Negative electrode binder, negative electrode active material slurry containing negative electrode binder, negative electrode plate for lithium ion cylindrical battery cell and lithium ion cylindrical battery cell

Abstract

The invention provides a negative electrode binder, negative electrode active material slurry containing the same, a negative electrode plate for a lithium ion cylindrical battery cell and the lithium ion cylindrical battery cell, and relates to the technical field of lithium batteries. The negative electrode binder is mainly obtained by copolymerization of a first polymeric monomer, a second polymeric monomer and a third polymeric monomer, and the negative electrode binder can construct a stable ion solvation and lyophilic interface in negative electrode slurry, so that the volume change of a silicon-based negative electrode in the circulation process is effectively relieved. In addition, a fiber reinforced surface layer with controllable orientation is also arranged on one side, facing the diaphragm, of the negative plate for the cylindrical lithium ion battery cell, and the fiber reinforced surface layer can bear out-of-plane bulging and silicon expansion and shrinkage. Therefore, through the two improvements, the negative plate for the cylindrical lithium ion battery cell provided by the invention realizes systematic improvements on gas production, hole collapse and cycle retention rate.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a negative electrode binder and a negative electrode active material slurry containing the same, a negative electrode sheet for lithium-ion cylindrical cells, and a lithium-ion cylindrical cell. Background Technology

[0002] Silicon-based anodes undergo significant volume changes during cycling, which can easily lead to particle cracking, repeated SEI generation, and gas production from side reactions. This is even more pronounced in lithium-ion cylindrical cells, further manifesting as core stress accumulation, central hole shrinkage, and cycle decay.

[0003] The aforementioned problems arise from two main causes. Firstly, traditional bonding systems such as PAA and CMC crosslinking often involve a trade-off between bond strength, ion migration, and electrolyte wettability. This leads to increased electrode strength often accompanied by network embrittlement, decreased wettability, and restricted lithium-ion migration. Reducing the degree of crosslinking, on the other hand, results in insufficient adhesion and cohesion, particle debonding, and pulverization. Simultaneously, residual sodium salts and strongly hydrophilic groups in aqueous systems easily cause liquid absorption swelling and interfacial stress fluctuations. Microcracks trigger repeated SEI repair and lithium source consumption, leading to increased gas production, increased impedance, and accelerated cycle capacity decay. Secondly, while relying solely on electrode compaction or graphite layered structure buffering can temporarily reduce contact resistance and provide some deformation buffering, it significantly increases tortuosity due to decreased porosity and channel connectivity, making it difficult for the electrolyte to fully wet the electrode. Thick electrodes also experience limited mass transfer, increased polarization, and increased heat accumulation. In cylindrical winding, radial stress gradients and a "breathing" effect easily form, leading to central hole shrinkage, gas retention, and decreased uniformity.

[0004] Therefore, it is both necessary and urgent to research and develop a negative electrode for lithium-ion cylindrical cells, thereby effectively alleviating the technical problems of stress accumulation, central hole shrinkage, and cycle decay in existing lithium-ion cylindrical cells.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a negative electrode binder that can construct a stable ion solvation and hydrophilic interface in the negative electrode slurry, thereby effectively mitigating the volume change of the silicon-based negative electrode during cycling and improving the electrochemical performance and stability of the lithium-ion battery core.

[0007] The second objective of this invention is to provide a method for preparing a negative electrode binder.

[0008] A third objective of this invention is to provide a negative electrode slurry.

[0009] A fourth objective of this invention is to provide a negative electrode sheet for lithium-ion cylindrical cells. The active material coating of the negative electrode sheet is prepared using the aforementioned negative electrode binder. Furthermore, the negative electrode sheet of this application also has an orientation-controllable fiber-reinforced surface layer on the side facing the separator. This fiber-reinforced surface layer can withstand out-of-plane bulging and silicon expansion and contraction. Through these two improvements, the negative electrode sheet for lithium-ion cylindrical cells provided by this application achieves a systematic improvement in gas generation, pore collapse, and cycle retention.

[0010] The fifth objective of this invention is to provide a lithium-ion cylindrical battery cell.

[0011] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention provides a negative electrode binder, wherein the negative electrode binder is an amphiphilic polymer, and the amphiphilic polymer is mainly obtained by copolymerization of a first polymeric monomer, a second polymeric monomer, and a third polymeric monomer, wherein: The first polymeric monomer includes: acrylic acid (AA) and / or methacrylic acid (MA); The second polymerization monomer includes one or more of the following: sulfobetaine methacrylate (SBMA), carboxybetaine methacrylate (CBMA), and 2-methacryloyloxyethyl phosphorylcholine (MPC); The third monomer is polyethylene glycol methacrylate (PEGMA).

[0012] Furthermore, the molar fraction range of each polymerizing monomer in the monomer solution where the polymerization reaction takes place in the negative electrode binder includes: The first polymerizable monomer is 30~35 mol%; The second monomer has a content of 45-55 mol% The third polymerizing monomer is 15-25 mol.

[0013] This invention provides a method for preparing a negative electrode binder, the method comprising: The first, second, and third monomers were dissolved in a solvent to prepare a monomer solution. The monomer solution was then subjected to a free radical copolymerization reaction under a red oxygen initiation system to obtain a solution containing a negative electrode binder.

[0014] Furthermore, the solvent is a mixed solution of deionized water and isopropanol; Preferably, the mass ratio of deionized water to isopropanol is 60-80:20-40; Preferably, the red oxygen initiation system is composed of ammonium persulfate (APS) and sodium metabisulfite (SMBS); More preferably, the amount of ammonium persulfate (APS) used is 0.3~0.8 wt% of the total mass of the monomers. More preferably, the amount of sodium metabisulfite (SMBS) used is 0.2~0.6 wt% of the total mass of the monomers; Preferably, the copolymerization reaction is carried out at a temperature of 60-80°C. Preferably, the copolymerization reaction is carried out under dropping conditions, the dropping time is 30-120 min, and the heat preservation time after dropping is 30-90 min.

[0015] Furthermore, the preparation method further includes a step of post-treating the solution containing the negative electrode binder; Preferably, the post-processing steps include: cooling the solution containing the negative electrode binder obtained from the copolymerization reaction to 20~40°C, neutralizing it with lithium hydroxide (LiOH) to pH 7.0~9.0; then filtering to remove impurities and adjusting the solid content to 6~12 wt%.

