrode comprises the following components: a first polymerization monomer, a second polymerization monomer, a RAFT reagent, a chain extender, a crosslinking agent, an initiator and a solvent; the acrylic ester binder for the silicon-based negative electrode provided by the application has a relatively high molecular weight and moderate viscosity, and exhibits relatively high mechanical strength and flexibility when used for bonding the silicon-based negative electrode and the current collector, can effectively inhibit volume expansion of the silicon-based negative electrode in the charging and discharging cycle process, and improves the electrochemical performance and cycle life of the lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, specifically relating to an acrylate adhesive for silicon-based anodes, its preparation method, and its application. Background Technology

[0002] Silicon (Si) is considered the preferred anode material for next-generation high-energy-density lithium-ion batteries due to its extremely high theoretical specific capacity (4200 mAh / g) and abundant reserves. However, silicon undergoes huge volume expansion (>300%) during charging and discharging, which leads to the pulverization of active particles, the destruction of conductive networks, and the continuous rupture and regeneration of the solid electrolyte interface film. Ultimately, this causes the electrode structure to collapse and the battery capacity to decay rapidly, thus affecting the battery's coulombic efficiency and cycle life.

[0003] Using high-performance polymer binders is one of the key and cost-effective strategies to alleviate the above problems. Acrylic polymers have been widely studied due to their good flexibility and strong affinity for silicon surfaces. The applicant has also conducted relevant research and development on binders for silicon-based anodes and applied for related patents. Among them, the Chinese patent with publication number CN 120590888 A uses monomer A as an acrylic monomer, monomer B as a branched monomer, and monomer C as a functional monomer. By optimizing the types and ratios of monomers A, B, and C, a waterborne acrylic resin with a branched structure is obtained. The lignin is modified to introduce unsaturated bonds, enabling it to copolymerize with the polymer monomers. This introduces lignin into the structure of the waterborne acrylic resin, which not only improves the peelability of the waterborne acrylic resin but also effectively resists the volume expansion of the silicon anode and improves the electrochemical performance of the battery. However, this technical solution uses a relatively high amount of waterborne acrylic resin (10%), and the cycle performance needs to be improved.

[0004] Chinese patent CN120209217B discloses a polyacrylic acid resin with a hyperbranched network structure prepared by using specific water-based acrylic resin, monomer A, monomer B, monomer C, chain extender, crosslinking agent, and silane coupling agent. The resulting polyacrylic acid resin has high viscosity and peel strength and is used to prepare negative electrode materials for lithium-ion batteries, suppressing material expansion and increasing the structural stability of the negative electrode material. However, the polyacrylic acid resin used in this technical solution is also relatively high (10%), and the discharge specific capacity can only reach 900 mA h / g after 500 cycles.

[0005] Existing commercially available or literature-reported acrylic adhesives (such as polyacrylic acid PAA) generally suffer from the following drawbacks: First, insufficient molecular weight and wide distribution: Adhesives prepared by traditional free radical polymerization have limited molecular weight (typically Mw < 500,000 g / mol). This low molecular weight results in insufficient cohesive strength and mechanical toughness, making it difficult to effectively confine the enormous stress generated by silicon particles during expansion and contraction; overall performance is difficult to optimize. Second, uncontrollable structure: Polymers synthesized by traditional methods have a random coil structure, limiting their stress dissipation capacity, elastic recovery capacity, and multi-point bonding ability with silicon particles. Third, traditional polymers lack active sites for further chemical modification or reaction, limiting their potential to form strong chemical bonds with silicon surface functional groups or other electrode components (such as conductive agents). Adhesive strength mainly relies on physical forces, resulting in insufficient overall strength. Summary of the Invention

[0006] The present invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial solution. Specifically, the present invention provides an acrylate binder for silicon-based anodes, its preparation method, and its application. The acrylate binder for silicon-based anodes provided by the present invention has a high molecular weight and moderate viscosity, exhibiting high mechanical strength and flexibility when used to bond silicon-based anodes and current collectors. It can effectively suppress the volume expansion of silicon-based anodes during charge-discharge cycles, thereby improving the electrochemical performance and cycle life of lithium-ion batteries.

