A binder for lithium-ion batteries and its application

Abstract

This invention discloses a binder for lithium-ion batteries, wherein the binder is a copolymer formed from acrylic monomers and vinyl sulfonic acid monomers; the copolymer also contains a metal element, which combines with sulfonic acid groups to form a corresponding salt; the metal element is one or more metal elements from Group II main metals and transition metals with a radius larger than that of silicon atoms; the amount of the metal element added is 10 ppm to 3000 ppm of the vinyl sulfonic acid monomers. This invention utilizes the random copolymerization of acrylic acid and p-styrene sulfonic acid, and by introducing multiple groups onto the polyacrylic acid (PAA) chain, it can significantly improve the problems of poor flexibility, easy cracking, shrinkage cavities, poor dispersibility, and large swelling in electrolyte of electrodes made with negative electrode binders.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and more specifically to a binder for lithium-ion batteries and its application. Background Technology

[0002] Lithium-ion batteries have become the most sought-after rechargeable batteries due to their high energy density and excellent cycle performance. Binders are one of the important functional additives in batteries; although they do not contribute to capacity and constitute a small proportion, they have a significant impact on various aspects of battery performance. Therefore, providing higher-performance binders helps improve battery performance.

[0003] Currently, commercially available binders for negative electrodes mostly utilize polymers formed from monomers such as acrylic acid, acrylonitrile, and acrylates, as well as styrene-acrylic emulsions and styrene-butadiene emulsions. For example, polyacrylic acid has good elasticity and high modulus, and as a water-soluble polymer, it is also very environmentally friendly. However, electrodes made from it have poor flexibility, are prone to cracking, and exhibit shrinkage cavities. Styrene-butadiene emulsion (SBR) has high bonding strength and good conductivity, and is also water-soluble, but it has poor dispersibility and swells significantly in the electrolyte. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of this invention is to provide a binder for lithium-ion batteries and its application, so as to solve the problems of poor flexibility, easy cracking, shrinkage cavities, poor dispersibility, and large swelling in electrolyte of the electrode sheets made by the prior art negative electrode binders.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A binder for lithium-ion batteries, wherein the binder is a copolymer formed from acrylic monomers and vinyl sulfonic acid monomers; the copolymer further contains a metal element, wherein the metal element combines with sulfonic acid groups to form a corresponding salt; the metal element is one or more metal elements larger than the atomic radius of silicon, which are group II metal elements and transition metal elements; the amount of the metal element added is 10 ppm to 3000 ppm of the vinyl sulfonic acid monomers.

[0007] Preferably, the acrylic monomer includes one or more of acrylic acid, acrylate, and methacrylic acid.

[0008] Preferably, the vinyl sulfonic acid monomers include one or more of styrene sulfonic acid and vinyl sulfonic acid.

[0009] Preferably, the mass of the metal element accounts for 50 ppm to 1000 ppm of the mass of the vinyl sulfonic acid monomer.

[0010] Preferably, the molecular weight of the copolymer is 100,000 to 800,000.

[0011] Preferably, the metallic element is at least one of calcium or magnesium.

[0012] Preferably, the acrylic monomer accounts for 95-99% of the total mass of the monomer.

[0013] Preferably, the vinyl sulfonic acid monomer accounts for 1 to 5% of the total mass of the monomer.

[0014] The present invention provides a negative electrode sheet for a lithium-ion battery, comprising a current collector and a coating applied to the current collector, wherein the coating comprises an adhesive as described above.

[0015] The present invention provides a lithium-ion battery, comprising a positive electrode, a separator, and an electrolyte, and further comprising the aforementioned lithium-ion battery negative electrode.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] This invention unexpectedly discovers a binder for lithium-ion batteries. Through random copolymerization of acrylic acid and p-styrene sulfonic acid, the introduction of multiple groups onto the polyacrylic acid (PAA) chain significantly improves the problems of poor flexibility, easy cracking, pinholes, poor dispersibility, and excessive swelling in electrolytes in electrodes made with this binder. In particular, this invention also discovers that introducing benzene rings onto the PAA chain can utilize the steric hindrance effect of the benzene rings to provide a certain degree of anti-precipitation performance for lithium-ion battery slurries; introducing conductive benzene rings and sulfonic acid groups onto the PAA chain can improve the conductivity of the PAA chain, thereby bringing better electrochemical performance to lithium-ion batteries; introducing trace amounts of calcium and magnesium elements into the binder can form ion exchange with lithium ions during charging and discharging, further increasing the lithium-ion mobility and improving the internal resistance of lithium-ion batteries. The deposition of trace amounts of calcium and magnesium elements into the silicon anode active material forms a solid solution, generating holes and dislocations. The increase in holes and dislocations has a certain effect on increasing lithium-ion migration. The formation of dislocations also helps to improve the tendency of silicon anodes to pulverize due to volume changes during charging. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0019] The numerical ranges in this invention should be understood to also specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0020] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail. The terms “comprising,” “including,” “having,” “containing,” etc., as used herein are open-ended, meaning that they include but are not limited to.