[0016] The present invention provides a negative electrode active material slurry, the negative electrode active material slurry comprising: a negative electrode active material, a conductive agent and the above-mentioned negative electrode binder.

[0017] Furthermore, by mass percentage, the negative electrode active material slurry comprises: The negative electrode active material comprises 95-96%, the conductive agent comprises 1-2%, and the above-mentioned negative electrode binder comprises 2.5-3.5%. Preferably, the negative electrode active material is selected from at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbide, silicon oxide, and pre-lithium silicon oxide, and the silicon content in the negative electrode active material is 1.0 to 25.0 wt%. Preferably, the conductive agent is selected from carbon nanotubes or a combination of carbon nanotubes and conductive carbon black; Preferably, the solid content of the negative electrode active material slurry is 40-60%, more preferably 42%.

[0018] The present invention provides a negative electrode sheet for lithium-ion cylindrical cells, the negative electrode sheet comprising a negative electrode current collector, a first negative electrode active material coating, a second negative electrode active material coating, and a fiber-reinforced surface layer; Wherein: the side of the negative electrode sheet facing the separator is sequentially provided with a first negative electrode active material coating and a fiber-reinforced surface layer; the first negative electrode active material coating is disposed on the current collector, and the fiber-reinforced surface layer is disposed on the first negative electrode active material coating; The negative electrode sheet is coated with a second negative electrode active material on the other side of the separator; The first negative electrode active material coating and the second negative electrode active material coating are prepared from the above-mentioned negative electrode active material slurry; Preferably, the compaction density of the negative electrode sheet is 1.5~1.7 g / cm³. 3 .

[0019] Furthermore, the fiber-reinforced surface layer is an aramid fiber film layer obtained by electrospinning; Preferably, the fiber orientation factor of the electrospinning is ≥0.55, and the fiber diameter of the electrospinning is 100~300 nm; Preferably, the surface density of the aramid fiber membrane layer is 0.35~0.6 mg•cm. -2 The equivalent thickness is 0.5~3μm.

[0020] The present invention provides a lithium-ion cylindrical battery cell, wherein the lithium-ion cylindrical battery cell includes the above-mentioned negative electrode sheet.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: The negative electrode binder provided by this invention is an amphiphilic polymer, which is mainly obtained by copolymerization of a first polymeric monomer, a second polymeric monomer, and a third polymeric monomer. The first polymeric monomer includes acrylic acid and / or methacrylic acid; the second polymeric monomer includes one or more of sulfobetaine methacrylate, carboxybetaine methacrylate, and 2-methacryloyloxyethyl phosphorylcholine; and the third polymeric monomer is polyethylene glycol methacrylate. The amphiphilic polymer formed by the copolymerization of the first, second, and third polymeric monomers of this application has amphiphilic structural ends, possessing both electrolyte-loving properties and a copolymer network that can adhere to the conductive framework / Si-based surface. Therefore, applying the negative electrode binder of this application to the negative electrode slurry can construct a stable ion-solubilized and liquid-loving interface, thereby effectively mitigating the volume change of the silicon-based negative electrode during cycling and improving the electrochemical performance and stability of the lithium-ion battery core.

[0022] The preparation method of the negative electrode binder of the present invention includes: dissolving a first polymeric monomer, a second polymeric monomer, and a third polymeric monomer in a solvent to prepare a monomer solution; subsequently, subjecting the monomer solution to a free radical copolymerization reaction under a red oxygen initiation system to obtain a solution containing the negative electrode binder. The above preparation method has the technical advantages of simple processing and ease of industrial production.

[0023] The negative electrode slurry provided by the present invention includes a negative electrode active material, a conductive agent and the above-mentioned negative electrode binder. Due to the characteristics of the above-mentioned negative electrode binder, the negative electrode sheet prepared by the negative electrode slurry of this application has better stability.

[0024] This invention provides a negative electrode sheet for lithium-ion cylindrical cells, comprising a negative electrode current collector, a first negative electrode active material coating, a second negative electrode active material coating, and a fiber-reinforced surface layer; wherein: (i) the first and second negative electrode active material coatings are prepared using the binder described above in this application. Because this negative electrode binder contains quaternary ammonium cations and sulfonate, carboxylate, or phosphorylcholine groups, it effectively mitigates the volume change of the silicon-based negative electrode sheet during cycling; (ii) the negative electrode sheet also has an orientable fiber-reinforced surface layer on the side facing the separator, which can withstand out-of-plane bulging and silicon expansion and contraction. Therefore, through the above two improvements, the negative electrode sheet for lithium-ion cylindrical cells provided in this application achieves a systematic improvement in gas generation, pore collapse, and cycle retention.

[0025] The lithium-ion cylindrical battery cell provided by this invention includes the aforementioned negative electrode sheet. Due to the performance of the negative electrode sheet, the lithium-ion cylindrical battery cell of this application can effectively alleviate the technical problems of stress accumulation, center hole shrinkage, and cycle degradation in existing wound cores. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] According to one aspect of the present invention, a negative electrode binder is an amphiphilic polymer, said amphiphilic polymer being mainly obtained by copolymerization of a first polymeric monomer, a second polymeric monomer, and a third polymeric monomer, wherein: The first polymerizing monomer includes: acrylic acid and / or methacrylic acid; The second polymerizing monomer includes one or more of the following: sulfobetaine methacrylate, carboxybetaine methacrylate, and 2-methacryloyloxyethyl phosphorylcholine; The third monomer is polyethylene glycol methacrylate.

[0028] The negative electrode binder provided by this invention is an amphiphilic polymer, which is mainly obtained by copolymerization of a first polymeric monomer, a second polymeric monomer, and a third polymeric monomer, wherein: the first polymeric monomer includes acrylic acid and / or methacrylic acid; the second polymeric monomer includes one or more of sulfobetaine methacrylate, carboxybetaine methacrylate, and 2-methacryloyloxyethylphosphorylcholine; and the third polymeric monomer is polyethylene glycol methacrylate. The negative electrode binder (amphiphilic polymer) formed by the copolymerization of the above-mentioned first polymeric monomer, second polymeric monomer, and third polymeric monomer has amphiphilic structural ends, specifically: 1) Ionic / polar end: Copolymerizing amphiphilic monomers (second monomers) on the backbone formed by the first polymerizing monomer (acrylic acid / methacrylic acid), such as sulfobetaine methacrylate (SBMA), carboxybetaines, or phosphorylcholine methacrylate (MPC), whose quaternary ammonium cation (N + ) and fixed anions (SO3) - / COO - / PO3 2- The coexistence of these elements imparts a highly polar and strongly solvable layer.

