Binder, negative pole piece, preparation method of negative pole piece, battery and electric device

Abstract

The invention relates to a binder, a negative pole piece, a preparation method of the negative pole piece, a battery and an electric device, and belongs to the technical field of battery materials. The adhesive has a bi-crosslinking interpenetrating network structure comprising a first crosslinking network and a second crosslinking network, crosslinking components of the first crosslinking network comprise polyethyleneimine and epoxy resin, and crosslinking components of the second crosslinking network comprise polybenzimidazole and epoxy resin. The binder has excellent bonding strength, mechanical strength and flexibility, has long-term stability in heat, solvent and other environments, can be effectively applied to a battery system, is especially suitable for a silicon-based negative electrode system, can effectively relieve volume expansion of a negative electrode active material in a charge-discharge cycle process, and has good stability. And the interface bonding force between the negative electrode film layer and the negative electrode current collector is enhanced, so that the cycle performance of the battery can be effectively improved.

Description

An adhesive, a negative electrode sheet and its preparation method, a battery and an electrical device. Technical Field

[0001] This application relates to the field of battery materials technology, and in particular to a binder, a negative electrode sheet and its preparation method, a battery and an electrical device. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, and environmental friendliness, have been widely used in various fields such as new energy vehicles, portable electronic devices, and energy storage systems. The negative electrode, as the core site for lithium-ion insertion / extraction, directly affects the overall performance of the battery. The negative electrode active material is a core component of the negative electrode. Currently, commonly used negative electrode active materials include graphite, hard carbon, silicon-based materials, and tin-based materials. Among these, silicon-based and other novel high-capacity active materials are considered a key breakthrough for improving the energy density of lithium-ion batteries due to their theoretical specific capacity far exceeding that of traditional graphite materials. However, during charging and discharging, the insertion / extraction of lithium ions causes dramatic volume expansion, with an expansion rate as high as 300%. This leads to a series of problems such as particle pulverization of the negative electrode active material, failure of the conductive network, and shedding of the negative electrode film, ultimately resulting in poor battery cycle performance.

[0003] The negative electrode binder, as the core link maintaining the structural integrity of each component of the negative electrode sheet, tightly bonds the negative electrode active material, conductive agent, and negative electrode current collector together. Currently, to alleviate the volume expansion of the negative electrode active material and maintain the stability and integrity of the electrode structure, polymers such as polyacrylic acid (PAA), sodium alginate (SA), chitosan (CS), and sodium carboxymethyl cellulose (CMC) are widely used. However, these single linear polymer binders have poor mechanical properties and simple interactions with the negative electrode active material particles. The sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) composite system has poor electrolyte resistance, low bonding strength, and weak deformation resistance, all of which are difficult to effectively solve a series of problems caused by the expansion of the negative electrode active material system. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a negative electrode sheet and its preparation method, a battery, and an electrical device, which effectively improves the problems of insufficient bonding strength, poor mechanical properties, and weak deformation resistance of existing adhesives.

[0005] In a first aspect, embodiments of this application provide an adhesive having a double cross-linked interpenetrating network structure including a first cross-linked network and a second cross-linked network, wherein the cross-linking components of the first cross-linked network include polyethyleneimine and epoxy resin, and the cross-linking components of the second cross-linked network include polyphenylene imidazole and epoxy resin.

[0006] In the above technical solution, compared with the single linear molecular chain and single cross-linked network in existing adhesives, the adhesive provided in this application has a double cross-linked interpenetrating network structure in which the molecular chains of the first cross-linked network formed by the covalent cross-linking of polyethyleneimine and epoxy resin and the second cross-linked network formed by the covalent cross-linking of polyphenylene sulfide and epoxy resin interpenetrate and entangle. Polyethyleneimine is rich in highly polar amino and imino groups, which can form hydrogen bonds or electrostatic interactions with the bonded materials, thereby achieving tight encapsulation. Furthermore, the flexible molecular chains of polyethyleneimine and the first cross-linked network formed with epoxy resin can serve as a flexible cross-linked backbone, providing a certain degree of elasticity to the interpenetrating network and endowing the adhesive with excellent resistance to deformation. Meanwhile, the rigid benzimidazole heterocycles of polyphenylene sulfide endow the second cross-linked network with excellent mechanical strength. The interpenetration and entanglement of the rigid second cross-linked network and the flexible first cross-linked network give the adhesive both good mechanical strength and flexibility, and consequently, good chemical and thermal stability.

[0007] This binder possesses excellent adhesive strength, mechanical strength, and flexibility, and exhibits long-term stability under thermal and solvent conditions, making it suitable for use in battery systems, especially silicon-based anode systems. It can effectively alleviate the volume expansion of the anode active material during charge-discharge cycles, enhance the interfacial adhesion between the anode film and the anode current collector, and thus effectively improve the cycle performance of the battery.

