Negative electrode binder, secondary battery, and electric device

Abstract

The invention provides a negative electrode binder, a secondary battery and an electric device, and belongs to the technical field of battery materials. The negative electrode binder comprises a hydroxyl group, a carboxyl group, an amino group, an ester group and a benzene ring structure, and when the negative electrode binder containing the hydroxyl group, the carboxyl group, the amino group, the ester group and the benzene ring structure is applied to a secondary battery, the cycle performance and the rate capability of the secondary battery can be improved.

Description

Technical Field

[0001] This application relates to the field of battery materials technology, specifically to negative electrode binders, secondary batteries, and electrical devices. Background Technology

[0002] In recent years, with the increasing severity of the energy crisis and environmental pollution, the development of new energy technologies has received widespread attention globally. Among numerous new energy technologies, secondary batteries have become a research and application hotspot due to their advantages such as high energy density, long lifespan, and lack of memory effect. However, traditional graphite anode materials have approached the limit of their theoretical capacity and cannot meet the ever-increasing demand for high energy density. Therefore, silicon-based anode materials, due to their high theoretical specific capacity (approximately 4200 mAh / g, more than ten times that of graphite), have become an ideal alternative to graphite. However, silicon-based anode materials undergo significant volume changes during charge and discharge, leading to the destruction of the electrode structure and a decline in cycle performance.

[0003] In secondary batteries, binders can bond active materials (such as silicon-based anode materials) and conductive agents to the current collector, reducing the adverse effects of volume changes during lithium insertion / extraction processes on the electrode and stabilizing its internal structure. Commonly used silicon-based anode binders include CMC (carboxymethyl cellulose), PAA (polyacrylic acid), and PVDF (polyvinylidene fluoride). PVDF has a relatively weak interaction with silicon particles; when silicon particles expand significantly, the PVDF binder is easily damaged, leading to electrode instability and affecting battery cycle performance. CMC contains a rigid six-membered heterocyclic structure, resulting in relatively poor flexibility. During charging and discharging, this rigid structure can easily cause cracking of the electrode, affecting the battery's cycle stability. PAA is relatively brittle, and its polymer chains are quite fragile, making it prone to breakage during battery charging and discharging. Once subjected to external forces, PAA binder is also prone to permanent deformation, causing the active material to agglomerate, thereby affecting the capacity of the active material. This not only reduces the rate performance of the battery but also has an adverse effect on the cycle stability of the battery. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of the prior art and to provide a negative electrode binder, a secondary battery, and an electrical device.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: Firstly, a negative electrode binder is provided, wherein the negative electrode binder comprises hydroxyl, carboxyl, amino, ester and benzene ring structures.

[0006] In some embodiments, the molar ratio of the hydroxyl group to the benzene ring is 1:(0.04~0.36).

[0007] In some embodiments, the negative electrode binder has the following structural formula: , Where m = 3000~10000.

[0008] In some embodiments, the tensile strength of the negative electrode binder is 2.8~3.6 MPa, and the strain is 18~24%.

[0009] In some embodiments, the negative electrode binder is formed by polymerization of γ-polyglutamic acid, p-aminobiphenyl, gallic acid, and sorbitol.

[0010] In some embodiments, the molar ratio of the γ-polyglutamic acid to the p-aminobiphenyl is 1:(0.05~0.35).

[0011] In some embodiments, the molar ratio of the γ-polyglutamic acid to the p-aminobiphenyl is 1:(0.02~0.25).

[0012] In some embodiments, the molar ratio of the γ-polyglutamic acid to the sorbitol is 1:(0.02~0.18).

[0013] In some embodiments, the molecular weight of the γ-polyglutamic acid is 700,000 to 2,000,000.

[0014] In a second aspect, a secondary battery is provided, including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active layer disposed on at least one side surface of the negative current collector, the negative active layer including an adhesive, the adhesive including the negative electrode adhesive.

[0015] In some embodiments, the adhesive further includes a second adhesive, which includes at least one of PAA, CMC, SBR, and PVDF.

[0016] In some embodiments, the second adhesive comprises CMC and SBR.

[0017] In some embodiments, based on the mass of the binder, the negative electrode binder has a mass percentage of 60% to 80%, the CMC has a mass percentage of 5% to 20%, and the SBR has a mass percentage of 15% to 25%.

[0018] In some embodiments, the mass percentage of the SBR in the negative electrode is greater than the mass percentage of the CMC.

[0019] In some embodiments, the negative electrode active layer further includes a negative electrode active material, which includes a silicon-based material.

[0020] In some embodiments, the binder has a mass percentage of 3-8% based on the mass of the negative electrode active layer.

[0021] Thirdly, an electrical device is provided, including the aforementioned secondary battery.

