An environmentally friendly water-based low-temperature curing adhesive for use in an electric cell

Abstract

The application discloses an environmentally-friendly water-based low-temperature curing type adhesive for use in an electric core and belongs to the technical field of lithium battery materials.The environmentally-friendly water-based low-temperature curing type adhesive for use in an electric core comprises, in mass fractions, 10-30 parts of polyacrylic acid emulsion, 40-70 parts of acrylate grafted styrene-butadiene rubber, 5-20 parts of nano filler, 2-8 parts of water-based curing agent and 100-200 parts of deionized water, wherein the solid content of the polyacrylic acid emulsion is 20-30%, the grafting rate of the acrylate grafted styrene-butadiene rubber is 8-15 DEG C, and the nano filler is ultrasonically dispersed by using a dispersant.The adhesive provided by the application has the properties of environmental protection, high adhesion, volume expansion inhibition capacity for a silicon-based negative electrode, can meet the requirements of the heat resistance and low moisture of a diaphragm, realizes the adaptive application of the diaphragm and the positive and negative electrodes of the electric core, and improves the comprehensive performance and environmental protection of the lithium battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery material technology, and particularly relates to a water-based environmentally friendly low-temperature curing adhesive suitable for coating the positive and negative electrodes and separators of lithium-ion cells, its preparation method and application. Background Technology

[0002] Lithium-ion batteries are widely used in new energy vehicles, energy storage devices, and consumer electronics due to their advantages such as high energy density, long cycle life, and environmental friendliness. The binder inside the battery cell is one of the key auxiliary materials for lithium batteries, and its performance directly determines the rate performance, cycle stability, low-temperature performance, and safety performance of the battery.

[0003] Currently, the mainstream lithium battery binder in the industry is polyvinylidene fluoride (PVDF). However, PVDF requires the organic solvent N-methylpyrrolidone (NMP) for dissolution. NMP is toxic, highly volatile, and has high recycling costs, which not only increases production costs but also easily causes environmental pollution. At the same time, traditional aqueous binder systems have many technical defects: First, the SBR / CMC composite binder system has insufficient adhesion to the positive and negative electrode materials, leading to the shedding of active materials during cell cycling and reducing battery cycle life; second, when applied to silicon-based negative electrodes, it cannot effectively suppress the volume expansion of silicon-based materials during lithium insertion and extraction, resulting in rapid battery capacity decay and poor safety; third, binders used for separator coating are difficult to balance heat resistance and low moisture requirements. Insufficient heat resistance can easily lead to thermal shrinkage of the separator, causing battery short circuits, while excessive moisture affects cell interface stability and cycle performance.

[0004] Therefore, developing an integrated water-based binder that is environmentally friendly, has high adhesion, is compatible with the volume expansion suppression capability of silicon-based anodes, and can also take into account the heat resistance and low moisture requirements of the separator has become a key technological requirement for improving the overall performance of lithium batteries and promoting the green development of the industry. Summary of the Invention

[0005] To address the problems of existing lithium battery binders, such as the presence of toxic NMP in oily PVDF, insufficient adhesion of SBR / CMC, poor tolerance to volume expansion of silicon-based anodes, and difficulty in balancing the heat resistance and low moisture content of separators, this invention provides a water-based, environmentally friendly, low-temperature curing integrated binder. This binder enables the application of coatings for the positive and negative electrodes of battery cells and separators, thereby improving the overall performance and environmental friendliness of lithium batteries.

[0006] To achieve the purpose of this invention, this invention provides a water-based environmentally friendly low-temperature curing adhesive for use in battery cells, which is composed of the following raw materials in parts by weight: 10-30 parts of polyacrylic acid emulsion, 40-70 parts of acrylate-grafted styrene-butadiene rubber, 5-20 parts of nanofiller, 2-8 parts of water-based curing agent, and 100-200 parts of deionized water.

[0007] Furthermore, the polyacrylic acid emulsion is made by using acrylic acid monomers as raw materials, adding emulsifiers and water-soluble initiators, mixing with deionized water, and then polymerizing through a low-temperature emulsion polymerization reaction. After the reaction is completed, the solid content of the emulsion is 20% to 30%.

[0008] Further, by mass parts, the raw material components of the polyacrylic acid emulsion are: 15-25 parts acrylic monomer, 2-2.5 parts emulsifier, 0.3-0.4 parts water-soluble initiator, and 80-100 parts deionized water.

[0009] Furthermore, the grafting rate of the acrylate-grafted styrene-butadiene rubber is 8% to 15%.

[0010] Furthermore, the preparation method of the acrylate-grafted styrene-butadiene rubber is as follows: styrene-butadiene rubber, acrylate monomer, and initiator are added to deionized water, and the grafting reaction is carried out at 60~80℃ for 4~6 hours. After demulsification, washing, and drying, the product is obtained.

[0011] Further, by mass parts, the raw material composition of the acrylate-grafted styrene-butadiene rubber is: 45-50 parts of styrene-butadiene rubber, 5-6 parts of acrylate monomer, 0.5-0.6 parts of initiator, and 120-160 parts of deionized water.

[0012] Furthermore, the styrene-butadiene rubber is lithium-ion battery styrene-butadiene rubber, with a solid content of 45%–55%, a styrene to butadiene mass ratio of (20–30):(80–70), a viscosity of 50–300 mPa·s, a surface tension of 35–45 mN / m, and a particle size D. 50 The wavelength is 80~150nm; The acrylate monomer is one or more of hydroxyl-type acrylate monomers, carboxyl-type acrylate monomers, or epoxy-type acrylate monomers.

[0013] Furthermore, the nanofiller is one or more of nano-silica, nano-alumina, and nano-zinc oxide, with a particle size of 20~100nm; The water-based curing agent is a water-based modified amine epoxy curing agent or / and a water-based isocyanate curing agent.

[0014] This invention provides a method for preparing a water-based, environmentally friendly, low-temperature curing adhesive for use in battery cells, comprising the following steps: S1. Preparation of nanocomposite dispersion: Add nanofiller to deionized water, ultrasonically disperse for 30-60 min, add dispersant, and continue stirring for 1-2 h to obtain nanocomposite dispersion; S2. After mixing polyacrylic acid emulsion, acrylate-grafted styrene-butadiene rubber, and nanocomposite dispersion evenly, add water-based curing agent and deionized water, stir for 2-4 hours, and adjust the pH value to 7-9 to obtain water-based environmentally friendly low-temperature curing adhesive.

