A negative electrode binder, a method for preparing a negative electrode binder, a negative electrode sheet, and a battery

Abstract

The application provides a negative electrode binder, a preparation method of the negative electrode binder, a negative electrode sheet and a battery; the negative electrode binder comprises a polymer, and the polymer comprises a core and a plurality of connecting arms connected to the core; the core is formed by cross-linking itaconic acid units, first acrylic acid units and a cross-linking agent; the connecting arms are block copolymers, and the block copolymers comprise a chain segment A and a chain segment B at the end of the chain segment A; the chain segment A is a polybutadiene chain segment with an acrylate at the end; and the chain segment B is an acrylic acid polymer chain segment obtained by polymerization of second acrylic acid units. The negative electrode binder provided by the application is cross-linked by itaconic acid units, first acrylic acid units and a cross-linking agent, and a large number of polar groups strengthen the interfacial bonding force; in the block structure of the connecting arms, the chain segment A improves the peeling strength, and the chain segment B gives flexibility to buffer the volume expansion of the negative electrode, thereby effectively solving the problems of brittle fracture of the negative electrode sheet, powder dropping of the thick electrode and insufficient adhesion of the water-based binder.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode binder, a method for preparing the negative electrode binder, a negative electrode sheet, and a battery. Background Technology

[0002] In the field of lithium-ion battery anode manufacturing, conventional anode preparation processes suffer from problems such as easy brittleness during rolling and low electrode yield. Especially when the areal density and thickness of the electrode increase, powder shedding becomes severe and the electrode peel strength decreases. While water-based binders (such as CMC, PAA, and SA) have emerged in recent years and are environmentally friendly, they generally suffer from high brittleness, insufficient adhesion, and rapid capacity decay in the later stages of cycling. Furthermore, existing water-based anodes commonly use pre-dissolved polymers (such as CMC-SBR and PAA-CMC), and their Tg (glass transition temperature) increases after drying, leading to easy brittleness during rolling. Simultaneously, the trend towards higher energy density (>300Wh / kg) in power batteries further exacerbates these issues. -1 The development of high-load processes and thick electrodes is underway, but existing water-based processes cannot meet the high load requirements and need to be adapted to existing production lines to solve problems such as brittleness, thick electrodes and energy consumption. Summary of the Invention

[0003] To address the problems of powder shedding and low peel strength of existing negative electrode sheets, which lead to electrode brittleness and inapplicability to thick electrodes and high-energy-consumption batteries, this paper provides a negative electrode binder, a method for preparing the negative electrode binder, a negative electrode sheet, and a battery.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: On one hand, the present invention provides a negative electrode binder comprising a polymer, the polymer comprising a core and a plurality of connecting arms connected to the core; The core is formed by crosslinking itaconic acid units, first acrylic acid units and a crosslinking agent; The kernel and multiple connecting arms connected to the kernel; The core is formed by crosslinking itaconic acid units, first acrylic acid units and a crosslinking agent; The connecting arm is a block copolymer, wherein the block copolymer includes segment A and segment B located at the end of segment A, segment A is a polybutadiene segment with acrylate end, and segment B is an acrylic polymer segment obtained by polymerization of a second acrylic unit.

[0005] Optionally, the degree of polymerization of A is 45-65, and the degree of polymerization of segment B is 10-15; and / or The number of connecting arms connected to a single core is 4-8.

[0006] Optionally, the crosslinking agent comprises a first crosslinking unit and a second crosslinking unit, wherein the first crosslinking unit comprises a reversible crosslinking monomer with carboxylic acid coordination function, and the reversible crosslinking monomer with carboxylic acid coordination function comprises one or more of itaconic acid-zinc chelate or acrylic acid-copper chelate; and / or, The second crosslinking unit includes one or more of N,N′-methylenebisacrylamide monomer, ethylene glycol dimethacrylate monomer, trimethylolpropane triacrylate monomer, and divinylbenzene monomer.

[0007] Optionally, in the core, the itaconic acid unit has a molar fraction of 55-75 mol%, and the molar ratio of the second crosslinking unit to the carboxylic acid unit is 1:20-1:30, wherein the carboxylic acid unit includes an itaconic acid unit and a first acrylic acid unit.

[0008] Optionally, based on the total amount of the polymer, the mass percentage of the first crosslinking unit is 0.05%-0.3%; the mass percentage of the second crosslinking unit is 0.1%-1.0%; and / or, The molar ratio of the first crosslinking unit to the second crosslinking unit is (1:3) - (1:10).

[0009] Optionally, the mass ratio of the itaconic acid unit, the first acrylic acid unit and the crosslinking agent is (10~25):(60~80):(2~5).

[0010] Optionally, the molar ratio of cis-1,4, trans-1,4, and 1,2-vinyl in the polybutadiene segments is (20-30):(40-50):(20-30).

[0011] Optionally, the diameter of the core is 5-20 nm, and the length of the connecting arm is 30-100 nm.

[0012] Optionally, the glass transition temperature of the core is 125-140°C, and the glass transition temperature of the connecting arm is -75 to -65°C.

[0013] Optionally, the carboxylic acid content of the kernel is 6.5-8.0 mmol g. -1 .

[0014] Optionally, the number-average molecular weight Mn of the polymer is 120,000-180,000 g / mol. -1 Molecular weight distribution K≤1.25; The viscosity of the polymer in an aqueous solution with a solid content of 2 wt% at 25 °C is 100-2000 mPa·s; The average molecular weight (Mn) of the negative electrode binder after drying and film formation is 30,000-150,000 g / mol. -1 The tensile strength is 5-20 MPa, and the elongation at break is 60-200%.

[0015] Optionally, the swelling degree of the negative electrode binder is ≤80%.

[0016] Optionally, the method for preparing the negative electrode binder includes the following steps: The itaconic acid unit, the first acrylic acid unit, and the crosslinking agent react under high temperature conditions to form the core. Add polybutadiene block arms with acrylate ends, and initiate a polymerization reaction; A second acrylic acid unit is added, and a polymerization reaction is carried out to obtain a negative electrode binder.

