Binder composition and preparation method thereof, negative pole piece and battery

Abstract

The invention provides a binder composition and a preparation method thereof, a negative pole piece and a battery in order to solve the problem that gas production of a water and silicon carbon interface cannot be effectively inhibited by an existing water-based binder. The adhesive composition comprises a carboxyl-containing siloxane-acrylate block polymer and an interface passivation coupling agent, the interface passivation coupling agent comprises a sulfydryl silane compound and a fluorocarboxylic acid compound, and the mass ratio of the carboxyl-containing siloxane-acrylate block polymer to the interface passivation coupling agent is (35-55): (10-25). Through the synergistic effect of the carboxyl-containing siloxane-acrylate block polymer and the interface passivation coupling agent, the adhesive composition forms a water-resistant barrier layer on the silicon carbon surface in aqueous system slurry, and hydrolysis gas production of the aqueous system slurry is inhibited.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to a binder composition and a preparation method thereof, a negative electrode sheet and a battery. BACKGROUND

[0002] With the development of green preparation technology of lithium ion batteries, the water-based homogenization process has become an important development direction for electrode preparation due to the advantages of no organic solvent volatilization, high safety and low cost. However, silicon-carbon materials in the water-based homogenization process face two technical problems: one is that silicon particles are easy to hydrolyze and generate H2 (Si+2H2O→SiO2+2H2) when in contact with water, and the other is that the surface active sites (such as Si-H bonds) react with water to generate more gas, resulting in the aggregation of bubbles in the slurry and the deterioration of uniformity.

[0003] Although the commonly used water-based binders (such as CMC / SBR and PAA) have water solubility, they cannot effectively block the interface reaction between water and silicon-carbon, and the gas production inhibition rate is less than 50% Therefore, there is an urgent need for a binder that can inhibit gas production in a water-based environment. SUMMARY

[0004] In view of the problem that the existing water-based binder cannot effectively inhibit the gas production at the interface between water and silicon-carbon, the application provides a binder composition and a preparation method thereof, a negative electrode sheet and a battery.

[0005] To solve the above technical problems, in a first aspect, the application provides a binder composition, which comprises a carboxyl-containing siloxane-acrylate block polymer and an interface passivation coupling agent, the interface passivation coupling agent comprises a mercaptosilane compound and a fluorocarboxylic acid compound, and the mass ratio of the carboxyl-containing siloxane-acrylate block polymer to the interface passivation coupling agent is (35-55):(10-25).

[0006] Preferably, the carboxyl-containing siloxane-acrylate block polymer has a structural formula as shown in Formula 1, -[Si(CH3)2O] a -[CH2CH (COOH)] b -[CH2CH (COO (CH2)3Si(CH3)2O) n H] e Formula 1. In Formula 1, a:b:e=(0.5-2):(1-4):(0.5-2), and n=3-10.

[0007] Preferably, the total polymerization degree of the carboxyl-containing siloxane-acrylate block polymer is 76-223, and the number average molecular weight is 8*10 4 -12*10 4g / mol.

[0008] Preferably, the carboxyl-containing siloxane-acrylate block polymer comprises siloxane structural units and acrylic structural units, the siloxane structural units are structural units obtained by polymerization of siloxane monomers, the siloxane monomers comprise at least one of octamethylcyclotetrasiloxane, carboxypropyl methyl siloxane oligomer and maleic anhydride modified siloxane copolymer; The acrylic structural units are structural units obtained by polymerization of acrylic monomers, the acrylic monomers comprise at least one of acrylic acid, methacrylic acid, beta-carboxyethyl acrylate and itaconic acid.

[0009] Preferably, the molar ratio of the mercaptosilane compound to the fluorocarboxylic compound is 1: (0.8-1.5).

[0010] Preferably, the mercaptosilane compound comprises at least one of mercaptopropyl trimethoxysilane, mercaptopropyl triethoxysilane, mercaptoethyl trimethoxysilane and mercaptopropyl methyl dimethoxysilane; And / or, the fluorocarboxylic compound comprises at least one of perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluoropentanoic acid and fluoropropionic acid.

[0011] Preferably, the adhesive composition further comprises a dynamic crosslinking agent, the dynamic crosslinking agent comprises at least one of dialdehyde starch, bisphenol A diglycidyl ether and adipoyl dihydrazine; The mass ratio of the carboxyl-containing siloxane-acrylate block polymer, the interfacial passivation coupling agent and the dynamic crosslinking agent is (35-55): (10-25): (8-18).

[0012] Preferably, the adhesive composition further comprises an ion conduction aid, the ion conduction aid comprises hydroxylated multi-walled carbon nanotubes and lithium salt; The mass ratio of the carboxyl-containing siloxane-acrylate block polymer, the interfacial passivation coupling agent and the ion conduction aid is (35-55): (10-25): (12-22).

