High-silicon-content negative electrode sheet, preparation method thereof, and lithium ion battery

Abstract

This disclosure provides a high-silicon-content negative electrode sheet and its preparation method, as well as a lithium-ion battery. The high-silicon-content negative electrode sheet includes a current collector and a negative electrode slurry. The silicon-carbon composite material of the negative electrode slurry includes chemical vapor deposition (CVD) silicon-carbon material, graphite, and nano-silicon-carbon spheres; the particle size of graphite > the particle size of the CVD silicon-carbon material > the particle size of the nano-silicon-carbon spheres; the binder includes an ionic cellulose ether binder, a polyacrylic acid binder, and an elastomer binder; the negative electrode slurry also includes a multifunctional epoxy crosslinking agent and a photoinitiator; the negative electrode slurry after coating is subjected to an irradiation intensity of 40 mW / cm². 2 -60mW / cm 2 The electrode undergoes 20-40 seconds of continuous pre-crosslinking under light irradiation, followed by drying at 75-85°C for 10-20 minutes to form a negative electrode active layer with a highly elastic and tough organic three-dimensional constrained network. This high-silicon content negative electrode sheet, while reducing the total amount of binder used, ensures the stability of the coating process, suppresses the expansion of the high-silicon content negative electrode sheet, and improves the initial coulombic efficiency of the lithium-ion battery.

Description

Technical Field

[0001] This disclosure relates to the field of high silicon content anode technology, and in particular to a high silicon content anode and its preparation method, and a lithium-ion battery. Background Technology

[0002] Silicon-based anode materials, with a theoretical specific capacity of up to 4200 mAh / g, far exceeding the limits of traditional graphite anodes, are widely recognized as the breakthrough direction for next-generation high-energy-density batteries. However, silicon materials experience a volume expansion effect of approximately 300% during lithium insertion / extraction, leading to repeated pulverization and failure of the electrode structure. This results in a chain of problems, including active material shedding, conductive network collapse, and exacerbated interfacial side reactions, severely hindering the commercialization of silicon-carbon anode materials.

[0003] To address the problems of traditional silicon-carbon anode materials, current mainstream approaches focus on two main dimensions: bonding systems and structural design. In optimizing bonding systems, the combination of lithium carboxymethyl cellulose and styrene-butadiene rubber latex can improve adhesion, but it suffers from insufficient elastic modulus, typically <0.5 GPa, making it difficult to withstand the high expansion rate of high-silicon-content anode sheets. While polyacrylic acid binders can enhance the mechanical strength of the binder, they can cause a sharp increase in the viscosity of the anode slurry to over 20,000 cP, leading to uncontrolled coating processes. Regarding structural design, simply using chemical vapor deposition to coat micron- or nano-silicon particles with carbon can buffer expansion stress to some extent, but the single particle size results in a compaction density of less than 1.4 g / cm³ for high-silicon-content anode sheets. 3 This leads to the problem of low utilization rate of active materials in high-silicon-content negative electrode sheets. Summary of the Invention

[0004] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide a high-silicon-content negative electrode sheet and its preparation method, and a lithium-ion battery, which, while reducing the total amount of adhesive used, ensure the stability of the coating process, suppress the expansion of the high-silicon-content negative electrode sheet, and improve the first coulombic efficiency of the lithium-ion battery, thereby improving the utilization rate of the active material of the high-silicon-content negative electrode sheet, so as to better adapt to the application of high-pressure high-silicon-content negative electrode sheets.

[0005] The purpose of this disclosure is achieved through the following technical solution: A high-silicon-content negative electrode includes a current collector and a negative electrode slurry, wherein the negative electrode slurry is coated on at least one side of the current collector, and the negative electrode slurry includes a silicon-carbon composite material, a binder, a conductive agent, and a solvent. The silicon-carbon composite material includes chemical vapor deposition silicon-carbon material, graphite, and silicon-carbon nanospheres; wherein the particle size of the graphite is greater than the particle size of the chemical vapor deposition silicon-carbon material, which is greater than the particle size of the silicon-carbon nanospheres. The adhesive includes ionic cellulose ether binders, polyacrylic acid binders, and elastomer binders; the negative electrode slurry also includes multifunctional epoxy crosslinking agents and photoinitiators; The negative electrode slurry after coating is subjected to photo-pre-crosslinking to reduce the viscosity of the negative electrode slurry. The pre-crosslinked negative electrode slurry is dried and deeply crosslinked to form a negative electrode active layer with a highly elastic and tough organic three-dimensional constraint network. The conditions for the photo-induced pre-crosslinking are: irradiation intensity 40 mW / cm². 2 -60mW / cm 2 Last 20-40 seconds; The conditions for the drying depth crosslinking are: temperature 75℃-85℃; time 10min-20min.