[0017] Optionally, the reaction temperature of the itaconic acid unit, the first acrylic acid unit, and the crosslinking agent is 68°C to 72°C, and an initiator is added dropwise during the reaction.

[0018] Optionally, the reaction temperature for adding the polybutadiene block arm with acrylate end is 63°C to 68°C, and an initiator is added dropwise during the reaction.

[0019] Optionally, the reaction temperature for adding the second acrylic acid unit is 70°C to 74°C, and an initiator is added dropwise during the reaction.

[0020] On the other hand, the present invention provides a negative electrode sheet, comprising the aforementioned negative electrode adhesive, or a negative electrode adhesive prepared by the method for preparing the aforementioned negative electrode adhesive.

[0021] On the other hand, the present invention provides a battery including the aforementioned negative electrode.

[0022] The beneficial effects of this application are as follows: The negative electrode binder provided in this application has a core formed by crosslinking itaconic acid units, first acrylic acid units, and a crosslinking agent. A large number of polar groups enhance the interfacial bonding force with the negative electrode active material and current collector. In the block copolymer of its connecting arms, the polybutadiene segment A, which is an acrylate ester, provides polar bonding sites, improving the problem of low peel strength of the negative electrode sheet. The acrylic polymer segment (B) imparts flexibility, giving the polymer high toughness and buffering the volume expansion stress during the charging and discharging process of the silicon-based negative electrode, reducing electrode sheet brittleness and powder shedding. The core formed by the crosslinking of the itaconic acid units, first acrylic acid units, and crosslinking agent, along with the flexible connecting arms in the block copolymer, synergistically form a network structure that combines rigidity and flexibility. This structure can limit swelling through core crosslinking and alleviate volume change stress through the flexible acrylic polymer segments, effectively solving the problems of easy brittleness of negative electrode sheets during rolling, powder shedding of thick electrodes, and insufficient adhesion of aqueous binders in conventional processes. This allows the prepared negative electrode sheet to be adapted to thick electrodes and high-energy-density power batteries. Detailed Implementation

[0023] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] This invention provides a negative electrode binder comprising a polymer, the polymer comprising a core and a plurality of connecting arms connected to the core; The core is formed by crosslinking itaconic acid units, first acrylic acid units and a crosslinking agent; The connecting arm is a block copolymer, wherein the block copolymer includes segment A and segment B located at the end of segment A, segment A is a polybutadiene segment with acrylate end, and segment B is an acrylic polymer segment obtained by polymerization of a second acrylic unit.

[0025] Specifically, in the negative electrode binder provided in this application, its core is formed by cross-linking itaconic acid units, first acrylic acid units, and a cross-linking agent. A large number of polar groups can enhance the interfacial bonding force with the negative electrode active material and the current collector. In the block copolymer of its connecting arms, the end of the polybutadiene segment A of acrylate provides polar bonding sites, improving the problem of low peel strength of the negative electrode sheet. The acrylic polymer segment (B) imparts flexibility. The flexible segment makes the polymer have high toughness, which can buffer the volume expansion stress during the charging and discharging process of silicon-based negative electrodes and reduce the phenomenon of electrode sheet brittleness and powder shedding. The core formed by cross-linking itaconic acid units, first acrylic acid units, and cross-linking agents works synergistically with the flexible connecting arms in the block copolymer to form a network structure that combines rigidity and flexibility. It can limit swelling through core cross-linking and alleviate volume change stress with the help of flexible acrylic polymer segments, thereby effectively solving the problems of easy brittleness of negative electrode sheets during rolling, powder shedding of thick electrodes, and insufficient adhesion of water-based binders in conventional processes. This allows the prepared negative electrode sheet to be adapted to thick electrodes and high energy density power batteries.

[0026] In some embodiments, the degree of polymerization of segment A is 45-65, and the degree of polymerization of segment B is 10-15; and / or The number of connecting arms connected to a single core is 4-8.

[0027] Specifically, the degree of polymerization of the chain segment A (degree of polymerization 45-65) can ensure sufficient polar bonding sites while avoiding dispersion of bonding force caused by excessive chain length, thus ensuring the interfacial bonding strength with the negative electrode active material and the current collector. The degree of polymerization of segment B (degree of polymerization 10-15) is conducive to controlling the length of the butadiene flexible segment, so that it has sufficient toughness to buffer the volume expansion stress of the silicon-based anode, and will not affect the overall structural stability of the electrode due to excessively long segments. The configuration of a single core connecting 4-8 connecting arms can form a three-dimensional network structure with a corresponding density. This can enhance the encapsulation of binder and active material through the synergy of multiple connecting arms, reducing the risk of powder shedding in the preparation of thick electrodes. It can also avoid excessive density of the three-dimensional network structure due to too many connecting arms, ensuring electrolyte wettability and ion transport efficiency. In this way, while strengthening the bonding performance and alleviating the brittleness of the negative electrode sheet, it can further adapt to the needs of thick electrodes and high-energy-density power batteries.

[0028] In some embodiments, the crosslinking agent comprises a first crosslinking unit and a second crosslinking unit, wherein the first crosslinking unit comprises a reversible crosslinking monomer with carboxylic acid coordination function, and the reversible crosslinking monomer with carboxylic acid coordination function comprises one or more of itaconic acid-zinc chelate or acrylic acid-copper chelate; and / or, The second crosslinking unit includes one or more of N,N′-methylenebisacrylamide monomer, ethylene glycol dimethacrylate monomer, trimethylolpropane triacrylate monomer, and divinylbenzene monomer.

