Negative plate adhesive, preparation method thereof and negative plate

Abstract

The invention relates to a negative electrode plate adhesive, a preparation method thereof and a negative electrode plate, the negative electrode plate adhesive comprises an epoxy resin grafted acrylic polymer, and the epoxy resin grafted acrylic polymer is formed by reaction polymerization of an acrylic polymer, epichlorohydrin, a diol / diphenol compound and an initiator in a molar ratio of 1: (800-80000): (750-75000): (750-1500). According to the scheme provided by the invention, strength and flexibility can be achieved at the same time, cyclic expansion of the battery can be resisted, and the capacity of the battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to negative electrode adhesives, their preparation methods, and negative electrode sheets. Background Technology

[0002] Binders are a key component of battery slurries. Although used in small quantities, they have a significant impact on battery performance. During charge and discharge, lithium-ion active materials undergo volume expansion and contraction, which can easily lead to the rupture of active particles and the breakage of the conductive network, thereby damaging the electrode structure and affecting cycle life and rate performance. Therefore, an ideal binder must possess excellent flexibility to buffer the stress caused by volume changes in the electrode, while providing sufficient adhesion to ensure a tight bond between the active material and the current collector, and between particles, preventing material detachment and structural damage.

[0003] In related technologies, PAA-type compounds are used as binders. PAA-type binders have high strength, and when added to the electrode, they can improve the electrode's peel strength and cohesion. However, due to the poor flexibility of PAA-type binders, they are insufficient to resist local stress and break during the cycling expansion of silicon-carbon batteries, resulting in electrode powder shedding and capacity decay. Summary of the Invention

[0004] To address or partially address the problems existing in related technologies, this application provides a negative electrode adhesive, its preparation method, and a negative electrode sheet that simultaneously possesses strength and flexibility, can resist battery cycle expansion, and improve battery capacity.

[0005] The first aspect of this application provides a negative electrode adhesive, comprising an epoxy resin grafted with an acrylic polymer, wherein the epoxy resin grafted with an acrylic polymer, an epichlorohydrin, a glycol / diphenol compound and an initiator are polymerized by reaction in a molar ratio of 1:800~80000:750~75000:750~1500.

[0006] As an optional embodiment, the acrylic polymer is polymerized from acrylic monomers, which include at least one of α-cyanoacrylate, methacrylic acid, ethylacrylic acid, propylacrylic acid, methyl α-cyanoacrylate, acrylamide, acrylonitrile, and hydroxymethylacrylamide.

[0007] As an optional embodiment, the diol / diphenol compound includes at least one of bisphenol A, tetraphenol ethane, glycerol, diphenol methane, resorcinol, and phenolphthalein.

[0008] As an optional embodiment, the molecular weight of the acrylic polymer is 300,000 to 1,000,000.

[0009] As an optional embodiment, the epoxy resin grafted with acrylic polymer has a molecular weight of 450,000 to 1,500,000; and / or, the viscosity of the epoxy resin grafted with acrylic polymer is 1,000 Pa·s to 50,000 mPa·s.

[0010] As an optional embodiment, the mass grafting rate of the epoxy resin in the epoxy resin grafted acrylic polymer is 5% to 30%; and / or, the side chain of the epoxy resin grafted acrylic polymer has 10 to 50 repeating units, and the molecular weight of a single epoxy resin unit is 2000 to 10000; and / or, the epoxy value of the epoxy resin grafted acrylic polymer is 0.003 to 0.02.

[0011] A second aspect of this application provides a method for preparing a negative electrode adhesive, comprising: An acrylic polymer, epichlorohydrin, glycol / diphenol compounds, and an initiator are mixed in a molar ratio of 1:800~80000:750~75000:750~1500 and a polymerization reaction is carried out to obtain epoxy resin grafted acrylic polymer.

[0012] As an optional embodiment, the epoxy resin grafted with acrylic polymer comprises: The acrylic polymer is dissolved in the first solvent and stirred at 70℃~90℃ for 1h~24h. Add epichlorohydrin and glycol / diphenol compounds; At 60℃~80℃, an initiator and a second solvent are added to polymerize an epoxy resin-grafted acrylic polymer.

