Lithium battery negative electrode binder and preparation method and application thereof

Abstract

The invention relates to the technical field of batteries, and particularly discloses a lithium battery negative electrode binder and a preparation method and application thereof.The lithium battery negative electrode binder is obtained through polymerization of an acrylic monomer, an acrylonitrile monomer and an acrylate monomer, the acrylate monomer is acrylate containing sulfydryl, and the acrylonitrile monomer is acrylic ester containing sulfydryl. During polymerization, the proportion of the three monomers is as follows: 4-10wt% of acrylic monomer, 75-95wt% of acrylonitrile monomer and 1-21wt% of sulfydryl-containing acrylate monomer. The negative electrode binder has good binding power and strong cohesive force, is added into a negative electrode doped with 1-100% of silicon, especially a high-silicon negative electrode doped with 10 wt% or more of silicon, is beneficial for obtaining an active substance coating layer with mechanical strength and flexibility and high stripping force, and can effectively inhibit volume expansion of a silicon material; and the obtained negative pole piece does not fall powder after multiple cycles, and the obtained lithium battery cell is low in cycle expansion rate, good in cycle stability and excellent in high-temperature and low-temperature performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, in particular to a lithium battery negative electrode binder and a preparation method and application thereof. Background Art

[0002] Lithium batteries have the characteristics of high output power and high energy density, and are widely used in many fields such as electric vehicles and energy storage facilities. Silicon-based negative electrodes are currently widely used in lithium batteries. They have the following advantages: 1. Extremely high theoretical capacity; 2. Low working potential; 3. Rich resources. Although silicon-based negative electrodes have the above advantages, the inherent disadvantages of silicon also bring difficulties and challenges in the practical application of silicon-based negative electrodes. First, silicon has low conductivity and Li + diffusion coefficient, resulting in poor dynamic performance; secondly, silicon has a large volume expansion rate during the charge and discharge process. The stress and strain caused by this large volume change can easily cause the active material to fall off from the current collector, the rupture and reorganization of the SEI film, resulting in low initial efficiency and capacity attenuation. In addition, the strong volume change also causes cracks to appear on the surface of the electrode and exposes a new contact surface, destroying the already stable solid electrolyte membrane (SEI). The new contact surface will form a new unstable SEI after contacting the electrolyte, thus causing irreversible loss of lithium. In addition, cracks also lead to the rupture of the electrode and the pulverization of silicon particles, resulting in the detachment of the active material from the current collector, the interruption of the conductive network, and the capacity is so low that the battery fails completely.

[0003] As an essential non-electrochemically active component of an electrode, the binder not only ensures connectivity between particles but also maintains close contact between the coating and the current collector to prevent the coating from falling off. Polymer binders directly coated on the active material surface also modify the electrode surface properties and stabilize the SEI during battery cycling. Selecting a high-performance binder is crucial for silicon-based anode materials, which experience significant volume expansion during charge and discharge.

[0004] Polyacrylic acid-type oily binder is a common binder in silicon-based negative electrodes. Through molecular structure design and solvent system optimization, it has shown certain advantages in solving interfacial adhesion with silicon-based negative electrodes, inhibiting the volume expansion of silicon materials, and improving cycle stability. However, it still has limitations, such as mechanical strength, cohesion, high and low temperature performance, and electrochemical stability.

[0005] This application is filed for this purpose. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the prior art, the present invention provides a lithium battery negative electrode binder and a preparation method and application thereof.

[0007] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0008] First, the present invention proposes a lithium battery negative electrode binder, which is obtained by polymerizing acrylic acid monomer, acrylonitrile monomer and acrylic ester monomer, wherein the acrylic ester monomer is an acrylic ester containing a mercapto group, and the ratio of the three monomers during polymerization is: 4wt%-10wt% of acrylic acid monomer, 75wt%-95wt% of acrylonitrile monomer and 1wt%-21wt% of acrylic ester containing a mercapto group.

[0009] In the prior art, acrylonitrile is a relatively common monomer for the polymerization of acrylic binders and is generally used in combination with acrylic acid monomers. Given that acrylonitrile polymers have relatively strong rigidity but are inferior to acrylic acid in terms of degree of polymerization, flexibility, and toughness, when used to prepare binders, especially negative electrode binders, their addition should not be excessive. Otherwise, the resulting binder's elastic buffering properties will deteriorate, making it unable to adapt to the volume expansion of the negative electrode sheet. Furthermore, the viscosity and fluidity will deteriorate, leading to increased glass transition temperature, brittle and prone to cracking of the electrode sheet, reduced elongation, and decreased flexibility and toughness. Furthermore, the highly polar cyano group increases the electrode sheet's surface energy, impairs electrolyte wettability, hinders lithium ion transmission, and affects rate performance. Furthermore, after being used in the electrode sheet, chain segment shrinkage may occur during drying, leading to electrode sheet warping, among other issues.

[0010] The present invention has discovered that when a mercapto-containing acrylate is used, the amount of acrylonitrile added can be significantly increased. By rationally matching the content of acrylic acid monomer, acrylonitrile monomer, and mercapto-containing acrylate, not only can the adverse effects of high acrylonitrile content on the binder preparation process and binder properties be avoided, but also a lithium battery negative electrode binder with good adhesion, strong cohesion, excellent elastic cushioning, high mechanical strength, and good thermal and electrochemical stability can be obtained. The present invention speculates that the reason for this is that during the polymerization reaction of the mercapto-containing acrylate, the mercapto group (SH) may undergo a nucleophilic addition reaction with the cyano group (CN) of acrylonitrile to form a thioamide structure, which in turn reduces the order and crystallinity of the polyacrylonitrile and changes the thermodynamic properties of the polymer, such as the glass transition temperature. Ultimately, the adhesion of the copolymer is improved, resulting in good mechanical strength and strong cohesion, as well as good softness, elasticity, and toughness.

[0011] Furthermore, the acrylate containing mercapto group is selected from mercapto polyethylene glycol acrylate and / or mercapto methacrylate;

[0012] Preferably, at least a portion of the acrylic acid monomer is pre-neutralized with a base such as NaOH, KOH, etc. to form a carboxylate. Pre-neutralization can significantly improve the solubility of the acrylic acid monomer, regulate the polymerization reaction, and optimize the properties of the final polymer.

[0013] Preferably, the molecular weight of the mercapto polyethylene glycol acrylate is 2000-5000. Considering the flexibility of the copolymer product alone, the longer the PEG chain length in the mercapto polyethylene glycol acrylate, the better, that is, the larger the molecular weight, the better. However, too long a chain length will excessively sacrifice mechanical strength. Through repeated experiments, the present invention found that when the molecular weight of the mercapto polyethylene glycol acrylate is 2000-5000, the copolymer product has both good mechanical strength and flexibility.