[0007] In a first aspect, the present invention provides an acrylate binder for silicon-based anodes, comprising the following components: a first polymerizing monomer, a second polymerizing monomer, a RAFT reagent, a chain extender, a crosslinking agent, an initiator, and a solvent; The first polymerizable monomer is monomer A and monomer B in a mass ratio of 1-9:9-1; The second polymerization monomer is monomer A and monomer B in a mass ratio of 1.5-3:1; The monomer A is selected from at least one of butyl acrylate, hydroxyethyl acrylate, ethyl acrylate, lauryl acrylate, vinyl acetate, ethoxyethoxyethyl acrylate, and methoxy polyethylene glycol acrylate. The monomer B is selected from at least one of acrylonitrile, isobornyl methacrylate, diallylamine, triallylamine, acrylic acid, acrylamide, methacrylamide, and N-hydroxymethylacrylamide.

[0008] Preferably, the acrylate binder used for silicon-based anodes has a weight-average molecular weight of 700,000-1,000,000 g / mol and a viscosity of 7,000-10,000 mPa·s under 5% solid content conditions.

[0009] Preferably, the first polymerizing monomer is a mixture of butyl acrylate and acrylic acid; the second polymerizing monomer is a mixture of butyl acrylate and diallylamine.

[0010] Preferably, the first polymerizing monomer is a mixture of acrylamide, lauryl acrylate, and ethoxyethoxyacrylate; the second polymerizing monomer is a mixture of acrylamide and methoxy polyethylene glycol acrylate.

[0011] Preferably, the first polymerizing monomer is a mixture of hydroxyethyl acrylate and acrylic acid; the second polymerizing monomer is a mixture of hydroxyethyl acrylate, methoxy polyethylene glycol acrylate and N-hydroxymethylacrylamide.

[0012] Preferably, the mass ratio of the first polymeric monomer to the second polymeric monomer is 3-7:7-3.

[0013] Preferably, the RAFT reagent is selected from at least one of 2-(dodecyl trithiocarbonate)-2-methylpropionic acid, bis(carboxymethyl)trithiocarbonate, and N-alkyl-N-aryl dithiocarbamate.

[0014] Preferably, the amount of RAFT reagent used is 1-3% of the total mass of the first and second polymerizing monomers.

[0015] Preferably, the chain extender is selected from dodecyl mercaptan and / or 2-mercaptoethanol.

[0016] Preferably, the amount of chain extender used is 0.5-2% of the total mass of the first and second polymerizing monomers.

[0017] Preferably, the crosslinking agent is selected from at least one of polyols, polyamines, β-cyclodextrin and carboxymethyl cellulose.

[0018] Preferably, the polyol is selected from at least one of ethylene glycol, hexanediol, pentanediol, and sorbitol.

[0019] Preferably, the polyamine is selected from at least one of ethanolamine, N,N-dihydroxyaniline, polyetheramine, and ethylenediamine.

[0020] Preferably, the amount of crosslinking agent used is 5-15% of the total mass of the first polymerizing monomer and the second polymerizing monomer.

[0021] Preferably, the initiator is selected from at least one of ammonium persulfate, potassium persulfate, ammonium persulfate, sodium bisulfite, and hydrogen peroxide.

[0022] Preferably, the amount of the initiator used is 0.5-1% of the total mass of the first and second polymerizing monomers.

[0023] Preferably, the solvent is selected from at least one of deionized water, water, N-methylpyrrolidone, and N,N-dimethylformamide.

[0024] Preferably, the mass ratio of the first polymeric monomer to the solvent is 10-30:100.

[0025] Secondly, the present invention provides a method for preparing an acrylate binder for silicon-based anodes, comprising the following steps: (1) Under an inert atmosphere, the first polymerization monomer, part of the initiator and part of the solvent are mixed, and then RAFT reagent is added. The mixture is heated to react and a reactive prepolymer is obtained. (2) Maintain the reaction temperature and slowly add a mixed solution of the second polymerizing monomer, chain extender, crosslinking agent, remaining initiator and remaining solvent to the system of step (1). After the addition is complete, allow the reaction to mature. (3) After the reaction is completed, the temperature is lowered and the pH value is adjusted to 6-8 using a pH adjuster to obtain an acrylate binder for silicon-based anodes.

[0026] Preferably, the conditions for the heating reaction in step (1) are: reacting at 50-85℃ for 0.5-2h.

[0027] Preferably, the ripening reaction conditions in step (2) are: reacting at 80-90℃ for 1-3 hours.

[0028] Preferably, the cooling in step (3) is to cool down to 40-60℃.

[0029] Preferably, the pH adjuster is selected from at least one of sodium hydroxide, lithium hydroxide, sodium bicarbonate, lithium carbonate, and ammonia water.

