Binder for graphite negative electrode, method for preparing the same, and use thereof

Abstract

This application provides a binder for graphite anodes, its preparation method, and its application, relating to the field of battery technology. The method includes: preparing a binder precursor liquid based on a variety of monomers and an initiator solution; wherein the variety of monomers includes soft monomers among hydrophobic monomers and hydrophilic monomers, the hydrophilic monomers include hydrophilic functional monomers and hydrophilic monomers, the hydrophilic monomers accounting for 45%~55% of the mass of the variety of monomers, and the soft monomers include a first soft monomer and a second soft monomer, the second soft monomer having a glass transition temperature less than -50°C. Then, the binder precursor liquid is cooled and the pH value is adjusted to a preset range to obtain the binder. The binder prepared by the above method possesses excellent electrode flexibility, slurry stability, and interfacial bonding strength, providing reliable support for improving the cycle life, rate performance, and structural stability of the battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a binder for use in graphite anodes, its preparation method, and its application. Background Technology

[0002] In the manufacturing process of lithium-ion batteries, binders are one of the key materials.

[0003] Traditional binders used in graphite anodes are typically blends of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC), or blends of polyacrylic acid (PAA). However, both SBR and CMC are petrochemical derivatives, resulting in high raw material costs. Furthermore, PAA blends often fail to balance electrode flexibility, slurry stability, and interfacial bonding strength.

[0004] In summary, providing a binder for graphite anodes in lithium-ion batteries that can reduce raw material costs while simultaneously ensuring electrode flexibility, slurry stability, and interfacial bonding strength is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] This application provides a binder for use in graphite anodes, its preparation method, and its application, which aims to reduce raw material costs while effectively balancing electrode flexibility, slurry stability, and interfacial bonding strength, thereby improving the cycle performance and reliability of lithium-ion batteries.

[0006] In a first aspect, embodiments of this application provide a binder for use in graphite anodes, comprising a polymer synthesized from a variety of monomers;

[0007] The plurality of monomers includes soft monomers among hydrophobic monomers and hydrophilic monomers; wherein, the hydrophilic monomers include hydrophilic functional monomers and hydrophilic monomers, the mass of the hydrophilic monomers accounts for 45% to 55% of the mass of the plurality of monomers, the soft monomers include a first soft monomer and a second soft monomer, and the glass transition temperature of the second soft monomer is less than -50°C.

[0008] In one possible implementation, the mass of the soft monomer accounts for 30% to 40% of the mass of the plurality of monomers;

[0009] The mass of the first soft monomer is greater than the mass of the second soft monomer.

[0010] In one possible implementation, the hydrophilic functional monomer includes at least one of acrylate, methacrylate, methacrylamide, and acrylamide;

[0011] And / or,

[0012] The hydrophilic functional monomer accounts for 3% to 8% of the total mass of the various monomers;

[0013] And / or,

[0014] The hydrophilic monomer includes at least one of acrylic acid, methacrylic acid, ethyl acrylate, butyl acrylate, isooctyl acrylate, acrylamide, and methacrylamide.

[0015] In one possible implementation, the first soft monomer includes at least one of ethyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylene tert-carbonate, n-octyl acrylate, and laurate.

[0016] And / or,

[0017] The second soft monomer includes any one of 2-ethylhexyl acrylate, n-butyl acrylate, and isooctyl acrylate.

[0018] In one possible implementation, the plurality of monomers further includes the hard monomer among the hydrophobic monomers;

[0019] The hard monomer includes at least one of acrylic acid, methyl acrylate, vinyl acetate, methyl methacrylate, ethyl methacrylate, acrylonitrile, isopropyl methacrylate, and isobutyl methacrylate.

[0020] Secondly, embodiments of this application provide a method for preparing a binder for use in graphite anodes, the method comprising:

[0021] A bonding precursor fluid is prepared based on a variety of monomers and an initiator solution; wherein the variety of monomers includes soft monomers among hydrophobic monomers and hydrophilic monomers, the hydrophilic monomers include hydrophilic functional monomers and hydrophilic monomers, the mass of the hydrophilic monomers accounts for 45% to 55% of the mass of the variety of monomers, the soft monomers include a first soft monomer and a second soft monomer, and the glass transition temperature of the second soft monomer is less than -50°C.

[0022] The binder is obtained by cooling the precursor fluid and adjusting its pH value to a preset range.

[0023] In one possible implementation, the initiator solution is prepared by dissolving the initiator in deionized water, wherein the initiator accounts for 0.5% to 2% of the mass of the plurality of monomers.

[0024] In one possible implementation, the plurality of monomers further includes the hard monomer among the hydrophobic monomers; the method further includes:

[0025] The soft monomer and the hydrophilic monomer are weighed according to a mass ratio of (30%~40%):(45%~55%), wherein the mass of the first soft monomer is greater than the mass of the second soft monomer.

[0026] The hydrophilic functional monomers were obtained by weighing, accounting for 3% to 8% of the mass of the various monomers.

[0027] Thirdly, embodiments of this application provide a graphite negative electrode sheet, comprising graphite, a conductive agent, and a binder as described in the first aspect and / or various possible methods of the first aspect, or a binder prepared by the second aspect and / or various possible methods of the second aspect.

[0028] Fourthly, embodiments of this application provide a lithium-ion battery, including a positive electrode, an electrolyte, a separator, and the graphite negative electrode described in the third aspect.

[0029] This application provides a binder for graphite anodes, its preparation method, and its application. The binder comprises a polymer synthesized from multiple monomers. These monomers include soft monomers (hydrophobic monomers) and hydrophilic monomers. The hydrophilic monomers include hydrophilic functional monomers and hydrophilic monomers, with the hydrophilic monomers accounting for 45% to 55% of the total mass of the various monomers. The soft monomers include a first soft monomer and a second soft monomer, with the second soft monomer having a glass transition temperature less than -50°C. This binder effectively balances electrode flexibility, slurry stability, and interfacial bonding strength, thereby improving the cycle performance and reliability of lithium-ion batteries. Attached Figure Description

[0030] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0031] Figure 1 This is a schematic flowchart illustrating a method for preparing a binder for use in graphite anodes, as provided in this application.

[0032] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0034] The application background of this application is explained as follows:

[0035] Lithium-ion batteries, as high-energy-density energy storage devices, are widely used in new energy vehicles, consumer electronics (such as smartphones and laptops), energy storage systems, and power tools. In the preparation of graphite anodes for lithium-ion batteries, binders are one of the key materials, and their main functions include:

[0036] (1) Bonding active material and current collector: Ensure that a stable interface bond is formed between the negative electrode active material and the copper foil current collector to avoid the active material falling off due to volume changes during the cycle;

[0037] (2) Maintain the integrity of the electrode structure: During battery processing such as coating, rolling, and bending, as well as during use, the binder must give the electrode sufficient flexibility to withstand mechanical stress;

[0038] (3) Slurry stability: During the preparation of negative electrode slurry, the binder needs to provide sufficient suspension and dispersibility to prevent active materials from settling or agglomerating and to ensure slurry stability;

[0039] (4) Electrochemical performance support: The binder must be compatible with the electrolyte and maintain structural stability during charging and discharging to avoid battery capacity decay due to bonding failure.

[0040] Traditional binders used in graphite anodes are typically a blend of SBR and CMC. CMC ensures the suspension and dispersion of the slurry and provides thickening, while SBR imparts flexibility and interfacial bonding strength to the electrode. However, the SBR / CMC blend suffers from high raw material costs, complex processes, and insufficient compatibility. Another traditional binder for graphite anodes is PAA. PAA, a water-soluble polymer, has carboxyl groups (-COOH) on its molecular chain that can form hydrogen bonds with the active material surface of the graphite anode, possessing potential bonding capabilities. However, existing PAA has two major drawbacks: 1) its rigid molecular chain leads to insufficient electrode flexibility, failing to meet the bending and rolling requirements of battery processing; 2) an imbalanced ratio of hydrophobic to hydrophilic groups, making it difficult to simultaneously achieve slurry stability and interfacial bonding strength.

[0041] In the field of new energy vehicles, higher requirements have been placed on the cycle life, safety and cost control of batteries. The industry urgently needs to provide a binder that can replace SBR, CMC and PAA binding systems for use in graphite anodes of lithium-ion batteries, so as to reduce raw material costs and simultaneously take into account electrode flexibility, slurry stability and interfacial bonding strength.

[0042] Based on the aforementioned technical problems, the inventors, in the process of researching lithium-ion battery binders, discovered that by optimizing the performance of PAA-based binders through molecular structure design, and by controlling the structural selection and dosage of hydrophilic and hydrophobic monomers, followed by multi-source copolymerization, specifically, controlling the mass of hydrophilic monomers (hydrophilic monomers and hydrophilic functional monomers) to account for 45%~55% of the total monomer mass, and simultaneously selecting soft monomers with a glass transition temperature less than -50℃ as an important component of the hydrophobic monomers, a binder for graphite anodes was finally prepared, which can ensure high stability of the slurry, high interfacial bonding strength, and good electrode flexibility. Based on this, this application provides a binder for graphite anodes, its preparation method, and its application.

[0043] The technical solution of this application and how it solves the above-mentioned technical problems will be described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will be described below with reference to the accompanying drawings.

[0044] This application provides a binder for use in graphite anodes, comprising a polymer composed of multiple monomers.

[0045] Among them, the various monomers include soft monomers in hydrophobic monomers and hydrophilic monomers. The hydrophilic monomers include hydrophilic functional monomers and hydrophilic monomers. The mass of the hydrophilic monomers accounts for 45% to 55% of the mass of the various monomers. The soft monomers include a first soft monomer and a second soft monomer. The glass transition temperature of the second soft monomer is less than -50℃.

[0046] Understandably, hydrophobic monomers are small molecule compounds whose molecular structure is dominated by hydrophobic groups, are poorly soluble in water, have weak interactions with water, and are more likely to interact with nonpolar substances. Based on their glass transition temperature (Tg), the temperature at which a polymer transitions from a glassy state to a highly elastic state, hydrophobic monomers are classified into soft monomers and hard monomers. Soft monomers have a lower Tg, stronger molecular chain flexibility, and combine hydrophobicity with flexibility, thus imparting good flexibility and elasticity to adhesives. Hard monomers have a higher Tg than soft monomers, stronger molecular chain rigidity, and can improve the hardness, strength, and structural stability of adhesives.