[0015] The water-based, environmentally friendly, low-temperature curing binder provided by this invention can be applied to the positive electrode slurry, negative electrode slurry, and separator coating of lithium-ion battery cells; In the positive electrode slurry, the mass ratio of the positive electrode active material, the conductive material and the water-based environmentally friendly low-temperature curing binder is (90~95):(2~5):(1~4). In the negative electrode slurry, the mass ratio of the negative electrode active material, the conductive material and the water-based environmentally friendly low-temperature curing binder is (85~93):(1~3):(3~10). In the diaphragm coating process, the water-based environmentally friendly low-temperature curing adhesive is diluted to a solid content of 1% to 3%.

[0016] The present invention has achieved the following beneficial effects: 1. The binder of this invention is a polyacrylic acid emulsion (PAA)-modified styrene-butadiene rubber (SBR)-nanocomposite system. Through the synergistic effect of PAA-modified SBR, combined with the physical reinforcement effect of nanofillers, it has excellent bonding performance and significantly improves the bonding force of lithium iron phosphate (LFP) / lithium manganese oxide (LMO) positive electrode and graphite / silicon-based negative electrode active materials, effectively preventing the active material from falling off during the cell cycle and improving the cycle stability of the battery.

[0017] 2. The binder of this invention, through the synergistic effect of the modified elastic network structure of SBR and the polar groups of PAA, can effectively buffer the volume expansion during the lithium insertion and extraction process of silicon-based anodes, reduce the capacity decay rate, and improve the cycle life and safety of silicon-based anode cells.

[0018] 3. After the adhesive of the present invention is coated on the surface of the diaphragm, it can form a dense and high-temperature resistant coating after low-temperature curing, which improves the thermal shrinkage performance of the diaphragm. At the same time, the water-based system preparation process can effectively control the moisture content of the adhesive, meet the low moisture requirements of the diaphragm, and avoid cell interface failure.

[0019] 4. The binder of this invention has low-temperature curing characteristics, and its curing temperature is only 80~120℃. Compared with traditional binders, it significantly reduces the energy consumption in the cell preparation process, is compatible with the process requirements of existing lithium battery water-based slurry production lines, and has prospects for industrial application.

[0020] 5. The binder of this invention is a water-based system, which completely replaces the traditional oil-based PVDF system. It does not require the use of toxic solvent NMP, thus eliminating the environmental pollution and recycling cost problems of NMP from the source, which meets the requirements of green development in the lithium battery industry. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] This invention provides a water-based, environmentally friendly, low-temperature curing adhesive for use in battery cells. It is a polyacrylic acid emulsion (PAA) – modified SBR – nanocomposite system, and its preparation method is as follows: (1) Preparation of modified SBR (i.e. acrylate-grafted SBR): By mass fraction, 45-50 parts of styrene-butadiene rubber, 5-6 parts of acrylate monomer, and 0.5-0.6 parts of initiator are added to 120-160 parts of deionized water. The grafting reaction is carried out at 60-80℃ for 4-6 hours. After demulsification, washing, and drying, acrylate-grafted styrene-butadiene rubber with a grafting rate of 8%-15% is obtained.

[0023] The modified SBR of this invention uses butadiene flexible segments as the elastic matrix and styrene rigid segments as the structural support. After grafting with acrylate monomers (grafting rate 8%–15%), polar groups such as ester groups (-COOR) and carboxyl groups (-COOH) are uniformly introduced onto the molecular chain. The butadiene segments endow the SBR with high elasticity and large deformation recovery ability, acting as an "elastic buffer layer" in the network; the grafted polar groups provide reaction sites for subsequent crosslinking and anchoring, solving the problems of insufficient polarity and incompatibility with PAA in ordinary SBR.

[0024] In this invention, the styrene-butadiene rubber is lithium-ion grade styrene-butadiene rubber with a solid content of 45%–55%, a styrene to butadiene mass ratio of (20–30):(80–70), a viscosity of 50–300 mPa·s, a surface tension of 35–45 mN / m, and a particle size D. 50 The wavelength range is 80-150 nm. Butadiene segments provide high elasticity (elongation at break > 300%), which can buffer the volume expansion of silicon-based lithium intercalation / deintercalation; styrene segments provide mechanical strength, ensuring that the electrode does not detach during rolling / cycling. However, styrene-butadiene rubber (SBR) lacks polar groups and is incompatible with the PAA emulsion in this invention, failing to form a synergistic network. Therefore, this invention grafts and modifies SBR to possess polarity, enabling it to be miscible and stable with the PAA emulsion, without delamination or demulsification.

[0025] Compared with conventional styrene-butadiene rubber, the lithium-ion grade styrene-butadiene rubber of the present invention has the following advantages: 1. Precise and controllable elasticity, suitable for silicon-based expansion buffering. The styrene-butadiene rubber of this invention has a mass ratio of (20~30):(80~70) for butadiene and styrene, an elongation at break >300%, and a Tg of -45~-30℃. Therefore, its elasticity is uniform and its deformation recovery is good. When used in this invention, it can ensure that the binder can continuously buffer the expansion of silicon-based materials by more than 300% of lithium insertion and extraction, and the electrode will not crack. Conventional methods have large fluctuations in the ratio, elongation is often less than 250%, and Tg is relatively high. In this invention, the elasticity is insufficient and the recovery is poor, and the electrode is prone to cracking and powdering when silicon expands.

[0026] 2. The styrene segment ratio in the styrene-butadiene rubber of this invention is precise, balancing elasticity and mechanical strength. It does not detach or shed powder during rolling and cycling, and its use in binders can ensure the integrity of the conductive network of lithium batteries. In contrast, conventional styrene-butadiene rubber with a high styrene content has high rigidity and poor elasticity, while a low styrene content will result in insufficient binder strength, easy powder shedding, and short cycle life.

[0027] 3. The styrene-butadiene rubber of this invention strictly controls Na. + K + Ca² + Mg² + The concentrations of these impurities are all ≤50ppm, free of heavy metals and impurity ions, making them less prone to cell self-discharge and short circuits, with stable interfaces and low cycle decay. In contrast, conventional styrene-butadiene rubber often contains impurity ions >200ppm, and has more residual emulsifiers and additives, which can easily lead to self-discharge and rapid capacity decay, posing safety hazards.

