Binder and preparation method thereof, positive plate and battery

Abstract

The invention belongs to the technical field of batteries, and discloses a binder and a preparation method thereof, a positive plate and a battery. The adhesive comprises a copolymer, and the copolymer comprises the following components in percentage by mass: 10%-15% of an acrylic acid monomer polymerization unit, 40%-60% of a hard monomer polymerization unit, 15%-25% of a flexible monomer polymerization unit and 5%-20% of a polar modified monomer polymerization unit; in the acrylic monomer polymerization unit, the neutralization degree of the acrylic monomer is greater than or equal to 10%. According to the present invention, by designing the composition and the preparation method of the binder, the binding performance of the binder is improved, and the binder is used in the battery so as to easily improve the cycle performance of the battery.

Description

Technical Field

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

[0002] In recent years, lithium-ion batteries (LIBs) have become increasingly integral to our lives, demonstrating broad application prospects and market value in energy storage systems ranging from portable electronic devices to electric vehicles. Current developments in LIBs are focused on improving cycle performance, achieving high energy density, high transfer rates, low costs, and safety. Binders are a key component of LIB electrodes. Although used in relatively small quantities, their performance directly impacts the battery's capacity, lifespan, and cycle performance. Summary of the Invention

[0003] The present invention aims to at least partially address one of the technical problems in the related art. To this end, one object of the present invention is to provide a binder and a method for preparing the same, a positive electrode sheet, and a battery. The binder is beneficial for improving the cycle performance of the battery.

[0004] In the first aspect of the present application, an adhesive is proposed, which includes a copolymer. The copolymer includes, by mass percentage, 10% to 15% of acrylic monomer polymerization units, 40% to 60% of hard monomer polymerization units, 15% to 25% of flexible monomer polymerization units, and 5% to 20% of polar modified monomer polymerization units; in the acrylic monomer polymerization units, the neutralization degree of the acrylic monomer is greater than or equal to 10%.

[0005] The binder provided in this application reduces the content of hard monomer units and increases the content of flexible monomer units, thereby improving the material processing flexibility and film strength. A higher content of flexible monomer units can reduce the glass transition temperature of the copolymer, thereby enhancing the mechanical flexibility of the copolymer and improving the processing performance of the electrode. It reduces powder loss during processing and can also indirectly improve the bonding force, thereby increasing the loading capacity of the negative electrode active material and improving the surface density. The improvement in flexibility and peeling force can increase the processing window of the positive electrode, achieve a low binder dosage (as an example, the addition amount can be reduced by more than 15% compared to traditional PVDF) and exhibit better bonding performance. In terms of electrochemical performance, it can effectively improve battery cycle performance and reduce battery internal resistance.

[0006] In this application, by controlling the content of each component to meet the above conditions, the battery's cycle performance is improved. In particular, controlling the content of the flexible monomer unit and the hard monomer unit can further improve the battery's cycle performance. This is because: if the content of the flexible monomer unit is too high and the content of the hard monomer unit is too low, the film will swell and the battery's cycle performance will drop sharply in the later stages; if the content of the flexible monomer unit is too low and the content of the hard monomer unit is too high, the electrode will be too hard to meet the requirements of high-pressure dense processing.

[0007] In addition, in this application, the coordinated use of acrylic monomer units, hard monomer units, flexible monomer units and polar modified monomer units is beneficial to improving the mechanical strength and processing performance of the material, and is helpful for the long cycle of the battery.

[0008] In some embodiments, the copolymer comprises, by weight percentage, 10% to 15% of acrylic acid monomer polymerization units, 45% to 55% of hard monomer polymerization units, 15% to 25% of flexible monomer polymerization units, and 5% to 20% of polar modified monomer polymerization units.

[0009] In some embodiments, in the hard monomer polymerization unit, the hard monomer includes one or more of acrylonitrile, styrene, and acrylates; and / or, in the flexible monomer polymerization unit, the flexible monomer includes at least one of ethyl (meth)acrylate, lauryl (meth)acrylate, octadecyl (meth)acrylate, C13-C16 (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl methacrylate, vinyl acetate, alkoxyphenol acrylate, glycidyl (meth)acrylate, butylene, diisobutylene, octene, isobutyl acrylate, methyl acrylate, butadiene, and ethylene.

[0010] In some embodiments, the hard monomer includes at least one of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, styrene, and methyl methacrylate; and / or the flexible monomer includes at least one of isobutyl acrylate, methyl acrylate, butadiene, ethylene, C13-C16 (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl methacrylate, alkoxyphenol acrylate, and glycidyl (meth)acrylate.