[0047] Hydrophilic monomers are a class of polymeric monomers that carry polar hydrophilic groups in their molecular structure and can form hydrogen bonds with water molecules. They have good water compatibility and, when introduced into polymer systems, can endow materials with core properties such as hydrophilic wetting, water dispersion, water retention and solubilization, stability and anti-settling, and improved interfacial affinity. They are often copolymerized with hydrophobic soft monomers to balance the overall hydrophilic and oleophilic ratio.

[0048] Hydrophilic monomers include hydrophilic monomers and hydrophilic functional monomers. Hydrophilic monomers are polymeric monomers whose molecular structures contain hydrophilic groups such as hydroxyl, carboxyl, amino, and ether bonds. They are readily soluble in water or compatible with water, ensuring the dispersion stability of the slurry and facilitating interfacial bonding between the binder and the electrode active material and current collector. Specifically, the carboxyl groups provided by hydrophilic monomers can form hydrogen bonds with the hydroxyl and oxygen-containing functional groups on the surface of the active material, and coordinate with metal ions on the surface of the current collector, thereby ensuring good interfacial adhesion.

[0049] Hydrophilic functional monomers are the most functional among hydrophilic monomers. Their molecular structure is equipped with highly active and polar hydrophilic functional groups such as carboxyl groups, sulfonic acid groups, phosphate groups or quaternary ammonium salts, and amino groups. Relying on their ionization and deionization properties, they can significantly enhance the hydrophilic effect of polymers. When they are compounded and copolymerized with hydrophobic soft monomers and hydrophilic monomers, the charge characteristics and interfacial activity of polymer chain segments can be precisely controlled. This allows for precise control of target properties such as hydrophilicity / hydrophobicity, softness / hardness, crosslinking ability, adhesion, and reactivity of polymers. As a result, adhesives can have weather resistance, conductivity, adhesion, and water absorption, meeting the needs of different application scenarios.

[0050] Specifically, the hydrophilic monomer accounts for 45% to 55% of the mass of various monomers. For example, the mass of the hydrophilic monomer can account for 45%, 48%, 50%, 53%, or 55% of the mass of various monomers. By controlling the proportion of the hydrophilic monomer in the mass of various monomers, the hydrophilic groups it contains can ensure the dispersion stability of the slurry formed after mixing and stirring the solid components such as the binder, negative electrode active material (graphite), and conductive agent with solvents such as deionized water during the subsequent process of obtaining graphite negative electrode sheets based on this binder. This ensures that the solid components will not settle or agglomerate rapidly in the solvent and can maintain a uniform dispersion state for a long time. It can also take into account the interfacial bonding strength between the binder and the electrode material, thereby ensuring that when it is subsequently coated onto the current collector, the negative electrode sheet has a uniform thickness and consistent composition, ultimately ensuring the electrochemical performance and consistency of the lithium-ion battery.

[0051] The long-chain alkyl structure of the soft monomer in the hydrophobic monomer provides excellent flexibility to the molecular chain. It includes two types: a first soft monomer and a second soft monomer, with the second soft monomer having a Tg less than -50°C. The first soft monomer provides the basic molecular chain flexibility, while the second soft monomer, with a Tg less than -50°C, exhibits extremely strong low-temperature flexibility. By exerting its strong toughening effect, it further reduces the rigidity of the binder, allowing the molecular chain to deform to a certain extent without breaking when the electrode is bent or folded by external forces, thus meeting the flexibility requirements of the electrode at extreme temperatures (e.g., -30°C). The synergistic effect of the two soft monomers significantly improves the flexibility of the binder, thereby improving the problem of easy bending of the graphite anode sheet obtained based on this binder. This avoids problems such as cracking and powder shedding during the processing of the anode sheet, ultimately contributing to more stable electrochemical performance and longer cycle life of lithium-ion batteries.

[0052] In one possible implementation, the mass of the soft monomer accounts for 30% to 40% of the mass of the various monomers; the mass of the first soft monomer is greater than the mass of the second soft monomer.

[0053] Specifically, the mass of the soft monomer accounts for 30% to 40% of the mass of the multiple monomers. That is, the combined mass of the first soft monomer and the second soft monomer accounts for 30% to 40% of the mass of the multiple monomers. For example, the mass of the soft monomer can account for 30%, 33%, 35%, 37%, or 40% of the mass of the multiple monomers, etc.

[0054] The mass of the first soft monomer is greater than the mass of the second soft monomer. In one possible implementation, the mass ratio of the first soft monomer to the second soft monomer can be 2:1, or approximately 2:1. That is, the mass of the first soft monomer can account for 20% to 26.7% of the total mass of the various monomers, and the mass of the second soft monomer can account for 10% to 13.3% of the total mass of the various monomers. For example, the mass of the first soft monomer can account for 20%, 22%, 25%, 26%, or 26.7% of the total mass of the various monomers, etc., and correspondingly, the mass of the second soft monomer can account for 10%, 11%, 12.5%, 13%, or 13.3% of the total mass of the various monomers, etc. By adjusting the proportion of the soft monomer (first soft monomer and second soft monomer) to the total mass of the various monomers, the differentiated requirements of different lithium-ion batteries for the flexibility of the negative electrode sheet can be met, adapting to different battery processing scenarios and electrochemical performance design goals.

[0055] In one possible implementation, the first soft monomer includes at least one of ethyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylene tert-carbonate, n-octyl acrylate, and laurate.

[0056] And / or,

[0057] The second soft monomer includes any one of 2-ethylhexyl acrylate, n-butyl acrylate, and isooctyl acrylate.

[0058] Taking ethyl acrylate (EA) in the first soft monomer as an example, ethyl acrylate (EA) is an acrylate monomer with ester functional groups. Its chemical formula is C5H8O2. It is a colorless and transparent liquid at room temperature. It is easily soluble in organic solvents such as ethanol and ether, but sparingly soluble in water. It is chemically active and has good polymerization reactivity. The ester group gives the EA molecular chain a certain degree of flexibility. EA has moderate weather resistance and water resistance. The Tg of EA homopolymer is usually -22℃. When used as a soft monomer, it can provide basic flexibility and a certain degree of adhesion for adhesives. It has good compatibility when copolymerized with other monomers.

[0059] Taking 2-ethylhexyl acrylate, one of the second soft monomers, as an example, 2-ethylhexyl acrylate (EHA) is a long-chain acrylate soft monomer with the chemical formula C2. 11 H 20 O2 is a colorless and transparent liquid at room temperature. It is sparingly soluble in water but readily soluble in organic solvents such as ethanol and toluene. It is chemically active, with high polymerization reactivity and is not prone to self-polymerization. The 2-ethylhexyl long branch in its molecule can significantly reduce the intermolecular forces, giving the molecular chain extremely high flexibility (homogeneous polymer Tg is about -70℃). At the same time, the spatial structure of the ester group gives it good weather resistance, water resistance, and oil resistance. It has excellent compatibility with other monomers and can provide excellent low-temperature flexibility and ductility for binders. It can also enhance the interfacial compatibility between binders and non-polar electrode materials.

[0060] In one possible implementation, the hydrophilic functional monomer includes at least one of acrylate, methacrylate, methacrylamide, and acrylamide;

[0061] And / or,

[0062] The mass of hydrophilic functional monomers accounts for 3% to 8% of the mass of various monomers;

[0063] And / or,

[0064] The hydrophilic monomers include at least one of acrylic acid, methacrylic acid, ethyl acrylate, butyl acrylate, isooctyl acrylate, acrylamide, and methacrylamide.

[0065] For example, the mass percentage of the hydrophilic functional monomer among various monomers can be 8%, 7%, 6%, 4%, or 3%, etc. The nitrogen and oxygen atoms in the amide group (-CONH2) within its molecular structure have strong electronegativity, enabling them to form hydrogen bonds with polar groups (such as hydroxyl groups) on the electrode material surface, carboxyl groups (-COOH) in the hydrophilic monomer, and active sites on the current collector surface. This intermolecular hydrogen bond crosslinking effect significantly enhances the interfacial bonding force between the binder and its components, further improving the binder's adhesion performance. Furthermore, the relatively low proportion of the hydrophilic functional monomer compared to other monomers does not compromise the binder's original flexibility, slurry dispersion stability, or other core properties.

[0066] Understandably, if the mass of the hydrophilic monomer (hydrophilic monomer and hydrophilic functional monomer) accounts for 45% to 55% of the total mass of the monomers, and the mass of the hydrophilic functional monomer accounts for 3% to 8% of the total mass of the monomers, then the mass of the hydrophilic monomer accounts for 37% to 52% of the total mass of the monomers. For example, the mass of the hydrophilic monomer can be any value within the range of 37% to 52%, such as 37%, 40%, 43%, 46%, 48%, 50%, or 52%.

[0067] Taking acrylamide, a hydrophilic functional monomer, as an example, acrylamide, as an important polar functional modifier, possesses highly active amide polar groups in its molecular structure. These groups exhibit excellent hydrophilic affinity and reactive crosslinking activity. They can not only strengthen the intermolecular forces of polymers through the polar groups, significantly improving the cohesive strength, temperature resistance, and mechanical stability of the binder system, but also enhance the interfacial wetting and adsorption capacity between the adhesive layer and the graphite anode substrate, optimizing powder dispersion. Furthermore, the amide groups can provide potential crosslinking reaction sites during subsequent processing or use, further improving the overall water resistance and adhesion durability of the coating.

[0068] Taking acrylic acid, a hydrophilic monomer, as an example, acrylic acid, as a hydrophilic monomer containing carboxyl groups (-COOH), is chemically active and has extremely high polymerization reactivity. It can efficiently copolymerize with soft and hard monomers and stably embed itself in the polymer molecular chain. Specifically, the carboxyl groups in its molecular structure have strong polarity, which can form strong polar interactions and coordination bonds with the hydroxyl groups on the surface of graphite electrode materials and the metal active sites on the surface of current collectors (such as copper foil). At the same time, it can form hydrogen bonds with carboxyl groups and amide groups in hydrophilic functional monomers, further enhancing the bonding strength of the adhesive and improving the overall bonding performance of the adhesive. In addition, the hydrophilicity of the carboxyl groups can also help optimize the dispersion stability of the slurry and reduce the risk of agglomeration and sedimentation of solid components.

