Cross-linked silicon-based negative electrode binder and preparation method therefor

Abstract

The present invention relates to the field of cross-linked silicon-based negative electrode binders, and relates to a cross-linked silicon-based negative electrode binder and a preparation method therefor. The technical problem solved by the present invention is to provide a cross-linked silicon-based negative electrode binder having high adhesion. The binder comprises a polyurethane binder and a polyacrylic acid binder. In the present invention, an isocyanate is blocked by using a blocking agent, so that the properties of the isocyanate are stable during storage and transportation. During high-temperature thermal treatment, the blocking agent can be removed, and the exposed isocyanate undergoes a thermal cross-linking reaction with an active functional group in the polyacrylic acid binder to form a spatial network structure, thereby enhancing the bonding strength between a coating and a foil. The bonding form of chemical bonds ameliorates the problem of compatibility of different mixed systems, achieving superior softening and tackifying effects. In addition, the dense network structure formed by high-temperature cross-linking has multi-dimensional bonding sites, effectively improves interfacial bonding, and inhibits full-charge rebound of an electrode plate. The introduced polyurethane segments have excellent electrolyte affinity and wettability, thereby effectively enhancing ionic conduction, and reducing the DCR of a battery cell.

Description

Cross-linked silicon-based anode binder and its preparation method

[0001] Cross-references to related applications

[0002] This application claims the benefit and priority of Chinese patent application CN2025104904658, filed on April 18, 2025, which is incorporated herein by reference and for all other purposes. Technical Field

[0003] This invention relates to cross-linked silicon-based anode adhesives and their preparation methods, belonging to the category of cross-linked silicon-based anode adhesives. Background Technology

[0004] Silicon-based anodes are composite materials composed of silicon and carbon, used as anodes in batteries. This material combines the advantages of silicon and carbon, including high anode capacity, wide availability, and environmental friendliness, and is expected to replace the currently widely used graphite anodes, becoming the main anode material for next-generation lithium-ion batteries.

[0005] Silicon-based anode materials undergo severe volume expansion during lithium intercalation, damaging the integrity of the electrode and leading to rapid capacity decay. Possible causes of silicon-based anode material failure include: (1) Volume changes cause high internal stress on silicon particles, leading to material (anode active material, etc.) breakage and pulverization. (2) Continuous volume changes and pulverization of the anode material cause many active materials to lose their connection with the conductive network and current collector, resulting in the electrode layer peeling off from the current collector. (3) The drastic volume change of silicon during lithium intercalation damages the original SEI layer, exposing silicon on the surface, forming a new SEI layer with the electrolyte, continuously consuming lithium ions and electrolyte, and eventually depleting the electrolyte. Currently, there are many ways to improve the battery cycle performance caused by silicon anode volume changes. Among them, developing high-performance binders is a simple and effective method. Furthermore, binders play a crucial role in the electrochemical performance of the electrode, reducing the impact of silicon volume expansion and improving battery cycle performance.

[0006] The invention patent with application number 202411117798.8 discloses a method for preparing a biopolymer binder for lithium-ion silicon anode batteries. The binder includes the following raw materials by mass percentage: guar gum 0-30%, gum arabic 0-30%, polyacrylic acid 40-50%, and deionized water 20-30%.

[0007] The invention patent with application number 202111482065.0 discloses a binder for silicon-based materials of lithium battery negative electrode. The binder is composed of konjac gum-acrylic acid graft copolymer, guar gum, sodium alginate, hydroxyl-terminated polybutadiene and other components, which can promote the transport of lithium ions, enable the silicon particles to maintain electronic contact after differentiation, and effectively enhance the adhesion of the binder.

[0008] It is evident that currently, silicon-based anodes mostly use high molecular weight polyacrylic acid (PAA) or modified PAA binders. However, PAA is relatively hard and brittle, which can easily cause the electrode to detach during the charging and discharging process of lithium batteries, requiring further enhancement of flexibility and adhesion.

[0009] Summary of the Invention

[0010] To address the above deficiencies, the technical problem solved by this invention is to provide a highly adhesive cross-linked silicon-based anode adhesive.

[0011] The present invention relates to a crosslinked silicon-based negative electrode adhesive, comprising polyurethane and polyacrylic acid adhesive, wherein the polyurethane is a polyurethane with isocyanate groups capped by a blocking agent, and the polyacrylic acid adhesive comprises polyacrylic acid, wherein the polyacrylic acid has active functional groups, wherein the active functional groups are groups that react with isocyanate, and the weight of polyurethane is 5% to 50% based on 100% of the weight of polyurethane and polyacrylic acid adhesive.

[0012] In some embodiments of the present invention, the molecular weight Mn of polyurethane is 10,000 to 150,000, and the molecular weight Mn of polyacrylic acid is 50,000 to 1,500,000.