[0029] It should be noted that the first crosslinking agent described in this application includes a reversible crosslinking monomer with carboxylic acid coordination function. Compared with conventional crosslinking agents, the crosslinking unit with carboxylic acid coordination has a crosslinking point that depends on the coordination bond and can be dynamically adjusted under mild conditions, which can be regarded as dynamic crosslinking. Compared to the reversible crosslinking monomer (first crosslinking unit) with carboxylic acid coordination function, the second crosslinking agent undergoes free radical polymerization through double bonds to form C-C covalent crosslinking bonds. These covalent bonds have high bond energy and will not break or recombine under normal operating conditions (such as mild temperature and normal pH). That is, once the crosslinking network formed by the second crosslinking agent is solidified, the structure is fixed and cannot achieve dynamic exchange of crosslinking points through external stimulation, unlike the first crosslinking unit.

[0030] Specifically, the first crosslinking unit contains a reversible crosslinking monomer with carboxylic acid coordination function (such as itaconic acid-zinc chelate and acrylic acid-copper chelate). Its coordination bonds can be flexibly broken and recombined during the volume expansion of the silicon-based negative electrode during charging and discharging, effectively buffering stress impact and preventing the electrode from becoming brittle due to excessive rigidity. At the same time, the carboxylic acid group can strengthen the interfacial bonding with the active material and the current collector. The second crosslinking unit contains an N,N′-methylenebisacrylamide crosslinking monomer, which forms a strong crosslinking framework through stable covalent bonds, improving the binder's anti-swelling ability and structural strength, and preventing powder shedding from the thick electrode during preparation and cycling. The synergistic effect of the two types of crosslinking units can effectively ensure the structural integrity of the electrode during rolling and cycling.

[0031] In some embodiments, the core contains an itaconic acid unit with a molar fraction of 55-75 mol%, and the molar ratio of the second crosslinking unit to the carboxylic acid unit is 1:20-1:30, wherein the carboxylic acid unit comprises an itaconic acid unit and a first acrylic acid unit.

[0032] Specifically, in the core, the setting of itaconic acid unit molar fraction of 55-75 mol% can ensure that there are sufficient carboxylic acid polar groups in the core, maximize the interfacial bonding force with the negative electrode active material and the current collector, and thus improve the powder shedding of the electrode sheet. The molar ratio of the second crosslinking unit to the carboxylic acid unit is 1:20-1:30, which can ensure the stability of the core crosslinking structure and avoid swelling, while preventing the core from becoming too rigid due to excessive crosslinking. This allows the core and the connecting arms to work together to form a network structure that is both rigid and flexible.

[0033] In some embodiments, the mass percentage of the first crosslinking unit is 0.05%-0.3% based on the total amount of the polymer; the mass percentage of the second crosslinking unit is 0.1%-1.0%; and / or, The molar ratio of the first crosslinking unit to the second crosslinking unit is (1:3) - (1:10).

[0034] Specifically, when the mass percentage of the first crosslinking unit is limited to 0.05%-0.3% based on the total polymer content, it is beneficial to provide stress regulation capability to buffer the volume expansion of the negative electrode through coordination bonds, while avoiding a decrease in bonding strength due to excessive content. Similarly, when the mass percentage of the second crosslinking unit is 0.1%-1.0%, the network rigidity can be strengthened by stable covalent bonds, preventing the thick electrode from swelling and shedding powder during preparation and cycling, while avoiding the electrode sheet from becoming brittle due to excessive content. The molar ratio of the first crosslinking unit to the second crosslinking unit (1:3)-(1:10) is beneficial to further ensure the synergistic adaptation between dynamic crosslinking (first crosslinking unit) and permanent crosslinking (second crosslinking unit), which not only preserves the flexibility of the network to cope with volume changes, but also maintains the long-term stability of the structure, ultimately ensuring the reliability of the electrode's performance in high-energy-density batteries.

[0035] In some embodiments, the mass ratio of the itaconic acid unit, the first acrylic acid unit and the crosslinking agent is (10~25):(60~80):(2~5).

[0036] By setting the mass ratio of itaconic acid units, first acrylic acid units, and crosslinking agents to (10~25):(60~80):(2~5), sufficient polar sites are provided to ensure basic interfacial bonding with the negative electrode active material and current collector, reducing the risk of powder shedding. Specifically, itaconic acid units within this ratio range can further supplement carboxylic acid groups, enhancing the interaction between the binder and the active material, while providing more reaction sites for subsequent crosslinking reactions. Crosslinking agents within this range can ensure the formation of a stable crosslinked network in the core, avoid swelling and deformation during thick electrode fabrication, effectively buffer the volume expansion stress of the negative electrode during charging and discharging, and prevent electrode brittleness.

[0037] In some embodiments, the molar ratio of cis-1,4, trans-1,4, and 1,2-vinyl in the polybutadiene segments is (20-30):(40-50):(20-30).

[0038] Specifically, among the above molar ratios, the trans-1,4 structure (40-50 mol%) has the highest proportion, giving the polybutadiene segments a certain rigidity, ensuring the overall structural stability of the connecting arm, and preventing the electrode from deforming during rolling or cycling due to excessive flexibility; the cis-1,4 structure (20-30 mol%) can provide excellent segment flexibility, effectively absorbing the volume expansion stress during charging and discharging of the silicon-based negative electrode; the 1,2-vinyl structure (20-30 mol%) can enhance the interaction with the core and active materials through the side chain double bonds, supplementing the bonding sites. The synergy of these three factors helps to achieve the best balance between the flexibility and structural stability of the connecting arm, further optimizing the binder's ability to buffer the volume expansion of the negative electrode and prevent the electrode from becoming brittle.

[0039] In some embodiments, the diameter of the core is 5-20 nm, and the length of the connecting arm is 30-100 nm.