[0028] 4. The styrene-butadiene rubber of this invention has a uniform particle size of 80-150 nm, a pH of 6.5-8.0, and moderate viscosity, which stabilizes the grafting reaction of SBR, making it less prone to demulsification and stratification. The grafting rate can be precisely controlled within 8%-15%, and the modified rubber exhibits uniform polarity. In contrast, conventional styrene-butadiene rubber is prone to demulsification and stratification during grafting, with unstable grafting rates (<8% or >15%), uneven polarity after modification, incompatibility with PAA emulsions, and easy stratification.

[0029] This invention imposes rigid structural and functional requirements on acrylate monomers; not just any acrylate can be used. The essential functional groups and structures are as follows: Required polymerization sites containing carbon-carbon double bonds (C=C) to ensure free radical grafting with the styrene-butadiene rubber backbone for modification; core polar groups containing ester groups (-COOR), crucial for enhancing SBR polarity, achieving miscibility with PAA emulsions, and strengthening electrode adhesion; preferred auxiliary groups: may contain carboxyl groups (-COOH), hydroxyl groups (-OH), or epoxy groups to further strengthen the binding force with active materials and nanofillers, and adapt to the expansion suppression of silicon-based anodes. Therefore, non-polar, non-acrylate monomers without double bonds cannot achieve grafting modification and polarity enhancement, and cannot be used in this invention.

[0030] In specific embodiments of the present invention, the acrylate monomer is one or more of hydroxyl-type acrylate monomers, carboxyl-type acrylate monomers, or epoxy-type acrylate monomers. The present invention selects suitable functional acrylate monomers based on actual needs and the adhesive application system. For example, hydroxyl-type acrylate monomers include hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), and other hydroxyl-containing functional acrylate monomers, which can increase the crosslinking density with water-based curing agents and enhance the heat resistance and electrolyte resistance of the coating; carboxyl-type acrylate monomers include β-carboxyethyl acrylate, which can further strengthen polarity, improve electrode adhesion, and form a stronger synergistic effect with PAA; epoxy-type acrylate monomers include glycidyl methacrylate (GMA), which can improve the thermal stability of the separator coating, reduce the thermal shrinkage rate, and simultaneously improve the strength of the electrode structure.

[0031] This invention requires controlling the grafting rate of SBR within the range of 8% to 15% to avoid excessive rigidity and decreased elasticity, ensuring the introduction of sufficient polar groups while retaining the high elasticity of the SBR butadiene segments, thus achieving a balance between SBR polarity and elasticity. It ensures uniform miscibility between the modified SBR and PAA emulsion and nanofillers, preventing delamination and emulsion breakage, thus stabilizing the system. It optimizes the adhesion of the binder in this invention, achieving the required bonding strength for LFP cathodes and graphite / silicon-based anodes, preventing electrode powder shedding. Furthermore, it effectively buffers silicon volume expansion in conjunction with PAA, improving cell cycle life and safety. Finally, it ensures high crosslinking efficiency under low-temperature curing conditions of 80~120℃.

[0032] If the grafting rate of SBR is less than 8%, insufficient introduction of polar groups will result in poor compatibility between the modified SBR and PAA emulsion, leading to easy delamination and demulsification of the system. Furthermore, the adhesion to the positive and negative electrode active materials will decrease significantly, causing electrode powder shedding and active material detachment during cycling. Simultaneously, it cannot synergistically form an elastic network with PAA, resulting in the failure of silicon-based negative electrode volume expansion suppression and rapid cell capacity decay. The adhesion of the separator coating will also weaken, and its heat resistance and uniformity will fail to meet standards. If the grafting rate of SBR is higher than 15%, excessive grafted segments will destroy the SBR elastic network, causing a sharp drop in flexibility and excessive rigidity. It will also lose its ability to buffer the volume deformation of silicon-based lithium intercalation / deintercalation, making the electrode prone to cracking and significantly shortening cycle life. Moreover, its compatibility with nanofillers and water-based curing agents will decrease, resulting in poor slurry stability and increased defects in the separator coating. Therefore, only the acrylate-grafted SBR with a grafting rate of 8%–15% of this invention can simultaneously satisfy elasticity, polarity, and strength requirements.

[0033] (2) PAA emulsion preparation: by mass, 15-25 parts of acrylic monomer, 2-2.5 parts of emulsifier and 0.3-0.4 parts of water-soluble initiator are dissolved in 80-100 parts of deionized water, and emulsion polymerization is carried out at 70°C for 5 hours to obtain PAA emulsion, the solid content of which is controlled to be 20%-30%.

[0034] Ordinary PAA emulsions have low carboxyl group density, large molecular weight fluctuations, and insufficient polarity, making them unable to form strong hydrogen bonds / covalent bonds with electrode materials, and even less able to synergistically modify SBR to suppress silicon expansion. In contrast, the PAA emulsion of this invention uses acrylic monomers as the core raw material and is synthesized in situ via low-temperature emulsion polymerization. It is a lithium-ion battery-specific PAA emulsion, belonging to non-industrial grade polyacrylic acid. The PAA emulsion of this invention is rich in high-density carboxyl groups (-COOH), which are uniformly distributed. As strongly polar groups, these groups form strong hydrogen bonds with hydroxyl / oxygen atoms on the surface of silicon-based anodes, graphite, and conductive agents, firmly "anchoring" active particles and preventing them from detaching. It can also form intermolecular hydrogen bonds with the polar groups of modified SBR, achieving uniform miscibility between the two polymer chains and laying the foundation for network formation. Therefore, this PAA emulsion meets the triple requirements of high adhesion, low-temperature crosslinking, and anti-expansion in this invention.

[0035] The PAA emulsion of this invention has a linear polymer structure with uniform molecular chain distribution, and excellent compatibility with modified SBR and nanofillers; it is also resistant to electrolyte swelling, electrochemically stable, and does not undergo side reactions with lithium salt / electrolyte; it can also be precisely controlled by molecular weight to balance rigidity and toughness, and adapt to the volume deformation of silicon-based anodes.