[0013] Preferably, the mass of the lithium salt is 25%-35% of the mass of the hydroxylated multi-walled carbon nanotubes; And / or, the content of hydroxyl groups in the hydroxylated multi-walled carbon nanotubes is ≥5 mmol / g.

[0014] In a second aspect, the present application provides a preparation method of an adhesive composition, comprising the following steps: The siloxane monomer, the acrylic monomer and the initiator are mixed and subjected to ring-opening polymerization, and then a silane coupling agent is added to obtain a carboxyl-containing siloxane-acrylate block polymer, and the carboxyl-containing siloxane-acrylate block polymer is dissolved in water to form a colloidal solution; The mercaptosilane compound and the fluorocarboxylic acid compound are mixed and then added to the colloidal solution to obtain the binder composition by stirring.

[0015] In a third aspect, the present application provides a negative electrode tab, characterized in that the negative electrode tab comprises a current collector and an active material layer, the active material layer is arranged on at least one side of the current collector, and the active material layer comprises the binder composition according to any one of the above or is prepared by the preparation method according to any one of the above.

[0016] In a fourth aspect, the present application provides a battery comprising the negative electrode tab according to the above.

[0017] In the present application, the carboxyl-containing siloxane-acrylate block polymer realizes good dispersibility of the binder composition in water through the hydrophilicity of the carboxyl group, and no agglomeration or precipitation occurs in the homogenization process, a water-resistant interface layer is constructed through the hydrophobicity of the siloxane, and the siloxane segment provides flexible support for the binder composition and improves the buffering effect on the expansion of the negative electrode.

[0018] The mercaptosilane compound and the fluorocarboxylic acid compound in the interface passivation coupling agent form a water-resistant barrier layer on the surface of the silicon-based negative electrode material, so that the gas production in the aqueous slurry is reduced by more than 75% compared with the traditional PAA system. The mercaptosilane compound is condensed with the silicon hydroxyl group on the surface of the silicon-based negative electrode material through interface contact, and the product contains a -Si-O-Si- bond, so that the condensed product can be stably adsorbed on the surface of the silicon-based negative electrode material through van der Waals force and the hydrophobic effect of the fluorocarboxylic acid compound, forming a thermodynamically stable interface layer.

[0019] The fluorocarboxylic acid compound can reduce the surface energy of the silicon-based negative electrode material and synergistically inhibit the hydrolysis reaction with the mercaptosilane compound to enhance the interface stability. At the same time, the long-chain fluorinated alkyl group of the fluorocarboxylic acid compound has strong hydrophobicity and steric hindrance, and the carboxyl group in the aqueous system is partially ionized into a carboxyl ion, which repels the carboxyl group in the carboxyl-containing siloxane-acrylate block polymer, so that the interface passivation coupling agent is more easily migrated to the silicon-carbon surface.

[0020] Therefore, through the synergistic effect of the carboxyl-containing siloxane-acrylate block polymer and the interface passivation coupling agent, the binder composition forms a water-resistant barrier layer on the silicon-carbon surface in the aqueous system slurry, and inhibits the hydrolysis gas production of the aqueous system slurry. DETAILED DESCRIPTION

[0021] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0022] An embodiment of the present application provides a binder composition, comprising a carboxyl-containing siloxane-acrylate block polymer and an interface passivation coupling agent, the interface passivation coupling agent comprising a mercapto silane compound and a fluorinated carboxylic acid compound, and a mass ratio of the carboxyl-containing siloxane-acrylate block polymer to the interface passivation coupling agent being (35-55):(10-25).

[0023] Specifically, by limiting the mass ratio of the carboxyl-containing siloxane-acrylate block polymer to the interface passivation coupling agent within the above range, the interface passivation coupling agent is allowed to reduce the surface energy of the silicon-based negative electrode by condensing with the silicon hydroxyl on the surface of the silicon-based negative electrode, and to inhibit the hydrolysis reaction of the silicon-based negative electrode, while not affecting the dispersibility of the carboxyl-containing siloxane-acrylate block polymer and the adhesion of the binder composition.

[0024] The mass ratio of the carboxyl-containing siloxane-acrylate block polymer to the interface passivation coupling agent includes, but is not limited to, 35:10, 35:15, 35:25, 40:10, 40:25, 55:10, 55:15 or 55:25.

[0025] In the present application, the carboxyl-containing siloxane-acrylate block polymer realizes good dispersibility of the binder composition in water through the hydrophilicity of the carboxyl group, and no agglomeration or precipitation occurs during the homogenization process, a water-resistant interface layer is constructed through the hydrophobicity of the siloxane, and the siloxane segment provides flexible support for the binder composition and improves the buffering effect on the expansion of the negative electrode.