[0069] In one possible implementation, the plurality of monomers further includes a hard monomer among the hydrophobic monomers; wherein the hard monomer includes at least one of acrylic acid, methyl acrylate, vinyl acetate, methyl methacrylate, ethyl methacrylate, acrylonitrile, isopropyl methacrylate, and isobutyl methacrylate.

[0070] As mentioned in the previous embodiments, hydrophobic monomers are divided into soft monomers and hard monomers according to the difference in Tg. The Tg of hard monomers is higher than that of soft monomers, which enhances the rigidity and cohesion of the molecular chain, avoids the decrease in adhesion caused by excessive deformation of the molecular chain, and improves the hardness, strength and structural stability of the adhesive.

[0071] For example, the mass of hard monomers can account for 55% to 65% of the mass of various monomers. That is, the mass of hard monomers can account for 55%, 57%, 60%, 63%, or 65% of the mass of various monomers. By adjusting the proportion of hard monomers, the rigidity and flexibility balance of the binder can be flexibly controlled. When the proportion of hard monomers is biased towards 55% to 60%, the basic strength and structural stability of the binder can be guaranteed while better adapting to the flexibility contribution of soft monomers, avoiding the electrode from becoming too brittle. When the proportion is biased towards 60% to 65%, the hardness, deformation resistance and interfacial bonding strength of the binder can be further enhanced, meeting the battery processing scenarios with higher requirements for electrode structural stability, thereby adapting to the differentiated mechanical performance requirements of binders for different lithium-ion batteries.

[0072] Taking methyl acrylate (MA) as an example among hard monomers, it is a typical acrylate hard monomer with the chemical formula C4H6O2. It is a colorless and transparent liquid at room temperature with a strong pungent odor. It is easily soluble in organic solvents such as ethanol, ether, and acetone, and slightly soluble in water. It is chemically active, has high polymerization reactivity, and is prone to homopolymerization or copolymerization with other acrylate and vinyl monomers. It is also not prone to self-polymerization side reactions and has good storage stability. The MA molecule contains only short-chain methyl (-CH3) groups with low steric hindrance, resulting in strong intermolecular forces and high rigidity. Its homopolymer Tg is about 10℃, which is significantly higher than that of soft monomers, effectively improving the hardness, tensile strength and structural stability of the binder. At the same time, it has excellent compatibility when copolymerizing with soft monomers and hydrophilic monomers. It can balance the rigidity and flexibility of the binder through the synergistic effect of molecular chains (soft monomers provide flexible segments and hard monomers provide rigid support). This allows the electrode to withstand bending and folding operations during processing without breakage, while ensuring that the binder has sufficient cohesive force and bonding strength. The combination of these two factors gives the binder both good flexibility and adhesion.

[0073] Taking acrylic acid as an example among hard monomers, the glass transition temperature of acrylic acid homopolymer is as high as about 106℃. The molecular chain is rigid and the chain segment mobility is weak. After being introduced into the polymer system, it can significantly improve the cohesion, hardness and heat resistance of the film, and can effectively improve the mechanical strength and dimensional stability of the adhesive, playing the role of stiffening and reinforcing the hard monomer.

[0074] Understandably, acrylic acid possesses the dual properties of both hard monomers and hydrophilic monomers.

[0075] In one possible implementation, the molar ratio of the hydrophilic group in the hydrophilic monomer to the hydrophobic group in the hydrophobic monomer is (0.4~0.6):1.

[0076] In other words, the molar ratio of hydrophilic groups to hydrophobic groups can be 0.4:1, 0.45:1, 0.5:1, or 0.6:1, etc. The hydrophilic groups in the hydrophilic monomer can interact with the polar groups and water molecules on the surface of the negative electrode active material, which is beneficial to the dispersion stability of the slurry. The hydrophobic groups in the hydrophobic monomer can reduce the damage of water molecules to the interface between the binder and the electrode, improving the durability of the bond. By adjusting the molar ratio of hydrophilic to hydrophobic groups, the hydrophilicity and hydrophobicity of the binder are balanced, taking into account both the dispersion stability of the slurry and the bonding effect at the interface, avoiding the increased hygroscopicity of the electrode due to excessive hydrophilicity or the difficulty in slurry dispersion due to excessive hydrophobicity.

[0077] The binder for graphite anodes provided in this application is copolymerized from a variety of monomers, including hydrophilic and hydrophobic monomers. The hydrophilic monomers include both hydrophilic monomers and hydrophilic functional monomers, with the hydrophilic monomers accounting for 45% to 55% of the total monomer mass to ensure the dispersion stability of the slurry and the interfacial adhesion strength with the electrode material. The soft monomers in the hydrophobic monomers account for 30% to 40% of the total monomer mass, including a first soft monomer and a second soft monomer. The second soft monomer has a Tg below -50°C, and the first soft monomer has a greater mass than the second soft monomer, resulting in excellent flexibility and flexural strength of the electrode sheet even at extreme low temperatures. Furthermore, the hard monomers in the hydrophobic monomers account for 55% to 65% of the total monomer mass, providing rigid support and structural stability. Additionally, the hydrophilic functional monomers account for 3% to 8% of the total monomer mass. This binder also balances hydrophilic and hydrophobic properties by controlling the molar ratio of hydrophilic groups in the hydrophilic monomers to hydrophobic groups in the hydrophobic monomers to be between (0.4 to 0.6):1, thus considering both slurry stability and adhesion durability. This binder combines excellent electrode flexibility, slurry stability, and interfacial bonding strength, and its raw material cost is also lower than that of SBR and CMC. This helps to improve electrode processing yield and battery consistency, ultimately supporting lithium-ion batteries to achieve more stable electrochemical performance and longer cycle life.

[0078] Based on the above embodiments, in one possible implementation, the polymer number-average molecular weight of the binder applied to the graphite anode is 600,000 to 800,000.

[0079] Among them, the number-average molecular weight is a key indicator for measuring the average length of the polymer molecular chains of the adhesive. If the molecular weight is too low, the bonding strength will be insufficient, and if the molecular weight is too high, the bonding strength may be too high, which is not conducive to the uniform dispersion and coating process of the slurry, and may also affect the ion transport efficiency inside the electrode.

[0080] For example, the polymer number-average molecular weight of the adhesive can be 600,000, 620,000, 650,000, 680,000, 700,000, 730,000, 760,000, 790,000, or 800,000, etc. The higher the polymer number-average molecular weight, the longer the molecular chain segments, the more anchoring sites with the negative electrode active material particles, and the better the particle bonding effect. However, too much molecular chain segment molecular weight is detrimental; otherwise, the movement of the molecular chain segments will be inhibited, the electrode flexibility will decrease, bending will be difficult, and cracking will be easy. The lower the polymer number-average molecular weight, the shorter the molecular chain segments, and the fewer anchoring points with the negative electrode active material particles. The bonding effect is slightly weaker than that of adhesives with high polymer number-average molecular weight. However, due to the shorter molecular chain segments, the hydrogen bonding force within the molecular chain segments is reduced, the cohesive force of the adhesive molecules is reduced, and the electrode flexibility is greatly improved. Therefore, by adjusting the polymer number-average molecular weight of the adhesive, a balance between the adhesive strength and the electrode flexibility can be ensured.

[0081] In another possible implementation, the adhesive has a viscosity of 5000~15000 mPa at 25°C. s.

[0082] Viscosity is a physical quantity that measures the ease with which the binder flows. If the viscosity is too low (too fluid), the binder will lose its binding effect; if the viscosity is too high (too poor fluid), the binder will be difficult to mix evenly with the negative electrode active material, or uneven coating may occur during the electrode coating process.

[0083] For example, the viscosity of the adhesive at 25°C can be 5000 mPa. s, 7500mPa s, 9000mPa s, 13500mPa s, 14000mPa s or 15000mPa The properties of these components ensure that the binder can fully wet the surface of the graphite particles to form a uniform coating layer, while also preventing abnormal flowability from affecting the processing effect. This ensures that the binder has good processing adaptability to meet the requirements of continuous production, such as the material extraction by the compression pump.

[0084] Figure 1A flowchart illustrating a method for preparing a binder for use in graphite anodes provided in this application. Figure 1 ,like Figure 1 As shown, the method includes:

[0085] S101: A bonding precursor fluid is prepared based on a variety of monomers and an initiator solution; wherein, the variety of monomers includes soft monomers among hydrophobic monomers and hydrophilic monomers, the hydrophilic monomers include hydrophilic functional monomers and hydrophilic monomers, the mass of the hydrophilic monomers accounts for 45%~55% of the monomer mass, the soft monomers include a first soft monomer and a second soft monomer, the glass transition temperature of the second soft monomer is less than -50℃.

[0086] In this step, the initiator solution refers to a homogeneous system formed by dissolving the initiator in a solvent, used to initiate the polymerization reaction of monomers in polymer synthesis (such as binder preparation). As mentioned in the previous examples, the various monomers include hydrophobic monomers, including soft monomers such as a first soft monomer and a second soft monomer, as well as hydrophilic monomers. The hydrophilic monomers include hydrophilic functional monomers and hydrophilic monomers, with the hydrophilic monomers accounting for 45% to 55% of the total mass of the various monomers. It is understood that the mass of the hydrophilic monomers can be 45%, 48%, 50%, 53%, or 55% of the total mass of the various monomers, and other specific values ​​can be flexibly selected within the 45% to 55% range according to the actual electrode fabrication process requirements. Furthermore, the Tg of the second soft monomer is less than -50°C, providing a basis for the subsequent preparation of the binder, which gives the electrode sheet strong flexibility.

[0087] Optionally, the reaction apparatus for preparing the binder precursor liquid can be a four-necked flask, which is equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer, depending on the various monomers and initiator solutions.

