Crosslinking type polyacrylic acid / polyvinyl alcohol composite binder as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion battery key materials, in particular to a cross-linked polyacrylic acid / polyvinyl alcohol composite binder and a preparation method and application thereof. The binder is prepared by introducing N, N-dimethylformamide into a water-soluble acrylic monomer, an ethylenically-bond-containing acrylonitrile monomer and a vinyl ester monomer through ternary polymerization; n, N-methylene bisacrylamide (MBA) forms a rigid-flexible three-dimensional chemical cross-linked network, and then the rigid-flexible three-dimensional chemical cross-linked network and polyvinyl alcohol (PVA) construct an interpenetrating network (IPN) through hydrogen-bond interaction. The dual cross-linked network has the structural stability of chemical cross-linking and the dynamic adaptability of physical cross-linking, when the charging and discharging volume of the silicon-based negative electrode changes, stress is dissipated through network elastic deformation, meanwhile, interface bonding is strengthened through the ionic bond action of a lithium carboxylate group, active substance falling and electrode pulverization are inhibited, and the service life of the silicon-based negative electrode is prolonged. And the cycle life of the high-energy-density lithium ion battery is remarkably prolonged.

Description

Technical Field

[0001] This invention relates to the field of key materials technology for lithium-ion batteries, specifically a cross-linked polyacrylic acid / polyvinyl alcohol composite binder, its preparation method, and its application. Background Technology

[0002] Driven by the global energy transition and the rapid development of the electric vehicle industry, the demand for high-energy-density lithium-ion batteries is becoming increasingly urgent. Traditional graphite anodes, due to their low theoretical specific capacity (372 mAh / g), are no longer sufficient to meet the technical requirements of next-generation batteries breaking the 400 Wh / kg energy density barrier. Silicon-based anodes, with their high theoretical specific capacity of 4200 mAh / g and abundant crustal reserves, have become one of the most promising anode materials. However, during lithium intercalation, they undergo a dramatic volume expansion exceeding 300%, leading to the pulverization and shedding of active materials and electrode structure failure, becoming a core challenge restricting their industrialization. This places stringent requirements on binders: they must simultaneously possess strong interfacial adhesion to fix silicon particles, high elastic modulus to resist expansion stress, high elongation at break to buffer volume changes, and excellent electrolyte stability to maintain long-term cycle performance.

[0003] Currently, commercial binders are mainly divided into two categories: solvent-based (such as PVDF) and aqueous (such as PAA and SBR), both of which have significant technical bottlenecks. Solvent-based binders rely on toxic organic solvents such as NMP, resulting in severe pollution and high costs during the production process. More importantly, their bonding strength with silicon particles is insufficient due to van der Waals forces, and their low elastic modulus cannot support the high loading applications of silicon-based anodes. While aqueous binders solve the environmental problem, their core representative, PAA, suffers from a contradictory "rigid yet brittle" performance. Its elastic modulus is greater than 1 GPa, but its elongation at break is less than 30%, making it unable to adapt to the tensile deformation of silicon and prone to interface cracking. Furthermore, its swelling rate in the electrolyte is greater than 30%, making the bonded network prone to disintegration during long-term cycling. Styrene-butadiene rubber (SBR), another commonly used water-based adhesive, has a certain degree of flexibility, but its bonding strength relies on physical adsorption and mechanical winding. It is not effective in anchoring silicon particles with high specific surface area, and particles are prone to falling off. In addition, SBR molecular chains lack polar groups, have weak chemical interaction with silicon particles, and have poor resistance to electrolytes, making them prone to swelling and aging in electrolytes.

[0004] Novel binder technologies attempt to solve the above problems by physically blending rigid and flexible components (such as PAN and PEG), but poor compatibility leads to phase separation, causing stress concentration and decreased fatigue resistance. Interfacial bonding reinforcement relies only on single hydrogen or ionic bonds and lacks multi-interface synergistic design, so interfacial failure still accounts for more than half of the electrode failure modes.

[0005] In summary, how to prepare composite binders with strong interfacial adhesion, high elastic modulus, high elongation at break and excellent electrolyte stability is a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive, its preparation method and application. The composite adhesive prepared by this method has the characteristics of strong interfacial adhesion, high elastic modulus, high elongation at break and excellent electrolyte stability, thus overcoming the drawbacks of the adhesives provided by the existing technology.

[0007] To solve the above-mentioned technical problems, the present invention provides a method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive, comprising the following steps: A mixed monomer solution is obtained by uniformly mixing water-soluble acrylic monomers, acrylonitrile monomers containing olefin bonds, and vinyl ester monomers. Mix 1 / 6 to 1 / 2 of the total volume of the mixed monomer solution with deionized water to obtain a water-monomer premix, wherein the weight of deionized water is 80% to 95% of the total weight of the water-monomer premix. Under a nitrogen atmosphere, add a crosslinking agent and initiator solution one to the water-monomer premix to initiate the reaction, and then simultaneously add the remaining mixed monomer solution and initiator solution two. After the reaction is complete, filter to obtain powder. After washing the powder with deionized water, adjust the pH value to 7.0 to 9.0 with an inorganic alkali solution, and then dilute with deionized water to obtain a polyacrylic acid solution with a mass percentage of 5.0% to 20.0%.

[0008] Prepare a polyvinyl alcohol aqueous solution with a mass percentage of 5.0% to 20.0%, and then crosslink the polyvinyl alcohol aqueous solution with a polyacrylic acid solution at a temperature of 60℃ to 80℃ for 5h to 24h to obtain a polyacrylic acid / polyvinyl alcohol composite adhesive.

[0009] When the pH value is 7-9, most of the carboxyl groups (-COOH) in acrylic acid have been converted into carboxylates (-COO). - This ensures that the polymer dissolves well in water; when the pH is below 7, neutralization is insufficient, resulting in poor polymer solubility and easy precipitation. When the pH is above 9, the high pH environment is not conducive to the formation of a stable and dense solid electrolyte interphase (SEI) film, leading to continuous thickening of the SEI film, increased impedance, and accelerated irreversible consumption of active lithium, which seriously affects the battery's initial efficiency and cycle life.

[0010] Preferably, the weight percentages of the water-soluble acrylic monomer, the olefin-containing acrylonitrile monomer, and the vinyl ester monomer are 25%~45%: 35%~70%: 5%~20%.

[0011] Water-soluble acrylic monomers provide adhesion and dispersibility, olefin-containing acrylonitrile monomers enhance mechanical strength and electrolyte resistance, and vinyl ester monomers improve flexibility. A balanced ratio of these three components is necessary to meet the multiple requirements of the binder. The ratio range of this terpolymer binder is a comprehensive balance result of molecular design, electrochemical requirements, and process feasibility. Exceeding this range will amplify a performance weakness (such as excessive brittleness, excessive swelling, or excessive softness), thereby affecting the mechanical integrity, interfacial stability, or ion transport efficiency of the electrode, ultimately manifesting as capacity decay, impedance increase, or shortened cycle life.