[0026] The mercapto silane compound and the fluorinated carboxylic acid compound in the interface passivation coupling agent form a water-resistant barrier layer on the surface of the silicon-based negative electrode material, so that the gas production in the aqueous slurry is reduced by more than 75% compared with the traditional PAA system. The mercapto silane compound condenses with the silicon hydroxyl on the surface of the silicon-based negative electrode material through interface contact, and the product contains a -Si-O-Si- bond, so that the condensed product can be stably adsorbed on the surface of the silicon-based negative electrode material through van der Waals force and the hydrophobic effect of the fluorinated carboxylic acid compound, forming a thermodynamically stable interface layer.

[0027] The fluorocarboxylic acid compound can reduce the surface energy of the silicon-based negative electrode material, cooperatively inhibit the hydrolysis reaction with the mercapto silane compound, and enhance the interface stability. Meanwhile, the long-chain fluorinated alkyl group of the fluorocarboxylic acid compound has strong hydrophobicity and steric hindrance, and the carboxyl group is partially ionized into a carboxyl ion in the aqueous system, which forms a charge repulsion with the carboxyl group in the carboxyl-containing siloxane-acrylate block polymer, so that the interface passivation coupling agent is more easily migrated to the silicon-carbon surface.

[0028] Therefore, through the synergistic effect of the carboxyl-containing siloxane-acrylate block polymer and the interface passivation coupling agent, the binder composition forms a water-resistant barrier layer on the silicon-carbon surface in the aqueous system slurry, and inhibits the hydrolysis gas production of the aqueous system slurry.

[0029] In some embodiments, the structural formula of the carboxyl-containing siloxane-acrylate block polymer is shown as formula 1, -[Si(CH3)2O] a -[CH2CH (COOH)] b -[CH2CH (COO (CH2)3Si(CH3)2O) n H] e - formula 1. Wherein, a:b:e=(0.5-2):(1-4):(0.5-2), n=3-10. By limiting the range of a, b, and e in formula 1, the content of carboxyl and siloxane segments in the carboxyl-containing siloxane-acrylate block polymer is regulated, and then the dispersibility of the binder composition in the aqueous slurry and the water resistance of the water-resistant barrier layer formed on the silicon-carbon surface are regulated.

[0030] In some embodiments, the total polymerization degree of the carboxyl-containing siloxane-acrylate block polymer is 76-223, and the number average molecular weight is 8*10 4 -12*10 4 g / mol.

[0031] In some embodiments, the carboxyl-containing siloxane-acrylate block polymer includes siloxane structural units and acrylic structural units, the siloxane structural units are structural units obtained by polymerization of siloxane monomers, and the siloxane monomers include at least one of octamethylcyclotetrasiloxane, carboxypropyl methyl siloxane oligomer ([Si(CH3)(CH2CH2COOH)O] x -), and maleic anhydride modified siloxane copolymer ([Si(CH3)2O] m -[CH(COOH)CH(COOH)] f - m:f=8-10:3-4). The acrylic structural unit is a structural unit obtained by polymerization of an acrylic monomer, the acrylic monomer including at least one of acrylic acid, methacrylic acid (MAA), acrylic acid-β-carboxyethyl ester, and itaconic acid.

[0032] In some embodiments, the molar ratio of the mercaptosilane compound to the fluoro-carboxylic acid compound is 1:(0.8-1.5). By regulating the molar ratio of the mercaptosilane compound to the fluoro-carboxylic acid compound within the above range, the mercaptosilane compound and the fluoro-carboxylic acid compound can better synergistically inhibit the hydrolysis reaction, thereby enhancing the interfacial stability.

[0033] In some embodiments, the mercaptosilane compound includes at least one of mercaptopropyl trimethoxysilane, mercaptopropyl triethoxysilane, mercaptoethyl trimethoxysilane, and mercaptopropyl methyl dimethoxysilane; and / or, the fluoro-carboxylic acid compound includes at least one of perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluoropentanoic acid, and fluoro-propionic acid CF3CH2COOH.

[0034] In some embodiments, the adhesive composition further includes a dynamic crosslinking agent, the dynamic crosslinking agent including at least one of dialdehyde starch, bisphenol A diglycidyl ether, adipoyl dihydrazine; The mass ratio of the carboxyl-containing siloxane-acrylate block polymer, the interfacial passivation coupling agent, and the dynamic crosslinking agent is (35-55):(10-25):(8-18).

[0035] In the above dynamic crosslinking agent, the aldehyde group of the dialdehyde starch reversibly adds to the α-hydrogen at the carboxyl group of the carboxyl-containing siloxane-acrylate block polymer to form a β-hydroxy aldehyde structure, which can be broken and recombined under stress to construct an elastic-rigid composite network in the negative electrode sheet, buffer the volume expansion of the negative electrode sheet, and achieve dynamic repair of the adhesive composition. The bisphenol A diglycidyl ether crosslinks by ring-opening reaction of the epoxy group with the carboxyl group to construct a crosslinking network in the negative electrode sheet. The two hydrazine groups (-NH-NH2) in the adipoyl dihydrazine molecule can undergo hydrazide reaction with the carboxyl group to form a hydrazide bond, and the hydrogen bond between the hydrazine group and the carboxyl group can enhance the dynamic repair of the adhesive composition.

