Adhesives, negative electrode sheets and their preparation methods, batteries, battery packs and electrical equipment

Abstract

This invention discloses an adhesive, a negative electrode sheet, a method for preparing the same, a battery, a battery pack, and electrical equipment. The adhesive comprises styrene-butadiene rubber (SBR) particles, which include first SBR particles and second SBR particles. The ratio of the particle size Dv501 of the first SBR particles to the particle size Dv502 of the second SBR particles is K, where K ≥ 1.2. According to the adhesive of this invention, by controlling the particle size distribution of the adhesive, the bonding ability of the adhesive is improved, the overall bonding effect is enhanced, the peel force of the electrode sheet is increased, the structural stability of the electrode sheet using the above-mentioned adhesive is improved, the risk of delamination during use is reduced, and the service life of the electrode sheet is extended, thereby improving the cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a binder, a negative electrode sheet and its preparation method, a battery, a battery pack and an electrical device. Background Technology

[0002] In the battery industry, to improve the mechanical properties of electrodes during charging and discharging, the bonding performance of binders needs to be optimized, often through chemical modification. However, localized bonding failure can still occur, leading to delamination of the electrode during use and reducing its lifespan.

[0003] Therefore, there is an urgent need for an adhesive to meet the requirement of strong peeling force during the use of electrodes. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. Therefore, one object of this invention is to provide an adhesive that improves the adhesive's bonding ability, enhances the peeling force of the electrode sheet, reduces the risk of delamination of the electrode sheet during use, and thus helps to extend the service life of the electrode sheet.

[0005] According to an embodiment of the first aspect of the present invention, the adhesive comprises: styrene-butadiene rubber particles, the styrene-butadiene rubber particles comprising a first styrene-butadiene rubber particle and a second styrene-butadiene rubber particle, wherein the ratio of the particle size Dv501 of the first styrene-butadiene rubber particle to the particle size Dv502 of the second styrene-butadiene rubber particle is K, and K satisfies: K≥1.2.

[0006] According to the present invention, by adjusting the particle size distribution of the binder, the bonding ability of the binder is improved, the overall bonding effect is improved, the peeling force of the electrode is increased, the structural stability of the electrode using the above-mentioned binder is improved, the risk of delamination of the electrode during use is reduced, the service life of the electrode is improved, and thus the cycle performance of the battery is improved.

[0007] According to some embodiments of the present invention, the adhesive further satisfies: 1.4≤K≤5; and / or, 200nm≤Dv501≤2000nm; and / or, 2nm≤Dv502≤200nm.

[0008] According to some embodiments of the present invention, the adhesive further satisfies: 250nm ≤ Dv501 ≤ 500nm; and / or, 80nm ≤ Dv502 ≤ 180nm.

[0009] According to some embodiments of the present invention, the mass ratio of the first styrene-butadiene rubber particles to the second styrene-butadiene rubber particles is 1:(0.4-9); and / or, the first styrene-butadiene rubber particles account for 10%-70% of the mass of the adhesive; and / or, the second styrene-butadiene rubber particles account for 30%-90% of the mass of the adhesive.

[0010] According to some embodiments of the present invention, the mass ratio of the first styrene-butadiene rubber particle to the second styrene-butadiene rubber particle is 1:(0.6~2.2).

[0011] According to some embodiments of the present invention, the first styrene-butadiene rubber particles and / or the second styrene-butadiene rubber particles comprise modified styrene-butadiene rubber; wherein the modifying groups of the modified styrene-butadiene rubber comprise at least one of carboxyl, hydroxyl, and sulfonic acid groups.

[0012] According to some embodiments of the present invention, the carboxyl group in the modified styrene-butadiene rubber accounts for 1% to 10% of the mass percentage of the binder; and / or, the hydroxyl group in the modified styrene-butadiene rubber accounts for 0.5% to 8% of the mass percentage of the binder; and / or, the sulfonic acid group in the modified styrene-butadiene rubber accounts for 0.1% to 5% of the mass percentage of the binder.

[0013] According to some embodiments of the present invention, the carboxyl group in the modified styrene-butadiene rubber accounts for 1% to 5% of the mass percentage of the adhesive.

[0014] According to a second aspect of the present invention, a negative electrode sheet includes: a negative electrode active material layer, wherein the negative electrode active material layer includes the binder described in the first aspect of the present invention.

[0015] According to some embodiments of the present invention, the binder accounts for 1% to 3% of the mass of the negative electrode active material layer.

[0016] According to some embodiments of the present invention, the negative electrode active material layer further includes polyacrylic acid, wherein the mass percentage of the polyacrylic acid in the negative electrode active material layer is 0.5% to 8%.

[0017] The method for preparing a negative electrode sheet according to a third aspect embodiment of the present invention is suitable for preparing a negative electrode sheet according to the second aspect embodiment of the present invention, comprising the following steps: adding a first styrene-butadiene rubber particle and a second styrene-butadiene rubber particle to a negative electrode active material to form a negative electrode active coating, and coating the negative electrode active coating onto the surface of a current collector to obtain a negative electrode sheet.

[0018] A battery according to a fourth aspect embodiment of the present invention includes: a negative electrode sheet according to the second aspect embodiment of the present invention described above; or a negative electrode sheet prepared by the method for preparing a negative electrode sheet according to the third aspect embodiment of the present invention described above.

[0019] A battery pack according to a fifth aspect embodiment of the present invention includes: a negative electrode sheet according to the second aspect embodiment of the present invention described above; or a negative electrode sheet prepared by the method for preparing a negative electrode sheet according to the third aspect embodiment of the present invention described above; or a battery according to the fourth aspect embodiment of the present invention described above.

[0020] An electrical device according to a sixth aspect embodiment of the present invention includes: a negative electrode sheet according to the second aspect embodiment of the present invention; or a negative electrode sheet prepared by the method for preparing a negative electrode sheet according to the third aspect embodiment of the present invention; or a battery according to the fourth aspect embodiment of the present invention; or a battery pack according to the fifth aspect embodiment of the present invention.

[0021] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0022] In the battery industry, binders, through the viscoelasticity and bonding properties of their polymer chains, can uniformly fix active materials and conductive agents onto the current collector, while simultaneously buffering volume expansion, optimizing slurry dispersion, and improving the mechanical stability and electrochemical performance of the electrodes, thereby achieving high energy density and long cycle life. As market demands for energy density continue to rise, further optimization of the bonding properties of binders remains necessary.

[0023] Existing technologies mainly optimize the electrode through chemical modification (polar groups / crosslinking), composite systems (conductive / nanomaterials), process optimization (dispersion / drying / compacting), and the development of novel binders (self-healing / multifunctionality). However, these methods still cannot effectively solve problems such as localized bonding failure and easy delamination. As a result, the electrode is prone to delamination during use, which reduces the performance of the electrode and affects the cycle performance of the battery.

[0024] To address the aforementioned problems, this application utilizes the synergistic effect of first and second styrene-butadiene rubber particles of different particle sizes to enhance the adhesive's bonding ability, buffer volume changes, reduce crack formation, thereby increasing overall bonding efficiency, improving electrode peel strength, preventing electrode delamination during use, and extending electrode lifespan, thus improving battery cycle performance. The adhesive according to an embodiment of the first aspect of the present invention is described below.

[0025] According to a first aspect of the present invention, the binder comprises styrene-butadiene rubber (SBR) particles. The SBR molecular chain contains flexible segments of butadiene units and a rigid structure of styrene units. SBR possesses excellent elasticity, film-forming properties, and interfacial adhesion. The binder utilizes the viscoelasticity and adhesive properties of the SBR polymer chain to uniformly fix active materials and conductive agents onto the current collector, while simultaneously buffering volume expansion, optimizing slurry dispersion, and improving the mechanical stability and electrochemical performance of the electrode, thereby achieving high energy density and long cycle life in the battery.

[0026] The distribution of styrene-butadiene rubber (SBR) determines the mechanical properties of the electrode during the charging and discharging process. The uniformity of SBR distribution determines the stability of the electrode microstructure and the ion / electron transport efficiency, while the strength of the adhesive force dominates the mechanical strength and cycle life of the electrode.

