Binder composition, binder, preparation method of binder, negative plate and lithium ion battery

Abstract

The invention provides a binder composition, a binder, a preparation method of the binder, a negative plate and a lithium ion battery. The adhesive composition comprises sulfonic modified polybenzimidazole, a cross-linking agent and a solvent. The sulfonic group modified polybenzimidazole contains a benzimidazole structure and sulfonic groups, electrons and ions can be efficiently transmitted, and the sulfonic group modified polybenzimidazole and the cross-linking agent are cross-linked through covalent bonds to form a conductive network, so that the adhesive with relatively high conductivity is formed. Compared with a traditional polyacrylic acid binder, the binder provided by the invention can better meet the requirements of long-time and high-rate rapid charging and discharging of the silicon-based negative electrode plate. The binder can establish a continuous, stable and continuous electron and ion transmission channel for an electrode reaction, effectively improve the polarization problem caused by poor conductivity of a negative electrode active material, and significantly improve the charge-discharge efficiency and rate capability of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a binder composition, a binder and its preparation method, a negative electrode sheet, and a lithium-ion battery. Background Technology

[0002] With the rapid development of lithium-ion battery technology, the demand for batteries with higher energy density is becoming increasingly urgent. Silicon-based anode materials have become a highly promising next-generation anode material due to their significant advantage of high theoretical specific capacity (up to 4200 mAh / g, far exceeding the 372 mAh / g of traditional graphite anodes). However, in practical applications, silicon-based anode materials have revealed many problems that urgently need to be solved, which seriously restricts their commercialization process.

[0003] Silicon-based anode materials inherently possess a series of defects. First, silicon has low electronic conductivity, which hinders the rapid transport of electrons within the electrode, leading to increased polarization during charging and discharging, thus affecting the battery's charging and discharging efficiency and power performance. Second, during the continuous lithium extraction / intercalation process of lithium-ion batteries, silicon-based anodes undergo massive volume changes exceeding 300%. This drastic expansion and contraction causes silicon particles to continuously crack and pulverize, disrupting the original electrode structure and cutting off the electron conduction pathways within the electrode, resulting in a sharp decline in battery cycle stability. Simultaneously, an unstable solid electrolyte interphase (SEI) film continuously forms on the surface of the silicon-based anode. Each new SEI film formation consumes a large amount of electrolyte, not only reducing the initial coulombic efficiency of the battery but also causing rapid capacity decay, significantly shortening the battery's lifespan. Furthermore, the continuous volume expansion and contraction of the silicon-based anode can cause separation between the active material and the current collector, and between the active material and conductive additives, resulting in the active material losing effective electrical connections, ultimately leading to the battery's inability to function properly and complete failure.

[0004] There are also many shortcomings in the preparation of commonly used anode sheets. To improve the performance of silicon-based anodes, various binders and conductive agents are usually added during the anode sheet preparation process. Taking binders as an example, commonly used polymers containing abundant polar groups, such as polyacrylic acid and polyacrylonitrile, although they have a certain binding effect, are difficult to effectively suppress the irreversible slippage between the active material and the binder during the continuous lithiation / delithiation process of silicon-based anode materials due to their inherent linear structure characteristics. The large stress generated by the volume expansion of silicon particles cannot be effectively dissipated by the existing binder structure, making the electrode structure easily damaged during cycling and affecting battery performance. In addition, when single-walled carbon nanotubes are added as conductive agents during electrode preparation, it will have a negative impact on the bonding strength and slurry dispersibility. The addition of single-walled carbon nanotubes changes the rheological properties of the slurry, making it difficult to disperse the slurry uniformly during coating. This not only affects the preparation quality of the electrode, but also makes the active material more likely to detach from the current collector during charge and discharge due to the decrease in bonding strength, further reducing the cycle stability and lifespan of the battery.

[0005] The inherent performance defects of silicon-based anode materials and the shortcomings of existing anode sheet preparation technologies have severely restricted the improvement of lithium-ion battery performance and the large-scale application of silicon-based anode materials. New technologies and methods are urgently needed to solve these problems in order to promote the development of lithium-ion battery technology towards higher power and longer cycle life. Summary of the Invention

[0006] The main objective of this invention is to provide a binder composition, a binder and its preparation method, a negative electrode sheet and a lithium-ion battery, in order to solve the problem of poor cycle stability of lithium-ion batteries caused by low adhesion between the current collector and the negative electrode active coating in the prior art.