[0013] As an optional embodiment, the first solvent includes at least one of dichloroethane, dichloromethane, dimethyl sulfoxide, N,N-dimethylformamide, toluene, and benzene; and / or, the first solvent includes an alcohol solvent; and / or, the second solvent is an alkaline solvent.

[0014] A third aspect of this application provides a negative electrode sheet, including a current collector and a negative electrode active layer coated on at least one side of the current collector. The negative electrode active layer includes a negative electrode active material and an adhesive, wherein the adhesive is the aforementioned negative electrode sheet adhesive, or a negative electrode sheet adhesive prepared by the aforementioned method for preparing negative electrode sheet adhesive.

[0015] The technical solution provided in this application may include the following beneficial results: In the epoxy resin grafted acrylic polymer of this application, the epoxy resin provides rigidity, while the acrylic polymer provides flexibility. The epoxy resin provides a rigid three-dimensional cross-linked network, forming strong chemical bonds (such as Si-OC) with the negative electrode active material (such as silicon / graphite) through epoxy groups, significantly improving the mechanical strength of the electrode and preventing the active material from breaking and falling off during charging and discharging. Moreover, the high modulus of the epoxy resin can constrain the volume change of the silicon-based material, reducing electrode structure collapse. At the same time, the long-chain acrylic polymer imparts elasticity to the adhesive, absorbing cyclic expansion stress through the extension and rebound of the molecular chains, preventing electrode cracking; and the flexible chain segments buffer stress concentration between the active particles and the current collector, inhibiting interface delamination. Therefore, the negative electrode adhesive provided in this application can simultaneously possess strength and flexibility, resisting battery cyclic expansion and improving battery capacity.

[0016] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0017] The embodiments of this application will now be described in more detail. It should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0018] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0019] It should be understood that although the terms "first," "second," "third," etc., may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0020] An ideal binder must possess excellent flexibility to buffer the volumetric stress of the electrode while providing sufficient adhesion to ensure tight bonding between the active material and the current collector, and between particles, preventing material detachment and structural damage. In related technologies, PAA-type compounds are used as binders. PAA-type binders have high strength, and when added to the electrode, they can improve the electrode's peel strength and cohesion. However, due to the poor flexibility of PAA-type binders, they are insufficient to resist localized stress and fracture during the cycling expansion of silicon-carbon batteries, leading to electrode powder shedding and capacity decay.

[0021] To address the aforementioned issues, this application provides a negative electrode adhesive that possesses both strength and flexibility, can resist battery cyclic expansion, and improve battery capacity.

[0022] This application provides a negative electrode adhesive comprising an epoxy resin grafted with an acrylic polymer. The epoxy resin grafted with an acrylic polymer is formed by the reaction polymerization of an acrylic polymer, epichlorohydrin, a glycol / diphenol compound and an initiator in a molar ratio of 1:800~80000:750~75000:750~1500.

[0023] In this embodiment, epichlorohydrin and glycol / diphenol compounds directly participate in the grafting reaction, eliminating the need for pre-synthesization of epoxy resin and simplifying the process. Epichlorohydrin and glycol / diphenol compounds can generate epoxy resin in situ and graft acrylic acid chains, making it suitable for continuous production. Furthermore, the excess design of epichlorohydrin relative to glycol / diphenol compounds ensures sufficient reaction of epoxy groups, reduces unclosed chlorohydroxyl byproducts, and improves the electrolyte resistance of the adhesive; moreover, excess epichlorohydrin can participate in the grafting of acrylic acid chains, increasing the crosslinking point density and enhancing electrode strength.

[0024] In epoxy resin grafted with acrylic polymers, the epoxy resin provides rigidity, while the acrylic polymers provide flexibility. The epoxy resin provides a rigid three-dimensional cross-linked network, forming strong chemical bonds (such as Si-OC) with the negative electrode active material (such as silicon / graphite) through epoxy groups, significantly improving the mechanical strength of the electrode and preventing the active material from breaking and falling off during charging and discharging. Furthermore, the high modulus of the epoxy resin can constrain the volume change of the silicon-based material, reducing electrode structure collapse. Simultaneously, the long-chain acrylic polymer imparts elasticity to the adhesive, absorbing cyclic expansion stress through the stretching and rebound of the molecular chains, preventing electrode cracking; and the flexible chain segments buffer stress concentration between the active particles and the current collector, inhibiting interfacial delamination. Therefore, the negative electrode adhesive provided in this application embodiment possesses both strength and flexibility, resisting battery cyclic expansion and improving battery capacity.