[0011] In some embodiments, the binder satisfies at least one of the following: (a) the acrylic monomer comprises at least one of acrylic acid and methacrylic acid; (b) The neutralization degree of the acrylic acid monomer is 10% to 100%; (c) In the polar-modifying monomer polymerization unit, the polar-modifying monomer includes at least one of acrylamide, methacrylamide, N-hydroxymethyl acrylamide, N-hydroxyethyl acrylamide, N-methyl acrylamide and N,N-dimethyl acrylamide, itaconic acid, hydroxyethyl (meth)acrylate, and hydroxypropyl methacrylate.

[0012] The second aspect of the present application provides a method for preparing the adhesive provided in the first aspect, comprising: The acrylic monomer, the hard monomer, the flexible monomer and the polar modified monomer are subjected to precipitation polymerization reaction with a solvent to prepare a copolymer; the solvent comprises an organic solvent.

[0013] The present application prepares the binder through solution precipitation polymerization. In the precipitation polymerization reaction, acrylic monomers, hard monomers, flexible monomers and polar modified monomers can be well dissolved in a solvent containing an organic solvent (the solvent used in the embodiment of the present application can be a combination of an organic solvent and an inorganic solvent (such as water), or all of it can be an organic solvent). The copolymer obtained by the reaction has low solubility in the organic solvent and precipitates to form a precipitate. Therefore, more flexible monomers can be added to the oily reaction system to improve the processing performance of the product, increase the adhesion and surface density, and improve the battery cycle performance. In addition, conventional aqueous phase precipitation polymerization to prepare binders requires complex post-processing processes such as filtration, drying, and crushing to obtain the target product, and a large amount of wastewater will be generated. The embodiment of the present application adopts precipitation polymerization, which is conducive to simplifying the post-processing process. The powder binder sample can be obtained after drying and crushing. The simplified process can save preparation time and reduce production costs.

[0014] In some embodiments, the organic solvent includes cyclic hydrocarbon solvents and ester solvents.

[0015] In some embodiments, the organic solvent satisfies at least one of the following: (A) Cyclic hydrocarbon solvents include one or more of cyclohexane, cyclopentane, methylcyclohexane, toluene, and xylene; (B) ester solvents include one or more of ethyl acetate, butyl acetate, isopropyl acetate, and ethyl propionate; (C) The mass ratio of the cyclic hydrocarbon solvent to the ester solvent is 4:1 to 1:1.

[0016] In some embodiments, the mass of the solvent is 0.5 to 6 times the total mass of all monomers.

[0017] In some embodiments, the solvent satisfies at least one of the following: (I) the ratio of the total mass of all monomers to the mass of the solvent is 1.5:8.5 to 3:7; (II) The solvent further comprises water, wherein the mass content of water is 0-10% based on the total mass of the solvent, and the mass content of the organic solvent is 90%-100%.

[0018] In some embodiments, during the precipitation polymerization of the acrylic monomer, the hard monomer, the flexible monomer, the polar-modified monomer, and the solvent, at least one of the following conditions is met: (i) the initiator used comprises at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide and dodecanoyl peroxide; (ii) the amount of initiator used is 0.1% to 2% of the total mass of all monomers; (iii) the reaction temperature is 30°C to 100°C; (iv) Reaction time is 2 h to 24 h; (v) performing precipitation polymerization under stirring conditions at a stirring speed of 200 rpm to 1000 rpm.

[0019] In a third aspect, the present application provides a positive electrode sheet, comprising the binder described in the first aspect of the present application, or comprising the binder prepared by the method described in the second aspect of the present application.

[0020] The fourth aspect of the present application provides a battery, comprising the positive electrode sheet described in the third aspect of the present application.

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

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

[0023] Take lithium-ion batteries as an example. In lithium-ion batteries, binders are an important inactive material. They account for a small proportion, but they play an important role. They act as a bond between active materials, conductive agents and current collectors, stabilize the SEI film, and make them have overall connectivity, thereby reducing the ion transport resistance of the electrode. Among them, polyvinylidene fluoride (PVDF) is the most commonly used positive electrode binder, and its usage usually accounts for about 3% of the positive electrode active material. Lithium-ion batteries prepared based on PVDF can exhibit good cycle performance. However, as the demand for lithium-ion batteries continues to increase, the demand for binders is also increasing, especially for commonly used positive electrode binders such as polyvinylidene fluoride, which has an overall market supply shortage. Therefore, developing a new binder to improve the cycle performance of lithium-ion batteries is of great significance and value to the development of lithium-ion batteries.