[0029] 2) Organic-friendly / hydrophobic end: The main chain formed by the first polymerizing monomer is copolymerized with PEGMA (polyethylene glycol methacrylate) or a small amount of hydrophobic monomers (such as BMA / MMA). Since the PEG side chain is highly miscible with the carbonate electrolyte, the hydrophobic segment has good van der Waals force interaction with the graphite / carbon material.

[0030] Therefore, the negative electrode binder of this application has both electrolyte-loving properties and a copolymer network that is compatible with the conductive framework / Si-based surface. Applying the negative electrode binder of this application to the negative electrode slurry can build a stable ion solvation and hydrophilic interface, thereby effectively mitigating the volume change of silicon-based negative electrodes during cycling and improving the electrochemical performance and stability of lithium-ion battery cores.

[0031] It should be noted that the effect of the negative electrode binder in this application in mitigating the volume change (suppressing expansion) of the silicon-based negative electrode during cycling is manifested as follows: 1. Internal charge neutralization: The amphiphilic groups of the negative electrode binder in this application carry equal amounts of positive and negative charges, the polymer is electrically neutral, the osmotic pressure is low, and it is less prone to swelling than anionic / cationic polyelectrolytes.

[0032] 2. Ion-pair / dipole physical crosslinking: The quaternary ammonium cation (N⁺) in the negative electrode binder of this application and the fixed anion (SO₃) - / COO - / PO3 2-Reversible ion association sites are formed at the nanoscale, dispersing and dissipating volumetric stress, and limiting gelation and outward bulging of thick electrode sheets.

[0033] 3. Solvation and hydrophilic wetting: A dense solvation layer and a high dielectric local environment can be formed around the amphiphilic anode binder of this application, which can promote the uniform spread of electrolyte in the micropores of the coating rather than local aggregation, and reduce the non-uniform expansion caused by solvent selective adsorption.

[0034] 4. Interface anchoring: The anionic terminals of the negative electrode binder in this application are anchored to the ≡Si–OH and ≡Si–O atoms on the SiOx surface. - (Note: ≡ refers to surface anchoring) There are hydrogen bonds / ionic interactions, and the cationic end and the polar defects / π facets of the conductive carbon surface have ion-dipole / ion-π interactions, which can effectively improve adhesion and in-plane modulus, and suppress pulverization and interlayer slip during repeated cycles.

[0035] As an optional implementation, the molar fraction of the first polymerizing monomer in the monomer solution in which the polymerization reaction is carried out is in the range of 30~35 mol%, for example, it can be 30%, 31%, 32%, 34%, 35%, or any value between 30 and 35%. As an optional implementation, the molar fraction of the second polymerizing monomer in the monomer solution in which the polymerization reaction is carried out is in the range of 45~55 mol%, for example, it can be 45%, 48%, 50%, 52%, 55%, or any value between 45 and 55%. As an optional implementation, the molar fraction of the third polymerizing monomer in the monomer solution undergoing the polymerization reaction ranges from 15 to 25 mol%, for example, it can be 15%, 18%, 20%, 22%, 24%, 25%, or any value between 15 and 25%. According to one aspect of the present invention, a method for preparing a negative electrode binder, the method comprising: The first, second, and third monomers were dissolved in a solvent to prepare a monomer solution. The monomer solution was then subjected to a free radical copolymerization reaction under a red oxygen initiation system to obtain a solution containing a negative electrode binder.

[0036] The preparation method of the negative electrode binder of the present invention includes: dissolving a first polymeric monomer, a second polymeric monomer, and a third polymeric monomer in a solvent to prepare a monomer solution; subsequently, subjecting the monomer solution to a free radical copolymerization reaction under a red oxygen initiation system to obtain a solution containing the negative electrode binder. The above preparation method has the technical advantages of simple processing and ease of industrial production.

[0037] In a preferred embodiment of the present invention, the solvent is a mixed solution of deionized water and isopropanol; In the preferred embodiment described above, the mass ratio of deionized water to isopropanol is 60-80:20-40; In a preferred embodiment of the present invention, the red oxygen initiation system is composed of ammonium persulfate (APS) and sodium metabisulfite (SMBS); As an optional implementation, the amount of ammonium persulfate (APS) is 0.3 to 0.8 wt% of the total mass of the monomers, for example, it can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or any value between 0.3% and 0.8%. As an optional implementation, the amount of sodium metabisulfite (SMBS) is 0.2 to 0.6 wt% of the total mass of the monomers, for example, it can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or any value between 0.2% and 0.6%. As an optional implementation, the temperature of the copolymerization reaction is 60~80℃, for example, it can be 60℃, 65℃, 70℃, 75℃, 80℃, or any value between 60~80℃; As an optional implementation, the copolymerization reaction is carried out under dropping conditions, and the dropping time is 30-120 min; for example, it can be 30 min, 50 min, 80 min, 100 min, 120 min, or any value between 30 and 120 min; As an optional implementation, the copolymerization reaction is carried out under dropping conditions, and the heat preservation time after dropping is 30 to 90 minutes; for example, it can be 30 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, or 90 minutes, or any value between 30 and 90 minutes.

[0038] In a preferred embodiment of the present invention, the preparation method further includes a step of post-treatment of the solution containing the negative electrode binder; In the preferred embodiment above, the post-processing steps include: cooling the solution containing the negative electrode binder obtained from the copolymerization reaction to 20~40°C, neutralizing it with lithium hydroxide (LiOH) to pH 7.0~9.0; then filtering to remove impurities and adjusting the solid content to 6~12 wt%.

[0039] As a preferred embodiment, the reaction formula for neutralization (partial lithium salting of acrylic acid) using lithium hydroxide (LiOH) is as follows:

[0040] The neutralization effect of lithium hydroxide (LiOH) described above is as follows: 1. Swelling Inhibition: The lithium-ionized –COO⁻Li⁺ group, together with the amphiphilic groups (quaternary ammonium-sulfonate / carboxylate / phosphorylcholine), forms ion association sites. These “reversible ion crosslinks” maintain a certain coordination strength after solvation, limiting the free volume of chain segments and gelation, reducing electrode swelling due to liquid absorption, and improving ion strength.

[0041] 2. Interface and Adhesion: -COO⁻ Li⁺ can adhere to ≡Si–OH and ≡Si–O on the SiOx surface. - (Note: ≡ refers to surface anchoring) It forms ion-coordination synergistic anchoring, while the quaternary ammonium end and the carbon material π surface generate ion-π / dipole interaction, which enhances the three-phase adhesion of particles-binder-current collector and reduces microcracks and pulverization during circulation.

