Copolymer-modified lithium polyacrylate binder, preparation method thereof, negative electrode sheet, lithium ion battery and electric device

Abstract

The application discloses a kind of copolymer modified lithium polyacrylate binder and preparation method thereof, negative pole piece, lithium ion battery, electric device, the copolymer modified lithium polyacrylate binder is obtained by the copolymerization of first monomer and second monomer, the first monomer includes lithium acrylate;The second monomer includes olefin monomer, and the olefin monomer contains cationic ionic liquid group or intramolecular salt group.The binder can improve the fast-charging performance and low-temperature performance of lithium ion battery, reduce the risk of lithium precipitation, and improve the cycle stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a copolymer-modified lithium polyacrylate binder and its preparation method, a negative electrode sheet, a lithium-ion battery, and an electrical device. Background Technology

[0002] In related technologies, the graphite anode of lithium-ion batteries mainly adopts an aqueous binder system, which primarily uses water-soluble binders such as lithium carboxymethyl cellulose (CMC-Li) or sodium lithium carboxymethyl cellulose (CMC-Na), polyacrylic acid (PAA) or lithium polyacrylate (PAA-Li) in combination with styrene-butadiene rubber (SBR) emulsion. Compared with the earlier PVDF system, this system has advantages such as environmental friendliness, low cost, and simple process. However, this system also has some drawbacks, limiting the fast-charging performance and low-temperature performance of lithium-ion batteries, increasing the risk of lithium plating at the anode under high current, and degrading the cycle stability of the battery. Summary of the Invention

[0003] This invention aims to at least partially address one of the technical problems in related technologies. To this end, one object of this invention is to provide a copolymer-modified lithium polyacrylate binder that can improve the fast-charging performance and low-temperature performance of lithium-ion batteries, reduce the risk of lithium plating, and improve cycle stability.

[0004] Specifically, the first aspect of the present invention provides a copolymer-modified lithium polyacrylate adhesive, wherein the copolymer-modified lithium polyacrylate adhesive is obtained by copolymerizing a first monomer and a second monomer, wherein the first monomer includes lithium acrylate; and the second monomer includes an olefin monomer, wherein the olefin monomer contains a cationic ionic liquid group or an intramolecular salt group.

[0005] This invention introduces ionic liquid or intramolecular salt structural units with unique ion transport mechanisms onto the molecular chain through molecular structure design. These structural units contain ion pairs; compared to lithium carboxylate groups, the interaction between these ion pairs and lithium ions is weaker, reducing the strong binding effect of the binder on lithium ions and facilitating rapid lithium ion transport within the binder. Furthermore, the cations fixed on the main chain "hold back" anions (such as PF6) in the electrolyte through electrostatic interactions. -The structure enhances lithium-ion transport number by increasing the cation's electrostatic repulsion with lithium ions, promoting uniform distribution and efficient transport of lithium ions within the binder. This provides highly efficient ion channels for ion hopping and anion anchoring, resulting in higher lithium-ion conductivity and transport number compared to traditional binders containing lithium carboxylate groups. This improves the electrochemical reaction kinetics of lithium-ion batteries, significantly enhances lithium-ion transport capacity, reduces battery impedance, and ultimately achieves superior fast-charging and low-temperature performance while reducing the risk of lithium plating. Furthermore, introducing ionic liquid groups or intramolecular salt groups into the lithium polyacrylate molecular chain enhances affinity with the electrolyte. The electrolyte can effectively wet and penetrate the electrode network constructed with this binder, mitigating uneven lithium salt distribution caused by lithium salt extrusion during negative electrode expansion, reducing the risk of lithium plating, and improving battery cycle stability.

[0006] According to some embodiments of the present invention, the cationic ionic liquid group comprises a cation and an anion; the cation comprises one or more of imidazolium, pyridinium, pyrrolidineium, and quaternary ammonium cations; the anion comprises FSI. - The intramolecular salt groups include quaternary ammonium cations and sulfonate anions.

[0007] According to some embodiments of the present invention, the cationic ionic liquid group includes , , , At least one of the following; the intramolecular salt group includes .

[0008] According to some embodiments of the present invention, the copolymer-modified lithium polyacrylate binder has the structure shown in Formula I.

[0009] Formula I Wherein, R1 is selected from , , , or ; R2 is selected from hydrogen or methyl.

[0010] According to some embodiments of the present invention, y:(x+y)=(5-95):100; preferably, y:(x+y)=(10-40):100; the weight average molecular weight of the copolymerized modified lithium polyacrylate binder is 10kDa-10000kDa.

