Binder, secondary battery, and electric device

Abstract

This application belongs to the field of secondary battery technology, specifically relating to an adhesive, a secondary battery, and an electrical device. The adhesive provided in this application includes a polyacrylic acid backbone; it also includes grafted chains containing hydroxyl groups, grafted chains containing nitrogen atoms, grafted chains containing borate groups, grafted chains containing phosphate ester groups, and grafted chains containing thiol groups. By introducing multiple grafted chains onto the polyacrylic acid backbone, this application enables the adhesive to form a multidimensional synergistic reinforcement structure of "mechanics-electrochemistry," resulting in multidimensional adhesion between the adhesive and silicon-based materials, and improving the conductivity of the adhesive, thereby enhancing the cycle and rate performance of the battery.

Description

Technical Field

[0001] This application belongs to the field of secondary battery technology, specifically relating to an adhesive, a secondary battery, and an electrical device. Background Technology

[0002] Currently, silicon-based materials are attracting considerable attention as anode materials for lithium-ion batteries. However, the significant volume expansion effect of silicon-based materials limits their application, leading to electrode peeling during charge and discharge, which affects the battery's cycle performance. Electrode binders are crucial materials for lithium-ion batteries and a major source of electrode mechanical properties, significantly influencing the battery's electrochemical performance. Among them, polyacrylate adhesives possess good bonding and processing properties, but when used in combination with silicon-based materials, they cannot adapt to the significant volume expansion effect of silicon, easily resulting in detachment and insufficient adhesion. Furthermore, polyacrylate adhesives themselves have low ionic conductivity, all of which affect the battery's rate performance and cycle performance. Summary of the Invention

[0003] Therefore, the technical problem to be solved by this application is to overcome the fact that the application of polyacrylate adhesive in silicon-containing systems in the prior art cannot improve the cycle performance and rate performance of the battery.

[0004] In a first aspect, this application provides an adhesive comprising a polyacrylic acid backbone; It also includes grafted chains containing hydroxyl groups, grafted chains containing nitrogen atoms, grafted chains containing boric acid groups, grafted chains containing phosphate ester groups, and grafted chains containing thiol groups.

[0005] In one alternative embodiment, the adhesive satisfies at least one of the following conditions: (1) The amount of grafted chains containing hydroxyl groups accounts for 5wt%~25wt% of the adhesive; (2) The amount of grafted chains containing N atoms accounts for 4wt%~12wt% of the adhesive; (3) The amount of grafted chains containing boric acid groups accounts for 3wt%~20wt% of the adhesive; (4) The amount of grafted chains containing phosphate ester groups accounts for 1wt%~4wt% of the adhesive; (5) The amount of grafted chains containing thiol groups accounts for 2wt% to 7wt% of the adhesive.

[0006] In one alternative embodiment, the hydroxyl-containing graft chain contains at least two hydroxyl groups.

[0007] In one alternative embodiment, the N atom in the grafted chain containing N atoms is present as -NH2.

[0008] In one optional embodiment, the number-average molecular weight Mn of the adhesive is 150,000 to 300,000.

[0009] In one optional embodiment, the weight-average molecular weight (Mw) of the adhesive is 220,000 to 750,000.

[0010] In one optional embodiment, the molecular weight distribution (PDI) of the adhesive is 1.5 to 2.5, where PDI = Mw / Mn.

[0011] Secondly, this application also provides a secondary battery, including a negative electrode sheet containing a negative electrode active layer, wherein the negative electrode active layer includes a negative electrode active material and the binder described in the first aspect.

[0012] In one optional embodiment, the negative electrode active material comprises a silicon-based material, wherein the silicon-based material accounts for 5 wt% to 20 wt% of the total mass of the negative electrode active material.

[0013] In one alternative embodiment, the binder accounts for 2% to 4% of the total mass of the negative electrode active layer.

[0014] Thirdly, this application also provides an electrical device, including the secondary battery described in the second aspect, wherein the secondary battery serves as the power supply for the electrical device.

[0015] The technical solution of this application has the following advantages: The binder provided in this application includes a polyacrylic acid backbone; it also includes graft chains containing hydroxyl groups, graft chains containing nitrogen atoms, graft chains containing borate groups, graft chains containing phosphate ester groups, and graft chains containing thiol groups. By introducing multiple graft chains onto the polyacrylic acid backbone, this application enables the binder to form a multidimensional synergistic reinforcement structure of "mechanics-electrochemistry," resulting in multidimensional adhesion between the binder and the silicon-based material and improving the conductivity of the binder. This solves the problem of the one-dimensional linear structure of polyacrylic acid easily detaching from the substrate when the silicon-based material expands in volume, which is beneficial for improving the electronic and ion conduction rates of the battery, thereby improving the cycle and rate performance of the battery. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the bonding between the adhesive and the silicon-based material of this application. Detailed Implementation

[0018] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0019] In a first aspect, this application provides an adhesive comprising a polyacrylic acid backbone; It also includes grafted chains containing hydroxyl groups, grafted chains containing nitrogen atoms, grafted chains containing boric acid groups, grafted chains containing phosphate ester groups, and grafted chains containing thiol groups.