[0027] Specifically, the styrene-butadiene rubber particles in this application include first styrene-butadiene rubber particles and second styrene-butadiene rubber particles, wherein the ratio of the particle size Dv501 of the first styrene-butadiene rubber particles to the particle size Dv502 of the second styrene-butadiene rubber particles is K, and K satisfies: K≥1.2.

[0028] For example, K can be any value from 1.2, 2, 4, 6, 8, 10, 15, 20, or a range of any combination of both. The ratio of the particle size Dv501 of the first styrene-butadiene rubber (SBR) particles to the particle size Dv502 of the second SBR particles is greater than or equal to 1.2. The first SBR particles form a macroscopic continuous skeleton network, which is beneficial for improving the peel strength of the adhesive and resisting macroscopic stress, rolling stress, and cyclic stress. The second SBR particles can easily penetrate into the micropores, thereby enhancing local anchoring and improving interfacial bonding. Therefore, the ratio K of Dv501 to Dv502 is set reasonably, which is beneficial for fully utilizing the synergistic ability of the first and second SBR particles, improving the bonding ability of the adhesive, buffering volume changes, reducing crack generation, thereby increasing the overall bonding efficiency, preventing the weak layer of the adhesive formed at the electrode-current collector interface from delaminating during rolling or cycling, improving the connection stability and reliability of the electrode using the above-mentioned adhesive, and also improving the service life of the adhesive.

[0029] According to the present invention, by adjusting the particle size distribution of the binder, the bonding ability of the binder is improved, the overall bonding effect is improved, the peeling force of the electrode is increased, the structural stability of the electrode using the above-mentioned binder is improved, the risk of delamination of the electrode during use is reduced, the service life of the electrode is improved, and thus the cycle performance of the battery is improved.

[0030] According to some embodiments of the present invention, the adhesive further satisfies: 1.4 ≤ K ≤ 5.

[0031] For example, K can be any value from 1.4, 1.8, 2, 3, 4, 5, or a range of any combination of both. Under the constraint of the ratio K of Dv501 to Dv502, it helps to further ensure the compactness of the continuous skeleton network formed by the first styrene-butadiene rubber particles, and facilitates the effective filling of the pores of the continuous skeleton network by the second styrene-butadiene rubber particles. This helps to further improve the bonding efficiency of the binder, enhance the cycle performance of the battery, and extend the cycle life of the battery.

[0032] According to some embodiments of the present invention, 200nm ≤ Dv501 ≤ 2000nm, preferably 250nm ≤ Dv501 ≤ 500nm. That is, the particle size of the first styrene-butadiene rubber particle is 200nm to 2000nm, preferably 250nm to 500nm.

[0033] For example, the particle size of the first styrene-butadiene rubber (SBR) particles can be any one or any two of 200 nm, 250 nm, 300 nm, 400 nm, 500 nm, 800 nm, 1000 nm, 1500 nm, 1800 nm, and 2000 nm. When the particle size of the first SBR particles is greater than or equal to 200 nm, it is beneficial to form a suitable continuous skeleton network, and the pores in the continuous skeleton network are suitable for the filling of the second SBR particles, thereby facilitating the synergistic effect of the first and second SBR particles. When the particle size of the first SBR is less than or equal to 2000 nm, it is beneficial to improve the density of the continuous skeleton network formed by the first SBR, thereby ensuring the adhesion of the adhesive and resisting rolling and cyclic stress. The particle size of the first styrene-butadiene rubber (SBR) particles is in the range of 200 nm to 2000 nm, which is beneficial for the formation of a continuous styrene-butadiene rubber network. Simultaneously, it facilitates the filling of larger pores by the second SBR particles, thereby improving the peel strength of the adhesive, resisting macroscopic stress, and resisting rolling and cyclic stress. Furthermore, it provides support, enhancing the impact resistance of the adhesive. Even better results are achieved when the particle size of the first SBR particles is 250 nm ≤ Dv501 ≤ 500 nm.

[0034] According to some embodiments of the present invention, 2nm ≤ Dv502 ≤ 200nm, preferably 80nm ≤ Dv502 ≤ 180nm. That is, the particle size of the second styrene-butadiene rubber particles is 2nm to 200nm, preferably 80nm to 180nm.

[0035] For example, the particle size of the second styrene-butadiene rubber (SBR) particles can be any one or any two of 2 nm, 6 nm, 10 nm, 80 nm, 120 nm, 180 nm, and 200 nm. Therefore, when the particle size of the second SBR particles is within the range of 2 nm ≤ Dv502 ≤ 200 nm, it facilitates the penetration of the SBR particles into the micropores of the current collector surface, enhancing the adhesive performance of the adhesive. Furthermore, the effect is even better when the particle size of the second SBR particles is 80 nm ≤ Dv502 ≤ 180 nm.

[0036] Furthermore, the mass ratio of the first styrene-butadiene rubber granules to the second styrene-butadiene rubber granules is 1:(0.4-9), preferably 1:(0.6-2.3).

[0037] For example, the mass ratio of the first styrene-butadiene rubber (SBR) particle to the second SBR particle can be any one of 1:0.4, 1:0.6, 1:0.8, 1:1, 1:1.5, 1:2.3, 1:4, 1:6, 1:8, or 1:9, or a range between any two. Based on the mass of the first SBR particle, when the mass ratio of the second SBR particle to the first SBR particle is greater than or equal to 0.4, the second SBR particle can fully fill the pores in the continuous skeleton network, which helps ensure the density of the adhesive and thus its bonding strength. Based on the mass of the first SBR particle, when the mass ratio of the second SBR particle to the first SBR particle is less than or equal to 9, the continuous skeleton network formed by the mass of the first SBR particle can meet the filling requirements of the second SBR particle, which helps ensure the adhesiveness of the adhesive. Therefore, when the mass ratio of the first styrene-butadiene rubber (SBR) particles to the second SBR particles is 1:(0.4–9), the cross-linked network formed by the first SBR particles can fully fill the spaces between the second SBR particles, thereby maximizing the synergistic effect of the first and second SBR particles and improving the adhesive's bonding performance. Furthermore, the effect is even better when the mass ratio of the first SBR particles to the second SBR particles is 1:(0.6–2.3).

[0038] According to some embodiments of the present invention, the first styrene-butadiene rubber particles account for 10% to 70% of the mass percentage of the adhesive.

[0039] For example, the mass percentage of the first styrene-butadiene rubber (SBR) particles in the adhesive can be any one of 10%, 20%, 30%, 40%, 60%, or 70%, or a range between any two. When the mass percentage of the first SBR particles in the adhesive is greater than or equal to 10%, it is beneficial to ensure that the mass of the first SBR particles meets the requirements for improving the adhesiveness of the adhesive. When the mass percentage of the first SBR particles in the adhesive is less than or equal to 70%, it is beneficial to ensure the presence of the remaining components in the adhesive (such as the second SBR particles), thereby improving the performance of the adhesive. When the mass percentage of the first SBR particles in the adhesive is in the range of 10% to 70%, the macroscopically continuous network formed by the first SBR particles is suitable for meeting the requirements of the adhesiveness reliability and stability, while also facilitating the presence of the remaining components to improve the performance of the adhesive.

[0040] By mass percentage, the second styrene-butadiene rubber particles account for 30% to 90% of the adhesive.

[0041] For example, the mass percentage of the second styrene-butadiene rubber (SBR) particles in the binder can be any one of 30%, 40%, 50%, 70%, 80%, or 90%, or any value between any two. When the mass percentage of the second SBR particles in the binder is greater than or equal to 30%, the mass of the second SBR particles is sufficient to fill the pores in the continuous skeleton network; when the mass percentage of the second SBR particles in the binder is less than or equal to 90%, it is beneficial for the second SBR particles to be less dispersed after filling the pores, thus ensuring the adhesiveness of the binder. When the mass percentage of the second SBR particles in the binder is in the range of 30% to 90%, the specific surface area of ​​the second SBR particles is more reasonable, avoiding irreversible agglomeration of the binder due to van der Waals forces, hydrogen bonds, etc., thereby helping to ensure the uniformity of the binder's dispersion.