[0008] In some embodiments, the mass ratio of polyethyleneimine to epoxy resin in the adhesive is (1~3):(1~3); based on the total mass of polyethyleneimine, polyphenylene sulfide, and epoxy resin, the mass percentage of polyphenylene sulfide is 10wt%~20wt%. In the above technical solution, by adjusting the mass ratio of polyethyleneimine, epoxy resin, and polyphenylene sulfide, the proportions of the first and second crosslinking networks are adjusted accordingly, which is beneficial to further improve the adhesive strength of the adhesive, while further balancing mechanical strength and flexibility.

[0009] In some embodiments, polyethyleneimine includes branched polyethyleneimine and / or hyperbranched polyethyleneimine. In the above technical solutions, compared to linear polyethyleneimine, branched polyethyleneimine and / or hyperbranched polyethyleneimine have more amino and imino groups, i.e., more strongly polar active groups, which can form stronger hydrogen bonds and / or electrostatic adsorption with the bonded materials, thereby further improving the bonding strength of the adhesive.

[0010] Secondly, embodiments of this application provide a negative electrode sheet, including a negative current collector and a negative electrode film layer attached to at least one side surface of the negative current collector. The negative electrode film layer includes a negative electrode active material and a negative electrode binder. The negative electrode binder has a double cross-linked interpenetrating network structure including a first cross-linked network and a second cross-linked network. The cross-linking components of the first cross-linked network include polyethyleneimine and epoxy resin, and the cross-linking components of the second cross-linked network include polyphenylene imidazole and epoxy resin. In the above technical solution, this application introduces a negative electrode binder into the negative electrode sheet. Compared with the single linear molecular chain and single cross-linked network in existing negative electrode binders, the molecular chains of the first cross-linked network formed by the covalent cross-linking of polyethyleneimine and epoxy resin and the second cross-linked network formed by the covalent cross-linking of polyphenylene imidazole and epoxy resin interpenetrate and entangle to form a double cross-linked interpenetrating network structure. This gives it excellent adhesive strength, mechanical strength and flexibility, and long-term stability under heat, solvent and other environments. It can tightly wrap the negative electrode active material, effectively alleviate the volume expansion of the negative electrode active material during charge and discharge cycles, and give the negative electrode sheet excellent resistance to deformation. At the same time, it effectively improves the adhesion between the negative electrode film layer and the negative electrode current collector, thereby effectively resisting the internal stress generated by the "expansion-contraction" of the negative electrode active material during charge and discharge cycles, improving problems such as the powdering and shedding of the negative electrode active material, the failure of the conductive network, and the shedding of the negative electrode film layer. Even after long-term cycling, the electrode sheet structure can still remain dense and intact.

[0011] Polyethyleneimine, rich in highly polar amino and imine groups, can form hydrogen bonds with negative electrode active materials (such as graphite and silicon-based materials) to achieve effective and tight encapsulation. It can also form electrostatic interactions with negative electrode current collectors (such as copper foil), effectively improving interfacial adhesion strength. Furthermore, polyethyleneimine's flexible molecular chains, combined with the epoxy resin to form a first cross-linking network, serve as a flexible cross-linking framework, providing elasticity to the interpenetrating network and effectively mitigating repeated volume expansion and contraction of the negative electrode active material. Meanwhile, the rigid benzimidazole heterocycles of polyphenyleneimidazole endow the second cross-linking network with excellent mechanical strength. The interpenetrating entanglement of the rigid second cross-linking network and the flexible first cross-linking network gives the negative electrode binder both good mechanical strength and flexibility, resulting in excellent electrolyte resistance and thermal stability.

[0012] In some embodiments, the mass ratio of polyethyleneimine to epoxy resin in the adhesive is (1~3):(1~3); based on the total mass of polyethyleneimine, polyphenylene sulfide, and epoxy resin, the mass percentage of polyphenylene sulfide is 10wt%~20wt%. In the above technical solution, by adjusting the mass ratio of polyethyleneimine, epoxy resin, and polyphenylene sulfide, the proportions of the first crosslinking network and the second crosslinking network are correspondingly adjusted, which is beneficial to improving the bonding strength of the negative electrode adhesive, while further balancing mechanical strength and flexibility.

[0013] In some embodiments, polyethyleneimine includes branched polyethyleneimine and / or hyperbranched polyethyleneimine. In the above technical solutions, compared to linear polyethyleneimine, branched polyethyleneimine and / or hyperbranched polyethyleneimine have more amino and imino groups, i.e., more strongly polar active groups. These groups can form stronger hydrogen bonds with the negative electrode active material and more stable electrostatic adsorption with the surface of the negative electrode current collector, thereby further improving the adhesive strength and interfacial adhesion of the binder, and thus further mitigating the volume expansion of the negative electrode active material.