[0040] Specifically, when the core diameter is in the range of 5-20 nm, a core anchoring point of appropriate size can be formed, which can not only densely distribute polar groups to enhance the interfacial bonding force with the negative electrode active material and current collector, reducing the risk of powder shedding, but also avoid excessive voids in the network due to an excessively large core, thus ensuring the compactness of the electrode structure. With an arm length range of 30-100nm, the connecting arms can ensure sufficient bridging between different active material particles. This effectively buffers the volume expansion stress during charging and discharging of the silicon-based negative electrode through flexible chain segments, preventing the electrode from becoming brittle. It also avoids insufficient connection between particles due to excessively short arm length, or chain segment entanglement due to excessively long arm length, thus ensuring the uniformity and stability of the internal network of the thick electrode.

[0041] In some embodiments, the glass transition temperature of the core is 125~140°C, and the glass transition temperature of the connecting arm is -75~-65°C.

[0042] Specifically, the high glass transition temperature of the core (125-140°C) ensures that it maintains structural rigidity during the high-temperature process of battery manufacturing, avoiding a decrease in adhesion due to softening. At the same time, it provides stable skeleton support for the electrode, reducing the risk of deformation and powder shedding of thick electrodes during processing and cycling. The low glass transition temperature of the connecting arm (-75~-65℃) ensures excellent flexibility within the normal operating temperature range of the battery. This effectively buffers the volume expansion stress during charging and discharging of the silicon-based negative electrode, preventing the electrode from becoming brittle due to excessive rigidity. The combination of a core with a high glass transition temperature and a connecting arm with a low glass transition temperature, along with their synergistic thermodynamic properties, ensures structural stability during electrode processing and provides the ability to regulate stress during cycling.

[0043] In some embodiments, the carboxylic acid content of the kernel is 6.5-8.0 mmol g. -1 .

[0044] Specifically, the carboxylic acid content within this range ensures that there are sufficient polar carboxylic acid groups in the core, which can tightly bind the surface of the negative electrode active material and the current collector through strong interactions such as hydrogen bonds and coordination bonds, significantly improving the interfacial bonding strength. At the same time, this content will not cause excessive hydrophilicity of the core or uncontrolled cross-linking reaction due to excessive carboxylic acid groups, thus maintaining the stability of the core structure and avoiding swelling and deformation of the thick electrode after being wetted by the electrolyte, achieving a balance between bonding performance and battery electrochemical stability.

[0045] In some embodiments, the number-average molecular weight Mn of the polymer is 120,000-180,000 g / mol. -1 Molecular weight distribution K≤1.25; The viscosity of the polymer in an aqueous solution with a solid content of 2 wt% at 25°C is 100-2000 mPa·s; The average molecular weight (Mn) of the negative electrode binder after drying and film formation is 30,000-150,000 g / mol. -1 The tensile strength is 5-20 MPa, and the elongation at break is 60-200%.

[0046] Specifically, the polymer has a number-average molecular weight of 120,000-180,000 g / mol and a distribution ≤1.25, which ensures uniform molecular chain length and avoids insufficient adhesion due to excessively low molecular weight or difficulties in homogenization and dispersion due to excessively high molecular weight. The viscosity of the 2wt% aqueous solution at 25℃ is 100-2000 mPa·s, which is suitable for coating processes of thick electrode homogenates, ensuring the fluidity of the slurry to achieve uniform coating, while avoiding uneven coating thickness caused by excessively low viscosity.

[0047] In addition, the average molecular weight (Mn) of the negative electrode binder after drying and film formation is 30,000-150,000 g mol. -1 Compared to the decrease in polymer molecular weight, the reasons are speculated to be due to the effects of the drying process and changes in the molecular chain. Specifically, firstly, during drying and baking, the polymer molecular chain may undergo partial controllable degradation, such as the breakage of chain ends or weak bond sites under heat, resulting in a shortening of the molecular chain length; secondly, during film formation, some low molecular weight fragments may be lost with the evaporation of moisture, or due to the selectivity of the crosslinking reaction (such as preferential formation of short chain crosslinks), the average length of the effective molecular chain in the final film decreases; thirdly, during in-situ polymerization, if the activity of the initiator or catalyst changes during the drying stage, some long chains may not fully participate in crosslinking and break, further reducing the average molecular weight after film formation.

[0048] In some embodiments, the swelling degree of the negative electrode binder is ≤80%.

[0049] It should be noted that a low degree of swelling ensures that the binder undergoes only a very small amount of volume expansion in the electrolyte wetting environment, avoiding the loosening of the cross-linked network and the decrease in adhesion due to excessive swelling, thereby reducing the interfacial separation between the active material and the current collector. Specifically, the swelling degree of the negative electrode binder described in this application is ≤80%. A negative electrode binder within this swelling degree range is beneficial to maintaining the compactness and integrity of the internal structure of the thick electrode, ensuring the assembly accuracy and internal space stability of the battery, and ensuring the stability of the electrochemical performance of the high energy density battery during long-term cycling.

[0050] Furthermore, test results show that when the swelling degree of the negative electrode binder described in this application is between 10% and 40%, it has a better overall effect when applied to the negative electrode sheet.

[0051] In some embodiments, the method for preparing the negative electrode binder includes the following operations: The itaconic acid unit, the first acrylic acid unit, and the crosslinking agent react under high temperature conditions to form the core. Add polybutadiene block arms with acrylate ends, and initiate a polymerization reaction; A second acrylic acid unit is added, and a polymerization reaction is carried out to obtain a negative electrode binder.

[0052] Specifically, the first step of high-temperature reaction to prepare the core ensures that the itaconic acid unit, the first acrylic acid unit, and the crosslinking agent are fully crosslinked to form a stable core with sufficient polar groups, laying the foundation for subsequent enhancement of interfacial adhesion. The second step of adding polybutadiene block arms with acrylate ends can precisely introduce a flexible and polar connecting arm structure, ensuring its function of buffering volume expansion and supplementing bonding sites. The third step of adding the second acrylic acid unit can further optimize the polar characteristics of the connecting arm ends and strengthen the interaction with the active material.