[0036] This invention controls the solid content of the PAA emulsion to a range of 20%–30%, which significantly improves adhesion, ensures sufficient carboxyl-anchored active particles, and achieves the required bonding strength for LFP positive electrodes and graphite / silicon-based negative electrodes. It also ensures no powder shedding or active material detachment during cycling, with a capacity retention rate of ≥92% after 1000 cycles. Furthermore, it is uniformly miscible with modified SBR and nanofillers, without delamination or emulsion breakage, forming a stable three-dimensional interpenetrating network to guarantee long-term slurry stability. This invention enables rapid crosslinking at 80–120°C, resulting in high crosslinking density, a dense and high-temperature resistant coating, a diaphragm thermal shrinkage rate ≤1.2%, and strong resistance to electrolyte swelling of the electrode sheets. Through the synergistic effect of carboxyl anchoring and the elastic network of modified SBR, the volume expansion rate of the silicon-based negative electrode after 500 cycles is only 16.5%–18%, far lower than traditional binders, significantly extending cycle life.

[0037] If the solid content is less than 20%, there is too little solid matter, insufficient total carboxyl groups, and a significant decrease in adhesion, making it impossible to firmly anchor silicon-based / graphite particles, and causing easy powder shedding during cycling; insufficient polarity results in weak hydrogen bonding with modified SBR, making the system prone to delamination and demulsification; too low viscosity leads to excessively thin slurry, making coating prone to sagging, uneven electrode thickness, and easy cracking after drying; excessive moisture causes heat to evaporate during curing, resulting in insufficient local temperature, inadequate crosslinking, low density, and decreased adhesion and heat resistance. If the solid content is >30%, the solid concentration is too high, the carboxyl density is supersaturated, the molecular chains are excessively entangled, the emulsion viscosity increases sharply, and the fluidity is extremely poor. Too many carboxyl groups will react excessively with the curing agent, causing premature cross-linking in some areas, and the slurry is prone to gelation. If the viscosity is too high, the slurry is too thick, making mixing difficult and dispersion uneven. The coating resistance is high, which can easily clog the screen, cause the scraper to stick to the material, and make the electrode surface rough, affecting the conductive network. The molecular chains are tightly packed, which hinders the penetration of the curing agent, resulting in uneven cross-linking, local over-cross-linking, and easy cracking of the coating. The silicon-based negative electrode is prone to falling off when it expands.

[0038] The emulsifiers used in this invention are selected from one or more of the following: sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), sodium fatty alcohol polyoxyethylene ether sulfate (AES, such as AES-25), sodium n-alkyl sulfonate (SAS, C12~C14), fatty alcohol polyoxyethylene ether (AEO-9, AEO-10), nonylphenol polyoxyethylene ether (NP-7, NP-9, lithium battery low EO type), Tween 80 (polysorbate 80), and dodecyl betaine (BS-12). In specific embodiments of this invention, SDS or SDS / AEO-9 is preferred, as it is suitable for the low-temperature emulsion polymerization of this invention and does not affect the high carboxyl density of the PAA emulsion and the subsequent binder performance.

[0039] Preparation of nanocomposite dispersion: By mass, 5-20 parts of nanofiller are added to 40-60 parts of deionized water, and after ultrasonic dispersion for 30-60 min, 0.5-1.0 parts of dispersant are added, and stirring is continued for 1-2 h to obtain nanocomposite dispersion.

[0040] If micron-sized fillers are used in this invention, there is no nano-size effect, which cannot enhance adhesion and heat resistance; low-purity fillers contain impurity ions, leading to cell self-discharge and short circuits; undispersed fillers agglomerate to form defects, causing electrode powder shedding and uneven separator coating. Therefore, this invention uses high-purity, nano-sized fillers with controllable surface hydroxyl groups, which are pre-dispersed to achieve the requirements of physical reinforcement, heat resistance, and low water content.

[0041] In this invention, the nanofiller is a battery-grade high-purity nano-oxide prepared by a gas-phase / precipitation method, with a particle size of 20-100 nm, a purity >99.9%, and free of metal impurities and heavy metal ions. The nanofiller is one or more of nano-silica, nano-alumina, and nano-zinc oxide, with a particle size of 20-100 nm. Its surface is rich in hydroxyl groups, which can form hydrogen bonds with the polar groups of PAA and modified SBR to achieve stable dispersion and interfacial bonding; it can also be embedded in the network gaps as physical crosslinking points to improve the network modulus and deformation resistance; and it can also prevent polymer chain slippage, avoiding network relaxation and collapse during cycling.

[0042] The nanofiller used in this invention has a nanoscale particle size and high specific surface area, which can achieve physical reinforcement and heat resistance reinforcement; it has excellent thermal stability (decomposition temperature > 1000℃), which can improve the membrane's resistance to heat shrinkage; it is chemically inert and does not react with electrolyte or electrode materials, ensuring the stability of the cell interface; it can be ultrasonically dispersed uniformly without agglomeration or sedimentation.

[0043] (4) Mix the modified SBR from step (1), the PAA emulsion from step (2), and the nanocomposite dispersion from step (3), stir evenly, add the water-based curing agent, continue stirring for 2-4 hours, adjust the pH value of the system to 7-9, and obtain the water-based environmentally friendly low-temperature curing adhesive.

[0044] In this invention, the modified SBR in the adhesive provides an elastic network framework (flexible substrate); the PAA emulsion provides polar anchoring and rigid support (strong bonds and sites); nanofillers are used for physical reinforcement and network anchoring (network "reinforcing points"); and the water-based curing agent is used to build chemical crosslinks at low temperatures (network "locks"). During the low-temperature curing process at 80~120℃, the water-based curing agent (epoxy / isocyanate) undergoes a covalent crosslinking reaction with the carboxyl groups of PAA and the carboxyl / hydroxyl groups of modified SBR, covalently connecting the dispersed SBR elastic chains and PAA rigid chains into a continuous three-dimensional chemical network. The crosslinking points are evenly distributed, ensuring network strength without compromising the elasticity of SBR, achieving a balance of "rigid crosslinking + flexible buffering".

[0045] Existing solvent-based curing agents are toxic, damage water-based systems, and do not meet environmental protection requirements; room-temperature curing agents gel prematurely, making it impossible to prepare stable slurries; high-temperature curing agents (>150℃) easily damage the diaphragm and are not suitable for low-temperature processes. Therefore, this invention uses a low-temperature water-based curing agent that can achieve efficient crosslinking at 80~120℃, water-based stability, and no VOCs.