[0030] Thirdly, the present invention provides an application of an acrylate binder for silicon-based anodes in silicon-based lithium-ion batteries.

[0031] Fourthly, the present invention provides a silicon anode sheet comprising the above-mentioned acrylate binder for silicon-based anodes.

[0032] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. This invention introduces a RAFT reagent to regulate molecular weight and uses specific rigid monomers (monomer B) and flexible monomers (monomer A) for copolymerization, successfully preparing an acrylate binder with both ultra-high molecular weight and moderate viscosity. The acrylate binder of this invention has a rigid-flexible block structure, in which the hard segments act as physical crosslinking points, providing high cohesion and skeletal support, while the soft segments provide flexibility and the ability to wet and encapsulate active particles. Furthermore, the soft segments have excellent chain mobility, which can release the stress generated by expansion when applied to silicon-based anodes, reducing the changes in the electrode sheet caused by volume changes in silicon-based anodes. The acrylate binder provided by this invention achieves a balance of high adhesion, high toughness, and long cycle stability in silicon-based anodes after bonding, exhibiting electrode mechanical strength and long battery cycle life far exceeding that of ordinary PAA binders.

[0033] 2. The acrylate adhesive provided by the present invention has a weight-average molecular weight of 700,000-1,000,000 g / mol and a viscosity of 7,000-10,000 mPa·s under 5% solid content conditions.

[0034] 3. The acrylate binder provided by this invention has excellent bonding performance at a dosage of 2.5%. The silicon-based negative electrode lithium-ion battery prepared by it has a capacity retention rate of more than 89% after 500 cycles and a thickness expansion rate of ≤5.0%.

[0035] 4. The operation method of this invention is simple, and the required modifiers are all conventional and inexpensive reagents. The raw materials and synthesis process are suitable for large-scale production, which makes the prepared acrylate binder have broad application prospects in lithium-ion batteries. Attached Figure Description

[0036] Figure 1 The image shows a scanning electron microscope (SEM) image of a button cell after 500 cycles using Example 1 of this invention (modified PAA) and a conventional PAA binder (commercially available PAA binder in China). Figure 2 The graph shows the cycle performance of a button cell using Example 1 of this invention (modified PAA) and a conventional PAA binder (commercially available PAA binder in China) after 500 cycles. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1 This embodiment provides an acrylate binder for silicon-based anodes, which, by weight, consists of the following components: First polymerization monomer (2.5 parts acrylic acid, 2.2 parts butyl acrylate), second polymerization monomer (4.8 parts butyl acrylate, 2 parts diallylamine), RAFT reagent (0.288 parts 2-(dodecyl trithiocarbonate)-2-methylpropionic acid), chain extender (0.15 parts 2-mercaptoethanol), crosslinking agent (0.8 parts ethylene glycol), initiator (0.096 parts ammonium persulfate), mixed solvent (1.5 parts N,N-dimethylformamide, 25.2 parts deionized water, 37.8 parts ethanol).

[0039] The method for preparing the acrylate binder for silicon-based anodes includes the following steps: Dissolve the first monomer and half of the ammonium persulfate in a mixed solvent (the mass ratio of the first monomer to the mixed solvent is 24:100). Add RAFT reagent and place the mixture in a three-necked flask with a condenser. Purge with nitrogen to remove oxygen and heat to 60°C for 30 min. Slowly add a mixed solution of the second monomer, 2-mercaptoethanol, ethylene glycol, the remaining potassium persulfate, and the remaining mixed solvent over a period of 5.5 h. After the reaction is complete, heat to 80°C for aging for 3 h, then cool to 45°C and add 15 wt% lithium carbonate aqueous solution to adjust the pH to 7.