[0014] Preferably, the ratio of the three monomers during polymerization is: 5wt%-8wt% of acrylic acid monomer, 80wt%-85wt% of acrylonitrile monomer and 8wt%-13wt% of mercapto-containing acrylate. Within this ratio range, the obtained adhesive has better properties.

[0015] In this embodiment, mercapto polyethylene glycol acrylate and / or mercapto methacrylate are copolymerized with acrylic acid monomer and acrylonitrile monomer. The intermolecular forces of various functional groups in the raw materials, such as carboxyl group, cyano group, double bond, ester group, ether oxygen bond, etc., jointly determine the glass transition temperature Tg of the resulting polymer. When the three monomers are mixed in the required proportion, the resulting product has a high elastic modulus, tensile strength and elongation at break after forming a film, and rebounds in time during the battery cell cycle, which is beneficial to the construction of a cyclic conductive network and reducing the battery cell expansion rate.

[0016] Furthermore, the molecular weight of the lithium battery negative electrode binder is 15W-25W, and the glass transition temperature is 85-110°C.

[0017] Tests have found that when the above-mentioned raw materials react according to a specified ratio, the molecular weight of the obtained product is 15W-25W. The binder within this molecular weight range has good solubility in oily solvents, which helps to obtain a binder glue with moderate viscosity and good fluidity. When the binder glue is used for the preparation of negative electrode sheets, it has both good adhesion and coating properties.

[0018] Further testing revealed that the glass transition temperature (Tg) of the binder within this molecular weight range is 85-110°C, which can provide sufficient bonding strength to prevent cracking of the electrode while maintaining a certain toughness to avoid embrittlement. During the charge and discharge process, when the volume of active materials, such as silicon-containing active materials, expands, the binder with this Tg value can buffer stress through elastic deformation and reduce damage to the electrode structure. It can also have an appropriate degree of swelling in the electrolyte, ensuring that the electrolyte fully infiltrates the electrode pores without causing bonding failure. At the same time, it forms a stable SEI and reduces side reactions. Combining the above advantages, the binder proposed by the present invention helps to build a circulating conductive network and effectively inhibit the expansion of the battery cell, thereby improving the cycle life and safety of the battery.

[0019] Secondly, the present invention provides a preparation method of the above-mentioned lithium battery negative electrode binder, which adopts a micro-suspension polymerization method. The specific operation is: adding an acrylate monomer, an acrylonitrile monomer, and an acrylic acid monomer in a water-alcohol solvent in order according to a proportion, then adding an emulsifier and a dispersant and stirring to obtain a suspension; heating the suspension and adding an initiator dropwise while stirring to polymerize under an inert atmosphere; filtering, washing, drying, crushing, and sieving;

[0020] The invention relates to a method for preparing a slurry-forming polymer having a hydroalcoholic solvent and a mixed solvent of water and ethanol, wherein the volume of water is greater than that of ethanol; and considering that sulfhydryl groups are easily oxidized, the hydroalcoholic solvent is preferably purged with nitrogen for more than 15 minutes before use; the emulsifier is at least one of sodium lauryl sulfate, sodium dodecylbenzenesulfonate, Span 80, and Tween 20; the dispersant is at least one of polyvinyl pyrrolidone, polyvinyl alcohol, hydroxypropyl cellulose, gelatin, and polyacrylate; the initiator is one of potassium persulfate, sodium persulfate, azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate; the added mass of the initiator is 0.2%-1% of the total mass of the monomers; the polymerization temperature is 60-80° C., and the polymerization time is 12-18 hours.

[0021] By mixing acrylic acid monomer, acrylonitrile monomer and acrylic ester monomer in the required ratio and under the conditions specified in the above preparation method, an adhesive with a molecular weight of 15W-25W and a glass transition temperature of 85-110°C can be obtained.

[0022] It should be noted that the above preparation method is only one way to obtain the binder of the present invention. Other preparation methods in the technical field are also possible. The present invention only lists them and does not limit them.

[0023] Thirdly, the present invention provides a binder glue solution, which is prepared from the above-mentioned lithium battery negative electrode binder. During the preparation, the above-mentioned lithium battery negative electrode binder is first mixed and stirred with an oily solvent, and then glued at the dew point.

[0024] Furthermore, its solid content is 3%-9%. If the solid content is too low, the viscosity of the glue is low, which will lead to weakened shearing effect of the negative electrode slurry, poor slurry dispersion, large slurry particle size and easy agglomeration, and coating cannot be carried out smoothly; if the solid content is too high, the viscosity of the glue is high, which will easily lead to uneven dispersion of slurry particles, which will also affect the coating effect and cannot ensure the consistency of battery performance;

[0025] Furthermore, the dew point is ≤-35°C. The main purpose of dew point control is to prevent oily solvents such as N-methylpyrrolidone from absorbing water, causing the glue to gel or hydrolyze, affecting the surface properties of the electrode, SEI and gap, and thus having an adverse effect on battery performance.

[0026] Preferably, the oily solvent is selected from one of dimethylacetamide, N-methylpyrrolidone, acetone, and dimethyl sulfoxide;

[0027] Preferably, the binder having a molecular weight of 15W-25W and a glass transition temperature Tg of 85-110°C is added to an N-methylpyrrolidone oily solvent according to the above solid content, and the viscosity of the resulting binder glue is 4000-17000 mPa·s. When used in the negative electrode slurry, the slurry has a strong shearing effect, good dispersibility, and the slurry particles are not easy to agglomerate, which is conducive to the smooth coating and ensures the consistency of the battery core performance. If the solid content is lower than 3%, the slurry shearing effect becomes weak and the dispersibility is poor, and the smooth coating cannot be guaranteed. If the solid content is higher than 9%, the dispersion performance requirements of the equipment are high, and the consistency of the battery core performance cannot be guaranteed. Further, after the binder glue is formed into a film, the resulting film meets at least one of the following conditions: 1) elastic modulus 52-65 MPa; 2) peak tensile force 59-85 N; 3) tensile strength 9-13.4 MPa; 4) elongation at break 149%-160%.

[0028] Fourthly, the present invention proposes a lithium battery negative electrode plate, which is prepared by first dispersing a silicon-containing negative electrode active material, a conductive agent and the above-mentioned lithium battery negative electrode binder in an oily solvent to form a negative electrode slurry, and then coating the negative electrode slurry on a negative electrode collector. After coating, the negative electrode slurry is baked in multiple temperature zones, and then rolled, slit, slotted and die-cut.