[0012] Preferably, the water-soluble acrylic monomer is at least one of acrylic acid, methacrylic acid, styrene sulfonic acid, vinyl sulfonic acid, itaconic acid, fumaric acid, or maleic acid; the olefin-containing acrylonitrile monomer is at least one of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-bromoacrylonitrile, α-ethylacrylonitrile, or styrene; and the vinyl ester monomer is at least one of methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, butyl acrylate, butyl methacrylate, isooctyl acrylate, lauryl methacrylate, or vinyl acetate.

[0013] Preferably, the total amount of initiator is 0.01% to 1% of the mixed monomer solution, the amount of initiator added in initiator solution one is 1 / 2 to 2 / 3 of the total amount of initiator, the amount of initiator added in initiator solution two is 1 / 3 to 1 / 2 of the total amount of initiator, and the mass percentage of initiator in both initiator solution one and initiator solution two is 0.01% to 20%.

[0014] Insufficient initiator dosage leads to difficulty in reaction initiation, low monomer conversion rate, and the formation of polymers with excessively high molecular weight and uneven distribution. This results in excessively high slurry viscosity and potential gelation, severely impacting processing coating properties and electrode uniformity. Conversely, excessive dosage poses a risk of explosive polymerization, causing thermal runaway in the reaction. Furthermore, excessive free radicals exacerbate chain termination, generating polymers with excessively low molecular weight, insufficient strength, and overly broad distribution. This prevents the binder from effectively buffering the volume expansion of the negative electrode material, ultimately compromising the battery's cycle life and safety. Therefore, precisely controlling the dosage within the range of 0.01% to 1% of the total monomer mass in the mixed monomer solution is crucial for balancing reaction safety, processing performance, and final battery application performance.

[0015] If the concentrations of initiator solution one and initiator solution two are too high (>20%), the high concentration solution is very likely to cause the absolute amount of initiator added to run out of control in a short time due to small fluctuations in the flow rate during dropwise addition. This will cause a sudden increase in the local free radical concentration, thereby destroying the polymerization stability and greatly increasing the risk of violent exothermic reaction (burst polymerization) and irregular branching or even gelation of product molecular chains. If the concentration is too low (<0.01%), a very large amount of solvent needs to be introduced, which will seriously dilute the reaction system. This will not only significantly reduce the reaction efficiency, increase energy consumption and subsequent processing costs, but may also affect the polymerization rate, molecular weight growth and even the composition and performance consistency of the final product.

[0016] Preferably, the initiator is at least one of ammonium persulfate, sodium persulfate, or potassium persulfate.

[0017] Preferably, the amount of crosslinking agent added is 0.01% to 1% of the total mass of monomers in the mixed monomer solution, and the crosslinking agent is N,N-methylenebisacrylamide.

[0018] N,N-methylenebisacrylamide molecules contain active double bonds at both ends, enabling efficient copolymerization with three monomers in post-initiated free radical polymerization to form stable covalent cross-links, ensuring the uniformity of the three-dimensional network structure. Its excellent water solubility ensures complete compatibility with aqueous reaction systems, avoiding localized uneven cross-linking issues caused by insufficient solubility.

[0019] When the amount of crosslinking agent added is less than 0.01% of the total mass of monomers in the mixed monomer solution, there are insufficient crosslinking points between polymer molecular chains, making it impossible to form a stable three-dimensional network structure. This results in insufficient bonding strength, and the electrode is prone to powdering and peeling during coating and rolling processes. Furthermore, poor resistance to electrolyte swelling causes the electrode structure to collapse rapidly during cycling, leading to severe battery capacity decay and a significantly shortened cycle life. Insufficient thermal stability and the lack of crosslinked network support also make the polymer prone to softening and deformation under high-temperature battery conditions, increasing the risk of electrode short circuits.

[0020] When the amount of crosslinking agent exceeds 1% of the total mass of monomers in the mixed monomer solution, the crosslinking density is too high. The polymer molecular chains are excessively bound, the polymer brittleness increases dramatically, and it cannot buffer the volume changes of the negative electrode active material. During cycling, the electrode cracks and detaches due to stress concentration, which in turn exacerbates capacity decay. The dense crosslinking network hinders electron conduction inside the electrode and reduces the electrolyte penetration efficiency, resulting in poor battery rate performance.

[0021] Preferably, the inorganic alkali solution contains 1% to 10% by mass of inorganic alkali, and the inorganic alkali is at least one of sodium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, lithium carbonate, or lithium bicarbonate.

[0022] The salts formed after neutralization with inorganic bases (such as lithium polyacrylate) exhibit good electrochemical stability in batteries and do not introduce organic residues that may affect battery performance, unlike organic bases. Inorganic bases completely ionize in aqueous solutions, and the neutralization reaction is rapid and easily controlled. In contrast, organic amines are mostly weak bases, with lower neutralization efficiency and more difficult-to-control reaction processes. Compared to some organic bases (such as amines), inorganic bases have lower volatility, higher operational safety, and less environmental impact. Inorganic bases are inexpensive, widely available, and suitable for large-scale industrial production.

[0023] Preferably, the degree of alcoholysis of polyvinyl alcohol is 85%~90%, the degree of polymerization of polyvinyl alcohol is 1650~1850, and the polyacrylic acid solution and the polyvinyl alcohol solution are mixed at a mass ratio of 1~10:1 before crosslinking.

[0024] Polyvinyl alcohol with a degree of hydrolysis of 85%~90% and a degree of polymerization of 1650~1850 is chosen because it not only has good water solubility, dissolving rapidly in water at room temperature or lower temperatures, but also has moderate adhesive strength. The acetyl groups retained in the molecule enhance the affinity for hydrophobic materials, while the hydroxyl groups provide hydrogen bonding, significantly improving the adhesive strength. It also has film-forming properties and water resistance, forming films with good tensile strength and flexibility, and better solvent resistance and abrasion resistance than products with low degrees of hydrolysis.

[0025] The reason why polyacrylic acid (PAA) and polyvinyl alcohol (PVA) can be blended and crosslinked in a ratio of 1:1 to 10:1 to form a high-performance adhesive is that a stable three-dimensional network structure with both rigidity and flexibility is formed within this range. Outside this range, the balance of this structure is disrupted, leading to the deterioration of key properties.

[0026] If the PAA ratio is too low, the adhesion will be severely insufficient, resulting in poor adhesion of the electrode slurry and easy pulverization and detachment of the electrode sheet during cycling; the cross-linking network strength will be weak, and the overall network mechanical strength will be low. It will also have poor electrolyte resistance; high PVA content will easily swell or even partially dissolve in the electrolyte, losing its bonding and supporting properties.

[0027] If the PAA ratio is too high, flexibility is lost and brittleness increases. When the PVA content is too low, it cannot effectively toughen the material. The resulting cross-linked network is rigid and cannot buffer the huge volume changes of the active material (especially silicon), causing a large number of microcracks to form in the electrode during charging and discharging, eventually leading to structural collapse.

