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 hydroxyl, carboxyl, ether group and disulfide bond, and the cycle performance and rate capability of the secondary battery can be improved by applying the negative electrode binder containing hydroxyl, carboxyl, ether group and disulfide bond to the secondary battery.

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, ether, and disulfide bonds.

[0006] In some embodiments, the molar ratio of the carboxyl group to the ether group is 1:(0.8~0.98).

[0007] In some embodiments, the negative electrode binder has the following structural formula: , Where n = 10~100.

[0008] In some embodiments, the swelling rate of the negative electrode binder is ≤8%.

[0009] In some embodiments, the negative electrode binder is mainly obtained by polymerizing α-lipoic acid, glyceryl triglycidyl ether and pentaerythritol tetraacrylate.

[0010] In some embodiments, the molar ratio of α-lipoic acid to glyceryl triglycidyl ether is 1:(0.05~0.2). The molar ratio of α-lipoic acid to pentaerythritol tetraacrylate is 1:(0.05~0.2).

[0011] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active layer including an adhesive, the adhesive including the negative electrode adhesive.

[0012] In some embodiments, the peeling force of the negative electrode sheet is 15~22 N / m.

[0013] In some embodiments, the adhesive further includes a second adhesive, which includes at least one of PAA, CMC, SBR, and PVDF.

[0014] In some embodiments, the second adhesive includes PAA.

[0015] In some embodiments, the negative electrode binder has a mass percentage content of 60% to 90% and the PAA has a mass percentage content of 10% to 40%, based on the mass of the binder.

[0016] In some embodiments, the binder has a mass percentage content of 5% to 15% based on the mass of the negative electrode active layer.

[0017] Thirdly, an electrical device is provided, including the aforementioned secondary battery.

[0018] Compared with the prior art, the beneficial effects of this application are as follows: In this application, hydroxyl and carboxyl groups can form hydrogen bonds on the surface of the negative electrode active material, improving the adhesion between the negative electrode binder and the negative electrode active material. Together with dynamic disulfide bonds, they effectively suppress the volume expansion of silicon-based materials during charge and discharge, improving the cycle performance of the secondary battery. The negative electrode binder has a stable and dense three-dimensional network structure, improving its mechanical properties and thus enhancing the structural stability of the negative electrode sheet. The ether group can form a weak coordination with lithium ions, lowering the lithium ion diffusion barrier, promoting lithium ion transport, enhancing ionic conductivity, reducing the internal resistance of the secondary battery, and improving the rate performance of the secondary battery. Attached Figure Description

[0019] Figure 1 This is a graph showing the change in swelling rate of the adhesives in Example 2 and Comparative Example 5 at different times; Figure 2 The image shows the SEM surface images of the negative electrode sheet after the secondary batteries of Example 2 and Comparative Example 5 have been cycled 300 times. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0025] "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.

[0026] "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).

[0027] In a first aspect, a negative electrode binder is provided, the negative electrode binder comprising hydroxyl, carboxyl, ether, and disulfide bonds.

[0028] In this application, hydroxyl and carboxyl groups can form hydrogen bonds on the surface of the negative electrode active material, improving the adhesion between the negative electrode binder and the negative electrode active material. Together with dynamic disulfide bonds, they effectively suppress the volume expansion of silicon-based materials during charge and discharge, improving the cycle performance of the secondary battery. The negative electrode binder possesses a stable and dense three-dimensional network structure, improving its mechanical properties and thus enhancing the structural stability of the negative electrode sheet. The ether group can form a weak coordination with lithium ions, lowering the lithium ion diffusion barrier, promoting lithium ion transport, enhancing ionic conductivity, reducing the internal resistance of the secondary battery, and improving its rate performance. The negative electrode binder groups (hydroxyl, carboxyl, ether, and disulfide bonds) can be obtained using one of the following methods: infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), or Raman spectroscopy.

[0029] In some embodiments, the molar ratio of the carboxyl group to the ether group is 1:(0.8~0.98); for example, it can be a range of values ​​consisting of one or any two of 1:0.80, 1:0.85, 1:0.90, 1:0.98.

[0030] In this application, the molar ratio of carboxyl groups and ether groups is within the above-mentioned range, which improves the contact anchoring point between the negative electrode binder and the negative electrode active material, as well as the structural stability of the three-dimensional network structure, further suppressing the volume expansion of silicon-based materials during charging and discharging, thereby improving the cycle performance and rate performance of the secondary battery.