[0036] Specifically, the mass ratio of the carboxyl-containing siloxane-acrylate block polymer, the interfacial passivation coupling agent, and the dynamic crosslinking agent includes but is not limited to 35:10:8, 35:15:15, 35:25:18, 40:10:8, 40:25:18, 55:10:8, 55:15:14, or 55:25:18.

[0037] In some embodiments, the dialdehyde starch has an aldehyde group content of ≥25%. By limiting the content of aldehyde groups to be greater than or equal to 25%, it is ensured that the elastic-rigid composite network formed by the binder composition in the negative electrode sheet can inhibit the volume expansion of the negative electrode sheet.

[0038] In some embodiments, the binder composition further comprises an ion-conducting aid, the ion-conducting aid comprising hydroxylated multi-walled carbon nanotubes (OH-MWCNT) and a lithium salt; The mass ratio of the carboxyl-containing siloxane-acrylate block polymer, the interfacial passivation coupling agent, and the ion-conducting aid is (35-55):(10-25):(12-22).

[0039] The ion-conducting agent forms a hydrogen bond network through hydroxyl groups and Li + Coordination builds fast ion channels, improving the electrochemical kinetic performance of the battery.

[0040] Specifically, the mass ratio of the carboxyl-containing siloxane-acrylate block polymer, the interfacial passivation coupling agent, and the ion-conducting aid includes but is not limited to 35:10:12, 35:15:17, 35:25:22, 40:10:12, 40:25:22, 55:10:12, 55:15:17, or 55:25:22.

[0041] In some embodiments, the lithium salt has a mass of 25%-35% of the mass of the hydroxylated multi-walled carbon nanotubes; And / or, the content of hydroxyl groups in the hydroxylated multi-walled carbon nanotubes is ≥5 mmol / g.

[0042] Further, the lithium salt includes but is not limited to LiTFSI, LiFSI, LiPF6, LiBF4.

[0043] In an embodiment, the hydroxylated multi-walled carbon nanotubes have a tube diameter of 10-20 nm.

[0044] In an embodiment, the binder composition comprises 35%-55% of the carboxyl-containing siloxane-acrylate block polymer, 10%-25% of the interfacial passivation coupling agent, 8%-18% of the dynamic crosslinking agent, and 12%-22% of the ion-conducting aid.

[0045] An embodiment of the present application provides a preparation method of a binder composition, comprising the following steps: The siloxane monomer, acrylic monomer, initiator, and solvent are mixed and subjected to a polymerization reaction, and then a silane coupling agent is added to introduce a carboxyl side chain to obtain a carboxyl-containing siloxane-acrylate block polymer. The carboxyl-containing siloxane-acrylate block polymer is dissolved in water to form a colloidal solution. Specifically, the solid content of the colloidal solution is 25% to 35%. The carboxyl side chain is derived from the acrylic monomer.

[0046] The mercapto silane compound and the fluoro carboxylic acid compound are mixed and then added to the colloidal solution, and stirring is performed to obtain the adhesive composition.

[0047] Specifically, the reaction conditions for introducing the carboxyl side chain are as follows: the silane coupling agent is added, and the reaction temperature is controlled to be 60 to 80°C. If the temperature is lower than 60°C, the hydrolysis rate of the silane coupling agent is slow, and the condensation reaction with the main chain is incomplete. If the temperature is higher than 80°C, the double bond of the acrylate segment may homopolymerize, and the block structure may be destroyed.

[0048] The reaction time is maintained for 2 to 4 hours to ensure that the silane coupling agent is fully hydrolyzed (to generate -Si-OH) and subjected to a condensation reaction with the main chain -Si-OH (to form a -Si-O-Si- bond). If the time is too long (> 4 hours), the side chain may be excessively crosslinked, and the water solubility of the polymer may be reduced.

[0049] The solvent is a mixed solvent of N,N-dimethylformamide and deionized water (volume ratio 1:1 to 3:1). If the siloxane monomer is a carboxypropyl methyl siloxane oligomer in the synthesis of the carboxyl-containing siloxane-acrylate block polymer, concentrated sulfuric acid is added to cause an esterification reaction between the carboxypropyl methyl siloxane oligomer and the carboxyl groups of the acrylic monomer, and a condensation product is obtained.

[0050] After the synthesis of the carboxyl-containing siloxane-acrylate block polymer is completed, the system is heated to 90°C, and distilled under reduced pressure for 1 hour to remove residual methanol (silane hydrolysis product) in the system, so as to avoid affecting the stability of the subsequent colloidal solution.

[0051] In an embodiment, the initiator includes at least one of benzoyl peroxide, dicumyl peroxide, and tert-butyl peroxide. The silane coupling agent includes at least one of 3-mercaptopropyl silane, 3-aminopropyl triethoxysilane, and vinyl trimethoxysilane.