[0028] This invention provides a method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive, which yields the polyacrylic acid / polyvinyl alcohol composite adhesive.

[0029] This invention provides the application of polyacrylic acid / polyvinyl alcohol composite binder in the preparation of lithium battery anodes.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention proposes an innovative strategy of rigid-flexible synergistic three-dimensional crosslinked network and dual interface reinforcement. Through a terpolymer of water-soluble acrylic monomers, acrylonitrile monomers containing olefin bonds, and vinyl ester monomers, N,N-methylenebisacrylamide (MBA) is introduced to form a three-dimensional chemical crosslinked network of polyacrylic acid containing rigid nitrile groups, flexible ester groups, and adhesive carboxyl groups in the molecular chain. This enables the adhesive to possess both high strength and high toughness, overcoming the paradox of traditional materials being either too rigid or too flexible. The resulting polyacrylic acid and polyvinyl alcohol (PVA) construct an interpenetrating network (IPN) through hydrogen bonding, forming a dual stable structure of a chemically crosslinked main network and a physically crosslinked secondary network. This structure strengthens interfacial adhesion through high-density hydrogen bonding between lithium carboxylate groups and hydroxyl groups on the silicon surface, while also enhancing overall tensile strength through the flexible segments of PVA. This achieves a synergistic effect of rigid support skeleton, flexible buffer layer, and strong interfacial adhesion. Combined with a multi-scale interfacial reinforcement mechanism, the adhesive possesses high elastic modulus, high elongation at break, and high adhesion.

[0031] Simultaneously, the innovative rigid-flexible synergistic network structure tightly encapsulates silicon-carbon particles. The lithium carboxylate groups form high-density hydrogen and ionic bonds with the hydroxyl groups on the silicon surface, significantly improving interfacial adhesion. Flexible segments impart high elongation at break to the binder, buffering the 300% volume expansion stress of the silicon-based anode. The rigid framework provides modulus to resist structural collapse, and the dual cross-linked network inhibits electrolyte swelling, stabilizing the formation of the SEI film on the silicon-carbon surface and reducing film rupture and active material shedding during cycling. This effectively solves the problems of adhesion failure and cycle stability in silicon-based anodes. This all-aqueous green process is suitable for industrial production, significantly improving the cycle stability of high-energy-density lithium-ion batteries in high-silicon-content anodes. Detailed Implementation

[0032] To make the above-mentioned objectives, features, and advantages of the embodiments of the present invention more apparent and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. The technical solution of this invention will be further illustrated below with specific examples.

[0034] In the following embodiments, unless otherwise specified, the methods described are conventional methods, and the reagents described are commercially available unless otherwise specified.

[0035] The water-soluble acrylic monomers used in this invention are at least one of acrylic acid, methacrylic acid, styrene sulfonic acid, vinyl sulfonic acid, itaconic acid, fumaric acid, or maleic acid; the following examples are based on acrylic acid, methacrylic acid, methacrylic acid, and styrene sulfonic acid.

[0036] The acrylonitrile monomers containing olefin bonds used in this invention are at least one of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-bromoacrylonitrile, α-ethylacrylonitrile, or styrene; the following examples are based on acrylonitrile, methacrylonitrile, acrylonitrile, and methacrylonitrile.

[0037] The vinyl ester monomers used in this invention are at least one of methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, butyl acrylate, butyl methacrylate, isooctyl acrylate, lauryl methacrylate, and vinyl acetate. The following examples are based on butyl acrylate, methyl acrylate, methyl acrylate and hydroxyethyl acrylate, ethyl acrylate and hydroxyethyl acrylate.

[0038] The inorganic base used in this invention is at least one of sodium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, lithium carbonate, or lithium bicarbonate. The following examples are based on sodium hydroxide.

[0039] The following is a specific example of a method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive.

[0040] Example 1 In this embodiment, water-soluble monomer acrylic acid (AA), olefin-containing monomer acrylonitrile (AN), and vinyl ester monomer butyl acrylate (BA) are used as comonomers. Ammonium persulfate is used as an initiator, and N,N-methylenebisacrylamide is used as a crosslinking agent. The polymer is copolymerized in the aqueous phase, and the pH is adjusted by sodium hydroxide solution. Then, it is crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0041] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 500 parts by weight of deionized water to the reactor, start stirring at 200 rpm, and purge with nitrogen to remove oxygen. Then add a mixed monomer solution consisting of 20 parts by weight of acrylic acid, 25 parts by weight of acrylonitrile, and 5 parts by weight of butyl acrylate, and heat to 70°C. Next, add an initiator solution consisting of 0.1 parts by weight of ammonium persulfate and 10 parts by weight of deionized water, and add 0.05 parts by weight of N,N-methylenebisacrylamide. Then, add dropwise the mixed monomer solution consisting of 20 parts by weight of acrylic acid, 25 parts by weight of acrylonitrile, and 5 parts by weight of butyl acrylate, and the initiator solution consisting of 0.05 parts by weight of ammonium persulfate and 100 parts by weight of deionized water. After 10 hours, stop stirring and remove the precipitate (polyacrylic acid).

[0042] A 1 wt% sodium hydroxide solution and deionized water were added to adjust the pH to 8 to obtain a 10 wt% polyacrylic acid waterborne adhesive.

[0043] Polyvinyl alcohol with a degree of hydrolysis of 88% and a degree of polymerization of 1700 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 10 wt%. 10 wt% of polyacrylic acid water-based adhesive was mixed with the polyvinyl alcohol aqueous solution at a weight ratio of 5:1 and reacted at 60°C for 5 h with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite adhesive.

[0044] Example 2 In this embodiment, water-soluble monomer methacrylic acid, olefin-containing monomer methacrylonitrile, and vinyl ester monomer methyl acrylate are used as comonomers. Ammonium persulfate is used as an initiator, and N,N-methylenebisacrylamide is used as a crosslinking agent. The polymer is copolymerized in the aqueous phase, and the pH is adjusted with sodium hydroxide solution as an alkali. Then, it is crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0045] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 450 parts by weight of deionized water to the reactor, start stirring at 200 rpm, and purge with nitrogen to remove oxygen. Then add a mixed monomer solution consisting of 10 parts by weight of methacrylic acid, 25 parts by weight of methacrylonitrile, and 5 parts by weight of methyl acrylate, and heat to 65°C. Next, add an initiator solution consisting of 0.06 parts by weight of ammonium persulfate and 10 parts by weight of deionized water, and add 0.06 parts by weight of N,N-methylenebisacrylamide. Then, add dropwise a mixed monomer solution consisting of 20 parts by weight of methacrylic acid, 50 parts by weight of methacrylonitrile, and 10 parts by weight of methyl acrylate, and an initiator solution consisting of 0.06 parts by weight of ammonium persulfate and 20 parts by weight of deionized water. After 10 hours, stop stirring and remove the precipitate (polyacrylic acid).