[0006] In one embodiment, the graphite has a particle size of 12 μm-15 μm; and / or, The particle size of the chemical vapor deposition silicon-carbon material is 8μm-12μm; and / or, The particle size of the nano-silicon carbide spheres is 80nm-100nm.

[0007] In one embodiment, the conductive agent includes graphene and single-walled carbon nanotubes.

[0008] In one embodiment, the graphene has a particle size of 100 nm-800 nm; and / or, The single-walled carbon nanotubes have a particle size of 0.4 nm-3 nm; and / or, The graphene is nitrogen-doped graphene; and / or, The single-walled carbon nanotubes are carboxylated single-walled carbon nanotubes; and / or... The amount of graphene used is 2.0-5.0 parts by weight; the amount of single-walled carbon nanotubes used is 1.5-2.0 parts.

[0009] In one embodiment, the polyacrylic adhesive includes at least one selected from polyacrylic acid, sodium polyacrylate, and lithium-ionized polyacrylic acid; and / or, The ionic cellulose ether binder comprises at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and carboxymethyl hydroxyethyl cellulose; and / or, The elastomeric binder includes at least one of styrene-butadiene rubber and nitrile rubber.

[0010] In one embodiment, the amount of the ionic cellulose ether binder used is 0.3 to 0.5 parts by weight; and / or, The amount of the polyacrylic adhesive used is 1.0 part to 2.0 parts; and / or, The amount of the elastomeric adhesive used is 0.5 parts to 1.0 parts.

[0011] In one embodiment, the multifunctional epoxy crosslinking agent comprises at least one selected from the following: trimethylolpropane triglycidyl ether solution, polyethylene glycol diglycidyl ether solution, glycerol triglycidyl ether solution, trimethylolpropane tris(3-mercaptopropionate) solution, pentaerythritol tetramercaptoacetate solution, and pentaerythritol tetraglycidyl ether solution; and / or, The photoinitiator comprises at least one selected from 2-hydroxy-2-methylphenylacetone, 1-hydroxycyclohexylphenyl ketone, and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone; and / or, The amount of the multifunctional epoxy crosslinking agent used is 0.3-0.9 parts by weight. The amount of photoinitiator used is 1.0 part to 2.0 parts; The amount of the chemical vapor deposition silicon-carbon material used is 30-35 parts; The amount of graphite used is 40-50 parts; The amount of the nano-silicon carbide spheres used is 10-15 parts.

[0012] In one embodiment, the solvent includes at least one of water and ethanol.

[0013] A method for preparing a high-silicon-content negative electrode includes the following steps: The ionic cellulose ether binder is dissolved in a solvent to obtain a cellulose adhesive solution; A conductive agent is added to the cellulose adhesive to obtain a conductive slurry; The silicon-carbon composite material is added to the conductive slurry in batches and kneaded to obtain a primary mixed slurry. A polyacrylic acid binder is added to the primary mixed slurry to obtain a secondary mixed slurry; The multifunctional epoxy crosslinking agent and photoinitiator are added to the secondary mixed slurry to obtain the tertiary mixed slurry; An elastomer binder is added to the three-stage mixed slurry to obtain a negative electrode slurry; The negative electrode slurry is coated onto the current collector to obtain a negative electrode precursor. The negative electrode precursor is subjected to photo-pre-crosslinking and drying-deep crosslinking in sequence to obtain the high silicon content negative electrode as described in any of the above embodiments.

[0014] A lithium-ion battery comprising the high-silicon-content negative electrode sheet described in any of the above embodiments.

[0015] Compared with the prior art, this disclosure has at least the following advantages: Since the adhesives include ionic cellulose ether binders, polyacrylic binders, and elastomer binders, and since the negative electrode slurry contains multifunctional epoxy crosslinking agents and photoinitiators, the introduced multifunctional epoxy crosslinking agents, photoinitiators, ionic cellulose ether binders, and polyacrylic binders can effectively reduce the overall viscosity of the negative electrode slurry. This makes the negative electrode slurry of this disclosure a low-viscosity system. On the one hand, it can better meet the stability requirements of the coating process, and on the other hand, it helps to reduce the sedimentation rate of the negative electrode slurry and improve the storage stability of the negative electrode slurry.