[0024] To this end, the first aspect of an embodiment of the present application proposes an adhesive, which includes a copolymer. Calculated by mass percentage, the copolymer includes: 10% to 15% acrylic monomer polymerization units, 40% to 60% hard monomer polymerization units, 15% to 25% flexible monomer polymerization units, and 5% to 20% polar modified monomer polymerization units; in the acrylic monomer polymerization units, the neutralization degree of the acrylic monomer is greater than or equal to 10%.

[0025] The binder provided in the embodiments of the present application has a high content of flexible monomer units and a low content of hard monomer units, which is beneficial for improving the material processing flexibility and film strength. The high content of flexible monomer units can reduce the glass transition temperature of the copolymer, thereby enhancing the mechanical flexibility of the copolymer and improving the processing performance of the electrode. It can also reduce powder loss during processing and indirectly improve the bonding force, thereby increasing the loading capacity of the negative electrode active material and improving the surface density. The improved flexibility and peeling force can increase the processing window of the positive electrode, achieve low binder dosage (for example, the addition amount can be reduced by more than 15% compared to traditional PVDF), and exhibit better bonding performance. In terms of electrochemical performance, it can effectively improve battery cycle performance and reduce battery internal resistance.

[0026] In the embodiments of the present application, by controlling the content of each component to meet the above conditions, the battery's cycling performance is improved. In particular, controlling the content of the flexible monomer units and the hard monomer units can further improve the battery's cycling performance. This is because: if the content of the flexible monomer units is too high and the content of the hard monomer units is too low, the film will swell and the battery's cycling performance will drop significantly in the later stages; if the content of the flexible monomer units is too low and the content of the hard monomer units is too high, the electrode will be too hard to meet the requirements of high-pressure dense processing.

[0027] In addition, in the embodiments of the present application, the coordinated use of acrylic monomer units, hard monomer units, flexible monomer units and polar modified monomer units is beneficial to improving the mechanical strength and processing performance of the material, and is helpful for the long cycle of the battery.

[0028] As an example, the content of acrylic monomer units can be 10%, 11%, 12%, 13%, 14%, 15%, etc.; the content of hard monomer units can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, etc.

[0029] As an example, the content of hard monomer polymerization units can be 40%~59%, 40%~58%, 40%~57%, 40%~56%, 40%~55%, 40%~54%, 40%~53%, 40%~52%, 40%~51%, 40%~50%, 40%~49%, 40%~48%, 40%~47%, 40%~46%, 40%~45%, etc., specifically, such as 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, etc.

[0030] As an example, the content of the flexible monomer polymerization unit can be 15%~25%, 16%~25%, 17%~25%, 18%~25%, 19%~25%, 20%~25%, 21%~25%, 22%~25%, etc., specifically, such as 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, etc.

[0031] As an example, the degree of neutralization of the acrylic monomer is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, etc.

[0032] In some embodiments of the present application, the copolymer comprises, by weight percentage: 10%~15% acrylic monomer polymerization units, 45%~55% hard monomer polymerization units, 15%~25% flexible monomer polymerization units, and 5%~20% polar modified monomer polymerization units.

[0033] In the embodiment of the present application, the content of the flexible monomer polymerization unit is relatively high and the content of the hard monomer polymerization unit is relatively low, which is beneficial to improving the processing performance, adhesion and loading amount of the negative electrode active material of the electrode, thereby better improving the cycle performance of the battery; and since the loading amount of the negative electrode active material is increased, the internal resistance of the battery can be reduced.

[0034] In addition, the acrylic acid monomer unit provides ionic conductivity, improving the product's electrical conductivity; the hard monomer unit enhances electrode cohesion and strength; the flexible monomer unit provides toughness, improving the product's flexibility; and the polarity-modifying monomer unit, derived from a highly polar monomer, enhances material adhesion and forms hydrogen bonds to create a stronger cross-linked network. The synergistic effect of these components improves the material's mechanical flexibility and processing properties, and contributes significantly to the battery's long cycle life.

[0035] In some embodiments of the present application, in the hard monomer polymerization unit, the hard monomer includes one or more of acrylonitrile, styrene, and acrylate; And / or, in the flexible monomer polymerization unit, the flexible monomer includes at least one of ethyl (meth)acrylate, lauryl (meth)acrylate, octadecyl (meth)acrylate, C13-C16 (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl methacrylate, vinyl acetate, alkoxyphenol acrylate, glycidyl (meth)acrylate, butylene, diisobutylene, octene, isobutyl acrylate, methyl acrylate, butadiene, and ethylene.

[0036] In the embodiment of the present application, the hard monomer polymerization unit is beneficial to improving the cohesion and strength of the electrode, and the flexible monomer polymerization unit plays a toughening role and improves the flexibility of the product. The two are used in conjunction with each other to help achieve better processing performance of the electrode.