[0046] A water-based polyacrylic acid adhesive was prepared by adding 10 wt% sodium hydroxide solution and deionized water to adjust the pH to 8 and the solid content to 5 wt%.

[0047] Polyvinyl alcohol with a degree of hydrolysis of 88% and a degree of polymerization of 1700 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 5 wt%. 5 wt% polyacrylic acid water-based adhesive was mixed with 5 wt% polyvinyl alcohol aqueous solution at a weight ratio of 5:1 and reacted at 60℃ for 5 h with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite adhesive.

[0048] Example 3 In this embodiment, water-soluble monomers acrylic acid and styrene sulfonic acid, olefin-containing monomers acrylonitrile and methacrylonitrile, and vinyl ester monomers methyl acrylate and hydroxyethyl acrylate are used as comonomers. Ammonium persulfate is used as an initiator, and N,N-methylenebisacrylamide is used as a crosslinking agent to copolymerize the polymer in the aqueous phase. Sodium hydroxide solution is used as an alkaline solution to adjust the pH, and then crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0049] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 550 parts by weight of deionized water to the reactor, start stirring at 200 rpm, and purge with nitrogen to remove oxygen. Then add a mixed monomer solution consisting of 8 parts by weight of methacrylic acid, 4 parts by weight of styrene sulfonic acid, 15 parts by weight of acrylonitrile, 7 parts by weight of methacrylonitrile, 3 parts by weight of methyl acrylate, and 3 parts by weight of hydroxyethyl acrylate, and heat to 75°C. Then add an initiator solution consisting of 0.1 parts by weight of ammonium persulfate and 10 parts by weight of deionized water, and add 0.1 parts by weight of N,N-methylenebisacrylamide. Subsequently, add dropwise a mixed monomer solution consisting of 32 parts by weight of methacrylic acid, 16 parts by weight of styrene sulfonic acid, 60 parts by weight of acrylonitrile, 28 parts by weight of methacrylonitrile, 12 parts by weight of methyl acrylate, and 12 parts by weight of hydroxyethyl acrylate, as well as an initiator solution consisting of 0.1 parts by weight of ammonium persulfate and 100 parts by weight of deionized water. After 10 hours, stop stirring and remove the precipitate (polyacrylic acid).

[0050] A water-based polyacrylic acid adhesive was prepared by adding 5 wt% sodium hydroxide solution and deionized water to adjust the pH to 8 and the solid content to 10 wt%.

[0051] Polyvinyl alcohol with a degree of hydrolysis of 88% and a degree of polymerization of 1700 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 10 wt%. 10 wt% polyacrylic acid water-based adhesive and 10 wt% polyvinyl alcohol aqueous solution were mixed at a weight ratio of 5:1 and reacted at 60°C for 5 h with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite adhesive.

[0052] Example 4 In this embodiment, water-soluble monomer acrylic acid, olefin-containing monomer acrylonitrile, and vinyl ester monomers ethyl acrylate and hydroxyethyl acrylate are used as comonomers. Ammonium persulfate is used as an initiator, and N,N-methylenebisacrylamide is used as a crosslinking agent. The polymer is copolymerized in the aqueous phase, and the pH is adjusted with sodium hydroxide solution as an alkali. Then, it is crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0053] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 515 parts by weight of deionized water to the reactor, start stirring at 200 rpm, and purge with nitrogen to remove oxygen. Then add a mixed monomer solution consisting of 15 parts by weight of acrylic acid, 20 parts by weight of acrylonitrile, 5 parts by weight of ethyl acrylate, and 2 parts by weight of hydroxyethyl acrylate, and heat to 68°C. Then add an initiator solution consisting of 0.1 parts by weight of ammonium persulfate and 10 parts by weight of deionized water, and add 0.05 parts by weight of N,N-methylenebisacrylamide. Subsequently, add dropwise a mixed monomer solution consisting of 30 parts by weight of acrylic acid, 40 parts by weight of acrylonitrile, 10 parts by weight of ethyl acrylate, and 4 parts by weight of hydroxyethyl acrylate, as well as an initiator solution consisting of 0.05 parts by weight of ammonium persulfate and 50 parts by weight of deionized water. After 10 hours, stop stirring and remove the precipitate (polyacrylic acid).

[0054] A water-based polyacrylic acid adhesive was prepared by adding 5 wt% sodium hydroxide solution and deionized water to adjust the pH to 9 and the solid content to 20 wt%.

[0055] Polyvinyl alcohol with a degree of hydrolysis of 85% and a degree of polymerization of 1650 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 20 wt%. 20 wt% polyacrylic acid water-based adhesive was mixed with 20 wt% polyvinyl alcohol aqueous solution at a weight ratio of 7:1 and reacted at 60℃ for 5 h with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite adhesive.

[0056] Example 5 In this embodiment, water-soluble monomer acrylic acid, olefin-containing monomer acrylonitrile, and vinyl ester monomers ethyl acrylate and hydroxyethyl acrylate are used as comonomers. Ammonium persulfate is used as an initiator, and N,N-methylenebisacrylamide is used as a crosslinking agent to copolymerize the polymer in the aqueous phase. Sodium hydroxide solution is used as an alkaline solution to adjust the pH, and then crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0057] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 550 parts by weight of deionized water to the reactor, start stirring at 200 rpm, and purge with nitrogen to remove oxygen. Then add a mixed monomer solution consisting of 15 parts by weight of acrylic acid, 10 parts by weight of acrylonitrile, 5 parts by weight of ethyl acrylate, and 2 parts by weight of hydroxyethyl acrylate, and heat to 68°C. Then add an initiator solution consisting of 0.1 parts by weight of ammonium persulfate and 10 parts by weight of deionized water, and add 0.05 parts by weight of N,N-methylenebisacrylamide. Subsequently, add dropwise a mixed monomer solution consisting of 30 parts by weight of acrylic acid, 25 parts by weight of acrylonitrile, 10 parts by weight of ethyl acrylate, and 3 parts by weight of hydroxyethyl acrylate, and an initiator solution consisting of 0.05 parts by weight of ammonium persulfate and 50 parts by weight of deionized water. After 10 hours, stop stirring and remove the precipitate (polyacrylic acid).

[0058] A water-based polyacrylic acid adhesive was prepared by adding 5 wt% sodium hydroxide solution and deionized water to adjust the pH to 7 and the solid content to 8 wt%.

[0059] Polyvinyl alcohol with a degree of hydrolysis of 90% and a degree of polymerization of 1850 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 8 wt%. 8 wt% polyacrylic acid water-based adhesive and 8 wt% polyvinyl alcohol aqueous solution were mixed at a weight ratio of 1:1 and reacted at 60℃ for 5 h with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite adhesive.