[0040] Example 2 This embodiment provides an acrylate binder for silicon-based anodes, which, by weight, consists of the following components: First polymerization monomer (1.6 parts acrylamide, 4 parts lauryl acrylate, 2 parts ethoxyethoxyacrylate), second polymerization monomer (0.7 parts acrylamide, 1.5 parts methoxy polyethylene glycol acrylate, molecular weight 200), RAFT reagent (0.196 parts 2-(dodecyl trithiocarbonate)-2-methylpropionic acid), chain extender (0.15 parts 2-mercaptoethanol), crosslinking agent (0.8 parts polyetheramine), initiator (0.049 parts potassium persulfate), mixed solvent (20.4 parts deionized water, 30.6 parts ethanol); The method for preparing the acrylate binder for silicon-based anodes includes the following steps: Dissolve the first monomer and 0.015 parts of potassium persulfate in a mixed solvent (the mass ratio of the first monomer to the mixed solvent is 20:100). Add RAFT reagent and place the mixture in a three-necked flask with a condenser. Purge with nitrogen to remove oxygen and heat to 60°C for 30 min. Slowly add the second monomer, 2-mercaptoethanol, polyetheramine, the remaining potassium persulfate, and the remaining mixed solvent solution over 6 h. After the reaction is complete, heat to 80°C for 3 h and then cool to 45°C. Add 20 wt% lithium carbonate aqueous solution to adjust the pH to 7.

[0041] Example 3 This embodiment provides an acrylate binder for silicon-based anodes, which, by weight, consists of the following components: First polymerization monomer (3 parts acrylic acid, 3 parts hydroxyethyl acrylate), second polymerization monomer (4 parts hydroxyethyl acrylate, 3 parts N-hydroxymethylacrylamide, 1.5 parts methoxy polyethylene glycol acrylate, molecular weight 400), RAFT reagent (0.18 parts 2-(dodecyl trithiocarbonate)-2-methylpropionic acid), chain extender (0.1 parts 2-mercaptoethanol), crosslinking agent (1 part ethanolamine), initiator (0.087 parts ammonium persulfate), solvent (82 parts deionized water).

[0042] The method for preparing the acrylate binder for silicon-based anodes includes the following steps: Dissolve the first monomer and 0.035 parts of ammonium persulfate in a solvent (the mass ratio of the first monomer to the solvent is 25:100). Add RAFT reagent and place the mixture in a three-necked flask with a condenser. Purge with nitrogen to remove oxygen and heat to 60°C for 1 hour. Slowly add a mixed solution of the second monomer, 2-mercaptoethanol, ethanolamine, the remaining potassium persulfate, and the remaining solvent over a period of 5.5 hours. After the reaction is complete, heat to 90°C for aging for 1 hour, then cool to 45°C and add 18 wt% lithium carbonate aqueous solution to adjust the pH to 7.

[0043] Comparative Example 1 This comparative example provides an acrylate binder for silicon-based anodes, which, by weight, consists of the following components: First polymerization monomer (2 parts acrylic acid, 0.5 parts acrylonitrile, 3 parts acrylamide), second polymerization monomer (1 part acrylic acid, 1.5 parts methoxy polyethylene glycol acrylate, molecular weight 600), RAFT reagent (0.1 part 2-(dodecyl trithiocarbonate)-2-methylpropionic acid), chain extender (0.1 part dodecyl mercaptan), crosslinking agent (1 part polyetheramine), initiator (0.06 parts potassium persulfate), mixed solvent (8 parts deionized water, 8 parts ethanol).

[0044] The method for preparing the acrylate binder for silicon-based anodes includes the following steps: Dissolve the first monomer and half of the potassium persulfate in a mixed solvent (the mass ratio of the first monomer to the mixed solvent is 20:100). Add RAFT reagent and place the mixture in a three-necked flask with a condenser. Purge with nitrogen to remove oxygen and heat to 60°C for 1 hour. Slowly add a mixed solution of the second monomer, dodecyl mercaptan, polyetheramine, the remaining potassium persulfate, and the remaining mixed solvent over a period of 6 hours. After the reaction is complete, heat to 90°C for aging for 1 hour, then cool to 40°C and add 20 wt% lithium carbonate aqueous solution to adjust the pH to 7.

[0045] Comparative Example 2 This comparative example provides an acrylate binder for silicon-based anodes, which, by weight, consists of the following components: First polymerization monomer (1 part acrylic acid, 8 parts hydroxyethyl methacrylate), second polymerization monomer (2 parts acrylic acid, 3 parts acrylamide), RAFT reagent (0.18 parts 2-(dodecyl trithiocarbonate)-2-methylpropionic acid), chain extender (0.15 parts dodecyl mercaptan), crosslinking agent (1 part ethanolamine), initiator (0.093 parts sodium persulfate), mixed solvent (1.5 parts N,N-dimethylformamide, 88 parts deionized water).