[0031] In some embodiments, the negative electrode binder has the following structural formula: , Where n = 10~100.

[0032] The negative electrode binder with the above-mentioned structure promotes intermolecular cohesion, improves the structural stability of the three-dimensional network structure, prevents electrolyte from excessively penetrating into the negative electrode active layer, enhances the structural stability of the negative electrode sheet, and improves the cycle performance and rate performance of the secondary battery.

[0033] In some embodiments, the swelling rate of the negative electrode binder is ≤8%; for example, it can be a range of one or any two of 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%.

[0034] In this application, the swelling rate of the negative electrode binder is ≤8%, which can effectively buffer the volume expansion of silicon-based materials during lithium insertion / extraction, promote the structural integrity of the negative electrode sheet, and improve the cycle performance and rate performance of the secondary battery.

[0035] In some embodiments, the negative electrode binder is mainly obtained by polymerizing α-lipoic acid, glyceryl triglycidyl ether and pentaerythritol tetraacrylate.

[0036] In this application, the dynamic disulfide bond in α-lipoic acid can buffer stress, and the carboxyl group can form non-covalent hydrogen bonds on the surface of the negative electrode active material, effectively suppressing the volume expansion of the silicon-based negative electrode material during charging and discharging, and extending the cycle life of the secondary battery; glycerol triglycidyl ether has reactive epoxy groups, and pentaerythritol tetraacrylate has multiple carbon-carbon double bonds. Glycerol triglycidyl ether and pentaerythritol tetraacrylate can act as crosslinking agents for a three-dimensional network, making the negative electrode binder more stable and dense. At the same time, the ether bonds in both can promote lithium-ion transport, reduce the internal resistance of the secondary battery, and thus improve the rate performance of the secondary battery.

[0037] In some embodiments, the molar ratio of α-lipoic acid and glyceryl triglycidyl ether is 1:(0.05~0.2); for example, it can be a range of values ​​consisting of one or any two of 1:0.05, 1:0.08, 1:0.1, 1:0.13, 1:0.15, 1:0.17, 1:0.2.

[0038] In some embodiments, the molar ratio of α-lipoic acid to pentaerythritol tetraacrylate is 1:(0.05~0.2); for example, it can be a range of values ​​consisting of one or any two of 1:0.05, 1:0.08, 1:0.1, 1:0.13, 1:0.15, 1:0.17, 1:0.2.

[0039] In this application, the molar ratio of α-lipoic acid (LA), glyceryl triglycidyl ether (GTE), and pentaerythritol tetraacrylate (PETEA) is within the above-mentioned range, which is beneficial to improving the mechanical properties of the negative electrode binder and effectively suppressing the volume expansion of the silicon-based negative electrode material during charging and discharging; thereby improving the cycle performance and rate performance of the secondary battery.

[0040] This application does not specifically limit the preparation method of the negative electrode binder, which can be obtained by polymerizing a composition of α-lipoic acid, glyceryl triglycidyl ether and pentaerythritol tetraacrylate.

[0041] 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.

[0042] In some embodiments, the method for preparing the negative electrode binder includes the following steps: α-Lipoic acid is placed in a container and heated to melt, forming an α-lipoic acid melt. Glyceryl triglycidyl ether and pentaerythritol tetraacrylate were added to α-lipoic acid melt and polymerized to obtain a negative electrode binder.

[0043] Specifically, the heating and melting temperature is 80-140℃, for example, it can be a range of one or any combination of 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, and 140℃.

[0044] Specifically, the polymerization temperature is 80-140℃, for example, it can be a range of one or any combination of two of the following: 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, and 140℃.

[0045] Specifically, the polymerization reaction time is 20-60 min, for example, it can be a range of one or any combination of 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, and 60 min.

[0046] Specifically, both the heating and dissolution and polymerization reactions are carried out under an inert atmosphere.

[0047] Specifically, with the polymerization reaction temperature at 120°C, the reaction equation for the negative electrode binder is as follows: .

[0048] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active layer including an adhesive, the adhesive including the negative electrode adhesive.

[0049] 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.