[0011] A second aspect of the present invention provides a method for preparing a copolymer-modified lithium polyacrylate adhesive according to the first aspect of the present invention, comprising the following steps: The first monomer and the second monomer are dissolved in water to obtain a mixed solution; A free radical initiator is added to the mixed solution, the temperature is raised to 60℃-80℃, and the reaction is carried out for 6h-12h to obtain the copolymerized modified lithium polyacrylate adhesive.

[0012] The preparation method of this invention is simple, operates under mild conditions, and is highly reproducible, making it suitable for large-scale industrial application. The copolymer-modified lithium polyacrylate binder prepared by this method can improve lithium-ion transport capacity, enhance fast-charging performance and low-temperature performance, and reduce the risk of lithium plating; it can also enhance electrolyte retention and improve cycle stability. This invention solves the problems of poor lithium-ion conductivity and insufficient electrolyte retention capacity in current aqueous binders for lithium-ion battery anodes.

[0013] According to some embodiments of the present invention, the first monomer has the structure shown in Formula II, and the second monomer has the structure shown in Formula III.

[0014] Wherein, R1 is selected from , , , or ; R2 is selected from hydrogen or methyl.

[0015] A third aspect of the present invention provides a negative electrode sheet comprising a copolymer-modified lithium polyacrylate binder according to the first aspect of the present invention or a copolymer-modified lithium polyacrylate binder obtained by the preparation method of the second aspect of the present invention.

[0016] Because of the use of the copolymerized modified lithium polyacrylate binder described above, the negative electrode sheet of the present invention has all the advantages of the binder described above, which will not be repeated here.

[0017] A fourth aspect of the present invention provides a lithium-ion battery, including the negative electrode sheet of the third aspect of the present invention.

[0018] Because of the use of the copolymerized modified lithium polyacrylate binder described above, the lithium-ion battery of the present invention has all the advantages of the binder described above, which will not be repeated here.

[0019] The fifth aspect of the present invention provides an electrical device including a lithium-ion battery according to the fourth aspect of the present invention.

[0020] Because of the use of the copolymerized modified lithium polyacrylate binder described above, the electrical device of the present invention has all the advantages of the aforementioned binder, which will not be elaborated further here.

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

[0022] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] In the description of this invention, unless otherwise stated, "a plurality of" means two or more. "Multiple" means two or more. Throughout this document, the terms "comprising" or "including" are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] The terms "first" and "second" used in this document are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0026] In related technologies, the graphite anode of lithium-ion batteries mainly adopts an aqueous binder system, which mainly uses water-soluble binders such as lithium carboxymethyl cellulose (CMC-Li) or sodium carboxymethyl cellulose (CMC-Na), polyacrylic acid (PAA) or lithium polyacrylate (PAA-Li) in combination with styrene-butadiene rubber (SBR) emulsion. Compared to earlier PVDF systems, this system offers advantages such as environmental friendliness, low cost, and simple processing. However, it also has some drawbacks. For example, its improvement in lithium-ion conductivity is limited. While the widely used CMC-Na system contains abundant polar groups with oxygen atoms, enhancing lithium-ion anchoring, its rigid molecular structure and limited electrolyte absorption hinder improvements in lithium-ion conductivity. Replacing sodium ions with lithium ions improves conductivity, but the conductivity remains insufficient. The lithium carboxylic acid groups strongly bind lithium ions, resulting in a low lithium-ion transference number, failing to provide an efficient channel for rapid lithium-ion transport. This phenomenon also occurs in PAA-Li binders. Furthermore, SBR binders are non-polar hydrocarbon resins that contribute almost nothing to lithium-ion conduction, acting as ion insulators. Therefore, the negative electrode using these aqueous binder systems exhibits high interfacial impedance, limiting fast-charging and low-temperature performance, and increasing the risk of lithium plating at high currents. In addition, the electrolyte retention of the above aqueous binder systems still needs to be improved. Although the polarity of aqueous binder systems is stronger than that of PVDF, their rigid molecular structure and strong intermolecular forces still result in insufficient affinity and absorption capacity for electrolytes. Especially during long-term cycling, the expansion and contraction of the electrodes lead to the extrusion and backflow of electrolytes, which in turn causes uneven distribution of lithium salts in the electrolyte, accelerates the degradation of electrochemical performance, and degrades the cycle stability of the battery.