[0022] Compared with the prior art, the beneficial effects of this application are as follows: The hydroxyl and carboxyl groups in the negative electrode binder of this application can form hydrogen bonds on the surface of the negative electrode active material, thereby improving the adhesion between the negative electrode binder and the negative electrode active material. The benzene ring structure forms a good interfacial adhesion with the carbon-based material through π-π conjugated stacking interaction. Under the dual effects of the negative electrode binder's "silicon affinity" and "carbon affinity", the dispersibility of silicon-based materials in the negative electrode active slurry is improved, as well as the adhesion between the negative electrode active material and the negative electrode current collector. The ester group can improve the chemical stability of the negative electrode binder. In addition, the hydroxyl group can also serve as a crosslinking site, enabling the negative electrode binder to build a stable three-dimensional crosslinked network structure around the negative electrode active material, effectively preventing irreversible slippage of the negative electrode active material. At the same time, it can also buffer the expansion stress generated by the silicon-based material, buffer the volume change of the negative electrode sheet, maintain the electrical connection and integrity of the negative electrode sheet, and improve the cycle performance and rate performance of the secondary battery.

[0023] Negative electrode binders enhance the bonding force between negative electrode active materials, improve interfacial stability, and effectively protect the negative electrode active materials from the influence of electrolyte, forming a stable SEI film, thereby improving the electrochemical performance of secondary batteries. Attached Figure Description

[0024] Figure 1 The tensile properties of the negative electrode binders in Example 4 and Comparative Example 2 are shown in the graph. Figure 2 The image shows the SEM surface images of the negative electrode sheet after the secondary batteries of Example 4 and Comparative Example 2 have been cycled 200 times. Detailed Implementation

[0025] To facilitate understanding of this application, a more complete description will be provided below. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0026] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0027] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0028] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1-5” is disclosed, the described range should be interpreted as including ranges “1-4”, “1-3”, “1-2”, “1-2 and 4-5”, “1-3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0029] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0030] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has 'a' parts by mass and component B has 'b' parts by mass, it means that the mass ratio of component A to component B is a:b. It is important to understand that, unlike mass percentage content, the sum of the mass parts of all components is not limited to 100 parts.

[0031] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0032] In a first aspect, a negative electrode binder is provided, the negative electrode binder comprising hydroxyl, carboxyl, amino, ester and benzene ring structures.

[0033] The hydroxyl and carboxyl groups in the negative electrode binder of this application can form hydrogen bonds on the surface of the negative electrode active material, thereby improving the adhesion between the negative electrode binder and the negative electrode active material. The benzene ring structure forms a good interfacial adhesion with the carbon-based material through π-π conjugated stacking interaction. Under the dual effects of the negative electrode binder's "silicon affinity" and "carbon affinity", the dispersibility of silicon-based materials in the negative electrode active slurry is improved, as well as the adhesion between the negative electrode active material and the negative electrode current collector. The ester group can improve the chemical stability of the negative electrode binder. In addition, the hydroxyl group can also serve as a crosslinking site, enabling the negative electrode binder to build a stable three-dimensional crosslinked network structure around the negative electrode active material, effectively preventing irreversible slippage of the negative electrode active material. At the same time, it can also buffer the expansion stress generated by the silicon-based material, buffer the volume change of the negative electrode sheet, maintain the electrical connection and integrity of the negative electrode sheet, and improve the cycle performance and rate performance of the secondary battery.

[0034] The negative electrode binder groups (hydroxyl, carboxyl, amino, ester and benzene ring) can be determined by specific testing methods, including at least one of infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR) and Raman spectroscopy.

[0035] In some embodiments, the molar ratio of the hydroxyl group to the benzene ring is 1:(0.04~0.36); for example, it can be a range of values ​​consisting of one or any two of 1:0.04, 1:0.07, 1:0.10, 1:0.13, 1:0.15, 1:0.18, 1:0.20, 1:0.22, 1:0.25, 1:0.27, 1:0.30, 1:0.33, and 1:0.36.

[0036] In this application, the molar ratio of hydroxyl groups to benzene rings is within the above-mentioned range, which is beneficial to improving the "silicophilic" and "carbonophilic" effects of the negative electrode binder, as well as improving the structural stability of the three-dimensional cross-linked network formed by the negative electrode binder, thereby improving the cycle performance and rate performance of the secondary battery.

[0037] In some embodiments, the negative electrode binder has the following structural formula: , Where m = 3000~10000; for example, it can be a range of values ​​consisting of one or any two of 3000, 4000, 5000, 6000, 7000, 8000, 9000, and 10000.

[0038] In this application, the above-mentioned negative electrode binder can improve the mechanical strength and toughness of the three-dimensional cross-linked network structure formed by the negative electrode binder, suppress the volume expansion of silicon-based negative electrode materials, prevent the binder from being too brittle and causing breakage and detachment, and improve the cycle performance and rate performance of secondary batteries containing negative electrode binders.

[0039] In some embodiments, the tensile strength of the negative electrode binder is 2.8~3.6 MPa, for example, it can be a range of one or any two of 2.8 MPa, 2.9 MPa, 3 MPa, 3.1 MPa, 3.2 MPa, 3.3 MPa, 3.4 MPa, 3.5 MPa, and 3.6 MPa; the strain is 18~24%, for example, it can be a range of one or any two of 18%, 18.5%, 19%, 19.5%, 20%, 20.5%, 21%, 21.5%, 22%, 22.5%, 23%, 23.5%, and 24%.