[0014] In some implementations, the mass percentage of the negative electrode binder is 1 wt% to 10 wt% based on the total mass of the negative electrode film.

[0015] In the above technical solution, the negative electrode binder of this application can effectively form a three-dimensional adhesive network structure without increasing the dosage, ensuring high energy density of the battery while effectively mitigating the volume expansion of the negative electrode active material. In some embodiments, the negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, or lithium titanate. In the above technical solution, the negative electrode binder not only has excellent adhesive strength but also good mechanical strength and flexibility, and has better long-term stability under thermal and solvent environments. It is suitable for the above-mentioned negative electrode active material system, which can not only alleviate volume expansion but also effectively improve the deformation resistance of the electrode sheet compared with traditional binders, further improving the cycle performance of the battery. In some embodiments, the negative electrode active material includes silicon-based materials, which include at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, or silicon alloys. In the above-mentioned technical solutions, the volume expansion of silicon-based materials during charge-discharge cycles can reach 300%, accompanied by internal stress generated by repeated "expansion-contraction," which can lead to a series of problems such as particle crushing, electrode structure damage, conductive network failure, and interface instability during charge-discharge. Using the negative electrode binder of this application, the polyethyleneimine in the first cross-linked network can form hydrogen bonds with the silicon-based material. The double cross-linked interpenetrating network structure, possessing both mechanical strength and flexibility, can effectively and tightly encapsulate the silicon-based material, thereby effectively alleviating volume expansion and ensuring the integrity of the electrode structure. Thirdly, embodiments of this application provide a method for preparing a negative electrode sheet, comprising the following steps: mixing epoxy resin, polyethyleneimine, polyphenylene imidazole, negative electrode active material, and conductive agent in a solvent to form a negative electrode slurry; coating the negative electrode slurry onto at least one side of the negative electrode current collector; drying at 60°C to 100°C and reacting for 12 to 24 hours to form a negative electrode film layer, thereby obtaining a negative electrode sheet.

[0016] In the above technical solution, this application uses epoxy resin, polyethyleneimine, and polyphenylene sulfide as raw materials to prepare a negative electrode binder simultaneously with the preparation of the negative electrode sheet. Under heating conditions, the epoxy groups of the epoxy resin undergo a ring-opening reaction with the amino and imino groups in the polyethyleneimine to form a flexible first cross-linked network; simultaneously, the epoxy groups of the epoxy resin undergo a ring-opening reaction with the imino groups in the polyphenylene sulfide to form a rigid second cross-linked network. Because the epoxy resin, polyethyleneimine, polyphenylene sulfide, negative electrode active material, and conductive agent are uniformly mixed and dispersed in the negative electrode slurry, the first and second cross-linked networks interpenetrate and entangle to form a double cross-linked interpenetrating network structure. This structure provides a fully and uniform coating of the negative electrode active material and conductive agent and forms a strong bond with the negative electrode current collector, effectively mitigating the volume expansion of the negative electrode active material (and conductive agent) and improving a series of problems caused by the volume change of the negative electrode active material, such as particle pulverization, conductive network failure, and negative electrode film detachment.

[0017] Furthermore, this preparation method simultaneously mixes binder raw materials during the formation of the negative electrode slurry. During the drying process of the coating slurry, it slowly shrinks and gradually cross-links as the solvent evaporates, thus forming the binder in situ while preparing the negative electrode sheet. The process is simple, efficient, highly compatible with existing electrode preparation processes, and easy for large-scale industrial production. In some embodiments, the mass ratio of the negative electrode active material, epoxy resin, polyethyleneimine, polyphenylene sulfide, and conductive agent in the negative electrode slurry is (93~97):(1~3):(1~3):(0.5~1):(1~3). In the above technical solution, the mass ratio of the raw materials epoxy resin, polyethyleneimine, and polyphenylene sulfide in the negative electrode binder is within a suitable range, which is beneficial for further controlling the ratio of the first cross-linking network and the second cross-linking network, thereby effectively improving mechanical strength and flexibility while increasing adhesive strength. Furthermore, the amount of negative electrode active material is in a relatively high range, which is beneficial for maintaining high energy density.

[0018] In some embodiments, polyethyleneimine includes branched polyethyleneimine and / or hyperbranched polyethyleneimine.