[0046] In this embodiment of the invention, the water-based curing agent is a water-based epoxy curing agent and / or a water-based isocyanate curing agent, which has excellent water dispersibility, is fully compatible with water-based systems, and does not precipitate or gel; it cures at low temperatures (80~120℃), matching the low-temperature curing process of this invention and reducing energy consumption; it is stable at room temperature storage, does not react prematurely with PAA or modified SBR, and meets the shelf life standard; after crosslinking, it forms a dense network, improving bonding strength, heat resistance, and electrolyte resistance.

[0047] The waterborne epoxy curing agent is a latent modified amine specifically for lithium batteries, containing amino (-NH2) or imino (-NH-), stable at room temperature, and rapidly crosslinks with PAA carboxyl groups at 60~120℃.

[0048] In this embodiment of the invention, the lithium battery-specific latent modified amines include waterborne epoxy addition amine curing agents, aliphatic amines / alicyclic amines modified by addition to epoxy monomers (such as modified ethylenediamine, modified isophorone diamine IPDA, modified m-phenylenediamine), polyether modified aliphatic amine curing agents, polyethylene glycol / polypropylene glycol modified aliphatic amines (such as polyether modified diethylenetriamine), waterborne amide curing agents, fatty acid modified polyamines (such as oleic acid modified diethylenetriamine), ketimine / aldehyde imine type latent amine curing agents, aliphatic amines modified by ketaldehyde condensation (such as acetone condensed ethylenediamine), and other waterborne epoxy curing agents containing amino or imine groups.

[0049] The waterborne isocyanate curing agent is a low-temperature closed-type aqueous dispersion that unblocks and releases active-NCO crosslinking at 80~120℃, with no VOC emissions.

[0050] It is worth noting that the deionized water used in this invention is lithium-ion battery-grade ultrapure water with a resistivity >18.2 MΩ. Ultrapure water, free of impurity ions, microorganisms, and particulate impurities, serves as the sole dispersion medium, dissolving and dispersing all raw materials, completely replacing the toxic solvent NMP, thus achieving environmental protection from the source. If ordinary tap water or pure water is used in this invention, its impurity ions can lead to short circuits, capacity decay, and cycle failure in the battery cells. Therefore, only ultrapure water can meet the requirements for lithium battery production in this invention.

[0051] In this invention, the modified SBR elastic chains and PAA polar chains interpenetrate each other without chemical grafting, relying solely on hydrogen bonds and covalent bonds to form a three-dimensional interpenetrating network (IPN) structure. The modified SBR forms a continuous elastic phase, providing deformation buffering capacity; the PAA forms a continuous polar rigid phase, providing particle anchoring and structural strength; the curing agent and nanofillers form uniform crosslinking points to construct stable network nodes, thereby enabling the entire invention to form a recoverable elastic network. This allows the cured layer of this invention to quickly rebound after being stretched, without permanent deformation.

[0052] The water-based, environmentally friendly, low-temperature curing binder provided by this invention can be applied to the positive electrode slurry, negative electrode slurry, and separator coating of lithium-ion battery cells.

[0053] The following describes the specific application of the water-based, environmentally friendly, low-temperature curing binder of this invention in lithium-ion battery cells: Preparation of positive electrode slurry: The positive electrode active material (LFP / LMO), conductive agent and binder of the present invention are mixed in a mass ratio of (90~95):(2~5):(1~4), and deionized water is added and stirred evenly to obtain a positive electrode slurry; the positive electrode slurry is coated on the surface of the positive electrode current collector, dried and rolled to obtain a positive electrode sheet.

[0054] Preparation of negative electrode slurry: The negative electrode active material (graphite / silicon-based), conductive agent, and binder of the present invention are mixed in a mass ratio of (85~93):(1~3):(3~10), and deionized water is added and stirred evenly to obtain a negative electrode slurry; the negative electrode slurry is coated on the surface of the negative electrode current collector, dried, and rolled to obtain a negative electrode sheet.

[0055] Silicon-based anodes experience volume expansion exceeding 300% during lithium insertion / extraction. The three-dimensional interpenetrating network of this invention provides constraint through a triple mechanism: First, elastic buffering, where the SBR elastic segments stretch synchronously with the silicon particle expansion, absorbing deformation stress and preventing electrode cracking; second, polarity anchoring, where PAA carboxyl groups firmly adsorb the silicon particles, preventing particle pulverization and detachment from the conductive network; and third, network constraint, where the three-dimensional covalent + physical network limits excessive silicon particle expansion, maintaining the integrity of the electrode structure. Using the binder of this invention in lithium-ion anode slurry results in a volume expansion rate of only 16.5%–18% for silicon-based anodes after 500 cycles, significantly lower than that of traditional PVDF (35%) and SBR / CMC (40%).

[0056] The butadiene segments of the modified SBR of this invention form a continuous elastic network with high elongation and deformation recovery capability, serving as a flexible framework to buffer expansion. This network specifically absorbs the volume change stress during silicon lithium insertion / extraction, providing an elastic buffer (responsible for "resisting deformation"). The high-density carboxyl groups (-COOH) of the PAA molecular chain are highly polar groups that can form strong hydrogen bonds with silicon particles, graphite, and current collector surfaces. These act as anchoring points to fix active particles, preventing them from pulverizing or detaching after expansion, thus providing highly polar anchoring groups (responsible for "grabbing particles"). Therefore, this invention utilizes the synergistic buffering of volume expansion by modified SBR and PAA, the principle of which is as follows: S1. Initial Expansion Stage: Anchoring + Pre-buffering When silicon lithium intercalation begins to expand, the PAA carboxyl groups firmly "grab" the silicon particles to prevent them from loosening and shifting directly; at the same time, the modified SBR elastic chain is slightly stretched to initially bear the expansion stress. The two work together to prevent the particles from moving around.

[0057] S2. Peak Expansion Period: Elastic stress absorption + interlocking structure ensures significant expansion of silicon volume (up to approximately 300%). The modified SBR elastic network is fully stretched, absorbing all expansion stress like a spring without breaking. At this time, the PAA polar groups form intermolecular hydrogen bonds with the grafted ester / carboxyl groups of the modified SBR, locking the elastic chain and anchoring chain together. This ensures that the SBR can buffer freely while preventing silicon particles from detaching from the conductive network, thus preventing the electrode from cracking or shedding powder.