[0037] In some embodiments of the present application, the hard monomer includes at least one of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, styrene, and methyl methacrylate; and / or the flexible monomer includes at least one of isobutyl acrylate, methyl acrylate, butadiene, ethylene, C13-C16 (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl methacrylate, alkoxyphenol acrylate, and glycidyl (meth)acrylate.

[0038] In the embodiment of the present application, by using the flexible monomer polymerization unit and the hard monomer polymerization unit in combination with each other and controlling their respective contents, it is beneficial to achieve better processing performance of the electrode, improve the cycle performance of the battery, and reduce the internal resistance of the battery.

[0039] Furthermore, the hard monomer includes at least one of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and methyl methacrylate.

[0040] In some embodiments of the present application, the binder satisfies at least one of the following: (a) the acrylic monomer comprises at least one of acrylic acid and methacrylic acid; (b) The neutralization degree of the acrylic acid monomer is 10% to 100%; (c) In the polar-modifying monomer polymerization unit, the polar-modifying monomer includes at least one of acrylamide, methacrylamide, N-hydroxymethyl acrylamide, N-hydroxyethyl acrylamide, N-methyl acrylamide and N,N-dimethyl acrylamide, itaconic acid, hydroxyethyl (meth)acrylate, and hydroxypropyl methacrylate.

[0041] In the embodiment of the present application, at least one acrylic monomer selected from acrylic acid and methacrylic acid is beneficial for improving the conductivity of the adhesive.

[0042] In the examples of this application, the neutralization degree of the acrylic acid monomer is 10% to 100%. Experiments have shown that controlling the neutralization degree of the acrylic acid monomer to meet the above conditions can improve the binding force of the binder and increase the loading capacity of the negative electrode active material. A low binder dosage can meet the requirements and further reduce the internal resistance of the battery.

[0043] Furthermore, the neutralization degree of the acrylic monomer is 70% to 100%.

[0044] In the embodiments of the present application, the polar modified monomer is beneficial to improving the bonding strength of the material and forming hydrogen bonds to build a stronger cross-linked network, thereby improving the bonding strength of the adhesive.

[0045] A second aspect of the present application provides a method for preparing the above-mentioned adhesive, comprising: The acrylic monomer, the hard monomer, the flexible monomer and the polar modified monomer are subjected to precipitation polymerization reaction with a solvent to prepare a copolymer; the solvent comprises an organic solvent.

[0046] In the embodiment of the present application, the binder is prepared by solution precipitation polymerization. In the precipitation polymerization reaction, each raw material such as acrylic monomer, hard monomer, flexible monomer and polar modified monomer can be well dissolved in a solvent containing an organic solvent. The copolymer obtained by the reaction has low solubility in the organic solvent and precipitates to form a precipitate. Therefore, more flexible monomers can be added to the reaction system to improve the processing performance of the product, increase the bonding force and surface density, and improve the battery cycle performance. In addition, conventional aqueous phase precipitation polymerization to prepare binders requires complex post-processing processes such as filtration, drying, and crushing to obtain the target product, and a large amount of wastewater will be generated. The embodiment of the present application adopts precipitation polymerization, which is conducive to simplifying the post-processing process. After drying and crushing, the powder binder sample can be obtained. The simplified process can save preparation time and reduce production costs.

[0047] In some embodiments, the organic solvent includes cyclic hydrocarbon solvents and ester solvents.

[0048] The cooperation between the cyclic hydrocarbon solvent and the ester solvent is beneficial to promoting the reaction efficiency of the precipitation polymerization reaction.

[0049] In some embodiments, the organic solvent satisfies at least one of the following: (A) Cyclic hydrocarbon solvents include one or more of cyclohexane, cyclopentane, methylcyclohexane, toluene, and xylene; (B) ester solvents include one or more of ethyl acetate, butyl acetate, isopropyl acetate, and ethyl propionate; (C) The mass ratio of the cyclic hydrocarbon solvent to the ester solvent is 4:1 to 1:1.

[0050] In the examples of this application, the organic solvent facilitates dissolution of raw materials, such as acrylic monomers, hard monomers, flexible monomers, and polar-modified monomers. Furthermore, the organic solvent is required to precipitate the copolymer, meaning that the copolymer has low solubility or is insoluble in the organic solvent. Furthermore, the organic solvent provided in the examples of this application has a low boiling point, facilitating drying and removal.

[0051] As an example, the mass ratio of the cyclic hydrocarbon solvent to the ester solvent is 4:1, 3:1, 2:1, 1:1, etc.

[0052] In some embodiments, the mass of the solvent is 0.5 to 6 times the total mass of all monomers.