[0040] In some embodiments, the negative electrode binder is formed by polymerization of γ-polyglutamic acid, p-aminobiphenyl, gallic acid, and sorbitol.

[0041] In some embodiments, the molar ratio of the γ-polyglutamic acid to the p-aminobiphenyl is 1:(0.05~0.35); for example, it can be a range of values ​​consisting of one or any two of 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35.

[0042] In some embodiments, the molar ratio of the γ-polyglutamic acid to the p-aminobiphenyl is 1:(0.02~0.25); for example, it can be a range of values ​​consisting of one or any two of 1:0.02, 1:0.05, 1:0.07, 1:0.1, 1:0.13, 1:0.15, 1:0.18, 1:0.2, 1:0.22, and 1:0.25.

[0043] In some embodiments, the molar ratio of the γ-polyglutamic acid to the sorbitol is 1:(0.02~0.18); for example, it can be a range of one or any two of 1:0.02, 1:0.04, 1:0.06, 1:0.08, 1:0.1, 1:0.12, 1:0.14, 1:0.16, 1:0.18.

[0044] The above molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid, and sorbitol can generate more crosslinking sites during the polymerization reaction, thereby improving the mechanical strength and cohesive force of the negative electrode binder, and enhancing its adhesion to the negative electrode active material.

[0045] In some embodiments, the molecular weight of the γ-polyglutamic acid is 700,000 to 2,000,000; for example, it can be a range of one or any combination of 700,000, 800,000, 900,000, 1,000,000, 1,100,000, 1,200,000, 1,300,000, 1,400,000, 1,500,000, 1,600,000, 1,700,000, 1,800,000, 1,900,000, and 2,000,000.

[0046] This application does not specifically limit the preparation method of the negative electrode binder, which can be obtained by polymerizing a composition of γ-polyglutamic acid (γ-PGA), p-aminobiphenyl (AP), gallic acid (GA) and sorbitol (SL).

[0047] There are no particular restrictions on the polymerization method; any method can be used, such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization. Known emulsifiers and crosslinking agents can be used in each polymerization method as needed.

[0048] In some embodiments, the method for preparing the negative electrode binder includes the following steps: Add γ-polyglutamic acid to deionized water and stir to dissolve, forming an aqueous solution of γ-polyglutamic acid; A cross-linking agent was added to an aqueous solution of γ-polyglutamic acid, and after stirring and dissolving, p-aminobiphenyl was added to carry out the first reaction to obtain a mixture of the first products. Gallic acid and sorbitol were added to the first product mixture to carry out a second reaction. The product obtained from the second reaction was dialyzed and dried to obtain a negative electrode binder.

[0049] Specifically, the crosslinking agents are 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS).

[0050] Specifically, the time for the first reaction is 8 to 18 hours, for example, it can be a range of one or any two of 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, and 18 hours.

[0051] Specifically, the time for the second reaction is 6 to 16 hours, for example, it can be a range of one or any combination of 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, and 16 hours.

[0052] Specifically, the temperatures of the first and second reactions are each independently 60~100℃, for example, they can be a range of one or any two of 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, and 100℃.

[0053] Specifically, the dialysis time is 24 to 36 hours, for example, it can be one or any combination of 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, and 36 hours.

[0054] Taking 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as crosslinking agents, and the temperature of both the first and second reactions being 80℃ as an example, the reaction equation of the negative electrode adhesive is as follows: .

[0055] In a second aspect, a secondary battery is provided, including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active layer disposed on at least one side surface of the negative current collector, the negative active layer including an adhesive, the adhesive including the negative electrode adhesive.

[0056] Using the negative electrode binder of this application in the negative electrode sheet of a secondary battery can significantly improve the cycle performance and rate performance of the secondary battery.

[0057] In some embodiments, the adhesive further includes a second adhesive, which includes at least one of PAA, CMC, SBR, and PVDF.

[0058] In this application, the negative electrode sheet containing the aforementioned second binder can further improve the cycle performance and rate performance of the secondary battery.

[0059] In some embodiments, the second adhesive comprises CMC and SBR.

[0060] In this application, the second binder composed of CMC and SBR is used in combination with the aforementioned negative electrode binder for the negative electrode sheet of the secondary battery, which can further increase the cycle performance and rate performance of the secondary battery. The combination of the second binder composed of CMC and SBR with the negative electrode binder can achieve all-round anchoring with "point-to-surface bonding". The negative electrode binder can act as a strong "point" anchoring, wherein the benzene ring is tightly bonded to the carbon layer through π-π conjugated stacking, while polar groups such as carboxyl and hydroxyl groups are tightly bonded to the silanol bonds on the silicon surface, achieving strong point-to-point anchoring; the second binder composed of CMC and SBR acts as a "surface" coating, like a fishing net covering the negative electrode active material, rather than forming a strong anchoring effect on the surface of a single particle; the all-round anchoring effect of "point-to-surface bonding" can most effectively suppress the pulverization and shedding caused by the volume effect of silicon particles, as well as the contact failure with the negative electrode current collector, thereby further increasing the cycle performance and rate performance of the secondary battery.