[0042] According to other embodiments of the present invention, the first styrene-butadiene rubber particles and / or the second styrene-butadiene rubber particles comprise modified styrene-butadiene rubber. Modifying the styrene-butadiene rubber through chemical modification is beneficial for improving the performance of the corresponding first and / or second styrene-butadiene rubber particles on the adhesive.

[0043] The modified styrene-butadiene rubber (SBR) incorporates at least one of carboxyl, hydroxyl, and sulfonic acid groups. Carboxyl groups can form hydrogen bonds or coordination bonds with metals (such as copper or aluminum foil for battery current collectors) and polar substrates, significantly enhancing adhesion. Simultaneously, the interaction between carboxyl groups improves the film density of the adhesive and enhances its ability to encapsulate active particles. Hydroxyl groups are smaller than carboxyl groups but have higher permeability, achieving interfacial bonding through a multi-point hydrogen bond network and weak coordination with metal ions. They are also heat-resistant and lower in cost. Sulfonic acid groups possess strong acidity and high ionization, making them stable in electrolytes. They provide higher bond energies through electrostatic adsorption and ion bridging, making them particularly suitable for high-voltage or acidic environments.

[0044] In addition, the polar groups (such as carboxyl groups, hydroxyl groups, etc.) in the molecular chain of modified styrene-butadiene rubber can form hydrogen bonds or van der Waals forces with the polar groups (such as metal oxides, hydroxyl groups, carboxyl groups) on the current collector surface of the negative electrode sheet, thereby improving the adhesion of the adhesive.

[0045] Furthermore, the carboxyl groups in the modified styrene-butadiene rubber account for 1% to 10% of the mass percentage of the adhesive, preferably 1% to 5%.

[0046] For example, the percentage of carboxyl groups in the modified styrene-butadiene rubber (SBR) as a percentage of the binder can be any one of 1%, 2%, 4%, 5%, 7%, 9%, or 10%, or any value between any two. When the percentage of carboxyl groups in the modified SBR as a percentage of the binder is greater than or equal to 1%, it is beneficial to utilize the carboxyl-modified SBR, improving the adhesive's tack and film-forming properties. When the percentage of carboxyl groups in the modified SBR as a percentage of the binder is less than or equal to 10%, it is beneficial to reduce the cost of the binder. A percentage of carboxyl groups in the modified SBR as a percentage of the binder within the range of 1% to 10% is considered reasonable, helping to fully utilize the carboxyl-modified SBR, improving the adhesive's tack, mechanical properties, and solvent resistance, while simultaneously reducing the mass of the carboxyl-modified SBR, thus contributing to cost reduction. Furthermore, when the percentage of carboxyl groups in the modified SBR as a percentage of the binder is 1% to 5%, the effect is even better.

[0047] Furthermore, the hydroxyl groups in the modified styrene-butadiene rubber account for 0.5% to 8% of the adhesive's mass.

[0048] For example, the percentage of hydroxyl groups in the modified styrene-butadiene rubber (SBR) as a percentage of the binder can be any one of 0.5%, 2%, 4%, 5%, 6%, 7%, or 8%, or any value between any two. When the percentage of hydroxyl groups in the modified SBR as a percentage of the binder is greater than or equal to 0.5%, the hydroxyl-modified SBR can improve the high-temperature resistance of the binder and optimize its performance. When the percentage of hydroxyl groups in the modified SBR as a percentage of the binder is less than or equal to 8%, it helps to reduce the cost of the binder. A percentage of hydroxyl groups in the modified SBR as a percentage of the binder within the range of 0.5% to 8% is considered reasonable, helping to fully utilize the role of the hydroxyl-modified SBR, improve the high-temperature resistance of the binder, and simultaneously reduce the mass of the hydroxyl-modified SBR, thus contributing to cost reduction.

[0049] Furthermore, the sulfonic acid groups in the modified styrene-butadiene rubber account for 0.1% to 5% of the mass of the adhesive.

[0050] For example, the percentage of sulfonic acid groups in the modified styrene-butadiene rubber (SBR) as a percentage of the adhesive can be any one of 0.1%, 2%, 3%, 4%, or 5%, or any value between two of these. When the percentage of sulfonic acid groups in the modified SBR as a percentage of the adhesive is greater than or equal to 0.1%, the sulfonic acid-modified SBR can function effectively, improving the adhesive's high-pressure resistance and acid resistance, thus optimizing the adhesive's performance. When the percentage of sulfonic acid groups in the modified SBR as a percentage of the adhesive is less than or equal to 5%, it helps to reduce the cost of the adhesive. A percentage of sulfonic acid groups in the modified SBR as a percentage of the adhesive within the range of 0.1% to 5% is considered reasonable, helping to fully utilize the function of the sulfonic acid-modified SBR, improving the adhesive's bonding ability, oil resistance, and aging resistance, while simultaneously reducing the mass of the sulfonic acid-modified SBR, thus contributing to cost reduction.

[0051] According to some embodiments of the present invention, the adhesive further includes acrylic monomers. Introducing polar groups of acrylic monomers into the styrene-butadiene rubber molecular chain helps to improve the adhesion between the first and second styrene-butadiene rubber particles, thereby effectively optimizing the adhesion of the adhesive. In addition, it also helps to improve the oil resistance, abrasion resistance and compatibility with polar materials of the adhesive.

[0052] Preferably, the acrylic monomer accounts for 1% to 8% of the binder by mass. For example, the acrylic monomer percentage of the binder by mass can be any one or a range between 1%, 1.5%, 2%, 2.5%, 3%, 5%, and 8%. When the acrylic monomer percentage of the binder is greater than or equal to 1%, the binder modified with the acrylic monomer has stable performance and suitable hardness, which is beneficial for its use in electrodes. When the acrylic monomer percentage of the binder is less than or equal to 8%, the acrylic monomer has a good modification effect on the styrene-butadiene rubber in the binder and helps to reduce the cost of the binder. When the acrylic monomer percentage of the binder is within the range of 1% to 8% by mass, the amount of acrylic monomer added to the binder is reasonable, which helps to balance the performance improvement and cost of the binder.

[0053] According to a second aspect of the present invention, the negative electrode sheet includes: a negative electrode active material layer, the negative electrode active material layer including a binder, the binder being the binder of the first aspect of the present invention described above.

[0054] According to the embodiments of the present invention, by using the above-mentioned binder, the structural stability of the negative electrode active material layer and the connection stability and reliability between the negative electrode active material layer and adjacent structures are improved, thereby extending the service life of the negative electrode.

[0055] Furthermore, the binder accounts for 1% to 3% of the mass of the negative electrode active material layer.

[0056] For example, the mass percentage of the binder in the negative electrode active material layer can be any one of 1%, 1.5%, 2%, 2.5%, 3%, or any value between any two. When the mass percentage of the binder in the negative electrode active material layer is greater than or equal to 1%, it is beneficial to fully utilize the role of the binder, ensuring that the negative electrode active material layer does not shed powder and that the current collector peel strength meets the standard. When the mass percentage of the binder in the negative electrode active material layer is less than or equal to 3%, it reduces costs while ensuring the presence of the remaining components in the negative electrode active material layer, thus guaranteeing the performance of the negative electrode active material layer. Setting the mass percentage of the binder in the negative electrode active material layer within the range of 1% to 3% aims to minimize the binder content while ensuring that the negative electrode active material layer does not shed powder and that the current collector peel strength meets the standard, thereby improving energy density and conductivity efficiency.

[0057] According to some embodiments of the present invention, the negative electrode active material layer further includes polyacrylic acid. The carboxyl groups of polyacrylic acid mainly combine with unsaturated carboxyl groups or residual sites of carbon materials (e.g., hard carbon) on the SBR molecular chain to form an "SBR-hard carbon-PAA" bridging structure, further enhancing interfacial bonding. Furthermore, the polyacrylic acid molecular chain possesses a certain degree of flexibility and elasticity; when the negative electrode active material in the negative electrode active material layer expands, it can absorb stress through chain segment extension, and after expansion and contraction, it can restore its adhesive effect, reducing the generation of cracks in the negative electrode sheet.