[0019] In the above technical solutions, compared with linear polyethyleneimine, branched polyethyleneimine and / or hyperbranched polyethyleneimine have more amino and imino groups, i.e., more strongly polar active groups. These groups can form stronger hydrogen bonds with the negative electrode active material and more stable electrostatic adsorption on the surface of the negative electrode current collector, thereby further improving the bonding strength of the binder and further mitigating the volume expansion of the negative electrode active material. In some embodiments, the solid content of the negative electrode slurry is 40%~60%. In the above technical solutions, the solid content of the negative electrode slurry is within a suitable range, which is beneficial for uniform mixing and dispersion of the components, while improving the production efficiency of the drying-crosslinking step and the molding quality of the binder. In some embodiments, the solvent includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, or N,N-dimethylacetamide. In the above technical solutions, the above solvents are all aprotic strongly polar solvents, which can fully dissolve the components in the slurry, thus improving the stability of the slurry. Furthermore, they are adaptable to the drying-crosslinking reaction process, achieving a synergistic effect of slow solvent evaporation and gradual crosslinking molding of the binder. In some embodiments, the preparation method of the negative electrode slurry includes: dissolving polyphenylene imidazole in a solvent, and sequentially adding epoxy resin, polyethyleneimine, a conductive agent, and a negative electrode active material under stirring conditions to obtain the negative electrode slurry. In the above technical solution, by controlling the mixing order of each component, it is beneficial to improve the mixing uniformity, enhance the stability of the slurry, and further improve the structural stability of the negative electrode sheet. Fourthly, embodiments of this application provide a battery, including the negative electrode sheet provided in the second aspect or the negative electrode sheet prepared by the preparation method provided in the third aspect.

[0020] In the above technical solution, since the negative electrode binder has excellent bonding strength, mechanical strength and flexibility, and has better long-term stability in environments such as heat and solvents, it can effectively alleviate the volume expansion of the negative electrode active material during charge and discharge cycles, improve the interfacial adhesion between the negative electrode film layer and the negative electrode current collector, so that the negative electrode sheet has excellent structural stability and anti-deformation ability, thereby enabling the battery to have excellent cycle performance.

[0021] Fifthly, embodiments of this application also provide an electrical device, including the battery provided in the fourth aspect. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 is a schematic diagram of the double cross-linked interpenetrating network structure in the adhesive provided in the embodiment of this application.

[0024] Figure 2 is a process flow diagram of the method for preparing the negative electrode sheet provided in one embodiment of this application. Detailed Implementation

[0025] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the binder, negative electrode sheet, method for preparing the negative electrode sheet, battery, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0026] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0027] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0028] As the core site for lithium-ion insertion / deintercalation, the performance of the negative electrode directly affects the overall performance of the battery. The negative electrode binder, as the core link to maintain the structural integrity of the components of the negative electrode, tightly binds the negative electrode active material, conductive agent and negative electrode current collector together. Its performance is crucial to mitigating the volume expansion of the negative electrode active material and maintaining the stability and integrity of the electrode structure.

[0029] Currently, when dealing with anode active materials that experience significant volume expansion, such as silicon-based materials (with expansion rates reaching up to 300%), polymer binders such as polyacrylic acid (PAA), sodium alginate (SA), chitosan (CS), and sodium carboxymethyl cellulose (CMC) are widely used. However, these single linear polymer binders have poor mechanical properties and limited interaction with the anode active material particles. Although the sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) composite system is widely used, its poor electrolyte resistance, low bonding strength, and weak deformation resistance make it difficult to effectively solve a series of problems caused by the volume change of the anode material, such as particle pulverization, conductive network failure, and anode film detachment.

[0030] Based on this, the first aspect of this application provides an adhesive having a double cross-linked interpenetrating network structure including a first cross-linked network and a second cross-linked network, wherein the cross-linking components of the first cross-linked network include polyethyleneimine and epoxy resin, and the cross-linking components of the second cross-linked network include polyphenylene imidazole and epoxy resin.

[0031] The chemical structural formulas of epoxy resin (ER), polyethyleneimine (PEI), and polybenzimidazole (PBI) are as follows: , , .

[0032] As can be seen, epoxy resin (ER) contains abundant epoxy groups, polyethyleneimine (PEI) contains abundant amino and imino groups, and polyphenylene benzopyrazole (PBI) contains rigid benzopyrazole rings and imino groups. The epoxy groups in epoxy resin (ER) can undergo ring-opening reactions with the amino and imino groups in polyethyleneimine (PEI) and the imino groups in polyphenylene benzopyrazole (PBI) to form covalent crosslinks. Figure 1 is a schematic diagram of the double crosslinked interpenetrating network structure in the adhesive provided in the embodiments of this application. As can be seen from Figure 1, polyethyleneimine (PEI) and epoxy resin (ER) crosslink to form a first crosslinked network, and polyphenylene benzopyrazole (PBI) and epoxy resin (ER) crosslink to form a second crosslinked network. The first and second crosslinked networks interpenetrate and entangle to form a double crosslinked interpenetrating network structure.