[0058] S3. Delithiation and contraction period: Elastic recovery + resetting solid particles silicon delithiation and contraction, modified SBR elastic chains quickly rebound, driving silicon particles back to their original positions; PAA continues to anchor, maintaining particle spacing and conductive pathways, avoiding gaps and network collapse after contraction.

[0059] Preparation of diaphragm coating: The adhesive of the present invention is diluted to a solid content of 1% to 3%, coated on the surface of the diaphragm, and cured at a low temperature of 80 to 120°C to obtain the coated diaphragm.

[0060] Cell assembly: After the positive electrode sheet, coated separator, and negative electrode sheet are wound or stacked, electrolyte is injected, and lithium-ion cells are produced through processes such as encapsulation, electrolyte injection, formation, and capacity testing.

[0061] The water-based, environmentally friendly, low-temperature curing adhesive for the battery cell of the present invention will be described below with reference to specific embodiments.

[0062] Example 1 The preparation method of the water-based environmentally friendly low-temperature curing adhesive for the battery cell of this invention is as follows: (1) Preparation of modified SBR: 50 parts of styrene-butadiene rubber (selected from BASF's Styronal® D819), 5 parts of methyl acrylate, and 0.5 parts of ammonium persulfate initiator were added to 120 parts of deionized water. The grafting reaction was carried out by stirring at 70°C for 5 hours. Demulsification was carried out by electrolyte salt precipitation. The lithium battery grade ultrapure water was centrifuged and washed at 40~50°C. After vacuum drying at 50°C for 10 hours, a modified SBR with a grafting rate of 10% was obtained.

[0063] In the above demulsification process, the demulsifier is a 10wt% calcium chloride aqueous solution. The demulsifier is added slowly (completely within 60 minutes) while stirring at a rate of 300 r / min. Gentle stirring is used to prevent excessive breakage of the colloidal particles. Demulsification is performed at room temperature to avoid degradation of grafted chains due to high temperature. Once the emulsion is completely demulsified, white flocculent colloidal particles appear, and the upper clear liquid is transparent. After standing for 30 minutes, the colloidal particles are allowed to settle and precipitate completely.

[0064] During the centrifugal washing process described above, the centrifugation speed is 4000 r / min and the centrifugation time is 10 min / cycle. The washing process ends when the conductivity of the washing waste liquid is ≤10 μS / cm.

[0065] (2) PAA emulsion preparation: 15 parts acrylic acid, 2 parts sodium dodecyl sulfate emulsifier and 0.3 parts ammonium persulfate initiator were dissolved in 80 parts deionized water and emulsion polymerized at 70°C for 5 hours to obtain PAA emulsion with a solid content of 25%.

[0066] (3) Preparation of nanocomposite dispersion: 8 parts of nano silica (particle size of 30~50nm) were added to 40 parts of deionized water and ultrasonically dispersed for 40min. 0.5 parts of polyethylene glycol (PEG-400) dispersant were added and stirred at a stirring rate of 800r / min for 1.5h to obtain nanocomposite dispersion.

[0067] (4) Adhesive compounding: Mix the above 50 parts modified SBR, 15 parts PAA emulsion and nanocomposite dispersion, stir at 800 r / min for 3 h, add 3 parts water-based modified cycloaliphatic amine epoxy curing agent (Wanamine® A102 of Wanhua Chemical) and 80 parts deionized water, continue stirring for 3 h, adjust the pH value to 8 with ammonia water to obtain the adhesive.

[0068] The steps for manufacturing battery cells are as follows: Positive electrode preparation: LFP positive electrode active material, conductive carbon black, and the binder prepared in Example 1 are mixed in a ratio of 94:3:3 to form a slurry, which is then coated on the surface of aluminum foil, dried at 100°C, and rolled to obtain a positive electrode sheet.

[0069] Negative electrode preparation: Graphite / silicon-based composite negative electrode active material (silicon content 10%), conductive carbon black, and binder prepared in Example 1 are mixed in a ratio of 90:2:8 to form a slurry, which is then coated onto the surface of copper foil, dried at 100°C, and rolled to obtain a negative electrode sheet.

[0070] Separator coating: The adhesive prepared in Example 1 was diluted with lithium-ion grade ultrapure water to a solid content of 2%, coated on the surface of PP separator, and cured at 100°C for 2 hours to obtain a coated separator.

[0071] Cell assembly: winding into cells, liquid injection, formation, and performance testing.

[0072] Tests showed that the capacity retention rate was 92.5% after 1000 cycles at 25℃, 78% at -20℃, the volume expansion rate of the silicon-based anode after 500 cycles was 18%, and the thermal shrinkage rate of the diaphragm (150℃ / 2h) was 1.2%.

[0073] Example 2 (1) Preparation of modified SBR: 45 parts of styrene-butadiene rubber (WanSBR® L106 of Wanhua Chemical), 6 parts of butyl acrylate, and 0.6 parts of ammonium persulfate initiator were added to 160 parts of deionized water. The grafting reaction was carried out by stirring at 65°C for 4.5 h. Demulsification was carried out by electrolyte salt precipitation. The lithium battery grade ultrapure water was centrifuged and washed at 40~50°C. After vacuum drying at 50°C for 10 h, a modified SBR with a grafting rate of 12% was obtained.

[0074] (2) PAA emulsion preparation: 25 parts acrylic acid, 2.5 parts sodium dodecyl sulfate emulsifier and 0.4 parts ammonium persulfate initiator were dissolved in 100 parts deionized water and emulsion polymerized at 70°C for 5 hours to obtain PAA emulsion with a solid content of 28%.

[0075] (3) Preparation of nanocomposite dispersion: 12 parts of nano alumina (particle size of 30~60nm) were added to 60 parts of deionized water, ultrasonically dispersed for 50min, 1.0 part of polyethylene glycol (PEG-400) dispersant was added, and stirred for 2h to obtain nanocomposite dispersion.

[0076] (4) Adhesive compounding: Mix the above 45 parts modified SBR, 25 parts PAA emulsion and nanocomposite dispersion at a stirring rate of 800 r / min for 3.5 h, add 5 parts blocked waterborne hexamethylene diisocyanate trimer curing agent and 100 parts deionized water, continue stirring for 2.5 h, adjust the pH value to 7.5 with ammonia water to obtain the adhesive.

[0077] The cell preparation method is the same as in Example 1, and the specific details are as described in Example 1.