[0007] To achieve the above objectives, according to one aspect of the present invention, an adhesive composition is provided comprising sulfonic acid-modified polybenzimidazole, a crosslinking agent, and a solvent.

[0008] Furthermore, the mass ratio of sulfonic acid-modified polybenzimidazole to crosslinking agent is 7:(2~5).

[0009] Furthermore, the weight-average molecular weight of polybenzimidazole in sulfonic acid-modified polybenzimidazole is 500,000 to 2,000,000 g / mol; and / or, the mass percentage of sulfonic acid groups in sulfonic acid-modified polybenzimidazole is 20 to 30%.

[0010] Further, the crosslinking agent is selected from any one or more of glycerol, ethylene glycol, pentaerythritol, 1,4-butanediol and trimethylolethane; preferably, the crosslinking agent is a combination of ethylene glycol and pentaerythritol, and the mass ratio of ethylene glycol to pentaerythritol is (1~3):1.

[0011] According to another aspect of the present invention, a method for preparing an adhesive is provided, wherein the adhesive is prepared using the aforementioned adhesive composition, and the preparation method includes: mixing sulfonic acid-modified polybenzimidazole, a crosslinking agent and a solvent and then carrying out a crosslinking reaction to obtain the adhesive.

[0012] Furthermore, the cross-linking reaction temperature is 60~90℃; and / or, the cross-linking reaction time is 6~15h; and / or, the solid mass content of the mixed solution is 5~10%.

[0013] According to another aspect of the present invention, an adhesive is provided, which is prepared by the aforementioned preparation method, preferably having an electrical conductivity of 10. -3 ~10 -2 S / m.

[0014] According to another aspect of the present invention, a negative electrode sheet is provided, comprising a current collector and a negative electrode active layer, the negative electrode active layer comprising the aforementioned binder and negative electrode active material.

[0015] Furthermore, the mass ratio of the binder to the negative electrode active material is (2~4):(6~8).

[0016] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, an electrolyte, and a negative electrode, wherein the negative electrode is the aforementioned negative electrode.

[0017] Applying the technical solution of this application, the sulfonic acid-modified polybenzimidazole contains a benzimidazole structure and sulfonic acid groups, which can efficiently transport electrons and ions. The sulfonic acid-modified polybenzimidazole and the crosslinking agent are crosslinked through covalent bonds to form a conductive network, thereby forming a binder with high conductivity. Compared with traditional polyacrylic acid binders, the binder of this application can better meet the requirements of long-term, high-rate, and rapid charge-discharge of silicon-based negative electrode sheets. On the one hand, the binder can tightly encapsulate silicon particles in the conductive network. Due to the reversible dynamic interaction between molecules, when the silicon particles expand in volume due to lithium intercalation, the binder can deform accordingly without breaking, effectively buffering the stress generated by the expansion. When the silicon particles shrink due to lithium delithiation, it can provide a force to restore their volume, ensuring that a dynamically stable interface structure is formed between the negative electrode active coating and the current collector in the electrode, avoiding structural damage and electrical connection failure caused by silicon volume changes, thereby helping to improve the stability and lifespan of the battery under long-term, high-rate charge-discharge cycles. On the other hand, the binder can build a continuous, stable and continuous electron and ion transport channel for the electrode reaction, effectively improve the polarization problem caused by the poor conductivity of the negative electrode active material, and significantly improve the charge and discharge efficiency and rate performance of the battery. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0019] As analyzed in the background section of this application, the low adhesion between the current collector and the active coating of the negative electrode in the prior art leads to poor cycle stability of lithium-ion batteries. In order to solve this problem, this application provides a binder composition, a binder and its preparation method, a negative electrode and a lithium-ion battery.

[0020] In one typical embodiment of this application, an adhesive composition is provided comprising sulfonic acid-modified polybenzimidazole, a crosslinking agent, and a solvent.