[0058] For example, during the preparation process, first and second styrene-butadiene rubber particles can be added to the negative electrode active material and then mixed with polyacrylic acid (PAA) to form a negative electrode active coating. The polyacrylic acid molecular chain contains a large number of carboxyl groups (-COOH), which can form hydrogen bonds or coordination bonds with the hydroxyl groups (-OH) on the surface of active materials such as silicon (Si) and carbon (C), significantly improving the interfacial adhesion strength.

[0059] Furthermore, the mass percentage of polyacrylic acid in the negative electrode active material layer is 0.5% to 8%.

[0060] For example, the mass percentage of polyacrylic acid in the negative electrode active material layer can be any one or a range between any two of 0.5%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.5%, 3%, 5%, and 8%. Polyacrylic acid can be omitted from the negative electrode active material layer while still meeting the structural stability requirements of the negative electrode sheet. When the mass percentage of polyacrylic acid in the negative electrode active material layer is greater than 0.5%, it can effectively enhance the structural stability and reliability of the negative electrode sheet. When the mass percentage of polyacrylic acid in the negative electrode active material layer is less than 8%, it is easier to control the amount of polyacrylic acid added, thereby controlling the cost of the negative electrode sheet. Therefore, the content of polyacrylic acid in the negative electrode active material layer is relatively reasonable, which helps to reduce the agglomeration and expansion of the negative electrode active material, thus improving the service life of the negative electrode sheet.

[0061] According to some embodiments of the present invention, the negative electrode active material layer includes a negative electrode active substance, which includes at least one of carbon materials and silicon-based materials. The negative electrode active substance and the binder are structurally compatible and synergistically effective. At least one of the carbon materials and silicon-based materials has weak surface polarity, thus it is well-suited to weakly polar binders (including styrene-butadiene rubber particles), thereby ensuring surface polarity compatibility between the negative electrode active substance and the binder. Simultaneously, the binder is suitable for filling the pores of the negative electrode active substance to macroscopically bond and form a stable structure.

[0062] Furthermore, the carbon materials include at least one of graphite, hard carbon, carbon nanoparticles, and graphene. Graphite exhibits excellent cycle stability, a stable layered structure, and minimal volume change. Hard carbon offers high lithium storage capacity, improving battery energy density, but suffers from low initial coulombic efficiency. Carbon nanoparticles have a large specific surface area, excellent rate performance, and low cost. Graphene possesses excellent electrical and thermal conductivity, improving electron transport in the negative electrode, and exhibits superior mechanical properties, serving as a structural support to buffer the volume expansion of other materials (such as silicon). Furthermore, graphene has a high theoretical capacity. Therefore, employing these carbon materials helps improve the structural stability of the negative electrode active material and the negative electrode active material layer, thereby enhancing the energy density, power density, and lifespan of the negative electrode.

[0063] Silicon-based materials include at least one of Si grains (pure silicon), SiO (silicon monoxide), SiO2 (silicon dioxide), and SiOx (0 < x < 2). For example, SiOx (0 < x < 2) can be SiO2. 0.2 No specific limitations are made here. Among them, Si grains have a high theoretical specific capacity, abundant raw material reserves, and good rate performance. SiO has a large theoretical specific capacity and long cycle life. SiO2 has a large theoretical specific capacity and low expansion rate. SiOx can be adapted to diverse needs through x-tuning.

[0064] According to other embodiments of the present invention, the specific surface area of ​​the silicon-based material is 1 m². 2 / g~5m 2 / g. The specific surface area of ​​the above silicon-based materials is relatively reasonable, which can effectively shorten the diffusion path of ions, accelerate ion migration, and effectively avoid poor interparticle contact caused by the agglomeration of silicon-based material particles to form a porous structure. This is conducive to controlling the electronic conduction resistance and improving high-rate performance.

[0065] According to further embodiments of the present invention, the particle size Dv50 of the carbon material satisfies: 10 μm to 30 μm. Therefore, the carbon material is advantageous in that stress can be buffered through the interparticle gaps during charge-discharge expansion, avoiding cracking caused by stress concentration within a single particle, while simultaneously maintaining both packing density and rate capability.

[0066] The particle size distribution of silicon-based materials satisfies the following condition: Dv10 ranges from 3μm to 5μm. Dv10 refers to the particle size of 10% of the silicon-based material by volume that is smaller than this value, i.e., the "10% particle size". In the aforementioned silicon-based materials, 10% of the particles by volume have a particle size smaller than 3μm to 5μm.

[0067] The Dv50 range is 4μm to 9.5μm. In silicon-based materials, 50% of the particles by volume have a diameter smaller than 4μm to 9.5μm. This results in a finer overall silicon-based material with a reasonable specific surface area, reducing the occurrence of side reactions and facilitating the use of negative electrode sheets. Simultaneously, the volume expansion of silicon-based materials is also more reasonable.

[0068] The Dv90 range is 8μm to 12μm. In silicon-based materials, the particles that make up 90% of the volume have a diameter smaller than 8μm to 12μm. The lower number of coarse particles in silicon-based materials increases the overall uniformity and stability of the material.

[0069] The combination of any two of Dv10, Dv50 and Dv90 indicates that the particle size distribution of silicon-based materials is relatively concentrated, which helps to ensure the performance stability of silicon-based materials.

[0070] The method for preparing a negative electrode sheet according to a third aspect embodiment of the present invention is suitable for preparing the negative electrode sheet of the second aspect embodiment of the present invention described above, and includes the following steps:

[0071] First styrene-butadiene rubber particles and second styrene-butadiene rubber particles are added to the negative electrode active material to form a negative electrode active coating. The negative electrode active coating is then applied to the surface of the current collector to obtain the negative electrode sheet.

[0072] According to the method for preparing the negative electrode sheet according to the embodiments of the present invention, the above preparation method is relatively simple and is conducive to improving the preparation efficiency of the negative electrode sheet.

[0073] According to further embodiments of the present invention, the stirring time and stirring speed can be designed based on the particle size distribution of the first and second styrene-butadiene rubber particles. For example, the stirring speed after adding the first styrene-butadiene rubber particles is 400 rpm to 800 rpm, and the stirring time is 10 min to 30 min. At the above stirring speed and time, the first styrene-butadiene rubber particles are thoroughly mixed, which helps to improve the continuous skeletal network in the negative electrode active coating, thereby improving the peel strength of the binder, while reducing the stirring time and improving the preparation efficiency of the negative electrode active coating.

[0074] After adding the second styrene-butadiene rubber particles, the stirring speed is 600 rpm to 1200 rpm, and the stirring time is 10 min to 30 min. At these stirring speeds and times, excessive shearing is avoided to prevent damage to the structure of the second styrene-butadiene rubber particles, facilitating their full penetration into the micropores of the negative electrode active material and ensuring thorough mixing of the particles. Simultaneously, the stirring time is reduced, thereby improving the preparation efficiency of the negative electrode active coating.

[0075] A battery according to a fourth aspect of the present invention includes: a negative electrode sheet according to the second aspect of the present invention described above; or a negative electrode sheet prepared using the method for preparing a negative electrode sheet according to the third aspect of the present invention described above.

[0076] The battery according to the embodiments of the present invention is beneficial to improving the structural stability of the battery, improving the cycle performance of the battery, and extending the battery's service life.

[0077] A battery pack according to a fifth aspect embodiment of the present invention includes: a negative electrode sheet according to the second aspect embodiment of the present invention described above; or a negative electrode sheet prepared by the method for preparing a negative electrode sheet according to the third aspect embodiment of the present invention described above; or a battery according to the fourth aspect embodiment of the present invention described above.