[0053] In the embodiments of the present application, the amount of solvent used satisfies the above conditions and is conducive to the normal progress of the precipitation polymerization reaction. As an example, the amount of solvent used is 0.5 times, 0.6 times, 0.7 times, 0.8 times, 0.9 times, 1 times, 1.5 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, 5 times, 5.5 times, 6 times, etc., of the total mass of all monomers.

[0054] In some embodiments, the solvent satisfies at least one of the following: (I) the ratio of the total mass of all monomers to the mass of the solvent is 1.5:8.5 to 3:7; (II) The solvent further comprises water, wherein the mass content of water is 0-10% based on the total mass of the solvent, and the mass content of the organic solvent is 90%-100%.

[0055] The ratio of the total mass of all monomers to the mass of the solvent is 1.5:8.5 to 3:7, wherein the sum of the first and second terms of the mass ratio of the total mass of all monomers to the solvent is 10. As examples, the ratio of the total mass of all monomers to the mass of the solvent is 1.5:8.5, 1.6:8.4, 1.7:8.3, 1.8:8.2, 1.9:8.1, 2.0:8.0, 2.1:7.9, 2.2:7.8, 2.3:7.7, 2.4:7.6, 2.5:7.5, 2.6:7.4, 2.7:7.3, 2.8:7.2, 2.9:7.1, 3:7, and the like.

[0056] As an example, based on the total mass of the solvent, the mass content of water is 0-10%, and the mass content of the organic solvent is 90%-100%.

[0057] In the embodiments of the present application, all organic solvents can be used as solvents. A mixed solvent of an organic solvent and water can also be used as a solvent. As an example, based on the total mass of the solvent: the mass content of water is 1%, the mass content of the organic solvent is 99%, the mass content of water is 2%, the mass content of the organic solvent is 98%, the mass content of water is 4%, the mass content of the organic solvent is 96%, the mass content of water is 6%, the mass content of the organic solvent is 94%, the mass content of water is 8%, the mass content of the organic solvent is 92%, the mass content of water is 9%, the mass content of the organic solvent is 91%, etc.

[0058] In some embodiments of the present application, during the precipitation polymerization reaction of acrylic monomers, hard monomers, flexible monomers, polar-modified monomers, and organic solvents, at least one of the following conditions is met: (i) the initiator used comprises at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide and dodecanoyl peroxide; (ii) the amount of initiator used is 0.1% to 2% of the total mass of all monomers; (iii) the reaction temperature is 30°C to 100°C; (iv) Reaction time is 2 h to 24 h; (v) performing precipitation polymerization under stirring conditions at a stirring speed of 200 rpm to 1000 rpm.

[0059] In the examples of the present application, an initiator is used to initiate a precipitation polymerization reaction to prepare a binder.

[0060] As an example, the amount of initiator used is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, etc., based on the total mass of all monomers.

[0061] As an example, the reaction temperature is 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc.

[0062] As an example, the reaction time is 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, 24 h, etc.

[0063] As an example, the precipitation polymerization reaction is carried out under stirring conditions, and the stirring speed is 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, etc.

[0064] A third aspect of the embodiments of the present application provides a positive electrode sheet, comprising the above-mentioned binder, or comprising the binder prepared by the above-mentioned method.

[0065] The positive electrode sheet provided in the embodiment of the present application has the above-mentioned binder and has the beneficial effects described in the first and second aspects of the embodiment of the present application, which will not be repeated here.

[0066] In some embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active material layer contains a positive electrode active material.

[0067] In some embodiments of the present application, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material base layer and a metal layer formed on at least one side of the polymer material base layer. For example, the composite positive electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0068] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0069] In some embodiments of the present application, the positive electrode active material may be a positive electrode active material for batteries known in the art.

[0070] As an example, when the battery is a lithium-ion battery, the positive electrode active material includes but is not limited to lithium iron phosphate materials, lithium cobalt oxide materials (such as LiCoO2), LiNi x Co y Mn z O2 (x+y+z = 1) materials, lithium-rich manganese-based materials (xLi2MnO3·(1-x)LiMO2), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) materials, etc. Therefore, matching this high-voltage positive electrode material with the battery's electrolyte can significantly improve the battery's energy density.

[0071] As an example, when the battery is a sodium ion battery, the positive electrode active material is not limited to a three-dimensional tunnel type Na 0.44 MnO2, P2 layered NaMO2 (M is one, two or three of Ni, Mn, Fe), NaFePO4, Na4Fe3(PO4)2P2O7, Na3V2(PO4)3, Na3V2(PO4)2F3, Na2Fe(CN)6, Na2MnFe(CN)6.