[0027] To address the above problems, this invention provides a copolymer-modified lithium polyacrylate binder. Through molecular structure design, ionic liquid or intramolecular salt structural units with unique ion transport mechanisms are introduced into the molecular chain. These structural units contain ion pairs; compared to lithium carboxylate groups, these ion pairs interact weakly with lithium ions, reducing the strong binding effect of the binder on lithium ions and facilitating rapid lithium ion transport within the binder. Furthermore, the cations fixed on the main chain "hold back" anions (such as PF6) in the electrolyte through electrostatic interactions. -The structure enhances lithium-ion transport number by increasing the cation's electrostatic repulsion with lithium ions, promoting uniform distribution and efficient transport of lithium ions within the binder. This provides highly efficient ion channels for ion hopping and anion anchoring, resulting in higher lithium-ion conductivity and transport number compared to traditional binders containing lithium carboxylate groups. This improves the electrochemical reaction kinetics of lithium-ion batteries, significantly enhances lithium-ion transport capacity, reduces battery impedance, and ultimately achieves superior fast-charging and low-temperature performance while reducing the risk of lithium plating. Furthermore, introducing ionic liquid groups or intramolecular salt groups into the lithium polyacrylate molecular chain enhances affinity with the electrolyte. The electrolyte can effectively wet and penetrate the electrode network constructed with this binder, mitigating uneven lithium salt distribution caused by lithium salt extrusion during negative electrode expansion, reducing the risk of lithium plating, and improving battery cycle stability.

[0028] Specifically, the first aspect of the present invention provides a copolymer-modified lithium polyacrylate adhesive, wherein the copolymer-modified lithium polyacrylate adhesive is obtained by copolymerizing a first monomer and a second monomer, wherein the first monomer includes lithium acrylate; and the second monomer includes an olefin monomer, wherein the olefin monomer contains a cationic ionic liquid group or an intramolecular salt group.

[0029] In this article, "cationic ionic liquid group" refers to the cationic portion of the ionic liquid group after monomer polymerization that is covalently linked to the polymer molecular chain, for example... The imidazolium cation is covalently linked to the polymer molecular chain. In this paper, * in the structural formula indicates the connection point with the main molecular chain.

[0030] In this article, "intramolecular salt group" refers to a pair of covalently linked anionic and cationic groups on the same molecular backbone.

[0031] In some embodiments, the cationic ionic liquid group comprises a cation and an anion. The cation comprises one or more of imidazolium, pyridinium, pyrrolidineium, and quaternary ammonium cations. The anion comprises FSI. - As a specific example, the cation is an imidazolium, pyridinium, pyrrolidineium, or quaternary ammonium cation; the anion is FSI. - (i.e., bis(fluorosulfonyl)imide anion). In some embodiments, the intramolecular salt group includes a quaternary ammonium cation and a sulfonate anion. Both the cationic ionic liquid group and the intramolecular salt group contain ion pairs. Compared to the lithium carboxylate group, the interaction between this ion pair and lithium ions is weaker, reducing the strong binding effect of the binder on lithium ions and facilitating the rapid transport of lithium ions in the binder. In addition, the cations fixed on the main chain "hold back" the anions in the electrolyte (such as PF6) through electrostatic interactions. -The cations increase the lithium-ion transference number; the cations can also promote the uniform distribution and efficient transport of lithium ions in the binder through electrostatic repulsion. The unique ion transport mechanisms of ionic liquid groups and intramolecular salt groups significantly improve the electrochemical reaction kinetics of lithium-ion batteries and reduce their impedance. Therefore, introducing these cationic ionic liquid groups and intramolecular salt groups into the molecular chain of polymer binders can effectively improve the electrochemical performance of the battery.

[0032] In some embodiments, the cationic ionic liquid group includes , , , At least one of the following. The intramolecular salt group includes This effectively improves lithium-ion transport capacity, thereby enhancing the fast-charging and low-temperature performance of lithium-ion batteries and reducing the risk of lithium plating. Furthermore, during long-term cycling, electrolyte consumption and uneven distribution due to electrode volume changes exacerbate the risk of lithium plating, especially at high rates, which is detrimental to battery life and safety. The polymer molecular chains of this invention exhibit high similarity and compatibility with ester-based electrolytes, generating strong intermolecular forces that enhance the effective wetting and absorption of the electrolyte by the electrode. During cycling, the binder acts like a "molecular sponge," locking in the electrolyte, increasing lithium salt concentration, promoting uniform lithium salt distribution, improving battery cycle stability, and extending cycle life.