[0042] 3. Ion migration and wetting: Amphiphilic units increase the local dielectric constant and build a stable solvation layer. Lithium salting provides dispersed Li⁺ sites / transition sites, promoting interface desolvation and uniform deposition, making the SEI denser and with less gas.

[0043] 4. Chemical stability and safety: Neutralization removes free acid, reducing the risk of acid-induced decomposition and gas generation of copper foil and electrolyte.

[0044] According to one aspect of the present invention, a negative electrode active material slurry comprises: a negative electrode active material, a conductive agent, and the aforementioned negative electrode binder.

[0045] The negative electrode slurry provided by the present invention includes a negative electrode active material, a conductive agent and the above-mentioned negative electrode binder. Due to the characteristics of the above-mentioned negative electrode binder, the negative electrode sheet prepared by the negative electrode slurry of this application has better stability.

[0046] In a preferred embodiment of the present invention, the negative electrode active material slurry comprises, by mass percentage: The negative electrode active material comprises 95-96%, the conductive agent comprises 1-2%, and the above-mentioned negative electrode binder comprises 2.5-3.5%. In the preferred embodiment described above, the negative electrode active material is selected from at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-carbon, silicon-oxygen, and pre-lithium silicon-oxygen, and the silicon content in the negative electrode active material is 1.0–25.0 wt%. In the preferred embodiment described above, the conductive agent is selected from carbon nanotubes or a combination of carbon nanotubes and carbon black. In the preferred embodiment described above, the solid content of the negative electrode active material slurry is 42%.

[0047] According to one aspect of the present invention, a negative electrode sheet for a lithium-ion cylindrical battery cell, the negative electrode sheet comprising a negative electrode current collector, a first negative electrode active material coating, a second negative electrode active material coating, and a fiber-reinforced surface layer; Wherein: the side of the negative electrode sheet facing the separator is sequentially provided with a first negative electrode active material coating and a fiber-reinforced surface layer; the first negative electrode active material coating is disposed on the current collector, and the fiber-reinforced surface layer is disposed on the first negative electrode active material coating; The negative electrode sheet is coated with a second negative electrode active material on the other side of the separator; The first negative electrode active material coating and the second negative electrode active material coating are prepared from the above-mentioned negative electrode active material slurry; This invention provides a negative electrode sheet for lithium-ion cylindrical cells, comprising a negative electrode current collector, a first negative electrode active material coating, a second negative electrode active material coating, and a fiber-reinforced surface layer; wherein: (i) the first and second negative electrode active material coatings are prepared using the binder described above in this application. Because this negative electrode binder contains quaternary ammonium cations and sulfonate, carboxylate, or phosphorylcholine groups, it effectively mitigates the volume change of the silicon-based negative electrode sheet during cycling; (ii) the negative electrode sheet also has an orientable fiber-reinforced surface layer on the side facing the separator, which can withstand out-of-plane bulging and silicon expansion and contraction. Therefore, through the above two improvements, the negative electrode sheet for lithium-ion cylindrical cells provided in this application achieves a systematic improvement in gas generation, pore collapse, and cycle retention.

[0048] As an optional implementation, the compaction density of the negative electrode sheet is 1.5~1.7 g / cm³. 3 For example, it could be 1.5g / cm³. 3 1.6g / cm 3 1.7g / cm 3 It can also be 1.5~1.7g / cm³. 3 Any value between.

[0049] In a preferred embodiment of the present invention, the fiber-reinforced surface layer is an aramid fiber film layer obtained by electrospinning; In the preferred embodiment described above, the fiber orientation factor of the electrospinning is ≥0.55; In the preferred embodiment described above, the surface density of the aramid fiber membrane is 0.35~0.6 mg•cm³. -2 The equivalent thickness is 0.5~3 μm.

[0050] According to one aspect of the present invention, a lithium-ion cylindrical cell includes the aforementioned negative electrode sheet.

[0051] The lithium-ion cylindrical battery cell provided by this invention includes the aforementioned negative electrode sheet. Due to the performance of the negative electrode sheet, the lithium-ion cylindrical battery cell of this application can effectively alleviate the technical problems of stress accumulation, center hole shrinkage, and cycle degradation in existing wound cores.

[0052] The technical solution of the present invention will be further described below with reference to the embodiments.

[0053] Example 1 A negative electrode sheet for lithium-ion cylindrical cells, the negative electrode sheet comprising: a negative electrode current collector, a first negative electrode active material coating, a second negative electrode active material coating, and a fiber-reinforced surface layer; Wherein: the side of the negative electrode sheet facing the separator is sequentially provided with a first negative electrode active material coating and a fiber-reinforced surface layer; The first negative electrode active material coating is disposed on the current collector, and the fiber-reinforced surface layer is disposed on the first negative electrode active material coating; The negative electrode sheet is coated with a second negative electrode active material on the other side of the separator; The method for preparing the negative electrode sheet for lithium-ion cylindrical cells includes: (1) Preparation of negative electrode binder: 1. Solvent and monomer pre-mixing: The solvent was prepared by mixing water and isopropanol (IPA) at a mass ratio of 7:3, heating to 70 °C, and deoxygenating by bubbling with nitrogen for 20 min. First monomer: acrylic acid (AA, Mw=72.06 g / mol); Second monomer for polymerization: sulfobetaine methacrylate (SBMA, Mw≈295.36 g / mol); Third polymerization monomer: polyethylene glycol methacrylate (PEGMA, selected with Mn≈475 g / mol); Add the first monomer to the above solvent in a molar ratio of "first monomer: second monomer: third monomer = 30: 50: 20" and stir at 300 rpm until clear. That is, AA 21.62 g, SBMA 147.68 g, PEGMA 95 g, total monomer mass ≈ 264.3 g, to obtain clear monomer solvent.

[0054] 2. Red oxygen free radical copolymerization: The APS solution (total monomer mass 0.5wt%: 1.32g APS dissolved in 20g water) and the SMBS solution (total monomer mass 0.3wt%: 0.79g SMBS dissolved in 20g water) were simultaneously and dropwise added to the clarified monomer solvent in step 1 above at the same rate, while maintaining the system at 70°C and stirring at 400 rpm during the dropwise addition. After the addition is complete, the mixture is kept at a constant temperature for 60 minutes to complete the polymerization, resulting in a solution containing the negative electrode binder.