[0020] This study found that introducing multiple grafted chains onto the polyacrylic acid backbone enables the binder to form a multidimensional synergistic reinforcing structure based on both mechanical and electrochemical processes. This allows for multidimensional adhesion between the binder and the silicon-based material, improving the binder's conductivity. This addresses the problem of the one-dimensional linear structure of polyacrylic acid easily detaching from the substrate when the silicon-based material expands in volume, thus improving the electronic and ion conduction rates of the battery. Figure 1 As shown, the adhesive provided in this application adheres and bonds to silicon-based materials through a multi-dimensional network structure.

[0021] Furthermore, firstly, this application grafts hydroxyl-containing graft chains onto the polyacrylic acid backbone, providing more hydrogen bond sites and improving the adhesion between the binder and the silicon-based material, thereby enhancing the electrode peel strength and thus improving the battery cycle performance. Secondly, the borate groups can form multiple dynamically reversible hydrogen bonds in the binder, effectively limiting the volume expansion of the silicon-based material during battery charging and discharging, and improving the mechanical properties of the binder, thereby improving the battery cycle performance. Thirdly, the thiol groups can suppress lithium dendrite formation and SEI film decomposition, enhancing interfacial bonding and benefiting battery cycle performance. Fourthly, the phosphate ester groups can preferentially participate in the formation of the negative electrode side solid electrolyte interfacial film (SEI film) on the negative electrode surface, improving the stability and density of the SEI film, reducing direct contact between the negative electrode and the electrolyte, thereby reducing the risk of electrolyte oxidation decomposition and side reactions occurring in the silicon-based material, and improving the overall cycle performance. The battery's cycle and rate performance are improved. Furthermore, the dynamic hydrogen bonds in the borate group help the negative electrode active layer repair cracks and inhibit pulverization. The phosphate-stabilized SEI film further reduces crack enlargement, jointly enhancing the interface stability on the negative electrode side. Simultaneously, both the phosphate and thiol groups are highly polar, serving as ion transport channels to aid lithium-ion transport. Based on the stable interface of the borate and phosphate groups, the ion transport rate at the interface is further enhanced. Fifthly, the grafted chains containing nitrogen atoms are rich in lone pairs of electrons, enabling coordination with lithium ions and providing polar channels. The hydrogen bond network with hydroxyl groups provides more ion transport channels, thereby improving the lithium-ion transport rate. It can also work with the phosphate groups to enhance interface stability, which is beneficial for the battery's cycle and rate performance. In addition, the hydrogen bonds of the hydroxyl groups can further enhance the polarity of the nitrogen atoms, increasing ionic conductivity and improving the battery's rate performance.

[0022] In one alternative embodiment, the adhesive satisfies at least one of the following conditions: (1) The amount of grafted hydroxyl-containing grafted chains accounts for 5wt% to 25wt% of the adhesive; thus, the adhesive can improve the peel strength of the electrode and avoid high viscosity, thereby ensuring the flexibility of the adhesive and reducing the possibility of cracking. The amount of grafted hydroxyl-containing grafted chains can be obtained by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), or X-ray photoelectron spectroscopy (XPS). For example, the amount of grafted hydroxyl-containing grafted chains can be 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 25wt%, etc., or values ​​within any two of the above ranges.

[0023] (2) The amount of grafted chains containing N atoms accounts for 4wt% to 12wt% of the binder; thus, while ensuring low interfacial impedance, the ionic conductivity of the binder can be effectively improved, the rate performance of the battery can be enhanced, and the binder can be guaranteed to have good stability and reduce side reactions. The amount of grafted chains containing N atoms can be obtained by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), or elemental analysis. For example, the amount of grafted chains containing N atoms can be 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, etc., or values ​​within any two of the above ranges.

[0024] (3) The grafting amount of the borate-containing grafted chain accounts for 3wt% to 20wt% of the binder; in this way, a hydrogen bond network can be formed, thereby effectively suppressing the volume expansion of the silicon-based material and ensuring the stability of the main chain structure of polyacrylic acid, thereby improving the mechanical properties and coating uniformity of the binder, reducing the occurrence of side reactions, lowering the interfacial impedance, which is beneficial to the cycle and rate performance of the battery, and avoiding problems such as excessive borate affecting the interfacial impedance or increasing side reactions, and weakening the bonding force with the negative electrode sheet; the grafting amount of the borate-containing grafted chain can be obtained by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS). For example, the grafting amount of the borate-containing grafted chain can be 3wt%, 5wt%, 7wt%, 10wt%, 13wt%, 15wt%, 17wt%, 20wt%, etc., or values ​​within any two of the above values.