[0013] In some embodiments of the present invention, the blocking agent is at least one selected from phenol, methyl ethyl ketone oxime, caprolactam, 2-pyridinephenol, 3-hydroxyquinoline, triphenylthiol, hexamethylenetetramine, 3,5-dimethylpyrazole, and 1,2,4-triazole.

[0014] In some embodiments of the present invention, the active functional group is a hydroxyl or an amino group.

[0015] In some embodiments of the present invention, the polymeric monomer of polyacrylic acid with active functional groups includes acrylic acid and acrylate with active functional groups.

[0016] In some specific embodiments of this invention, the acrylate with active functional groups is at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate.

[0017] The present invention also provides a method for preparing the cross-linked silicon-based negative electrode adhesive described herein.

[0018] The preparation method of the crosslinked silicon-based negative electrode adhesive of the present invention includes the following steps:

[0019] a. Preparation of polyurethane: Macromolecular diol and diisocyanate are prepolymerized under a catalyst to obtain polyurethane prepolymer. Organic solvent is added to reduce viscosity, and then chain extender is added to extend chain to obtain isocyanate-terminated hydrophilic polyurethane prepolymer. Then, blocking agent is added to block isocyanate, salting agent is added to neutralize hydrophilic groups, and finally organic solvent is removed to obtain polyurethane.

[0020] b. Preparation of polyacrylic acid adhesive: The polymeric monomers are copolymerized in water to obtain polyacrylic acid containing active functional groups, which is then neutralized to obtain a polyacrylic acid adhesive; the polymeric monomers include acrylic acid, acrylates with active functional groups, and acrylic acid derivatives.

[0021] c. Mixing: Polyurethane and polyacrylic acid adhesive are blended to obtain cross-linked silicon-based anode adhesive.

[0022] In some embodiments of the present invention, the macromolecular diol is at least one selected from polyether diol, polyester diol, polycarbonate diol, and polyhydroxyl-terminated butadiene diol, and the number average molecular weight Mn of the macromolecular diol is 500-3000; the diisocyanate is at least one selected from hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, dicyclohexylmethane 4,4-diisocyanate, diphenylmethane diisocyanate, methylcyclohexane diisocyanate, phenylenediamine diisocyanate, and tetramethyl-m-phenylenediamine diisocyanate; the catalyst is at least one selected from organotin, organobismuth, or organic amine; and the organic solvent is acetone, butanone, tetrahydrofuran, or ethyl acetate. At least one of ethyl acetate and toluene; the chain extender is at least one of dimethylolpropionic acid, dimethylolbutyric acid, tartaric acid, sodium 1,4-butanediol sulfonate, sodium 2,4-diaminobenzene sulfonate, 2,3-dihydroxypropane-1-sulfonic acid, 1,4-butanediol, and 1,6-hexanediol; the salt forming agent is at least one of triethylamine, triethanolamine, N-methyldiethanolamine, sodium hydroxide, lithium hydroxide, and potassium hydroxide; the acrylic acid derivative includes acrylonitrile, styrene, or (meth)acrylates, wherein (meth)acrylates include at least one of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and octyl (meth)acrylate.

[0023] In some embodiments of the present invention, in step a, the temperature of the prepolymerization reaction is 50–90°C and the time is 1–6 h.

[0024] In step b, the acrylate with active functional groups accounts for 5 to 50% of the weight of the polyacrylic acid adhesive polymer monomer.

[0025] The present invention also provides a silicon-based anode sheet.

[0026] The silicon-based anode sheet of the present invention comprises an anode active material and an adhesive, wherein the adhesive is the cross-linked silicon-based anode adhesive described in the present invention.

[0027] In one embodiment of the present invention, during the heat treatment process, the polyurethane deseals the sealing agent, and the exposed isocyanate undergoes a thermal crosslinking reaction with the active functional groups in the polyacrylic acid adhesive, forming a spatial network structure on the surface of the negative electrode active material particles.

[0028] In one embodiment of the present invention, the heat treatment temperature is 100-180°C and the baking time is 1-5 h.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The adhesive of this invention uses a sealant to encapsulate the isocyanate, ensuring its stability during storage and transportation. During high-temperature heat treatment, the sealant is released, and the exposed isocyanate undergoes a thermal crosslinking reaction with the active functional groups in the polyacrylic acid adhesive, forming a spatial network structure. Chemical crosslinking occurs between the PU and PAA, enhancing the adhesion between the coating and the foil. This chemical bonding improves the compatibility of different mixed systems, resulting in superior flexibility and adhesion. Furthermore, the high-temperature crosslinking creates a dense network structure; this 3D network structure has multi-dimensional bonding sites, effectively improving interfacial adhesion, suppressing electrode rebound when fully charged, and the introduced polyurethane segments exhibit excellent electrolyte affinity and wettability, effectively enhancing ion conduction and reducing cell DCR. Attached Figure Description

[0031] Figure 1 is a schematic diagram of the reaction principle of the cross-linked silicon-based negative electrode adhesive of the present invention during the heat treatment process.