[0025] The embodiments of this application also optimize the adhesive network structure by setting the molar ratio of acrylic polymer, epichlorohydrin, glycol / diphenol compound and initiator to 1:800~80000:750~75000:750~1500.

[0026] The molar ratio of acrylic polymers, epichlorohydrin, and glycol / bisphenol compounds is 1:800~80000:750~75000. When the molar ratio of acrylic polymers, epichlorohydrin, and glycol / bisphenol compounds is too low, the epoxy resin grafting rate is too low, which cannot ensure sufficient crosslinking density to form a rigid skeleton and provide the electrode with anti-pulverization ability. When the molar ratio of acrylic polymers to epoxy resin is too high, the excess epoxy resin will lead to excessive brittleness and will not be able to retain the flexibility of acrylic segments. Moreover, when the molar ratio of acrylic polymers to epoxy resin is low, such as 1:800~10000, it is suitable for low-expansion active material systems for negative electrodes, such as graphite negative electrodes. When the molar ratio of acrylic polymers to epoxy resin is high, such as 1:10000~80000, it is suitable for high-expansion active material systems for negative electrodes, such as silicon-based negative electrodes. The molar ratio of acrylic polymer to initiator is 1:750~1500, which can control the degree of grafting reaction and prevent excessive crosslinking (too much initiator) or insufficient branching (too little initiator), thus affecting the performance of the adhesive.

[0027] Therefore, the embodiments of this application can achieve a balance between strength and flexibility by limiting the molar ratio of acrylic polymers, epichlorohydrin, glycol / bisphenol compounds and initiators within the above range, making the adhesive adaptable to diverse negative electrode systems.

[0028] As an optional embodiment, the acrylic polymer is polymerized from acrylic monomers, including at least one of α-cyanoacrylate, methacrylic acid, ethylacrylic acid, propylacrylic acid, methyl α-cyanoacrylate, acrylamide, acrylonitrile, and hydroxymethylacrylamide.

[0029] In the embodiments of this application, α-cyanoacrylate is polymerized to generate poly(α-cyanoacrylate). Poly(α-cyanoacrylate) contains cyano groups (-CN) and carboxyl groups (-COOH), has high polarity, and easily forms hydrogen bond networks.

[0030] Methacrylic acid (MAA) is polymerized to produce polymethacrylic acid (PMAA). The side chain of polymethacrylic acid (PMAA) is methyl (-CH3), which can enhance hydrophobicity and reduce water absorption.

[0031] Ethyl acrylic acid is polymerized to produce polyethyl acrylic acid, whose side chains contain ethyl (-CH2CH3), which provides more flexible chain segments and improves ductility.

[0032] Propylene acrylic acid is polymerized to produce polypropyl acrylic acid. The long propyl chains (-CH2CH2CH3) contained in polypropyl acrylic acid can increase hydrophobicity and reduce electrolyte swelling.

[0033] Methyl α-cyanoacrylate is polymerized to produce poly(methyl α-cyanoacrylate), which contains cyano groups and ester groups (-COOCH3), and can have both high adhesive strength and rapid curing properties.

[0034] Acrylamide (AM) is polymerized to produce polyacrylamide (PAM). Polyacrylamide (PAM) contains amide groups (-CONH2), which have strong hydrophilicity and can enhance the adhesion between the electrode and the current collector through hydrogen bonding.

[0035] Acrylonitrile (AN) is polymerized to produce polyacrylonitrile (PAN). The cyano group (-CN) of polyacrylonitrile (PAN) gives it high rigidity, which can improve the mechanical strength of the electrode and resist electrolyte corrosion.

[0036] Hydroxymethylacrylamide (NMA) is polymerized to form poly(hydroxymethylacrylamide). Poly(hydroxymethylacrylamide) contains hydroxymethyl (-CH2OH), which can participate in cross-linking reactions and enhance the high-temperature resistance of adhesives.