[0033] Compared to existing adhesives with single linear molecular chains and single cross-linked networks, the adhesive provided in this application features a double-crosslinked interpenetrating network structure formed by the intervalent cross-linking of polyethyleneimine and epoxy resin into a first cross-linked network and a second cross-linked network formed by the intervalent cross-linking of polyphenylene sulfide and epoxy resin. Polyethyleneimine is rich in highly polar amino and imine groups, which can form hydrogen bonds or electrostatic interactions with the bonded materials, thus achieving tight encapsulation. Furthermore, the flexible molecular chains of polyethyleneimine and epoxy resin provide a flexible cross-linked backbone, offering elasticity to the interpenetrating network and endowing the adhesive with excellent resistance to deformation. Meanwhile, the rigid benzimidazole heterocycles of polyphenylene sulfide impart excellent mechanical strength to the second cross-linked network. The interpenetration and entanglement of the rigid second cross-linked network and the flexible first cross-linked network give the adhesive both good mechanical strength and flexibility, resulting in excellent chemical and thermal stability.

[0034] This binder possesses excellent adhesive strength, mechanical strength, and flexibility, and exhibits long-term stability under thermal and solvent conditions, making it suitable for use in battery systems, especially silicon-based anode systems. It can effectively alleviate the volume expansion of the anode active material during charge-discharge cycles, enhance the interfacial adhesion between the anode film and the anode current collector, and thus effectively improve the cycle performance of the battery.

[0035] In some embodiments, the mass ratio of polyethyleneimine to epoxy resin in the adhesive is (1~3):(1~3); the mass percentage of polyphenylene benzoylazole is 10wt%~20wt% based on the total mass of polyethyleneimine, polyphenylene benzoylazole, and epoxy resin. As an example, the mass ratio of polyethyleneimine to epoxy resin is any one of 1:1, 1:2, 1:3, 2:1, or 3:1, or a range between any two of these values; the mass percentage of polyphenylene benzoylazole in the total mass of the three components is any one of 10wt%, 12wt%, 15wt%, 18wt%, or 20wt%, or a range between any two of these values.

[0036] In some embodiments, polyethyleneimine includes branched polyethyleneimine and / or hyperbranched polyethyleneimine.

[0037] Branched polyethyleneimine typically refers to a polymer synthesized from ethyleneimine monomers under acidic catalysts (such as hydrochloric acid or sulfuric acid). Its molecular chain contains randomly distributed primary, secondary, and tertiary amine groups, forming a dendritic, randomly branched topology. Hyperbranched polyethyleneimine typically refers to a polymer synthesized from ethyleneimine monomers under acidic catalysts (such as hydrochloric acid or sulfuric acid). xPolymers synthesized from monomers (such as 2-aminoethanol, diethylenetriamine, etc.) through stepwise condensation reactions initiated by core molecules have a quasi-spherical regular branched topology, with a clearly defined central core molecule. The branches grow radially from the core outwards, and the branching units are regular and free of chain entanglement, forming an open core-shell structure with a branching degree of 0.5~1.0.

[0038] In some embodiments, the weight-average molecular weight of polyphenylene imidazole is 50,000 to 200,000, the weight-average molecular weight of polyethyleneimine is 10,000 to 70,000, and the weight-average molecular weight of epoxy resin is 500 to 7,000.

[0039] A second aspect of this application provides a negative electrode sheet using the above-mentioned binder, comprising a negative electrode current collector and a negative electrode film layer attached to at least one side surface of the negative electrode current collector. The negative electrode film layer comprises a negative electrode active material and a negative electrode binder. The negative electrode binder has a double cross-linked interpenetrating network structure comprising a first cross-linked network and a second cross-linked network. The cross-linking components of the first cross-linked network include polyethyleneimine and epoxy resin, and the cross-linking components of the second cross-linked network include polyphenylene imidazole and epoxy resin.

[0040] Understandably, in the negative electrode film layer, the negative electrode binder encapsulates the negative electrode active material and is at least partially in contact with the surface of the negative electrode current collector.

[0041] In some embodiments, the mass percentage of the negative electrode binder is 1 wt% to 10 wt% based on the total mass of the negative electrode film. As examples, the mass percentage of the negative electrode binder is 1 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, etc.

[0042] In some embodiments, the negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, or lithium titanate.

[0043] Furthermore, the negative electrode active material includes silicon-based materials. Even further, the silicon-based material includes at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, or silicon alloys.

[0044] Preferably, the negative electrode active material includes silicon-carbon composite and graphite (artificial graphite or natural graphite).

[0045] In some embodiments, the negative electrode film layer further includes a conductive agent, which includes at least one of superconducting carbon black (Super P), acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes (CNTs), graphene, or carbon nanofibers.

[0046] The third aspect of this application also provides a method for preparing the above-mentioned negative electrode sheet. Figure 2 is a process flow diagram of the method for preparing the negative electrode sheet provided in one embodiment of this application. Referring to Figure 2, the preparation method includes the following steps: mixing epoxy resin, polyethyleneimine, polyphenylimidazolium, negative electrode active material and conductive agent in a solvent to form a negative electrode slurry; coating the negative electrode slurry on at least one side surface of the negative electrode current collector, drying it at 60°C to 100°C and reacting it for 12h to 24h to form a negative electrode film layer, thereby obtaining a negative electrode sheet.