[0033] In some embodiments, the copolymer-modified lithium polyacrylate adhesive has the structure shown in Formula I.

[0034] Formula I Wherein, R1 is selected from , , , or R2 is selected from hydrogen or methyl. The polymer binder of the present invention is not a simple lithium carboxylate-containing polymer binder in the related art, but introduces cationic ionic liquid groups and intramolecular salt groups into the molecular chain, thereby effectively improving the fast charging performance and low-temperature performance of lithium-ion batteries, reducing the risk of lithium plating, and improving cycle stability.

[0035] In some embodiments, y:(x+y) = (5-95):100. Preferably, y:(x+y) = (10-40):100. Optimizing the proportion of the degree of polymerization y is beneficial for balancing the ion transport performance and mechanical properties of the polymer, taking into account both the continuity of ion channels and the structural integrity during cycling, thereby improving the fast-charging performance and low-temperature performance of lithium-ion batteries, reducing the risk of lithium plating, and simultaneously improving cycle stability.

[0036] In some specific embodiments, y:(x+y) can be 5:100, 10:100, 20:100, 30:100, 40:100, 50:100, 60:100, 70:100, 80:100, 90:100 or 95:100.

[0037] In some embodiments, y is 3-95, such as 3, 5, 10, 20, 40, or 95. x is 5-97, such as 97, 95, 90, 80, 60, or 5.

[0038] In Formula I, the total molar ratio of lithium carboxylate repeating units to repeating units containing ionic liquid groups or intramolecular salt groups in the polymer is 100%. Among them, the repeating units containing ionic liquid groups or intramolecular salt groups account for 5%-95% of the total molar ratio of repeating units.

[0039] In some embodiments, the weight-average molecular weight of the copolymerized lithium polyacrylate binder can be 10 kDa to 10,000 kDa. Too low a molecular weight results in lower polymer mechanical and adhesive properties, which is detrimental to battery stability; too high a molecular weight results in excessively high slurry viscosity, making processing impossible. Therefore, using a binder with an appropriate molecular weight can improve the fast-charging and low-temperature performance of lithium-ion batteries, reduce the risk of lithium plating, and improve cycle stability.

[0040] In some specific embodiments, the weight-average molecular weight of the copolymerized modified lithium polyacrylate binder may be 10 kDa, 100 kDa, 1000 kDa, 2000 kDa, 4000 kDa, 6000 kDa, 8000 kDa or 10000 kDa.

[0041] A second aspect of the present invention provides a method for preparing a copolymer-modified lithium polyacrylate adhesive according to the first aspect of the present invention, comprising the following steps: The first monomer and the second monomer are dissolved in water to obtain a mixed solution; A free radical initiator is added to the mixed solution, the temperature is raised to 60℃-80℃, and the reaction is carried out for 6h-12h to obtain the copolymerized modified lithium polyacrylate adhesive.

[0042] The preparation method of this invention is simple, operates under mild conditions, and is highly reproducible, making it suitable for large-scale industrial application. The copolymer-modified lithium polyacrylate binder prepared by this method can improve lithium-ion transport capacity, enhance fast-charging performance and low-temperature performance, and reduce the risk of lithium plating; it can also enhance electrolyte retention and improve cycle stability. This invention solves the problems of poor lithium-ion conductivity and insufficient electrolyte retention capacity in current aqueous binders for lithium-ion battery anodes.

[0043] In some embodiments, the first monomer has the structure shown in Formula II, and the second monomer has the structure shown in Formula III.

[0044] Wherein, R1 is selected from , , , or ; R2 is selected from hydrogen or methyl.

[0045] The copolymerized lithium polyacrylate binder is obtained by free radical copolymerization of lithium acrylate as shown in Formula II and olefin monomers as shown in Formula III. This reaction can be carried out under mild conditions, facilitating large-scale industrial application.

[0046] The olefin monomer shown in Formula III contains a cationic ionic liquid group or an intramolecular salt group. Olefin monomers containing cationic ionic liquid groups have the following characteristics: the polymer backbone obtained after polymerization of this monomer is connected by covalently bonded organic cations (including quaternary ammonium cations, imidazoline cations, or pyridine cations, etc.) and mobile bis(fluorosulfonyl)imide anions (FSI) paired with them through electrostatic interactions. - "Mobile" means that the anion and cation are not covalently bonded. In the electrolyte environment of a battery, the anion and cation pair dissociates, and the anion can move freely without being confined to the vicinity of the cation. Alkene monomers containing intramolecular salt groups have the following characteristic: the monomer molecule simultaneously contains covalently bonded cationic and anionic groups.