[0088] For example, in order to provide a basic liquid phase environment for the dispersion and dissolution of various monomers and initiator solutions, and in order to stably control the temperature field during the heating process in the reactor (the internal space of the four-necked flask), avoid the risk of localized agglomeration caused by concentrated initial feeding, and assist in the rapid formation of uniform emulsion micelles to ensure the smooth progress of seed initiation and to ensure that the subsequent addition of various monomers and initiator solutions can be quickly mixed and dispersed, a portion of deionized water is added to the four-necked flask as the bottom liquid, and the mixture is stirred and heated to 70°C~85°C. Then, the uniformly mixed various monomers and initiator solutions are added dropwise to the four-necked flask through a dropping funnel.

[0089] Meanwhile, to ensure a stable and uniform polymerization reaction of the binder precursor liquid, the dropping rate is controlled to complete the addition within a preset time. Excessive dropping speed can cause multiple monomers and initiators to enter the reaction system instantaneously, leading to excessively high local reaction concentrations, a large accumulation of active centers, and intense, difficult-to-dissipate exothermic reactions. This can disrupt the temperature stability of the reaction system and may also cause a broadening of the polymer molecular weight distribution and excessive cross-linking, causing the viscosity, bonding strength, and other key properties of the subsequent binder to deviate from design requirements, thus affecting the binder's performance. Controlling the dropping rate uniformly within the preset time ensures that the monomers and initiators maintain a reasonable reaction concentration, guaranteeing a uniform polymer molecular weight distribution and regular structure in the resulting binder. This ensures the stability of the binder precursor liquid's quality and provides a foundation for the subsequent preparation of a qualified binder. For example, this preset time can be 3-4 hours. After the dropping is complete, the reaction is maintained at a constant temperature for 2-5 hours to obtain the intermediate product formed by the reaction of multiple monomers with the initiator solution, i.e., the binder precursor liquid.

[0090] S102: Cool the precursor fluid and adjust the pH value to a preset range to obtain the binder.

[0091] On the one hand, polymerization reactions are typically carried out at a certain temperature (such as 70℃~85℃ mentioned in S101). After the reaction, the polymerization system remains at a relatively high temperature. Sustained high temperatures may lead to side reactions or cause the polymer molecular chains to continue to grow and cross-link, disrupting the stability of the target molecular weight and structure. Cooling can quickly terminate the polymerization reaction and lock in the chemical structure of the binder precursor liquid. On the other hand, after the polymerization reaction, the pH value of the polymerization system may be acidic or alkaline due to reaction byproducts such as initiator decomposition products and monomer residues. An unsuitable pH value can affect the storage stability of the binder and may cause corrosion or reaction when the binder comes into contact with graphite particles or current collectors, affecting the structural integrity of the electrode. Therefore, by cooling and pH adjustment, the binder precursor liquid after the polymerization reaction is transformed into a stable binder suitable for graphite anode applications.

[0092] Specifically, the binder precursor liquid after the polymerization reaction is completed is cooled, for example, to below 40°C, and the pH value is adjusted to 6.0~8, so that the final binder is in a near-neutral, mild range. Then, deionized water is slowly added to the binder precursor liquid with the pH value adjusted to the preset range while continuously stirring to control its solid content. Finally, the product is filtered through a filter cloth to obtain a binder product with compliant performance.

[0093] The method for preparing a binder for graphite anodes provided in this application involves preparing a binder precursor solution based on a variety of monomers and an initiator solution. The monomers include soft monomers (hydrophobic monomers) and hydrophilic monomers. The hydrophilic monomers include hydrophilic functional monomers and hydrophilic monomers, with the hydrophilic monomers accounting for 45% to 55% of the total mass of the monomers. The soft monomers include a first soft monomer and a second soft monomer, with the second soft monomer having a glass transition temperature less than -50°C. The binder precursor solution is then cooled and its pH value adjusted to a preset range to obtain the binder. The binder prepared by this method possesses excellent electrode flexibility, slurry stability, and interfacial bonding strength, effectively adapting to the charge-discharge volume changes required by graphite anodes, and providing reliable support for improving battery cycle life, rate performance, and structural stability.

[0094] exist Figure 1 Based on the embodiments, prior to S101, the preparation method of the binder for graphite anodes provided in this application further includes raw material preparation, wherein the preparation of various monomers and initiator solutions specifically includes:

[0095] In one possible implementation, the initiator solution is prepared by dissolving an initiator in deionized water, wherein the initiator accounts for 0.5% to 2% of the mass of various monomers.

[0096] Using deionized water as a solvent avoids impurities in the water from interfering with the initiator's activity or causing side reactions with the monomers, ensuring the directional polymerization reaction. It also improves the uniformity of the initiator solution's dispersion, allowing the initiator to smoothly release active centers in subsequent reactions. For example, initiator solutions can be prepared by dissolving 0.5%, 0.8%, 1%, 1.5%, 1.8%, or 2% of the mass of various monomers in deionized water. By adjusting the amounts of initiator and deionized water, the molecular weight and distribution of the polymer can be precisely controlled, providing a foundation for the core properties of the binder, such as viscosity and bond strength. This allows for flexible adaptation to different process requirements, ultimately leading to the preparation of standardized and controllable initiator solutions that contribute to the obtaining of stable binders suitable for graphite anode applications.

[0097] In addition to the soft monomers and hydrophilic monomers among the hydrophobic monomers mentioned in S101, various monomers also include hard monomers among the hydrophobic monomers. The preparation method of the binder used in graphite anodes also includes:

[0098] In another possible implementation, soft monomers, hard monomers, and hydrophilic monomers are weighed according to a mass ratio of (30%~40%):(55%~65%):(45%~55%) to obtain hydrophilic functional monomers, which account for 3%~8% of the mass of the various monomers. The mass of the first soft monomer is greater than the mass of the second soft monomer.

[0099] The selection of the quality and technical effects of the soft monomers (first soft monomer and second soft monomer), hard monomers, hydrophilic monomers and hydrophilic functional monomers are consistent with those mentioned in the foregoing embodiments, and will not be repeated here.

[0100] This application provides a graphite negative electrode sheet, comprising graphite, a conductive agent, and the binder mentioned in the above embodiments, or a binder prepared by the method in the above method embodiments.

[0101] The preparation method of this graphite anode is as follows:

[0102] For example, graphite (the negative electrode active material), acetylene black (the conductive agent), and the binder are mixed in a mass ratio of 96.5:1:2.5, and deionized water is added as a solvent. The mixture is stirred using a vacuum mixer until the system is homogeneous, thus obtaining a negative electrode slurry. Then, deionized water is added to adjust the initial static viscosity of the slurry to 3000~6000 mPa. The solid content of the negative electrode slurry is maintained at 51%~57%. Finally, the negative electrode slurry is uniformly coated onto the copper foil of the negative electrode current collector using a coating machine, and then rolled and slit to obtain graphite negative electrode sheets.

[0103] This application provides a lithium-ion battery, including a positive electrode, an electrolyte, a separator, and the graphite negative electrode mentioned in the previous embodiment.

[0104] The preparation method of this lithium-ion battery is as follows:

[0105] (1) Preparation of positive electrode sheet

[0106] For example, lithium iron phosphate (LiFePO4, LFP) as the positive electrode active material, carbon black as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder are mixed in a mass ratio of 96:2:2. Then, N-methyl-2-pyrrolidone (NMP) as the solvent is added to the mixture, and the mixture is then continuously stirred in a vacuum mixer until a uniform and stable positive electrode slurry is formed. The positive electrode slurry is then uniformly coated onto the surface of the positive electrode current collector aluminum foil using a coating machine. Following this, the positive electrode sheet is obtained by sequentially undergoing a rolling process (to increase the density of the electrode sheet) and a slitting process (to obtain the target size).

[0107] (2) Preparation of electrolyte

[0108] For example, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0109] (3) Preparation of the separating membrane

[0110] For example, polyethylene film is selected as the separation film.

[0111] (4) Preparation of graphite negative electrode sheet

[0112] The graphite anode sheet was prepared using the method mentioned in the previous embodiment.

[0113] (5) Stack the above positive electrode sheet, separator and graphite negative electrode sheet in sequence, so that the separator is between the positive electrode sheet and the graphite negative electrode sheet to play a role in isolation, and then wind them to obtain a bare cell; finally, place the bare cell in the outer packaging shell, dry it and inject electrolyte, and then obtain a lithium-ion battery through vacuum sealing, standing, formation and shaping processes.

[0114] The following will provide a detailed description of the binder for use in graphite anodes and its preparation method provided in this application through specific embodiments.

[0115] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0116] I. Preparation of binders for use in graphite anodes

[0117] Example 1

[0118] This embodiment provides a binder for use in graphite anodes, the preparation method of which includes the following steps:

[0119] (1) Preparation of multiple monomers

[0120] Weigh out 23.3g of ethyl acrylate, 11.7g of isooctyl acrylate, 15g of acrylonitrile, 45g of acrylic acid, and 5g of acrylamide sequentially into a 250mL dry beaker. Then place the beaker on a magnetic stirrer and stir at room temperature for 15-20 minutes until the acrylamide powder is completely dissolved and the mixed monomers (multiple monomers) are homogeneous and transparent. The glass transition temperature of isooctyl acrylate is -70℃.

[0121] (2) Preparation of initiator solution

[0122] Weigh 1.0g of ammonium persulfate and dissolve it in 99g of deionized water. Stir to dissolve and obtain an initiator solution with a mass fraction of 1.0%.

[0123] (3) Preparation of bottom liquid

[0124] Add 180g of deionized water to a 1500mL four-necked flask as the bottom solution. Each of the four flasks is equipped with: a mechanical stirrer with a PTFE impeller, a reflux condenser with cooling water, a 100mL constant-pressure dropping funnel for adding the mixed monomers, a 50mL constant-pressure dropping funnel for adding the initiator solution, and a thermometer with a range of 0-100℃. Then, turn on the mechanical stirrer and control the stirring speed to 200-250rpm, while simultaneously heating the contents of the vessel to 78℃ using a water bath / water bath temperature control.

[0125] (4) Seed-induced

[0126] When the temperature inside the reactor stabilizes at 78°C, add 10g of initiator solution at once through a 50mL constant pressure dropping funnel as a seed initiator. React for 15 minutes and observe whether a slight blue light appears in the liquid inside the four-necked flask (blue light indicates the formation of emulsion micelles and the start of polymerization). If no blue light is seen after 15 minutes, continue to observe for 20 minutes.