[0061] In some embodiments, based on the mass of the binder, the negative electrode binder has a mass percentage of 60% to 80%, the CMC has a mass percentage of 10% to 20%, and the SBR has a mass percentage of 15% to 25%.

[0062] In this application, the aforementioned percentages of negative electrode binder, CMC, and SBR can further enhance the cycle performance and rate performance of the secondary battery.

[0063] Specifically, based on the mass of the adhesive, the mass percentage of the negative electrode adhesive can be a range of one or any two of 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, and 80%.

[0064] Specifically, based on the mass of the adhesive, the mass percentage of CMC can be a range of one or any two of the following: 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20%.

[0065] Specifically, based on the mass of the adhesive, the mass percentage of the SBR can be a range of one or any two of the following: 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, and 25%.

[0066] In some embodiments, the mass percentage of the SBR in the negative electrode is greater than the mass percentage of the CMC.

[0067] In some embodiments, the mass percentage of the binder is 3 to 8% based on the mass of the negative electrode active layer; for example, it can be a range of one or any two of 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, and 8%.

[0068] In some embodiments, the negative electrode active layer further includes a negative electrode active material, which includes a silicon-based material.

[0069] In some embodiments, the silicon-based material has a mass percentage content of 60%-100% based on the mass of the negative electrode active material.

[0070] In some embodiments, the silicon-based material includes at least one of Si material, silicon-carbon (Si-C) composite material, silicon-nitrogen (Si-N) composite material, and silicon-oxygen (Si-O) composite material. Wherein, Si material represents elemental silicon, or elemental silicon doped with elements such as B, P, and S; silicon-carbon (Si-C) composite material represents a material in which elemental silicon is distributed within the pores of porous carbon; and silicon-oxygen (Si-O) composite material represents SiO₂. x (0 < x < 2).

[0071] In some embodiments, the negative electrode active material may further include a carbon-based material, which includes at least one of natural graphite particles, artificial graphite particles, hard carbon, soft carbon, and mesophase carbon microspheres (MCMB). The negative electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as negative electrode active materials for secondary batteries.

[0072] In some embodiments, the negative current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is a copper foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0073] In some embodiments, the conductive layer may include at least one of graphite, carbon black, acetylene black, Super-P, Ketjen black, carbon fiber, carbon nanotubes, graphene, and amorphous carbon.

[0074] In some embodiments, the negative electrode active layer includes a negative electrode conductive agent, which may include at least one selected from graphite, carbon black, acetylene black, Super-P, Ketjen black, carbon fiber, carbon nanotubes, graphene, and amorphous carbon. The negative electrode conductive agent in this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode conductive agents.

[0075] In some embodiments, the secondary battery further includes a positive electrode, a separator, and an electrolyte.

[0076] In some embodiments, the positive electrode may include a positive current collector and a layer of positive active material disposed on at least one side of the positive current collector.

[0077] In some embodiments, the positive current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is an aluminum foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0078] In some embodiments, the conductive layer may include at least one of graphite, carbon black, acetylene black, Super-P, Ketjen black, carbon fiber, carbon nanotubes, graphene, and amorphous carbon.

[0079] In some embodiments, the positive electrode active material layer may include a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0080] In some embodiments, the positive electrode active material may be, but is not limited to, a chemical formula such as Li a Ni x Co y M z O 2-b N b(where 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from one or more combinations of Mn and Al, and N is selected from one or more combinations of F, P, and S) The positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 The cathode active material can be one or more of the following: O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, and TiS2. The cathode active material can also be modified. Methods for modifying the cathode active material are known to those skilled in the art. For example, coating, doping, and other methods can be used to modify the cathode active material. The materials used for modification can be one or more of the following: Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W.

[0081] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery positive electrode binders.

[0082] In some embodiments, the positive electrode conductive agent may include at least one selected from graphite, carbon black, acetylene black, Super-P, Ketjen black, carbon fiber, carbon nanotubes, graphene, and amorphous carbon. The positive electrode conductive agent in this application is not limited to the above materials, but also includes other materials that can be used as positive electrode conductive agents in batteries.

[0083] In some embodiments, the diaphragm porous substrate comprises woven or nonwoven polymer fibers. In some embodiments, the porous substrate is a nonwoven material comprising polymer fibers.

[0084] In some embodiments, the porous substrate is, but is not limited to, at least one of polyolefin, polyester, polyacetal, polyamide, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate.

[0085] Some non-limiting examples of polyolefins include at least one of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene-polypropylene copolymer (PE-PP), and polyethylene-polypropylene-polyethylene copolymer.

[0086] In some embodiments, the thickness of the separator is from 4 μm to 10 μm, for example, but not limited to 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, or within any two of the above values. A separator thickness within this range not only allows the separator to possess higher puncture strength to better suppress lithium dendrites, but also maintains lower internal resistance and higher energy density.