[0025] (4) The grafting amount of the phosphate ester-containing grafted chains accounts for 1wt% to 4wt% of the binder; thus, a more stable and dense SEI film can be formed, and the adverse effects of excessive phosphorus leading to electrolyte decomposition or increased interfacial impedance can be avoided; the grafting amount of the phosphate ester-containing grafted chains can be obtained by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDS). For example, the grafting amount of the phosphate ester-containing grafted chains can be 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, etc., or values ​​within any two of the above ranges.

[0026] (5) The grafting amount of the thiol-containing grafted chains accounts for 2wt% to 7wt% of the binder; this effectively suppresses lithium dendrites and reduces the generation of sulfur-containing byproducts, thereby ensuring the battery capacity; the grafting amount of the thiol-containing grafted chains can be obtained by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), or elemental analysis. For example, the grafting amount of the phosphate ester-containing grafted chains can be 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, etc., or values ​​within any two of the above ranges.

[0027] In one alternative embodiment, the hydroxyl-containing graft chain contains at least two hydroxyl groups; this further increases the number of hydrogen bond sites in the graft chain, thereby further improving the adhesion between the binder and the silicon-based material, which is beneficial to the cycle performance of the battery.

[0028] In one optional embodiment, the N-atom-containing graft chain exists as -NH2; this can improve the stability and ionic conductivity of the binder. Furthermore, when the negative electrode active material includes a silicon-based material, -NH2 can also combine with the hydroxyl groups on the surface of the silicon-based material, increasing the interfacial bonding force and preventing the silicon-based material from being corroded by acidic byproducts during cycling, thereby improving the cycle and rate performance of the battery.

[0029] In one alternative embodiment, the hydroxyl-containing graft chain is introduced via a grafting reaction of a polyhydroxy compound with the polyacrylic acid backbone.

[0030] In one alternative embodiment, the graft chain containing N atoms is introduced via a grafting reaction of an amino-containing compound with the polyacrylic acid backbone.

[0031] In one alternative embodiment, the graft chain containing borate groups is introduced via a grafting reaction of a borate-containing compound with the polyacrylic acid backbone.

[0032] In one alternative embodiment, the phosphate ester-containing graft chain is introduced via a grafting reaction of a phosphorus-containing organic compound with the polyacrylic acid backbone.

[0033] In one alternative embodiment, the thiol-containing graft chain is introduced via a grafting reaction of a sulfur-containing organic compound with the polyacrylic acid backbone.

[0034] In one alternative embodiment, the adhesive satisfies at least one of the following conditions: ①The polyhydroxy compound includes at least one of propylene glycol, ethylene glycol, polyhydroxyphenol, and glycerol; further, the polyhydroxyphenol includes at least one of 1,2-benzenediol, 1,3-benzenediol, or 1,6-trihydroxyphenol; ②The amino-containing compound includes at least one of acrylamide, methacrylamide, and dopamine; ③ The boronic acid-containing compound includes at least one of boric acid and sodium tetraborate; ④ The phosphorus-containing organic compound includes at least one of monomethyl phosphate, monoethyl phosphate, trimethyl phosphate, phosphate acrylate, and diethyl phosphate; ⑤ The sulfur-containing organic compounds include at least one of mercaptoacetic acid, mercaptopropionic acid, mercaptoethyl acrylate, and disulfides.

[0035] In one optional embodiment, the number-average molecular weight Mn of the binder is 150,000 to 300,000. This ensures a low viscosity and uniform coating of the electrode slurry, while maintaining good adhesion between the binder and the current collector or active material, forming a stable hydrogen bond network to suppress volume expansion of the active material. Simultaneously, the binder exhibits good flexibility, preventing cracking when in contact with the active material, and ensures uniform distribution of polar groups within the binder, resulting in a better ion transport rate and lower interfacial impedance, which is beneficial for the battery's cycle performance and rate capability. The number-average molecular weight Mn of the binder can be... The sample is determined using conventional methods in the art, such as gel permeation chromatography (GPC): the binder is dissolved in a solvent (e.g., at least one of tetrahydrofuran (THF), water, or N,N-dimethylformamide (DMF)) at a concentration controlled between 0.1 and 0.5 wt%, the solution is filtered to remove impurities, and the sample is calibrated using a polystyrene (PS) standard of known molecular weight. The sample is injected into the GPC system and passed through the column at a constant flow rate (e.g., 1.0 mL / min). The elution curves of different molecular weight components are recorded by a detector (e.g., a differential refractive index detector or a UV detector), and the number-average molecular weight Mn is calculated from the calibration curve.