[0021] The sulfonate-modified polybenzimidazole of this application contains a benzimidazole structure and sulfonate groups, which can efficiently transport electrons and ions. The sulfonate-modified polybenzimidazole and the crosslinking agent are crosslinked through covalent bonds to form a conductive network, thereby forming a binder with high conductivity. Compared with traditional polyacrylic acid binders, the binder of this application can better meet the requirements of long-term, high-rate, and rapid charge-discharge of silicon-based negative electrodes. On the one hand, the binder can tightly encapsulate silicon particles in the conductive network. Due to the reversible dynamic interaction between molecules, when the silicon particles expand in volume due to lithium intercalation, the binder can deform accordingly without breaking, effectively buffering the stress generated by the expansion. When the silicon particles shrink due to lithium delithiation, it can provide a force to restore their volume, ensuring that a dynamically stable interface structure is formed between the negative electrode active coating and the current collector in the electrode, avoiding structural damage and electrical connection failure caused by silicon volume changes, thereby helping to improve the stability and lifespan of the battery under long-term, high-rate charge-discharge cycles. On the other hand, the binder can build a continuous, stable and continuous electron and ion transport channel for the electrode reaction, effectively improve the polarization problem caused by the poor conductivity of the negative electrode active material, and significantly improve the charge and discharge efficiency and rate performance of the battery.

[0022] Including but not limited to, the solvent mentioned above is water.

[0023] In some embodiments of this application, the mass ratio of sulfonic acid-modified polybenzimidazole to crosslinking agent is 7:(2~5), specifically 7:2, 7:3, 7:4, 7:5, and any range between two ratios.

[0024] The composite network formed by sulfonic acid-modified polybenzimidazole and crosslinking agent can effectively dissipate stress. Controlling the mass ratio of sulfonic acid-modified polybenzimidazole to crosslinking agent within the above range helps to form a covalent network that can ensure sufficient bonding strength and has a certain degree of elasticity, thereby providing sufficient buffering when silicon particles expand and avoiding damage to the electrode structure.

[0025] In some embodiments of this application, the weight-average molecular weight of polybenzimidazole in the sulfonic acid-modified polybenzimidazole is 500,000 to 2,000,000 g / mol, preferably 800,000 to 1,500,000 g / mol, specifically 800,000 g / mol, 900,000 g / mol, 1,000,000 g / mol, 1,100,000 g / mol, 1,200,000 g / mol, 1,300,000 g / mol, 1,400,000 g / mol, 1,500,000 g / mol, and any range between two values; and / or, the mass percentage of sulfonic acid groups in the sulfonic acid-modified polybenzimidazole is 20% to 30%.

[0026] Controlling the weight-average molecular weight of polybenzimidazole in sulfonic acid-modified polybenzimidazole within the aforementioned range helps to form a stronger network structure, increases the crosslinking density of the binder, promotes electron transport, reduces polarization during battery charging and discharging, and improves the battery's energy density and power performance. Controlling the mass percentage of sulfonic acid groups in sulfonic acid-modified polybenzimidazole within the aforementioned range also helps to increase the crosslinking density of the binder, thereby further improving the binder's electrical conductivity.

[0027] In order to improve the structural stability and electrical conductivity of the binder, in some embodiments of this application, the crosslinking agent is selected from any one or more of glycerol, ethylene glycol, pentaerythritol, 1,4-butanediol and trimethylolethane. Preferably, the crosslinking agent is a combination of ethylene glycol and pentaerythritol, and the mass ratio of ethylene glycol to pentaerythritol is (1~3):1.

[0028] In another typical embodiment of this application, a method for preparing an adhesive is provided, which uses the aforementioned adhesive composition to prepare the adhesive. The preparation method includes: mixing sulfonic acid-modified polybenzimidazole, a crosslinking agent and a solvent and then carrying out a crosslinking reaction to obtain the adhesive.

[0029] This application describes a method for obtaining an adhesive by crosslinking sulfonic acid-modified polybenzimidazole with a crosslinking agent. The preparation method is simple and the cost is low.

[0030] In some embodiments of this application, the preparation method of sulfonic acid-modified polybenzimidazole includes: mixing polybenzimidazole with an organic solvent to form a mixed solution; cooling the mixed solution to 0-5°C; adding chlorosulfonic acid dropwise at a rate of 0.05-0.15 mL / min while stirring at 400-600 r / min (controlling the mass percentage of sulfonic acid groups in the sulfonic acid-modified polybenzimidazole to be 20-30%); continuing stirring for 0.5-1.5 h after the addition is complete; and then heating to 30°C. Continue the reaction for 4-6 hours at a rate ≤5℃ / h; slowly pour the reaction solution into ice water (ice water to reaction solution volume ratio of (4-6):1) and stir at a speed of 700-900 r / min. Adjust the pH of the solution to 6-7 with 0.5-1.5 mol / L NaOH aqueous solution (NaOH aqueous solution dropping rate ≤0.5 mL / min). Sulfonated polybenzimidazole flocculent precipitate will be formed. Wash and dry the precipitate to obtain sulfonate-modified polybenzimidazole powder.