[0046] The method for preparing the acrylate binder for silicon-based anodes includes the following steps: Dissolve the first monomer and 0.06 parts of sodium persulfate in a mixed solvent (the mass ratio of the first monomer to the mixed solvent is 15:100). Add RAFT reagent and place the mixture in a three-necked flask with a condenser. Purge with nitrogen to remove oxygen and heat to 55°C for 1 hour. Slowly add a mixed solution of the second monomer, dodecyl mercaptan, polyetheramine, the remaining potassium persulfate, and the remaining mixed solvent over a period of 5.5 hours. After the reaction is complete, heat to 85°C for aging for 1.5 hours, then cool to 45°C and add 18 wt% lithium carbonate aqueous solution to adjust the pH to 7.

[0047] Comparative Example 3 This comparative example provides an acrylate binder for silicon-based anodes, which, by weight, consists of the following components: First polymerization monomer (3 parts acrylic acid, 5.5 parts ethyl acrylate), second polymerization monomer (1.5 parts ethyl acrylate, 3 parts N-hydroxymethylacrylamide, 1.5 parts methoxy polyethylene glycol acrylate, molecular weight 400), RAFT reagent (0.18 parts 2-(dodecyl trithiocarbonate)-2-methylpropionic acid), chain extender (0.1 parts dodecyl mercaptan), crosslinking agent (1 part ethanolamine), initiator (0.087 parts ammonium persulfate), solvent (82 parts deionized water).

[0048] The method for preparing the acrylate binder for silicon-based anodes includes the following steps: Dissolve the first monomer and 0.035 parts of ammonium persulfate in a solvent (the mass ratio of the first monomer to the solvent is 25:100). Add RAFT reagent and place the mixture in a three-necked flask with a condenser. Purge with nitrogen to remove oxygen and heat to 60°C for 1 hour. Slowly add a mixed solution of the second monomer, 2-mercaptoethanol, ethanolamine, the remaining potassium persulfate, and the remaining solvent over a period of 5.5 hours. After the reaction is complete, heat to 90°C for aging for 1 hour, then cool to 45°C and add 18 wt% lithium carbonate aqueous solution to adjust the pH to 7.

[0049] Comparative Example 4 This comparative example provides an acrylate binder for silicon-based anodes, which, by weight, consists of the following components: First polymerization monomer (3 parts acrylic acid, 3 parts N-hydroxymethylacrylamide), second polymerization monomer (7 parts ethyl acrylate, 1.5 parts methoxy polyethylene glycol acrylate, molecular weight 400), RAFT reagent (0.18 parts 2-(dodecyl trithiocarbonate)-2-methylpropionic acid), chain extender (0.1 parts dodecyl mercaptan), crosslinking agent (1 part ethanolamine), initiator (0.087 parts ammonium persulfate), solvent (82 parts deionized water).

[0050] The method for preparing the acrylate binder for silicon-based anodes includes the following steps: Dissolve the first monomer and 0.035 parts of ammonium persulfate in a solvent (the mass ratio of the first monomer to the solvent is 25:100). Add RAFT reagent and place the mixture in a three-necked flask with a condenser. Purge with nitrogen to remove oxygen and heat to 60°C for 1 hour. Slowly add a mixed solution of the second monomer, 2-mercaptoethanol, ethanolamine, the remaining potassium persulfate, and the remaining solvent over a period of 5.5 hours. After the reaction is complete, heat to 90°C for aging for 1 hour, then cool to 45°C and add 18 wt% lithium carbonate aqueous solution to adjust the pH to 7.

[0051] Comparative Example 5 This comparative example provides an acrylate binder for silicon-based anodes, which, by weight, consists of the following components: First polymerization monomer (3 parts acrylic acid, 3 parts ethyl acrylate), second polymerization monomer (4 parts ethyl acrylate, 3 parts N-hydroxymethylacrylamide, 1.5 parts polyethylene glycol monomethyl ether acrylate), RAFT reagent (0.18 parts 2-(dodecyl trithiocarbonate)-2-methylpropionic acid), chain extender (0.1 parts 2-mercaptoethanol), crosslinking agent (1 part ethanolamine), initiator (0.087 parts ammonium persulfate), solvent (82 parts deionized water).

[0052] The method for preparing the acrylate binder for silicon-based anodes includes the following steps: Dissolve the first monomer and 0.035 parts of ammonium persulfate in a solvent (the mass ratio of the first monomer to the solvent is 25:100). Add RAFT reagent and place the mixture in a three-necked flask with a condenser. Purge with nitrogen to remove oxygen and heat to 60°C for 1 hour. Slowly add a mixed solution of the second monomer, 2-mercaptoethanol, ethanolamine, the remaining potassium persulfate, and the remaining solvent over a period of 5.5 hours. After the reaction is complete, heat to 90°C for aging for 1 hour, then cool to 45°C and add 18 wt% lithium carbonate aqueous solution to adjust the pH to 7.