[0087] In some embodiments, the porosity of the separator is 30% to 70%, for example, but not limited to 30%, 32%, 35%, 37%, 40%, 43%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 63%, 65%, 68%, or 70%, or within any two of the above values. A porosity within this range not only facilitates the separator having more ion channels, thereby reducing internal resistance and improving charge / discharge efficiency and high-rate discharge capability, but also gives the separator higher mechanical strength, thus reducing the risk of lithium dendrite penetration.

[0088] In some embodiments, the diaphragm includes an inorganic coating disposed on at least one side of the surface of the porous substrate.

[0089] In some embodiments, the inorganic coating includes inorganic fillers, which may include boehmite, ceramic fibers, Al2O3, SiO, SiO2, CaO, ZnO, TiO2, ZrO2, Mg(OH)2, MgO, SnO2, CaCO3, BaSO4, BaTi2O5, BaTiO3, TiN, AlN, Na2O·mTiO2 (m is 3 or 6), K2O·nTiO2 (n is 1, 2, 4, 6 or 8), BaO x(x is 1 or 2), MTiO3 (M is Ba, Sr or Ca) at least one of the following. Preferably, the inorganic particles include at least one of silica particles, barium disitinathate particles, zirconium dioxide particles, alumina particles, barium metatitanate particles, barium sulfate particles, tin oxide particles, titanium nitride particles, aluminum nitride particles, silica particles, calcium oxide particles, magnesium oxide particles, magnesium hydroxide particles, zinc oxide particles, titanium dioxide particles, boehmite particles, hydrated alumina particles, and ceramic particles.

[0090] This application does not impose any particular restrictions on the shape of the inorganic filler, as long as it can achieve the purpose of this application.

[0091] Inorganic fillers can be spherical, rod-shaped, sheet-shaped, disc-shaped, needle-shaped, cylindrical, irregular, or other known particle shapes. In some embodiments, the inorganic material is not spherical, rod-shaped, sheet-shaped, disc-shaped, needle-shaped, cylindrical, or irregular. Preferably, the inorganic filler is spherical. Spherical particles have a higher packing density, can form a continuous thermally conductive network, reduce the risk of local thermal runaway, and have a small surface curvature, a low contact angle with the electrolyte, higher liquid absorption, and better wettability.

[0092] In some embodiments, the electrolyte may also include a non-aqueous solvent and a lithium salt.

[0093] In some embodiments, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.

[0094] In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0095] In some embodiments, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.

[0096] In some embodiments, the chain carbonate compound may include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof.

[0097] In some embodiments, the cyclic carbonate compound may include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof.

[0098] In some embodiments, the fluorocarbonate compound may include at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0099] In some embodiments, the carboxylic acid ester compound may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate.

[0100] In some embodiments, the ether compound may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0101] In some embodiments, the non-aqueous solvent may also include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0102] Thirdly, an electrical device is provided, including the aforementioned secondary battery.

[0103] The electrical device used in this application is not particularly limited and can be any electrical device known in the prior art.

[0104] In some implementations, the electrical device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, and android robots.

[0105] Example 1 <Preparation of Negative Electrode Binder> Under a nitrogen atmosphere, γ-polyglutamic acid was added to deionized water and stirred to dissolve, forming an aqueous solution of γ-polyglutamic acid. Under a nitrogen atmosphere, EDC and NHS were added to an aqueous solution of γ-polyglutamic acid and stirred until dissolved. Then, p-aminobiphenyl was added, and the first reaction was carried out at 80°C for 10 hours to obtain a mixture of the first products. Gallic acid and sorbitol were added to the first product mixture under a nitrogen atmosphere and at 80°C, and a second reaction was carried out for 10 h. The product obtained from the second reaction was purified by dialyzing in deionized water for 24 h. The dialyzed product was freeze-dried to obtain the negative electrode binder. The molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol was 1:0.05:0.15:0.02, and the molecular weight of γ-polyglutamic acid was 1.2 million.

[0106] <Preparation of Negative Electrode Sheets> Silicon-carbon composite material, conductive carbon black and negative electrode binder were added to deionized water at a mass ratio of 88:4:8 and mixed evenly to obtain a negative electrode slurry. The obtained negative electrode slurry was coated on a double-sided copper foil with a thickness of 8μm, dried at room temperature and then transferred to an oven for further drying. After cold pressing and slitting, a negative electrode sheet was obtained. The total thickness of the double-sided negative electrode active material layer was 40μm.

[0107] <Preparation of the positive electrode> The positive electrode active material LiFePO4, conductive carbon black and polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 88:6:6 and uniformly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform positive electrode slurry. The obtained positive electrode slurry is coated on both sides of the positive electrode current collector aluminum foil, and after baking, rolling and cutting, a positive electrode sheet is obtained. The total thickness of the positive electrode active layer on both sides is 70 μm.

[0108] <Preparation of the diaphragm> Using a 12μm thick polyethylene microporous film as the substrate, inorganic alumina powder, polyvinylpyrrolidone, and deionized water were mixed evenly in a weight ratio of 3:1.5:5.5 to prepare an inorganic slurry. The inorganic slurry was then coated on both sides of the substrate and dried to form an inorganic layer with a thickness of 5μm, thus obtaining the diaphragm.