[0127] (5) Simultaneous dripping

[0128] Once blue light appears in the four-necked flask, the mixed monomer and the remaining 90g of initiator solution are added simultaneously. A variable-speed addition strategy with a slow initial addition followed by a faster addition is adopted, and the total addition time is controlled within 4.0 hours. By controlling the addition speed, the bonding precursor fluid is obtained.

[0129] Specifically, the dropping rate of the mixed monomers is approximately 2-3 drops / second for the first hour, 8-10 drops / second for the middle two hours, and 4-5 drops / second for the last hour; the dropping rate of the initiator solution is approximately 3-4 drops / second for the first hour, 7-8 drops / second for the middle two hours, and 4-5 drops / second for the last hour. During simultaneous dropping, the first hour is the slow initiation period, used to control initial exothermic reactions; the middle two hours are the main reaction period, used to stabilize polymerization; and the last hour is the supplementary addition period, used to improve conversion. Furthermore, the reaction temperature must be closely monitored during simultaneous dropping, and the dropping rate or water bath temperature should be adjusted to ensure the reaction temperature remains stable between 78℃ and 82℃. If the temperature exceeds 82℃, the dropping rate should be appropriately slowed down; if the temperature is below 78℃, the dropping rate can be slightly increased or the water bath temperature can be fine-tuned.

[0130] (6) Insulation reaction

[0131] After the addition is complete, raise the temperature inside the reactor to 80°C and continue the reaction for 2 hours to promote the full conversion of acrylonitrile and residual monomers.

[0132] (7) Add initiator (concentrate)

[0133] After incubation for 1 hour, a small amount of initiator solution is added to the binder precursor solution. Specifically, 0.2 g of ammonium persulfate is dissolved in 5 g of deionized water and added to the binder precursor solution all at once. This helps reduce the residual monomer content, improve the conversion rate, and reduce subsequent odors.

[0134] (8) Cooling

[0135] After the heat treatment reaction is complete, turn off the heating and circulate cooling water to lower the temperature to below 35°C. Continue stirring during the cooling process to prevent localized overheating.

[0136] (9) Neutralization

[0137] First, weigh 30g of sodium hydroxide (NaOH) and slowly add it to 170g of deionized water. After stirring and dissolving, cool to room temperature to obtain a 15% NaOH solution. Based on the theoretical alkali requirement: 45g of acrylic acid has a molar mass of 0.625mol (45÷72=0.625mol, where the molar mass of acrylic acid is 72g / mol). Therefore, the required mass of NaOH is 25.0g (0.625×40=25.0g, where the molar mass of NaOH is 40g / mol). The corresponding mass of the 15% NaOH solution is 167g (25.0÷15%=167g). Based on this, under rapid stirring, 167g of NaOH solution was added dropwise (approximately 2-3 drops / second) to the precursor fluid through a 100mL constant-pressure dropping funnel. When the pH reached 5.0-6.0, the dropping rate was reduced to 1 drop / second, and a small amount of deionized water (10-20g) was added to prevent localized gelation. The stirring intensity was increased (the rotation speed can be increased to 300-350rpm). NaOH solution was continuously added until the pH of the precursor fluid stabilized at 7.8.

[0138] (10) Adjusting the solid content of shipments

[0139] 459.8 g of deionized water was slowly added to the binder precursor solution with a pH stabilized at 7.8, and the mixture was stirred for 30 minutes to ensure homogeneity, adjusting the solid content to 10%. The mixture was then filtered through a 200-mesh filter cloth to obtain the binder for use in graphite anodes.

[0140] Example 2

[0141] This embodiment provides a binder for use in graphite anodes, the preparation method of which includes the following steps:

[0142] (1) Preparation of multiple monomers

[0143] Weigh out 20.0 g of ethyl acrylate, 10.0 g of isooctyl acrylate, 25 g of acrylonitrile, 37 g of acrylic acid, and 8 g of acrylamide sequentially into a 250 mL dry beaker. Then place the beaker on a magnetic stirrer and stir at room temperature for 15-20 minutes until the acrylamide powder is completely dissolved and the mixed monomers (multiple monomers) are homogeneous and transparent. The glass transition temperature of isooctyl acrylate is -70℃.

[0144] (2) Same as step (2) in Example 1.

[0145] (3) Same as step (3) in Example 1.

[0146] (4) Same as step (4) in Example 1.

[0147] (5) Same as step (5) in Example 1.

[0148] (6) Same as step (6) in Example 1.

[0149] (7) Same as step (7) in Example 1.

[0150] (8) Same as step (8) in Example 1.

[0151] (9) Referring to Example 1, a 15% NaOH solution was prepared. Based on the theoretical alkali requirement calculation: 37g of acrylic acid has a molar mass of 0.514mol (37÷72≈0.514mol, where the molar mass of acrylic acid is 72g / mol), so the required mass of NaOH is 20.56g (0.514×40=20.56g, where the molar mass of NaOH is 40g / mol), corresponding to a 15% NaOH solution mass of 137g (20.56÷15%≈137g). Based on this, under rapid stirring, 137g of NaOH solution was added dropwise (approximately 2-3 drops / second) to the precursor fluid through a 100mL constant-pressure dropping funnel. When the pH reached 5.0-6.0, the dropping rate was reduced to 1 drop / second, and a small amount of deionized water (10-20g) was added to prevent localized gelation. The stirring intensity was increased (the stirring speed can be increased to 300-350rpm). NaOH solution was continuously added until the pH of the precursor fluid was adjusted to 7.5±0.2.

[0152] (10) Adjusting the solid content of shipments

[0153] 489.8 g of deionized water was slowly added to the binder precursor solution with a stable pH of 7.5 ± 0.2, and the mixture was stirred for 30 minutes to ensure homogeneity, adjusting the solid content to 10%. The mixture was then filtered through a 200-mesh filter cloth to obtain the binder for use in graphite anodes.

[0154] Example 3

[0155] This embodiment provides a binder for use in graphite anodes, the preparation method of which includes the following steps:

[0156] (1) Preparation of multiple monomers

[0157] Weigh out 23.3g of ethyl acrylate, 11.7g of isooctyl acrylate, 10g of acrylonitrile, 52g of acrylic acid, and 3g of acrylamide sequentially into a 250mL dry beaker. Then place the beaker on a magnetic stirrer and stir at room temperature for 15-20 minutes until the acrylamide powder is completely dissolved and the mixed monomers (multiple monomers) are homogeneous and transparent. The glass transition temperature of isooctyl acrylate is -70℃.

[0158] (2) Same as step (2) in Example 1.

[0159] (3) Same as step (3) in Example 1.

[0160] (4) Same as step (4) in Example 1.

[0161] (5) Same as step (5) in Example 1.

[0162] (6) Same as step (6) in Example 1.

[0163] (7) Same as step (7) in Example 1.

[0164] (8) Same as step (8) in Example 1.

[0165] (9) Referring to Example 1, a 15% NaOH solution was prepared. Based on the theoretical alkali requirement calculation: 52g of acrylic acid has a molar mass of 0.722mol (52÷72≈0.722mol, where the molar mass of acrylic acid is 72g / mol), so the required mass of NaOH is 28.88g (0.722×40=28.88g, where the molar mass of NaOH is 40g / mol), corresponding to a 15% NaOH solution mass of 193g (28.88÷15%≈193g). Based on this, under rapid stirring, 193g of NaOH solution was added dropwise (approximately 2-3 drops / second) to the precursor fluid through a 100mL constant-pressure dropping funnel. When the pH reached 5.0-6.0, the dropping rate was reduced to 1 drop / second, and a small amount of deionized water (10-20g) was added to prevent localized gelation. The stirring intensity was increased (the rotation speed can be increased to 300-350rpm). The NaOH solution was continuously added until the pH of the precursor fluid stabilized at 7.8.

[0166] (10) Adjusting the solid content of shipments

[0167] 433.8 g of deionized water was slowly added to the binder precursor solution with a pH stability of 7.8, and the mixture was stirred for 30 minutes to ensure homogeneity, adjusting the solid content to 10%. The mixture was then filtered through a 200-mesh filter cloth to obtain the binder for use in graphite anodes.

[0168] Example 4

[0169] This embodiment provides a binder for use in graphite anodes, the preparation method of which includes the following steps:

[0170] (1) Preparation of multiple monomers

[0171] Weigh out 23.3g of ethyl acrylate, 11.7g of n-butyl acrylate, 15g of styrene, 40g of acrylic acid, 5g of methacrylic acid, and 5g of methacrylamide sequentially into a 250mL dry beaker. Then place the beaker on a magnetic stirrer and stir at room temperature for 15-20 minutes until the acrylamide powder is completely dissolved and the mixed monomers (multiple monomers) are homogeneous and transparent. The glass transition temperature of n-butyl acrylate is -55℃.

[0172] (2) Same as step (2) in Example 1.

[0173] (3) Same as step (3) in Example 1.

[0174] (4) Same as step (4) in Example 1.

[0175] (5) Same as step (5) in Example 1.

[0176] (6) Same as step (6) in Example 1.

[0177] (7) Same as step (7) in Example 1.

[0178] (8) Same as step (8) in Example 1.

[0179] (9) Referring to Example 1, a 15% NaOH solution was prepared. Based on the theoretical alkali requirement calculation: 40g of acrylic acid has a molar mass of 0.556mol (40÷72≈0.556mol, where the molar mass of acrylic acid is 72g / mol), so the required mass of NaOH is 22.24g (0.556×40=22.24g, where the molar mass of NaOH is 40g / mol), corresponding to a 15% NaOH solution mass of 148g (22.24÷15%≈148g); 5g of methacrylic acid has a molar mass of 0.058... 1 mol (5 ÷ 86.09 ≈ 0.0581 mol, where the molar mass of methacrylic acid is 86.09 g / mol), then the required mass of NaOH is 2.324 g (0.0581 × 40 = 2.324 g), which corresponds to a mass of 15 g of 15% NaOH solution (2.324 ÷ 15% ≈ 15 g). Therefore, the theoretical alkali required for 40 g of acrylic acid and 5 g of methacrylic acid is 163 g (148 + 15 = 163 g) of 15% NaOH solution. Based on this, under rapid stirring, 163g of NaOH solution was added dropwise (approximately 2-3 drops / second) to the precursor fluid through a 100mL constant-pressure dropping funnel. When the pH reached 5.0-6.0, the dropping rate was reduced to 1 drop / second, and a small amount of deionized water (10-20g) was added to prevent localized gelation. The stirring intensity was increased (the rotation speed can be increased to 300-350rpm). The NaOH solution was continuously added until the pH of the precursor fluid stabilized at 7.8.