[0029] The negative electrode binder proposed in the present invention has a high cohesive force after the negative electrode slurry is formed. The high cohesive force can not only prevent the edge of the electrode from falling off or delamination during slitting or grooving, which is especially important for high-silicon negative electrodes with a silicon doping of more than 10wt%, but also reduce the burr rate, improve the electrode processing accuracy, and maintain structural integrity during the winding or lamination process. More importantly, it can maintain a high cohesive force after the battery is cycled for 50cls, 100cls, and 150cls, effectively inhibiting the electrode from falling off and dropping during the cycle, which is beneficial to ensuring the integrity of the conductive network between the binder and the negative electrode main material during the cycle, improving long-term cycle stability and inhibiting cycle expansion; in addition, the raw materials for preparing the binder contain reducing thiol groups. When added to the negative electrode slurry, the thiol groups can scavenge free radicals in the negative electrode slurry, delaying the oxidation and degradation of the negative electrode slurry, while exerting good bonding properties, and improving the chemical stability of the negative electrode slurry. In addition, since there are a large number of carboxyl groups -COOH and cyano groups -CN in the binder, the two groups form dipole-dipole interactions or hydrogen bonds with the polar sites on the silicon surface. Therefore, they can improve the dispersion of the negative electrode active material containing silicon elements in the negative electrode slurry, reduce agglomeration, and improve the coating uniformity and mechanical stability. It also has high adhesion strength with the negative electrode active material containing silicon elements, which can enhance interface bonding, improve peel strength, and then reduce the expansion rate of the battery cell during cycling, thereby improving cycle performance.

[0030] It should be noted that: the binder is pre-dispersed before use, that is, it is first mixed and stirred with an oily solvent, and then glued at the dew point to obtain a binder glue solution, and then mixed with an oily solvent (preferably the same oily solvent as when the binder was pre-dispersed), a silicon-containing negative electrode active material, a conductive agent, etc. to prepare a slurry, and the slurrying is also carried out at the dew point; preferably, the binder accounts for 2wt%-4wt% of the mixed material composed of the silicon-containing negative electrode active material, the conductive agent, and the binder.

[0031] Furthermore, the zone baking includes five temperature zones, with the temperature of zone one being 80-90°C, the temperatures of zones two to four being 80-100°C, the temperature of zone five being 80-95°C, and the temperatures of zones two to four being not lower than the temperatures of zone one and zone five; preferably, the temperature of zone one is 80-85°C, the temperatures of zones two to four are all 95-100°C, and the temperature of zone five is 80-90°C.

[0032] Considering that polyacrylonitrile material lacks flexible segments in its molecular chain, its impact strength at room temperature is low, it is prone to brittle fracture, and it is sensitive to moisture. Its strong polar cyano group easily forms hydrogen bonds with moisture, resulting in strong hygroscopicity of the material. After absorbing moisture, it may not only cause a decrease in adhesion and an increase in the risk of electrolyte compatibility, but also further reduce the toughness of the polyacrylonitrile material, resulting in an increase in microcracks in the electrode after drying. Therefore, in this embodiment, five temperature zones are used for zoned baking. The five temperature zones can sequentially achieve solvent volatilization, preliminary curing and complete curing, while further improving the peel strength and cohesion of the electrode, while ensuring the complete volatilization of the oily solvent. More importantly, it can significantly improve the interfacial compatibility, making the negative electrode slurry film more uniform and reducing cracks and shedding. If baking is carried out in one temperature zone, if the temperature in the temperature zone is too high, the surface of the negative electrode plate will dry too quickly, the surface of the plate will densify, and the internal solvent residue will form bubbles, resulting in blockage of the lithium ion transmission channel; if the temperature in the temperature zone is too low, the oily solvent will not evaporate sufficiently, which will cause the roller to stick during rolling, and the resulting plate will have poor flexibility, many burrs on the edges, and poor mechanical properties, and will also cause battery bloating and increased internal resistance, and poor rate performance; even if the temperature is suitable, there will be a temperature gradient between the surface and internal temperature of the electrode during the drying process, the surface temperature will be higher than the internal temperature, the surface will dry first, and the substance concentration will be higher than the internal concentration. Under such driving force, the binder will gradually enrich and migrate to the surface as the solvent evaporates, and float up, and precipitate on the surface of the active material and the conductive agent, resulting in a decrease in the bonding force between the active material and the current collector, easy powder loss during rolling of the plate, and poor peel strength.

[0033] The present invention synergistically optimizes the formula of the negative electrode binder and the electrode baking process. On the basis of adding mercaptoacrylate as a flexible component, the drying curve is adjusted by baking in five temperature zones, which further effectively avoids the brittleness and moisture absorption defects of the product when a high-content acrylonitrile monomer is polymerized. This helps the negative electrode binder to exert high bonding strength and high elasticity, better adapt to the volume expansion of the silicon material, and the structure and performance of the electrode after film formation are excellent.

[0034] Furthermore, the negative electrode binder of lithium batteries accounts for 0.5wt%-11wt% of the negative electrode slurry;

[0035] Preferably, the ratio of the negative electrode main material, the conductive agent, and the lithium battery negative electrode binder is: 87wt%-98.9wt% of the negative electrode main material, 0.5wt%-11wt% of the lithium battery negative electrode binder, and 0.05wt%-2wt% of the conductive agent. Generally speaking, the higher the silicon content in the negative electrode main material, the higher the amount of the lithium battery negative electrode binder added.

[0036] Preferably, the negative electrode main material is selected from at least one of nano-silicon, SiO, SiO2, silicon-carbon composite materials, silicon-polymer composite materials, and silicon alloy materials;

[0037] Preferably, the conductive agent is selected from at least one of conductive carbon black, acetylene black, carbon fiber, carbon nanotube, Ketjen black, and graphene;

[0038] Preferably, the negative electrode main material, the conductive agent, and the lithium battery negative electrode binder are first dispersed in an oily solvent and then mixed evenly;

[0039] Preferably, the preparation of the negative electrode slurry and the coating of the negative electrode slurry are both performed under controlled dew point, which is ≤-35°C.

[0040] Fifth, the present invention proposes a lithium battery cell, comprising the above-mentioned lithium battery negative electrode plate and positive electrode plate, a separator, an electrolyte, etc. The pressure of the lithium battery cell during formation is 0.2-2MPa and the temperature is 50-90°C.

[0041] The negative electrode sheets, positive electrode sheets, and diaphragm are stacked or wound to form bare cells, which are then welded, packaged, baked, and filled with liquid to obtain a battery pack. The battery pack undergoes formation and capacity separation to obtain shipping cells. When the existing formation pressure and formation temperature are used in the battery pack of the present invention, it is very easy to cause the film formation speed to be too fast, the film layer to be too thick or uneven, and even cracks or defects to appear, affecting the cycle life and safety of the battery cell. In addition, under the existing formation pressure and formation temperature, the electrolyte will enter the gap between the electrodes to participate in the film formation reaction and consume active lithium, thereby affecting the gram capacity and cycle performance.