[0078] The battery pack according to the embodiments of the present invention is beneficial to improving the stability of the battery pack, improving the battery pack's range performance, extending the battery pack's cycle life, and reducing the battery pack's operation and maintenance costs.

[0079] An electrical device according to a sixth aspect embodiment of the present invention includes: a negative electrode sheet according to the second aspect embodiment of the present invention; or a negative electrode sheet prepared by the method for preparing a negative electrode sheet according to the third aspect embodiment of the present invention; or a battery according to the fourth aspect embodiment of the present invention; or a battery pack according to the fifth aspect embodiment of the present invention.

[0080] According to the embodiments of the present invention, the power supply stability of the power supply is improved, the user experience is enhanced, the operation and maintenance costs of the power supply are reduced, and the safety of the power supply is improved, thereby helping to enhance the market competitiveness of the power supply.

[0081] The electrical equipment can include vehicles, aircraft, ferries, computers, energy storage cabinets, etc. No specific limitations are specified here.

[0082] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0083] The composite materials of the present invention will be described through exemplary embodiments and comparative examples. The following describes the performance tests performed on the composite materials of the embodiments and comparative examples.

[0084] Example 1

[0085] The method for preparing the negative electrode sheet includes the following steps:

[0086] 1. Slurry preparation:

[0087] (1) Premixed negative electrode active material and dispersant

[0088] Graphite (Dv50=20μm), conductive agent (SuperP / CNT) and sodium carboxymethyl cellulose (CMC) were mixed at a mass ratio of 96:1:1; then deionized water (50% solid content) was added, and the mixture was dispersed at 1000 rpm for 60 min to obtain a uniform slurry.

[0089] (2) Add adhesive

[0090] Add styrene-butadiene rubber particles to the obtained uniform slurry, and control the mass ratio of graphite: conductive agent: sodium carboxymethyl cellulose: styrene-butadiene rubber particles to be 96:1:1:2.

[0091] Dv501 with a diameter of 250 nm was selected as the first styrene-butadiene rubber particle, and Dv502 with a diameter of 180 nm was selected as the second styrene-butadiene rubber particle. The particles were added to the obtained homogeneous slurry in sequence according to the mass ratio of the first styrene-butadiene rubber particle to the second styrene-butadiene rubber particle = 31:69.

[0092] First, add the first styrene-butadiene rubber granules, then stir at 400 rpm for 20 minutes, then add the second styrene-butadiene rubber granules, and stir at 800 rpm for 15 minutes.

[0093] A negative electrode active coating was prepared.

[0094] The ratio K of Dv501 to Dv502 is 1.4, and the mass ratio of the first styrene-butadiene rubber particle to the second styrene-butadiene rubber particle is 2.2.

[0095] 2. Coating and Drying

[0096] (1) Coating process

[0097] The negative electrode active coating is applied to the negative electrode current collector using slit coating (300 μm gap) or blade coating at a speed of 10 m / min to 30 m / min (preferably 20 m / min).

[0098] The thickness of the formed negative electrode active material layer is controlled to be 200μm to 250μm, wherein the mass percentage of the binder in the negative electrode active material layer is 2%.

[0099] (2) Gradient drying

[0100] First stage: 80℃×10min (quickly remove surface moisture to prevent cracking);

[0101] Second stage: 120℃×30min (deep removal of bound water);

[0102] The thickness of the dried negative electrode active material layer is 100μm to 120μm.

[0103] 3. Roll pressing and slitting

[0104] (1) Gradient roll pressing

[0105] Step 1: Roll pressing at 8MPa to initially densify the negative electrode sheet;

[0106] Step 2: Roll pressing at 10MPa to adjust the density of the negative electrode sheet to 1.60g / cm³. 3 ~1.75g / cm 3 .

[0107] (2) Slitting and quality inspection

[0108] The slitting width tolerance is ±0.1mm, which makes the burrs on the negative electrode sheet less than 5μm.

[0109] Examples 2-26 and Comparative Examples 1-3

[0110] The preparation methods of Examples 2-26 and Comparative Examples 1-3 are largely the same as those of Example 1, with the main differences being the particle size Dv501 of the first styrene-butadiene rubber particles, the particle size Dv502 of the second styrene-butadiene rubber particles, the ratio K of Dv501 to Dv502, the mass ratio of the first styrene-butadiene rubber particles to the second styrene-butadiene rubber particles, the mass percentage of the first styrene-butadiene rubber particles in the binder, the type and content of the modified styrene-butadiene rubber, and the mass percentage of the binder in the negative electrode active material layer. The specific parameter limitations for Examples 1-26 and Comparative Examples 1-3 are detailed in Table 1.

[0111] It should be noted that Examples 15-23 modify styrene-butadiene rubber particles.

[0112] Example 15

[0113] Example 15 is basically the same as Example 1, except that:

[0114] In step (2) of slurry preparation, after determining the amount of the first styrene-butadiene rubber particles to be added to the uniform slurry, 1 / 31 of the first styrene-butadiene rubber particles are taken for carboxyl modification. The first styrene-butadiene rubber particles: modifier (specifically acrylic acid): initiator (specifically potassium persulfate) are prepared according to the mass ratio of first styrene-butadiene rubber particles: modifier (specifically acrylic acid): initiator (specifically potassium persulfate) = 1:1:0.1. First, the first styrene-butadiene rubber particles are diluted with water to a uniform solution (solid content is 15%), and then transferred to the reactor. Under nitrogen protection, the modifier and initiator are added and stirred at a stirring speed of 500 rpm. The temperature is raised to 75°C and the reaction is carried out for 7 hours. Stirring is stopped when the reaction is completed.

[0115] After the reaction solution was cooled, the pH was adjusted to 8.0; the bottom precipitate was removed by centrifugation, purified by dialysis, and then freeze-dried to obtain modified styrene-butadiene rubber particles.

[0116] The modified first styrene-butadiene rubber particles and the unmodified 30 / 31 first styrene-butadiene rubber particles were added to the resulting homogeneous slurry, and subsequent steps were carried out.

[0117] Example 16

[0118] Example 16 is basically the same as Example 1, except that:

[0119] In step (2) of slurry preparation, after determining the amount of the first styrene-butadiene rubber particles to be added to the uniform slurry, 5 / 31 of the first styrene-butadiene rubber particles are taken for carboxyl modification. The first styrene-butadiene rubber particles: modifier (specifically acrylic acid): initiator (specifically potassium persulfate) are prepared according to the mass ratio of first styrene-butadiene rubber particles: modifier (specifically acrylic acid): initiator (specifically potassium persulfate) = 1:1:0.1. First, the first styrene-butadiene rubber particles are diluted with water to a uniform solution (solid content is 15%), and then transferred to the reactor. Under nitrogen protection, the modifier and initiator are added and stirred at a stirring speed of 500 rpm. The temperature is raised to 75°C and the reaction is carried out for 7 hours. Stirring is stopped when the reaction is completed.

[0120] After the reaction solution was cooled, the pH was adjusted to 8.0; the bottom precipitate was removed by centrifugation, purified by dialysis, and then freeze-dried to obtain modified styrene-butadiene rubber particles.

[0121] The modified first styrene-butadiene rubber particles and the unmodified 26 / 31 first styrene-butadiene rubber particles were added to the resulting homogeneous slurry, and subsequent steps were carried out.

[0122] Example 17

[0123] Example 17 is basically the same as Example 1, except that:

[0124] In step (2) of slurry preparation, after determining the amount of the first styrene-butadiene rubber particles added to the uniform slurry, 10 / 31 of the first styrene-butadiene rubber particles are taken for carboxyl modification. The first styrene-butadiene rubber particles: modifier (specifically acrylic acid): initiator (specifically potassium persulfate) are prepared according to the mass ratio of first styrene-butadiene rubber particles: modifier (specifically acrylic acid): initiator (specifically potassium persulfate) = 1:1:0.1. First, the first styrene-butadiene rubber particles are diluted with water to a uniform solution (solid content is 15%), and then transferred to the reactor. Under nitrogen protection, the modifier and initiator are added and stirred at a stirring speed of 500 rpm. The temperature is raised to 75°C and the reaction is carried out for 7 hours. Stirring is stopped when the reaction is completed.