[0053] The preparation method of the negative electrode binder includes the following specific operations: S1: Mix itaconic acid unit, first acrylic acid unit and crosslinking agent with emulsifier in a ratio of (10~25): (60~80): (2~5)), and dissolve the mixture in deionized water to obtain a premixed solution; The premixed liquid was heated under a protective atmosphere (N2) and stirred (stirring speed controlled at 6-8 ms). -1 ), forming micelles (average micelle size 80-120 nm). The initiator (potassium persulfate / sodium bisulfite redox pair) is added dropwise at a uniform rate, and the temperature is maintained. The itaconic acid unit provides α,β-unsaturated carboxylic acid active sites, which undergo free radical copolymerization with the double bond of the crosslinking agent to obtain the core. S2: 1,5-cyclooctadiene, cis-1,4-butanediol monoacrylate (chain transfer agent), Grubbs-II catalyst, and toluene are reacted at 50°C for 0.5-2 h in a mass percentage ratio of (20-25):(3-4):(0.05-0.1):(70-76) to obtain α,ω-dihydroxypolybutadiene oligomer (Mn 3000-6000, K≤1.25); The oligomer was acylated with acryloyl chloride-triethylamine at 0-5℃ for 4 h, washed with water and dried to obtain a butadiene grafting agent with acrylate double bonds at the end; S3: Cool down to 63-68℃, add 40 wt% of the above butadiene grafting agent at a uniform rate within 60-120 min, and simultaneously add 0.2-0.4 wt% of initiator (potassium persulfate). The acrylate double bond at the end of the butadiene grafting agent combines with the free radical on the core surface to form acrylate polybutadiene block arms. S4: After the block arm reaction is complete, raise the temperature to 70-74℃ and add acrylic monomers (acrylic acid, methacrylic acid or 2-carboxyethyl acrylate, in an amount of 3-6 wt% of the total monomers). Prepare a 5 wt% aqueous solution with the remaining initiator (0.1-0.3 wt%) and add it dropwise in 2-3 batches to ensure that the free radical concentration decreases batch by batch and avoids rapid polymerization. Acrylic monomers couple or transfer with the terminal free radicals of the block arms within 30-60 min, forming terminal carboxyl groups with a density of 0.4-0.8 mmol g. -1 After the reaction is complete, the temperature is rapidly reduced to ≤40℃, and NaHCO3 or NH3·H2O is added to adjust the pH to 6.5-7.5 to terminate the residual free radicals. The mixture is then filtered to remove impurities and obtain the negative electrode binder.

[0054] In short, in S1, itaconic acid units, first acrylic acid units and crosslinking agents are mixed in a specific ratio, and micelles are formed under nitrogen protection and a specific stirring speed. Then, free radical copolymerization is initiated by an initiator to achieve a high-temperature reaction to form the core. S2 first prepares oligomers and acylates them to obtain butadiene grafting agents. S3 adds the butadiene grafting agents at a specific temperature and adds an initiator to combine them with free radicals on the core surface, thus completing the process of polybutadiene of acrylate. After heating S4, acrylic monomers are added, and initiators are added dropwise in batches to control the concentration of free radicals, allowing the monomers to react with the free radicals at the end of the block arms to form end-capped segments. Finally, the pH is adjusted and the mixture is filtered to obtain the negative electrode binder.

[0055] In some embodiments, the reaction temperature of the itaconic acid unit, the first acrylic acid unit, and the crosslinking agent is 68°C to 72°C, and an initiator is added dropwise during the reaction.

[0056] Specifically, the reaction temperature of 68℃~72℃ is conducive to the copolymerization of itaconic acid unit, first acrylic acid unit, and crosslinking agent. It can ensure sufficient monomer activity, promote the full crosslinking reaction, and form a dense core with uniformly distributed polar groups. It can also avoid excessive temperature causing monomer volatilization or excessive crosslinking, preventing the core from becoming too rigid and causing electrode brittleness, or excessive temperature causing incomplete reaction and insufficient core bonding performance. At the same time, the method of adding the initiator dropwise can control the concentration of free radicals in the system, avoid local bursting caused by adding the initiator all at once, ensure uniform core particle size and structural stability, and reduce the problem of electrode powder shedding caused by uneven core morphology.

[0057] In some embodiments, the reaction temperature for adding the polybutadiene block arm with acrylate end is 63°C to 68°C, and an initiator is added dropwise during the reaction.

[0058] Specifically, the temperature range of 63℃~68℃ can ensure that the acrylate double bond at the end of the butadiene grafting agent reacts efficiently with the free radicals on the core surface to achieve a stable connection between the block arm and the core, while avoiding excessive polymerization of butadiene segments and reduced flexibility due to excessively high temperature, or slow reaction rate and insufficient grafting of block arms due to excessively low temperature. Adding an initiator can prevent block arm entanglement or uneven particle size, ensuring the uniformity of block arm spatial distribution. This allows the butadiene segments to fully exert their flexible buffering effect, relieving the volume expansion stress of the negative electrode, while also allowing the acrylic segments to uniformly provide polar bonding sites, enhancing interfacial bonding.

[0059] In some embodiments, the reaction temperature for adding the second acrylic unit is 70°C to 74°C, and an initiator is added dropwise during the reaction.

[0060] Specifically, the temperature range of 70℃~74℃ ensures efficient coupling between acrylic monomers and the terminal free radicals of the block arms, achieving uniform grafting of the end-capping segments and supplementing sufficient polar carboxylic acid groups to enhance the interfacial bonding with the negative electrode active material and current collector. It also avoids the situation where the temperature is too high, causing thermal aging and reduced flexibility of the butadiene segments in the block arms, or the temperature is too low, resulting in incomplete end-capping reaction and insufficient polar sites. At the same time, the addition of initiator prevents localized burst polymerization caused by adding initiator at once, ensuring uniform length and consistent distribution of the end-capping segments. This avoids both the loosening of the binder network caused by excessively long segments and the insufficient interfacial bonding caused by excessively short segments.