[0047] In some embodiments, after adding a free radical initiator, the temperature of the reaction system can be raised to, for example, 60°C, 65°C, 70°C, 75°C, or 80°C. The reaction time for free radical copolymerization can be, for example, 6 hours, 8 hours, 10 hours, or 12 hours. This promotes the full copolymerization of the first and second monomers, effectively controls the molecular weight and distribution of the polymer, improves the uniformity of the copolymer structure, and reduces side reactions.

[0048] In some embodiments, before adding the free radical initiator, the preparation method further includes: purging the mixed solution with an inert gas for 20-30 minutes to completely remove oxygen from the reaction system, thereby reducing oxygen inhibition of polymerization, ensuring smooth polymerization, reducing side reactions and impurity generation, and improving polymer structural stability and purity. The inert gas includes nitrogen or argon. The purging time of the inert gas can be 20 minutes, 25 minutes, or 30 minutes.

[0049] In some embodiments, the molar ratio of the second monomer to the total molar ratio of the first and second monomers is (5-95):100, for example, 5:100, 10:100, 20:100, 30:100, 40:100, 50:100, 60:100, 70:100, 80:100, 90:100, or 95:100; preferably (10-40):100. This allows control over the proportion of the degree of polymerization y in Formula I, thereby balancing the polymer's ion transport performance and mechanical properties, taking into account both ion channel continuity and structural integrity during cycling, thus improving the fast-charging performance and low-temperature performance of lithium-ion batteries, reducing the risk of lithium plating, and simultaneously improving cycle stability.

[0050] In some embodiments, the free radical initiator includes at least one of potassium persulfate and ammonium persulfate. The free radical initiator is used to decompose and generate active free radicals, initiate monomer copolymerization reactions, and regulate the polymerization rate, polymer structure, and properties.

[0051] In some embodiments, the molar amount of the free radical initiator accounts for 0.1%-1.0% of the total molar amount of all monomers, for example, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, or 1.0%. This allows for precise control of the polymerization rate and reaction stability, avoiding excessive initiator leading to overly rapid reaction, localized overheating, rapid polymerization, or gelation, and also avoiding insufficient initiator leading to slow reaction and low conversion rate, effectively controlling the molecular weight of the polymer.

[0052] The copolymer-modified lithium polyacrylate binder of the present invention can be used in the negative electrode of lithium-ion batteries.

[0053] A third aspect of the present invention provides a negative electrode sheet comprising a copolymer-modified lithium polyacrylate binder according to the first aspect of the present invention or a copolymer-modified lithium polyacrylate binder obtained by the preparation method of the second aspect of the present invention.

[0054] Because of the use of the copolymerized modified lithium polyacrylate binder described above, the negative electrode sheet of the present invention has all the advantages of the binder described above, which will not be repeated here.

[0055] In lithium-ion batteries, the negative electrode typically includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative active material layer includes a negative active material (which may include graphite and hard carbon materials), a dispersant, a conductive agent, and a binder. The binder includes the copolymer-modified lithium polyacrylate binder of this invention and styrene-butadiene latex (SBR). In the negative active material layer, the mass ratio of the negative active material, the conductive agent, the binder of this invention, and the SBR can be 100:(0.5-1.0):(0.5-1.5):(1.0-2.0).

[0056] The negative electrode current collector can be a conventional metal foil, such as copper foil. The negative electrode active material layer is obtained by coating the negative electrode slurry onto the negative electrode current collector and then performing processes such as drying, rolling, and slitting. The negative electrode slurry includes a negative electrode active material (e.g., graphite), a conductive agent, the copolymerized modified lithium polyacrylate binder, and styrene-butadiene latex (SBR).

[0057] A fourth aspect of the present invention provides a lithium-ion battery, including the negative electrode sheet of the third aspect of the present invention.

[0058] Because of the use of the copolymerized modified lithium polyacrylate binder described above, the lithium-ion battery of the present invention has all the advantages of the binder described above, which will not be repeated here.

[0059] The fifth aspect of the present invention provides an electrical device including a lithium-ion battery according to the fourth aspect of the present invention.

[0060] Because of the use of the copolymerized modified lithium polyacrylate binder described above, the electrical device of the present invention has all the advantages of the aforementioned binder, which will not be elaborated further here.