[0037] The adhesive strength and flexibility of the adhesive can be controlled by selecting different acrylic monomers in the embodiments of this application.

[0038] The embodiments of this application can also achieve both high rigidity (PAN) and strong adhesion (PAM) by mixing different monomers (such as acrylonitrile + acrylamide).

[0039] As an optional embodiment, the diol / diphenol compound includes at least one of bisphenol A, tetraphenol ethane, glycerol, diphenolmethane, resorcinol, and phenolphthalein. Correspondingly, the epoxy resin includes at least one of bisphenol A type epoxy resin, tetraphenol epoxy resin, glycerol epoxy resin, diphenolmethane epoxy resin, resorcinol epoxy resin, and phenolphthalein epoxy resin.

[0040] In this embodiment, the raw material composition of the bisphenol A type epoxy resin is epichlorohydrin + bisphenol A (BPA, 2,2-bis(4-hydroxyphenyl)propane). The bisphenol A type epoxy resin has high mechanical strength, is resistant to electrolyte corrosion, and has a long cycle life.

[0041] Tetraphenolic epoxy resin is composed of epichlorohydrin and tetraphenolic ethane. It has a high crosslinking density, and the four phenolic hydroxyl groups can form a dense crosslinking network, resulting in extremely strong resistance to powdering of the electrode. It also has high temperature resistance.

[0042] The raw material composition of glycerol epoxy resin is epichlorohydrin + glycerol. The trihydroxy structure of glycerol in glycerol epoxy resin gives it elasticity, which is suitable for the expansion of silicon-based negative electrodes; and it is hydrophilic, which can improve the dispersibility of slurry and reduce agglomeration.

[0043] The raw material composition of bisphenol methane epoxy resin is epichlorohydrin + bisphenol propane, and bisphenol propane epoxy resin has high reactivity.

[0044] The raw material composition of resorcinol epoxy resin is epichlorohydrin + resorcinol. Resorcinol epoxy resin has high heat resistance and thermal stability better than bisphenol A.

[0045] The raw material composition of phenolphthalein epoxy resin is epichlorohydrin + phenolphthalein. The phenolphthalein structure of phenolphthalein epoxy resin can resist the corrosion of electrolyte decomposition byproducts.

[0046] The epoxy resins in this application can be selected from rigid (bisphenol A) to flexible (glycerol) to meet the needs of different negative electrode materials.

[0047] As an alternative embodiment, the molecular weight of the acrylic polymer is 300,000 to 1,000,000.

[0048] In this embodiment, the molecular weight of the acrylic polymer is limited to not less than 300,000, which allows the acrylic polymer to have long molecular chains. The long molecular chains intertwine to form a physical cross-linking network, which can give the electrode high toughness. The molecular weight of the acrylic polymer is limited to not more than 1 million, which can avoid the slurry viscosity from increasing dramatically due to excessively high molecular weight (affecting coating uniformity) or the chain segment mobility from decreasing (loss of flexibility).

[0049] In addition, the molecular weight in the embodiments of this application is the number average molecular weight.

[0050] As an alternative embodiment, the epoxy resin grafted with acrylic polymer has a molecular weight of 450,000 to 1,500,000.

[0051] In this embodiment, the molecular weight of the epoxy resin grafted with acrylic polymer is limited to not less than 450,000, which allows the molecular chains of the epoxy resin grafted with acrylic polymer to be long enough to form a strong physical entanglement network, improve the peel strength of the electrode, and resist the expansion stress of the silicon anode; the molecular weight of the epoxy resin grafted with acrylic polymer is limited to not more than 1,500,000, which can avoid the brittleness caused by the excessively high molecular weight of the epoxy resin grafted with acrylic polymer and retain the flexibility of the acrylic chain segments.

[0052] In addition, the molecular weight in the embodiments of this application is the number average molecular weight.

[0053] As an optional embodiment, the viscosity of the epoxy resin grafted with the acrylic polymer is 1000 Pa·s to 50000 mPa·s.

[0054] In this embodiment, the viscosity of the epoxy resin grafted with acrylic polymer is limited to not less than 1000 Pa·s to ensure the fluidity of the slurry and avoid coating cracking or uneven thickness. The viscosity of the epoxy resin grafted with acrylic polymer is limited to not more than 50000 mPa·s to prevent sedimentation and maintain uniform dispersion of the active material.