[0053] Comparative Example 6 This comparative example provides an acrylate binder for silicon-based anodes, which, by weight, consists of the following components: First polymerization monomer (3 parts acrylic acid, 3 parts ethyl acrylate), second polymerization monomer (4 parts ethyl acrylate, 3 parts N-hydroxymethylacrylamide, 1.5 parts ethyl acetoacetate methacrylate), RAFT reagent (0.18 parts 2-(dodecyl trithiocarbonate)-2-methylpropionic acid), chain extender (0.1 parts 2-mercaptoethanol), crosslinking agent (1 part ethanolamine), initiator (0.087 parts ammonium persulfate), solvent (82 parts deionized water).

[0054] The method for preparing the acrylate binder for silicon-based anodes includes the following steps: Dissolve the first monomer and 0.035 parts of ammonium persulfate in a solvent (the mass ratio of the first monomer to the solvent is 25:100). Add RAFT reagent and place the mixture in a three-necked flask with a condenser. Purge with nitrogen to remove oxygen and heat to 60°C for 1 hour. Slowly add a mixed solution of the second monomer, 2-mercaptoethanol, ethanolamine, the remaining potassium persulfate, and the remaining solvent over a period of 5.5 hours. After the reaction is complete, heat to 90°C for aging for 1 hour, then cool to 45°C and add 18 wt% lithium carbonate aqueous solution to adjust the pH to 7.

[0055] Comparative Example 7 This comparative example provides an acrylate binder for silicon-based anodes, which, by weight, consists of the following components: First polymerization monomer (3 parts acrylic acid, 3 parts ethyl acrylate), second polymerization monomer (4 parts ethyl acrylate, 3 parts N-hydroxymethylacrylamide, 1.5 parts methoxy polyethylene glycol acrylate, molecular weight 400), RAFT reagent (0.18 parts 2-(dodecyl trithiocarbonate)-2-methylpropionic acid), crosslinking agent (1 part ethanolamine), initiator (0.087 parts ammonium persulfate), solvent (82 parts deionized water).

[0056] The method for preparing the acrylate binder for silicon-based anodes includes the following steps: Dissolve the first monomer and 0.035 parts of ammonium persulfate in a solvent (the mass ratio of the first monomer to the solvent is 25:100). Add RAFT reagent and place the mixture in a three-necked flask with a condenser. Purge with nitrogen to remove oxygen and heat to 60°C for 1 hour. Slowly add a mixed solution of the second monomer, ethanolamine, the remaining potassium persulfate, and the remaining solvent over a period of 5.5 hours. After the reaction is complete, heat to 90°C for aging for 1 hour, then cool to 45°C and add 18 wt% lithium carbonate aqueous solution to adjust the pH to 7.

[0057] Comparative Example 8 This comparative example provides an acrylate binder for silicon-based anodes, which, by weight, consists of the following components: First polymerization monomer (3 parts acrylic acid, 3 parts ethyl acrylate), second polymerization monomer (4 parts ethyl acrylate, 3 parts N-hydroxymethylacrylamide, 1.5 parts methoxy polyethylene glycol acrylate, molecular weight 400), RAFT reagent (0.18 parts 2-(dodecyl trithiocarbonate)-2-methylpropionic acid, 0.1 parts trimethylolpropane), crosslinking agent (1 part ethanolamine), initiator (0.087 parts ammonium persulfate), solvent (82 parts deionized water).

[0058] The method for preparing the acrylate binder for silicon-based anodes includes the following steps: Dissolve the first monomer and 0.035 parts of ammonium persulfate in a solvent (the mass ratio of the first monomer to the solvent is 25:100). Add RAFT reagent and place the mixture in a three-necked flask with a condenser. Purge with nitrogen to remove oxygen and heat to 60°C for 1 hour. Slowly add a mixed solution of the second monomer, trimethylolpropane, ethanolamine, the remaining potassium persulfate, and the remaining solvent over a period of 5.5 hours. After the reaction is complete, heat to 90°C for aging for 1 hour, then cool to 45°C and add 18 wt% lithium carbonate aqueous solution to adjust the pH to 7.