[0036] For example, the number average molecular weight Mn of the adhesive can be 150,000, 170,000, 190,000, 200,000, 220,000, 240,000, 250,000, 260,000, 280,000, 300,000, or a value within the range of any two of the above values.

[0037] The binder has a weight-average molecular weight (Mw) of 220,000 to 750,000. This ensures a low viscosity and uniform coating of the electrode slurry, while also providing good adhesion between the binder and the current collector or active material, forming a stable hydrogen bond network to suppress volume expansion of the active material. Simultaneously, the binder exhibits good flexibility, preventing cracking when in contact with the active material, and ensures a uniform distribution of polar groups within the binder, resulting in a good ion transport rate and low interfacial impedance, which is beneficial for the battery's cycle performance and rate capability. The weight-average molecular weight (Mw) of the binder can be a commonly used parameter in the art. The weight-average molecular weight (Mw) is determined by a standard method, such as gel permeation chromatography (GPC): the binder is dissolved in a solvent (e.g., at least one of tetrahydrofuran (THF), water, or N,N-dimethylformamide (DMF)) at a concentration controlled between 0.1 and 0.5 wt%, the solution is filtered to remove impurities, and the system is calibrated using a polystyrene (PS) standard of known molecular weight. The sample is injected into the GPC system and passed through the column at a constant flow rate (e.g., 1.0 mL / min). The elution curves of different molecular weight components are recorded by a detector (e.g., a differential refractive index detector or a UV detector), and the weight-average molecular weight (Mw) is calculated from the calibration curve.

[0038] For example, the weight-average molecular weight Mw of the adhesive can be 220,000, 250,000, 300,000, 350,000, 400,000, 450,000, 500,000, 550,000, 600,000, 650,000, 700,000, 750,000, etc., or a value within the range of any two of the above values.

[0039] In one optional embodiment, the molecular weight distribution (PDI) of the binder is 1.5 to 2.5, where PDI = Mw / Mn. This moderate molecular weight distribution of the binder improves its mechanical strength and toughness, effectively mitigating the volume expansion of the active material. It also ensures a uniform distribution of polar groups in the binder, enhancing the lithium-ion transport rate. Furthermore, the electrode solution containing the binder has a moderate viscosity, resulting in uniform coating and strong adhesion to the current collector and active material, leading to good interfacial stability and improved battery cycle performance and rate capability. For example, the molecular weight distribution (PDI) of the binder can be 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, or a value within any two of the above ranges.

[0040] Secondly, this application provides a secondary battery, including a negative electrode sheet containing a negative electrode active layer, wherein the negative electrode active layer includes a negative electrode active material and a binder, and the binder includes the binder described in the first aspect.

[0041] In one optional embodiment, the negative electrode active material comprises a silicon-based material, which accounts for 5wt% to 20wt% of the total mass of the negative electrode active material. This approach fully utilizes the high specific capacity of the silicon-based material to improve the battery's energy density while ensuring structural stability, thus benefiting the battery's cycle performance and rate performance. The method for determining the proportion of silicon-based material in the total mass of the negative electrode active material includes using scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS). Specifically, the negative electrode material is dispersed in ethanol, drop-coated onto a conductive tape, vacuum dried, and its morphology observed under SEM. Multiple randomly selected regions are then subjected to EDS energy dispersive spectroscopy analysis. The atomic percentages of Si and C in the EDS (which require correction) are then calculated.

[0042] For example, the silicon-based material may account for 5 wt%, 7 wt%, 10 wt%, 13 wt%, 15 wt%, 17 wt%, 20 wt%, or a value within any two of the above values.

[0043] The binder accounts for 2wt% to 4wt% of the total mass of the negative electrode active layer. This ensures the bonding force between the active layer and the current collector, improves electrode stability, and allows for the addition of more active material, thereby increasing the battery's specific capacity and ion transport efficiency. The test method for determining the mass of the binder as a percentage of the total mass of the negative electrode active layer is thermogravimetric analysis (TGA). Specifically, approximately 5-10 mg of the negative electrode sample is taken, cut into small pieces, placed in a TGA crucible, and heated to 800°C in air at a rate of 10°C / min. The mass loss Δm is obtained, and the mass of the binder as a percentage of the total mass of the negative electrode active layer is calculated as Δm / (m 负极极片样品 -m 样品箔材 )×100%.

[0044] For example, the mass of the binder as a percentage of the total mass of the negative electrode active layer can be 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, or a value within any two of the above values.

[0045] In one alternative embodiment, the silicon-based material includes at least one of silicon-carbon materials, silicon-oxygen materials, and elemental silicon, wherein the silicon-carbon material includes materials in which single-crystal silicon is deposited in a porous carbon framework.

[0046] In one optional embodiment, the negative electrode active material further includes a carbon-based material; the carbon-based material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, and amorphous carbon.