[0032] Figure 2 shows the infrared spectra of methyl ethyl ketone oxime, hydroxyl polyacrylate, methyl ethyl ketone oxime blocked polyurethane, and thermally crosslinked polyurethane in Example 2 of the present invention. Detailed Implementation

[0033] The present invention relates to a crosslinked silicon-based negative electrode adhesive, comprising polyurethane and polyacrylic acid adhesive, wherein the polyurethane is polyurethane with isocyanate groups capped by a blocking agent, and the polyacrylic acid adhesive comprises polyacrylic acid with active functional groups, wherein the active functional groups are groups that react with isocyanates, and the weight of polyurethane is 5% to 50% based on 100% of the weight of polyurethane and polyacrylic acid adhesive.

[0034] The adhesive described in this invention allows the polyurethane ends to release the sealing agent and expose isocyanate groups during the high-temperature heat treatment of the manufactured negative electrode sheet. These groups can then undergo a thermal crosslinking reaction with the active functional groups in the polyacrylic acid adhesive, forming a spatial network structure. By utilizing the end-capped isocyanate to thermally crosslink with PAA at high temperature, the compatibility between PU and PAA is improved, while the flexible PU toughens the PAA, resulting in a superior tackifying effect. Furthermore, the dense network structure formed by the high-temperature crosslinking method can effectively suppress adhesive flotation and enhance ion conduction.

[0035] In some embodiments of the present invention, the molecular weight Mn of polyurethane is 10,000 to 150,000, and the molecular weight Mn of polyacrylic acid is 50,000 to 1,500,000. Unless otherwise specified, all molecular weights in the present invention are number average molecular weights Mn.

[0036] In some embodiments of the present invention, the blocking agent is at least one selected from phenols, ketoximes, amides, thiols, and pyridines. In some specific embodiments of the present invention, the blocking agent is at least one selected from phenol, methyl ethyl ketone oxime, caprolactam, 2-pyridinephenol, 3-hydroxyquinoline, triphenylthiol, hexamethylenetetramine, 3,5-dimethylpyrazole, and 1,2,4-triazole.

[0037] In some embodiments of the present invention, the active functional group is a hydroxyl or an amino group.

[0038] In some embodiments of the present invention, the polymer monomers of polyacrylic acid include acrylic acid and acrylates with active functional groups.

[0039] In some specific embodiments of this invention, the acrylate with active functional groups is at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate.

[0040] In some embodiments of the present invention, the polymerizing monomer of polyacrylic acid further includes acrylic acid derivatives. Acrylic acid derivatives commonly used in the art are applicable to the present invention. In some specific embodiments, the acrylic acid derivatives include acrylonitrile, styrene, or (meth)acrylates, wherein (meth)acrylates include at least one of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and octyl (meth)acrylate.

[0041] In some embodiments of the present invention, during heat treatment, the cross-linked silicon-based negative electrode adhesive releases the sealing agent, and the exposed isocyanate undergoes a thermal cross-linking reaction with the active functional groups in the polyacrylic acid adhesive to form a spatial network structure. Taking polyacrylic acid with hydroxyl groups as an example, the reaction principle during high-temperature heat treatment is shown in Figure 1. In Figure 1, RH is the sealing agent.

[0042] In some embodiments of the present invention, the heat treatment temperature is 100–180°C and the heat treatment time is 1–5 h.

[0043] The present invention also provides a method for preparing the cross-linked silicon-based negative electrode adhesive described herein.

[0044] The preparation method of the crosslinked silicon-based negative electrode adhesive of the present invention includes the following steps:

[0045] a. Preparation of polyurethane: Macromolecular diol and diisocyanate are prepolymerized under a catalyst to obtain polyurethane prepolymer. Organic solvent is added to reduce viscosity, and then chain extender is added to extend chain to obtain isocyanate-terminated hydrophilic polyurethane prepolymer. Then, blocking agent is added to block isocyanate, salting agent is added to neutralize hydrophilic groups, and finally organic solvent is removed to obtain polyurethane.

[0046] b. Preparation of polyacrylic acid adhesive: Acrylic acid, acrylate with active functional groups and acrylic acid derivatives are copolymerized in water to obtain a polyacrylic acid solution containing active functional groups. After neutralization, polyacrylate adhesives are obtained.

[0047] c. Mixing: Polyurethane and polyacrylic acid adhesive are blended to obtain cross-linked silicon-based anode adhesive.