[0060] Example 6 In this embodiment, water-soluble monomer acrylic acid, olefin-containing monomer acrylonitrile, and vinyl ester monomers ethyl acrylate and hydroxyethyl acrylate are used as comonomers. Ammonium persulfate is used as an initiator, and N,N-methylenebisacrylamide is used as a crosslinking agent. The polymer is copolymerized in the aqueous phase, and the pH is adjusted with sodium hydroxide solution as an alkali. Then, it is crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0061] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 520 parts by weight of deionized water to the reactor, start stirring at 200 rpm, and purge with nitrogen to remove oxygen. Then add 40 parts by weight of acrylic acid, 80 parts by weight of acrylonitrile, and 10 parts by weight of butyl acrylate, and heat to 68°C. Next, add an initiator solution consisting of 0.017 parts by weight of ammonium persulfate and 170 parts by weight of deionized water, and add 0.013 parts by weight of N,N-methylenebisacrylamide. Then, add dropwise 40 parts by weight of acrylic acid, 80 parts by weight of acrylonitrile, and 10 parts by weight of butyl acrylate, and an initiator solution consisting of 0.0087 parts by weight of ammonium persulfate and 87 parts by weight of deionized water. After 10 hours, stop stirring and remove the precipitate (polyacrylic acid).

[0062] A water-based polyacrylic acid adhesive was prepared by adding 5 wt% sodium hydroxide solution and deionized water to adjust the pH to 7.5 and the solid content to 15 wt%.

[0063] Polyvinyl alcohol with a degree of hydrolysis of 90% and a degree of polymerization of 1700 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 15 wt%. 15 wt% polyacrylic acid water-based adhesive was mixed with 15 wt% polyvinyl alcohol aqueous solution at a weight ratio of 10:1 and reacted at 60℃ for 5 h with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite adhesive.

[0064] Example 7 In this embodiment, water-soluble monomer acrylic acid, olefin-containing monomer acrylonitrile, and vinyl ester monomers ethyl acrylate and hydroxyethyl acrylate are used as comonomers. Ammonium persulfate is used as an initiator, and N,N-methylenebisacrylamide is used as a crosslinking agent. The polymer is copolymerized in the aqueous phase, and the pH is adjusted with sodium hydroxide solution as an alkali. Then, it is crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0065] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 500 parts by weight of deionized water to the reactor, start stirring at 200 rpm, and purge with nitrogen to remove oxygen. Then add 10 parts by weight of acrylic acid, 30 parts by weight of acrylonitrile, and 2 parts by weight of butyl acrylate, and heat to 68°C. Next, add an initiator solution consisting of 0.5 parts by weight of ammonium persulfate and 2.5 parts by weight of deionized water, and add 1 part by weight of N,N-methylenebisacrylamide. Then, add dropwise 15 parts by weight of acrylic acid, 40 parts by weight of acrylonitrile, and 3 parts by weight of butyl acrylate, as well as the initiator solution consisting of 0.5 parts by weight of ammonium persulfate and 2.5 parts by weight of deionized water. After 10 hours, stop stirring and remove the precipitate (polyacrylic acid).

[0066] A water-based polyacrylic acid adhesive was prepared by adding 5 wt% sodium hydroxide solution and deionized water to adjust the pH to 7.5 and the solid content to 15 wt%.

[0067] Polyvinyl alcohol with a degree of hydrolysis of 90% and a degree of polymerization of 1700 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 15 wt%. 15 wt% polyacrylic acid water-based adhesive was mixed with 15 wt% polyvinyl alcohol aqueous solution at a weight ratio of 10:1 and reacted at 60℃ for 5 h with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite adhesive.

[0068] Comparative Example 1 In this comparative example, water-soluble monomer acrylic acid, olefin-containing monomer acrylonitrile, and vinyl ester monomer ethyl acrylate were used as comonomers. Ammonium persulfate was used as an initiator, and N,N-methylenebisacrylamide was used as a crosslinking agent. The polymer was copolymerized in the aqueous phase, and the pH was adjusted with sodium hydroxide solution as an alkali. Then, it was crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0069] The difference between Comparative Example 1 and Example 1 is that the weight percentage ratios of water-soluble acrylic monomers, olefin-containing acrylonitrile monomers, and vinyl ester monomers are different. The weight percentages given in Comparative Example 1 are 50%:40%:10%.

[0070] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 500 parts by weight of deionized water to the reactor, start stirring at 200 rpm, and purge with nitrogen to remove oxygen. Then add a mixed monomer solution consisting of 25 parts by weight of acrylic acid, 20 parts by weight of acrylonitrile, and 5 parts by weight of ethyl acrylate, and heat to 70°C. Next, add an initiator solution consisting of 0.05 parts by weight of ammonium persulfate and 10 parts by weight of deionized water, and then add 0.05 parts by weight of N,N-methylenebisacrylamide. Then, add dropwise the mixed monomer solution consisting of 25 parts by weight of acrylic acid, 20 parts by weight of acrylonitrile, and 5 parts by weight of ethyl acrylate, and the initiator solution consisting of 0.05 parts by weight of ammonium persulfate and 10 parts by weight of deionized water. After 10 hours, stop stirring and remove the precipitate (polyacrylic acid).

[0071] A water-based polyacrylic acid adhesive was prepared by adding 1 wt% sodium hydroxide solution and deionized water to adjust the pH to 8 and the solid content to 10 wt%.

[0072] Polyvinyl alcohol with a degree of hydrolysis of 88% and a degree of polymerization of 1700 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 10 wt%. Aqueous polyacrylic acid binder was mixed with the polyvinyl alcohol aqueous solution at a weight ratio of 5:1 and reacted at 60°C for 5 hours with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite binder.

[0073] Comparative Example 2 In this comparative example, water-soluble monomer acrylic acid, olefin-containing monomer acrylonitrile, and vinyl ester monomer ethyl acrylate were used as comonomers. Ammonium persulfate was used as an initiator, and N,N-methylenebisacrylamide was used as a crosslinking agent. The polymer was copolymerized in the aqueous phase, and the pH was adjusted with sodium hydroxide solution as an alkali. Then, it was crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0074] The difference between Comparative Example 2 and Example 1 is that the mixed monomer solution was not added to the reaction vessel in steps.

[0075] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 300 parts by weight of deionized water to the reactor, start stirring at 200 r / min, and purge with nitrogen to remove oxygen. Then add a mixed monomer solution consisting of 40 parts by weight of acrylic acid, 50 parts by weight of acrylonitrile, and 10 parts by weight of ethyl acrylate, and heat to 70°C. Then add an initiator solution consisting of 0.1 parts by weight of ammonium persulfate and 10 parts by weight of deionized water, and add 0.05 parts by weight of N,N-methylenebisacrylamide. After 10 hours, stop stirring and remove the precipitate.

[0076] A water-based polyacrylic acid adhesive was prepared by adding 1 wt% sodium hydroxide solution and deionized water to adjust the pH to 8 and the solid content to 10 wt%.

[0077] Polyvinyl alcohol with a degree of hydrolysis of 88% and a degree of polymerization of 1700 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 10 wt%. Aqueous polyacrylic acid binder was mixed with the polyvinyl alcohol aqueous solution at a weight ratio of 5:1 and reacted at 60 °C for 5 h with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite binder.