[0059] Test Example 1 The molecular weight of the acrylate binder in this example and the comparative example was tested using an Agilent 1260 Infinity gel permeation chromatography (GPC) system, and the results are shown in Table 1.

[0060] Test Example 2 The acrylate adhesives in this example and the comparative example were diluted with deionized water to a solid content of 5%, and the viscosity was tested at 25°C using a viscometer. The results are shown in Table 1.

[0061] Table 1 As shown in Table 1, the acrylate adhesives prepared in Examples 1-3 and Comparative Example 1 of this invention have a viscosity of 7000-10000 mPa·s and a weight-average molecular weight of 700,000-1,000,000. Under the same adhesive addition amount, the viscosity is moderate, the adhesive layer coating thickness is uniform, and the molecular weight is large, resulting in higher adhesion.

[0062] The acrylate adhesive prepared in Comparative Example 2 has a moderate viscosity but a low weight-average molecular weight. In Comparative Example 3, the soft and hard segments in the first and second polymer monomers are not within the scope of protection of this invention. The prepared acrylate adhesive has a large weight-average molecular weight, but also a high viscosity. In Comparative Example 4, the first polymerizing monomers were all hard monomers and the second polymerizing monomers were all soft monomers. The prepared acrylate adhesive had a large weight-average molecular weight, but also a high viscosity. Comparative Example 5 replaced methoxy polyethylene glycol acrylate with polyethylene glycol monomethyl ether acrylate, and Comparative Example 6 replaced methoxy polyethylene glycol acrylate with ethyl acetoacetate methacrylate; the prepared acrylate adhesives all had relatively high weight-average molecular weights, but also relatively high viscosity. Comparative Example 7 did not contain a chain extender, and the prepared acrylate adhesive had a large weight-average molecular weight, but also a high viscosity. Comparative Example 8 showed that the acrylate adhesive prepared by replacing 2-mercaptoethanol with trimethylolpropane had higher viscosity and lower weight-average molecular weight.

[0063] Test Example 3 Nano-silicon, conductive carbon black, and acrylate binder from the examples or comparative examples were mixed in a mass ratio of 95.5:2:2.5. Deionized water was added to form a negative electrode slurry with a solid content of 53%. The negative electrode slurry was coated on the surface of a copper foil negative electrode sheet and dried overnight in a vacuum drying oven at 100°C. Using lithium metal sheets as the counter electrode, Celgard 2325 as the separator, and 1 mol / L LiPF6 (a 1:1 volume ratio mixture of ethylene carbonate and dimethyl carbonate) as the electrolyte, a CR2032 type button cell casing was assembled into a button cell in an argon-protected glove box. Charge-discharge tests were performed using the Blue Electric test procedure with a current density of 1 A / g, a voltage range of 0.01–3 V, and 500 cycles. After 500 cycles, the battery was disassembled to measure the expansion rate of the electrodes. The results are shown in Table 2. Scanning electron microscope (SEM) images of button cells using Example 3 of this invention (modified PAA) and a traditional PAA binder (commercially available PAA binder in China) after 500 cycles are shown below. Figure 1 As shown in the figure, the cycle performance graph is as follows: Figure 2 As shown.

[0064] Depend on Figure 1It can be seen that the acrylate adhesive of Example 3 of the present invention has excellent bonding effect at 2.5%, and the number of cracks in the tablets after cycling is small, while the traditional PAA adhesive has a large number of cracks.