[0047] For example, the reaction temperature can be 60℃, 70℃, 80℃, 90℃, 100℃, etc.; the reaction time can be 12h, 15h, 18h, 20h, 24h, etc.

[0048] It should be noted that the reaction is carried out in an air atmosphere. The coating steps can be found in conventional negative electrode preparation methods, such as doctor blade / microgravure coating.

[0049] In some embodiments, the mass ratio of the negative electrode active material, epoxy resin, polyethyleneimine, polyphenylene sulfide, and conductive agent is (93~97):(1~3):(1~3):(0.5~1):(1~3). As an example, the mass ratio of the negative electrode active material, epoxy resin, polyethyleneimine, polyphenylene sulfide, and conductive agent can be 93.4:2.5:1.5:1:1.6, 96:1:1:0.5:1.5, etc.

[0050] In some embodiments, the solid content of the negative electrode slurry is 40% to 60%. As examples, the solid content of the negative electrode slurry is 40%, 45%, 50%, 55%, 60%, etc.

[0051] In some embodiments, the solvent includes at least one selected from N-methylpyrrolidone, dimethyl sulfoxide, or N,N-dimethylacetamide. Further, the solvent may also include water. For example, the solvent may include N-methylpyrrolidone and water, dimethyl sulfoxide and water, etc. Preferably, the solvent is N-methylpyrrolidone.

[0052] In some embodiments, the preparation method of the negative electrode slurry may include: dissolving polyphenylimidazolium in a solvent, and under stirring conditions, sequentially adding epoxy resin, polyethyleneimine, conductive agent and negative electrode active material to mix and obtain the negative electrode slurry.

[0053] Furthermore, the stirring speed can be from 200 rpm to 1000 rpm, such as 200 rpm, 500 rpm, 800 rpm, 1000 rpm, etc.

[0054] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0055] In addition, a fourth aspect of the present application provides a battery including the aforementioned negative electrode sheet.

[0056] In some embodiments, the battery can be a lithium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a separator. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator is disposed between the positive and negative electrodes, primarily to prevent short circuits between the positive and negative electrodes, while also allowing ions to pass through.

[0057] Understandably, the positive electrode, electrolyte, and separator can all be obtained using conventional materials and preparation methods in the field, and this application does not impose any specific limitations.

[0058] In addition, the fifth aspect of this application also provides an electrical device, which is a terminal product equipped with the battery. The electrical device may be a vehicle, aircraft, robot, computer, mobile phone, etc.

[0059] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0060] The sources of some of the raw materials used in the following examples and comparative examples are shown in Table 1.

[0061] Table 1. Sources of some raw materials

[0062] Example 1 This example provides a negative electrode sheet, the preparation method of which includes the following steps: (1) under the stirring condition of 1000 rpm, polybenzimidazole is dissolved in N-methylpyrrolidone, and then epoxy resin, polyethyleneimine, conductive agent and negative electrode active material are added in sequence and mixed evenly to obtain negative electrode slurry.

[0063] The mass ratio of the negative electrode active material, epoxy resin, polyethyleneimine, polyphenylene sulfide, and conductive agent is 93.4:1.5:2.5:1:1.6; the negative electrode active material includes 20.4% silicon carbide and 73% graphite; the conductive agent includes 1.5% Super P and 0.1% CNT; and the solid content of the negative electrode slurry is 45%.

[0064] (2) The negative electrode slurry is transferred to a coating machine and evenly coated on both sides of the negative electrode current collector copper foil (thickness 8μm). It is baked in air atmosphere at 60℃ for 12h, and then rolled to obtain the negative electrode sheet.

[0065] Example 2 This example provides a negative electrode sheet, the preparation method of which differs from that of Example 1 in that the mass ratio of epoxy resin, polyethyleneimine and polyphenylimidazolium in step (1) is 2.5:1.5:1.

[0066] Example 3 This example provides a negative electrode sheet, the preparation method of which differs from that of Example 1 in that the mass ratio of epoxy resin, polyethyleneimine and polyphenylimidazolium in step (1) is 2:2.5:0.5.

[0067] Example 4 This example provides a negative electrode sheet, the preparation method of which differs from that of Example 1 in that: in step (1), the mass ratio of negative electrode active material, epoxy resin, polyethyleneimine, polyphenylimidazolium and conductive agent is 96:1:1:0.5:1.5, and the negative electrode active material includes 22% silicon carbide material and 74% graphite material.

[0068] Example 5 This example provides a negative electrode sheet, the preparation method of which differs from that of Example 1 in that the solid content of the negative electrode slurry in step (1) is 50%.