[0048] The method of this invention is simple, requires no special equipment, has low cost, and can be mass-produced industrially.

[0049] Step a involves preparing a polyurethane prepolymer with a blocking agent. This is achieved by prepolymerizing a macromolecular diol and a diisocyanate under a catalyst to obtain a polyurethane prepolymer. An organic solvent is then added to reduce the viscosity, followed by chain extension with a chain extender to obtain an isocyanate-terminated hydrophilic polyurethane prepolymer. A blocking agent is then added to block the isocyanate, a salting agent is added to neutralize the hydrophilic groups, and finally, the organic solvent is removed to obtain the final product.

[0050] Commonly used macromolecular diols in this field are applicable to this invention. In some embodiments of this invention, the macromolecular diol is at least one of polyether diol, polyester diol, polycarbonate diol, and polyhydroxyl-terminated butadiene diol, and the number-average molecular weight Mn of the macromolecular diol is 500 to 3000.

[0051] The diisocyanate can be a commonly used diisocyanate in the synthesis of polyurethanes. In some embodiments of the present invention, the diisocyanate is at least one selected from hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, dicyclohexylmethane 4,4-diisocyanate, diphenylmethane diisocyanate, methylcyclohexane diisocyanate, phenylenediethylene diisocyanate, and tetramethyl-m-phenylenedimethyl diisocyanate.

[0052] The ratio of diol to diisocyanate is a conventional ratio in the art. In some embodiments of the present invention, the molar ratio of hydroxyl groups in the diol to isocyanates in the diisocyanate is 0.1 to 0.5:1, preferably 0.3:1.

[0053] Catalysts commonly used in the art are all suitable for this invention. In some embodiments of this invention, the catalyst is at least one of organotin, organobismuth, or organoamine.

[0054] After prepolymerization of macromolecular diols and diisocyanates, organic solvents are added to reduce the viscosity of the system. The organic solvents are added in proportions of 1 to 5 times the total mass of solids, so that the prepolymer can be well emulsified and dispersed during neutralization and salt formation.

[0055] The organic solvent used here can be a commonly used organic solvent in the art. In some embodiments of the present invention, the organic solvent is at least one selected from acetone, butanone, tetrahydrofuran, ethyl acetate, and toluene.

[0056] By rationally designing the molar ratio of isocyanate groups to hydroxyl and amino groups and controlling the molar ratio, an isocyanate-terminated prepolymer can be prepared.

[0057] In some embodiments of the present invention, commonly used diol chain extenders in the art are applicable to the present invention, including but not limited to at least one of dimethylolpropionic acid, dimethylolbutyric acid, tartaric acid, sodium 1,4-butanediol sulfonate, sodium 2,4-diaminobenzenesulfonate, 2,3-dihydroxypropane-1-sulfonic acid, 1,4-butanediol, and 1,6-hexanediol.

[0058] The amount of chain extender added is 1wt% to 15wt%, that is, the weight of the chain extender accounts for 1wt% to 15wt% of the total solids of the adhesive formulation.

[0059] Adding a blocking agent can block the isocyanate at the end of the polyurethane prepolymer, preventing it from reacting with the hydroxyl groups in the PAA when placed at room temperature. However, after heating to remove the blocking agent, the isocyanate at the end of the polyurethane can be exposed and cross-linked.

[0060] A salt-forming agent is added to neutralize the hydrophilic groups in the polyurethane. In some embodiments of the present invention, the salt-forming agent is at least one selected from triethylamine, triethanolamine, N-methyldiethanolamine, sodium hydroxide, lithium hydroxide, and potassium hydroxide.

[0061] In some embodiments of the present invention, in step a, the temperature of the prepolymerization reaction is 50–90°C and the time is 1–6 h.

[0062] Step b is to prepare polyacrylic acid adhesive by copolymerizing the first monomer acrylic acid, the second monomer acrylate with active functional groups, and the third monomer acrylic acid derivative in water to obtain polyacrylic acid containing active functional groups, which is then neutralized to obtain polyacrylic acid adhesive.

[0063] In some embodiments of the present invention, the second monomer acrylate with an active functional group is at least one selected from hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate.

[0064] In some embodiments of the present invention, the third monomer acrylic acid derivative includes acrylonitrile, styrene, or (meth)acrylates, wherein (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, octyl (meth)acrylate, etc.

[0065] In step b, the acrylate with active functional groups accounts for 5 to 50% of the weight of the polyacrylic acid adhesive polymer monomer.

[0066] This step can employ copolymerization reactions from existing technologies. For example, copolymerization can be carried out via precipitation polymerization, with an initiator added to initiate the reaction. Commonly used initiators in the art are suitable for this invention, including but not limited to ammonium persulfate, sodium persulfate, or a mixture of sodium persulfate, ammonium persulfate, sodium sulfite, sodium bisulfite, etc.