[0021] Unless otherwise specified, the experimental methods used in this invention are all conventional methods.

[0022] Unless otherwise specified, all materials and reagents used in this invention can be purchased or synthesized by known methods.

[0023] In the quantitative experiments of this invention, each experiment was repeated three times, and the average value of the results was taken.

[0024] I. A binder for lithium-ion batteries

[0025] The adhesive of the present invention is a copolymer formed by acrylic monomers and vinyl sulfonic acid monomers; the copolymer also contains a metal element, which combines with sulfonic acid groups to form a corresponding salt; the metal element is one or more metal elements larger than silicon atomic radius among group II metal elements and transition metal elements; the amount of the metal element added is 10 ppm to 3000 ppm of vinyl sulfonic acid monomers.

[0026] In specific implementation, the acrylic monomers include one or more of acrylic acid, acrylates, and methacrylic acid, more preferably acrylic acid. Compared with other monomers, polyacrylic acid has the advantages of high modulus and good elasticity. The vinyl sulfonic acid monomers include one or more of styrene sulfonic acid and vinyl sulfonic acid, more preferably p-styrene sulfonic acid, because p-styrene sulfonic acid has better water solubility, while other compounds containing benzene ring structures have relatively poor water solubility and cause significant pollution. P-styrene sulfonic acid can be directly polymerized with acrylic acid in aqueous solution, and the synthesis reaction process has less environmental pollution. Moreover, only p-styrene sulfonic acid has both vinyl and acidic benzene ring groups. The metal element is one or more of Group II metal elements and transition metal elements with an atomic radius larger than silicon, more preferably calcium or magnesium. In principle, the larger the atomic radius of the metal element, the better, so other metal elements can be selected to combine with the sulfonic acid group to form the corresponding salt. Except for Rb, Cs, and Fr, Group I metal elements such as lithium, sodium, and potassium cannot form metal element substitution and are not of reference significance for practical applications. Among the elements with larger atomic radii, only the second group remains. Considering the cost of using rare elements, calcium or magnesium is preferred.

[0027] After in-depth research on the copolymer, this invention discovered that polyacrylic acid already possesses advantages such as good elasticity and high modulus. The introduction of sulfonic acid groups and benzene rings enhances the conductivity of the binder through the synergistic conductive effect of the sulfonic acid groups and benzene rings. The strong steric hindrance effect of the benzene rings provides a certain degree of anti-precipitation performance for the prepared battery slurry. The added trace amounts of calcium and magnesium ions react with the sulfonic acid groups, and during charging and discharging, lithium ions in the battery undergo ion exchange reactions with them. The calcium and magnesium ions precipitate in the negative electrode active material and, as the charging and discharging process progresses, enter the crystal interior to form a solid solution. The atomic radius of calcium and magnesium is larger than that of silicon, generating holes that facilitate electron conduction and dislocations that enhance crystal toughness, thus mitigating the gradual disintegration of the active material during charging and discharging. The lithium sulfonate formed by ion exchange also helps increase the lithium ion mobility during the charging and discharging process of the lithium-ion battery, improving the battery's internal resistance.

[0028] In some embodiments, the molecular weight of the copolymer is in the range of 100,000 to 800,000 and all subranges or specific values ​​therebetween, such as 100,000 to 200,000, 200,000 to 300,000, 300,000 to 400,000, 400,000 to 500,000, 500,000 to 600,000, 700,000 to 800,000, 600,000 to 700,000, 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000, etc.