[0061] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0062] Example 1 1. Preparation of adhesive solution: (1) Preparation of 3-methyl-1-vinylimidazolium difluorosulfonylimide salt (see Formula IV): N-vinylimidazolium (10.0 g, 110 mmol) and a small excess of iodomethane (19.5 g, 140 mmol) were stirred in acetone (20 mL) at room temperature for 12 h. Then, the acetone and unreacted iodomethane were completely removed under reduced pressure. The obtained solid was recrystallized from acetonitrile / ethyl acetate (1 / 2, volume ratio) and dried under high vacuum at 40 °C to give a solid intermediate (24.8 g, 90% yield). The obtained intermediate (5.0 g, 20 mmol) was then dissolved in deionized water (60 mL), a small excess of LiFSI (4.2 g, 22 mmol) was added, and the mixture was stirred at room temperature for 3 h. The bottom 1-vinyl-3-methylimidazolium difluorosulfonylimide organic layer was separated and washed with deionized water until no iodide ions were detected with AgNO3 solution. The prepared product was vacuum dried at 50°C for 24 hours to obtain a pure product, which was a colorless oil.

[0063]

[0064] Formula IV (2) Material preparation and dissolution: Add 253g of deionized water, 8.38g of lithium acrylate and 7.77g of 3-methyl-1-vinylimidazolium difluorosulfonylimide salt to the reaction vessel, start stirring, and stir at room temperature for at least 1 hour to obtain a clear and homogeneous solution.

[0065] (3) Deoxygenation: Nitrogen gas is introduced below the liquid surface and high-purity nitrogen gas (purity ≥99.999%) is bubbled into the solution at a flow rate of 50 mL / min; bubble continuously for 30 min to completely remove oxygen from the water and create an oxygen-free environment for free radical polymerization.

[0066] (4) Polymerization reaction: Under continuous nitrogen purging and stirring, 0.0613 g of ammonium persulfate was weighed and slowly added to the reaction solution, and then the temperature was slowly raised to 70 °C; the reaction was continued to be stirred at this temperature for 9 h. After cooling, the adhesive solution (structural formula as shown in Formula I above) was obtained, with a solid content of 6%, y:(x+y)=20:100, and the molar amount of initiator was 0.2% of the total molar amount of monomer.

[0067] 2. Preparation of lithium-ion batteries: (1) Negative electrode preparation process: Graphite, carbon black, the above-mentioned binder solution, SBR, water, and NMP are mixed in a mass ratio of 100: 1.0: 1.0: 1.5: 85:3. Specifically, after stirring and mixing graphite and carbon black, the above-mentioned binder solution is added and stirred to disperse it. Water and NMP are added and stirred to dilute it. Finally, SBR emulsion is added and stirred to obtain graphite negative electrode slurry. The above slurry is coated on the surface of copper foil, and then dried, rolled, and slit to obtain negative electrode sheet.

[0068] (2) Preparation process of positive electrode sheet: Lithium iron phosphate, carbon black, PVDF binder, and NMP are mixed in a mass ratio of 100:0.5:2.0:50 and a positive electrode slurry is prepared by high-speed dispersion. The slurry is coated on the surface of aluminum foil, and then dried, rolled, and slit to obtain the positive electrode sheet.

[0069] (3) Battery assembly: The aforementioned negative electrode, polypropylene separator (14 μm thick), and positive electrode were packaged and then injected with electrolyte (1 M LiPF6, solvent being a 1:1 volume ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC)) to form a 7+8 small soft-pack stacked full cell (1C=1.8Ah). After sealing and formation, it was kept for later use. "7+8 small soft-pack stacked full cell" refers to a full cell using 7 positive electrode sheets and 8 negative electrode sheets.

[0070] Example 2 The binder solution and lithium-ion battery were prepared according to the method described in Example 1, except that the olefin monomer containing the ionic liquid group (i.e., the second monomer) was [2-(methacryloyloxy)ethyl]trimethylammonium difluorosulfonylimide salt (CAS No.: 1246462-74-7), as shown in Formula V.

[0071]

[0072] Formula V Example 3 The binder solution and lithium-ion battery were prepared according to the method described in Example 1, except that the olefin monomer containing the ionic liquid group (i.e., the second monomer) was [2-(propenyl)ethyl]methylpyrrolidine onium bisfluorosulfonyl imide salt (CAS No.: 3111833-35-0), as shown in Formula VI.