[0067] The neutralization in step b can be achieved using common neutralizing agents, such as one or more of sodium hydroxide, lithium hydroxide, and potassium hydroxide.

[0068] In this invention, steps a and b have no temporal order. Step a can be performed first, followed by step b, or step b can be performed first, followed by step a. To save time, steps a and b can also be performed simultaneously.

[0069] Step c involves mixing, where polyurethane and polyacrylic acid adhesive are blended to obtain a cross-linked silicon-based anode adhesive. This step is a physical blending process, requiring only the two substances to be mixed together.

[0070] The present invention also provides a silicon-based anode sheet.

[0071] The silicon-based anode sheet of the present invention comprises an anode active material and an adhesive, wherein the adhesive is the cross-linked silicon-based anode adhesive described in the present invention.

[0072] In one embodiment of the present invention, during the heat treatment process, the polyurethane deseals the sealing agent, and the exposed isocyanate undergoes a thermal crosslinking reaction with the active functional groups in the polyacrylic acid adhesive, forming a spatial network structure on the surface of the negative electrode active material particles.

[0073] In one embodiment of the present invention, the heat treatment temperature is 100-180°C and the baking time is 1-5 h.

[0074] In one embodiment of the invention, the amount of adhesive used is 0.5 to 5 wt% based on solid content, preferably 2.5 wt% based on solid content.

[0075] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the examples described herein. The polyester polyol in the examples is poly(1,4-butanediol adipate) diol with a molecular weight of 2000, abbreviated as PBA2000, purchased from Asahikawa Chemical (Suzhou) Co., Ltd.

[0076] Example 1

[0077] (1) Preparation of polyacrylic acid solution with active functional groups: Deionized water was purged with nitrogen for 1 hour to remove oxygen. Then, 50g of acrylic acid, 5g of hydroxyethyl acrylate and 45g of acrylonitrile were added to the deoxygenated deionized water. Ammonium persulfate initiator was added at a rate of 3wt‰. The reaction was carried out at 70°C for 10 hours to obtain polyacrylic acid precipitate. Then, lithium hydroxide was added for neutralization to form a polyacrylic acid solution with a molecular weight of 650254.

[0078] (2) Preparation of polyurethane emulsion: 100 g of polyester polyol was dehydrated at 100°C for 2 h under vacuum, and then 57 g of isophorone diisocyanate was added and prepolymerized at 85°C for 2 h. Then, under reflux, 200 mL of acetone and 12.5 g of dihydroxymethyl acrylate were added and reacted at 55°C for 2 h. Then, 2.5 g of 1,4-butanediol was added and the reaction continued for 1 h. Then, 16.1 g of phenol was added and the reaction continued for 3 h. Triethylamine was added to neutralize for 0.5 h. The emulsion was dispersed in deionized water under high-speed stirring to form an end-capped polyurethane emulsion. Then, acetone was removed under vacuum negative pressure to obtain a polyurethane emulsion with a number average molecular weight of 32951.

[0079] (3) Mix polyurethane emulsion and polyacrylic acid solution at a solid content of 20wt% : 80wt% to obtain cross-linked silicon-based negative electrode adhesive.

[0080] Example 2

[0081] A cross-linked silicon-based negative electrode adhesive was prepared according to the method of Example 1, except that the blocking agent in Example 1 was changed from 16.1 g phenol to 14.9 g methyl ethyl ketone oxime, and the resulting polyurethane had a molecular weight of 28153.

[0082] After drying, the cross-linked silicon-based anode adhesive was subjected to high-temperature baking at 140℃ for 2 hours for thermal cross-linking to obtain thermally cross-linked polyurethane. The infrared spectrum involved is shown in Figure 1.

[0083] The black curve represents the infrared absorption spectrum of methyl ethyl ketone oxime, in the range of 3100-3500 cm⁻¹. -1 In the range of 3100-3500 cm⁻¹, the hydroxyl absorption peak of methyl ethyl ketone oxime is clearly visible, while the red curve represents hydroxyl polyacrylate (i.e., polyacrylic acid with active functional groups). -1 A distinct hydroxyl absorption peak can also be observed in the [range]. The blue curve represents methyl ethyl ketone oxime-blocked polyurethane; the hydroxyl absorption peak of methyl ethyl ketone oxime disappears and transforms into a peak at 3300 cm⁻¹. -1 The characteristic absorption peak of the stretching vibration of the -NH group of urethane esters is at 1550 cm⁻¹. -1 The left and right sides represent the bending vibration absorption peaks of the -NH group in urethane, indicating that the methyl ethyl ketone oxime has been successfully incorporated into the polyurethane. The green curve is the infrared spectrum of the thermally cross-linked polyurethane, showing the significant disappearance of the hydroxyl absorption peak of the hydroxyl polyacrylic acid. This indicates that the unsealed isocyanate reacted with the hydroxyl groups of the hydroxyl polyacrylic acid, leading to the disappearance of the hydroxyl absorption peak. Simultaneously, in the green curve, at 1550 cm⁻¹... -1 The left and right sides are the bending vibration absorption peaks of the -NH group of carbamate and the peak at 3300 cm⁻¹. -1 The characteristic absorption peak of the -NH stretching vibration of the urethane remains, indicating that the polyurethane structure has not undergone significant changes.