[0055] As an optional embodiment, the mass grafting rate of epoxy resin in the epoxy resin grafted acrylic polymer is 5% to 30%.

[0056] In the embodiments of this application, the grafting rate of epoxy resin (%) = (mass of grafted functional groups / total mass of polymer) × 100%.

[0057] In this embodiment, the mass grafting rate of epoxy resin in the epoxy resin-grafted acrylic polymer is not less than 5%, which can retain the flexibility advantage of the acrylic polymer and adapt to the electrode charging and discharging expansion; and the mass grafting rate of epoxy resin in the epoxy resin-grafted acrylic polymer is not higher than 30%, which can ensure sufficient epoxy resin crosslinking points and provide high bonding strength.

[0058] As an optional embodiment, the epoxy resin in the side chain of the epoxy resin grafted acrylic polymer has 10 to 50 repeating units, and the molecular weight of a single epoxy resin unit is 2,000 to 10,000.

[0059] In this embodiment, 10 to 50 repeating units provide an appropriate molecular chain length for epoxy resin grafted with acrylic polymer, ensuring sufficient crosslinking density (improving adhesive strength) while retaining the molecular chain mobility (maintaining flexibility).

[0060] The molecular weight of a single epoxy resin unit is 20,000 to 10,000, which can balance reactivity and steric hindrance, avoiding a sharp increase in slurry viscosity due to excessively long side chains or insufficient crosslinking due to excessively short side chains.

[0061] As an optional embodiment, the epoxy value of the epoxy resin grafted with the acrylic polymer is 0.003 to 0.02.

[0062] Epoxy value = (M1 × v × n) / (M2 × M3) × 100 mol Where M1 is the mass of the acrylic polymer, M2 is the molecular weight of the epoxy resin-grafted acrylic polymer, and M3 is the molecular weight of a single epoxy resin unit; ν is the mass grafting ratio of the epoxy resin in the epoxy resin-grafted acrylic polymer; and n is the number of hydroxyl groups on the diol / bisphenol compound (n=1,2,3...). In the embodiments of this application, the epoxy value of a single epoxy resin unit is 0.003~0.02, which means that every 100g of epoxy resin grafted with acrylic polymer contains 0.003mol~0.02mol of epoxy groups. This can ensure a moderate crosslinking rate, avoid excessive crosslinking (increased brittleness) caused by excessively high epoxy values ​​(>0.02), and reduce chemical stability and high temperature stability; and prevent insufficient adhesion caused by excessively low epoxy values ​​(<0.003).

[0063] In this embodiment, the epoxy resin grafted with acrylic polymer was analyzed by nuclear magnetic resonance (NMR). 1 In the 1H NMR spectrum, the two characteristic peaks of the side-chain epoxy resin appear at 3.0 ppm–4.5 ppm, 3.0 ppm–5.2 ppm, and 8 ppm–11 ppm, while the characteristic peaks of the PAA backbone appear at 2.0 ppm–3.0 ppm and 3.0 ppm–5.0 ppm. The two characteristic peaks of the epoxy resin on the side chain represent hydrogen atoms on the hydroxyl and epoxy groups, respectively, while the characteristic peaks on the PAA backbone represent hydrogen atoms on the carbonyl-linked carbon of the ester group and the ether-linked carbon of the ester group, respectively. The grafting rate can be calculated using 1H NMR spectroscopy.

[0064] In this embodiment, the glass transition temperature (Tg) of the epoxy resin grafted with acrylic polymer is in the range of -50℃ to 50℃. The higher the Tg, the greater the strength of the adhesive, but the worse the flexibility. Therefore, a Tg range of -50℃ to 50℃ can ensure both flexibility and strength.

[0065] In this embodiment, the epoxy resin grafted with acrylic polymer has two or more weight loss regions with weight loss temperatures ranging from 140°C to 280°C and from 260°C to 550°C. These two decomposition temperatures are the decomposition temperatures of the epoxy resin side chain and the main chain acrylic polymer, respectively. In the embodiments of this application, the tensile strength of epoxy resin grafted with acrylic polymer is 10MPa~100MPa at room temperature, and the elongation at break is 100%~300%.