[0078] Comparative Example 3 In this comparative example, water-soluble monomer acrylic acid, olefin-containing monomer acrylonitrile, and vinyl ester monomer ethyl acrylate were used as comonomers. Ammonium persulfate was used as an initiator, and N,N-methylenebisacrylamide was used as a crosslinking agent. The polymer was copolymerized in the aqueous phase, and the pH was adjusted with sodium hydroxide solution as an alkali. Then, it was crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0079] The difference between Comparative Example 3 and Example 1 is that the monomer heating temperature is different.

[0080] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 500 parts by weight of deionized water to the reactor, start stirring at 200 rpm, and purge with nitrogen to remove oxygen. Then add a mixed monomer solution consisting of 20 parts by weight of acrylic acid, 25 parts by weight of acrylonitrile, and 5 parts by weight of ethyl acrylate, and heat to 55°C. Next, add an initiator solution consisting of 0.05 parts by weight of ammonium persulfate and 10 parts by weight of deionized water, and then add 0.05 parts by weight of N,N-methylenebisacrylamide. Then, add dropwise the mixed monomer solution consisting of 25 parts by weight of acrylic acid, 20 parts by weight of acrylonitrile, and 5 parts by weight of ethyl acrylate, and the initiator solution consisting of 0.05 parts by weight of ammonium persulfate and 10 parts by weight of deionized water. After 10 hours, stop stirring and remove the precipitate.

[0081] A water-based polyacrylic acid adhesive was prepared by adding 1 wt% sodium hydroxide solution and deionized water to adjust the pH to 8 and the solid content to 10 wt%.

[0082] Polyvinyl alcohol with a degree of hydrolysis of 88% and a degree of polymerization of 1700 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 10 wt%. Aqueous polyacrylic acid binder was mixed with the polyvinyl alcohol aqueous solution at a weight ratio of 5:1 and reacted at 60 °C for 5 h with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite binder.

[0083] Comparative Example 4 In this comparative example, water-soluble monomer acrylic acid, olefin-containing monomer acrylonitrile, and vinyl ester monomer ethyl acrylate were used as comonomers. Ammonium persulfate was used as an initiator, and N,N-methylenebisacrylamide was used as a crosslinking agent. The polymer was copolymerized in the aqueous phase, and the pH was adjusted with sodium hydroxide solution as an alkali. Then, it was crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0084] The difference between Comparative Example 4 and Example 1 is that the amount of ammonium persulfate is different.

[0085] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 500 parts by weight of deionized water to the reactor, start stirring at 200 r / min, and purge with nitrogen to remove oxygen. Then add a mixed monomer solution consisting of 20 parts by weight of acrylic acid, 25 parts by weight of acrylonitrile, and 5 parts by weight of ethyl acrylate, and heat to 70°C. Then add an initiator solution consisting of 1 part by weight of ammonium persulfate and 10 parts by weight of deionized water, and add 0.05 parts by weight of N,N-methylenebisacrylamide. Next, add dropwise the mixed monomer solution consisting of 20 parts by weight of acrylic acid, 25 parts by weight of acrylonitrile, and 5 parts by weight of ethyl acrylate, and the initiator solution consisting of 1 part by weight of ammonium persulfate and 10 parts by weight of deionized water. After 10 hours, stop stirring, remove the precipitate, and...

[0086] A water-based polyacrylic acid adhesive was prepared by adding 1 wt% sodium hydroxide solution and deionized water to adjust the pH to 8 and the solid content to 10 wt%.

[0087] Polyvinyl alcohol with a degree of hydrolysis of 88% and a degree of polymerization of 1700 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 10 wt%. Aqueous polyacrylic acid binder was mixed with the polyvinyl alcohol aqueous solution at a weight ratio of 5:1 and reacted at 60°C for 5 h with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite binder.

[0088] Comparative Example 5 In this comparative example, water-soluble monomer acrylic acid, olefin-containing monomer acrylonitrile, and vinyl ester monomer ethyl acrylate were used as comonomers. Ammonium persulfate was used as an initiator, and N,N-methylenebisacrylamide was used as a crosslinking agent. The polymer was copolymerized in the aqueous phase, and the pH was adjusted with sodium hydroxide solution as an alkali. Then, it was crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0089] The difference between Comparative Example 5 and Example 1 is that the pH value is different.

[0090] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 500 parts by weight of deionized water to the reactor, start stirring at 200 rpm, and purge with nitrogen to remove oxygen. Then add a mixed monomer solution consisting of 20 parts by weight of acrylic acid, 25 parts by weight of acrylonitrile, and 5 parts by weight of ethyl acrylate, and heat to 70°C. Next, add an initiator solution consisting of 0.05 parts by weight of ammonium persulfate and 10 parts by weight of deionized water, and then add 0.05 parts by weight of N,N-methylenebisacrylamide. Then, add dropwise the mixed monomer solution consisting of 20 parts by weight of acrylic acid, 25 parts by weight of acrylonitrile, and 5 parts by weight of ethyl acrylate, and the initiator solution consisting of 0.05 parts by weight of ammonium persulfate and 10 parts by weight of deionized water. After 10 hours, stop stirring and remove the precipitate.

[0091] A water-based polyacrylic acid adhesive was prepared by adding 1 wt% sodium hydroxide solution and deionized water to adjust the pH to 11 and the solid content to 10 wt%.

[0092] Polyvinyl alcohol with a degree of hydrolysis of 88% and a degree of polymerization of 1700 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 10 wt%. Aqueous polyacrylic acid binder was mixed with the polyvinyl alcohol aqueous solution at a weight ratio of 5:1 and reacted at 60 °C for 5 h with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite binder.

[0093] Comparative Example 6 In this comparative example, water-soluble monomer acrylic acid, olefin-containing monomer acrylonitrile, and vinyl ester monomer ethyl acrylate were used as comonomers. Ammonium persulfate was used as an initiator, and N,N-methylenebisacrylamide was used as a crosslinking agent. The polymer was copolymerized in the aqueous phase, and the pH was adjusted with sodium hydroxide solution as an alkali. Then, it was crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0094] The difference between Comparative Example 6 and Example 1 is that the pH value is different and the crosslinking temperature of acrylic acid, acrylonitrile and ethyl acrylate in the reaction vessel is different.

[0095] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 500 parts by weight of deionized water to the reactor, start stirring at 200 r / min, and purge with nitrogen to remove oxygen. Then add a mixed monomer solution consisting of 20 parts by weight of acrylic acid, 25 parts by weight of acrylonitrile, and 5 parts by weight of ethyl acrylate, and heat to 85°C. Then add an initiator solution consisting of 0.05 parts by weight of ammonium persulfate and 10 parts by weight of deionized water, and add 2 parts by weight of N,N-methylenebisacrylamide. Next, add dropwise the mixed monomer solution consisting of 20 parts by weight of acrylic acid, 25 parts by weight of acrylonitrile, and 5 parts by weight of ethyl acrylate, and the initiator solution consisting of 0.05 parts by weight of ammonium persulfate and 10 parts by weight of deionized water. After 10 hours, stop stirring and remove the precipitate.