[0055] The free radical copolymerization reaction equation is as follows:

[0056] 3. Neutralization: The solution containing the negative electrode binder was cooled to 30-35℃, and 1.0 M LiOH was slowly added dropwise. The pH was monitored online to be 7.8±0.2, and the solid content was 8.0±0.3 wt%. XPS reverse characteristics: N1s 402–403 eV (quaternary ammonium) and S2p 167–169 eV (–SO3) - () coexist; no B1s (boric acid) and F1s (F–S / F–N) peaks.

[0057] The above-mentioned reverse XPS characteristics prove the presence of quaternary ammonium cations + sulfonate ions: 1) N 1s (quaternary ammonium): main peak at 402–403 eV, characterizing the presence of a permanent positive charge in quaternary ammonium; 2) S2p (sulfonate ions): bimodal S 2p peaks. 3 / 2 ≈168.0–168.6 eV, S2p 1 / 2 ≈ 169.2–170.0 eV, with intervals of approximately 1.2 eV.

[0058] 4. Filtration and storage: The neutralized solution was filtered through a 5μm polypropylene filter to obtain the negative electrode binder solution.

[0059] (2) Preparation of negative electrode slurry: 1. Mix 95.5% of the active material, 0.75% of SWCNT, 0.75% of the conductive carbon black, and 3% of the binder prepared in step (1) by mass percentage to obtain a homogeneous mixture; The active material is composed of silicon oxide, silicon carbon and graphite, and the mass ratio of silicon oxide, silicon carbon and graphite is 24:16:60.

[0060] 2. Add the above-mentioned mixed material to deionized water and stir to form a negative electrode coating material with a solid content of 42%, and prepare a negative electrode slurry.

[0061] (3) Preparation of the intermediate for the negative electrode sheet: The negative electrode slurry prepared in step (2) is coated on both sides of the negative electrode current collector (copper foil), and after drying and cold pressing, a negative electrode intermediate is formed with a compaction density of 1.6 g / cm³. 3 ; (4) Electrospinning to prepare fiber-reinforced surface layer: 1. Preparation of spinning solution: Add 980g of DMSO and 52g of KOH (solid-liquid mass ratio ≈ 1:19) to a three-necked flask and stir to dissolve. Add 20g of Kevlar chopped fibers (aramid fibers) and stir for 72h under nitrogen protection at room temperature (25℃) to obtain a 2.0wt% ANF dark brown dispersion. Centrifuge at 3000rpm for 10 min as the spinning solution.

[0062] 2. Spinning to form a film: The above spinning solution is used to spin and form a fiber membrane. The specific process parameters are as follows: Needle-collection distance: 18 cm; Voltage: 18 kV; Flow rate: 0.8 mL·h -1 / Nozzle; Rotary drum covering PET, linear velocity 1.0 m / s -1 Orientation factor f≈0.60). The areal density of aramid fibers was determined to be 0.45 mg·cm³ by time-calibrated control. -2 ; The fiber membrane was then lightly sprayed and washed in deionized water for 0.5 h (to remove KOH), and then vacuum dried at 50 °C for 1 h.

[0063] 3. Transfer hot pressing: The fiber membrane was aligned and attached to the negative electrode coating surface, and hot-pressed at 90°C, 5MPa, and 120s. Subsequently, it was cooled to 40°C and the PET was peeled off to obtain an aramid fiber membrane surface layer (fiber-reinforced surface layer) with an equivalent thickness of ≈1.2μm, thus preparing the negative electrode sheet for lithium-ion cylindrical cells in this embodiment.

[0064] Examples 2-4 Except for "(1) Step 1 in preparing the negative electrode binder", which is different from Example 1, Examples 2-4 of this application are the same as Example 1. Specifically, as follows: (1) Preparation of negative electrode binder: 1. Solvent and monomer pre-mixing: The solvent was prepared by mixing water and isopropanol (IPA) at a mass ratio of 7:3, heating to 70 °C, and deoxygenating by bubbling with nitrogen for 20 min. First polymerizable monomer: Same as in Example 1; Second polymerizable monomer: Same as in Example 1; Third polymerizable monomer: Same as in Example 1; The first monomer (AA), the second monomer (SBMA), and the third monomer (PEGMA) were added to the above solvent by molar ratio and stirred at 300 rpm until clear, thus obtaining the clear monomer solvent.

[0065] Table 1. Molar ratios of the first, second, and third monomers in Examples 2-4:

[0066] Example 5 Except for the binder content of 3.5% in step 1 of "(2) preparing the negative electrode slurry", the contents of Example 5 of this application are the same as those in Example 1. Specifically: (2) Preparation of negative electrode slurry: 1. Mix 95% of the active material, 0.75% of the conductive agent, 0.75% of the conductive carbon black, and 3.5% of the binder prepared in step (1) by mass percentage to obtain a homogeneous mixture; The active substance is the same as in Example 1. Example 6 Except for the binder content of 2.5% in step 1 of "(2) preparing the negative electrode slurry", the contents of Example 6 of this application are the same as those in Example 1. Specifically: (2) Preparation of negative electrode slurry: 1. Mix 96% of the active material, 0.75% of the conductive agent, 0.75% of the conductive carbon black, and 2.5% of the binder prepared in step (1) by mass percentage to obtain a homogeneous mixture; The active substance is the same as in Example 1. Examples 7-9 Except for the composition of the active material in "(2) Step 1 of preparing the negative electrode slurry", the compositions of Examples 7-9 of this application are the same as those in Example 1. Specifically, they are as follows: (2) Preparation of negative electrode slurry: 1. Mix 95.5% of the active material, 0.75% of the conductive agent, 0.75% of the conductive carbon black, and 3% of the binder prepared in step (1) by mass percentage to obtain a homogeneous mixture; Table 2: Composition of active substances in Examples 7-9

[0067] Example 10 In Example 10 of this application, except for "(4) Step 2 of preparing the fiber-reinforced surface layer by electrospinning", the areal density of the aramid fiber is controlled to be 0.35 mg·cm³. -2 Except for the above, the rest is the same as in Example 1. Specifically: 2. Spinning to form a film: The above spinning solution is used to spin and form a fiber membrane. The specific process parameters are as follows: Needle-collection distance: 18 cm; Voltage: 18 kV; Flow rate: 0.8 mL·h -1 / Nozzle; Rotary drum covering PET, linear velocity 1.0 m / s -1 (Orientation factor f≈0.60); The areal density of aramid fibers was determined to be 0.35 mg·cm³ by time-calibrated control. -2 ; The fiber membrane was then lightly sprayed and washed in deionized water for 0.5 h (to remove KOH), and then vacuum dried at 50 °C for 1 h.