[0052] Further, when the adhesive composition contains a dynamic crosslinking agent and an ion conduction aid, the adhesive composition further includes: The dynamic crosslinking agent is dissolved in a phosphate buffer solution with a pH of 7 to 9 to prepare a solution with a concentration of 20% to 30%, and then slowly added to the colloidal solution containing the interfacial passivation coupling agent, and reacted at 30°C to 50°C for 30 to 60 minutes.

[0053] The OH-MWCNT and lithium salt are ultrasonically dispersed in water in a ratio to form a uniform slurry, and then added into a colloidal solution containing an interfacial passivation coupling agent and an ion conduction aid, and stirred uniformly to obtain the binder.

[0054] An embodiment of the present application provides a negative electrode sheet, characterized in that it comprises a current collector and an active material layer, the active material layer is arranged on at least one side of the current collector, and the active material layer comprises the binder composition according to any one of the above embodiments or the binder composition prepared by the preparation method according to any one of the above embodiments.

[0055] An embodiment of the present application provides a battery comprising the negative electrode sheet described above.

[0056] The present application is further described below through examples.

[0057] The binder composition, the negative electrode sheet and the battery disclosed by the present application are specifically described.

[0058] Example 1 1) Preparation of the binder composition S1, synthesis of carboxyl-containing siloxane-acrylate block polymer: 30 g of octamethylcyclotetrasiloxane is polymerized with 18 g of acrylic acid under the initiation of benzoyl peroxide, and then 12 g of 3-mercaptopropyl silane coupling agent is added to obtain a carboxyl-containing siloxane-acrylate block polymer, the structural formula of which is -[Si(CH3)2O]-[CH2CH (COOH)]2-[CH2CH (COO (CH2)3Si(CH3)2O)7H]-, the number average molecular weight is 100,000 g / mol, and the polymerization degree is 120, which is dissolved in 60 mL of deionized water to form a colloidal solution.

[0059] S2, compounding of interfacial passivation coupling agent: 10.1 g of mercapto silane (HS(CH2)3Si(OCH3)3) is mixed with 17.0 g of CF3(CF2)5COOH at a molar ratio of 1:1.05, and then added into the colloidal solution after stirring at 60°C for 1 hour.

[0060] S3, pretreatment of dynamic crosslinking agent: 15 g of dialdehyde starch is dissolved in 50 mL of phosphate buffer (pH=7), and then added dropwise into the S2 system, and reacted at 30°C for 30 minutes.

[0061] S4, addition of ion conduction aid: 16 g of OH-MWCNT is ultrasonically dispersed in 30 mL of water with 4.8 g of LiTFSI, and then added into the S3 system, and stirred uniformly to obtain the binder.

[0062] The binder comprises 48.8% of carboxyl-containing siloxane-acrylate block polymer, 22.1% of interface passivation coupling agent, 12.2% of dynamic crosslinking agent, and 16.9% of ion conduction aid.

[0063] 2) Preparation of negative electrode sheet CVD silicon carbon, binder, and conductive agent acetylene black are mixed in a mass ratio of 7:2:1 and added to water to obtain a negative electrode slurry.

[0064] The prepared negative electrode slurry is coated on a copper foil by a coating machine, and a drying roller is pressed to obtain a negative electrode sheet.

[0065] 3) Preparation of positive electrode sheet: 97.8% of positive electrode active material LiFePO4, 1% of positive electrode conductive agent conductive carbon black, and 1.2% of binder PVDF are added to N-methyl pyrrolidone for stirring to prepare a positive electrode slurry. Then the positive electrode slurry is coated on both surfaces of the positive electrode current collector Al foil, and after processes such as drying, cold pressing, and cutting, a positive electrode sheet is obtained.

[0066] 4) Battery preparation: The separator, positive electrode sheet, and negative electrode sheet are stacked in order, with the separator film between the positive electrode and the negative electrode to act as a barrier, to form an electrode assembly. The electrode assembly is placed in an outer package, injected with a commercially available electrolyte and packaged, and then subjected to processes such as liquid injection, formation, and exhaust to obtain a battery.

[0067] Example 2 Example 2 and most of the steps of Example 1 are the same, except that, The carboxyl-containing siloxane-acrylate block polymer has a structural formula of -[Si(CH3)2O]-[CH2CH(COOH)]3-[CH2CH(COO (CH2)3Si(CH3)2O)7H], with a number average molecular weight of 109,000 g / mol.

[0068] The interface passivation coupling agent is HS(CH2)3Si(OCH3)3 and CF3(CF2)7COOH, with a molar ratio of 1:1.2.

[0069] Example 3 Example 3 and most of the steps of Example 1 are the same, except that, The carboxyl-containing siloxane-acrylate block polymer has a structural formula of -[Si(CH3)2O] 0.5 -[CH2CH(COOH)]4-[CH2CH (COO (CH2)3Si(CH3)2O)6H]2, with a number average molecular weight of 115,000 g / mol.