[0069] Example 6 This example provides a negative electrode sheet, the preparation method of which differs from that of Example 1 in that the reaction conditions in step (2) are: baking at 80°C for 15 hours.

[0070] Comparative Example 1 This comparative example provides a negative electrode sheet, the preparation method of which includes the following steps: (1) Under stirring conditions of 1000 rpm, carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, conductive agent and negative electrode active material are mixed evenly in N-methylpyrrolidone to obtain a negative electrode slurry. Among them, the mass ratio of negative electrode active material, carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid and conductive agent is 93.4:1.5:2.5:1:1.6; the negative electrode active material includes 20.4% silicon carbide material and 73% graphite material; the conductive agent includes 1.5% Super P and 0.1% CNT; the solid content of the negative electrode slurry is 45%.

[0071] (2) The negative electrode slurry is transferred to a coating machine and evenly coated on both sides of the negative electrode current collector copper foil (thickness 8μm). It is baked in air atmosphere at 60℃ for 12h, and then rolled to obtain the negative electrode sheet.

[0072] Comparative Example 2 This comparative example provides a negative electrode sheet, the preparation method of which differs from that of Example 1 in that: polyphenylimidazolium is not added in step (1), and the mass ratio of negative electrode active material, epoxy resin, polyethyleneimine and conductive agent is 94.4:1.5:2.5:1.6.

[0073] The preparation process parameters of the above embodiments and comparative examples are shown in Table 2.

[0074] Table 2. Partial fabrication process parameters of the negative electrode sheet

[0075] Performance testing and result analysis: The negative electrode sheets prepared in the above examples and comparative examples were assembled into lithium-ion batteries. The assembly method is as follows: (1) The positive electrode active material lithium nickel cobalt manganese LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black (Super-P), carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) binder were mixed uniformly at a mass ratio of 96.8:1.5:0.5:1.2. N-methylpyrrolidone (NMP) was then added, and the mixture was stirred uniformly using a vacuum mixer to obtain a positive electrode active material slurry. The slurry was then uniformly coated on both sides of an aluminum foil (13 μm thick) current collector. After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0076] (2) The separator is placed between the above positive electrode and negative electrode to prepare a bare cell by stacking. Then, the bare cell is placed in the packaging bag (shell) using aluminum-plastic film composite material to obtain a dry cell. The dry cell is then subjected to baking to remove water, liquid injection, sealing, standing, formation, degassing and packaging and capacity testing to obtain a lithium-ion battery.

[0077] The electrolyte composition is an organic solvent consisting of ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) in a ratio of 2:3:5, with LiPF6 as a 1 mol / L lithium salt and 10% fluoroethylene carbonate (FEC) added as an electrolyte additive.

[0078] The negative electrode sheets and lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to performance tests, and the test results are shown in Table 3. The specific test methods are as follows: 1. Negative electrode sheet (1) Peel strength Wipe the surface of the stainless steel plate with acetone 4 times and let it dry for 10 minutes. Then, attach double-sided tape with a width of 30 mm and a length of 80 mm to the surface of the steel plate. Cut an electrode sample with a width of 25 mm and a length of 100 mm with a cutter and attach it to the surface of the double-sided tape. Fold one end of the cut sample with the adhesive side facing up to form a folded layer about 20 mm long. Attach the other end of the sample to one end of the steel plate and roll it twice with a pressure roller at a speed of 600 mm / min. Then, clamp the free end of the steel plate and the sample in the upper and lower fixtures of the universal material testing machine. Then, perform a 180-degree peel test at a speed of 10 mm / min and a load of 10 N to obtain the peel strength value.

[0079] (2) The negative electrode full charge expansion rate: The lithium-ion battery was charged to 4.2V at a constant current rate of 1C and then constant voltage to 0.02C at 4.2V. The battery was disassembled and the thickness of the negative electrode sheet V2 was measured by micrometer. The thickness of the negative electrode after rolling was V1, of which the copper foil thickness was V0. The negative electrode full charge expansion rate was calculated as follows: negative electrode full charge expansion rate = (V2-V1) / (V1-V0)*100%.

[0080] 2. Lithium-ion battery (1) Cyclic performance At 25°C, the battery is charged at a constant current of 1C to 4.25V, then charged at a constant voltage until the current is less than or equal to 0.05C, then left to stand for 5 minutes, then discharged at a constant current of 1C to 2.8V, then left to stand for 5 minutes. This is one charge-discharge cycle. The battery cell is subjected to multiple charge-discharge cycles in the above manner. The charge-discharge capacity of the 1000th cycle is detected, and the capacity retention rate of the battery cell after the cycle is calculated by the following formula.

[0081] The capacity retention rate (%) of the battery after 1000 cycles = [discharge capacity of the 1000th cycle / discharge capacity of the 1st cycle] × 100%.