[0042] Taking into account the particularity of the binder used in the present invention, the formation pressure and formation temperature of the present invention are lower than conventional values. By reducing the formation pressure, the integrity and stability of the SEI can be promoted, which helps to improve the specific capacity and extend the cycle life. At the above-mentioned formation pressure and formation temperature, the stress is released in advance during the charge and discharge process of the formation capacity, thereby suppressing the expansion of the battery cell in the later cycle. Moreover, the pressure release of the battery pack during the formation stage can also reduce the thickness of the battery cell in the shipping state. In addition: (1) The strong interaction between the highly polar cyano functional group in the binder and the foil and the silicon-containing negative electrode active material can inhibit the decomposition of the electrolyte, promote the insertion and extraction of active lithium, and reduce the expansion rate of the lithium battery cell during the cycle; (2) The residual thiol group in the binder is oxidized to form a disulfide bond -SS-, which can dynamically repair the cracks in the electrode during the cycle; the above two methods further improve the specific capacity and cycle stability of the lithium battery.

[0043] Aside from the negative electrode, all other components of this lithium battery cell, such as the positive electrode, separator, and electrolyte, can be manufactured using existing technologies, including the existing manufacturing process. To prevent moisture from affecting cell performance, the negative electrode still needs to be baked at 50-80°C for 6-24 hours before being assembled into the lithium battery cell.

[0044] Compared with the prior art, the negative electrode binder obtained in the present invention has strong adhesion to the foil and the negative electrode active material containing silicon elements. After coating, a coating with good mechanical strength, thermal stability, and chemical stability can be obtained, which can effectively inhibit the volume expansion of the silicon material. The obtained negative electrode plate will not fall off after multiple cycles. The obtained lithium battery cell has a low cycle expansion rate, good cycle stability, and excellent high and low temperature performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0046] Figure 1 This is a comparison chart of the expansion rate of the lithium battery cell obtained in Example 1 of the present invention and the lithium battery cell obtained in Comparative Example 1 when cycled at room temperature (25°C).

[0047] Figure 2 This is a comparison chart of the cycle performance of the lithium battery cell obtained in Example 1 of the present invention and the lithium battery cell obtained in Comparative Example 1 at room temperature of 25°C.

[0048] Figure 3The low-temperature test data of the lithium battery cell obtained in Example 1 of the present invention and the lithium battery cell obtained in Comparative Example 1 under the national standard of -10°C (repeated three times): yellow is Comparative Example 1, and green is Example 1.

[0049] Figure 4 This is a photograph of the adhesive solution obtained in Example 1 of the present invention forming a film instantly when it comes into contact with water. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, and are not all embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0051] The chemical raw materials used in the following examples and comparative examples were all commercially available. Some of the raw materials were purchased from the following suppliers: mercaptopolyethylene glycol acrylate was purchased from Shaanxi Xingbei Aike Biotechnology Co., Ltd.; mercapto methacrylate was purchased from Tianmen Hengchang Chemical Co., Ltd.; 2-methylthioethyl acrylate was purchased from Alpha Chemical Co., Ltd.; allyl thioacetate was purchased from Shandong Xiya Chemical Co., Ltd.; and sulfoethyl methacrylate was purchased from Shanghai Saikerui Biotechnology Co., Ltd. Any preparation or testing procedures not described in detail in the following examples and comparative examples are conventional in the art and are well known to those skilled in the art.

[0052] Example 1

[0053] A lithium battery negative electrode binder is obtained by polymerizing acrylic acid monomer, acrylonitrile monomer and mercapto methacrylate monomer, wherein the proportion of the three monomers is 4 wt% of acrylic acid monomer, 90 wt% of acrylonitrile monomer and 6 wt% of mercapto methacrylate monomer.

[0054] The preparation method of the above-mentioned lithium battery negative electrode binder is as follows: mercapto methacrylate monomer, acrylonitrile monomer, and acrylic acid monomer are added in proportion in sequence to a water-ethanol solvent with a volume ratio of 6:4, and then sodium dodecylbenzenesulfonate (added in an amount of 0.7% of the total weight of the monomers) and polyvinyl pyrrolidone (added in an amount of 1% of the total weight of the monomers) are added and stirred to obtain a suspension; the suspension is heated to 60° C. and azobisisoheptanenitrile is added dropwise while stirring and polymerized under an inert atmosphere for 16 hours, wherein the added amount of azobisisoheptanenitrile is 0.5% of the total weight of the monomers; and the mixture is filtered, washed, dried, crushed, and sieved to obtain a powdery product.

[0055] A binder glue solution is prepared by mixing a powdered product with NMP, controlling the solid content to be 4.5 wt%, stirring, and applying glue at a dew point of -35°C.

[0056] A lithium battery negative electrode plate includes a copper foil and a negative electrode slurry. The negative electrode slurry includes a silicon-carbon composite material (doped with 30 wt% silicon), a conductive agent (conductive carbon and carbon nanotubes in a mass ratio of 1:1), a binder and an oily solvent. The oily solvent is NMP. The proportion of solid raw materials is 96 wt% of the silicon-carbon composite material, 1 wt% of the conductive agent, and 3 wt% of the binder. After coating, it is baked in five temperature zones. The specific temperature zones are set as: 83°C in temperature zone one, 98°C in temperature zones two to four, and 90°C in temperature zone five.

[0057] A lithium battery cell is assembled from the aforementioned negative and positive electrode sheets, an electrolyte, and a separator into a semi-solid lithium battery for electrochemical performance testing. The positive electrode slurry comprises: 96.5 wt% positive electrode active material LCO, 1.5 wt% conductive agent, and 2 wt% positive electrode binder; the electrolyte is a 12.5% ​​by mass LiPF6 solution (using a mixed solution of fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 as the solvent, with 3% by mass of succinonitrile (SN) added); and the separator is a polyolefin-based double-sided ceramic-coated separator. During assembly, the positive and negative electrode sheets are die-cut into individual sheets, and then stacked with a separator having one ceramic side and one adhesive side to form a bare cell, with the ceramic side corresponding to the positive electrode. The bare cell is placed in a shell, sealed on the top and side, and then baked, filled with liquid, and allowed to stand to form a battery pack. The battery pack is then formed into a capacity, wherein the pressure during formation is 0.2 MPa and the temperature is 70°C.