[0125] After the reaction solution was cooled, the pH was adjusted to 8.0; the bottom precipitate was removed by centrifugation, purified by dialysis, and then freeze-dried to obtain modified styrene-butadiene rubber particles.

[0126] The modified first styrene-butadiene rubber particles and the unmodified 21 / 31 first styrene-butadiene rubber particles were added to the resulting homogeneous slurry, and subsequent steps were carried out.

[0127] Example 18

[0128] Example 18 is basically the same as Example 1, except that:

[0129] In step (2) of slurry preparation, after determining the amount of the first styrene-butadiene rubber particles to be added to the uniform slurry, 1 / 62 of the first styrene-butadiene rubber particles are taken for hydroxyl modification. The first styrene-butadiene rubber particles: modifier (specifically hydroxyethyl acrylate): initiator (specifically potassium persulfate) are prepared according to the mass ratio of first styrene-butadiene rubber particles: modifier (specifically hydroxyethyl acrylate): initiator (specifically potassium persulfate) = 1:1:0.1. First, the first styrene-butadiene rubber particles are diluted with water to a uniform solution (solid content is 15%), and then transferred to a light-proof reactor. Under nitrogen protection, the modifier and initiator are added and stirred at a stirring speed of 350 rpm. The temperature is raised to 65℃ and the reaction is carried out for 5 hours. Stirring is stopped when the reaction is completed.

[0130] After the reaction solution was cooled, 4 times the volume of ethanol was added to obtain a precipitate; the bottom precipitate was obtained by filtration, washed and purified, and dried under vacuum to obtain modified styrene-butadiene rubber particles.

[0131] The modified first styrene-butadiene rubber particles and the unmodified 61 / 62 first styrene-butadiene rubber particles were added to the resulting homogeneous slurry, and subsequent steps were carried out.

[0132] Example 19

[0133] Example 19 is basically the same as Example 1, except that:

[0134] In step (2) of slurry preparation, after determining the amount of the first styrene-butadiene rubber particles to be added to the uniform slurry, 8 / 31 of the first styrene-butadiene rubber particles are taken for hydroxyl modification. The first styrene-butadiene rubber particles: modifier (specifically hydroxyethyl acrylate): initiator (specifically potassium persulfate) are prepared according to the mass ratio of first styrene-butadiene rubber particles: modifier (specifically hydroxyethyl acrylate): initiator (specifically potassium persulfate) = 1:1:0.1. First, the first styrene-butadiene rubber particles are diluted with water to a uniform solution (solid content is 15%), and then transferred to a light-proof reactor. Under nitrogen protection, the modifier and initiator are added and stirred at a stirring speed of 350 rpm. The temperature is raised to 65℃ and the reaction is carried out for 5 hours. Stirring is stopped when the reaction is completed.

[0135] After the reaction solution was cooled, 4 times the volume of ethanol was added to obtain a precipitate; the bottom precipitate was obtained by filtration, washed and purified, and dried under vacuum to obtain modified styrene-butadiene rubber particles.

[0136] The modified first styrene-butadiene rubber particles and the unmodified 23 / 31 first styrene-butadiene rubber particles were added to the resulting homogeneous slurry, and subsequent steps were carried out.

[0137] Example 20

[0138] Example 20 is basically the same as Example 1, except that:

[0139] In step (2) of slurry preparation, after determining the amount of the first styrene-butadiene rubber particles to be added to the uniform slurry, 1 / 310 of the first styrene-butadiene rubber particles are taken for sulfonic acid modification. The first styrene-butadiene rubber particles and the modifier (specifically NaHSO3) are mixed in a mass ratio of 1:1. The first styrene-butadiene rubber particles are first diluted with water to a uniform solution (solid content of 25%), and then transferred to the reactor. Under nitrogen protection, the modifier is added and stirred at a stirring speed of 350 rpm. Dilute sulfuric acid is added dropwise to adjust the pH to 4.0, the temperature is raised to 65℃, and the reaction is carried out for 5 hours. Stirring is stopped when the reaction is completed.

[0140] After the reaction solution was cooled, it was neutralized with alkali to pH 7.0; purified by dialysis (MWCO 3000Da~5000Da), and freeze-dried to obtain modified styrene-butadiene rubber particles.

[0141] The modified first styrene-butadiene rubber particles and the unmodified 309 / 310 first styrene-butadiene rubber particles were added to the resulting homogeneous slurry, and subsequent steps were carried out.

[0142] Example 21

[0143] Example 21 is basically the same as Example 1, except that:

[0144] In step (2) of slurry preparation, after determining the amount of the first styrene-butadiene rubber particles added to the uniform slurry, 5 / 31 of the first styrene-butadiene rubber particles are taken for sulfonic acid modification. The first styrene-butadiene rubber particles and the modifier (specifically NaHSO3) are mixed in a mass ratio of 1:1. First, the first styrene-butadiene rubber particles are diluted with water to a uniform solution (solid content of 25%), and then transferred to the reactor. Under nitrogen protection, the modifier is added and stirred at a stirring speed of 350 rpm. Dilute sulfuric acid is added dropwise to adjust the pH to 4.0, the temperature is raised to 65℃, and the reaction is carried out for 5 hours. Stirring is stopped when the reaction is completed.

[0145] After the reaction solution was cooled, it was neutralized with alkali to pH 7.0; purified by dialysis (MWCO 3000Da~5000Da), and freeze-dried to obtain modified styrene-butadiene rubber particles.

[0146] The modified first styrene-butadiene rubber particles and the unmodified 26 / 31 first styrene-butadiene rubber particles were added to the resulting homogeneous slurry, and subsequent steps were carried out.

[0147] Example 22

[0148] Example 22 is basically the same as Example 1, except that:

[0149] In step (2) of slurry preparation, after determining the amount of the first styrene-butadiene rubber particles to be added to the uniform slurry, 9 / 31 of the first styrene-butadiene rubber particles are taken for carboxyl and hydroxyl modification. The first styrene-butadiene rubber particles are mixed according to the following ratio: first styrene-butadiene rubber particles: modifier (specifically, acrylic acid: hydroxyethyl acrylate mass ratio = 5:4): initiator (specifically, potassium persulfate) mass ratio = 1:1:0.1. First, the first styrene-butadiene rubber particles are diluted with water to a uniform solution (solid content is 15%), and then transferred to a light-proof reactor. Under nitrogen protection, the stirring speed is 400 rpm, the temperature is raised to 65℃, and the reaction is carried out for 7 hours.

[0150] After the reaction solution was cooled, 4 times the volume of ethanol was added to precipitate and modify the SBR; the pH was adjusted to 8.0; the bottom precipitate was obtained by filtration, washed and purified, and vacuum dried to obtain modified styrene-butadiene rubber particles.

[0151] The modified first styrene-butadiene rubber particles and the unmodified 22 / 31 first styrene-butadiene rubber particles were added to the resulting homogeneous slurry, and subsequent steps were carried out.

[0152] Example 23

[0153] Example 23 is basically the same as Example 1, except that:

[0154] In step (2) of slurry preparation, after determining the amount of the first styrene-butadiene rubber particles added to the uniform slurry, 9 / 31 of the first styrene-butadiene rubber particles were carboxyl and sulfonic acid modified. The first styrene-butadiene rubber particles were mixed with the modifier (specifically, acrylic acid: NaHSO3 mass ratio = 5:4) and the initiator (specifically, potassium persulfate) mass ratio = 1:1:0.1. The first styrene-butadiene rubber particles were first diluted with water to a uniform solution (solid content of 15%), and then transferred to a light-proof reactor. Under nitrogen protection, the modifier and initiator were added and stirred. Dilute sulfuric acid was added dropwise to adjust the pH to 4.0. The stirring speed was 350 rpm, the temperature was raised to 65℃, and the reaction was carried out for 5 hours. Stirring was stopped when the reaction was completed.