[0070] Example 4 Example 4 and Example 1 are the same in most steps, except that, carboxyl-containing siloxane-acrylate block polymer, having the structure [Si(CH3)2O]2-[CH2CH(COOH)]-[CH2CH(COO(CH2)3Si(CH3)2O)5H] 0.5 , having a number average molecular weight of 90,000 g / mol.

[0071] Example 5 Example 5 and Example 1 are the same in most steps, except that, in the synthesis step of the carboxyl-containing siloxane-acrylate block polymer, the siloxane monomer is a maleic anhydride-modified siloxane copolymer (— [Si(CH3)2O] 10 — [CH(COOH)CH(COOH)]4— ), and the acrylic monomer is beta-carboxyethyl acrylate.

[0072] Example 6 Example 6 and Example 1 are the same in most steps, except that, in the interface passivation coupling agent, the molar ratio of HS(CH2)3Si(OCH3)3 and CF3(CF2)5COOH is 1:0.8.

[0073] Example 7 Example 7 and Example 1 are the same in most steps, except that, in the interface passivation coupling agent, the molar ratio of HS(CH2)3Si(OCH3)3 and CF3(CF2)5COOH is 1:1.5.

[0074] Example 8 Example 8 and Example 1 are the same in most steps, except that, in the interface passivation coupling agent, the molar ratio of HS(CH2)3Si(OCH3)3 and CF3(CF2)5COOH is 1:0.3.

[0075] Example 9 Example 9 and Example 1 are the same in most steps, except that, in the interface passivation coupling agent, the molar ratio of HS(CH2)3Si(OCH3)3 and CF3(CF2)5COOH is 1:2.

[0076] Example 10 Example 10 and Example 1 are the same in most steps, except that, in the interface passivation coupling agent, the molar ratio of HS(CH2)3Si(OCH3)3 and CF3(CF2)5COOH is 1:0.3.

[0077] Example 11 Example 11 and Example 1 are the same in most steps, except that, in the interface passivation coupling agent, the molar ratio of HS(CH2)3Si(OCH3)3 and CF3(CF2)5COOH is 1:0.3.

[0078] Example 12 Example 12 is the same as most of the steps of Example 1, except that the dynamic crosslinker is bisphenol A diglycidyl ether.

[0079] Example 13 Example 13 is the same as most of the steps of Example 1, except that the mass of LiTFSI is 25% of the mass of the hydroxylated multi-walled carbon nanotubes.

[0080] Example 14 Example 14 is the same as most of the steps of Example 1, except that the mass of LiTFSI is 35% of the mass of the hydroxylated multi-walled carbon nanotubes.

[0081] Examples 15-29 Examples 15-29 are the same as most of the steps of Example 1, except that the formulations in Table 1 are used.

[0082] Table 1 Comparative Examples 1-6 Comparative Examples 1-6 are the same as most of the steps of Example 1, except that the formulations in Table 1 are used.

[0083] Comparative Example 7 Comparative Example 7 is the same as most of the steps of Example 1, except that the binder is polyacrylic acid with a number average molecular weight of 150,000 g / mol.

[0084] Comparative Example 8 Comparative Example 8 is the same as most of the steps of Example 1, except that the binder is a 1:1 mass ratio mixture of carboxymethyl cellulose (CMC) with a number average molecular weight of 80,000 g / mol and butadiene-styrene rubber (SBR).

[0085] Electrical performance tests: The batteries prepared in the above examples and comparative examples were tested as follows.

[0086] 1. Water-based slurry gas production test CVD silicon carbon, binder, and conductive agent (acetylene black) were mixed in a mass ratio of 7:2:1, deionized water was added to prepare a slurry with a solid content of 40%, and the slurry was homogenized at 3000 rpm for 2 hours. The slurry was sealed in a transparent container to observe the generation of bubbles, and the gas production was measured by the drainage method.

[0087] 2. Volume expansion inhibition test After the battery is left to stand in a constant-temperature test room at 25℃±2℃ for 1h, the battery is charged at 1C (150mAh / g) constant current and constant voltage to 4.2V, and the cutoff current is 0.05C; the battery is discharged at 1C constant current to 2.5V, and the thickness change of the battery is monitored using an in-situ dilatometer.

[0088] 3. Electrochemical performance test First discharge specific capacity: After the battery is left to stand in a constant-temperature test room at 25℃±2℃ for 1h, the battery is charged at 0.2C (150mAh / g) constant current and constant voltage to 4.2V, and the cutoff current is 0.05C; the battery is discharged at 0.2C constant current to 2.5V, and the discharge capacity is recorded; the first discharge specific capacity = discharge capacity / weight of the negative electrode sheet.