[0109] <Preparation of Electrolyte> At room temperature, in an argon-filled glove box (H2O < 1 ppm, O2 < 1 ppm), ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate were mixed uniformly in a volume ratio of 1.2:1:4:4, and water was removed using a 4 Å molecular sieve to obtain a mixed solvent. Lithium salt LiPF6 was added to the mixed solvent and mixed uniformly to obtain an electrolyte. The molar concentration of LiPF6 was 1 mol / L.

[0110] <Preparation of Secondary Batteries> The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrode. After winding, hot pressing and shaping, and welding of the tabs, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte prepared above is injected into the dried battery, and the battery is allowed to stand, form, and be tested for capacity to complete the preparation of the secondary battery.

[0111] Example 2 The difference between Example 2 and Example 1 is that the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol in the <Preparation of Negative Electrode Binder> is different. In this example, the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol is 1:0.1:0.13:0.04.

[0112] Example 3 The difference between Example 3 and Example 1 is that the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol in the <Preparation of Negative Electrode Binder> is different. In this example, the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol is 1:0.15:0.11:0.06.

[0113] Example 4 The difference between Example 4 and Example 1 is that the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol in the <Preparation of Negative Electrode Binder> is different. In this example, the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol is 1:0.2:0.09:0.08; the negative electrode binder in this example is denoted as PG-AGS.

[0114] Example 5 The difference between Example 5 and Example 1 is that the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol in the <Preparation of Negative Electrode Binder> is different. In this example, the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol is 1:0.25:0.07:0.1.

[0115] Example 6 The difference between Example 6 and Example 1 is that the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol in the <Preparation of Negative Electrode Binder> is different. In this example, the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol is 1:0.3:0.05:0.12.

[0116] Example 7 The difference between Example 7 and Example 1 is that the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol in the <Preparation of Negative Electrode Binder> is different. In this example, the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol is 1:0.35:0.02:0.15.

[0117] Example 8 The difference between Example 8 and Example 1 is that the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol in the <Preparation of Negative Electrode Binder> is different. In this example, the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol is 1:0.2:0.09:0.18.

[0118] Example 9 The difference between Example 9 and Example 1 is that the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol in the <Preparation of Negative Electrode Binder> is different. In this example, the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol is 1:0.2:0.25:0.02.

[0119] Example 10 The difference between Example 10 and Example 1 is that the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol in the <Preparation of Negative Electrode Binder> is different. In this example, the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol is 1:0.02:0.3:0.01.

[0120] Example 11 The difference between Example 11 and Example 1 is that the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol in the <Preparation of Negative Electrode Binder> is different. In this example, the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol is 1:0.40:0.01:0.25.

[0121] Example 12 The difference between Example 12 and Example 1 is that the molecular weight of γ-polyglutamic acid in <Preparation of negative electrode binder> is different. In this example, the molecular weight of γ-polyglutamic acid is 700,000.

[0122] Example 13 The difference between Example 13 and Example 1 is that the molecular weight of γ-polyglutamic acid in <Preparation of negative electrode binder> is different. In this example, the molecular weight of γ-polyglutamic acid is 2 million.

[0123] Example 14 The difference between Example 14 and Example 1 is that the molecular weight of γ-polyglutamic acid in <Preparation of negative electrode binder> is different. In this example, the molecular weight of γ-polyglutamic acid is 500,000.

[0124] Example 15 The difference between Example 15 and Example 1 is that the molecular weight of γ-polyglutamic acid in <Preparation of negative electrode binder> is different. In this example, the molecular weight of γ-polyglutamic acid is 2.5 million.

[0125] Example 16 The difference between Example 16 and Example 1 is that the mass ratio of silicon-carbon composite material, conductive carbon black and negative electrode binder is different in <Preparation of negative electrode sheet>. In this example, the mass ratio of silicon-carbon composite material, conductive carbon black and negative electrode binder is 93:4:3.

[0126] Example 17 The difference between Example 17 and Example 1 is that the mass ratio of silicon-carbon composite material, conductive carbon black and negative electrode binder is different in <Preparation of negative electrode sheet>. In this example, the mass ratio of silicon-carbon composite material, conductive carbon black and negative electrode binder is 91:4:5.

[0127] Example 18 The difference between Example 18 and Example 17 lies in the <preparation of the negative electrode sheet>. In this example, the <preparation of the negative electrode sheet> includes the following steps: Silicon-carbon composite material, conductive carbon black, negative electrode binder and PAA were added to deionized water at a mass ratio of 91:4:3:2 and mixed evenly to obtain a negative electrode slurry. The obtained negative electrode slurry was coated on a double-sided copper foil with a thickness of 8 μm, dried at room temperature and then transferred to an oven for further drying. After cold pressing and slitting, a negative electrode sheet was obtained. The total thickness of the double-sided negative electrode active material layer was 40 μm.