[0031] Including but not limited to, the above-mentioned organic solvent may be N,N-dimethylacetamide.

[0032] In some embodiments of this application, the temperature of the crosslinking reaction is 60~90°C; and / or the time of the crosslinking reaction is 6~15h; and / or the solid mass content of the mixture after mixing is 5~10%.

[0033] Controlling the temperature and time of the crosslinking reaction within the above-mentioned range helps to promote the reaction, improve reaction efficiency, and reduce the occurrence of side reactions. Controlling the solid content of the mixed solution within the above-mentioned range helps to increase the contact area between the sulfonic acid-modified polybenzimidazole and the crosslinking agent, thereby helping to increase the density of the conductive network and further improving the conductivity of the binder.

[0034] In another typical embodiment of this application, an adhesive is provided, which is prepared by the aforementioned preparation method. Preferably, the adhesive has an electrical conductivity of 10. -3 ~10 -2 S / m.

[0035] Since the binder described above is prepared using the method described in this application, it exhibits high electrical conductivity. A binder with such high conductivity is more suitable as a binder for negative electrode sheets, and is particularly suitable for silicon-based negative electrode sheets.

[0036] In another typical embodiment of this application, a negative electrode sheet is provided, including a current collector and a negative electrode active layer, the negative electrode active layer including the aforementioned binder and negative electrode active material.

[0037] Traditional anode fabrication, especially silicon-based anode fabrication, often requires the addition of various conductive agents to improve conductivity. However, the binder in this application, with its unique structure and properties, allows the electrode to achieve good conductivity without the need for additional conductive agents. This not only optimizes the dispersion of the slurry, avoiding problems such as uneven slurry dispersion and decreased bonding strength caused by the addition of conductive agents, but also greatly simplifies the electrode fabrication process, reduces the types of raw materials and preparation steps, lowers production costs and process complexity, and the aforementioned anode exhibits high peel strength.

[0038] Including but not limited to, the above-mentioned negative electrode active materials are selected from silicon particles or silicon-carbon materials.

[0039] In some embodiments of this application, the mass ratio of binder to negative electrode active material is (2~4):(6~8).

[0040] The binder can effectively coat and bind the active material particles to form a stable electrode structure. Controlling the mass ratio of the binder to the negative electrode active material within the above range helps to form a good physical and chemical bond. This ensures the uniform distribution of the active material in the electrode and provides necessary support and buffer for the volume change of the negative electrode active material, especially the silicon-based negative electrode active material, during the charging and discharging process. This avoids the separation of the active material from the current collector and improves the structural stability and cycle stability of the electrode.

[0041] In another typical embodiment of this application, a lithium-ion battery is provided, including a positive electrode, an electrolyte, and a negative electrode, wherein the negative electrode is the aforementioned negative electrode.

[0042] Because the lithium-ion battery contains the negative electrode of this application, the lithium-ion battery has high rate performance and cycle stability.

[0043] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0044] Example 1

[0045] Polybenzimidazole (weight average molecular weight of 1,000,000 g / mol) was mixed with N,N-dimethylacetamide to form a mixed solution. The temperature of the mixed solution was lowered to 0℃, and 1.08~1.35 mL of chlorosulfonic acid was added dropwise at a rate of 0.15 mL / min while stirring at 500 r / min (controlling the mass ratio of sulfonic acid groups in the sulfonic acid-modified polybenzimidazole to be 25%). After the addition was completed, stirring was continued for 1 h, and then the temperature was raised to 30℃ (heating rate of 5℃ / h) and the reaction was continued for 5 h. The reaction solution was slowly poured into ice water (ice water to reaction solution volume ratio of 5:1) and stirred at a speed of 800 r / min. The pH of the solution was adjusted to 6 with 1 mol / L NaOH aqueous solution (the dropping rate of NaOH aqueous solution was 0.5 mL / min), and sulfonated polybenzimidazole flocculent precipitate was formed. The precipitate was washed and dried to obtain sulfonated polybenzimidazole powder.

[0046] Ethylene glycol was dispersed in water, and then the sulfonic acid-modified polybenzimidazole prepared above was added to dissolve and mix. The mass ratio of sulfonic acid-modified polybenzimidazole to ethylene glycol was 7:3 to obtain a mixed solution (solid mass content of 5%). The mixed solution was heated to 80°C for crosslinking reaction for 10 hours, and then washed and dried to obtain the adhesive.