[0096] A water-based polyacrylic acid adhesive was prepared by adding 1 wt% sodium hydroxide solution and deionized water to adjust the pH to 6 and the solid content to 10 wt%.

[0097] Polyvinyl alcohol with a degree of hydrolysis of 95% and a degree of polymerization of 1900 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 10 wt%. Aqueous polyacrylic acid binder was mixed with the polyvinyl alcohol aqueous solution at a weight ratio of 5:1 and reacted at 60°C for 5 hours with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite binder.

[0098] Comparative Example 7 In this comparative example, water-soluble monomer acrylic acid and olefin-containing monomer acrylonitrile were used as comonomers, ammonium persulfate was used as an initiator, and N,N-methylenebisacrylamide was used as a crosslinking agent to copolymerize the polymer in the aqueous phase. The pH was adjusted by using sodium hydroxide solution as an alkaline solution, and then crosslinked with PVA to prepare an aqueous adhesive for lithium-ion batteries.

[0099] The difference between Comparative Example 7 and Example 1 is that the reactive monomers consist only of acrylic acid and acrylonitrile.

[0100] A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive includes the following steps: Add 500 parts by weight of deionized water to the reactor, start stirring at 200 r / min, and purge with nitrogen to remove oxygen. Then add a mixed monomer solution consisting of 20 parts by weight of acrylic acid and 30 parts by weight of acrylonitrile, and heat to 70°C. Then add an initiator solution consisting of 0.05 parts by weight of ammonium persulfate and 10 parts by weight of deionized water, and add 0.05 parts by weight of N,N-methylenebisacrylamide. Then add dropwise the mixed monomer solution consisting of 20 parts by weight of acrylic acid and 30 parts by weight of acrylonitrile, and the initiator solution consisting of 0.05 parts by weight of ammonium persulfate and 10 parts by weight of deionized water. After 10 hours, stop stirring, remove the precipitate, add sodium hydroxide solution and deionized water to adjust the pH to 8, and obtain a solution with a solid content of 10 wt% to prepare a waterborne polyacrylic acid adhesive.

[0101] Polyvinyl alcohol with a degree of hydrolysis of 88% and a degree of polymerization of 1700 was mixed with deionized water to obtain a polyvinyl alcohol aqueous solution with a solid content of 10 wt%. Aqueous polyacrylic acid binder was mixed with the polyvinyl alcohol aqueous solution at a weight ratio of 5:1 and reacted at 60°C for 5 hours with a stirring speed of 50 r / min to obtain a polyacrylic acid / polyvinyl alcohol composite binder.

[0102] The preparation methods of cross-linked polyacrylic acid / polyvinyl alcohol composite adhesives given in Examples 1 to 7 above can all prepare cross-linked polyacrylic acid / polyvinyl alcohol composite adhesives. The performance of the cross-linked polyacrylic acid / polyvinyl alcohol composite adhesives prepared in Examples 1 to 7 and Comparative Examples 1 to 7 will be experimentally verified.

[0103] (1) 180° peel force test and electrode adhesion test Using the adhesives from Examples 1 to 7 and Comparative Examples 1 to 7, negative electrode sheets were prepared, and their 180° peel strength was measured. The specific methods and results are as follows: Artificial graphite (used as the negative electrode active material), binders (the binders used in Examples 1-7 and Comparative Examples 1-7, respectively), and conductive carbon black (super-p) were added to deionized water according to the proportions in Table 1 to prepare a negative electrode slurry. This negative electrode slurry was coated onto a 10 μm thick copper foil current collector and then dried. An areal density of 20 mg / cm³ was formed. 2 Compacted density 1.6 g / cm³ 3 Negative electrode sheet.

[0104] Table 1 shows the weight ratio of various solid components in the negative electrode slurry. Note: The above proportions are the weight proportions of the various solid components.

[0105] The prepared electrode sheets were cut into rectangles (3cm × 15cm) and adhered to an aluminum plate with 3M double-sided tape (20 mm). They were then rolled five times with a roller. A universal tensile testing machine (TFL-2S) was then used to test the peel strength of the tape, with a machine speed of 5 mm / s and a peel angle of 180°. Specific results are shown in Table 2.

[0106] Table 2. Peel strength test values ​​of the adhesives in Examples 1-7 and Comparative Examples 1-7. Table 2 shows that the peel strength of the composite binders prepared in Examples 1-7 is all above 33.9 N / m, with Example 6 exhibiting the highest peel strength at 37.0 N / m. In contrast, the peel strength of Comparative Examples 1-7 is all below 31.1 N / m, with the lowest being 28.2 N / m in Comparative Example 3. This indicates that the composite binder prepared by the method of this invention possesses stronger interfacial bonding ability and can effectively fix silicon-based anode active materials.

[0107] (2) Tensile test Using the adhesives from the above embodiments and comparative examples, adhesive films were prepared, and tensile tests were performed on them. The specific methods and results are as follows: The adhesive was poured into a polytetrafluoroethylene tank and dried into a film. The film was then cut into test samples using a dumbbell-shaped cutter, and a tensile testing machine was used. The experimental results are shown in Table 3 below.

[0108] Table 3 Mechanical strength test values ​​of the adhesives in Examples 1-7 and Comparative Examples 1-7 As shown in Table 3, the elongation at break of the composite binders in Examples 1-7 is significantly better than that of the comparative examples. Example 5 has the highest elongation at break at 253%, while the highest elongation at break of the comparative examples is only 58% of that of Comparative Example 3, and the lowest is only 9% of that of Comparative Example 5. In terms of tensile strength, Examples 1-7 are all above 59.8 MPa, while the comparative examples are generally below 43.6 MPa. In terms of elastic modulus, the examples are all kept within a reasonable range of 1000 MPa to 2000 MPa, taking into account both rigid support and flexible buffering capacity, while the comparative examples have problems with elastic modulus that are too high or too low, which cannot adapt to the volume change requirements of silicon-based anodes.

[0109] (3) Swelling test Adhesive films were prepared using the adhesives from Examples 1 to 7 and Comparative Examples 1 to 7, and swelling tests were performed on them. The specific methods and results are as follows: The adhesive was poured into a polytetrafluoroethylene (PTFE) tank and dried into a film. The adhesive film was then cut into 10mm diameter discs, weighed, and its mass recorded as M1. The film was then immersed in the electrolyte for 72 hours. After 72 hours, it was removed, the electrolyte on the surface was wiped off, and its mass was weighed and recorded as M2. The swelling rate was calculated as (M2-M1) / M1*100%. The electrolyte was 1.0 M lithium hexafluorophosphate (LiPF6) with 5% vol fluoroethylene carbonate (FEC) added, and the solvent was ethylene carbonate / diethyl carbonate (EC / DEC, volume ratio 1:1). The experimental results are shown in Table 4 below.