[0073]

[0074] Style VI Example 4 The binder solution and lithium-ion battery were prepared according to the method described in Example 1, except that the olefin monomer containing the ionic liquid group (i.e., the second monomer) was 1-methyl-4-vinylpyridinium bis(fluorosulfonyl)imide salt (see Formula VII). The synthesis steps are as follows: Methyl bromide was added to a 500 mL three-necked flask. 200 mL of acetonitrile and 4-vinylpyridine (concentration 1.0 M) were added to the flask. The solution was refluxed to form an alkylpyridine bromide. The concentrated solution was added to pure water to dissolve the alkylpyridine bromide, yielding an aqueous solution. The aqueous solution was washed three times with hexane to remove unreacted methyl bromide and 4-vinylpyridine. After drying, pure alkylpyridine bromide was obtained. The alkylpyridine bromide was added to methanol, and two molar amounts of LiFSI were weighed and dissolved in 500 mL of water. The LiFSI aqueous solution was added to the alkylpyridinium bromide solution to react the bromide with FSI. - Anion exchange occurred between the molecules, and the mixture became turbid over time. After 24 hours, a brown liquid appeared at the bottom of the mixture. After removing the turbid water, the brown liquid was dried in a vacuum at 80°C to obtain the second monomer of formula VII.

[0075]

[0076] Equation VII Example 5 The binder solution and lithium-ion battery were prepared according to the method described in Example 1, except that the olefin monomer containing the ionic liquid group (i.e., the second monomer) was 3-[[2-(acryloyloxy)ethyl]dimethylammonium]propane-1-sulfonate (CAS No.: 88992-91-0).

[0077] Examples 6-15 The binder solution and lithium-ion battery were prepared according to the method described in Example 1, with differences shown in Table 1.

[0078] Example 16 The binder solution and lithium-ion battery were prepared according to the method described in Example 1, except that in the polymerization reaction step (3), the temperature was slowly raised to 60°C; and the reaction was continuously stirred at this temperature for 12 hours.

[0079] Example 17 The binder solution and lithium-ion battery were prepared according to the method described in Example 1, except that in the polymerization reaction step (3), the temperature was slowly raised to 80°C; and the reaction was continuously stirred at this temperature for 6 hours.

[0080] Comparative Example 1 This comparative example uses commercially available PAA-Li (Guangdong Kelude New Energy Technology Co., Ltd., model: MA-EN-BI-0013) as the negative electrode binder for lithium-ion batteries, and the preparation process of the lithium-ion batteries is the same as in Example 1.

[0081] Comparative Example 2 This comparative example uses commercially available CMC-Li (Guangdong Kelude New Energy Technology Co., Ltd., model: MA-EN-BI-0021) as the negative electrode binder for lithium-ion batteries, and the preparation process of the lithium-ion batteries is the same as in Example 1.

[0082] Comparative Example 3 The adhesive solution and lithium-ion battery were prepared according to the method described in Example 1, except that sodium p-styrene sulfonate (CAS No.: 2695-37-6) was used instead of 3-methyl-1-vinylimidazolium difluorosulfonylimide salt.

[0083] Comparative Example 4 The binder solution and lithium-ion battery were prepared according to the method described in Example 1, except that the 3-methyl-1-vinylimidazolium difluorosulfonylimide salt was replaced with an anionic ionic liquid second monomer (CAS No.: 2217640-25-8, see Formula VIII).

[0084]

[0085] Formula VIII Adhesive characterization test (1) Testing of the weight-average molecular weight and y:(x+y) of the adhesive: The molecular weight of the binder was characterized by gel permeation chromatography (GPC) using water as the solvent; the copolymerization ratio was characterized by proton nuclear magnetic resonance (NMR) spectroscopy. 1 Characterized by 1H NMR, using D2O as the deuterated reagent, the copolymerization ratio was calculated by the integral area ratio of the absorption peaks of hydrogen atoms of the characteristic groups of the ionic liquid to those of hydrogen atoms of lithium polyacrylate.

[0086] The test results are shown in Table 1.

[0087] Lithium-ion battery performance testing (1) Low-temperature DCIR test: Discharge the battery in a stable state at 25°C to 50% SOC, and then place it at -10°C for 6 hours. Set the test parameters according to the following ratio: 1.5C charging (Note: After the DCIR test, use 0.05C to balance the capacity). Record the DCIR test results under the 1.5C charging condition.