[0155] After the reaction solution was cooled, the pH was adjusted to 7.0; the solution was purified by dialysis (MWCO 3000Da~5000Da) and then freeze-dried to obtain modified styrene-butadiene rubber particles.

[0156] The modified first styrene-butadiene rubber particles and the unmodified 22 / 31 first styrene-butadiene rubber particles were added to the resulting homogeneous slurry, and subsequent steps were carried out.

[0157] It should be noted that polyacrylic acid was added to the negative electrode active material layer in Example 26.

[0158] Example 26

[0159] Example 26 is basically the same as Example 1, except that:

[0160] In step (2) of slurry preparation, styrene-butadiene rubber particles and polyacrylic acid are added to the obtained uniform slurry, and the mass ratio of graphite: conductive agent: sodium carboxymethyl cellulose: styrene-butadiene rubber particles: polyacrylic acid is controlled to be 95.5:1:1:2:0.5.

[0161] After adding the first styrene-butadiene rubber granules and the second styrene-butadiene rubber granules, polyacrylic acid was added, and then the mixture was stirred at 800 rpm for 15 minutes.

[0162] A negative electrode active coating was prepared.

[0163] Assemble batteries

[0164] A positive electrode slurry was prepared according to a mass ratio of positive electrode active material (specifically lithium iron phosphate): lithium supplementer (specifically lithium ferrite): positive electrode conductive agent (specifically carbon black): positive electrode binder (specifically polyvinylidene fluoride) = 95:1.7:1.1:2.2. The positive electrode sheet prepared with it was used as the positive electrode, and the negative electrode sheet prepared with the examples and comparative examples was used as the negative electrode. An electrolyte with a concentration of 1 mol / L and lithium hexafluorophosphate was prepared with ethylene carbonate:dimethyl carbonate volume ratio of 3:7 as the solvent. A 14 μm PP membrane was used as the separator, and the positive and negative electrode sheets were stacked to form a lithium-ion battery.

[0165] Table 1

[0166]

[0167] Test methods

[0168] I. Particle Size Testing

[0169] The particle size and distribution of the first and second styrene-butadiene rubber particles in the binder of the negative electrode sheet can be characterized by SEM-EDS / BSE. The specific operation is as follows:

[0170] The negative electrode sheet was separated from the battery to obtain a negative electrode sheet sample.

[0171] 1. Sample preparation

[0172] (1) Freeze-break method: The negative electrode sheet is rapidly frozen in liquid nitrogen at -196℃ for less than 30 seconds to avoid SBR particle migration; the sample is rapidly broken with a pre-cooled (liquid nitrogen-immersed) blade to expose the fresh cross-section; the sample is immediately transferred to a scanning electron microscope (SEM) for testing (to prevent water vapor condensation).

[0173] (2) Conductive treatment: Light coating is applied using a magnetron sputtering instrument, with Au or C target material selected, and the thickness is strictly controlled to 2nm (too thick will mask the signal of styrene-butadiene rubber particles).

[0174] Expected result: Obtain a cross-section free of ice crystal contamination and with clear exposure of SBR particles.

[0175] 2. Scanning Electron Microscopy (SEM) Imaging Strategy

[0176] (1) Backscattered electron (BSE) mode:

[0177] The parameters are set as follows: Accelerating voltage: 1kV~3kV (to enhance the contrast between low and high atomic number elements). Beam current: 1nA~5nA (to balance the image signal-to-noise ratio and resolution). In BSE mode, SBR particles appear as dark areas (atomic number Z≈6), the conductive agent as gray areas (atomic number Z≈12), and the active material as bright areas (atomic number Z>20).

[0178] Expected result: High-contrast BSE images that clearly distinguish SBR particles from other components.

[0179] 3. EDS (Energy Dispersive Spectroscopy) Element Labelling and Decoupling

[0180] Element labeling: Select O element (532eV, characteristic of carboxylated SBR) and C element (284eV, to distinguish SBR from conductive agent).

[0181] Scanning parameters: Area scan: 1024×1024 pixels, dwell time 50μs / point.

[0182] Layered scanning: First, use 5kV to quickly locate the SBR region, and then use 2kV for high-resolution acquisition (resolution <10nm).

[0183] Interference elimination: For O signal: subtract background from active material regions (such as oxygen in NCM / LCO). For C signal: separate the conductive agent from the SBR by CK-edge peak shape fitting.

[0184] Expected results: Obtain the O / C elemental distribution map of SBR particles and verify the chemical composition of the particles.

[0185] 4. Data Analysis Methods

[0186] Convert the BSE image to 8-bit grayscale; perform adaptive threshold segmentation (Otsu or Li algorithm); apply the watershed algorithm to separate adhered particles; and calculate the maximum distance between the parallel tangents at both ends of the particle projection image, which is the particle size.

[0187] Calculation results:

[0188] Output the particle size distribution (Dv10 / Dv50 / Dv90) and distribution width of SBR particles.

[0189] II. Characterization schemes for carboxyl groups, sulfonic acid groups, hydroxyl groups, and polyacrylic acid

[0190] (1) Characterization scheme for carboxyl groups

[0191] 1. Proton nuclear magnetic resonance (¹H-NMR) spectrum

[0192] The SBR sample was dissolved in deuterated chloroform (CDCl3); the peak area ratio of δ=5.5ppm-6.5ppm (butadiene olefin hydrogen) to δ=12.3ppm (carboxyl hydrogen) was analyzed.

[0193] 2. Potentiometric titration

[0194] Dissolve SBR in tetrahydrofuran (THF); titrate with 0.1M KOH / ethanol solution to the endpoint (pH abrupt change).

[0195] Calculation result: Carboxyl content (mol%) = (KOH consumption × 0.1 / sample mass) × 100.

[0196] Verification requirements: The deviation between the NMR and titration results must be ≤0.3 mol%, otherwise a retest is required.

[0197] (2) Characterization scheme for sulfonic acid groups

[0198] For qualitative analysis using infrared spectroscopy, background acquisition is first performed on a blank KBr plate or a clean ATR crystal; then, the prepared SBR sample is placed, the scan is started, and the spectrum is recorded. These steps are repeated at least three times to ensure spectral reproducibility.

[0199] Data analysis: If 1180cm exists -1 and 1040cm -1 The presence of bimodal peaks can be used to determine the presence of sulfonic acid groups in SBR samples.

[0200] Quantitative analysis of SBR samples dissolved in a methanol / water mixture (8:2, volume ratio) was performed using potentiometric titration and ultrasonically dispersed for 10 min. Titration was then conducted at pH 7 using 0.1 M NaOH standard solution. Calculations were performed using the following formula:

[0201] Sulfonic acid content (mmol / g) = V NaOH ×C NaOH / m sample ,

[0202] Among them, V NaOH : Volume of NaOH consumed (mL);

[0203] C NaOH NaOH concentration (mol / L);

[0204] m sample Sample mass (g).

[0205] (3) Hydroxyl characterization scheme

[0206] 1. Qualitative analysis (FTIR method)

[0207] First, perform background acquisition on a blank KBr plate or a clean ATR crystal; then place the prepared SBR sample, start the scan, and record the spectrum. Repeat the above steps at least three times to ensure spectral reproducibility.

[0208] Data analysis: If 3400cm - The presence of a distinct absorption peak near ¹ indicates the presence of hydroxyl groups in the SBR sample.

[0209] 2. Quantitative analysis

[0210] Take 0.1 g of SBR sample powder, add 10 mL of acetic anhydride / pyridine mixture (volume ratio 1:1), and react in a water bath at 60 °C for 2 h; add 10 mL of deionized water, stir for 10 min to hydrolyze unreacted acetic anhydride; titrate with 0.1 M NaOH until neutral (phenolphthalein endpoint, pH=7).

[0211] Calculation result: Hydroxyl content (mmol / g) = [(V 空白 -V 样品 )×C] / m,

[0212] Among them, V 空白 : Volume of NaOH consumed in the blank experiment (mL);

[0213] V 样品 : Volume of NaOH consumed in SBR sample titration (mL);

[0214] C: NaOH concentration (mol / L);

[0215] m: Sample mass (g).