[0110] Table 4 shows the swelling test values ​​of the adhesives in Examples 1-7 and Comparative Examples 1-7. As shown in Table 4, the swelling rates of the composite adhesives in Examples 1-7 at both 25°C and 60°C are significantly lower than those in the comparative examples. Example 5 exhibits the lowest swelling rate at 25°C (4.4%), and the lowest at 60°C (7.7%, the same as Example 2). In contrast, among the comparative examples, the highest swelling rate is observed at 25°C (40.2%), and at 60°C (83.2%), the same as Comparative Example 7. This indicates that the composite adhesive of the present invention possesses excellent electrolyte stability and can maintain the integrity of the adhesive network structure during long-term cycling.

[0111] (4) Battery performance test The polyacrylic acid / polyvinyl alcohol composite binder used in the above cases was used to prepare negative electrode sheets and assembled into lithium-ion batteries. The specific steps are as follows: Preparation of negative electrode sheet: 1.5 wt% binder, 0.5 wt% sodium carboxymethyl cellulose thickener, 0.5 wt% styrene-butadiene rubber, 1.0 wt% conductive agent Super.P, 96.5 wt% graphite and a certain amount of deionized water are mixed to prepare a negative electrode slurry with a solid content of 57.5 wt%. The negative electrode slurry is then coated on the surface of copper foil, dried and rolled to obtain the negative electrode sheet. Preparation of positive electrode sheet: 96.5 wt% lithium iron phosphate material, 1.5 wt% conductive agent Super.P, 2 wt% binder polyvinylidene fluoride and N-methylpyrrolidone are mixed to prepare a positive electrode slurry with a solid content of 68 wt%. The positive electrode slurry is then coated on the surface of aluminum foil, and the positive electrode sheet is obtained after drying and rolling. Lithium-ion battery fabrication: Positive electrode, negative electrode, and electrolyte (Zhongbang LBC338B86) were assembled to obtain a 3Ah pouch battery. The cell cycle performance was tested. The cycle performance test conditions were: charging to 3.65V at a 1C rate at 25℃ or 45℃, maintaining a constant voltage of 3.65V, and then discharging to a cutoff voltage of 2.5V at a 1C rate. This process was repeated. The experimental results are shown in Table 5 below.

[0112] Table 5 shows the battery performance test values ​​of the lithium-ion batteries prepared in Examples 1 to 7 and Comparative Examples 1 to 7. As shown in Table 5, the battery cycle performance of Examples 1-7 is significantly better than that of the comparative examples. After 1000 cycles at 25°C, Example 1 exhibits the highest capacity retention rate at 98.50%, while the remaining examples all exceed 96.80%. After 1000 cycles at 45°C, Example 1 retains 90.60% of its capacity, while Examples 2-6 all retain over 88.70%. In contrast, the comparative examples show the highest capacity retention rate at 25°C (96.20%), but only a maximum of 85.00% at 45°C, with the lowest being 81.00% for Comparative Example 7. This clearly demonstrates that the composite binder of this invention can effectively improve the cycle stability of lithium-ion batteries, especially maintaining good performance under high-temperature conditions.

[0113] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0114] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive, characterized in that, Includes the following steps: A mixed monomer solution is obtained by uniformly mixing water-soluble acrylic monomers, acrylonitrile monomers containing olefin bonds, and vinyl ester monomers. Mix 1 / 6 to 1 / 2 of the total volume of the mixed monomer solution with deionized water to obtain a water-monomer premix, wherein the weight of deionized water is 80% to 95% of the total weight of the water-monomer premix. Under a nitrogen atmosphere, a crosslinking agent and initiator solution one are added to a water-monomer premix to initiate the reaction. Then, the remaining mixed monomer solution and initiator solution two are added dropwise. After the reaction is complete, the mixture is filtered to obtain a powder. The powder is washed with deionized water, and the pH is adjusted to 7.0–9.0 using an inorganic alkali solution. Then, deionized water is added to dilute the powder to obtain a polyacrylic acid solution with a mass percentage of 5.0%–20.0%. A polyvinyl alcohol aqueous solution with a mass percentage of 5.0%–20.0% is prepared, and then the polyvinyl alcohol aqueous solution is crosslinked with the polyacrylic acid solution to obtain a polyacrylic acid / polyvinyl alcohol composite binder.

2. The preparation method of the cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive according to claim 1, characterized in that, The weight percentages of the water-soluble acrylic monomers, olefin-containing acrylonitrile monomers, and vinyl ester monomers are 25%~45%: 35%~70%: 5%~20%.

3. The method for preparing the cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive according to claim 1, characterized in that, The water-soluble acrylic monomer is at least one of acrylic acid, methacrylic acid, styrene sulfonic acid, vinyl sulfonic acid, itaconic acid, fumaric acid, or maleic acid; the olefin-containing acrylonitrile monomer is at least one of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-bromoacrylonitrile, α-ethylacrylonitrile, or styrene; the vinyl ester monomer is at least one of methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, butyl acrylate, butyl methacrylate, isooctyl acrylate, lauryl methacrylate, or vinyl acetate.

4. The preparation method of the cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive according to claim 1, characterized in that, The total amount of initiator is 0.01% to 1% of the total mass of the mixed monomer solution. The amount of initiator added in initiator solution one is 1 / 2 to 2 / 3 of the total amount of initiator, and the amount of initiator added in initiator solution two is 1 / 3 to 1 / 2 of the total amount of initiator. The mass percentage of initiator in both initiator solution one and initiator solution two is 0.01% to 20%.

5. The method for preparing the cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive according to claim 4, characterized in that, The initiator is at least one of ammonium persulfate, sodium persulfate, or potassium persulfate.

6. The method for preparing the cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive according to claim 1, characterized in that, The amount of crosslinking agent added is 0.01% to 1% of the total mass of monomers in the mixed monomer solution, and the crosslinking agent is N,N-methylenebisacrylamide.

7. The method for preparing the cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive according to claim 1, characterized in that, The inorganic alkaline solution contains 1% to 10% by mass of inorganic alkali, and the inorganic alkali is at least one of sodium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, lithium carbonate, or lithium bicarbonate.

8. The method for preparing the cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive according to claim 1, characterized in that, The degree of alcoholysis of the polyvinyl alcohol is 85%~90%, the degree of polymerization of the polyvinyl alcohol is 1650~1850, and the polyacrylic acid solution and the polyvinyl alcohol solution are crosslinked after being mixed at a mass ratio of 1~10:

1.

9. The cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive prepared by the preparation method of the cross-linked polyacrylic acid / polyvinyl alcohol composite adhesive according to any one of claims 1 to 8.

10. The application of the cross-linked polyacrylic acid / polyvinyl alcohol composite binder according to claim 9 in the preparation of lithium battery anodes.

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