[0088] (2) 60℃ Cyclic Capacity Test: Charge and discharge test cabinet, ambient temperature set to 60℃, charging and discharging conditions: 1C constant current charging to 3.8V, rest for 10min, 1C constant current discharging to 2.0V, rest for 10min, after 500 cycles, record the battery capacity retention rate, that is, the ratio of discharge capacity to initial capacity.

[0089] (3) 10C rate discharge test: The battery was charged at 0.33C at 25℃ to 60% SOC, left to stand for 30 minutes, discharged at 10C for 5 seconds, left to rest for 10 seconds, and the discharge process was repeated 4 times, with a rest period of 10 seconds after each discharge. The initial voltage of the discharge and the ending voltage after each discharge were recorded to obtain the voltage retention rate at the end of the third discharge: the ratio of the ending voltage after discharge to the initial discharge voltage.

[0090] (4) 75℃ fast charging cycle test: Charge and discharge test cabinet, ambient temperature set to 75℃, charging and discharging conditions: 3C constant current charging to 3.8V, rest for 10min, 1C constant current discharging to 2.0V, rest for 10min, after 200 cycles, record the battery capacity retention rate: that is, the ratio of discharge capacity to initial discharge capacity.

[0091] The test results are shown in Table 1.

[0092] Table 1

[0093] Based on the results of the above embodiments and comparative examples, it is evident that introducing ionic liquid groups or amphoteric intramolecular salt groups onto the lithium polyacrylate molecular chain improves lithium-ion transport kinetics and enhances electrolyte retention. This results in batteries using the binder of the present invention exhibiting low DC resistance at low temperatures, and the DCIR of batteries using the binder of the present invention is lower than that of batteries using conventional PAA-Li and CMC-Li binders. Furthermore, batteries using the binder of the present invention maintain a higher voltage during 10C high-rate discharge, improving the battery's power density. In addition, batteries using the binder of the present invention exhibit superior cycle stability, with a capacity retention of over 85% after 500 cycles, superior to the comparative examples (<80%). Further, the results of 3C fast-charging cycles demonstrate that the battery of the present invention also exhibits good cycle stability and fast-charging capability during high-rate, high-temperature operation.

[0094] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0095] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A copolymer-modified lithium polyacrylate adhesive, characterized in that, The copolymerized modified lithium polyacrylate adhesive is obtained by copolymerizing a first monomer and a second monomer, wherein the first monomer includes lithium acrylate; and the second monomer includes an olefin monomer, wherein the olefin monomer contains a cationic ionic liquid group or an intramolecular salt group.

2. The copolymer-modified lithium polyacrylate adhesive according to claim 1, characterized in that, The cationic ionic liquid group includes cations and anions; the cations include one or more of imidazolium, pyridinium, pyrrolidineium, and quaternary ammonium cations; the anions include FSI. - ; The intramolecular salt groups include quaternary ammonium cations and sulfonate anions.

3. The copolymer-modified lithium polyacrylate adhesive according to claim 1, characterized in that, The cationic ionic liquid group includes , , , At least one of them; The intramolecular salt groups include .

4. The copolymer-modified lithium polyacrylate adhesive according to claim 1, characterized in that, It has the structure shown in Equation I. Formula I Wherein, R1 is selected from , , , or ; R2 is selected from hydrogen or methyl.

5. The copolymer-modified lithium polyacrylate adhesive according to claim 4, characterized in that, y:(x+y)=(5-95):100; Preferably, y:(x+y)=(10-40):100; The copolymerized modified lithium polyacrylate binder has a weight-average molecular weight of 10kDa-10000kDa.

6. A method for preparing a copolymer-modified lithium polyacrylate adhesive according to any one of claims 1-5, characterized in that, Includes the following steps: The first monomer and the second monomer are dissolved in water to obtain a mixed solution; A free radical initiator is added to the mixed solution, the temperature is raised to 60℃-80℃, and the reaction is carried out for 6h-12h to obtain the copolymerized modified lithium polyacrylate adhesive.

7. The preparation method according to claim 6, characterized in that, The first monomer has the structure shown in Formula II, and the second monomer has the structure shown in Formula III. Wherein, R1 is selected from , , , or ; R2 is selected from hydrogen or methyl.

8. A negative electrode sheet, characterized in that, The adhesive includes the copolymer-modified lithium polyacrylate adhesive according to any one of claims 1-5 or the copolymer-modified lithium polyacrylate adhesive obtained by the preparation method according to claim 6 or 7.

9. A lithium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 8.

10. An electrical device, characterized in that, Including the lithium-ion battery as described in claim 9.

Images