[0047] The binder and silicon are added to water at a mass ratio of 3:7 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0048] Example 2

[0049] The difference from Example 1 is that ethylene glycol is dispersed in water, and then sulfonic acid-modified polybenzimidazole (with a weight-average molecular weight of 800,000 g / mol) is added for dissolution and mixing. The mass ratio of sulfonic acid-modified polybenzimidazole to ethylene glycol is 7:3 to obtain a mixed solution (with a solid mass content of 5%). The mixed solution is heated to 80°C for crosslinking reaction for 10 hours, and then washed and dried to obtain the adhesive.

[0050] The binder and silicon are added to water at a mass ratio of 3:7 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0051] Example 3

[0052] The difference from Example 1 is that ethylene glycol is dispersed in water, and then sulfonic acid-modified polybenzimidazole (with a weight-average molecular weight of 1,500,000 g / mol) is added for dissolution and mixing. The mass ratio of sulfonic acid-modified polybenzimidazole to ethylene glycol is 7:3 to obtain a mixed solution (with a solid mass content of 5%). The mixed solution is heated to 80°C for a crosslinking reaction for 10 hours, and then washed and dried to obtain the adhesive.

[0053] The binder and silicon are added to water at a mass ratio of 3:7 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0054] Example 4

[0055] The difference from Example 1 is that ethylene glycol is dispersed in water, and then sulfonic acid-modified polybenzimidazole (with a weight-average molecular weight of 2,000,000 g / mol) is added for dissolution and mixing. The mass ratio of sulfonic acid-modified polybenzimidazole to ethylene glycol is 7:3 to obtain a mixed solution (with a solid mass content of 5%). The mixed solution is heated to 80°C for crosslinking reaction for 10 hours, and then washed and dried to obtain the adhesive.

[0056] The binder and silicon are added to water at a mass ratio of 3:7 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0057] Example 5

[0058] The difference from Example 1 is that ethylene glycol is dispersed in water, and then sulfonic acid-modified polybenzimidazole (with a weight-average molecular weight of 500,000 g / mol) is added for dissolution and mixing. The mass ratio of sulfonic acid-modified polybenzimidazole to ethylene glycol is 7:3 to obtain a mixed solution (solid mass content of 5%). The mixed solution is heated to 80°C for crosslinking reaction for 10 hours, and then washed and dried to obtain the adhesive.

[0059] The binder and silicon are added to water at a mass ratio of 3:7 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0060] Example 6

[0061] The difference from Example 1 is that ethylene glycol is dispersed in water, and then sulfonic acid-modified polybenzimidazole (with a weight-average molecular weight of 400,000 g / mol) is added for dissolution and mixing. The mass ratio of sulfonic acid-modified polybenzimidazole to ethylene glycol is 7:3 to obtain a mixed solution (solid mass content of 5%). The mixed solution is heated to 80°C for crosslinking reaction for 10 hours, and then washed and dried to obtain the adhesive.

[0062] The binder and silicon are added to water at a mass ratio of 3:7 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0063] Example 7

[0064] The difference from Example 1 is that ethylene glycol is dispersed in water, and then sulfonic acid-modified polybenzimidazole is added for dissolution and mixing. The mass ratio of sulfonic acid-modified polybenzimidazole to ethylene glycol is 7:2 to obtain a mixed solution (solid mass content is 5%). The mixed solution is heated to 80°C for crosslinking reaction for 10 hours, and then washed and dried to obtain the adhesive.

[0065] The binder and silicon are added to water at a mass ratio of 3:7 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0066] Example 8

[0067] The difference from Example 1 is that ethylene glycol is dispersed in water, and then sulfonic acid-modified polybenzimidazole is added for dissolution and mixing. The mass ratio of sulfonic acid-modified polybenzimidazole to ethylene glycol is 7:5 to obtain a mixed solution (solid mass content of 5%). The mixed solution is heated to 80°C for crosslinking reaction for 10 hours, and then washed and dried to obtain the adhesive.

[0068] The binder and silicon are added to water at a mass ratio of 3:7 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0069] Example 9

[0070] The difference from Example 1 is that ethylene glycol is dispersed in water, and then sulfonic acid-modified polybenzimidazole is added for dissolution and mixing. The mass ratio of sulfonic acid-modified polybenzimidazole to ethylene glycol is 7:6 to obtain a mixed solution (solid mass content is 5%). The mixed solution is heated to 80°C for crosslinking reaction for 10 hours, and then washed and dried to obtain the adhesive.