[0068] Example 11 In Example 10 of this application, except for "(4) Step 2 of preparing the fiber-reinforced surface layer by electrospinning", the areal density of the aramid fiber is controlled to be 0.6 mg•cm. -2 Except for the above, the rest is the same as in Example 1. Specifically: 2. Spinning to form a film: The above spinning solution is used to spin and form a fiber membrane. The specific process parameters are as follows: Needle-collection distance: 18 cm; Voltage: 18 kV; Flow rate: 0.8 mL·h -1 / Nozzle; Rotary drum covering PET, linear velocity 1.0 m / s -1 (Orientation factor f≈0.60); The areal density of aramid fibers was determined to be 0.6 mg·cm³ by time-calibrated control. -2 ; The fiber membrane was then lightly sprayed and washed in deionized water for 0.5 h (to remove KOH), and then vacuum dried at 50 °C for 1 h.

[0069] Example 12 In Example 10 of this application, except for "(3) Preparation of the intermediate negative electrode sheet", the compaction density is 1.5 g / cm³. 3 Except for the above, the rest is the same as in Example 1. Specifically: Example 13 In Example 10 of this application, except for "(3) Preparation of the intermediate negative electrode sheet", the compaction density is 1.7 g / cm³. 3 Except for the above, the rest is the same as in Example 1. Specifically: Comparative Example 1 Except for the step 1 of “(1) preparing the negative electrode binder”, in which the molar ratio of the first polymeric monomer, the second polymeric monomer and the third polymeric monomer is 15:25:60, the Comparative Example 1 of this application is the same as Example 1.

[0070] Comparative Example 2 The Comparative Example 2 of this application is the same as Example 1, except that the binder content in "(2) Step 1 of preparing negative electrode slurry" is 0.8%.

[0071] Comparative Example 3 Except for the fact that the mass ratio of silicon oxide, silicon carbon, and graphite in the active material of Comparative Example 3 in “(2) Step 1 of preparing negative electrode slurry” is 34:6:60, the rest of Comparative Example 3 is the same as Comparative Example 3.

[0072] Comparative Example 4 In Comparative Example 4 of this application, except for "(4) Step 2 of preparing the fiber-reinforced surface layer by electrospinning", the areal density of the aramid fiber is controlled to be 0.05 mg•cm. -2 Except for the above, the rest is the same as in Example 1.

[0073] Comparative Example 5 (excluding the electrospun layer) The present application’s Comparative Example 4 is the same as Example 1 except that it does not include step “(4) electrospinning to prepare fiber-reinforced surface”. That is, the negative electrode of Comparative Example 5 is the negative electrode intermediate in Example 1.

[0074] To illustrate this more clearly, the applicant has listed the differences between Examples 1-13 and Comparative Examples 1-5, as shown in the table below: Table 3: Parameter variation table for Examples 1-13 and Comparative Examples 1-5:

[0075] Experimental Example 1 (a) In this experimental example, the negative electrode sheets prepared in Examples 1 to 13 and Comparative Examples 1 to 5 above are assembled into lithium-ion batteries.

[0076] The lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein: the negative electrode is prepared in Examples 1-13 and Comparative Examples 1-5 above, and the positive electrode, electrolyte, separator, and assembly method are as follows: (1) Preparation of the positive electrode: Positive electrode active material, conductive carbon black, carbon nanotubes and polyvinylidene fluoride (PVDF) were taken and thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96:1:1:2 to obtain a positive electrode coating material. The positive electrode coating material was then coated onto a 12.0 μm thick aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained. (2) Preparation of electrolyte: An electrolyte was prepared by mixing lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), and vinylene carbonate (VC) in a mass percentage ratio of 10.0: 22.0: 53.0: 3.0: 7.0: 5.0.

[0077] (3) Preparation of the diaphragm: A high-porosity membrane was selected, in which the thickness of the PE base membrane was 9 μm, the thickness of the ceramic coating on both sides of the base membrane was 1.0 μm, and the thickness of the PVDF coating was 1.0 μm. (4) Assembly of lithium-ion batteries: After the positive and negative electrode sheets are rolled and slit respectively, they are wound together with the separator according to a set process to form a 21700 cylindrical battery core. The fiber-reinforced surface of the negative electrode sheet faces the separator. Subsequently, the battery core is fixed to the prefabricated connecting piece by welding and then installed into the metal battery casing. After completing key processes such as electrolyte injection, sealing, and formation, a lithium-ion battery is produced. This lithium-ion battery adopts a cylindrical casing with external dimensions of 21.0 mm in diameter and 70.0 mm in length, conforming to the 21700 standard specification.

[0078] (II) The lithium-ion batteries obtained by assembling the negative electrode sheets of Examples 1-13 and Comparative Examples 1-5 were subjected to performance testing. The specific testing methods are as follows: (1) XRD, XPS, Raman and HRTEM tests: First, the lithium-ion battery is discharged at a constant current to 2.5V to ensure it is in a safe state, reducing the risk of short circuits or thermal runaway during disassembly. The battery is carefully disassembled inside a glove box (protected by argon or other inert atmosphere), and the electrodes of the cylindrical cell are removed. The electrodes are peeled off using plastic tweezers, taking care not to damage the active material layer. Next, the removed electrodes are cut to appropriate sizes and immersed in anhydrous dimethyl carbonate (DMC) solution for 30 minutes to dissolve and remove residual electrolyte and possible byproducts. After removing the electrodes, the surface is gently wiped with lint-free paper, and then the immersion-wiping process is repeated three times with fresh DMC solution to ensure no residual contaminants remain on the electrode surface. Subsequently, the electrodes are rinsed with anhydrous ethanol and wiped again to further remove solvent and impurities. After cleaning, the electrodes are placed in a glove box and left to stand for 48 hours to ensure they are completely dry, preventing interference from residual solvents in subsequent testing. After drying, the active material layer is gently scraped off using a plastic scraper, ensuring the collected powder is not contaminated. The scraped powder was transferred to centrifuge tubes containing anhydrous ethanol and ultrasonically dispersed for 30 minutes in an ultrasonic cleaner to further remove any possible residual electrolyte and impurities. After ultrasonic treatment, the sample was centrifuged (at 5000 rpm for 2 minutes), the supernatant was discarded, and the powder was redispersed with anhydrous ethanol, ultrasonicated again for 10 minutes, and then centrifuged again. This process was repeated three times to ensure the purity of the powder sample. Finally, the precipitate was collected and transferred to a vacuum drying oven and dried at 80°C for 12 hours to ensure complete removal of residual solvent. The dried powder was placed in a sealed bag or sealed sample box, immediately removed from the glove box, and the sample was quickly subjected to XRD, XPS, Raman, and HRTEM tests.