[0089] First coulombic efficiency: After the battery is left to stand in a constant-temperature test room at 25℃±2℃ for 1h, the battery is charged at 0.2C (150mAh / g) constant current and constant voltage to 4.2V, and the cutoff current is 0.05C; the battery is discharged at 0.2C constant current to 2.5V, and the discharge capacity is recorded; the first coulombic efficiency = discharge capacity / charge capacity.

[0090] Cycle performance test: After the battery is left to stand in a constant-temperature test room at 25℃±2℃ for 1h, the battery is charged at 1C constant current and constant voltage to 4.2V, and the cutoff current is 0.05C; the battery is discharged at 1C constant current to 2.5V, and the discharge capacity is recorded; the above steps are repeated 100 times, and the capacity retention rate is calculated.

[0091] 4. Interface impedance test: EIS test is performed on the battery using an electrochemical workstation, and the charge transfer resistance (RCT) is recorded.

[0092] The test results obtained from the examples and comparative examples are filled in Table 2.

[0093] Table 2 From the test results in Table 2, it can be seen that, Gas production and bubble generation: the carboxyl-containing siloxane-acrylate block copolymer (main binder) has good compatibility and high hydrolytic stability, so the gas production of examples 1-26 is more than 0.1mL / g and no obvious bubbles are generated; when at least one of the carboxyl-containing siloxane-acrylate block copolymer, the interface passivation coupling agent, the dynamic crosslinking agent, and the ion conduction aid in the binder composition is missing (examples 27-29, comparative examples 5-6) or the component proportion is abnormal (examples 21-22, 25-26), the system has poor dispersibility, the hydrolysis of the additives is accelerated, the gas production increases to 0.09-0.45mL / g, and the bubbles increase.

[0094] Thickness change rate (volume expansion inhibition): dynamic crosslinking agent (dialdehyde starch / bisphenol A diglycidyl ether) cooperates with main binder to build elastic network, so the thickness change rate of examples (1-26) containing sufficient crosslinking agent is <17%; when there is no crosslinking agent (examples 27, 29) or the amount of crosslinking agent is excessive (example 22), the expansion inhibition ability decreases.

[0095] First discharge specific capacity: the main binder has strong interfacial bonding with CVD silicon carbon (siloxane segment anchors silicon hydroxyl), so the specific capacity of examples 1-26 is >1350 mAh / g; when the main binder or other components are missing (examples 29, comparative example 6), the silicon carbon particles agglomerate, and the specific capacity decreases to 1150-1250 mAh / g.

[0096] First coulombic efficiency: interfacial passivation coupling agent (mercapto silane + fluorinated carboxylic acid) can inhibit excessive growth of SEI film, so the efficiency of examples (1-16, 18-20, 23-24) with reasonable proportion of interfacial passivation coupling agent is >87%; when the molar ratio of mercapto silane compound to fluorinated carboxylic acid compound in the interfacial passivation coupling agent is not within the range or is missing (comparative example 5), the SEI film is unstable, and the efficiency is <85%.

[0097] 1C capacity retention rate: ion conduction aid (OH-MWCNT + LiTFSI) improves ion transport efficiency, so the retention rate of examples (1-20, 23-24) with reasonable proportion of ion conduction aid is >90%; when the ion conduction aid is excessive / insufficient (examples 25-26) or missing (examples 28, 29), the capacity decay in the cycle is accelerated, and the retention rate is <85%.

[0098] Charge transfer resistance (Rct): the main binder-interfacial passivation coupling agent-ion conduction aid cooperatively optimizes the interface, so the Rct of examples 1-16, 18-20, 23-24 is <90Ω; when there are many interface defects (examples 27-29, comparative examples 5-6), the charge transfer is hindered, and the Rct is >120Ω.

[0099] Difference in block copolymer structure (examples 2-4): example 5 (maleic anhydride modified siloxane copolymer + acrylic acid-β-carboxyethyl ester) has the highest carboxyl density, and has the best expansion inhibition (thickness change rate 9.8%) and capacity (1480 mAh / g); examples 3-4 have slightly inferior performance to example 1 due to slight adjustment of the proportion of siloxane segments.

[0100] Interface passivation coupling agent ratio / type difference (Examples 6-11): Example 6 (1:0.8), 7 (1:1.5) have similar performance to Example 1 due to close coupling agent ratio to optimal (1:1.05 of Example 1 converted and adapted); Example 8 (1:0.3), 9 (1:2) have slightly increased gas production (0.07-0.08 mL / g) due to unbalanced ratio; Example 10 (mercapto propyl methyl dimethoxy silane), 11 (mercapto ethyl trimethoxy silane) have slightly higher Rct than Example 1 (83-89 Ω) due to silane type replacement.

[0101] Dynamic crosslinker type (Example 12): Bisphenol A diglycidyl ether has higher crosslinking efficiency than dialdehyde starch, so Example 12 has better thickness change rate (10.2%) and Rct (78 Ω).