[0058] Example 2

[0059] Compared with Example 1, the following differences are present: (1) the raw material ratio of the binder is adjusted: 10 wt% of acrylic acid monomer, 75 wt% of acrylonitrile monomer, and 15 wt% of mercapto methacrylate monomer; (2) the solid content of the binder glue is adjusted to 4 wt%; (3) the silicon-carbon composite material in the negative electrode slurry is doped with 10 wt% of silicon, and the temperature of the zone baking after the negative electrode slurry is coated is adjusted: 80°C in the first zone, 90°C in the second to fourth zones, and 90°C in the fifth zone; (4) the formation conditions during the preparation of the lithium battery cell are adjusted: the pressure during formation is 1 MPa and the temperature is 70°C. All other conditions remain the same as in Example 1.

[0060] Example 3

[0061] Compared with Example 1, the following differences exist: (1) the raw material ratio of the binder is adjusted: 4 wt% of acrylic acid monomer, 75 wt% of acrylonitrile monomer, and 21 wt% of mercapto methacrylate monomer; (2) the solid content of the binder glue is adjusted to 9 wt%; (3) the silicon-carbon composite material in the negative electrode slurry is doped with 20 wt% of silicon, and the temperature of the zone baking after the negative electrode slurry is coated is adjusted: 90°C in the first temperature zone, 100°C in the second to fourth temperature zones, and 90°C in the fifth temperature zone; (4) the formation conditions during the preparation of the lithium battery cell are adjusted: the pressure during formation is 2 MPa and the temperature is 70°C. All other conditions remain the same as in Example 1.

[0062] Example 4

[0063] Compared with Example 1, the following differences are present: (1) the raw material ratio of the binder is adjusted: 10 wt% of acrylic acid monomer, 79 wt% of acrylonitrile monomer, and 11 wt% of mercapto methacrylate monomer; (2) the solid content of the binder glue is adjusted to 3.85 wt%; (3) the temperature of the zone baking after the negative electrode slurry is coated is adjusted: 85°C in the first zone, 90°C in the second to fourth zones, and 80°C in the fifth zone; (4) the formation conditions during the preparation of the lithium battery cell are adjusted: the pressure during formation is 0.5 MPa and the temperature is 50°C. All other conditions remain the same as in Example 1.

[0064] Example 5

[0065] Compared with Example 1, the following differences are present: (1) the raw material ratio of the binder is adjusted: 10 wt% of acrylic acid monomer, 84 wt% of acrylonitrile monomer, and 6 wt% of mercapto methacrylate monomer; (2) the solid content of the binder glue is adjusted to 3 wt%; (3) the temperature of the zone baking after the negative electrode slurry is coated is adjusted: 80°C in the first zone, 85°C in the second to fourth zones, and 90°C in the fifth zone; (4) the formation conditions during the preparation of the lithium battery cell are adjusted: the pressure during formation is 1.5 MPa and the temperature is 90°C. All other conditions remain the same as in Example 1.

[0066] Example 6

[0067] Compared with Example 1, the following differences are present: (1) the raw material ratio of the binder is adjusted: 7 wt% of acrylic acid monomer, 80 wt% of acrylonitrile monomer, and 13 wt% of mercapto methacrylate monomer; (2) the solid content of the binder glue is adjusted to 7.36 wt%; (3) the temperature of the zone baking after the negative electrode slurry is coated is adjusted: 80°C in the first zone, 90°C in the second to fourth zones, and 85°C in the fifth zone; (4) the formation conditions during the preparation of the lithium battery cell are adjusted: the pressure during formation is 1 MPa and the temperature is 75°C. All other conditions remain the same as in Example 1.

[0068] Example 7

[0069] Compared with Example 1, the following differences exist: (1) the solid content of the binder paste is adjusted to 7.68 wt%; (2) the temperature of the zoned baking after the negative electrode slurry is applied is adjusted: 82°C for zone 1, 99°C for zones 2 to 4, and 91°C for zone 5; (3) the formation conditions during the preparation of the lithium battery cell are adjusted: the pressure during formation is 1 MPa and the temperature is 75°C. All other conditions remain the same as in Example 1.

[0070] Example 8

[0071] Compared with Example 1, the following differences exist: (1) the solid content of the binder paste is adjusted to 7.13 wt%; (2) the temperature of the zoned baking after the negative electrode slurry is applied is adjusted: 84°C in zone 1, 96°C in zones 2 to 4, and 82°C in zone 5; (3) the formation conditions during the preparation of the lithium battery cell are adjusted: the pressure during formation is 1 MPa and the temperature is 75°C. All other conditions remain the same as in Example 1.

[0072] Example 9

[0073] Compared with Example 1, the following differences exist: (1) the solid content of the binder paste is adjusted to 6.94 wt%; (2) the temperature of the zone baking after the negative electrode slurry is applied is adjusted: 81°C in zone 1, 86°C in zones 2 to 4, and 84°C in zone 5; (3) the formation conditions during the preparation of the lithium battery cell are adjusted: the pressure during formation is 1 MPa and the temperature is 75°C. All other conditions remain the same as in Example 1.

[0074] Example 10

[0075] Compared with Example 1, the following differences exist: (1) the solid content of the binder paste is adjusted to 8.13 wt%; (2) the temperature of the zoned baking after the negative electrode slurry is applied is adjusted: 83°C in zone 1, 88°C in zones 2 to 4, and 83°C in zone 5; (3) the formation conditions during the preparation of the lithium battery cell are adjusted: the pressure during formation is 1 MPa and the temperature is 75°C. All other conditions remain the same as in Example 1.

[0076] Example 11

[0077] Compared with Example 6, the following differences exist: the preparation method of the binder has been modified: an acrylate monomer, an acrylonitrile monomer, and a mercapto methacrylate monomer are added in order to a water-ethanol solvent in a volume ratio of 6:4. Then, sodium lauryl sulfate (0.7% by weight of the total monomers) and polyvinyl alcohol (1% by weight of the total monomers) are added and stirred to obtain a suspension; the suspension is heated to 75°C, and azobisisobutyronitrile (0.6% by weight of the total monomers) is added dropwise to the suspension while stirring, and polymerization is carried out under an inert atmosphere for 16 hours; the amount of azobisisobutyronitrile added is 0.6% by weight of the total monomers; the product is filtered, washed, dried, pulverized, and sieved to obtain a powdery product. All other procedures remain the same as in Example 6.

[0078] Example 12

[0079] Compared to Example 6, the following differences exist: the binder preparation method has been modified: an acrylate monomer, acrylonitrile monomer, and mercapto methacrylate are added sequentially in a water-ethanol solvent at a volume ratio of 6:4. A mixture of Span 80 and Tween 20 at a mass ratio of 1:1 (0.7% of the total monomer mass) and hydroxypropyl cellulose (1% of the total monomer mass) are then added and stirred to obtain a suspension. The suspension is heated to 80°C and azobisisobutyronitrile is added dropwise with stirring under an inert atmosphere for 16 hours. The amount of azobisisobutyronitrile added is 0.8% of the total monomer mass. The product is then filtered, washed, dried, pulverized, and sieved to obtain a powdered product. All other procedures remain the same as in Example 6.