[0065] Table 2 Results analysis: The batteries prepared using the acrylate binders of Examples 1-3 have high initial discharge specific capacity and high capacity retention after 500 cycles. The thickness expansion rate after 500 cycles is also low, indicating that the acrylate binder prepared in this invention can effectively buffer the volume expansion of the electrode and extend its service life. Although the acrylate binder in Comparative Example 1 had a moderate viscosity and a relatively large molecular weight, the capacity retention rate of the prepared battery decreased significantly after 500 cycles, and the thickness expansion rate also increased after 500 cycles. The capacity retention of the battery prepared using the acrylate binder prepared in Comparative Example 2 decreased significantly after 500 cycles, and the thickness expansion rate also increased after 500 cycles. In Comparative Example 3, the soft and hard segments in the first and second polymer monomers are not within the scope of protection of this invention. The capacity retention rate of the battery prepared with the acrylate binder prepared in this comparative example decreased after 500 cycles, and the thickness expansion rate also increased after 500 cycles. In Comparative Example 4, the first polymerizing monomers were all hard monomers and the second polymerizing monomers were all soft monomers. The capacity retention rate of the battery prepared with the acrylate binder prepared in this comparative example decreased significantly after 500 cycles, and the thickness expansion rate also increased after 500 cycles. Comparative Example 5 replaced methoxy polyethylene glycol acrylate with polyethylene glycol monomethyl ether acrylate, and Comparative Example 6 replaced methoxy polyethylene glycol acrylate with ethyl acetoacetate methacrylate. The capacity retention of batteries prepared with the acrylate binder prepared in these comparative examples decreased after 500 cycles, and the thickness expansion rate also increased after 500 cycles. Comparative Example 7 does not contain chain extenders. The capacity retention rate of the battery prepared with the acrylate binder prepared in this comparative example decreased significantly after 500 cycles, and the thickness expansion rate also increased after 500 cycles. In Comparative Example 8, 2-mercaptoethanol was replaced with trimethylolpropane. The batteries prepared using the acrylate binder prepared in this comparative example had good capacity retention after 500 cycles, but the thickness expansion rate increased significantly after 500 cycles.

[0066] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An acrylate binder for silicon-based anodes, characterized in that, It includes the following components: first polymerization monomer, second polymerization monomer, RAFT reagent, chain extender, crosslinking agent, initiator, and solvent; The first polymerizable monomer is monomer A and monomer B in a mass ratio of 1-9:9-1; The second polymerization monomer is monomer A and monomer B in a mass ratio of 1.5-3:1; The monomer A is selected from at least one of butyl acrylate, hydroxyethyl acrylate, ethyl acrylate, lauryl acrylate, vinyl acetate, ethoxyethoxyethyl acrylate, and methoxy polyethylene glycol acrylate. The monomer B is selected from at least one of acrylonitrile, isobornyl methacrylate, diallylamine, triallylamine, acrylic acid, acrylamide, methacrylamide, and N-hydroxymethylacrylamide.

2. The acrylate binder for silicon-based anodes according to claim 1, characterized in that, The acrylate binder used for silicon-based anodes has a weight-average molecular weight of 700,000-1,000,000 g / mol and a viscosity of 7,000-10,000 mPa·s under 5% solid content conditions.

3. The acrylate binder for silicon-based anodes according to claim 2, characterized in that, The mass ratio of the first polymeric monomer to the second polymeric monomer is 3-7:7-3.

4. The acrylate binder for silicon-based anodes according to claim 3, characterized in that, The RAFT reagent is selected from at least one of 2-(dodecyl trithiocarbonate)-2-methylpropionic acid, bis(carboxymethyl)trithiocarbonate and N-alkyl-N-aryl dithiocarbamate; the amount of the RAFT reagent used is 1-3% of the total mass of the first and second polymerizing monomers.

5. The acrylate binder for silicon-based anodes according to claim 4, characterized in that, The chain extender is selected from dodecyl mercaptan and / or 2-mercaptoethanol; the amount of the chain extender used is 0.5-2% of the total mass of the first and second polymerizing monomers.

6. The acrylate binder for silicon-based anodes according to claim 5, characterized in that, The crosslinking agent is selected from at least one of polyols, polyamines, β-cyclodextrin and carboxymethyl cellulose.

7. The acrylate binder for silicon-based anodes according to claim 6, characterized in that, The polyol is selected from at least one of ethylene glycol, hexanediol, pentanediol, and sorbitol; the polyamine is selected from at least one of ethanolamine, N,N-dihydroxyaniline, polyetheramine, and ethylenediamine.

8. The method for preparing the acrylate binder for silicon-based anodes according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Under an inert atmosphere, the first polymerization monomer, part of the initiator and part of the solvent are mixed, and then RAFT reagent is added. The mixture is heated to react and a reactive prepolymer is obtained. (2) Maintain the reaction temperature and slowly add a mixed solution of the second polymerizing monomer, chain extender, crosslinking agent, remaining initiator and remaining solvent to the system of step (1). After the addition is complete, allow the reaction to mature. (3) After the reaction is completed, the temperature is lowered and the pH value is adjusted to 6-8 using a pH adjuster to obtain an acrylate binder for silicon-based anodes.

9. The use of the acrylate binder for silicon-based anodes according to any one of claims 1-7 in silicon-based anode lithium-ion batteries.

10. A silicon anode sheet, characterized in that, Includes the acrylate binder for silicon-based anodes as described in any one of claims 1-7.

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