[0066] Corresponding to the aforementioned application function implementation method embodiments, this application also provides a method for preparing a negative electrode adhesive, a negative electrode, and corresponding embodiments.

[0067] This application also provides a method for preparing a negative electrode adhesive, comprising: An acrylic polymer, epichlorohydrin, glycol / diphenol compounds, and an initiator are mixed in a molar ratio of 1:800~80000:750~75000:750~1500 and a polymerization reaction is carried out to obtain epoxy resin grafted acrylic polymer.

[0068] This application's embodiments involve epichlorohydrin and glycol / diphenol compounds directly participating in the grafting reaction, eliminating the need for pre-synthesizing epoxy resin and simplifying the process. Epichlorohydrin and glycol / diphenol compounds can generate epoxy resin in situ and graft acrylic acid chains, making it suitable for continuous production. Furthermore, the excess design of epichlorohydrin relative to glycol / diphenol compounds ensures sufficient reaction of epoxy groups, reduces unclosed chlorohydroxyl byproducts, and improves the electrolyte resistance of the adhesive; moreover, excess epichlorohydrin can participate in the grafting of acrylic acid chains, increasing the crosslinking point density and enhancing electrode strength.

[0069] As a preferred embodiment, an epoxy resin grafted with an acrylic polymer is obtained, comprising: The acrylic polymer is dissolved in the first solvent and stirred at 70℃~90℃ for 1h~24h. Add epichlorohydrin and glycol / diphenol compounds; At 60℃~80℃, an initiator and a second solvent are added to polymerize an epoxy resin-grafted acrylic polymer.

[0070] In this embodiment, the acrylic polymer is pre-dissolved using a first solvent to ensure complete dissolution and chain extension, avoiding uneven subsequent reactions. Furthermore, the reaction is carried out in stages: epichlorohydrin and glycol / bisphenol are added first to pre-activate the epoxy groups, followed by the introduction of the initiator and the second solvent, which reduces side reactions. Moreover, the initiator is added after monomer premixing to ensure efficient grafting of the epoxy resin onto the acrylic backbone.

[0071] In a preferred embodiment, the solvent includes at least one of dichloroethane, dichloromethane, DMSO, DMF, toluene, and benzene; and / or, the first solvent includes an alcohol solvent.

[0072] In the embodiments of this application, when the first solvent includes at least one of dichloroethane, dichloromethane, DMSO, DMF, toluene, and benzene, such solvents have strong solubility and can fully dissolve acrylic polymers (especially those containing polar groups such as cyano and amide groups); and create an inert environment to inhibit the hydrolysis of epichlorohydrin. When the first solvent includes an alcohol solvent, methanol, ethanol, etc., can be selected. The hydroxyl groups of alcohol solvents can promote the ring-opening of epoxy groups and accelerate the grafting reaction.

[0073] In the embodiments of this application, the second solvent is an alkaline solvent, including NaOH.

[0074] This application also provides a negative electrode sheet, including a current collector and a negative electrode active layer coated on at least one side of the current collector. The negative electrode active layer includes a negative electrode active material and an adhesive. The adhesive is the aforementioned negative electrode sheet adhesive, or a negative electrode sheet adhesive prepared by the aforementioned method for preparing negative electrode sheet adhesive.

[0075] In the embodiments of this application, the negative electrode active material can be one or more of graphite, carbon nanoparticles, graphene, hard carbon, silicon carbon, and silicon oxide.

[0076] As an optional embodiment, the binder has a mass percentage content of 1% to 10% in the negative electrode active layer, and the negative electrode active material has a mass percentage content of 90% to 99% in the negative electrode active layer.

[0077] To further understand the present invention, the following embodiments are provided to illustrate the present application. These embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0078] Example 1 1. Preparation of adhesive 1 mol of an acrylic polymer with α-cyanoacrylate monomer was dissolved in dichloromethane, 75 mol of methanol was added, and the mixture was stirred at 85°C for 10 h. Then, 800 mol of epichlorohydrin and 750 mol of bisphenol A were added, and 750 mol of azobisisobutyronitrile and 750 mol of NaOH were added at 70°C to copolymerize the acrylic polymer with epoxy resin. The epoxy resin-grafted acrylic polymer was used as a binder.