[0047] In one alternative embodiment, the negative electrode active material further includes lithium titanate.

[0048] In one optional embodiment, the negative electrode further includes a conductive agent. The type and amount of the conductive agent are not limited, and conventionally selected materials in the art are acceptable. Further, the conductive agent includes at least one of conductive carbon black, carbon nanotubes, and graphene.

[0049] In one alternative embodiment, the secondary battery further includes a positive electrode, a separator, and an electrolyte.

[0050] In one optional embodiment, the positive electrode sheet includes a positive current collector and a positive active material, a positive binder, and a conductive agent covering the positive current collector. This application does not limit the type and content of the conductive agent and the positive binder; conventional selections in the art are acceptable.

[0051] In one alternative embodiment, the conductive agent includes at least one of conductive carbon black, carbon nanotubes, and graphene.

[0052] In one alternative embodiment, the positive electrode binder comprises polyvinylidene fluoride.

[0053] In one optional embodiment, the diaphragm can be any material conventionally selected in the art, and this application does not impose specific limitations. Further, in one optional embodiment, the diaphragm includes at least one of a polypropylene membrane, a polyethylene membrane, a polyvinylidene fluoride membrane, a spandex membrane, an aramid membrane, or a multilayer composite membrane modified with a coating.

[0054] In one optional embodiment, the electrolyte comprises a lithium salt, an organic solvent, and additives, which can be selected using conventional methods in the art, and this application does not impose specific limitations. Further, in one optional embodiment, the lithium salt comprises lithium hexafluorophosphate. Further, in one optional embodiment, the organic solvent comprises at least one selected from ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and propyl propionate.

[0055] Thirdly, this application provides an electrical device including the secondary battery described in the second aspect, wherein the secondary battery serves as the power supply for the electrical device.

[0056] Example A1 This embodiment provides a method for preparing an adhesive, including the following steps: (1) Add 10g of polyacrylic acid (PAA) (molecular weight of 10000~200000g / mol) binder to 100mL of water, stir and mix to dissolve, then add 1wt% of initiator ammonium persulfate (APS), transfer to a reaction vessel, and then add ethylene glycol according to the weight ratio of ethylene glycol to polyacrylic acid of 0.1:1. Adjust the temperature to 60℃ under nitrogen atmosphere, mix and stir for 3h to obtain intermediate product A; (2) Add 0.5wt% of initiator hydrogen peroxide (H2O2) to intermediate product A, stir evenly, add acrylamide according to the weight ratio of acrylamide to polyacrylic acid of 0.06:1, adjust the temperature to 50℃ under nitrogen atmosphere, mix and stir for 4h to obtain intermediate product B; (3) Add an appropriate amount of phosphate buffer solution to intermediate product B, adjust the pH of the solution to 8, and then add boric acid solution according to the weight ratio of boric acid to polyacrylic acid of 0.05:1. Adjust the temperature to 60°C under nitrogen atmosphere, mix and stir for 3 hours to obtain intermediate product C. (4) Add 0.5wt% N,N'-methylenebisacrylamide catalyst to intermediate product C, stir evenly, and then add mercaptoacetic acid according to the weight ratio of mercaptoacetic acid to polyacrylic acid of 0.03:1. Adjust the temperature to 60℃ under nitrogen atmosphere, mix and stir for 2h to obtain intermediate product D. (5) Add 0.5wt% concentrated sulfuric acid to intermediate product D, stir evenly, and then add trimethyl phosphate according to the weight ratio of trimethyl phosphate to polyacrylic acid of 0.02:1. Adjust the temperature to 60℃ under nitrogen atmosphere, mix and stir for 3h to obtain the adhesive.

[0057] The number-average molecular weight (Mn) of the adhesive in this embodiment is 200,000; the weight-average molecular weight (Mw) of the adhesive is 300,000; PDI = 1.5; and based on the mass of the adhesive in this embodiment, the grafting amount of the hydroxyl-containing grafted chain is 8 wt%, the grafting amount of the nitrogen-containing grafted chain is 4.5 wt%, the grafting amount of the boric acid-containing grafted chain is 4 wt%, the grafting amount of the thiol-containing grafted chain is 2.4 wt%, and the grafting amount of the phosphate ester-containing grafted chain is 1.6 wt%.