[0029] In some embodiments, the acrylic monomers comprise 95 to 99% of the total monomer mass and all ranges and subranges or specific values ​​therebetween, such as 95 to 96%, 96 to 97%, 97 to 98%, 98 to 99%, 95%, 96%, 97%, 98%, 99%, etc.

[0030] In some embodiments, the mass of the vinyl sulfonic acid monomer accounts for 1 to 5% of the total mass of the monomer and all ranges and subranges or specific values ​​therebetween, such as 1 to 2%, 2 to 3%, 3 to 4%, 4 to 5%, 1%, 2%, 3%, 4%, 5%, etc.

[0031] In some embodiments, the introduction of metal elements must be, and must be, in trace amounts. This is because if too many metal elements are introduced, during charging and discharging, the generated lithium will reduce these metal elements, excessively consuming the lithium in the battery and reducing its reversible capacity. Simultaneously, the crystallization and precipitation of these metal elements will damage the structure of the negative electrode active material, affecting the battery's capacity. Therefore, the introduction of metal elements must be controlled within a trace range, specifically 10 ppm to 3000 ppm of the vinyl sulfonic acid monomer mass, or any range and subrange or specific value within that range. For example, 50 ppm... ppm~1000ppm, 100ppm~500ppm, 50ppm~200ppm, 100ppm~400ppm, 100ppm~300ppm, 500ppm~1000ppm, 800ppm~1500ppm, 1 000ppm~3000ppm, 1500ppm~2700ppm, 10ppm, 50ppm, 100ppm, 500ppm, 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, etc.

[0032] In some embodiments, the synthesis method used for the copolymers described in this invention is well-known and not particularly limited. For example, polymerization can be achieved by adding various monomers to a solvent. As a solvent, an aqueous solvent is preferred, and a mixture of water, water, and a hydrophilic organic solvent may be selected. From a safety and environmental perspective, aqueous solution polymerization using water as a solvent is preferred. Aqueous solution polymerization can be carried out using polymerization initiators (e.g., sodium persulfate, ammonium persulfate, potassium persulfate, etc.) and polymerization accelerators (e.g., sodium L-ascorbate, sodium bisulfite, etc.).

[0033] II. A lithium-ion battery negative electrode slurry

[0034] The anode material is prepared by stirring a negative electrode material and a solvent. The negative electrode material comprises the binder, active material, and thickener used in lithium-ion batteries. The active material content is 90-99%, the thickener content is 0.5-2.5%, and the binder content is 0.5-5%.

[0035] In some embodiments, the content of the active material in the negative electrode material is 90-99% and all ranges and subranges or specific values ​​therebetween, for example, 90-92%, 90-95%, 93-99%, 92-96%, 94-98%, 96-99%, 90%, 93%, 95%, 98%, 99%, etc.; the content of the thickener is 0.5-2.5% and all ranges and subranges or specific values ​​therebetween, for example, 0.5-1.0%, 1.0-1.5%. %, 1.5-2.0%, 2.0-2.5%, 0.5-1.5%, 1.0-2.5%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, etc.; the binder content is 0.5-5% and all ranges and subranges or specific values ​​therebetween, for example, 0.5-2.5%, 1.0-3.5%, 1.0-4.5%, 2.5-5.0%, 1.5-2.5%, 0.5%, 1%, 2%, 3%, 4%, 5%, etc. The negative electrode slurry also contains a conductive agent, the content of which is 0 to 2.5% and all ranges and subranges or specific values ​​therebetween, such as 0 to 1.0%, 0.5 to 1.0%, 1.0 to 1.5%, 1.5 to 2.0%, 2.0 to 2.5%, 0%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, etc.

[0036] The active material in the negative electrode material can be a mixture of one of the following: mesophase carbon microsphere artificial graphite, needle coke artificial graphite, petroleum coke graphite, and composite graphite, and nano-silicon, with a graphite to nano-silicon mass ratio of 95:5.

[0037] More specifically, the conductive agent in the negative electrode material can be one of carbon black or carbon nanotubes.

[0038] More specifically, the thickener in the negative electrode material can be one of carboxymethyl cellulose, sodium carboxymethyl cellulose, or lithium carboxymethyl cellulose.