[0102] Ion assistant ratio (Examples 13-14): LiTFSI accounts for 25%-35% of OH-MWCNT (Examples 13-14), ion conduction efficiency is optimal, Rct is reduced to 76-77 Ω, capacity retention rate is 93%.

[0103] Component ratio anomaly (21-22, 25-29): Example 21 (5% less dynamic crosslinker), Example 22 (5% less ion conduction assistant) have significantly decreased performance due to component imbalance; Examples 27-29 (no dynamic crosslinker / main binder) have similar performance to Comparative Examples, reflecting the necessity of core components.

[0104] Comparative Examples comparison: Comparative Examples 7 (polyacrylic acid), 8 (CMC / SBR) have worse performance than Example 1 due to lack of siloxane-block structure; Comparative Examples 5-6 (no main binder / interface passivation coupling agent) have the worst performance due to lack of interface optimization, reflecting the innovativeness of the binder composition of the present application.

[0105] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A binder composition characterized in that, The adhesive composition comprises a carboxyl-containing siloxane-acrylate block polymer and an interface passivation coupling agent, the interface passivation coupling agent comprises a mercapto silane compound and a fluorinated carboxylic acid compound, the mass ratio of the carboxyl-containing siloxane-acrylate block polymer to the interface passivation coupling agent is (35-55):(10-25).

2. The binder composition of claim 1, wherein The structure of the carboxyl-containing siloxane-acrylate block polymer is shown in Formula 1, -[Si(CH3)2O] a -[CH2CH (COOH)] b -[CH2CH (COO (CH2)3Si(CH3)2O) n H] e -, formula 1; Wherein, a:b:e=(0.5-2):(1-4):(0.5-2), n=3-10.

3. The binder composition of claim 1, wherein The total degree of polymerization of the carboxyl group-containing siloxane-acrylate block polymer is 76-223, and the number average molecular weight is 8*10 4 -12*10 4 g / mol.

4. The binder composition of claim 1, wherein The carboxyl-containing siloxane-acrylate block polymer comprises siloxane structural units and acrylic structural units, the siloxane structural units are structural units obtained by polymerization of siloxane monomers, the siloxane monomers comprise at least one of octamethylcyclotetrasiloxane, carboxypropyl methyl siloxane oligomer and maleic anhydride modified siloxane copolymer; The acrylic structural units are structural units obtained by polymerization of acrylic monomers, the acrylic monomers comprise at least one of acrylic acid, methacrylic acid, acrylic acid-beta-carboxyethyl ester and itaconic acid.

5. The binder composition of claim 1, wherein The molar ratio of the mercapto silane compound to the fluorinated carboxylic acid compound is 1:(0.8-1.5).

6. The binder composition of claim 1, wherein The mercapto silane compound comprises at least one of mercaptopropyl trimethoxysilane, mercaptopropyl triethoxysilane, mercaptoethyl trimethoxysilane and mercaptopropyl methyl dimethoxysilane; And / or, the fluorinated carboxylic acid compound comprises at least one of perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluoropentanoic acid and fluorinated propionic acid.

7. The binder composition of claim 1, wherein The adhesive composition further comprises a dynamic crosslinking agent, the dynamic crosslinking agent comprises at least one of dialdehyde starch, bisphenol A diglycidyl ether and adipoyl dihydrazine; The mass ratio of the carboxyl-containing siloxane-acrylate block polymer, the interface passivation coupling agent and the dynamic crosslinking agent is (35-55):(10-25):(8-18).

8. The binder composition of claim 1, wherein, The adhesive composition further comprises an ion conduction aid, the ion conduction aid comprises hydroxylated multi-walled carbon nanotubes and lithium salt; The mass ratio of the carboxyl-containing siloxane-acrylate block polymer, the interface passivation coupling agent and the ion conduction aid is (35-55):(10-25):(12-22).

9. The binder composition of claim 8, wherein, The mass of the lithium salt is 25%-35% of the mass of the hydroxylated multi-walled carbon nanotubes; And / or, the content of hydroxyl in the hydroxylated multi-walled carbon nanotubes is ≥5mmol / g.

10. The method of producing a binder composition according to any one of claims 1 to 9, characterized by, The method comprises the following steps: Mixing siloxane monomers, acrylic monomers and an initiator, and performing ring-opening polymerization, then adding a silane coupling agent to obtain a carboxyl-containing siloxane-acrylate block polymer, dissolving the carboxyl-containing siloxane-acrylate block polymer in water to form a colloidal solution; Mixing a mercapto silane compound and a fluorinated carboxylic acid compound, then adding the colloidal solution to obtain an adhesive composition.

11. A negative electrode sheet characterized by comprising: An electrode including a current collector and an active material layer provided on at least one side of the current collector, the active material layer including the binder composition according to any one of claims 1 to 9, or, the binder composition prepared by the production method according to claim 10.

12. A battery, characterized by The negative electrode sheet according to claim 11.

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