[0080] Example 13

[0081] Compared with Example 6, the following differences were observed: the raw material mercapto methacrylate monomer of the binder was adjusted to an equivalent amount of mercapto polyethylene glycol acrylate with a molecular weight of 2000, and the preparation method was also adjusted accordingly. All other steps remained the same as in Example 6.

[0082] Example 14

[0083] Compared with Example 6, the following differences exist: the binder's raw material, mercapto methacrylate monomer, is adjusted to an equivalent amount of mercapto polyethylene glycol acrylate with a molecular weight of 3400, and the preparation method is also adjusted accordingly. All other steps remain the same as in Example 6.

[0084] Example 15

[0085] Compared with Example 6, the raw material mercapto methacrylate monomer of the adhesive was adjusted to an equal amount of mercapto polyethylene glycol acrylate with a molecular weight of 5000, and the preparation method was also adjusted accordingly.

[0086] Example 16

[0087] Compared with Example 6, the solid content of the adhesive solution is adjusted to 3 wt %, and the rest remains the same as Example 6.

[0088] Example 17

[0089] Compared with Example 6, the solid content of the adhesive solution is adjusted to 5.5 wt %, and the rest remains the same as Example 6.

[0090] Example 18

[0091] Compared with Example 6, the solid content of the adhesive solution is adjusted to 8 wt %, and the rest remains the same as Example 6.

[0092] Example 19

[0093] Compared with Example 6, the solid content of the adhesive solution is adjusted to 9 wt %, and the rest remains the same as Example 6.

[0094] Example 20

[0095] Compared with Example 1, the temperature of the zoned baking after the negative electrode slurry coating was adjusted: 80°C in the first zone, 95°C in the second to fourth zones, and 80°C in the fifth zone. The rest remained the same as in Example 1.

[0096] Example 21

[0097] Compared with Example 1, the temperature of the zoned baking after the negative electrode slurry is coated is adjusted: 85°C for zone 1, 100°C for zones 2 to 4, and 95°C for zone 5. The rest remain the same as in Example 1.

[0098] Example 22

[0099] Compared with Example 1, the temperature of the zoned baking after the negative electrode slurry coating was adjusted: 84°C in the first zone, 97°C in the second to fourth zones, and 90°C in the fifth zone. The rest remained the same as in Example 1.

[0100] Example 23

[0101] Compared with Example 1, the temperature of the zoned baking after the negative electrode slurry coating was adjusted: 80°C in the first temperature zone, 80°C in the second to fourth temperature zones, and 80°C in the fifth temperature zone. The rest remained the same as in Example 1.

[0102] Example 24

[0103] Compared with Example 7, the raw material ratio of the adhesive is adjusted to: 7 wt % of acrylic acid monomer, 85 wt % of acrylonitrile monomer and 8 wt % of mercapto methacrylate monomer, and the rest are the same as in Example 7.

[0104] Example 25

[0105] Compared with Example 7, the raw material ratio of the adhesive is adjusted to: 5 wt % of acrylic acid monomer, 82 wt % of acrylonitrile monomer and 13 wt % of mercapto methacrylate monomer, and the rest are the same as in Example 7.

[0106] Example 26

[0107] Compared with Example 7, the raw material ratio of the adhesive is adjusted to: 8 wt % of acrylic acid monomer, 80 wt % of acrylonitrile monomer and 12 wt % of mercapto methacrylate monomer, and the rest are the same as in Example 7.

[0108] Example 27

[0109] Compared with Example 7, the raw material ratio of the adhesive is adjusted to: 5 wt % of acrylic acid monomer, 85 wt % of acrylonitrile monomer and 10 wt % of mercapto methacrylate monomer, and the rest are the same as in Example 7.

[0110] Example 28

[0111] Compared with Example 1, when preparing the negative electrode sheet of a lithium battery: the negative electrode slurry includes nano-silicon, a conductive agent (conductive carbon and carbon nanotubes in a mass ratio of 1:1), a binder, and an oily solvent. The oily solvent is NMP. The solid raw materials account for 87 wt% of nano-silicon, 2 wt% of the conductive agent, and 11 wt% of the binder. After coating, it is baked in five temperature zones. The specific temperature zones are set as: 83°C in temperature zone 1, 97°C in temperature zones 2 to 4, and 90°C in temperature zone 5. All other conditions remain the same as in Example 1.

[0112] Example 29

[0113] Compared with Example 1, the raw material ratio of the adhesive is adjusted to: 4 wt % of acrylic acid monomer, 95 wt % of acrylonitrile monomer and 1 wt % of mercapto methacrylate monomer, and the rest are the same as in Example 1.

[0114] Comparative Example 1

[0115] A mixture of aqueous binder CMC (sodium carboxymethyl cellulose, molecular weight of about 300 kDa) and SBR (styrene-butadiene rubber) in a mass ratio of 1:2.5 was used as a binder (the amount of binder added was consistent with that in Example 6), and the oily solvent was adjusted to water. The negative electrode sheet of the lithium battery was prepared by an operation similar to that in Example 6 and assembled into a lithium battery cell.

[0116] Comparative Example 2

[0117] Compared with Example 6, the mercapto methacrylate in the binder preparation raw material was replaced with an equal mass of 2-methylmercaptoethyl acrylate, and the rest remained the same as Example 6.

[0118] Comparative Example 3

[0119] Compared with Example 6, the mercapto methacrylate in the binder preparation raw material was replaced with allyl thioacetate of equal mass, and the rest remained the same as Example 6.

[0120] Comparative Example 4

[0121] Compared with Example 6, the mercapto methacrylate in the binder preparation raw material was replaced with sulfoethyl methacrylate of equal mass, and the rest remained the same as Example 6.

[0122] Comparative Example 5

[0123] Compared with Example 6, mercapto methacrylate in the raw materials for preparing the binder was removed, and the rest remained the same as in Example 6.

[0124] Comparative Example 6

[0125] Compared with Example 6, the raw material mercapto methacrylate monomer of the adhesive was adjusted to an equal amount of mercapto polyethylene glycol acrylate with a molecular weight of 600, and the preparation method was also adjusted accordingly.

[0126] Comparative Example 7

[0127] Compared with Example 6, the raw material mercapto methacrylate monomer of the adhesive was adjusted to an equal amount of mercapto polyethylene glycol acrylate with a molecular weight of 10,000, and the preparation method was also adjusted accordingly.