[0128] Example 19 The difference between Example 19 and Example 17 lies in the <preparation of the negative electrode sheet>. In this example, the <preparation of the negative electrode sheet> includes the following steps: Silicon-carbon composite material, conductive carbon black, negative electrode binder and PVDF were added to deionized water at a mass ratio of 91:4:3:2 and mixed evenly to obtain a negative electrode slurry. The obtained negative electrode slurry was coated on a double-sided copper foil with a thickness of 8μm, dried at room temperature and then transferred to an oven for further drying. After cold pressing and slitting, a negative electrode sheet was obtained. The total thickness of the double-sided negative electrode active material layer was 40μm.

[0129] Example 20 The difference between Example 20 and Example 17 lies in the <preparation of the negative electrode sheet>. In this example, the <preparation of the negative electrode sheet> includes the following steps: Silicon-carbon composite material, conductive carbon black, negative electrode binder, CMC and SBR were added to deionized water at a mass ratio of 91:4:3:0.9:1.1 and mixed evenly to obtain a negative electrode slurry. The obtained negative electrode slurry was coated on a double-sided copper foil with a thickness of 8 μm, dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, a negative electrode sheet was obtained. The total thickness of the double-sided negative electrode active material layer was 40 μm.

[0130] Example 21 The difference between Example 21 and Example 20 is that the mass ratio of silicon-carbon composite material, conductive carbon black, negative electrode binder, CMC and SBR is different in <Preparation of negative electrode sheet>. In this example, the mass ratio of silicon-carbon composite material, conductive carbon black, negative electrode binder, CMC and SBR is 91:4:3:1:1.

[0131] Example 22 The difference between Example 22 and Example 20 is that the mass ratio of silicon-carbon composite material, conductive carbon black, negative electrode binder, CMC and SBR is different in <Preparation of negative electrode sheet>. In this example, the mass ratio of silicon-carbon composite material, conductive carbon black, negative electrode binder, CMC and SBR is 91:4:3.25:0.5:1.25.

[0132] Example 23 The difference between Example 23 and Example 20 is that the mass ratio of silicon-carbon composite material, conductive carbon black, negative electrode binder, CMC and SBR is different in <Preparation of negative electrode sheet>. In this example, the mass ratio of silicon-carbon composite material, conductive carbon black, negative electrode binder, CMC and SBR is 91:4:4:0.25:0.75.

[0133] Example 24 The difference between Example 24 and Example 20 is that the mass ratio of silicon-carbon composite material, conductive carbon black, negative electrode binder, CMC and SBR is different in <Preparation of negative electrode sheet>. In this example, the mass ratio of silicon-carbon composite material, conductive carbon black, negative electrode binder, CMC and SBR is 91:4:2.5:1.5:1.

[0134] Example 25 The difference between Example 25 and Example 20 is that the mass ratio of silicon-carbon composite material, conductive carbon black, negative electrode binder, CMC and SBR is different in <Preparation of negative electrode sheet>. In this example, the mass ratio of silicon-carbon composite material, conductive carbon black, negative electrode binder, CMC and SBR is 91:4:4.5:0.01:0.04.

[0135] Comparative Example 1 The difference between Comparative Example 1 and Example 1 lies in the <preparation of the negative electrode sheet>. In this example, the <preparation of the negative electrode sheet> includes the following steps: Silicon-carbon composite material, conductive carbon black, CMC and SBR were added to deionized water at a mass ratio of 88:4:4:4 and mixed evenly to obtain a negative electrode slurry. The obtained negative electrode slurry was coated on a double-sided copper foil with a thickness of 8 μm, dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, a negative electrode sheet was obtained. The total thickness of the double-sided negative electrode active material layer was 40 μm.

[0136] Comparative Example 2 The difference between Comparative Example 2 and Example 1 lies in the <preparation of the negative electrode sheet>. In this example, the <preparation of the negative electrode sheet> includes the following steps: Silicon-carbon composite material, conductive carbon black and PAA were added to deionized water at a mass ratio of 88:4:8 and mixed evenly to obtain a negative electrode slurry. The obtained negative electrode slurry was coated on a double-sided copper foil with a thickness of 8 μm, dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, a negative electrode sheet was obtained. The total thickness of the double-sided negative electrode active material layer was 40 μm.

[0137] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol in the <Preparation of Negative Electrode Binder> is different. In this example, the molar ratio of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol is 1:0:0:0.15, that is, p-aminobiphenyl and gallic acid are not added in this example.

[0138] The performance parameters of Examples 1-25 and Comparative Examples 1-3 are shown in Table 1. In Table 1, the molar ratio refers to the molar ratio of p-aminobiphenyl, gallic acid and sorbitol to γ-polyglutamic acid, with 1 mol of γ-polyglutamic acid as the basis. W1 refers to the mass percentage of the binder based on the mass of the negative electrode active layer. W2 refers to the mass percentage of the negative electrode binder based on the mass of the binder.