[0058] Example A2 This embodiment provides a method for preparing an adhesive, including the following steps: (1) Add 10g of polyacrylic acid (PAA) binder to 100mL of water, stir and mix to dissolve, then add 1wt% of initiator ammonium persulfate (APS), transfer to a reactor, and then add ethylene glycol according to the weight ratio of ethylene glycol to polyacrylic acid of 0.15:1. Adjust the temperature to 80℃ under a nitrogen atmosphere, mix and stir for 2h to obtain intermediate product A; (2) Add 0.5wt% of initiator hydrogen peroxide (H2O2) to intermediate product A, stir evenly, add acrylamide according to the weight ratio of acrylamide to polyacrylic acid of 0.06:1, adjust the temperature to 70℃ under nitrogen atmosphere, mix and stir for 3h to obtain intermediate product B; (3) Add an appropriate amount of phosphate buffer solution to intermediate product B, adjust the pH of the solution to 8, and then add boric acid solution according to the weight ratio of boric acid to polyacrylic acid of 0.05:1. Adjust the temperature to 60°C under nitrogen atmosphere, mix and stir for 3 hours to obtain intermediate product C. (4) Add 0.5wt% N,N'-methylenebisacrylamide catalyst to intermediate product C, stir evenly, and then add mercaptoacetic acid according to the weight ratio of mercaptoacetic acid to polyacrylic acid of 0.04:1. Adjust the temperature to 60℃ under nitrogen atmosphere, mix and stir for 2h to obtain intermediate product D. (5) Add 0.5wt% concentrated sulfuric acid to intermediate product D, stir evenly, and then add trimethyl phosphate according to the weight ratio of trimethyl phosphate to polyacrylic acid of 0.02:1. Adjust the temperature to 60℃ under nitrogen atmosphere, mix and stir for 3h to obtain the adhesive.

[0059] The number-average molecular weight (Mn) of the adhesive in this embodiment is 180,000; the weight-average molecular weight (Mw) of the adhesive is 400,000; PDI = 2.22; and based on the mass of the adhesive in this embodiment, the grafting amount of the hydroxyl-containing grafted chain is 9 wt%, the grafting amount of the nitrogen-containing grafted chain is 4.2 wt%, the grafting amount of the boric acid-containing grafted chain is 4 wt%, the grafting amount of the thiol-containing grafted chain is 3 wt%, and the grafting amount of the phosphate ester-containing grafted chain is 1.6 wt%.

[0060] Example A3 This embodiment provides a method for preparing an adhesive, including the following steps: (1) Add 10g of polyacrylic acid (PAA) binder to 100mL of water, stir and mix to dissolve, then add 1wt% of initiator ammonium persulfate (APS), transfer to a reactor, and then add ethylene glycol according to the weight ratio of ethylene glycol to polyacrylic acid of 0.2:1. Adjust the temperature to 70℃ under a nitrogen atmosphere, mix and stir for 3h to obtain intermediate product A; (2) Add 0.5wt% of initiator hydrogen peroxide (H2O2) to intermediate product A, stir evenly, add acrylamide according to the weight ratio of acrylamide to polyacrylic acid of 0.06:1, adjust the temperature to 80℃ under nitrogen atmosphere, mix and stir for 2h to obtain intermediate product B; (3) Add an appropriate amount of phosphate buffer solution to intermediate product B, adjust the pH of the solution to 8, and then add boric acid solution according to the weight ratio of boric acid to polyacrylic acid of 0.06:1. Adjust the temperature to 60°C under nitrogen atmosphere, mix and stir for 3 hours to obtain intermediate product C. (4) Add 0.5wt% N,N'-methylenebisacrylamide catalyst to intermediate product C, stir evenly, and then add mercaptoacetic acid according to the weight ratio of mercaptoacetic acid to polyacrylic acid of 0.04:1. Adjust the temperature to 60℃ under nitrogen atmosphere, mix and stir for 2h to obtain intermediate product D. (5) Add 0.5wt% concentrated sulfuric acid to intermediate product D, stir evenly, and then add trimethyl phosphate according to the weight ratio of trimethyl phosphate to polyacrylic acid of 0.04:1. Adjust the temperature to 60℃ under nitrogen atmosphere, mix and stir for 3h to obtain the adhesive.

[0061] The number-average molecular weight (Mn) of the adhesive in this embodiment is 190,000; the weight-average molecular weight (Mw) of the adhesive is 380,000; PDI = 2.00; and based on the mass of the adhesive in this embodiment, the grafting amount of the hydroxyl-containing graft chain is 12 wt%, the grafting amount of the N-atom-containing graft chain is 4.1 wt%, the grafting amount of the borate-containing graft chain is 4 wt%, the grafting amount of the thiol-containing graft chain is 3 wt%, and the grafting amount of the phosphate ester-containing graft chain is 2.5 wt%.

[0062] Example A4 This embodiment provides a method for preparing an adhesive. The only difference from Example 1 is that propylene glycol is used instead of ethylene glycol in step (1).

[0063] Example A5 This embodiment provides a method for preparing an adhesive. The only difference from Example 1 is that in step (2), methacrylamide is used instead of acrylamide in Example 1.

[0064] Example A6 This embodiment provides a method for preparing an adhesive. The only difference from Example 1 is that sodium tetraborate is used instead of boric acid in step (3).