[0039] The method for preparing the negative electrode sheet includes the following steps:

[0040] Step 1: Stir and mix the active material and the conductive agent;

[0041] Step 2: Weigh out a certain amount of the thickener and binder composition according to the formula and stir to mix;

[0042] Step 3: Use deionized water as a dispersant and stir the mixture obtained in Step 1 and Step 2 in the dispersant until it is evenly mixed.

[0043] Step four: Coat the mixture obtained in step three onto the current collector, dry it, and roll it to obtain the negative electrode sheet.

[0044] In specific implementation, the content of the active material in the negative electrode material is 96%. The content of the conductive agent in the negative electrode material is 1%. The content of the thickener in the negative electrode material is 1%. The content of the binder composition in the negative electrode material is 2%. The selected coating speed is 15 m / min. The selected drying conditions are 100℃~130℃. The selected coating thickness is 100 μm.

[0045] III. A type of lithium-ion battery

[0046] The present invention also provides a lithium-ion battery comprising the above-mentioned lithium-ion battery negative electrode slurry.

[0047] IV. Examples, Comparative Examples, and Performance Analysis

[0048] Example 1

[0049] Preparation of the binder: An aqueous solution of a polymer formed by emulsion polymerization of two monomers and the addition of trace metal elements. It consists of monomer 1 and monomer 2, with the addition of trace metal elements, which exist in the polymer in the form of salts.

[0050] In this embodiment, monomer 1 is acrylic acid, monomer 2 is p-styrene sulfonic acid, and the selected metal element is calcium. The amount of acrylic acid used is 95% of the total mass of monomers 1 and 2; the amount of p-styrene sulfonic acid used is 5% of the total mass of monomers 1 and 2; and the calcium element is bonded to the sulfonic acid group in the form of a sulfonate, and the amount used is 10 ppm by mass of monomer 2.

[0051] The polymerization method used in this embodiment is emulsion polymerization, but the preparation method of this invention is not particularly limited. First, distilled water or deionized water, used as the dispersion medium, is placed in a reaction vessel, stirred, and an emulsifier is added. The mixture is stirred until homogeneous, then high-purity nitrogen is introduced to remove oxygen, and the temperature is raised to a predetermined reaction temperature. Finally, an initiator is added under a nitrogen atmosphere, and monomer 1 and monomer 2 are added dropwise. After reacting for a certain time, the reaction is terminated, and the small amount of gel produced during the reaction is removed by filtration to obtain the polymer emulsion. The polymer structure obtained in Example 1 is as follows:

[0052]

[0053] The initiator used in this embodiment is potassium persulfate, but the initiator described in this invention is not particularly limited. Water-soluble initiators such as ammonium persulfate, potassium persulfate, hydrogen peroxide, and azobisisobutyramidine can be used, with the amount being 0.5% of the monomer weight.

[0054] The emulsifier used in this embodiment is sodium dodecyl sulfate, but the emulsifier described in this invention is not particularly limited and can be any commonly used emulsifier in emulsion polymerization, such as sodium dodecylbenzenesulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, etc., and its amount is 1% of the monomer weight.

[0055] The solutions used in this embodiment are described as follows:

[0056] Solution 1: A 19% aqueous solution of acrylic acid.

[0057] Solution 2: A 5% p-styrene sulfonic acid solution.

[0058] Solution 3: A calcium hydroxide aqueous solution with a concentration of 0.0925 g / L.

[0059] The specific process is as follows: 400g of deionized water and 1.0g of sodium dodecyl sulfate are added to a multi-opening glass reactor equipped with a condenser. The mixture is heated to a constant temperature of 70°C. Nitrogen is purged for 30 minutes while stirring to remove oxygen. When the temperature stabilizes at 70°C, 0.50g of potassium persulfate is added. 500g of solution 1 is added dropwise. 1ml of solution 3 is mixed with 100g of solution 2 to form an aqueous solution, which is then added dropwise. The dropwise addition time is 4 hours. The reaction continues for another 2 hours to obtain a polymer emulsion.

[0060] Preparation of negative electrode sheet: The negative electrode active material, conductive agent, thickener and binder composition are prepared into a negative electrode slurry according to the following mass percentages: 96%, 1%, 1%, 2%. This ratio is the dry material mass ratio. In this embodiment, the negative electrode active material is a uniform mixture of artificial graphite and nano-silicon with a mass ratio of 95:5, the conductive agent is conductive carbon black (Super-P), and the thickener is carboxymethyl cellulose.