[0071] The binder and silicon are added to water at a mass ratio of 3:7 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0072] Example 10

[0073] The difference from Example 1 is that the amount of chlorosulfonic acid added is adjusted so that the mass ratio of sulfonic acid groups in the sulfonic acid-modified polybenzimidazole is 20%, and the negative electrode sheet is finally obtained.

[0074] Example 11

[0075] The difference from Example 1 is that the amount of chlorosulfonic acid added is adjusted so that the mass ratio of sulfonic acid groups in the sulfonic acid-modified polybenzimidazole is 30%, and the negative electrode sheet is finally obtained.

[0076] Example 12

[0077] The difference from Example 1 is that the amount of chlorosulfonic acid added is adjusted so that the mass ratio of sulfonic acid groups in the sulfonic acid-modified polybenzimidazole is 35%, and the negative electrode sheet is finally obtained.

[0078] Example 13

[0079] The difference from Example 1 is that ethylene glycol is dispersed in water, and then sulfonic acid-modified polybenzimidazole is added for dissolution and mixing. The mass ratio of sulfonic acid-modified polybenzimidazole to ethylene glycol is 7:3 to obtain a mixed solution (solid mass content is 5%). The mixed solution is heated to 80°C for crosslinking reaction for 10 hours, and then washed and dried to obtain the adhesive.

[0080] The binder and silicon are added to water at a mass ratio of 2:8 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0081] Example 14

[0082] The difference from Example 1 is that ethylene glycol is dispersed in water, and then sulfonic acid-modified polybenzimidazole is added for dissolution and mixing. The mass ratio of sulfonic acid-modified polybenzimidazole to ethylene glycol is 7:3 to obtain a mixed solution (solid mass content is 5%). The mixed solution is heated to 80°C for crosslinking reaction for 10 hours, and then washed and dried to obtain the adhesive.

[0083] The binder and silicon are added to water at a mass ratio of 4:6 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0084] Example 15

[0085] The difference from Example 1 is that ethylene glycol is dispersed in water, and then sulfonic acid-modified polybenzimidazole is added for dissolution and mixing. The mass ratio of sulfonic acid-modified polybenzimidazole to ethylene glycol is 7:3 to obtain a mixed solution (solid mass content is 5%). The mixed solution is heated to 80°C for crosslinking reaction for 10 hours, and then washed and dried to obtain the adhesive.

[0086] The binder and silicon are added to water at a mass ratio of 1:9 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0087] Example 16

[0088] The difference from Example 1 is that trimethylolethane was dispersed in water, and then sulfonic acid-modified polybenzimidazole was added for dissolution and mixing. The mass ratio of sulfonic acid-modified polybenzimidazole to pentaerythritol was 7:3 to obtain a mixed solution (solid mass content of 10%). The mixed solution was heated to 90°C for crosslinking reaction for 6 hours, and then washed and dried to obtain the adhesive.

[0089] The binder and silicon are added to water at a mass ratio of 3:7 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0090] Example 17

[0091] The difference from Example 1 is that a combination of ethylene glycol and pentaerythritol is used to replace ethylene glycol, and the mass ratio of ethylene glycol to pentaerythritol in the combination of ethylene glycol and pentaerythritol is 1:1, finally obtaining a negative electrode sheet.

[0092] Example 18

[0093] The difference from Example 1 is that a combination of ethylene glycol and pentaerythritol is used to replace ethylene glycol, and the mass ratio of ethylene glycol to pentaerythritol in the combination of ethylene glycol and pentaerythritol is 3:1, finally obtaining a negative electrode sheet.

[0094] Comparative Example 1

[0095] The difference from Example 1 is that sulfonic acid-modified polybenzimidazole and silicon are added to water in a mass ratio of 3:7 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0096] Comparative Example 2

[0097] The difference from Example 1 is that polyacrylic acid and silicon are added to water in a mass ratio of 3:7 to form a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil and dried to obtain a negative electrode sheet.

[0098] Battery manufacturing

[0099] The negative electrode sheet, polyethylene separator and lithium iron phosphate positive electrode sheet prepared in the examples and comparative examples are wound together to prepare a dry cell. Lithium hexafluorophosphate electrolyte is injected into the dry cell to obtain a lithium-ion battery.