[0050] In some embodiments, the peeling force of the negative electrode sheet is 15~22 N / m; for example, it can be a range of one or any combination of two of the following values: 15 N / m, 15.5 N / m, 16 N / m, 16.5 N / m, 17 N / m, 17.5 N / m, 18 N / m, 18.5 N / m, 19 N / m, 19.5 N / m, 20 N / m, 20.5 N / m, 21 N / m, 21.5 N / m, and 22 N / m.

[0051] In this application, the peeling force of the negative electrode sheet is within the above-mentioned range, which is beneficial to improving the bonding strength between the negative electrode active layer and the negative electrode current collector, improving the mechanical properties of the silicon-based material, thereby improving the structural integrity of the negative electrode sheet, and thus improving the cycle performance and rate performance of the secondary battery.

[0052] In some embodiments, the adhesive further includes a second adhesive, which includes at least one of PAA, CMC, SBR, and PVDF.

[0053] In some embodiments, the second adhesive includes PAA.

[0054] In this application, PAA is used in combination with the above-mentioned 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.

[0055] In some embodiments, the negative electrode binder has a mass percentage content of 60% to 90% and the PAA has a mass percentage content of 10% to 40%, based on the mass of the binder.

[0056] In this application, the aforementioned mass percentages of negative electrode binder and PAA can further enhance the cycle performance and rate performance of the secondary battery.

[0057] Specifically, based on the quality of the binder, the mass percentage of the negative electrode binder can be a range of one or any two of the following: 60%, 62%, 65%, 67%, 70%, 73%, 75%, 78%, 80%, 82%, 85%, 87%, and 90%.

[0058] Specifically, based on the quality of the adhesive, the mass percentage of PAA can be a range of one or any combination of 10%, 12%, 15%, 17%, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 37%, and 40%.

[0059] In some embodiments, the mass percentage of the binder is 5% to 15% based on the mass of the negative electrode active layer; for example, it can be a range of one or any two of 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, and 15%.

[0060] In some embodiments, the negative electrode active layer further includes a negative electrode active material, which includes a silicon-based material.

[0061] In some embodiments, the mass percentage of the silicon-based material is 60% to 100% based on the mass of the negative electrode active material; for example, it can be a range of one or any two of 60%, 62%, 65%, 67%, 70%, 73%, 75%, 78%, 80%, 82%, 85%, 87%, 90%, 93%, 95%, 98%, and 100%.

[0062] In some embodiments, the silicon-based material includes at least one of Si material, silicon-carbon (Si-C) 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).

[0063] In some embodiments, the negative electrode active material may further include a carbon-based material, which includes at least one of natural graphite particles, synthetic 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] In some embodiments, the secondary battery further includes a positive electrode, a separator, and an electrolyte.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] In some embodiments, the diaphragm includes an inorganic coating disposed on at least one side of the surface of the porous substrate.

[0081] 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 At least one of (x is 1 or 2) and MTiO3 (M is Ba, Sr or Ca). Inorganic coatings can improve the thermal stability of the separator and enhance battery safety performance.

[0082] 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.

[0083] Inorganic fillers can be spherical, rod-shaped, sheet-shaped, disc-shaped, needle-shaped, cylindrical, irregular, or other known particle shapes. Preferably, the inorganic filler is spherical, as 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.

[0084] In some embodiments, the electrolyte may also include a non-aqueous solvent and a lithium salt.

[0085] 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.

[0086] In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0087] In some embodiments, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] Thirdly, an electrical device is provided, including the aforementioned secondary battery.

[0095] The electrical device used in this application is not particularly limited and can be any electrical device known in the prior art.

[0096] 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.

[0097] Example 1 <Preparation of Negative Electrode Binder> Under an argon atmosphere, α-lipoic acid is placed in a container and heated to 120°C to dissolve it, forming an α-lipoic acid solution. Next, glycerol triglycidyl ether and pentaerythritol tetraacrylate were added to the α-lipoic acid solution, and the polymerization reaction was carried out at 120°C for 30 min to obtain the negative electrode binder; wherein the molar ratio of α-lipoic acid, glycerol triglycidyl ether and pentaerythritol tetraacrylate was 1:0.2:0.05.