[0061] Slurry preparation process: Deionized water and carboxymethyl cellulose mixed colloid are added to a double planetary mixer. During the mixing process, ground conductive carbon black is added and dispersed at 1500 rpm and 15 rpm for 45 min. After uniform mixing, active material is added and stirred at 2000 rpm and 20 rpm for 4 h to complete the dispersion process of conductive carbon and active material. Binder composition is added and stirred at 2000 rpm and 20 rpm for 25 min. Vacuum is then applied to remove air bubbles, and the mixture is filtered through a 300-mesh stainless steel screen to complete the preparation of negative electrode slurry.

[0062] The negative electrode slurry was coated onto the surface of the current collector using a transfer coating machine at a speed of 15 m / min. After coating, it was dried in a 5-stage oven at a temperature of 100–130 °C. After drying, it was pressurized using a roller press to achieve a coating thickness of 100 μm and a compaction density of 1.79 g / cm³.

[0063] The positive electrode sheet is prepared using a conventional formula. The positive electrode materials include lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride. The lithium iron phosphate, conductive carbon black, polyvinylidene fluoride, and NMP solvent are stirred into a positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector to obtain the positive electrode sheet.

[0064] The diaphragm is a standard single-layer 12μm PE diaphragm.

[0065] The standard electrolyte formulation used is: 1.0M LiF6 in EC:DMC:EMC = 1:1:1 (Vol%).

[0066] The positive electrode, negative electrode, and separator are wound into a battery cell, encapsulated with an aluminum-plastic film, baked in a vacuum for 48 hours to remove moisture, and then injected with electrolyte. The battery is then formed and sorted to obtain a square soft-pack lithium-ion battery with a thickness, width, and length of 4mm, 60mm, and 72mm, respectively.

[0067] Example 2

[0068] The difference between this implementation and Example 1 is that 5 ml of solution 3 and 100 g of solution 2 are mixed to form an aqueous solution before being added dropwise.

[0069] Example 3

[0070] The difference between this implementation and Example 1 is that 10 ml of solution 3 and 100 g of solution 2 are mixed to form an aqueous solution before being added dropwise.

[0071] Example 4

[0072] The difference between this implementation and Example 1 is that 50 ml of solution 3 and 100 g of solution 2 are mixed to form an aqueous solution before being added dropwise.

[0073] Example 5

[0074] The difference between this implementation and Example 1 is that 100 ml of solution 3 and 100 g of solution 2 are mixed to form an aqueous solution before being added dropwise.

[0075] Example 6

[0076] The difference between this implementation and Example 1 is that 300 ml of solution 3 and 100 g of solution 2 are mixed to form an aqueous solution before being added dropwise.

[0077] Example 7

[0078] The difference between this embodiment and embodiment 1 is that instead of using solution 3 to mix with solution 2, 0.12 mg of magnesium hydroxide is added to solution 2 and added dropwise after it is completely dissolved.

[0079] Example 8

[0080] The difference between this embodiment and embodiment 1 is that instead of using solution 3 to mix with solution 2, 0.6 mg of magnesium hydroxide is added to solution 2 and added dropwise after it is completely dissolved.

[0081] Example 9

[0082] The difference between this embodiment and embodiment 1 is that instead of using solution 3 to mix with solution 2, 1.2 mg of magnesium hydroxide is added to solution 2 and added dropwise after it is completely dissolved.

[0083] Example 10

[0084] The difference between this embodiment and embodiment 1 is that instead of using solution 3 to mix with solution 2, 6.0 mg of magnesium hydroxide is added to solution 2 and added dropwise after it is completely dissolved.

[0085] Example 11

[0086] The difference between this embodiment and embodiment 1 is that instead of using solution 3 to mix with solution 2, 12.0 mg of magnesium hydroxide is added to solution 2 and added dropwise after it is completely dissolved.

[0087] Example 12

[0088] The difference between this embodiment and Embodiment 1 is that:

[0089] Solution 1: 30% acrylic acid solution.

[0090] The amount of solution 1 added is 1650g, the concentration of solution 2 remains unchanged and the amount added is still 100g, and 10ml of solution 3 is still mixed with 100g of solution 2 to form an aqueous solution before being added dropwise.