[0100] Performance testing

[0101] Electrical conductivity: determined using the four-probe method, with the sample being a 1 mm thick adhesive film, and the test temperature being 25 °C.

[0102] The crosslinking degree and conductivity of the binder prepared in the examples were tested, and the test results are shown in Table 1.

[0103] Peel strength: The 180° peel strength between the negative electrode active layer and the copper foil was tested at a rate of 50 mm / min according to GB / T 2790-1995 standard.

[0104] The negative electrode sheets prepared in the examples and comparative examples were subjected to peel strength tests, and the test results are shown in Table 1.

[0105] The lithium-ion batteries prepared in the examples and comparative examples were tested at 0.5C for their first discharge specific capacity and capacity retention after 800 cycles. The test results are shown in Table 1.

[0106] Table 1

[0107]

[0108] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0109] The sulfonate-modified polybenzimidazole of this application contains a benzimidazole structure and sulfonate groups, which can efficiently transport electrons and ions. The sulfonate-modified polybenzimidazole and the crosslinking agent are crosslinked through covalent bonds to form a conductive network, thereby forming a binder with high conductivity. Compared with traditional polyacrylic acid binders, the binder of this application can better meet the requirements of long-term, high-rate, and rapid charge-discharge of silicon-based negative electrodes. On the one hand, the binder can tightly encapsulate silicon particles in the conductive network. Due to the reversible dynamic interaction between molecules, when the silicon particles expand in volume due to lithium intercalation, the binder can deform accordingly without breaking, effectively buffering the stress generated by the expansion. When the silicon particles shrink due to lithium delithiation, it can provide a force to restore their volume, ensuring that a dynamically stable interface structure is formed between the negative electrode active coating and the current collector in the electrode, avoiding structural damage and electrical connection failure caused by silicon volume changes, thereby helping to improve the stability and lifespan of the battery under long-term, high-rate charge-discharge cycles. On the other hand, the binder can build a continuous, stable and continuous electron and ion transport channel for the electrode reaction, effectively improve the polarization problem caused by the poor conductivity of the negative electrode active material, and significantly improve the charge and discharge efficiency and rate performance of the battery.

[0110] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An adhesive composition, characterized in that, The adhesive composition comprises sulfonic acid-modified polybenzimidazole, a crosslinking agent, and a solvent.

2. The adhesive composition according to claim 1, characterized in that, The mass ratio of the sulfonic acid-modified polybenzimidazole to the crosslinking agent is 7:(2~5).

3. The adhesive composition according to claim 1 or 2, characterized in that, The weight-average molecular weight of the polybenzimidazole in the sulfonic acid-modified polybenzimidazole is 500,000 to 2,000,000 g / mol; and / or, the mass percentage of sulfonic acid groups in the sulfonic acid-modified polybenzimidazole is 20 to 30%.

4. The adhesive composition according to any one of claims 1 to 3, characterized in that, The crosslinking agent is selected from any one or more of glycerol, ethylene glycol, pentaerythritol, 1,4-butanediol and trimethylolethane; preferably, the crosslinking agent is a combination of ethylene glycol and pentaerythritol, and the mass ratio of ethylene glycol to pentaerythritol is (1~3):

1.

5. A method for preparing an adhesive, characterized in that, The adhesive is prepared using the adhesive composition according to any one of claims 1 to 4, the preparation method comprising: mixing sulfonic acid-modified polybenzimidazole, a crosslinking agent and a solvent and then carrying out a crosslinking reaction to obtain the adhesive.

6. The preparation method according to claim 5, characterized in that, The crosslinking reaction is carried out at a temperature of 60-90°C; and / or the crosslinking reaction takes 6-15 hours; and / or the solid content of the mixture is 5-10%.

7. An adhesive, characterized in that, The adhesive is prepared by the preparation method according to claim 5 or 6, preferably, the electrical conductivity of the adhesive is 10. -3 ~10 -2 S / m.

8. A negative electrode sheet, comprising a current collector and a negative electrode active layer, characterized in that, The negative electrode active layer comprises the binder and negative electrode active material as described in claim 7.

9. The negative electrode sheet according to claim 8, characterized in that, The mass ratio of the binder to the negative electrode active material is (2~4):(6~8).

10. A lithium-ion battery, comprising a positive electrode, an electrolyte, and a negative electrode, characterized in that, The negative electrode is the negative electrode as described in claim 8 or 9.

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