[0139] Performance testing (1) Tensile test: Place adhesive films of the same size (length*width*thickness=50mm*20mm*2mm) with a flat surface into a tensile testing machine for testing. The tensile speed is 50mm / min. Start the testing machine and continue the test until the sample is completely broken. Record the test data and calculate the data to obtain the tensile strength and strain curve.

[0140] (2) Room temperature DCR: Place the secondary battery in the charge and discharge test cabinet at a constant temperature of 25℃, charge the secondary battery to 3.65V, then discharge it with a 1C current for 30min, adjust it to 50% SOC, then discharge it with a 5C constant current pulse for 10s and charge it for 10s. Calculate DCR = (voltage before pulse discharge - voltage after pulse discharge) / discharge current.

[0141] (3) Room temperature cycle performance: The secondary battery was placed in a charge and discharge test cabinet at a constant temperature of 25°C, with a voltage range of 2.5~3.65V, a charge rate of 1C, and a discharge rate of 1C for cycle testing. When the capacity dropped to 80% of the initial capacity, the test was stopped and the number of cycles was recorded.

[0142] (4) High-temperature cycle performance: The secondary battery was placed in a charge-discharge test chamber at a constant temperature of 45°C, with a voltage range of 2.5~3.65V, a charge rate of 1C, and a discharge rate of 1C for cycle testing. When the capacity dropped to 80% of the initial capacity, the test was stopped and the number of cycles was recorded.

[0143] The test results are shown in Table 2 and Figure 1-2 As shown.

[0144] Table 1 Table 2 Figure 1 The tensile properties of the negative electrode binders in Example 4 and Comparative Example 2 are shown in the graphs. Figure 1 It can be seen that the tensile strength and strain of the negative electrode binder of this application are both greater than those of PAA, indicating that the negative electrode binder of this application has better mechanical properties, can withstand greater tensile strength and is not easy to break, which is beneficial to buffering the stress changes of the negative electrode sheet during charging and discharging, allowing the negative electrode sheet to maintain an intact conductive network, and improving the electrochemical performance and cycle life of the secondary battery.

[0145] Figure 2 The images show the SEM surface images of the negative electrode sheet after 200 cycles of the secondary batteries in Example 4 and Comparative Example 2; from... Figure 2 As can be seen, after 200 cycles, the surface of the negative electrode sheet in the secondary battery containing negative electrode binder maintains an intact and dense structure, which can effectively suppress the volume expansion of silicon-carbon negative electrode material during charging and discharging and maintain the structural stability of the negative electrode sheet; while after 200 cycles, a large number of cracks appear on the surface of the negative electrode sheet in the secondary battery containing PAA, the structure of the negative electrode sheet collapses, and the stability of the negative electrode sheet structure cannot be maintained.

[0146] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A negative electrode binder, characterized in that, The negative electrode binder contains hydroxyl, carboxyl, amino, ester and benzene ring structures.

2. The negative electrode binder according to claim 1, characterized in that, The molar ratio of the hydroxyl group to the benzene ring is 1:(0.04~0.36).

3. The negative electrode binder according to claim 1, characterized in that, The structural formula of the negative electrode binder is shown below: ， Where m = 3000~10000.

4. The negative electrode binder according to claim 1, characterized in that, The tensile strength of the negative electrode binder is 2.8~3.6MPa, and the strain is 18~24%.

5. The negative electrode binder according to claim 1, characterized in that, The negative electrode binder is mainly formed by the polymerization of γ-polyglutamic acid, p-aminobiphenyl, gallic acid and sorbitol.

6. The negative electrode binder according to claim 5, characterized in that, The molar ratio of the γ-polyglutamic acid to the p-aminobiphenyl is 1:(0.05~0.35). And / or, the molar ratio of the γ-polyglutamic acid to the gallic acid is 1:(0.02~0.25); And / or, the molar ratio of the γ-polyglutamic acid to the sorbitol is 1:(0.02~0.18). And / or, the molecular weight of the γ-polyglutamic acid is 700,000 to 2,000,000.

7. A secondary battery, comprising a negative electrode, characterized in that, The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one side surface of the negative current collector, the negative active layer including an adhesive, the adhesive including the negative electrode adhesive as described in any one of claims 1 to 6.

8. The secondary battery according to claim 7, characterized in that, The adhesive further includes a second adhesive, which includes at least one of PAA, CMC, SBR, and PVDF.

9. The secondary battery according to claim 8, characterized in that, The second adhesive comprises CMC and SBR.

10. The secondary battery according to claim 9, characterized in that, Based on the mass of the binder, the negative electrode binder has a mass percentage of 60% to 80%, the CMC has a mass percentage of 10% to 20%, and the SBR has a mass percentage of 15% to 25%.

11. The secondary battery according to claim 10, characterized in that, In the negative electrode, the mass percentage of SBR is greater than the mass percentage of CMC.

12. The secondary battery according to claim 7, characterized in that, The negative electrode active layer also includes a negative electrode active material, which includes a silicon-based material.

13. The secondary battery according to any one of claims 7 to 11, characterized in that, Based on the mass of the negative electrode active layer, the mass percentage of the binder is 3% to 8%.

14. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 7 to 13.

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