[0180] (10) Adjusting the solid content of shipments

[0181] 463.8 g of deionized water was slowly added to the binder precursor solution with a pH stability of 7.8, and the mixture was stirred for 30 minutes to ensure homogeneity, adjusting the solid content to 10%. The mixture was then filtered through a 200-mesh filter cloth to obtain the binder for use in graphite anodes.

[0182] Example 5

[0183] This embodiment provides a binder for use in graphite anodes, the preparation method of which includes the following steps:

[0184] (1) Preparation of multiple monomers

[0185] Weigh out 20.0 g of ethyl acrylate, 10.0 g of isooctyl acrylate, 20 g of acrylonitrile, 45 g of acrylic acid, and 5 g of acrylamide sequentially into a 250 mL dry beaker. Then place the beaker on a magnetic stirrer and stir at room temperature for 15-20 minutes until the acrylamide powder is completely dissolved and the mixed monomers (multiple monomers) are homogeneous and transparent. The glass transition temperature of isooctyl acrylate is -70℃.

[0186] (2) Same as step (2) in Example 1.

[0187] (3) Same as step (3) in Example 1.

[0188] (4) Same as step (4) in Example 1.

[0189] (5) Same as step (5) in Example 1.

[0190] (6) Same as step (6) in Example 1.

[0191] (7) Same as step (7) in Example 1.

[0192] (8) Same as step (8) in Example 1.

[0193] (9) Same as step (9) in Example 1.

[0194] (10) Same as step (10) in Example 1.

[0195] Example 6

[0196] This embodiment provides a binder for use in graphite anodes, the preparation method of which includes the following steps:

[0197] (1) Preparation of multiple monomers

[0198] Weigh out 26.7g of ethyl acrylate, 13.3g of isooctyl acrylate, 10g of acrylonitrile, 45g of acrylic acid, and 5g of acrylamide sequentially into a 250mL dry beaker. Then place the beaker on a magnetic stirrer and stir at room temperature for 15-20 minutes until the acrylamide powder is completely dissolved and the mixed monomers (multiple monomers) are homogeneous and transparent. The glass transition temperature of isooctyl acrylate is -70℃.

[0199] (2) Same as step (2) in Example 1.

[0200] (3) Same as step (3) in Example 1.

[0201] (4) Same as step (4) in Example 1.

[0202] (5) Same as step (5) in Example 1.

[0203] (6) Same as step (6) in Example 1.

[0204] (7) Same as step (7) in Example 1.

[0205] (8) Same as step (8) in Example 1.

[0206] (9) Same as step (9) in Example 1.

[0207] (10) Same as step (10) in Example 1.

[0208] Comparative Example 1

[0209] This embodiment provides a binder for use in graphite anodes, the preparation method of which includes the following steps:

[0210] (1) Preparation of multiple monomers

[0211] Weigh out 23.3g of ethyl acrylate, 11.7g of isooctyl acrylate, 9g of acrylonitrile, 51g of acrylic acid, and 5g of acrylamide sequentially into a 250mL dry beaker. Then place the beaker on a magnetic stirrer and stir at room temperature for 15-20 minutes until the acrylamide powder is completely dissolved and the mixed monomers (multiple monomers) are homogeneous and transparent. The glass transition temperature of isooctyl acrylate is -70℃.

[0212] (2) Same as step (2) in Example 1.

[0213] (3) Same as step (3) in Example 1.

[0214] (4) Same as step (4) in Example 1.

[0215] (5) Same as step (5) in Example 1.

[0216] (6) Same as step (6) in Example 1.

[0217] (7) Same as step (7) in Example 1.

[0218] (8) Same as step (8) in Example 1.

[0219] (9) Referring to Example 1, a 15% NaOH solution was prepared. Based on the theoretical alkali requirement calculation: 51g of acrylic acid has a molar mass of 0.708mol (51÷72≈0.708mol, where the molar mass of acrylic acid is 72g / mol), so the required mass of NaOH is 28.32g (0.708×40=28.32g, where the molar mass of NaOH is 40g / mol), corresponding to a 15% NaOH solution mass of 189g (28.32÷15%≈189g). Based on this, under rapid stirring, 189g of NaOH solution was added dropwise (approximately 2-3 drops / second) to the precursor fluid through a 100mL constant-pressure dropping funnel. When the pH reached 5.0-6.0, the dropping rate was reduced to 1 drop / second, and a small amount of deionized water (10-20g) was added to prevent localized gelation. The stirring intensity was increased (the rotation speed can be increased to 300-350rpm). NaOH solution was continuously added until the pH of the precursor fluid stabilized at 7.8.

[0220] (10) Adjusting the solid content of shipments

[0221] 437.8 g of deionized water was slowly added to the binder precursor solution with a pH stabilized at 7.8, and the mixture was stirred for 30 minutes to ensure homogeneity, adjusting the solid content to 10%. The mixture was then filtered through a 200-mesh filter cloth to obtain the binder for use in graphite anodes.

[0222] Comparative Example 2

[0223] This embodiment provides a binder for use in graphite anodes, the preparation method of which includes the following steps:

[0224] (1) Preparation of multiple monomers

[0225] Weigh out 23.3g of ethyl acrylate, 11.7g of isooctyl acrylate, 21g of acrylonitrile, 39g of acrylic acid, and 5g of acrylamide sequentially into a 250mL dry beaker. Then place the beaker on a magnetic stirrer and stir at room temperature for 15-20 minutes until the acrylamide powder is completely dissolved and the mixed monomers (multiple monomers) are homogeneous and transparent. The glass transition temperature of isooctyl acrylate is -70℃.

[0226] (2) Same as step (2) in Example 1.

[0227] (3) Same as step (3) in Example 1.

[0228] (4) Same as step (4) in Example 1.

[0229] (5) Same as step (5) in Example 1.

[0230] (6) Same as step (6) in Example 1.

[0231] (7) Same as step (7) in Example 1.

[0232] (8) Same as step (8) in Example 1.

[0233] (9) Referring to Example 1, a 15% NaOH solution was prepared. Based on the theoretical alkali requirement calculation: 39g of acrylic acid has a molar mass of 0.542mol (39÷72≈0.542mol, where the molar mass of acrylic acid is 72g / mol), so the required mass of NaOH is 21.68g (0.542×40=21.68g, where the molar mass of NaOH is 40g / mol), corresponding to a 15% NaOH solution mass of 145g (21.68÷15%≈145g). Based on this, under rapid stirring, 145g of NaOH solution was added dropwise (approximately 2-3 drops / second) to the precursor fluid through a 100mL constant-pressure dropping funnel. When the pH reached 5.0-6.0, the dropping rate was reduced to 1 drop / second, and a small amount of deionized water (10-20g) was added to prevent localized gelation. The stirring intensity was increased (the rotation speed can be increased to 300-350rpm). NaOH solution was continuously added until the pH of the precursor fluid stabilized at 7.8.

[0234] (10) Adjusting the solid content of shipments

[0235] 481.8 g of deionized water was slowly added to the binder precursor solution with a pH stabilized at 7.8, and the mixture was stirred for 30 minutes to ensure homogeneity, adjusting the solid content to 10%. The mixture was then filtered through a 200-mesh filter cloth to obtain the binder for use in graphite anodes.

[0236] Comparative Example 3

[0237] This embodiment provides a binder for use in graphite anodes, the preparation method of which includes the following steps:

[0238] (1) Preparation of multiple monomers

[0239] Weigh out 23.3g of ethyl acrylate, 11.7g of 2-hydroxyethyl acrylate, 15g of acrylonitrile, 45g of acrylic acid, and 5g of acrylamide sequentially into a 250mL dry beaker. Then place the beaker on a magnetic stirrer and stir at room temperature for 15-20 minutes until the acrylamide powder is completely dissolved and the mixed monomers (multiple monomers) are homogeneous and transparent. The glass transition temperature of 2-hydroxyethyl acrylate is -15℃.

[0240] (2) Same as step (2) in Example 1.

[0241] (3) Same as step (3) in Example 1.

[0242] (4) Same as step (4) in Example 1.

[0243] (5) Same as step (5) in Example 1.

[0244] (6) Same as step (6) in Example 1.

[0245] (7) Same as step (7) in Example 1.

[0246] (8) Same as step (8) in Example 1.

[0247] (9) Same as step (9) in Example 1.

[0248] (10) Same as step (10) in Example 1.

[0249] Comparative Example 4

[0250] This embodiment provides a binder for use in graphite anodes, the preparation method of which includes the following steps:

[0251] (1) Preparation of multiple monomers

[0252] Weigh out 18.7g of ethyl acrylate, 9.3g of isooctyl acrylate, 22g of acrylonitrile, 45g of acrylic acid, and 5g of acrylamide sequentially into a 250mL dry beaker. Then place the beaker on a magnetic stirrer and stir at room temperature for 15-20 minutes until the acrylamide powder is completely dissolved and the mixed monomers (multiple monomers) are homogeneous and transparent. The glass transition temperature of isooctyl acrylate is -70℃.

[0253] (2) Same as step (2) in Example 1.

[0254] (3) Same as step (3) in Example 1.

[0255] (4) Same as step (4) in Example 1.

[0256] (5) Same as step (5) in Example 1.

[0257] (6) Same as step (6) in Example 1.

[0258] (7) Same as step (7) in Example 1.

[0259] (8) Same as step (8) in Example 1.

[0260] (9) Same as step (9) in Example 1.

[0261] (10) Same as step (10) in Example 1.

[0262] Comparative Example 5

[0263] This embodiment provides a binder for use in graphite anodes, the preparation method of which includes the following steps:

[0264] (1) Preparation of multiple monomers

[0265] Weigh out 28g of ethyl acrylate, 14g of isooctyl acrylate, 8g of acrylonitrile, 45g of acrylic acid, and 5g of acrylamide sequentially into a 250mL dry beaker. Then place the beaker on a magnetic stirrer and stir at room temperature for 15-20 minutes until the acrylamide powder is completely dissolved and the mixed monomers (multiple monomers) are homogeneous and transparent. The glass transition temperature of isooctyl acrylate is -70℃.