[0128] Comparative Example 8

[0129] The binder in Example 28 was adjusted to a mixture of a water-based binder CMC (sodium carboxymethyl cellulose, molecular weight of about 300k Da) and SBR (styrene-butadiene rubber) in a mass ratio of 1:2.5 as a binder (the amount of binder added remained consistent with Example 28), and the oily solvent was adjusted to water. The lithium battery negative electrode sheet was prepared using an operation similar to that in Example 6 and assembled into a lithium battery cell.

[0130] The main technical parameters involved in the above examples and comparative examples are shown in Table 1 below. For ease of listing, the mass ratios of acrylic acid monomer, acrylonitrile monomer, and acrylic ester monomer are expressed as PAA:PAN:PAN ester; Example 1, Example 2, etc. are represented by S1, S2, etc., respectively; Comparative Example 1, Comparative Example 2, etc. are represented by D1, D2, etc., respectively.

[0131] Table 1 Main technical parameters of each embodiment and comparative example

[0132]

[0133]

[0134] The viscosity of the adhesive solution obtained in each Example and Comparative Example was tested. The solution was then placed in a mold and baked at 80°C for 6 hours. The solution was then stretched on a tensile testing machine for tests such as elastic modulus, peak tensile force, tensile strength, and elongation at break. The gram capacity, initial efficiency, 25°C / 700cl capacity retention, and cell expansion rate of the lithium battery cells obtained in each Example and Comparative Example were tested at a voltage of 3-4.53V, an initial charge of 0.2C, and an initial discharge of 0.5C. The final test results are shown in Table 2.

[0135] Table 2 Test results of various embodiments and comparative examples

[0136]

[0137]

[0138] like Figure 1-Figure 4 , Table 1 and Table 2 show together:

[0139] (1) Comparison of the test results of Examples 1 to 27 with those of Comparative Example 1 shows that the binder proposed in the present invention has high elastic modulus, tensile strength and elongation at break after film formation. After being used for negative electrode plates and assembled into lithium battery cells, the gram capacity and initial efficiency are significantly improved. After 700 cycles at room temperature, the capacity retention rate is significantly improved and the expansion rate is significantly reduced. It can be seen that it can effectively inhibit silicon expansion and improve the long-cycle stability of lithium batteries. For the battery cell obtained in Example 1, Figure 1 As shown in the figure: after cycling for 700cls at 3.4°C and room temperature 25°C, the thickness expansion rate is only 13%, while the thickness expansion rate of the lithium battery cell assembled with water-based adhesive is nearly 23% under the same test conditions; Figure 2 As shown in Figure 1, the number of cycles in which the capacity retention rate at high temperature of 3.4°C and 45°C is above 80% is significantly greater than that in comparative example 1. Figure 3As shown: the capacity retention rate of the battery cell obtained in Example 1 in the -10°C national standard low-temperature test (GB / T 31486-2015: specifies the low-temperature discharge performance of monomers / modules; GB / T31467.3-2015: low-temperature operating condition test for battery packs / systems) is more than 80%, which is 6.7% higher than that of Comparative Example 1. Further testing found that the 3C rate discharge capacity of Example 1 was also slightly improved. Obviously, the binder proposed in the present invention improves high-temperature cycle performance and low-temperature performance. By comparing the test results of Example 28 with those of Comparative Example 8, it can be seen that when the negative electrode binder proposed in the present invention is applied to a pure silicon negative electrode, the performance of the battery cell is comparable to that of a silicon-doped graphite negative electrode, thanks to the fact that the negative electrode binder effectively reduces the expansion of the negative electrode. Obviously, the performance of the binder system of the present invention is generally better than that of the traditional CMC-SBR system.

[0140] (2) It can be seen from Examples 6, 13, 14, and 15 that when the mercapto-containing acrylate is selected from mercapto methacrylate or mercapto polyethylene glycol acrylate (molecular weight 2000, 3400, 5000), it can be copolymerized with acrylic acid monomer and acrylonitrile monomer to obtain a negative electrode binder with good bonding properties, which helps to improve the gram capacity and initial efficiency of lithium battery cells. By comparison, it was found that the polymer product of mercapto polyethylene glycol acrylate has better flexibility and elasticity than the polymer product of mercapto methacrylate, which may be related to the excellent segmental mobility of the long-chain PEG in mercapto polyethylene glycol acrylate, which can be stretched and retracted, and helps to improve flexibility and enhance elastic recovery. Furthermore, the present invention found that the PEG chain in mercapto polyethylene glycol acrylate should not be too short or too long, as shown in Comparative Examples 6 and 7: when the molecular weight of mercapto polyethylene glycol acrylate is 600, the mechanical strength of the polymer product is good but the flexibility is poor; when the molecular weight of mercapto polyethylene glycol acrylate is 10,000, the flexibility of the polymer product is optimal but the strength is significantly deteriorated. Taking into account flexibility and strength, the molecular weight of mercapto polyethylene glycol acrylate is preferably 2,000-5,000.

[0141] In addition, the present invention also investigated whether other sulfur-containing groups have similar effects to mercapto groups. As shown in Comparative Examples 2, 3, and 4, the present invention replaced the mercapto methacrylate in Example 6 with equal amounts of 2-methylthioethyl acrylate, allyl thioacetate, and sulfoethyl methacrylate. As shown in the test results of Example 6 and Comparative Examples 2, 3, and 4, the copolymer containing thioether bonds had acceptable flexibility but poor adhesion; the copolymer containing thioester bonds had unsatisfactory mechanical strength, possibly due to its easy hydrolysis and low polymerization stability; the copolymer containing sulfonyl groups had acceptable adhesion and mechanical strength but poor flexibility. Combined with the electrochemical test results, it was found that none of these three sulfur-containing acrylates were suitable for copolymerization with acrylic acid and high-content acrylonitrile to prepare adhesives.

[0142] (3) From the comparison between Example 6 and Example 16-Example 19, it can be seen that: under the premise of other conditions being the same, when the solid content is 3wt%-9wt%, the obtained film has both good flexibility and mechanical strength. Within this range, as the solid content increases, the viscosity of the adhesive glue gradually increases, and the flexibility and mechanical properties show a trend of first increasing and then decreasing, and the gram capacity and first effect also maintain the same trend of change. Obviously, the viscosity should not be too large or too small. If it is too small, the shear effect of the slurry will be weak, the dispersion of the slurry particles will be poor, and they will be easy to agglomerate. If it is too large, the slurry particles will not be easily dispersed, and it will be unfavorable for coating, and the consistency of the battery core cannot be guaranteed.