[0078] Tests showed that the capacity retention rate was 93.2% after 1000 cycles at 25℃, 79.5% at -20℃, the volume expansion rate of the silicon-based anode after 500 cycles was 16.5%, and the thermal shrinkage rate of the diaphragm (150℃ / 2h) was 1.0%.

[0079] Comparative Example 1 LFP / silicon-based cells were prepared using a conventional oil-based PVDF binder, as described in Example 1. Testing showed that the capacity retention rate was 85% after 1000 cycles at 25°C, 65% at -20°C, the volume expansion rate of the silicon-based negative electrode was 35% after 500 cycles, and the membrane thermal shrinkage rate (150°C / 2h) was 3.8%.

[0080] Comparative Example 2 LFP / silicon-based cells were prepared using a conventional oil-based SBR / CMC binder, as described in Example 1. Testing showed that the capacity retention rate was 82% after 1000 cycles at 25°C, 62% at -20°C, the volume expansion rate of the silicon-based negative electrode was 40% after 500 cycles, and the membrane thermal shrinkage rate (150°C / 2h) was 4.5%.

[0081] Comparative Example 3 Unlike Example 1, this comparative example uses styrene-butadiene rubber directly without acrylate grafting.

[0082] Testing revealed that the capacity retention rate after 1000 cycles at 25℃ was 79.2%, the capacity retention rate at -20℃ was 60.5%, the volume expansion rate of the silicon-based anode after 500 cycles was 42%, and the membrane thermal shrinkage rate (150℃ / 2h) was 5.1%. These results indicate that the unmodified SBR lacks polar groups, is incompatible with PAA, exhibits extremely poor adhesion, and cannot suppress silicon expansion.

[0083] Comparative Example 4 Unlike Example 1, this comparative example controls the grafting rate of the modified SBR to 5% by adjusting the amount of methyl acrylate.

[0084] Testing revealed that the capacity retention rate after 1000 cycles at 25℃ was 82.7%, the capacity retention rate at -20℃ was 64.3%, the volume expansion rate of the silicon-based anode after 500 cycles was 36%, and the thermal shrinkage rate of the diaphragm (150℃ / 2h) was 3.9%. The results indicate that insufficient introduction of polar groups resulted in poor system compatibility and a significant decrease in adhesion and expansion suppression capabilities.

[0085] Comparative Example 5 Unlike Example 1, this comparative example controls the grafting rate of the modified SBR to 18% by adjusting the amount of methyl acrylate.

[0086] Testing revealed that the capacity retention rate after 1000 cycles at 25℃ was 81.5%, the capacity retention rate at -20℃ was 63.1%, the volume expansion rate of the silicon-based anode after 500 cycles was 38%, and the thermal shrinkage rate of the separator (150℃ / 2h) was 4.2%. These results indicate that excessive grafting ratios damage the elasticity of the SBR, excessive rigidity fails to buffer silicon expansion, and the electrode is prone to cracking.

[0087] Comparative Example 6 Unlike Example 1, the nanofiller in this comparative example is used directly without the addition of a dispersant or ultrasonic dispersion treatment.

[0088] Testing revealed that the capacity retention rate after 1000 cycles at 25℃ was 83.4%, the capacity retention rate at -20℃ was 65.7%, the volume expansion rate of the silicon-based anode after 500 cycles was 34%, and the thermal shrinkage rate of the diaphragm (150℃ / 2h) was 3.6%. The results indicate that the nanofillers severely agglomerated, failing to form a uniform reinforcing network, resulting in decreased adhesion and heat resistance.

[0089] Comparative Example 7 The difference from Example 1 is that in step (2) of this comparative example, methacrylic acid is used instead of acrylic acid.

[0090] Testing revealed that the capacity retention rate after 1000 cycles at 25℃ was 84.1%, the capacity retention rate at -20℃ was 66.2%, the volume expansion rate of the silicon-based anode after 500 cycles was 32%, and the membrane thermal shrinkage rate (150℃ / 2h) was 3.3%. These results indicate that methacrylic acid exhibits high steric hindrance, low carboxyl group density, and weak anchoring ability, thus failing to synergistically suppress expansion in the SBR.

[0091] Comparative Example 8 Compared with Example 1, the difference is that in step (3) of this comparative example, 500nm micron-sized alumina is used instead of nano-alumina.

[0092] Testing revealed that the capacity retention rate after 1000 cycles at 25℃ was 82.9%, the capacity retention rate at -20℃ was 64.8%, the volume expansion rate of the silicon-based anode after 500 cycles was 35%, and the thermal shrinkage rate of the diaphragm (150℃ / 2h) was 3.8%. The results indicate a lack of nanoscale effect, failure of physical reinforcement, and substandard heat resistance and adhesion performance.

[0093] Comparative Example 9 The difference from Example 1 is that in step (4) of this comparative example, the pH is adjusted to 5.0.

[0094] Testing revealed that the capacity retention rate after 1000 cycles at 25℃ was 80.6%, the capacity retention rate at -20℃ was 61.9%, the volume expansion rate of the silicon-based anode after 500 cycles was 39%, and the membrane thermal shrinkage rate (150℃ / 2h) was 4.7%. The results indicate that an acidic environment leads to emulsion instability, hindered cross-linking, easy gelation of the slurry, and a significant decrease in performance.

[0095] Comparative Example 10 The difference from Example 1 is that in step (4) of this comparative example, no modified SBR is added, and only PAA emulsion is used as the binder.

[0096] Testing revealed that the capacity retention rate after 1000 cycles at 25℃ was 77.3%, the capacity retention rate at -20℃ was 59.2%, the volume expansion rate of the silicon-based anode after 500 cycles was 45%, and the thermal shrinkage rate of the diaphragm (150℃ / 2h) was 5.4%. The results clearly show that the lack of an elastic network completely fails to buffer silicon expansion, leading to severe electrode cracking and powder shedding.

[0097] Comparative Example 11 The difference from Example 1 is that in step (4) of this comparative example, no PAA emulsion is added, and only modified SBR is used as the binder.

[0098] Testing revealed that the capacity retention rate after 1000 cycles at 25℃ was 78.5%, the capacity retention rate at -20℃ was 60.1%, the volume expansion rate of the silicon-based anode after 500 cycles was 43%, and the membrane thermal shrinkage rate (150℃ / 2h) was 5.2%. The results indicate that the device lacks strong polar anchoring groups, has poor particle fixation, and experiences significant detachment of active material during cycling.