[0091] The amount of potassium persulfate added is 2.5g, and the amount of sodium dodecyl sulfate added is 5g.

[0092] Example 13

[0093] The difference between this embodiment and Embodiment 1 is that:

[0094] Solution 1: A 97% aqueous solution of acrylic acid.

[0095] Solution 2: A 3% aqueous solution of p-styrenesulfonic acid.

[0096] Take 100g of solution 1 and dilute it with deionized water to 1000g. Take 100g of solution 2 and 6ml of solution 3, mix them together, and then add the solution dropwise.

[0097] Comparative Example 1

[0098] The difference between this embodiment and embodiment 1 is that solution 3 and solution 2 are not mixed; instead, solution 1 and solution 2 are added dropwise simultaneously.

[0099] Table 1

[0100]

[0101] The binders prepared in the examples and comparative examples were used to fabricate lithium-ion batteries for testing, and the results are shown in Table 2.

[0102] Table 2

[0103] Performance parameters Number of cycles when capacity decays to below 80% 180° peel test (N / m) 25℃ 1C cycle 100 times (%) Example 1 332 8.67 94.1 Example 2 345 8.75 94.4 Example 3 367 8.56 94.3 Example 4 416 8.77 95.1 Example 5 422 8.88 94.9 Example 6 402 8.69 93.9 Example 7 322 8.71 94.2 Example 8 339 8.87 93.9 Example 9 370 9.01 94.5 Example 10 425 8.98 95.3 Example 11 412 8.79 95.1 Example 12 321 8.69 93.8 Example 13 301 8.78 93.4 Comparative Example 1 323 8.68 92.1

[0104] Comparing the cycle counts of Examples 1 to 11 with Comparative Example 1 when the capacity decayed to below 80%, it can be seen that the addition of trace metal elements enhances the battery's cycle performance. However, at the level of 10 ppm (Examples 1 and 7), the change in battery cycle performance is minimal. As the addition amount gradually increases, the difference between the 500 ppm level (Examples 4 and 10) and the 1000 ppm level (Examples 5 and 11) is not significant. It can be concluded that the addition of trace metal elements between 500 ppm and 1000 ppm helps to improve the battery's cycle performance. With further increases in the amount of trace metal elements added, the cycle performance of Examples 6 and 11 begins to decline, indicating that the addition of ultra-trace amounts of metal elements may reduce the battery's cycle performance.

[0105] A comparison of Example 3 with Examples 12 and 13 shows that the bonding performance of the binder does not change significantly with an addition of 1% to 5% p-styrene sulfonic acid. However, the introduction of more p-styrene sulfonic acid helps to improve the cycle performance of the battery, demonstrating that p-styrene sulfonic acid helps to improve ion conductivity in the polyacrylic acid (PAA) chain.

[0106] 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 the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A negative electrode sheet for a lithium-ion battery, comprising a current collector and a coating applied to the current collector, characterized in that, The coating comprises a binder and an active substance; the active substance comprises nano-silicon; the binder is a copolymer formed from acrylic monomers and vinyl sulfonic acid monomers; the copolymer also contains a metal element, which combines with sulfonic acid groups to form a corresponding salt; the amount of the metal element added is 500ppm to 1000ppm of the vinyl sulfonic acid monomer; wherein the metal element is at least one of calcium or magnesium; and the vinyl sulfonic acid monomer is styrene sulfonic acid.

2. The lithium-ion battery negative electrode sheet according to claim 1, characterized in that, The acrylic monomers include one or more of acrylic acid, acrylates, and methacrylic acid.

3. The lithium-ion battery negative electrode sheet according to claim 1, characterized in that, The molecular weight of the copolymer is 100,000 to 800,000.

4. The lithium-ion battery negative electrode sheet according to claim 1, characterized in that, The acrylic monomers account for 95-99% of the total monomer mass.

5. The lithium-ion battery negative electrode sheet according to claim 1, characterized in that, The vinyl sulfonic acid monomers account for 1 to 5% of the total monomer mass.

6. A lithium-ion battery, comprising a positive electrode, a separator, and an electrolyte, characterized in that, It also includes the lithium-ion battery negative electrode sheet as described in claim 1.

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