[0072] In some embodiments of the present application, the positive electrode active material layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0073] In some embodiments of the present application, the positive electrode material layer can be manufactured by the following manufacturing method. A positive electrode active material, a conductive agent, and a positive electrode binder are dry-mixed to prepare a positive electrode material mixture. Subsequently, the positive electrode material mixture is dispersed in a suitable organic solvent to prepare a positive electrode material mixture slurry, and the prepared positive electrode material mixture slurry is coated on a current collector, dried, and pressed to prepare a positive electrode active material layer.

[0074] A fourth aspect of the embodiments of the present application provides a battery comprising the above-mentioned positive electrode sheet.

[0075] In some embodiments of the present application, the battery further comprises a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material.

[0076] In some embodiments of the present application, the negative electrode active material may be a negative electrode active material for batteries known in the art. For example, the negative electrode active material may include at least one of the following materials: graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxides, and tin alloys.

[0077] In some embodiments of the present application, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0078] In some embodiments of the present application, the negative electrode active material layer may further optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), sodium carboxymethyl cellulose (CMC), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0079] In some embodiments of the present application, the negative electrode active material layer may further include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0080] In some embodiments of the present application, the battery further includes a separator. As a separator, it is desirable to use a porous film, a nonwoven fabric, etc. that exhibits improved high-rate discharge performance, and they can be used alone or in combination. The resin constituting the separator can be, for example, a polyolefin resin of polyethylene or polypropylene, a polyester resin such as polyethylene terephthalate or polybutylene terephthalate, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-vinyl fluoride copolymer, vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-ethylene-tetrafluoroethylene copolymer, etc.

[0081] In some embodiments of the present application, the battery further comprises an electrolyte. Further, the electrolyte comprises a non-aqueous electrolyte. The non-aqueous electrolyte is not particularly limited, as long as the non-aqueous electrolyte is a non-aqueous electrolyte that can be conventionally used in lithium-ion rechargeable batteries. The non-aqueous electrolyte may comprise an electrolyte salt in a non-aqueous solvent.

[0082] The present invention will be described below with reference to specific examples. It should be noted that these examples are merely illustrative and do not limit the present invention in any way. The reagents used in the examples are all from Aladdin Biochemical Technology Co., Ltd.

[0083] Example 1 Acrylic acid was dissolved in an organic solvent and neutralized by dropwise addition of lithium hydroxide under a chilled water circulation system to obtain an acrylic acid monomer with an 80% neutralization degree. Acrylonitrile (AN), a flexible monomer (isobutyl acrylate), and a polar-modifying monomer (methacrylamide) were then added. The weight percentages of the monomers, based on the total weight of the raw materials, were as follows: 15% acrylic acid monomer, 40% acrylonitrile, 25% flexible monomer, and 20% polar-modifying monomer. A mixed solvent of cyclohexane, ethyl acetate, and water (with a cyclohexane:ethyl acetate mass ratio of 2:1) was then added and rapidly stirred (500 rpm) to fully dissolve the monomers. Nitrogen was then introduced for approximately 1 hour to deoxygenate the mixture. After a period of nitrogen flow, the temperature was raised to 50°C, and azobisisobutyronitrile (azobisisobutyronitrile) was added (the amount of initiator added was 1% of the total weight of the monomers) to initiate precipitation polymerization. The polymerization reaction lasted for 10 hours. After completion of the reaction, the mixture was dried to obtain a powder binder. The mass ratio of the total mass of all monomers to the solvent is 2:8; based on the total mass of all solvents, the mass content of water is 5% and the mass content of the organic solvent is 95%.

[0084] Example 2-Example 25 Example 2-Example 25 The adhesive was prepared using the method of Example 1. The specific differences are shown in Table 1-1 and Table 1-2.

[0085] Comparative Example 1 Comparative Example 1: The adhesive was prepared using the method of Example 1. The specific differences are shown in Table 1-2.

[0086] Comparative Example 2 Comparative Example 2: The adhesive was prepared using the method of Example 1. The specific differences are shown in Table 1-2.

[0087] Comparative Example 3 Comparative Example 3: The adhesive was prepared using the method of Example 1. The specific differences are shown in Table 1-2.

[0088] Comparative Example 4 Comparative Example 4: The adhesive was prepared using the method of Example 1. The specific differences are shown in Table 1-2.

[0089] Comparative Example 5 Comparative Example 5: The adhesive was prepared using the method of Example 1. The specific differences are shown in Table 1-2.

[0090] The preparation parameters of Examples 1-25 and Comparative Examples 1-5 can be found in Table 1-2.