[0266] (2) Same as step (2) in Example 1.

[0267] (3) Same as step (3) in Example 1.

[0268] (4) Same as step (4) in Example 1.

[0269] (5) Same as step (5) in Example 1.

[0270] (6) Same as step (6) in Example 1.

[0271] (7) Same as step (7) in Example 1.

[0272] (8) Same as step (8) in Example 1.

[0273] (9) Same as step (9) in Example 1.

[0274] (10) Same as step (10) in Example 1.

[0275] Comparative Example 6

[0276] This embodiment provides a binder for use in graphite anodes, the preparation method of which includes the following steps:

[0277] (1) Preparation of multiple monomers

[0278] Weigh out 23.3g of ethyl acrylate, 11.7g of isooctyl acrylate, 15g of acrylonitrile, 40g of acrylic acid, and 10g of acrylamide sequentially into a 250mL dry beaker. Then place the beaker on a magnetic stirrer and stir at room temperature for 15-20 minutes until the acrylamide powder is completely dissolved and the mixed monomers (multiple monomers) are homogeneous and transparent. The glass transition temperature of isooctyl acrylate is -70℃.

[0279] (2) Same as step (2) in Example 1.

[0280] (3) Same as step (3) in Example 1.

[0281] (4) Same as step (4) in Example 1.

[0282] (5) Same as step (5) in Example 1.

[0283] (6) Same as step (6) in Example 1.

[0284] (7) Same as step (7) in Example 1.

[0285] (8) Same as step (8) in Example 1.

[0286] (9) Referring to Example 1, a 15% NaOH solution was prepared. Based on the theoretical alkali requirement calculation: 40g of acrylic acid has a molar mass of 0.556mol (40÷72≈0.556mol, where the molar mass of acrylic acid is 72g / mol), so the required mass of NaOH is 22.24g (0.556×40=22.24g, where the molar mass of NaOH is 40g / mol), corresponding to a 15% NaOH solution mass of 148g (22.24÷15%≈148g). Based on this, under rapid stirring, 148g of NaOH solution was added dropwise (approximately 2-3 drops / second) to the precursor fluid through a 100mL constant-pressure dropping funnel. When the pH reached 5.0-6.0, the dropping rate was reduced to 1 drop / second, and a small amount of deionized water (10-20g) was added to prevent localized gelation. The stirring intensity was increased (the rotation speed can be increased to 300-350rpm). NaOH solution was continuously added until the pH of the precursor fluid stabilized at 7.8.

[0287] (10) Adjusting the solid content of shipments

[0288] 478.8 g of deionized water was slowly added to the binder precursor solution with a pH stability of 7.8, and the mixture was stirred for 30 minutes to ensure homogeneity, adjusting the solid content to 10%. The mixture was then filtered through a 200-mesh filter cloth to obtain the binder for use in graphite anodes.

[0289] II. Preparation of negative electrode slurry

[0290] The negative electrode active material graphite, the conductive agent acetylene black, and the binder prepared in Example 1 were mixed at a mass ratio of 96.5:1:2.5, and deionized water was added as a solvent. The mixture was stirred in a vacuum mixer until the system was homogeneous, thus obtaining the negative electrode slurry corresponding to the binder in Example 1. Similarly, the negative electrode slurries corresponding to the binders in the other examples and comparative examples were prepared.

[0291] III. Preparation of Graphite Anode Sheets

[0292] Using the methods mentioned in the aforementioned graphite anode examples, graphite anode sheets corresponding to the binders in the examples and comparative examples were prepared by utilizing the anode slurries corresponding to the binders in the examples and comparative examples, respectively.

[0293] IV. Preparation of Lithium-ion Batteries

[0294] (1) The positive electrode and the separator were prepared by the method mentioned in the aforementioned lithium-ion battery examples;

[0295] (2) The positive electrode, separator, and graphite negative electrode are stacked in sequence, with the separator between the positive electrode and the graphite negative electrode to provide isolation. Then, the cells are wound to obtain the bare cells. Finally, the bare cells are placed in the outer packaging shell, dried, and injected with electrolyte. After vacuum sealing, standing, formation, and shaping, the lithium-ion batteries corresponding to the binders in the examples and comparative examples are obtained.

[0296] Test Example 1

[0297] Slurry stability test: First, prepare the slurry by thoroughly mixing the negative electrode slurry (solid content 51%~57%) to ensure no obvious particle agglomeration. Then, dispense the sample by evenly dispensing the well-mixed negative electrode slurry into three 100mL beakers, filling each beaker to the 80mL mark. After dispensing, seal the beakers to prevent water evaporation. Next, place the beakers containing the negative electrode slurry in a constant temperature environment of 25℃±1℃, avoiding environmental vibration and temperature fluctuations during the settling period. Test the viscosity of the negative electrode slurry at 0h and 48h settling times to determine slurry stability through viscosity changes at different settling times. Viscosity testing includes using a rotational viscometer (rotor model N0.4) at 25℃±0.5℃ and a rotation speed of 60r / min. Record the data after the readings stabilize, and take the average of three tests per sample.

[0298] Test Example 2

[0299] Electrode peel strength test: First, sample preparation is performed. The graphite negative electrode to be tested is cut into rectangular samples with a width of 25mm and a length of 100mm, ensuring that the edges of the sample are neat and burr-free and the coating is uniform and without peeling. Then, using double-sided tape with a width of ≥25mm, the uncoated side (copper foil side) of the rectangular sample is completely adhered and fixed to a flat stainless steel plate. A 2kg roller is used to roll back and forth 3 times along the length direction to ensure that the rectangular sample is tightly adhered to the stainless steel plate without air bubbles. Next, the peeling tape operation is performed. A polyester film tape with a width of 25mm and an adhesion strength of not less than 3N / m is selected and flatly adhered to the coating surface of the graphite negative electrode, with one end of the tape extending 50mm beyond the edge of the rectangular sample as the peeling end. Then, a 2kg roller is used to roll back and forth 3 times along the length direction to ensure that the tape is completely adhered to the coating. Finally, a peel force test was conducted. A stainless steel plate with a rectangular sample fixed to it was mounted on the lower clamp of the tensile testing machine, while the peeling end of the tape was fixed in the upper clamp, ensuring the peeling direction was 180° to the sample surface. The tensile speed was set to 300 mm / min, and the test stroke to 80 mm. The tensile testing machine was started, and the real-time force values ​​during the peeling process were recorded. Unstable data from the initial 5 mm and the last 5 mm were removed, and the average force value within the middle 70 mm stroke was taken as the peel force of the graphite negative electrode sheet (unit: N / m). Each test was repeated three times, and the arithmetic mean was taken as the final result.

[0300] Test Example 3

[0301] Molecular weight determination: The number-average molecular weight of the binder was determined by gel permeation chromatography (GPC).

[0302] Test Example 4

[0303] Electrode flexibility test: The graphite negative electrode sheet is bent 180° and the maximum number of bends without breakage or light leakage is recorded.

[0304] Test Example 5

[0305] 200-cycle retention rate test: at a current density of 1C and a voltage range of 2.7~4.3V (Li + The polarity cycle retention rate of lithium-ion batteries was tested under the test conditions of / Li).

[0306] Understandably, the 200-cycle retention rate refers to the percentage of the discharge capacity on the 200th charge-discharge cycle to the initial discharge capacity after 200 charge-discharge cycles for an all-solid-state battery. The calculation formula is: 200-cycle retention rate = initial discharge capacity / 200th discharge capacity × 100%. It is used to measure the battery's cycle stability. The higher the capacity retention rate, the better the integrity of the electrode structure, the interfacial compatibility between the electrolyte and the electrode, and the utilization rate of the active materials during multiple cycles, thus ensuring a longer battery life.

[0307] Test Example 6

[0308] Electrolyte swelling rate test: First, the adhesive is placed in a special mold, allowed to stand to degas, and then dried and cured to form a smooth and dense film. The film is then cut to a suitable size and placed in a 105℃ oven for 4 hours. After cooling, it is weighed and the initial mass M0 is recorded. The dried and weighed film is then completely immersed in a carbonate electrolyte solution and soaked at 70℃ and 25℃ for 48 hours each. Afterward, it is removed, excess electrolyte is absorbed with filter paper, and the film is weighed again to obtain the mass M1. Finally, through… The swelling rate of the electrolyte was calculated to evaluate the swelling tolerance of the adhesive film in the electrolyte environment.

[0309] Test Example 7

[0310] Solid content of negative electrode slurry: First, dry and cool a clean weighing bottle in advance and weigh it to constant weight. Then, accurately weigh a certain mass of negative electrode slurry sample and put it into the weighing bottle and record the initial mass of the sample m1. Then, place the weighing bottle containing the slurry sample stably in an oven and set the constant temperature baking temperature according to the specification (such as 105℃ or the corresponding battery material-specific drying temperature). Maintain the constant temperature baking for a sufficient time until the solvent inside the negative electrode slurry is completely evaporated and the powder components are completely dried. After drying, take out the weighing bottle and place it in a desiccator to cool to room temperature. Weigh the residue after drying again to obtain m2. Finally, calculate the ratio of m2 to m1 to obtain the solid content of the negative electrode slurry, which characterizes the proportion of non-volatile powder effective components in the negative electrode slurry.

[0311] The test results for test examples 1 to 7 are shown in Table 1.