[0065] The preparation methods of Examples A7-A16 are basically the same as those of Example 1, with the differences shown in Table 1. The performance parameters of the adhesives obtained in Examples A7-A16 are shown in Table 2. Note that " / " indicates that the item does not exist.

[0066] Table 1. Preparation methods of each embodiment and comparative example.

[0067] Table 2. Adhesives for each embodiment and comparative example

[0068] Comparative Example A1 This comparative example provides a method for preparing an adhesive, which differs from Example A1 in that step (1) is omitted.

[0069] Comparative Example A2 This comparative example provides a method for preparing an adhesive, which differs from Example A1 in that step (2) is omitted.

[0070] Comparative Example A3 This comparative example provides a method for preparing an adhesive, which differs from Example A1 in that step (3) is omitted.

[0071] Comparative Example A4 This comparative example provides a method for preparing an adhesive, which differs from Example A1 in that step (4) is omitted.

[0072] Comparative Example A5 This comparative example provides a method for preparing an adhesive, which differs from Example A1 in that step (5) is omitted.

[0073] Comparative Example A6 This comparative example uses commercially available polyacrylic acid adhesive.

[0074] Example B1 This embodiment provides a method for preparing a negative electrode sheet, including the following steps: Graphite, silicon carbide, conductive carbon black, binder prepared in Example A1, SBR, and carbon nanotubes in a weight ratio of 85.9:9.5:1:2.5:1.0:0.1 were added to water and thoroughly mixed. After being mixed evenly, the mixture was coated on both sides of a copper foil (6 μm). The electrode was then dried, rolled, slit, and cut to obtain a negative electrode with a thickness of 115 μm.

[0075] Examples B2-B16 This embodiment provides a method for preparing a negative electrode sheet. The difference from Embodiment B1 is that the binders of Embodiments A2-A16 are used to prepare the negative electrode sheet.

[0076] Example B17 This embodiment provides a method for preparing a negative electrode sheet. The difference from Embodiment B1 is that graphite, silicon carbide material, conductive carbon black, binder prepared in Embodiment A1, SBR, and carbon nanotubes in a weight ratio of 76.4:19.0:1:2.5:1.0:0.1 are used instead of graphite, silicon carbide material, conductive carbon black, binder prepared in Embodiment A1, SBR, and carbon nanotubes in a weight ratio of 85.9:9.5:1:2.5:1.0:0.1 in Embodiment B1.

[0077] Example B18 This embodiment provides a method for preparing a negative electrode sheet. The difference from Embodiment B1 is that graphite, silicon carbide material, conductive carbon black, binder prepared in Embodiment A1, SBR, and carbon nanotubes in a weight ratio of 90.6:4.8:1:2.5:1.0:0.1 are used instead of graphite, silicon carbide material, conductive carbon black, binder prepared in Embodiment A1, SBR, and carbon nanotubes in a weight ratio of 85.9:9.5:1:2.5:1.0:0.1 in Embodiment B1.

[0078] Comparative Examples B1-B6 This comparative example provides a method for preparing a negative electrode sheet. The difference between this method and Example B1 is that the binders of Comparative Examples A1-A6 are used to prepare the negative electrode sheets.

[0079] Test case The preparation of the batteries for each embodiment and comparative example includes the following steps: Positive electrode sheet: The positive electrode material (nickel-cobalt-manganese ternary material), conductive carbon black and PVDF are mixed in a weight ratio of 100:1:1.5 and dissolved in NMP (N-methylpyrrolidone). After being mixed evenly, the mixture is coated on both sides of aluminum foil (double-sided coating, aluminum foil thickness is 14μm). Then the electrode sheet is dried, rolled, slit and cut to obtain the positive electrode sheet; the thickness of the positive electrode sheet is 106μm.

[0080] Electrolyte: Ethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed in a 1:1:1 volume ratio. In an argon-atmosphere glove box with a water content of <10 ppm, thoroughly dried lithium hexafluorophosphate (LiPF6) was dissolved in the above organic solvent and mixed thoroughly to obtain the electrolyte. The concentration of lithium hexafluorophosphate in the electrolyte was 1.2 mol / L.

[0081] The positive electrode sheet and the negative electrode sheets prepared in each embodiment and comparative example are separated by a separator (12μm polyethylene film), wound into corresponding cores, and then subjected to processes such as shaping, welding, assembly, baking, liquid injection, formation, and capacity testing to obtain a soft-pack lithium-ion battery.

[0082] (1) Peel strength test: The electrode sheets of the examples and comparative examples were cut into electrode sheets with a length of 25cm and a width of 3.5cm, and the peel strength of the electrode sheets was tested using 3M tape with a width of 3.0cm.