[0061] Another embodiment of the present invention provides a negative electrode sheet, comprising the aforementioned negative electrode adhesive, or a negative electrode adhesive prepared by the method for preparing the aforementioned negative electrode adhesive.

[0062] Another embodiment of the present invention provides a battery including the aforementioned negative electrode.

[0063] Specifically, the negative electrode sheet of the battery includes the negative electrode binder provided in this application. The core of the negative electrode binder is formed by crosslinking itaconic acid units, a first acrylic acid unit, and a crosslinking agent. A large number of polar groups enhance the interfacial bonding force with the negative electrode active material and the current collector. In the block copolymer of its connecting arms, the polybutadiene segment A, which is an acrylate ester, provides polar bonding sites, improving the problem of low peel strength of the negative electrode sheet. The acrylic polymer segment (B) imparts flexibility, and the flexible segment gives the polymer high toughness, which can buffer the charging and discharging of the silicon-based negative electrode. The volume expansion stress during the electrical process reduces electrode brittleness and powder shedding. The core formed by the cross-linking of the itaconic acid unit, the first acrylic acid unit, and the cross-linking agent, along with the flexible connecting arms in the block copolymer, work synergistically to form a network structure that combines rigidity and flexibility. This structure can limit swelling through core cross-linking and alleviate volume change stress through the flexible acrylic acid polymer segments. This effectively solves the problems of easy brittleness of negative electrode sheets during rolling, powder shedding of thick electrodes, and insufficient adhesion of aqueous binders in conventional processes, enabling the produced negative electrode sheets to be adapted to thick electrodes and high-energy-density power batteries.

[0064] The present invention will be further illustrated by the following examples.

[0065] Table 1 Example 1 This embodiment illustrates the negative electrode binder, the preparation method of the negative electrode binder, the negative electrode sheet, and the battery disclosed in this invention, and includes the following operational steps: Itaconic acid units, first acrylic acid units, and crosslinking agents (itaconic acid-zinc chelate and N,N′-methylenebisacrylamide monomer) are added in a mass ratio of 10:60:2, and 0.2wt% sodium dodecyl sulfate (emulsifier) ​​is added and dissolved in deionized water to prepare a pre-emulsion. The preemulsion was heated to 68°C, and N2 30 was continuously introduced for 30 minutes while stirring (stirring speed controlled at 6 ms). -1 This forms micelles with an average particle size of 80 nm. 0.3 wt% of initiator (potassium persulfate / sodium bisulfite redox pair) was added dropwise to micelles at a uniform rate over 15 min. Then, it was kept at 68℃ for 45 min, where the itaconic acid units provided α,β-unsaturated carboxylic acid active sites, which underwent free radical copolymerization with the double bonds of the crosslinking agent to form a micro-crosslinking density of 2×10⁻⁶. -4 mol cm -3 A core with a diameter of 5 nm; 1,5-Cyclooctadiene, cis-1,4-butanediol monoacrylate (chain transfer agent), Grubbs-II catalyst, and toluene were reacted at 50 °C for 0.5 h in a mass percentage ratio of 20:3:0.05:70 to obtain α,ω-dihydroxypolybutadiene oligomer (Mn 3000-6000, K≤1.25). α,ω-dihydroxy polybutadiene oligomer was acylated with acryloyl chloride-triethylamine at 5°C for 4 h, washed with water and dried to obtain a butadiene grafting agent with acrylate double bonds at the end; Cool down to 63°C, add 40 wt% of the above grafting agent at a uniform rate within 60 min, and simultaneously add 0.2 wt% of initiator (potassium persulfate). The acrylate double bond at the end of the grafting agent combines with the free radical on the core surface to form a polybutadiene block arm of acrylate with an arm length of 30 nm and 4 arms. The molar ratio of cis-1,4-, trans-1,4-, and 1,2-vinyl polybutadiene segments is 20:40:20. After the block arm reaction is complete, the temperature is raised to 74°C, and an acrylic end-capping monomer (acrylic acid, methacrylic acid, or 2-carboxyethyl acrylate, in an amount of 3 wt% of the total monomers) is added. Prepare a 5 wt% aqueous solution by taking 0.3 wt% initiator and add it dropwise in batches to ensure that the free radical concentration decreases batch by batch and avoid rapid polymerization; The capped monomer couples with or transfers to the terminal free radical of the arm chain within 30 min, forming a terminal carboxyl group density of 0.8 mmol / g. -1 After the reaction is complete, rapidly cool to ≤40℃, add NaHCO3 or NH3·H2O to adjust pH to 6.5 to terminate the remaining free radicals; The gel and impurities are removed by vacuum filtration through a 200-400 mesh filter to obtain the negative electrode binder; Take the negative electrode binder, negative electrode active material, conductive agent and deionized water, and premix them in a ratio of 2:92:0.5:95 to obtain the negative electrode slurry; The negative electrode slurry is coated onto the negative electrode current collector, and after curing and drying, a negative electrode sheet is obtained. The negative electrode, positive electrode, and separator are assembled, and electrolyte is injected to obtain the battery.

[0066] Example 2-11 Examples 2-11 illustrate the negative electrode binder, the preparation method of the negative electrode binder, the negative electrode sheet, and the battery disclosed in this invention. They include most of the operations in Example 1, except that: The ratio of itaconic acid unit, first acrylic acid unit, crosslinking agent, type of crosslinking agent, percentage content of crosslinking agent (percentage content of first crosslinking unit, percentage content of second crosslinking unit), type of first crosslinking unit, and type of second crosslinking unit are all based on the data in the corresponding embodiments in Table 1.