[0084] Example 3

[0085] A cross-linked silicon-based negative electrode adhesive was prepared according to the method of Example 1, except that the blocking agent in Example 1 was changed from 16.1 g phenol to 19.3 g caprolactam, and the resulting polyurethane had a molecular weight of 42153.

[0086] Example 4

[0087] A cross-linked silicon-based anode adhesive was prepared according to the method of Example 1, except that the sealing agent in Example 1 was changed from 16.1 g phenol to 20.2 g hexamethylene mercaptan, and the resulting polyurethane had a molecular weight of 36153.

[0088] Example 5

[0089] A cross-linked silicon-based negative electrode adhesive was prepared according to the method of Example 1, except that the blocking agent in Example 1 was changed from 16.1 g phenol to 16.3 g 2-pyridinephenol, and the resulting polyurethane had a molecular weight of 30193.

[0090] Example 6

[0091] A cross-linked silicon-based negative electrode adhesive was prepared according to the method of Example 1, except that the blocking agent in Example 1 was changed from 16.1 g phenol to 16.4 g 3-5-dimethylpyrazole, and the resulting polyurethane had a molecular weight of 29383.

[0092] Example 7

[0093] A cross-linked silicon-based negative electrode adhesive was prepared according to the method of Example 1, except that the polyurethane emulsion and polyacrylic acid solution were mixed at a solid content of 5wt% : 95wt%.

[0094] Example 8

[0095] A cross-linked silicon-based anode adhesive was prepared according to the method of Example 1, except that the polyurethane emulsion and polyacrylic acid solution were mixed at a solid content of 50wt% : 50wt%.

[0096] Example 9

[0097] A cross-linked silicon-based negative electrode adhesive was prepared according to the method of Example 1, except that the polyurethane emulsion and polyacrylic acid solution were mixed at a solid content of 10wt% : 90wt%.

[0098] Example 10

[0099] A cross-linked silicon-based anode adhesive was prepared according to the method of Example 1, except that the polyurethane emulsion and polyacrylic acid solution were mixed at a solid content of 30wt% : 70wt%.

[0100] Comparative Example 1

[0101] A cross-linked silicon-based anode adhesive was prepared according to the method of Example 1. The only difference was that the 16.1 g phenol, the blocking agent in Example 1, was replaced with 7.5 g 1,4-butanediol, a small molecule chain extender, and the resulting polyurethane had a molecular weight of 58193.

[0102] Comparative Example 2

[0103] A cross-linked silicon-based negative electrode adhesive was prepared according to the method of Example 1, the only difference being that 5g of hydroxyethyl acrylate in Example 1 was replaced with 5g of acrylic acid.

[0104] Comparative Example 3

[0105] The negative electrode sheet prepared by mixing polyurethane emulsion and polyacrylic acid solution in Example 1 at a solid content of 20wt% : 80wt% does not undergo high-temperature heat treatment.

[0106] Comparative Example 4

[0107] The polyurethane emulsion prepared in Example 1 was used directly as the adhesive.

[0108] Comparative Example 5

[0109] The polyacrylic acid solution prepared in Example 1 was used directly as the adhesive.

[0110] Electrode fabrication: A silicon-carbon negative electrode sheet was prepared by mixing silicon-carbon S750, conductive carbon black (SP), carboxymethyl cellulose (CMC), and composite adhesive in a ratio of 96:1:0.5:2.5, where the composite adhesive was the binder prepared in the examples and comparative examples, respectively. The prepared electrode sheet was baked at 70°C for 0.5 h to remove moisture.