[0079] 1. Specific XRD measurement method: A copper target X-ray diffractometer (Cu-Kα radiation, 1.54 Å, tube voltage 40kV, tube current 40mA) was used. The sample was uniformly dispersed on a silicon substrate, and XRD patterns were acquired at a scanning rate of 2° / min in the range of 2θ = 15°~70°.

[0080] 2. Specific methods for determining the intensity (height) of elemental characteristic peaks in XPS spectra: XPS testing was performed using a PHI-5000 Versa Probe instrument, with Al Kα (1486.6 eV) as the X-ray source and a power of 150 W (15 kV × 10 mA). The test included full-spectrum scanning (0–1100 eV, step size 1 eV), background subtraction was performed using Shirley background correction, and C 1s (284.8 eV) was used as an internal standard for data normalization and elemental quantitative analysis.

[0081] (2) Test method for electrode compaction density: First, the positive electrode sheet, after being washed with dimethyl carbonate and vacuum dried, was cut into six standard-sized square samples (2.0cm × 2.0cm). Next, the active material on both sides of three of these square samples was removed, and they were rinsed with ethanol, dried, weighed, and their average mass M1 was calculated. Simultaneously, the average thickness L1 of the samples was measured using a micrometer. Then, the mass of the remaining three square samples was weighed, and their average mass M2 was calculated. The average thickness L2 of the samples was also measured. The electrode sheet thickness was calculated as: L2 - L1, in cm. The compacted density of the electrode sheet was calculated as: ρ = (M2 - M1) / (2 × 2 × (L2 - L1)), in g / cm³. 3 .

[0082] (3) Performance testing methods: 1. Gas production at 85℃ for 24 hours: Fully charge (0.5C CC–CV to 4.20 V, CV cutoff 0.05C), let stand for 1 h.

[0083] Place the battery cell (end face up) at a constant temperature of 85℃ for 24 hours.

[0084] After removing the battery, secure the positive and negative terminals with insulating tape and immerse it in deionized water (the device has been pre-calibrated to zero).

[0085] Record the rise in the displacement liquid level (i), which is then determined as the gas production rate.

[0086] 2. Collapse coefficient of the central hole of the cylinder: X-ray CT measures the initial center aperture D of the battery cell. O After 200 cycles of 1C / 1C charge / discharge, measure the center aperture D again. Collapse coefficient = (D...) O –D) / D O ×100%; 3. Capacity retention rate after 500 cycles at 25℃ and 1C: Place the battery in a 25°C constant temperature chamber for 6 hours and test it according to the following steps: 1) First round of constant current and constant voltage charging: Charge at a constant current of 0.1C to 4.20V, then switch to constant voltage charging until the current drops to 0.01C; 2) Let it stand for 30 minutes after charging is complete.

[0087] 3) Perform constant current discharge, discharging at a rate of 0.1C to 2.5V; 4) Cyclic charge and discharge process: constant current charging at a rate of 1C to 4.20V, then switch to constant voltage charging until the current drops to 0.1C; 5) Let it stand for another 30 minutes; 6) Discharge at a constant current rate of 1C to 2.5V; 7) Let it stand for another 30 minutes; 8) Repeat the charging and discharging process from 4) to 7) above for a total of 500 cycles.

[0088] 500-cycle capacity retention rate: After 1 cycle and 500 cycles, the discharge capacity Q1 and Q500 of the battery are calculated, and the capacity retention rate of the battery is calculated as: Q500 / Q1×100%.

[0089] (III) See the table below for specific test results.

[0090] Table 4: Detection results of Examples 1-13 and Comparative Examples 1-5

[0091] Referring to the table above, comparing Examples 1-4 with Comparative Example 1, it can be seen that when the SBMA ratio is slightly reduced, it leads to ion solvation of the amphiphilic layer on the negative electrode surface and weakened interfacial wettability, resulting in a looser initial SEI, increased gas production from side reactions, increased central pore shrinkage, and a decrease in the 500-cycle retention rate. When the SBMA ratio is slightly increased within a reasonable range (45-55 mol%), the ion pair density of quaternary ammonium and sulfonate is higher, the coordination hydration sheath is stable, lithium ion migration and electrolyte spreading are more complete, the SEI is denser and cracking regeneration is reduced, gas production decreases, pore collapse is suppressed, and the cycle retention rate is improved. In contrast, in Comparative Example 1 (molar ratio of AA, SBMA, and PEGMA is 15:25:60), the SBMA ratio is significantly lower and the PEGMA ratio is higher, resulting in insufficient polarity of the polymer network and insufficient ion fixation points, increased liquid absorption and swelling, leading to more prominent interfacial instability and gas accumulation.

[0092] Comparing Examples 1, 4, and 5 with Comparative Example 2, it can be seen that when the binder ratio is moderately increased (Example 5), interparticle bridging and coating continuity are enhanced, microcrack propagation is restricted, and pulverization and flaking are reduced, resulting in reduced gas production, stable central pores, and improved long-term retention. When the binder ratio is reduced (Example 6), cohesion and adhesion are insufficient, the pore structure is looser, and the side reactions caused by repeated SEI repair increase, leading to increased gas production and pore shrinkage. In Comparative Example 2, the binder ratio is too low, failing to form a stable stress transfer network and effective coverage. The microstructure of the electrode is significantly damaged during calendering and cycling, resulting in higher gas production, greater deformation, and significant capacity decay.

[0093] Comparing Examples 1, 6, 7, and 8 with Comparative Example 3, it can be seen that, under the premise of constant total silicon content, appropriately increasing the silicon-carbon ratio while maintaining the graphite framework can enhance electronic continuity and the interaction of embedded buffer phases, resulting in a more balanced distribution of interfacial stress, a decrease in central pore shrinkage, and an increase in retention rate. When the silicon-oxygen ratio is further increased, although the nominal reversible capacity potential increases, the volume change caused by alloying and the initial side reactions caused by oxidation components increase. Without additional buffering, this will lead to increased gas production and central pore collapse. The high silicon-oxygen ratio in Comparative Example 3 makes the internal cracking of particles and SEI regeneration more frequent, disrupting the electronic pathway, ultimately resulting in higher gas production, greater pore shrinkage, and lower cycle retention rate.