[0098] <Preparation of Negative Electrode Sheets> SiO, the negative electrode active material x(0 < x < 2) Conductive carbon black and negative electrode binder are added to 1-methyl-2-pyrrolidone in a mass ratio of 82:6:12 and mixed evenly to obtain a negative electrode slurry. The obtained negative electrode slurry is 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 is obtained. The total thickness of the double-sided negative electrode active material layer is 40 μm.

[0099] <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 97.5:0.5:2 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, wherein the total thickness of the positive electrode active layer on both sides is 70 μm.

[0100] <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.

[0101] <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.

[0102] <Preparation of Secondary Batteries> The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode sheets. After winding, hot pressing and shaping, and electrode tab welding, 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 capacity tested to complete the preparation of the secondary battery.

[0103] Example 2 The difference between Example 2 and Example 1 is that the molar ratio of α-lipoic acid, glyceryl triglycidyl ether, and pentaerythritol tetraacrylate is different in the <Preparation of Negative Electrode Binder>. In this example, the molar ratio of α-lipoic acid, glyceryl triglycidyl ether, and pentaerythritol tetraacrylate is 1:0.15:0.1; the negative electrode binder in this example is denoted as PLA-EG.

[0104] Example 3 The difference between Example 3 and Example 1 is that the molar ratio of α-lipoic acid, glyceryl triglycidyl ether and pentaerythritol tetraacrylate is different in the <Preparation of Negative Electrode Binder>. In this example, the molar ratio of α-lipoic acid, glyceryl triglycidyl ether and pentaerythritol tetraacrylate is 1:0.1:0.15.

[0105] Example 4 The difference between Example 4 and Example 1 is that the molar ratio of α-lipoic acid, glyceryl triglycidyl ether and pentaerythritol tetraacrylate is different in the <Preparation of Negative Electrode Binder>. In this example, the molar ratio of α-lipoic acid, glyceryl triglycidyl ether and pentaerythritol tetraacrylate is 1:0.05:0.2.

[0106] Example 5 The difference between Example 5 and Example 1 is that the molar ratio of α-lipoic acid, glyceryl triglycidyl ether, and pentaerythritol tetraacrylate is different in the <Preparation of Negative Electrode Binder>. In this example, the molar ratio of α-lipoic acid, glyceryl triglycidyl ether, and pentaerythritol tetraacrylate is 1:0.23:0.02.

[0107] Example 6 The difference between Example 6 and Example 1 is that the molar ratio of α-lipoic acid, glyceryl triglycidyl ether, and pentaerythritol tetraacrylate is different in the <Preparation of Negative Electrode Binder>. In this example, the molar ratio of α-lipoic acid, glyceryl triglycidyl ether, and pentaerythritol tetraacrylate is 1:0.02:0.23.

[0108] Example 7 The difference between Example 7 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 89:6:5.

[0109] Example 8 The difference between Example 8 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 79:6:15.

[0110] Example 9 The difference between Example 9 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, negative electrode binder and PAA were added to deionized water at a mass ratio of 82:6:7.2:4.8 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.

[0111] Example 10 The difference between Example 10 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, negative electrode binder and PAA were added to deionized water in a mass ratio of 82:6:9:3 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.

[0112] Example 11 The difference between Example 11 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, negative electrode binder and PAA were added to deionized water at a mass ratio of 82:6:10.8:1.2 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.

[0113] Example 12 The difference between Example 12 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, negative electrode binder and PAA were added to deionized water at a mass ratio of 82:6:6:6 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.

[0114] Example 13 The difference between Example 13 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, negative electrode binder and PVDF were added to deionized water at a mass ratio of 82:6:9:3 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.

[0115] Example 14 The difference between Example 14 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, negative electrode binder, CMC and SBR were added to deionized water in a mass ratio of 82:6:9:1.5:1.5 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.

[0116] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that glycerol triglycidyl ether and pentaerythritol tetraacrylate are not added in the <Preparation of Negative Electrode Binder>, that is, the negative electrode binder of this comparative example is α-lipoic acid.

[0117] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that glycerol triglycidyl ether is not added in the <Preparation of Negative Electrode Binder>. In this comparative example, the molar ratio of α-lipoic acid to pentaerythritol tetraacrylate is 1:0.05.

[0118] Comparative Example 3 The difference between Comparative Example 3 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 82:6:12 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.

[0119] Comparative Example 4 The difference between Comparative Example 4 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 PVDF were added to deionized water at a mass ratio of 82:6:12 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.