[0067] Comparative Example 1 This comparative example is used to illustrate the negative electrode binder, the preparation method of the negative electrode binder, the negative electrode sheet and the battery disclosed in this invention, including most of the operations in Example 1, except that the binder has no connecting arms: Itaconic acid units, first acrylic acid units, and crosslinking agents (itaconic acid-zinc chelate and N,N′-methylenebisacrylamide monomer) were added in a mass ratio of 10:60:2, and 0.2 wt% sodium dodecyl sulfate (emulsifier) ​​was added and dissolved in deionized water to prepare a pre-emulsion. The pre-emulsion was heated to 68°C, and N2 was continuously introduced for 30 minutes while stirring (stirring speed controlled at 6 ms). -1 This forms micelles with an average particle size of 80 nm. 0.3 wt% of initiator (potassium persulfate / sodium bisulfite redox pair) was added dropwise to micelles at a uniform rate over 15 min. Then, it was kept at 68℃ for 45 min, where the itaconic acid units provided α,β-unsaturated carboxylic acid active sites, which underwent free radical copolymerization with the double bonds of the crosslinking agent, forming a micro-crosslinking density of 2×10⁻⁶. -4 mol cm -3 A core with a diameter of 5nm.

[0068] Comparative Example 2 The comparative example uses commercially available negative electrode binders: main binder: Showa LB300; auxiliary binder: Daicel CMC 2200.

[0069] Comparative Example 3 This comparative example is used to illustrate the negative electrode binder, the preparation method of the negative electrode binder, the negative electrode sheet and the battery disclosed in this invention, including most of the operations in Example 1, except that there is no chain segment A in the connecting arm of this negative electrode binder.

[0070] Comparative Example 4 This comparative example is used to illustrate the negative electrode binder, the preparation method of the negative electrode binder, the negative electrode sheet and the battery disclosed in this invention, including most of the operations in Example 1, except that there is no chain segment B in the connecting arm of this negative electrode binder.

[0071] Performance testing To objectively evaluate the technical effects of Examples 1-11 and Comparative Examples 1-4, the following non-limiting test methods were used. Unless otherwise stated, all tests were conducted at 25°C and 45% RH. ① Core diameter Equipment: Field emission transmission electron microscope (FE-TEM, 200 kV); Procedure: Disperse the sample in anhydrous ethanol, sonicate for 5 min, then drop it onto a carbon support membrane copper grid and dry at 80℃; randomly collect 100 particle projection profiles and read the number average diameter using image analysis software.

[0072] ② Nucleic acid content Procedure: Weigh 0.1000 g of the dried sample and add 50 mL of 0.01 mol·L⁻¹ solution. -1 NaOH standard solution was prepared and magnetically stirred at 25°C for 2 hours; using phenolphthalein as an indicator, 0.01 mol·L⁻¹ solution was added. -1 Back titrate with HCl until the pink color disappears, then calculate the number of moles of carboxyl groups based on the amount of NaOH consumed, in mmol·g. -1 .

[0073] ③ Core glass transition temperature (Tg) Equipment: Differential scanning calorimeter (DSC, N2 atmosphere); Temperature range: 30~200℃, heating rate: 10℃·min -1 The midpoint of the secondary heating curve is taken as Tg.

[0074] ④ Connecting arm length Equipment: Atomic force microscope (AFM, tapping mode); Steps: Spin-coat a 0.01 wt% binder aqueous solution onto freshly peeled mica sheets and dry at 25°C; randomly measure the profile length of 50 single chains and take the average value.

[0075] ⑤ Connecting arm Tg The test conditions were the same as in ③, and the sample was a solid obtained by freeze-drying the purified linker solution.

[0076] ⑥ Tensile strength Steps: Cast the adhesive into a 50μm thick film and cut it into 20mm×4mm dumbbell strips; test the strips on a universal testing machine at 5mm·min. -1 Tension, record the maximum stress, in MPa.

[0077] ⑦ Swelling degree Procedure: Weigh 0.1000g of dry film (m0) and immerse it in 1mol·L⁻¹ solution. -1 In a LiPF6 EC / DEC = 1:1 (v / v) electrolyte solution, the solution was left to stand at 25°C for 24 hours; after removal, the surface liquid was quickly wiped off, and the wet weight (m1) was measured. Swelling degree = [(m1– m0) / m0] ×100%, and the result is averaged three times.

[0078] The performance of Examples 1-11 and Comparative Examples 1-4 prepared above was tested. The test results are entered into Table 2.

[0079] Table 2 As can be seen from the test results in Table 2, the negative electrode binders of Examples 1-11 have significantly better test performance than those of Comparative Examples 1-4. The core diameter of the examples is concentrated in the range of 6.8-15.1 nm, which is within the range of 5-20 nm in this application. This allows for the dense distribution of polar groups to enhance the interfacial bonding force. Examples 1-11 show that the connecting arm length is stable at 30-33 nm, which can effectively bridge active material particles and buffer volume expansion; The ribocarboxylic acid content in Examples 1-11 was maintained at 6.9-7.4 mmol / g, which met the high polarity requirement of 6.5-8.0 mmol / g, thus contributing to strong adhesion. The core glass transition temperature of Examples 1-11 is 125-129℃, and the glass transition temperature of the connecting arm is -74 to -69℃. The high and low temperature characteristics work together to ensure the stability of electrode processing and the ability to buffer cyclic stress. The tensile strength of Examples 1-11 ranged from 16.3 to 19.9 MPa, which was much higher than that of Comparative Example 1 (8.9 MPa), Comparative Example 2 (12.3 MPa), Comparative Example 3 (7.5 MPa) and Comparative Example 4 (9.2 MPa), indicating that their network structure was more robust. Compared to the swelling degrees of the comparative examples, the swelling degrees of the examples ranged from 13% to 38%, while the swelling degrees of the comparative examples were 49% (Comparative Example 1), 45% (Comparative Example 2), 52% (Comparative Example 3), and 44% (Comparative Example 4). The swelling degrees of the examples were all lower than those of the comparative examples, presumably because the swelling degrees of Comparative Example 1 were lower. Because of the lack of connecting arms, the core formed solely by the itaconic acid unit, the first acrylic acid unit, and the crosslinking agent cannot construct a complete three-dimensional anti-swelling network, and the electrolyte easily penetrates into the core, causing swelling. Comparative Example 2 uses a commercially available conventional aqueous binder, which lacks the core and connecting arms found in the negative electrode binder of this application. This results in insufficient crosslinking density, uneven distribution of polar groups, and weak resistance to electrolyte wetting and swelling. Comparative Example 3 lacks chain segment A in its connecting arms, thus missing the polar bonding sites and network densification enhancement provided by chain segment A. This leads to a decrease in the interfacial bonding force between the connecting arms and the core and active materials, and the presence of voids in the network, allowing the electrolyte to easily penetrate. Comparative Example 4 lacks chain segment B in its connecting arms, thus missing the flexibility and supplementary polar groups provided by chain segment B. This prevents the network from co-optimizing the crosslinking density with the core, resulting in insufficient resistance to electrolyte swelling. Consequently, the swelling degree of the comparative examples is significantly higher than that of the examples.