[0111] Electrode heat treatment: The dried electrode sheets are transferred to a 140℃ forced-air drying oven for 2 hours of heat treatment to deseal the polyurethane end-capping agent, allowing the exposed isocyanate groups and hydroxyl groups in the polyacrylic acid to undergo thermal cross-linking, thus obtaining a cross-linked negative electrode sheet. Performance testing:

[0112] Electrode peel strength: Cut a 100×20 mm copper foil electrode and lay it flat on a glass plate. Fix the sample to the test stage along its length using double-sided tape, and then bond the sample surface with 3M tape. Ensure a smooth, flat, and bubble-free adhesion between the sample and the tape. Then, roll the sample surface back and forth three times under its own weight to achieve uniform contact. Straighten one end of the sample (the end furthest from the testing machine) horizontally by 180° with transparent tape in the opposite direction of the electrode and fix it to the traction belt of the testing machine. Then, adjust the speed of the testing machine to 20 mm / min and click "run." The testing machine will start running. Record the peel strength value after the value displayed on the testing machine stabilizes. For the same sample, data should only be recorded after the peel strength value has stabilized. The same batch of samples should be tested at least three times. If the sample test error exceeds 2%, it needs to be retested. After the test, turn off the testing machine and compile the test data.

[0113] Electrode cohesive strength: Clean the surface of a glass plate, cut a 100×20 mm copper foil electrode, and lay it flat on the glass plate. Use double-sided tape to fix the sample to the test stage along its length. Gently cut off the blank ends of the sample with a blade and bond them to the electrode coating surface with 3M tape. Ensure that the sample and tape adhere smoothly and without air bubbles. Then, use a roller to roll back and forth on the sample surface three times under its own weight to achieve uniform contact. Adhere the sample horizontally at 180° along the length of the electrode with transparent tape, ensuring that the transparent tape completely covers the electrode surface. Then, fix the transparent tape to the traction belt of the testing machine, set the testing machine speed to 20 mm / min, and click run. The testing machine will start running. Record the cohesive strength value after the value displayed on the testing machine stabilizes. For the same sample, data should only be recorded after the cohesive strength value has stabilized. The same batch of samples should be tested no less than three times. If the sample test error exceeds 2%, it needs to be retested. After the test, turn off the testing machine and compile the test data.

[0114] Full-charge rebound rate: The silicon-based negative electrode sheet, after being pressed into place by the coating roller, is equilibrated for 2 hours at 30% ambient humidity. The initial coating thickness (total thickness - copper foil thickness) is measured and recorded as a1. Silicon-based cells are prepared using conventional methods, including electrolyte injection / formation. The cells are then fully charged and disassembled in a drying room (humidity < 1% RH). The negative electrode sheet is quickly removed, the surface electrolyte is wiped off, and the coating thickness (total thickness - copper foil thickness) is measured and recorded as a2.

[0115] The formula for calculating the rebound rate of electrode films is: Rebound rate = (a2 - a1) / a1 100%

[0116] 25°C Cell DCR: Take 3 packs of soft-pack cells and charge them using constant current charging method. Charge for 10 seconds and record the voltage before and after charging. Then DCR = (voltage after 10 seconds of charging - voltage before charging) / current.

[0117] The test results are shown in Table 1.

[0118] Table 1

[0119]

[0120] It is evident that the introduction of polyurethane for thermal crosslinking improves both peel strength and cohesive strength, while significantly reducing the electrode rebound rate. This indicates that the introduction of polyurethane for thermal crosslinking significantly promotes electrode performance and improves electrode adhesion. Comparing Comparative Example 1 and Example 1, the comparative example simply blends polyurethane and polyacrylic acid, failing to achieve chemical bonding, resulting in phase separation and a decrease in both peel strength and cohesive strength, while increasing the electrode rebound rate. In Comparative Example 2, the polyacrylic acid lacks hydroxyl groups to undergo thermal crosslinking with the unsealed isocyanate. Furthermore, although carboxyl groups can theoretically react with isocyanate, the reaction is relatively difficult in practice. Therefore, the polyurethane and polyacrylic acid in Comparative Example 2 are also in a simple blend state, leading to a corresponding decrease in electrode performance compared to the example. In Comparative Example 3, after dehydration, no further high-temperature heat treatment was performed, thus failing to reach the unsealing temperature of the sealant. This resulted in the polyurethane and polyacrylic acid remaining in a blend state, causing a decrease in electrode performance compared to the example. Through the above comparisons, the negative electrode sheets prepared by polyurethane containing end-capping agents and acrylic binders with active functional groups (hydroxyl or amino) show effective improvements in adhesion, cohesion, DCR, and full-charge rebound after heat treatment. Comparing the performance of electrodes made with different polyurethane to polyacrylic acid ratios reveals that as the polyacrylic acid content increases, peel strength and cohesion increase accordingly, while the electrode rebound rate decreases, but this leads to a negative effect of increased DCR at 0°C. While increasing the polyurethane content can reduce DCR, it also adversely affects peel strength, cohesion, and electrode rebound rate. Therefore, the polyurethane to polyacrylic acid ratio should be controlled within an appropriate range.