[0099] Comparative Example 12 Compared with Example 1, the difference is that in step (4) of this comparative example, no nanocomposite dispersion is added, that is, the binder is not reinforced by nanofillers.

[0100] Testing revealed that the capacity retention rate after 1000 cycles at 25℃ was 85.6%, the capacity retention rate at -20℃ was 67.4%, the volume expansion rate of the silicon-based anode after 500 cycles was 31%, and the thermal shrinkage rate of the diaphragm (150℃ / 2h) was 3.2%. The results indicate that without physical reinforcement and heat-resistant strengthening, the bonding strength and heat resistance of the diaphragm are significantly reduced.

[0101] Comparative Example 13 Compared with Example 1, the difference is that conventional industrial-grade styrene-butadiene rubber (SBR1502 from Qilu Petrochemical) is used to replace the lithium battery styrene-butadiene rubber of the present invention, while the other raw materials, proportions and preparation steps are completely consistent with Example 1.

[0102] Preparation steps Preparation of modified SBR: 50 parts of conventional industrial grade styrene-butadiene rubber, 5 parts of methyl acrylate, and 0.5 parts of ammonium persulfate were added to 120 parts of deionized water and the grafting reaction was carried out at 70°C for 5 hours. After demulsification, washing, and drying, the actual grafting rate was only 5% to 7% (far lower than the target range of 8% to 15% of this invention).

[0103] The preparation of PAA emulsion, nanocomposite dispersion, and binder compounding are all exactly the same as in Example 1.

[0104] Cell fabrication: Completely consistent with Example 1.

[0105] Tests showed that the capacity retention rate was 78.8% after 1000 cycles at 25℃, 59.8% at -20℃, the volume expansion rate of the silicon-based anode after 500 cycles was 41%, and the thermal shrinkage rate of the diaphragm (150℃ / 2h) was 5.0%.

[0106] Results Analysis: Conventional styrene-butadiene rubber (SBR) has a high styrene content and insufficient elasticity (low elongation at break), which cannot effectively buffer the volume expansion of silicon-based anodes; the high content of impurity ions easily triggers side reactions at the cell interface, accelerating capacity decay; the large particle size and uneven distribution lead to poor stability of acrylate grafting reaction, low grafting rate, insufficient polarity after modification, poor compatibility with PAA emulsion, and easy system stratification; ultimately, it exhibits weak adhesion, failure of silicon expansion inhibition, and poor heat resistance of the separator, with overall performance far inferior to Example 1, but close to that of Comparative Example 3 (unmodified SBR).

[0107] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A water-based, environmentally friendly, low-temperature curing adhesive for use in battery cells, characterized in that, It is composed of the following raw materials in parts by weight: 10-30 parts of polyacrylic acid emulsion, 40-70 parts of acrylate-grafted styrene-butadiene rubber, 5-20 parts of nanofiller, 2-8 parts of water-based curing agent, and 100-200 parts of deionized water.

2. The water-based environmentally friendly low-temperature curing adhesive for the battery cell according to claim 1, characterized in that, The polyacrylic acid emulsion is made by using acrylic acid monomers as raw materials, adding emulsifiers and water-soluble initiators, mixing with deionized water, and then polymerizing through a low-temperature emulsion polymerization reaction. After the reaction is completed, the solid content of the emulsion is 20% to 30%.

3. The water-based environmentally friendly low-temperature curing adhesive for the battery cell according to claim 2, characterized in that, The raw material components of the polyacrylic acid emulsion, by mass parts, are: 15-25 parts acrylic monomer, 2-2.5 parts emulsifier, 0.3-0.4 parts water-soluble initiator, and 80-100 parts deionized water.

4. The water-based environmentally friendly low-temperature curing adhesive for the battery cell according to claim 1, characterized in that, The grafting rate of the acrylate-grafted styrene-butadiene rubber is 8% to 15%.

5. The water-based environmentally friendly low-temperature curing adhesive for the battery cell according to claim 4, characterized in that, The method for preparing acrylate-grafted styrene-butadiene rubber is as follows: styrene-butadiene rubber, acrylate monomer, and initiator are added to deionized water, and the grafting reaction is carried out at 60-80°C for 4-6 hours. After demulsification, washing, and drying, the product is obtained.

6. The water-based environmentally friendly low-temperature curing adhesive for the battery cell according to claim 5, characterized in that, The raw material composition of the acrylate-grafted styrene-butadiene rubber, by mass parts, is: 45-50 parts styrene-butadiene rubber, 5-6 parts acrylate monomer, 0.5-0.6 parts initiator, and 120-160 parts deionized water.

7. The water-based environmentally friendly low-temperature curing adhesive for the battery cell according to claim 6, characterized in that, The styrene-butadiene rubber mentioned is lithium-ion battery styrene-butadiene rubber, with a solid content of 45% to 55%, a styrene to butadiene mass ratio of (20 to 30):(80 to 70), a viscosity of 50 to 300 mPa·s, a surface tension of 35 to 45 mN / m, and a particle size D. 50 The wavelength is 80~150nm; The acrylate monomer is one or more of hydroxyl-type acrylate monomers, carboxyl-type acrylate monomers, or epoxy-type acrylate monomers.

8. The water-based environmentally friendly low-temperature curing adhesive for the battery cell according to claim 1, characterized in that, The nanofiller is one or more of nano-silica, nano-alumina, and nano-zinc oxide, with a particle size of 20~100nm; The water-based curing agent is a water-based modified amine epoxy curing agent or / and a water-based isocyanate curing agent.

9. A method for preparing a water-based environmentally friendly low-temperature curing adhesive for use in a battery cell as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Preparation of nanocomposite dispersion: Add nanofiller to deionized water, ultrasonically disperse for 30-60 min, add dispersant, and continue stirring for 1-2 h to obtain nanocomposite dispersion; S2. After mixing polyacrylic acid emulsion, acrylate-grafted styrene-butadiene rubber, and nanocomposite dispersion evenly, add water-based curing agent and deionized water, stir for 2-4 hours, and adjust the pH value to 7-9 to obtain water-based environmentally friendly low-temperature curing adhesive.

10. The application of a water-based, environmentally friendly, low-temperature curing binder prepared by the method described in claim 9 in lithium-ion battery cells, characterized in that, It is used in the positive electrode slurry, negative electrode slurry, and separator coating of lithium-ion battery cells.