[0216] (4) Polyacrylic acid characterization scheme

[0217] 1. Qualitative Analysis

[0218] First, perform background acquisition on a blank KBr sheet or a clean ATR crystal; place the prepared negative electrode active material layer sample, start the scan, and record the spectrum; repeat the above steps at least 3 times to ensure spectral reproducibility.

[0219] Data analysis: If 1710cm -1 The presence of a distinct absorption peak nearby indicates the presence of PAA in the negative electrode active material layer sample.

[0220] 2. Quantitative analysis

[0221] Take 0.1g to 0.5g of the negative electrode active material powder, immerse it in 50mL of 0.1M NaOH solution, and sonicate for 30min to dissolve PAA; back titrate with 0.1M HCl standard solution until neutral (phenolphthalein indicator changes from pink to colorless, pH≈7).

[0222] Calculation result: PAA content (wt%) = [(V0-V)×C×72.06] / m×100%,

[0223] Wherein, V0: volume of blank NaOH (mL);

[0224] V: Volume of HCl consumed (mL);

[0225] C: NaOH concentration (mol / L);

[0226] m: Mass of the negative electrode active material layer sample (g).

[0227] III. Peel Strength Test Method

[0228] The adhesion strength between the negative electrode active material coating and the current collector was determined using the 180° peel method. The specific steps are as follows: 1. Sample preparation

[0229] A negative electrode sheet with a width of 15.0 ± 0.1 mm and a length of ≥ 150 mm was cut from the negative electrode sheet, and the sampling position was greater than or equal to 20 mm from the edge of the negative electrode sheet; then 3M 600 tape was applied to the current collector side of the negative electrode sheet, completely covering it without air bubbles, in order to suppress the deformation of the current collector of the negative electrode sheet during the peeling process; finally, the surface of the negative electrode active material coating was wiped unidirectionally with anhydrous ethanol and air-dried at room temperature for 10 seconds to obtain the sample.

[0230] 2. Standard substrate processing

[0231] SUS304 stainless steel plate was selected as the substrate and ultrasonically cleaned with acetone and anhydrous ethanol for 5 min in sequence, and then dried with nitrogen. After cleaning, the substrate was left to stand for ≥1 h in an environment of 23±2℃ and 50±5% RH to obtain a standard substrate.

[0232] 3. Sample bonding

[0233] The sample is attached to the standard substrate. One end is fixed first, and the sample is pressed towards the other end at a speed of 50 mm / s to remove air bubbles. Then, a standard pressure roller of 2000±50g is used to roll the sample three times at a speed of 300±10 mm / min. The sample is then left to stand in an environment of 23±2℃ and 50±5%RH for 60±5 min (same temperature and humidity environment).

[0234] 4. Peel test

[0235] Using a tensile testing machine (accuracy ±0.5%), clamp the standard substrate (upper clamp) and the free end of the sample (lower clamp), ensuring a peel angle of 180°±1°; peel at a speed of 300±10 mm / min, and record the force curve of the middle 60 mm peel segment. Test multiple samples in a single group, discarding the first data and outliers with a range >0.15 N / cm, and calculate the average peel force. Test data are shown in Table 2.

[0236] IV. Cycle Retention Rate Test Method

[0237] 1. Charging: Charge the battery at room temperature (25±3℃ according to 4.1 standard) at a constant current of 1 / 3C to 3.8V / cell, let it rest for 5 minutes, then charge it at a constant current of 0.05C to 3.8V / cell, record one data point per second; let it rest for 30 minutes.

[0238] 2. Discharge: Discharge the battery at room temperature (25±3℃) according to the 4.2 standard, discharge it at 1 / 3C constant current to 2.0V / cell, record one data point per second; let it rest for 30 minutes.

[0239] 3. Repeat the above two steps a total of 500 times. Record the discharge capacity of the third discharge as the initial discharge capacity C0, the discharge capacity of the 500th discharge as Cn, and the capacity retention rate μ = Cn / C0 × 100%. The test results are shown in Table 2.

[0240] Table 2

[0241]

[0242] Test Result Analysis

[0243] Analysis of Tables 1 and 2 shows that, compared to Comparative Examples 1-3, the peel force between the negative electrode active material coating and the current collector in Examples 1-26 is greater, indicating that the adhesive of this application has better bonding ability. Meanwhile, the batteries in Examples 1-26 exhibit high capacity retention after 500 cycles, indicating that the batteries using the adhesive of this application have better cycle performance.

[0244] Other configurations and operations of the batteries, battery packs, and electrical devices according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here.

[0245] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0246] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. An adhesive, characterized in that, include: The styrene-butadiene rubber (SBR) granules include a first SBR granule and a second SBR granule, wherein the ratio of the particle size Dv501 of the first SBR granule to the particle size Dv502 of the second SBR granule is K, and K satisfies: 1.2≤K≤100; 250nm≤Dv501≤500nm; 2nm≤Dv502≤200nm, and the mass ratio of the first SBR granule to the second SBR granule is 1:(1.0~9).

2. The adhesive according to claim 1, characterized in that, Furthermore, the condition 1.4 ≤ K ≤ 5 must be satisfied.

3. The adhesive according to claim 2, characterized in that, Furthermore, it satisfies: 80nm≤Dv502≤180nm.

4. The adhesive according to claim 1, characterized in that, The first styrene-butadiene rubber particles account for 10% to 70% of the mass percentage of the adhesive; And / or, the second styrene-butadiene rubber particles account for 30% to 90% of the mass percentage of the adhesive.

5. The adhesive according to claim 4, characterized in that, The mass ratio of the first styrene-butadiene rubber particle to the second styrene-butadiene rubber particle is 1:(1.0~2.2).

6. The adhesive according to any one of claims 1-5, characterized in that, The first styrene-butadiene rubber granules comprise modified styrene-butadiene rubber; The modified styrene-butadiene rubber includes at least one of carboxyl, hydroxyl, and sulfonic acid groups.

7. The adhesive according to claim 6, characterized in that, The carboxyl group in the modified styrene-butadiene rubber accounts for 1% to 10% of the mass percentage of the adhesive; And / or, the hydroxyl groups in the modified styrene-butadiene rubber account for 0.5% to 8% of the mass percentage of the adhesive; And / or, the sulfonic acid groups in the modified styrene-butadiene rubber account for 0.1% to 5% of the mass percentage of the adhesive.

8. The adhesive according to claim 7, characterized in that, The carboxyl group in the modified styrene-butadiene rubber accounts for 1% to 5% of the mass percentage of the adhesive.

9. A negative electrode sheet, characterized in that, It includes: a negative electrode active material layer, wherein the negative electrode active material layer includes the binder according to any one of claims 1-8.

10. The negative electrode sheet according to claim 9, characterized in that, The binder has a mass percentage of 1% to 3% in the negative electrode active material layer.

11. The negative electrode sheet according to claim 9, characterized in that, The negative electrode active material layer also includes polyacrylic acid, and the mass percentage of polyacrylic acid in the negative electrode active material layer is 0.5% to 8%.

12. A method for preparing a negative electrode sheet as described in any one of claims 9-11, characterized in that, Includes the following steps: First styrene-butadiene rubber particles and second styrene-butadiene rubber particles are added to the negative electrode active material to form a negative electrode active coating. The negative electrode active coating is applied to the surface of the current collector to obtain the negative electrode sheet.

13. A battery, characterized in that, include: The negative electrode sheet according to any one of claims 9-11; or the negative electrode sheet prepared by the method for preparing the negative electrode sheet according to claim 12.

14. A battery pack, characterized in that, include: The negative electrode sheet according to any one of claims 9-11; or the negative electrode sheet prepared by the method for preparing the negative electrode sheet according to claim 12; Or the battery as described in claim 13.

15. An electrical appliance, characterized in that, include: The negative electrode sheet according to any one of claims 9-11; or the negative electrode sheet prepared by the method for preparing the negative electrode sheet according to claim 12; or the battery according to claim 13; or the battery pack according to claim 14.

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