[0083] (2) Electrode expansion rate test: The cell was charged to 4.25V at 25℃ with constant current and constant voltage of 1C, and then discharged to 2.5V with constant current of 1C. This was recorded as one cycle. After 1000 cycles, the cell was disassembled in a drying room. The electrode thickness N after full charge was measured. Electrode expansion rate = (N-115) / (115-6)×100%. The thickness of the negative electrode was 115μm and the thickness of the negative copper foil was 6μm.

[0084] (3) Cyclic capacity retention rate: At 25±5℃, the battery is subjected to room temperature cycling test: 1C constant current and constant voltage charge to 4.25V, then constant current 1C discharge to 2.5V, and the initial capacity C0 is obtained. This is recorded as one cycle. After 1000 cycles, the capacity C1 is recorded. Then the cycle capacity retention rate = C1 / C0×100%.

[0085] (4) Rate discharge performance test: At 25±5℃, the battery was charged to 4.25V at a constant current and constant voltage of 0.33C, and then discharged to 2.5V at a constant current of 0.33C. The 0.33C discharge capacity C was obtained. 0.33 Charged at 0.33C constant current and constant voltage to 4.25V, then discharged at 4C constant current to 2.5V, yielding the 4C discharge capacity C4. The rate-discharge capacity retention rate is calculated as C4 / C. 0.33 ×100%.

[0086] (5) DCR test: Under the environment of 25±5℃, the battery is charged to 4.25V by constant current and constant voltage at 0.33C, then discharged at 50% SOC by constant current at 0.33C, left to stand for 60min, and discharged at 5C by constant current for 10s. The voltages U1 and U2 before and after 5C discharge are obtained. DCR=(U2-U1) / 5C, and DCR is R0. At 25±5℃, the battery was charged at 1C constant current and constant voltage to 4.25V, and then discharged at 1C constant current to 2.5V. This was recorded as one cycle. After 1000 cycles, a DCR test was performed, and Rn was measured. The DCR growth rate = Rn / R0 × 100%.

[0087] The specific results are shown in Table 3.

[0088] Table 3 Test results for each embodiment and comparative example

[0089] As shown in Table 3, the negative electrode sheet prepared by the binder provided in this application has high peel strength and low expansion rate, and exhibits good cycle performance and rate performance after battery preparation, with low DCR and DCR growth rate. As can be seen from Example 1 and Comparative Examples 1-3, the combined action of hydroxyl, nitrogen atom, thiol group, phosphate ester group and borate group can effectively improve the stability of the interface and ion transport performance. The formed hydrogen bond network can not only improve ion transport efficiency, but also effectively suppress the volume expansion of silicon-based materials, thereby improving the mechanical and electrical properties of the negative electrode sheet.

[0090] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. An adhesive, characterized in that, Including the polyacrylic acid backbone; It also includes grafted chains containing hydroxyl groups, grafted chains containing nitrogen atoms, grafted chains containing boric acid groups, grafted chains containing phosphate ester groups, and grafted chains containing thiol groups.

2. The adhesive according to claim 1, characterized in that, The adhesive satisfies at least one of the following conditions: (1) The amount of grafted chains containing hydroxyl groups accounts for 5wt%~25wt% of the adhesive; (2) The amount of grafted chains containing N atoms accounts for 4wt%~12wt% of the adhesive; (3) The amount of grafted chains containing boric acid groups accounts for 3wt%~20wt% of the adhesive; (4) The amount of grafted chains containing phosphate ester groups accounts for 1wt%~4wt% of the adhesive; (5) The amount of grafted chains containing thiol groups accounts for 2wt% to 7wt% of the adhesive.

3. The adhesive according to claim 2, characterized in that, The grafted chain containing hydroxyl groups contains at least two hydroxyl groups.

4. The adhesive according to claim 2, characterized in that, In the grafted chain containing N atoms, the N atoms exist as -NH2.

5. The adhesive according to any one of claims 1 to 4, characterized in that, The number-average molecular weight Mn of the adhesive is 150,000 to 300,000; And / or, the weight-average molecular weight (Mw) of the adhesive is 220,000 to 750,000.

6. The adhesive according to claim 5, characterized in that, The molecular weight distribution (PDI) of the adhesive is 1.5~2.5, and PDI = Mw / Mn.

7. A secondary battery, characterized in that, It includes a negative electrode sheet containing a negative electrode active layer, the negative electrode active layer comprising a negative electrode active material and a binder as described in any one of claims 1 to 6.

8. The secondary battery according to claim 7, characterized in that, The negative electrode active material includes silicon-based materials, and the silicon-based materials account for 5 wt% to 20 wt% of the total mass of the negative electrode active material.

9. The secondary battery according to claim 7 or 8, characterized in that, The mass of the binder accounts for 2wt% to 4wt% of the total mass of the negative electrode active layer.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 7-9, wherein the secondary battery serves as the power supply for the electrical device.

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