[0079] 2. Preparation of the negative electrode sheet The binder, graphite, silicon carbide, CMC, and SWCNTs were added in the following order: 5:72.5:19:1.2:2.3 and stirred. The mixture was then coated onto copper foil, dried, and rolled to obtain the negative electrode sheet.

[0080] Examples 2-17 and Comparative Examples 1-11 Examples 2-17 and Comparative Examples 1-11 follow the same basic steps as Example 1, with differences shown in Table 1.

[0081] Table 1 Formulation Table

[0082] 3. Performance Testing (1) Tensile strength and elongation at break of the adhesive Sample preparation: Select a uniform, crack-free, dried, and moisture-free adhesive film, cut it into dumbbell shapes of uniform size, and record the length l0, width W, and thickness H of the test area. The uniform cutting size is: l0 is 4cm, W is 1cm, and the thickness can be obtained by measuring the actual adhesive film with a micrometer. Test method: Fix both ends of the dumbbell-shaped adhesive film to the clamps of the tensile tester. With the adhesive film in a relaxed state, manually reset the tensile force and elongation of the device to zero and start the test. Read and record the peak tensile force F and the elongation l1. The tensile strength σ of the adhesive film can be calculated as σ = F / (W·H) and the elongation ε = l1 / l0 × 100%.

[0083] (2) Peel strength of negative electrode Sample preparation: Select dried electrode sheets that have been rolled and dried for 48 hours and cut them into rectangular electrode sheet samples with a size of 20cm*5cm; Test method: 90° peel strength test. Fix the electrode sheet to the platform below the tensile testing machine with tape. Tear off the negative electrode coating from one end of the foil and fix it on the movable fixture, keeping it perpendicular to the platform. Turn on the tensile testing machine and stretch the sample at a constant speed of 5 mm / min. After the values ​​stabilize, read the peel force and peel strength. Test three samples in parallel and take the average peel strength to obtain the peel strength of the negative electrode sheet.

[0084] (3) Bending strength and bending fracture angle of the negative electrode sheet Sample preparation: Select the dried electrode sheets after roller pressing and cut them into standard samples with a size of 38*80mm; Test method: Fix the flat electrode sheet on the test device, bend the electrode sheet by rotating the device, measure the stress and strain of the electrode sheet at different bending angles, and read the angle and strain intensity at which the electrode sheet breaks to obtain the bending fracture point and bending strength of the negative electrode sheet.

[0085] (4) Resistivity of the negative electrode Sample preparation: Select the dried electrode sheets after roller pressing and cut them into standard samples with a size of 30cm*20cm; Test method: Fix the flat electrode sheet on the test device, reset the resistance and thickness, set the test parameters of the device, holding time: 15s, pressure: 25Kg, number of samples: 12, output the test report after the test, and take the average value of the resistivity of the 12 films to obtain the film resistivity of the negative electrode sheet.

[0086] The test results for each embodiment and comparative example are shown in Table 2.

[0087] Table 2 Test Results

[0088] According to Tables 1 and 2, and through Examples 1 to 3, and Comparative Examples 2 to 7, it can be seen that when epoxy resin grafted with acrylic polymer is polymerized by reacting acrylic polymer, epichlorohydrin, glycol / diphenol compound and initiator in a molar ratio of 1:800~80000:750~75000:750~1500, epoxy resin grafted with acrylic polymer can simultaneously possess strength and flexibility, resist battery cycle expansion and improve battery capacity.

[0089] According to Examples 6 to 10 and Comparative Example 9, when the diol / diphenol compound is not selected from the compounds of the embodiments of this application, the mass grafting rate of epoxy resin in the prepared epoxy resin-grafted acrylic polymer is not in the range of 5% to 30%, the molecular weight of a single epoxy resin unit is not in the range of 2000 to 10000, and the epoxy value of the epoxy resin-grafted acrylic polymer is not in the range of 0.003 to 0.02. As a result, the prepared epoxy resin-grafted acrylic polymer cannot simultaneously possess both strength and flexibility.