[0091]

[0092]

[0093] Performance Testing 1. Test Method 1. Processing performance test: Mix the adhesive with the conductive main material, NMP (N-methylpyrrolidone), etc. in a certain proportion, homogenize to a certain viscosity and fineness, filter and then apply, and observe the flexibility of the electrode and the processing state of the electrode.

[0094] The results can be evaluated as "brittle", "relatively brittle" and "OK". "Brilliant" refers to a processing surface density of 40 g / cm 2 Powdering and demoulding under certain conditions; "brittle" means that the processing surface density can reach 42 g / cm 2 ~44 g / cm 2 "OK" means that the processing surface density can reach more than 44 g / cm 2 , there is no powder falling phenomenon and it has high flexibility.

[0095] 2. Pole piece peeling force test: After the pole piece is prepared and rolled, a 180° peeling force test is performed.

[0096] 3. Surface density test: Cut a sample of a certain area (e.g. 10 cm 2 ); Use a precision balance to weigh the total mass of the sample (m1); Use a solvent (such as NMP) to dissolve and remove the active material and binder, leaving only the current collector; Wash the current collector and dry it to remove any residual solvent. Use a precision balance to weigh the mass of the current collector (m2). Calculate the areal density: Calculate the surface density according to the formula: σ=(m1-m2) / A, where: m1 is the total mass of the sample (mg), m2 is the mass of the current collector (mg), and A is the area of the sample (cm 2 ).

[0097] 4. Cycle performance test: (1) Battery assembly: Positive electrode: NCM811 / Rongbai S85E, binder: the binder used in the above examples and comparative examples; negative electrode: graphite / B&T S360-L1, separator: Xingyuan separator, electrolyte: ternary electrolyte. Batteries obtained from Examples 1-25 are named B1-B25, respectively; batteries obtained from Comparative Examples 1-5 are named D1-D5, respectively.

[0098] (2) Cyclic performance test: The method for testing the room temperature cycle performance of the battery is as follows: a high temperature cycle test is performed on the batteries prepared with the binders obtained in the above examples and comparative examples using an electrochemical workstation at a temperature of 25°C, 1 C constant current and constant voltage charging, a cut-off current of 0.05C, and a 30 min rest period after the charge is completed. The battery is then discharged at a constant current of 1 C and a 30 min rest period after the discharge is completed. The cycle test is performed according to the above steps until the capacity decays to 80% of the initial capacity.

[0099] The method for testing the high-temperature cycle performance of the battery is as follows: a high-temperature cycle test is performed on the batteries prepared with the binders obtained in the above examples and comparative examples using an electrochemical workstation at a temperature of 45°C, 1 C constant current and constant voltage charging, a cut-off current of 0.05C, and a 30-min rest period after charging. The battery is then discharged at a constant current of 1 C and a 30-min rest period after discharging. The cycle test is performed according to the above steps until the capacity decays to 80% of the initial capacity, and the number of cycles is recorded.

[0100] The battery DCR test method is as follows: Test batteries prepared with the binders obtained in the above examples and comparative examples, ensuring that the battery surface temperature reaches 25±2°C; discharge at a constant current of 1 C to 2.5 V, and then discharge at a constant current of 1 C to 2.5 V; then charge at a constant current and constant voltage of 1 C to 3.65 V, with the current cut off at 0.05 C, and wait for 30 minutes until the battery surface temperature reaches 25±2°C; discharge at a constant current of 1 C to 2.5 V, with the discharge capacity recorded as C0; discharge at a constant current of 1 C to 2.5 V; charge at a constant current and constant voltage of 1 C to 3.65 V, and wait for 30 minutes; discharge at a constant current of 1 C for 30 minutes, wait for 30 minutes, and record the end voltage as U1; discharge at a constant current of 1 C for 10 seconds, with the end voltage recorded as U2. The above results can be obtained using the DCR calculation formula.

[0101] The calculation formula of DCR is: DCR=(U1-U2) / A; where A represents the discharge current, that is, 1 C current.

[0102] 2. Test Results The performance test results of Examples 1-25 and Comparative Examples 1-5 are shown in Table 2.

[0103] Table 2

[0104] As can be seen from Table 2, compared with Comparative Examples 1 to 5, Examples 1 to 25 of the present application use a deposition polymerization reaction to prepare the binder. By optimizing the composition and dosage of the hard monomer and the flexible monomer, and combining the polarity-modified monomer (which is beneficial to improving the high-temperature aging resistance of the battery), the battery cycle performance can be effectively improved and the battery impedance can be reduced.

[0105] Furthermore, by optimizing the precipitation polymerization reaction parameters, as shown in Examples 20-25, and optimizing the solvent components and dosage ratios, the present invention further enhances the battery's cycling performance and reduces battery impedance. Increasing the ratio of cyclohexane to ethyl acetate in the organic solvent, based on the principle of like dissolves like, improves the monomer solubility and efficiency of the precipitation polymerization reaction, resulting in a higher-performing binder and, consequently, improved overall battery performance.