[0143] (4) From the comparison of Example 1 and Example 20 to Example 23, it can be seen that: under the premise of other conditions being the same, the temperature settings of the five temperature zones have an impact on the peel strength and cohesive strength of the coating layer. The first temperature zone, the second to fourth temperature zones, and the fifth temperature zone preferably have a certain temperature gradient, especially when the second to fourth temperature zone> the fifth temperature zone> the first temperature zone, the baking effect is better. The resulting coating layer has strong peel strength and cohesive strength, which is more conducive to improving the gram capacity and initial efficiency after being assembled into a lithium battery cell.

[0144] In summary, the present invention combines mercapto-containing acrylate with acrylic acid monomer and high-content acrylonitrile monomer. By rationally matching the component contents of acrylic acid monomer, acrylonitrile monomer and mercapto-containing acrylate, not only can the adverse effects of high-content acrylonitrile on the binder preparation process and binder performance be avoided, but also helps to obtain a lithium battery negative electrode binder with good adhesion, strong cohesion, good elasticity, high mechanical strength, good thermal stability and good electrochemical stability. The binder is used in the negative electrode of the lithium battery to help build a circulating conductive network and effectively inhibit the expansion of the battery cell, thereby improving the cycle life and safety of the lithium battery.

[0145] Although embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are illustrative and are not to be construed as limiting the present invention. Those skilled in the art may alter, modify, replace, and modify the above embodiments within the scope of the present invention. Furthermore, those skilled in the art may combine and incorporate the various embodiments or examples described in this specification, as well as features thereof, without conflicting requirements.

Claims

1. A lithium battery negative electrode binder, characterized in that: It is obtained by polymerizing acrylic acid monomer, acrylonitrile monomer and acrylic ester monomer, wherein the acrylic ester monomer is an acrylic ester containing a mercapto group, and the ratio of the three monomers during polymerization is: 4wt%-10wt% of acrylic acid monomer, 75wt%-95wt% of acrylonitrile monomer and 1wt%-21wt% of acrylic ester containing a mercapto group.

2. The lithium battery negative electrode binder according to claim 1, wherein: The acrylate containing mercapto group is selected from mercapto polyethylene glycol acrylate and / or mercapto methacrylate; Preferably, the acrylic acid monomer is at least partially pre-neutralized; Preferably, the molecular weight of mercapto polyethylene glycol acrylate is 2000-5000; Preferably, the ratio of the three monomers during polymerization is: 5wt%-8wt% of acrylic acid monomer, 80wt%-85wt% of acrylonitrile monomer and 8wt%-13wt% of mercapto-containing acrylate.

3. The lithium battery negative electrode binder according to claim 1, wherein: The lithium battery negative electrode binder has a molecular weight of 15W-25W and a glass transition temperature of 85-110°C.

4. A method for preparing a negative electrode binder for a lithium battery according to any one of claims 1 to 3, characterized in that: The microsuspension polymerization method is adopted, and the specific operation is as follows: adding acrylate monomer, acrylonitrile monomer, and acrylic acid monomer in a water-alcohol solvent in order according to a proportion, then adding an emulsifier and a dispersant and stirring to obtain a suspension; heating the suspension and adding an initiator dropwise while stirring to polymerize under an inert atmosphere; filtering, washing, drying, crushing, and sieving; The method comprises the following steps: the hydroalcoholic solvent is a mixed solvent of water and ethanol, and the volume of water is greater than that of ethanol; the emulsifier is at least one of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, Span 80, and Tween 20; the dispersant is at least one of polyvinyl pyrrolidone, polyvinyl alcohol, hydroxypropyl cellulose, gelatin, and polyacrylate; the initiator is one of potassium persulfate, sodium persulfate, azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate; the added mass of the initiator is 0.2%-1% of the total mass of the monomers; the polymerization temperature is 60-80° C., and the polymerization time is 12-18 hours.

5. An adhesive glue, characterized in that: The negative electrode binder for lithium batteries is prepared by mixing and stirring the negative electrode binder for lithium batteries with an oily solvent, and then applying glue at the dew point.

6. The adhesive solution according to claim 5, characterized in that: Its solid content is 3%-9%, and its dew point is ≤-35℃; Preferably, the oily solvent is selected from one of dimethylacetamide, N-methylpyrrolidone, acetone, and dimethyl sulfoxide; Preferably, its viscosity is 4000-17000 mPa·s; Preferably, after film formation, the obtained film meets at least one of the following conditions: 1) elastic modulus 52-65 MPa; 2) peak tensile force 59-85 N; 3) tensile strength 9-13.4 MPa; 4) elongation at break 149%-160%.

7. A lithium battery negative electrode plate, characterized in that: The negative electrode slurry is prepared by dispersing a silicon-containing negative electrode active material, a conductive agent and the lithium battery negative electrode binder according to any one of claims 1 to 3 in an oily solvent, and then coating the negative electrode slurry on a negative electrode current collector. After coating, the negative electrode slurry is baked in multiple temperature zones, and then rolled, slit, slotted and die-cut.

8. The negative electrode plate of a lithium battery according to claim 7, characterized in that: Zone baking includes five temperature zones: zone 1 is 80-90°C, zones 2 to 4 are 80-100°C, zone 5 is 80-95°C, and zones 2 to 4 are not lower than zones 1 and 5. Preferably, the temperature of zone 1 is 80-85°C, the temperatures of zones 2 to 4 are all 95-100°C, and the temperature of zone 5 is 80-90°C.

9. The negative electrode plate of a lithium battery according to claim 7, characterized in that: The lithium battery negative electrode binder accounts for 0.5wt%-11wt% of the negative electrode slurry; Preferably, the ratio of the negative electrode main material, the conductive agent, and the lithium battery negative electrode binder is: 87wt%-98.9wt% of the negative electrode main material, 0.5wt%-11wt% of the lithium battery negative electrode binder, and 0.05w%-2wt% of the conductive agent; Preferably, the negative electrode main material is selected from at least one of nano-silicon, SiO, SiO2, silicon-carbon composite materials, silicon-polymer composite materials, and silicon alloy materials; Preferably, the conductive agent is selected from at least one of conductive carbon black, acetylene black, carbon fiber, carbon nanotube, Ketjen black, and graphene; Preferably, the negative electrode main material, the conductive agent, and the lithium battery negative electrode binder are first dispersed in an oily solvent and then mixed evenly; Preferably, the preparation of the negative electrode slurry and the coating of the negative electrode slurry are both performed under controlled dew point, which is ≤-35°C.

10. A lithium battery cell, characterized in that: The negative electrode plate of a lithium battery as claimed in any one of claims 7 to 9 is provided, wherein the pressure during formation of the lithium battery cell is 0.2-2 MPa and the temperature is 50-90° C.

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