[0120] Comparative Example 5 The difference between Comparative Example 5 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 82:6:6:6 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.

[0121] Some performance parameters of Examples 1-14 and Comparative Examples 1-5 are shown in Table 1.

[0122] Performance testing (1) Swelling rate of negative electrode binder: The same size binder film (length*width*thickness=10mm*10mm*1mm) to be tested was immersed in the same electrolyte (1mol LiPF6, VEC:VDEC=1:1, 10%wt FEC and 1%wt VC) for 16 hours. Every 4 hours, the sample was taken out, the surface electrolyte was wiped off and weighed, and the mass of the film before and after swelling was recorded. The formula for calculating the swelling rate is: = (M after - M before) / M before * 100%; (2) Peeling force of negative electrode sheet: After cutting the negative electrode sheet into a rectangle (length * width = 50mm * 20mm), stick the tape to the coated surface of the negative electrode sheet, and then place it in the upper and lower clamps of the testing machine. Set the speed to 15 mm / min and pull it evenly until the coated surface of the negative electrode sheet is completely peeled off. Record the test data to obtain the average peeling force of the negative electrode sheet. (3) 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.

[0123] (4) 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.

[0124] (5) 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.

[0125] The test results are shown in Table 1-2 and Figure 1-2 As shown.

[0126] Table 1 Table 2 Figure 1 This is a graph showing the swelling rate changes of the negative electrode binder in Example 2 and Comparative Example 5 at different times. Figure 1 As can be seen, the swelling rate of the negative electrode binder increases with time, and the swelling rate of the negative electrode binder in this application is much smaller than that of conventional binders (such as CMC and SBR). This indicates that the negative electrode binder in this application forms a dense network structure, which can prevent the electrolyte from penetrating into the binder film, thereby enhancing the structural stability of the negative electrode sheet.

[0127] Figure 2 The images show the SEM surface images of the negative electrode sheet after 300 cycles of the secondary batteries in Example 2 and Comparative Example 5; from... Figure 2 It can be seen that, after 300 cycles, the surface morphology of the negative electrode sheet in the secondary battery containing the negative electrode binder of this application remains intact, and the SiO₂ content remains high. x The particles are uniformly distributed and free of obvious defects. In secondary batteries containing CMC and SBR, severe structural collapse and cracks appear on the surface of the negative electrode sheet after 300 cycles. This causes the negative electrode active material to be continuously exposed to the electrolyte during cycling, repeatedly forming an SEI film, continuously consuming lithium ions, increasing battery internal resistance, and reducing electrochemical performance. This demonstrates that the negative electrode binder of this application can effectively buffer the volume expansion of the negative electrode active material during lithium insertion / extraction, improving the structural integrity of the negative electrode sheet.

[0128] 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, ether, and disulfide bonds.

2. The negative electrode binder as described in claim 1, characterized in that, The molar ratio of the carboxyl group to the ether group is 1:(0.8~0.98).

3. The negative electrode binder as described in claim 1, characterized in that, The structural formula of the negative electrode binder is shown below: ， Where n = 10~100.

4. The negative electrode binder as described in claim 1, characterized in that, The swelling rate of the negative electrode binder is ≤8%.

5. The negative electrode binder as described in claim 1, characterized in that, The negative electrode binder is mainly obtained by polymerization of α-lipoic acid, glyceryl triglycidyl ether and pentaerythritol tetraacrylate.

6. The negative electrode binder as described in claim 5, characterized in that, The molar ratio of α-lipoic acid to glyceryl triglycidyl ether is 1:(0.05~0.2). The molar ratio of α-lipoic acid to pentaerythritol tetraacrylate is 1:(0.05~0.2).

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 as described in claim 7, characterized in that, The peeling force of the negative electrode sheet is 15~22 N / m.

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

10. The secondary battery as described in claim 9, characterized in that, The second adhesive includes PAA.

11. The secondary battery as described in claim 10, characterized in that, Based on the mass of the binder, the negative electrode binder has a mass percentage content of 60% to 90%, and the PAA has a mass percentage content of 10% to 40%.

12. The secondary battery according to any one of claims 7 to 11, characterized in that, The binder has a mass percentage of 5% to 15%, depending on the mass of the negative electrode active layer.

13. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 7 to 12.

Images