Claims

1. A cross-linked silicon-based negative electrode adhesive, characterized in that: The invention includes polyurethane and polyacrylic acid adhesives, wherein the polyurethane is a polyurethane with isocyanate groups capped by a blocking agent, and the polyacrylic acid adhesive includes polyacrylic acid, wherein the polyacrylic acid has active functional groups, wherein the active functional groups are groups that react with isocyanates, and the polyurethane accounts for 5% to 50% of the total weight of the polyurethane and polyacrylic acid adhesives.

2. The cross-linked silicon-based negative electrode adhesive according to claim 1, characterized in that: The molecular weight Mn of the polyurethane is 10,000 to 150,000, and the molecular weight Mn of the polyacrylic acid with active functionality is 50,000 to 1,500,000.

3. The cross-linked silicon-based negative electrode adhesive according to claim 1, characterized in that: The blocking agent is at least one selected from phenol, methyl ethyl ketone oxime, caprolactam, 2-pyridinephenol, 3-hydroxyquinoline, triphenylthiol, hexamethylenetetramine, 3,5-dimethylpyrazole, and 1,2,4-triazole; the active functional group is hydroxyl or amino.

4. The cross-linked silicon-based negative electrode adhesive according to claim 1, characterized in that: Polyacrylic acid monomers include acrylic acid and acrylates with active functional groups.

5. The cross-linked silicon-based anode adhesive according to claim 4, characterized in that: The acrylate with active functional groups is at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate.

6. The method for preparing the cross-linked silicon-based negative electrode adhesive according to any one of claims 1 to 5, characterized in that, Includes the following steps: a. Preparation of polyurethane: Macromolecular diol and diisocyanate are prepolymerized under a catalyst to obtain polyurethane prepolymer. Organic solvent is added to reduce viscosity, and then chain extender is added to extend chain to obtain isocyanate-terminated hydrophilic polyurethane prepolymer. Then, blocking agent is added to block isocyanate, salting agent is added to neutralize hydrophilic groups, and finally organic solvent is removed to obtain polyurethane. b. Preparation of polyacrylic acid adhesive: Polymerizing monomers in water to obtain polyacrylic acid containing active functional groups, neutralizing to obtain polyacrylic acid adhesive; the polymerizing monomers include acrylic acid, acrylates with active functional groups and acrylic acid derivatives; c. Mixing: Polyurethane and polyacrylic acid adhesive are blended to obtain cross-linked silicon-based anode adhesive.

7. The method for preparing the cross-linked silicon-based negative electrode adhesive according to claim 6, characterized in that: The macromolecular diol is at least one of polyether diol, polyester diol, polycarbonate diol, and polyhydroxyl-terminated butadiene diol, and the number average molecular weight Mn of the macromolecular diol is 500 to 3000. The diisocyanate is at least one selected from hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, dicyclohexylmethane 4,4-diisocyanate, diphenylmethane diisocyanate, methylcyclohexane diisocyanate, phenyldimethylmethylene diisocyanate, and tetramethylisophthalic acid diisocyanate. The catalyst is at least one of organotin, organobismuth, or organoamine; The organic solvent is at least one of acetone, butanone, tetrahydrofuran, ethyl acetate, and toluene; The chain extender is at least one of dimethylolpropionic acid, dimethylolbutyric acid, tartaric acid, sodium 1,4-butanediol sulfonate, sodium 2,4-diaminobenzene sulfonate, 2,3-dihydroxypropane-1-sulfonic acid, 1,4-butanediol, and 1,6-hexanediol. The salt-forming agent is at least one of triethylamine, triethanolamine, N-methyldiethanolamine, sodium hydroxide, lithium hydroxide, and potassium hydroxide; Acrylic acid derivatives include acrylonitrile, styrene, or (meth)acrylates, wherein (meth)acrylates include at least one of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and octyl (meth)acrylate.

8. The method for preparing the cross-linked silicon-based negative electrode adhesive according to claim 6, characterized in that: In step a, the temperature of the prepolymerization reaction is 50–90°C, and the time is 1–6 h; In step b, the acrylate with active functional groups accounts for 5 to 50% of the weight of the polyacrylic acid adhesive polymer monomer.

9. A silicon-based negative electrode sheet, comprising negative electrode active material particles and a binder, characterized in that: The adhesive is the cross-linked silicon-based anode adhesive as described in any one of claims 1 to 5.

10. The silicon-based negative electrode according to claim 9, characterized in that: During the heat treatment process, the polyurethane deseals the sealing agent, and the exposed isocyanate undergoes a thermal crosslinking reaction with the active functional groups in the polyacrylic acid adhesive, forming a spatial network structure on the surface of the negative electrode active material particles.

11. The silicon-based negative electrode according to claim 10, characterized in that: The heat treatment temperature is 100–180℃, and the baking time is 1–5 h.

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