[0080] In summary, the negative electrode binder provided in this application forms a network structure that combines rigidity and flexibility through the synergistic effect of the core and the flexible connecting arms in the block copolymer. This structure can limit swelling through core crosslinking and alleviate volume change stress through the flexible acrylic polymer segments, thereby effectively solving the problems of easy brittleness of negative electrode sheets during rolling, powder shedding of thick electrodes, and insufficient adhesion of aqueous binders in conventional processes. This allows the prepared negative electrode sheets to be adapted to thick electrodes and high-energy-density power batteries.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A negative electrode binder, characterized in that, The polymer includes a core and a plurality of connecting arms connected to the core; The core is formed by crosslinking itaconic acid units, first acrylic acid units and a crosslinking agent; The connecting arm is a block copolymer, wherein the block copolymer includes segment A and segment B located at the end of segment A, segment A is a polybutadiene segment with acrylate end, and segment B is an acrylic polymer segment obtained by polymerization of a second acrylic unit; the crosslinking agent includes a first crosslinking unit and a second crosslinking unit, the first crosslinking unit includes a reversible crosslinking monomer with carboxylic acid coordination function, and the reversible crosslinking monomer with carboxylic acid coordination function includes one or more of itaconic acid-zinc chelate or acrylic acid-copper chelate; The second crosslinking unit includes one or more of N,N′-methylenebisacrylamide monomer, ethylene glycol dimethacrylate monomer, trimethylolpropane triacrylate monomer, and divinylbenzene monomer; In the polybutadiene segments, the molar ratio of cis-1,4, trans-1,4, and 1,2-vinyl is (20-30):(40-50):(20-30).

2. The negative electrode binder according to claim 1, characterized in that, The degree of polymerization of segment A is 45-65, and the degree of polymerization of segment B is 10-15; and / or The number of connecting arms connected to a single core is 4-8.

3. The negative electrode binder according to claim 1, characterized in that, In the core, the molar fraction of itaconic acid units is 55-75 mol%, and the molar ratio of the second crosslinking unit to the carboxylic acid unit is 1:20-1:

30. The carboxylic acid unit includes itaconic acid units and first acrylic acid units.

4. The negative electrode binder according to claim 1, characterized in that, Based on the total amount of the polymer, the first crosslinking unit has a mass percentage content of 0.05%-0.3%; the second crosslinking unit has a mass percentage content of 0.1%-1.0%; and / or, The molar ratio of the first crosslinking unit to the second crosslinking unit is (1:3) - (1:10).

5. The negative electrode binder according to claim 1, characterized in that, The mass ratio of the itaconic acid unit, the first acrylic acid unit and the crosslinking agent is (10~25):(60~80):(2~5).

6. The negative electrode binder according to claim 1, characterized in that, The diameter of the core is 5-20nm, and the length of the connecting arm is 30-100nm.

7. The negative electrode binder according to claim 1, characterized in that, The glass transition temperature of the core is 125-140℃, and the glass transition temperature of the connecting arm is -75~-65℃.

8. The negative electrode binder according to claim 1, characterized in that, The carboxylic acid content of the kernel is 6.5-8.0 mmol / g. -1 .

9. The negative electrode binder according to claim 1, characterized in that, The number-average molecular weight of the polymer is Mn, which is 120,000-180,000 g / mol. -1 Molecular weight distribution K≤1.25; The viscosity of the polymer in an aqueous solution with a solid content of 2wt% at 25°C is 100-2000 mPa·s. The average molecular weight (Mn) of the negative electrode binder after drying and film formation is 30,000-150,000 g / mol. -1 The tensile strength is 5-20 MPa, and the elongation at break is 60-200%.

10. The negative electrode binder according to claim 1, characterized in that, The swelling degree of the negative electrode binder is ≤80%.

11. The method for preparing the negative electrode binder according to any one of claims 1-10, characterized in that, Includes the following operations: The itaconic acid unit, the first acrylic acid unit, and the crosslinking agent react under high temperature conditions to form the core. Add polybutadiene block arms with acrylate ends, and initiate a polymerization reaction; A second acrylic acid unit is added, and a polymerization reaction is carried out to obtain a negative electrode binder.

12. The method for preparing the negative electrode binder according to claim 11, characterized in that, The reaction temperature of the itaconic acid unit, the first acrylic acid unit, and the crosslinking agent is 68℃~72℃, and an initiator is added dropwise during the reaction.

13. The method for preparing the negative electrode binder according to claim 11, characterized in that, The reaction temperature for adding polybutadiene block arms with acrylate ends is 63℃~68℃, and an initiator is added dropwise during the reaction.

14. The method for preparing the negative electrode binder according to claim 11, characterized in that, The reaction temperature for adding the second acrylic acid unit is 70℃~74℃, and an initiator is added dropwise during the reaction.

15. A negative electrode sheet, characterized in that, Includes the negative electrode adhesive as described in any one of claims 1-10, or the negative electrode adhesive prepared by the method described in any one of claims 11-14.

16. A battery, characterized in that, Includes the negative electrode sheet as described in claim 15.

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