[0082] Table 3 Performance test results of negative electrode sheet and lithium-ion battery

[0083] As shown in Table 3, compared with Comparative Example 1 and Comparative Example 2, the negative electrode sheets prepared in Examples 1 to 6 of this application have higher peel strength and lower full-charge expansion rate. The peel strength is ≥23N / m and the full-charge expansion rate is ≤12%. The corresponding lithium-ion batteries prepared have excellent cycle performance, with a capacity retention rate of ≥84% after 1000 cycles.

[0084] As can be seen from the performance test results of Example 1 and Comparative Example 1, compared with the conventional combination of carboxymethyl cellulose, styrene-butadiene rubber and polyacrylic acid binder, the negative electrode binder of this application can significantly improve the peel strength of the negative electrode sheet, reduce the volume expansion of the negative electrode sheet, and thus improve the cycle performance of the battery.

[0085] As can be seen from the performance test results of Example 1 and Comparative Example 2, compared with the single cross-linking network formed by epoxy resin and polyethyleneimine, the addition of polyphenylene imidazole in this application forms a second cross-linking network, which makes the negative electrode binder have a double cross-linking interpenetrating network structure, which can effectively improve the peel strength of the negative electrode sheet, reduce the volume expansion of the negative electrode sheet, and thus improve the cycle performance of the battery.

[0086] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. An adhesive, characterized in that, It has a double cross-linked interpenetrating network structure including a first cross-linked network and a second cross-linked network, wherein the cross-linking components of the first cross-linked network include polyethyleneimine and epoxy resin, and the cross-linking components of the second cross-linked network include polyphenylene imidazole and epoxy resin.

2. The adhesive according to claim 1, characterized in that, In the adhesive, the mass ratio of polyethyleneimine to epoxy resin is (1~3):(1~3); based on the total mass of polyethyleneimine, polyphenylimazole and epoxy resin, the mass percentage of polyphenylimazole is 10wt%~20wt%.

3. The adhesive according to claim 1, characterized in that, The polyethyleneimine includes branched polyethyleneimine and / or hyperbranched polyethyleneimine.

4. A negative electrode sheet, characterized in that, The device includes a negative electrode current collector and a negative electrode film layer attached to at least one side surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material and a negative electrode binder. The negative electrode binder has a double cross-linked interpenetrating network structure including a first cross-linked network and a second cross-linked network. The cross-linking components of the first cross-linked network include polyethyleneimine and epoxy resin, and the cross-linking components of the second cross-linked network include polyphenylene imidazole and epoxy resin.

5. The negative electrode sheet according to claim 4, characterized in that, In the adhesive, the mass ratio of polyethyleneimine to epoxy resin is (1~3):(1~3); based on the total mass of the polyethyleneimine, polyphenylenemiazole and epoxy resin, the mass percentage of polyphenylenemiazole is 10wt%~20wt%; and / or, the polyethyleneimine includes branched polyethyleneimine and / or hyperbranched polyethyleneimine.

6. The negative electrode sheet according to claim 4, characterized in that, The negative electrode binder accounts for 1 wt% to 10 wt% of the total mass of the negative electrode film; and / or, the negative electrode active material includes a silicon-based material, which includes at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, or silicon alloy.

7. A method for preparing a negative electrode sheet, characterized in that, The process includes the following steps: mixing epoxy resin, polyethyleneimine, polyphenylimidazolium, negative electrode active material and conductive agent in a solvent to form a negative electrode slurry; coating the negative electrode slurry onto at least one side of the negative electrode current collector, drying it at 60°C to 100°C and reacting it for 12 to 24 hours to form a negative electrode film layer, thereby obtaining a negative electrode sheet.

8. The preparation method according to claim 7, characterized in that, In the negative electrode slurry, the mass ratio of the negative electrode active material, epoxy resin, polyethyleneimine, polyphenylene sulfide, and conductive agent is (93~97):(1~3):(1~3):(0.5~1):(1~3); and / or, the polyethyleneimine includes branched polyethyleneimine and / or hyperbranched polyethyleneimine; and / or, the solid content of the negative electrode slurry is 40%~60%; and / or, the solvent includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, or N,N-dimethylacetamide; and / or, the preparation method of the negative electrode slurry includes: dissolving the polyphenylene sulfide in the solvent, and under stirring conditions, sequentially adding the epoxy resin, the polyethyleneimine, the conductive agent, and the negative electrode active material to mix and obtain the negative electrode slurry.

9. A battery, characterized in that, The negative electrode sheet includes any one of the negative electrode sheets as described in claims 4 to 6, or the negative electrode sheet prepared by the preparation method as described in claim 7 or 8.

10. An electrical appliance, characterized in that, Includes the battery as described in claim 9.

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