[0094] Comparing Examples 1, 8, and 9 with Comparative Examples 4 and 6, it can be seen that when the fiber surface density is moderate (0.35~0.6 mg•cm³), -2 This can form a continuous tensile stress layer, while also acting as a microscale barrier to mitigate side reactions induced by electrolyte infiltration, resulting in lower gas production, stable pore size, and higher circulation retention. When the areal density decreases slightly, the confinement effect weakens, and out-of-plane bulging and microcrack growth increase, leading to increased gas production. When the areal density increases, the mechanical confinement is more sufficient, further reducing gas generation and pore shrinkage. Comparative Example 4 shows an extremely low areal density (0.05 g / cm³). 3 It is almost impossible to form an effective stress-bearing layer, and the structure becomes obviously unstable during the cycle; Comparative Example 5 has no fiber layer at all, the winding and rolling stress cannot be shared, and the hole collapse and gas accumulation are the most serious.

[0095] Comparing Examples 1, 10, and 11, it can be seen that when the compaction density is moderate (1.5~1.7 g / cm³), the desired compaction density is achieved. 3 The compaction achieves a good balance between electron contact, ion channels, and pore structure, thus balancing low gas production, small central pore shrinkage, and high long-term retention. When the compaction is slightly reduced, the pores and channels become more open, and the polarization decreases, but the volumetric energy density and effective interparticle contact decrease accordingly, and the side reactions are not improved. When the compaction is increased, although the contact resistance decreases in the short term, local particle breakage and stress concentration increase, and the side reactions caused by repeated SEI regeneration are enhanced, manifested as increased gas production and greater pore shrinkage. At the same time, the cycle capacity retention rate decreases, indicating that excessive compaction is not conducive to the long-term stability of the structure and interface of the silicon-based system.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode binder characterized by, The negative electrode binder is an amphiphilic ionomer mainly obtained by copolymerization of a first polymerization monomer, a second polymerization monomer and a third polymerization monomer, wherein: The first polymerization monomer comprises: acrylic acid and / or methacrylic acid; The second polymerization monomer comprises: one or more of sulfobetaine methacrylate, carboxybetaine methacrylate and 2-methacryloyloxyethyl phosphorylcholine; The third polymerization monomer is polyethylene glycol methacrylate.

2. The negative electrode binder according to claim 1, characterized by, The mole fraction of each polymerization monomer in the monomer solution for the polymerization reaction of the negative electrode binder ranges from: The first polymerization monomer is 30-35 mol%; The second polymerization monomer is 45-55 mol%; The third polymerization monomer is 15-25 mol%.

3. A method for producing the negative electrode binder according to claim 1 or 2, characterized by, The preparation method comprises: The first polymerization monomer, the second polymerization monomer and the third polymerization monomer are dissolved in a solvent to obtain a monomer solution, and then the monomer solution is subjected to a free radical copolymerization reaction under a red oxygen initiation system to obtain a solution containing the negative electrode binder.

4. The method of claim 3, wherein the negative electrode binder is prepared by mixing the binder resin and the conductive agent in a weight ratio of 1 : 0.1 to 1 : 0.

5. The solvent is a mixed solution of deionized water and isopropyl alcohol; Preferably, the mass ratio of the deionized water to the isopropyl alcohol is 60-80:20-40; Preferably, the red oxygen initiation system is composed of ammonium persulfate and sodium metabisulfite; More preferably, the amount of ammonium persulfate is 0.3-0.8 wt% of the total mass of the monomers; More preferably, the amount of sodium metabisulfite is 0.2-0.6 wt% of the total mass of the monomers; Preferably, the temperature of the copolymerization reaction is 60-80°C; Preferably, the copolymerization reaction is carried out under dropwise addition, the dropwise addition time is 30-120 min, and the holding time after dropwise addition is 30-90 min.

5. The method of producing a negative electrode binder according to claim 3, wherein The preparation method further comprises a step of post-treatment of the solution containing the negative electrode binder; Preferably, the post-treatment step comprises: cooling the solution containing the negative electrode binder obtained by the copolymerization reaction to 20-40°C, neutralizing with lithium hydroxide to pH 7.0-9.0, then filtering out impurities and adjusting the solid content to 6-12 wt%.

6. A negative electrode active material slurry, characterized by, The negative electrode active material slurry comprises: a negative electrode active material, a conductive agent and the negative electrode binder according to any one of claims 1-5.

7. The negative electrode active material slurry according to claim 6, characterized by, The negative electrode active material slurry comprises, by mass percentage: The negative electrode active material is 95-96%, the conductive agent is 1-2%, and the negative electrode binder is 2.5-3.5%; Preferably, the negative electrode active material is selected from at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-carbon, silicon-oxygen and pre-lithiated silicon-oxygen, and the silicon content in the negative electrode active material is 1.0-25.0 wt%; Preferably, the conductive agent is selected from carbon nanotubes or a combination of carbon nanotubes and conductive carbon black; Preferably, the solid content of the negative electrode active material slurry is 40-60%, preferably 42%.

8. A negative electrode sheet for a lithium-ion cylindrical battery cell, characterized by comprising: The negative electrode sheet comprises a negative electrode current collector, a first negative electrode active material coating layer, a second negative electrode active material coating layer and a fiber reinforced surface layer. The negative plate is provided with a first negative active material coating and a fiber reinforced surface layer on the side of the separator. The negative plate is provided with a second negative active material coating on the other side of the separator. The first negative active material coating and the second negative active material coating are prepared from the negative active material slurry of claim 6 or 7. Preferably, the compacted density of the negative electrode sheet is 1.5 to 1.7 g / cm 3 .

9. The negative electrode sheet according to claim 8, characterized by The fiber reinforced surface layer is an aramid fiber membrane layer obtained by electrospinning. Preferably, the electrospun fiber orientation factor is ≥0.

55. Preferably, the electrospun fiber diameter is 100-300 nm. Preferably, the surface area density of the aramid fiber membrane layer is 0.35~0.6 mg•cm -2 , and the equivalent thickness is 0.5~3 μm.

10. A lithium-ion cylindrical cell, characterized by, The lithium ion cylindrical battery cell comprises the negative plate of claim 8 or 9.

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