[0312] Table 1. Test results of test examples 1-7

[0313]

[0314] Based on Table 1, the following conclusions can be drawn:

[0315] Examples 1 to 6 (all referring to the binders for graphite anodes, anode slurries containing the corresponding binders, graphite anode sheets containing the corresponding binders, or lithium-ion batteries containing the corresponding binders provided in the examples / comparative examples, which will not be described again below) show significantly better overall performance than the comparative examples. Specifically, the number-average molecular weights of the polymers in Examples 1 to 6 are concentrated in the range of 680,000 to 720,000, and the 0-hour static viscosity of the slurries is between 3700 and 4400 mPa. The static viscosity was 5200~6200 mPa after 48 hours. The static viscosity rebound rate was controlled at 40.5%~42.9% after 48 hours, the peel force was 15~17 N / m, the number of bends was more than 15 without cracking, light leakage, or breakage, the retention rate after 200 cycles reached 94%~97%, and the electrolyte swelling rate was 16%~20%. In contrast, Comparative Examples 1 to 6 either had excessively high slurry viscosity rebound rates (e.g., Comparative Example 1 reached 79.6%), insufficient peel force (e.g., Comparative Example 2 only had 8 N / m), poor bending performance (e.g., Comparative Examples 1 and 4 showed breakage, and Comparative Example 3 showed light leakage), low cycle retention rates (e.g., Comparative Example 2 only had 76%), and high electrolyte swelling rates (e.g., Comparative Example 1 reached 32%). Their overall performance was inferior to that of the Example.

[0316] The reasons are analyzed as follows:

[0317] The second soft monomer in Examples 1 to 6 has a glass transition temperature of -70℃ (isooctyl acrylate) or -55℃ (n-butyl acrylate), both lower than -50℃. This lowers the glass transition temperature of the copolymer, keeping the molecular chains in a highly elastic state at room temperature. With sufficient chain segment mobility, the binder can dissipate energy through chain segment rearrangement during electrode bending, preventing stress concentration. No cracking occurs after more than 15 bends. Secondly, the first soft monomer providing basic flexibility is mixed with the second soft monomer providing ultra-low temperature flexibility in a certain proportion, forming a gradient flexible structure that ensures both room temperature flexibility and low-temperature impact resistance. Thirdly, the hard monomer provides rigid segments, forming physical cross-linking points with the soft monomer to prevent excessive chain slippage and ensure cohesiveness and peel strength meet 15~17 N / m. Simultaneously, the appropriate amount of carboxyl groups provided by the hydrophilic monomer forms a dense network with the hydrophobic segments, inhibiting electrolyte penetration and reducing interfacial relaxation caused by binder swelling. In addition, the binder maintains structural integrity during repeated charging and discharging, effectively buffering the volume expansion of graphite (approximately 10%~12%) and ensuring that the interface does not fail due to fatigue.

[0318] Based on the test data from Examples 1 and 2 and Comparative Examples 1 and 2 in Table 1, it can be concluded that when the mass ratio of hydrophilic monomers (hydrophilic functional monomers and hydrophilic monomers) to the mass of various monomers is controlled at 45%~55%, the hydrophilic monomers can provide an appropriate amount of carboxyl groups -COOH. Under neutralization conditions at pH 7.5, some of these carboxyl groups will ionize to form -COO. - It also constructs a suitable hydration layer; at the same time, a microphase separation structure is formed between an appropriate amount of carboxyl groups and hydrophobic segments, in which the hydrophobic segments curl inward to provide sufficient cohesive force for the binder, while the hydrophilic segments extend outward, effectively ensuring the dispersion stability of the negative electrode slurry, thereby improving the overall performance of the electrode.

[0319] In Comparative Example 1, the hydrophilic monomers accounted for 56% of the total mass of various monomers, exceeding 55%. After neutralization, the -COO⁻ density was too high, resulting in excessively extended molecular chains and a highly hydrated "brush-like" structure. Upon standing, the electrostatic repulsion between chains weakened, leading to physical cross-linking and a surge in slurry viscosity. Furthermore, the excessive carboxyl groups formed a dense hydrogen bond network, providing initial strength but lacking an energy dissipation mechanism. When the electrode was bent, stress could not be released, resulting in brittle fracture. The excessive number of hydrophilic segments allowed for easy electrolyte penetration, and the network loosened after swelling, leading to poor long-term cycling performance.

[0320] In Comparative Example 2, the hydrophilic monomer accounted for 44% of the total mass of the various monomers, which is less than 45%. After neutralization, the -COO⁻ density was too low, resulting in weak hydrogen bonding between the polymer and water, and a thin hydration layer. The initial viscosity of the slurry was only 2400 mPa. After standing, the particles settle, and although the viscosity rebound is small, there is severe sedimentation at the bottom; at the same time, the carboxyl group ratio decreases, which reduces the bonding force with copper foil and graphite, and the electrode peeling force decreases.

[0321] Based on the test data of Example 1 and Comparative Example 3 in Table 1, it can be analyzed that the glass transition temperature of the second soft monomer (2-hydroxyethyl acrylate) in Comparative Example 3 is -15℃, which is greater than -50℃. This leads to an increase in the glass transition temperature of the copolymer. An increased glass transition temperature means that the chain segments are close to the glassy state at room temperature, resulting in decreased mobility. When the electrode is bent, stress concentration easily occurs, leading to microcracks and light leakage. At the same time, the periodic stress generated by the volume expansion of graphite during charging and discharging cannot be buffered, leading to gradual interface fatigue failure and a decrease in cycle retention rate.

[0322] Based on the test data of Example 1 and Comparative Example 4 in Table 1, it can be analyzed that when the mass ratio of soft monomers to the mass ratio of multiple monomers is low, only 28% (less than 30%), and the mass ratio of hard monomers to the mass ratio of multiple monomers is relatively high, reaching 67% (more than 65%), the polymer rigidity is enhanced. When the electrode is bent, stress cannot be released, leading to brittle fracture. Excessive cohesion causes embrittlement. Too many rigid segments provided by hard monomers result in an excessively high binder modulus, which cannot adapt to the bending deformation of the electrode, leading to poor electrode processing performance.

[0323] Based on the test data of Example 1 and Comparative Example 5 in Table 1, it can be analyzed that when the mass of soft monomers accounts for a high proportion of the mass of various monomers, reaching 42% or greater than 40%, and the mass of hard monomers accounts for a relatively low proportion of the mass of various monomers, only 53% or less than 55%, the physical entanglement between molecular chains decreases, the cohesive force decreases, and the peeling force drops from 17 N / m to 9 N / m. An excessively high proportion of soft monomers will also lead to a looser polymer network, making it easier for the electrolyte to penetrate and swell.

[0324] Based on the test data of Example 1 and Comparative Example 6 in Table 1, it can be concluded that the hydrophilic functional monomer acrylamide is prone to chain transfer during polymerization. When the dosage reaches 10% or more than 8%, the number of active centers in the reaction system increases, the molecular weight distribution widens, and the polymerization process becomes difficult to control. The amide group is strongly hydrophilic; in excess, the hygroscopicity of the binder increases, the electrode becomes easily damp, the interfacial bonding decreases, and excessive hydrogen bonds are formed between the amide and carboxyl groups, resulting in excessively high crosslinking density, restricted molecular chain movement, and a decrease in the number of bends.

[0325] In summary, the binder provided in this application for use in graphite anodes possesses excellent electrode flexibility, slurry stability, and interfacial bonding strength.

[0326] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A binder for use in graphite anodes, characterized in that, This includes polymers composed of multiple monomers; The plurality of monomers includes soft monomers among hydrophobic monomers and hydrophilic monomers; wherein, the hydrophilic monomers include hydrophilic functional monomers and hydrophilic monomers, the mass of the hydrophilic monomers accounts for 45% to 55% of the mass of the plurality of monomers, the soft monomers include a first soft monomer and a second soft monomer, and the glass transition temperature of the second soft monomer is less than -50°C.

2. The adhesive according to claim 1, characterized in that, The mass of the soft monomer accounts for 30% to 40% of the mass of the various monomers; The mass of the first soft monomer is greater than the mass of the second soft monomer.

3. The adhesive according to claim 1 or 2, characterized in that, The hydrophilic functional monomer includes at least one of acrylate, methacrylate, methacrylamide, and acrylamide; And / or, The hydrophilic functional monomer accounts for 3% to 8% of the total mass of the various monomers; And / or, The hydrophilic monomer includes at least one of acrylic acid, methacrylic acid, ethyl acrylate, butyl acrylate, isooctyl acrylate, acrylamide, and methacrylamide.

4. The adhesive according to claim 1 or 2, characterized in that, The first soft monomer includes at least one of ethyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylene tert-carbonate, n-octyl acrylate, and laurate. And / or, The second soft monomer includes any one of 2-ethylhexyl acrylate, n-butyl acrylate, and isooctyl acrylate.

5. The adhesive according to claim 1 or 2, characterized in that, The plurality of monomers also includes the hard monomers among the hydrophobic monomers; The hard monomer includes at least one of acrylic acid, methyl acrylate, vinyl acetate, methyl methacrylate, ethyl methacrylate, acrylonitrile, isopropyl methacrylate, and isobutyl methacrylate.

6. A method for preparing an adhesive as described in any one of claims 1 to 5, characterized in that, The method includes: A bonding precursor fluid is prepared based on a variety of monomers and an initiator solution; wherein the variety of monomers includes soft monomers among hydrophobic monomers and hydrophilic monomers, the hydrophilic monomers include hydrophilic functional monomers and hydrophilic monomers, the mass of the hydrophilic monomers accounts for 45% to 55% of the mass of the variety of monomers, the soft monomers include a first soft monomer and a second soft monomer, and the glass transition temperature of the second soft monomer is less than -50°C. The binder is obtained by cooling the precursor fluid and adjusting its pH value to a preset range.

7. The method according to claim 6, characterized in that, The initiator solution is prepared by dissolving the initiator in deionized water, wherein the mass of the initiator accounts for 0.5% to 2% of the mass of the plurality of monomers.

8. The method according to claim 6 or 7, characterized in that, The plurality of monomers further includes the hard monomers among the hydrophobic monomers; the method further includes: The soft monomer and the hydrophilic monomer are weighed according to a mass ratio of (30%~40%):(45%~55%), wherein the mass of the first soft monomer is greater than the mass of the second soft monomer. The hydrophilic functional monomers were obtained by weighing, accounting for 3% to 8% of the mass of the various monomers.

9. A graphite negative electrode sheet, characterized in that, It includes graphite, conductive agents, and adhesives as described in any one of claims 1 to 5, or adhesives prepared by the method described in any one of claims 6 to 8.

10. A lithium-ion battery, characterized in that, It includes a positive electrode, an electrolyte, a separator, and a graphite negative electrode as described in claim 9.

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