[0106] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0107] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A binder, characterized in that: The binder includes a copolymer, and the copolymer includes, by mass percentage: 10% to 15% of acrylic acid monomer polymerization units, 40% to 60% of hard monomer polymerization units, 15% to 25% of flexible monomer polymerization units, and 5% to 20% of polar modified monomer polymerization units; in the acrylic acid monomer polymerization units, the neutralization degree of the acrylic acid monomer is greater than or equal to 10%.

2. The adhesive according to claim 1, characterized in that Measured by mass percentage, the copolymer comprises: 10%~15% acrylic monomer polymerization units, 45%~55% hard monomer polymerization units, 15%~25% flexible monomer polymerization units, and 5%~20% polar modified monomer polymerization units.

3. The adhesive according to claim 1 or 2, characterized in that In the hard monomer polymerization unit, the hard monomer includes one or more of acrylonitrile, styrene, and acrylate; And / or, in the flexible monomer polymerization unit, the flexible monomer includes at least one of ethyl (meth)acrylate, lauryl (meth)acrylate, octadecyl (meth)acrylate, C13-C16 (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl methacrylate, vinyl acetate, alkoxyphenol acrylate, glycidyl (meth)acrylate, butylene, diisobutylene, octene, isobutyl acrylate, methyl acrylate, butadiene, and ethylene.

4. The adhesive according to claim 3, characterized in that The hard monomer includes at least one of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, styrene, and methyl methacrylate; and / or the flexible monomer includes at least one of isobutyl acrylate, methyl acrylate, butadiene, ethylene, C13-C16 (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl methacrylate, alkoxyphenol acrylate, and glycidyl (meth)acrylate.

5. The adhesive according to claim 1 or 2, characterized in that The binder satisfies at least one of the following: (a) the acrylic monomer comprises at least one of acrylic acid and methacrylic acid; (b) The neutralization degree of the acrylic acid monomer is 10% to 100%; (c) In the polar-modifying monomer polymerization unit, the polar-modifying monomer includes at least one of acrylamide, methacrylamide, N-hydroxymethyl acrylamide, N-hydroxyethyl acrylamide, N-methyl acrylamide and N,N-dimethyl acrylamide, itaconic acid, hydroxyethyl (meth)acrylate, and hydroxypropyl methacrylate.

6. A method for preparing the adhesive according to any one of claims 1 to 5, characterized in that: include: The acrylic monomer, the hard monomer, the flexible monomer, the polar modified monomer and the solvent are subjected to precipitation polymerization reaction to prepare a copolymer; the solvent comprises an organic solvent.

7. The method according to claim 6, characterized in that The organic solvent includes cyclic hydrocarbon solvents and ester solvents.

8. The method according to claim 7, characterized in that The organic solvent satisfies at least one of the following: (A) The cyclic hydrocarbon solvent includes one or more of cyclohexane, cyclopentane, methylcyclohexane, toluene, and xylene; (B) the ester solvent includes one or more of ethyl acetate, butyl acetate, isopropyl acetate, and ethyl propionate; (C) The mass ratio of the cyclic hydrocarbon solvent to the ester solvent is 4:1 to 1:

1.

9. The method according to any one of claims 6 to 8, characterized in that: The mass of the solvent is 0.5 to 6 times the total mass of all monomers.

10. The method according to claim 9, characterized in that The solvent satisfies at least one of the following: (I) the ratio of the total mass of all monomers to the mass of the solvent is 1.5:8.5 to 3:7; (II) The solvent further comprises water, wherein the mass content of the water is 0-10% and the mass content of the organic solvent is 90%-100% based on the total mass of the solvent.

11. The method according to claim 6, characterized in that In the precipitation polymerization reaction of the acrylic monomer, the hard monomer, the flexible monomer, the polar modified monomer and the solvent, at least one of the following conditions is satisfied: (i) the initiator used comprises at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide and dodecanoyl peroxide; (ii) the amount of initiator used is 0.1% to 2% of the total mass of all monomers; (iii) the reaction temperature is 30°C to 100°C; (iv) Reaction time is 2 h to 24 h; (v) performing precipitation polymerization under stirring conditions at a stirring speed of 200 rpm to 1000 rpm.

12. A positive electrode sheet, characterized in that: The adhesive comprises the adhesive according to any one of claims 1 to 5, or the adhesive prepared by the method according to any one of claims 6 to 11.

13. A battery, characterized in that: Including the positive electrode sheet according to claim 12.

Images