[0090] According to Examples 11 to 17 and Comparative Example 8, when the acrylic polymer is not selected from the compounds of the present application, the epoxy value of the epoxy resin grafted with acrylic polymer is not in the range of 0.003 to 0.02, which results in the epoxy resin grafted with acrylic polymer not having both strength and flexibility at the same time.

[0091] According to Examples 1 to 5, and Comparative Examples 10 and 11, when the molecular weight of the acrylic polymer is less than 300,000, the mass grafting rate of the epoxy resin in the prepared epoxy resin-grafted acrylic polymer is not in the range of 5% to 30%, and the molecular weight of the epoxy resin-grafted acrylic polymer is not in the range of 450,000 to 1,500,000. As a result, the prepared epoxy resin-grafted acrylic polymer cannot simultaneously possess both strength and flexibility.

[0092] Although this application has been described with reference to preferred embodiments, those skilled in the art will understand that various changes can be made and equivalents can be substituted for the elements, as long as they do not depart from the scope of this application. Furthermore, many modifications can be made to adapt particular situations or materials to the teachings of this application, as long as they do not depart from the essential scope of this application. Therefore, this application is not intended to be limited to the specific embodiments disclosed as the best mode of carrying out this application as conceived, but rather this application will include all embodiments falling within the scope of the appended claims.

[0093] All scopes disclosed in this application include endpoints, and endpoints can be combined with each other.

[0094] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A negative electrode sheet adhesive, characterized by comprising: The epoxy resin grafted acrylic polymer is prepared by polymerization of acrylic monomers, the acrylic monomers including at least one of alpha-cyanoacrylic acid, methacrylic acid, ethyl acrylic acid, propyl acrylic acid, methyl alpha-cyanoacrylate, acrylamide, acrylonitrile, and hydroxymethyl acrylamide.

2. The negative electrode sheet binder according to claim 1, characterized by The diol / diphenol compound includes at least one of bisphenol A, tetraphenyl ethane, glycerol, diphenol methane, resorcinol, and phenothalin.

3. The negative electrode sheet binder according to claim 1, wherein The acrylic polymer has a molecular weight of 300,000 to 1,000,000.

4. The negative electrode sheet binder according to claim 1, wherein The epoxy resin grafted acrylic polymer has a molecular weight of 450,000 to 1,500,000; and / or, the epoxy resin grafted acrylic polymer has a viscosity of 1,000 Pa·s to 50,000 mPa·s.

5. The negative electrode sheet binder according to claim 1, wherein The epoxy resin grafted acrylic polymer has a grafting rate of 5% to 30% of the epoxy resin; and / or, the epoxy resin grafted acrylic polymer has 10 to 50 repeating units of the epoxy resin in the side chain, and a molecular weight of 2,000 to 10,000 of a single epoxy resin unit; and / or, the epoxy resin grafted acrylic polymer has an epoxy value of 0.003 to 0.

02.

6. The negative electrode sheet binder according to claim 1, wherein The method comprises:

7. A method for producing a negative electrode sheet binder, characterized by comprising the steps of: The epoxy resin grafted acrylic polymer is prepared by mixing acrylic polymer, epichlorohydrin, diol / diphenol compound, and initiator in a molar ratio of 1:800-80,000:750-75,000:750-1,500, and then polymerizing. The method for preparing the epoxy resin grafted acrylic polymer comprises:

8. The preparation method according to claim 7, characterized in that, The acrylic polymer is dissolved in a first solvent, and stirred at 70-90°C for 1-24 hours; The epichlorohydrin and diol / diphenol compound are added; The initiator and a second solvent are added at 60-80°C, and polymerized to obtain the epoxy resin grafted acrylic polymer. The first solvent includes at least one of dichloroethane, dichloromethane, dimethyl sulfoxide, N,N-dimethylformamide, toluene, and benzene; and / or, the first solvent includes an alcohol solvent; and / or, the second solvent is an alkaline solvent.

9. The production method according to claim 8, characterized by, The negative electrode active layer includes a negative electrode active material and a binder, and the binder is the negative electrode sheet binder according to any one of claims 1 to 6, or the negative electrode sheet binder prepared by the method according to any one of claims 7 to 9.

10. A negative electrode sheet characterized by comprising: ​

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