[0016] By subjecting the coated negative electrode slurry to photo-pre-crosslinking at an irradiation intensity of 40 mW / cm², the photoinitiator is subjected to photo-pre-crosslinking. 2 -60mW / cm 2 Under conditions of 20-40 seconds, a small amount of active free radicals are generated, initiating a ring-opening reaction between the carboxyl and hydroxyl groups of the active groups in the multifunctional epoxy crosslinking agent and the polyacrylic binder and elastomer binder. This achieves partial pre-crosslinking of the binder to form a network, effectively increasing the viscosity of the negative electrode slurry, which is beneficial for subsequent deep crosslinking during drying. Under conditions of 75℃-85℃ and 10-20 minutes, the photoinitiator generates a large number of active free radicals, initiating a ring-opening reaction between the carboxyl and hydroxyl groups of the active groups in the multifunctional epoxy crosslinking agent and the polyacrylic binder and elastomer binder. The process achieves deep cross-linking of the binder during drying. On one hand, it forms a highly elastic and tough organic three-dimensional constraint network that can encapsulate and fix the silicon-carbon composite material and the conductive agent, forming the negative electrode active layer. This network effectively suppresses the expansion of the silicon-carbon composite material, making it better suited for applications with high silicon content negative electrodes. On the other hand, the viscosity of the negative electrode with deep cross-linking during drying does not increase suddenly, ensuring that air bubbles can escape effectively. This avoids defects such as pinholes and shrinkage cavities in the negative electrode active layer formed after drying, thereby reducing the probability of defects in the negative electrode active layer and further ensuring the stability of the coating process.

[0017] Furthermore, the high-elasticity and tough organic three-dimensional constraint network formed after drying and cross-linking has high bonding strength, which can effectively reduce the total amount of adhesive used, further reduce the viscosity of the negative electrode slurry, and reduce the viscosity of the negative electrode slurry to below 20,000 cP, further reducing the defect probability of the negative electrode active layer and further ensuring the stability of the coating process.

[0018] Because the silicon-carbon composite material comprises chemical vapor deposition silicon-carbon material, graphite, and silicon-carbon nanospheres; and the particle size of the graphite is greater than the particle size of the chemical vapor deposition silicon-carbon material, which is greater than the particle size of the silicon-carbon nanospheres, the smaller-sized silicon-carbon nanospheres can be better packed between the larger-sized chemical vapor deposition silicon-carbon material and the larger-sized graphite, thereby increasing the compaction density of the high-silicon content negative electrode sheet (≥1.4 g / cm³). 3 This improves the initial coulombic efficiency of lithium-ion batteries, thereby increasing the utilization rate of active materials in high-silicon-content anode sheets. Furthermore, the stacked graphite, together with the highly elastic and tough organic three-dimensional constraint network, forms a dual internal and external suppression system to rapidly transmit and buffer the internal expansion stress of the silicon-carbon composite material, thus better adapting it to the application of high-compact, high-silicon-content anode sheets. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a sedimentation diagram of the negative electrode slurry after 72 hours in Example 1 of the present invention; Figure 2 This is a sedimentation diagram of the negative electrode slurry of Comparative Example 2 of the present invention after 72 hours. Detailed Implementation

[0021] To facilitate understanding of this disclosure, a more complete description will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the present disclosure. However, this disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure.

[0022] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] To better understand the technical solutions and beneficial effects of this disclosure, the following detailed description is provided in conjunction with specific embodiments. An embodiment of a high-silicon content negative electrode sheet includes a current collector and a negative electrode slurry. The negative electrode slurry is coated on at least one side of the current collector. The negative electrode slurry includes a silicon-carbon composite material, a binder, a conductive agent, and a solvent. The silicon-carbon composite material includes chemical vapor deposition silicon-carbon material, graphite, and nano-silicon-carbon spheres. The particle size of the graphite is greater than the particle size of the chemical vapor deposition silicon-carbon material, which is greater than the particle size of the nano-silicon-carbon spheres. The binder includes an ionic cellulose ether binder, a polyacrylic binder, and an elastomer binder. The negative electrode slurry also includes a multifunctional epoxy crosslinking agent and a photoinitiator. After coating, the negative electrode slurry undergoes photo-pre-crosslinking to reduce its viscosity. The photo-pre-crosslinked negative electrode slurry is then dried for deep crosslinking to form a negative electrode active layer with a highly elastic and tough organic three-dimensional constrained network. The photo-pre-crosslinking conditions are: irradiation intensity 40 mW / cm². 2 -60mW / cm 2 The drying process lasts for 20-40 seconds; the conditions for the deep cross-linking are: temperature 75℃-85℃; time 10-20 minutes.

[0025] It is understandable that, since the adhesive includes ionic cellulose ether binders, polyacrylic binders, and elastomer binders, and since the negative electrode slurry contains multifunctional epoxy crosslinking agents and photoinitiators, the introduced multifunctional epoxy crosslinking agents, photoinitiators, ionic cellulose ether binders, and polyacrylic binders can effectively reduce the overall viscosity of the negative electrode slurry, making the negative electrode slurry of this disclosure a low-viscosity system. On the one hand, this can better meet the stability requirements of the coating process, and on the other hand, it helps to reduce the sedimentation rate of the negative electrode slurry and improve the storage stability of the negative electrode slurry.

[0026] It can also be understood that by subjecting the negative electrode slurry to photo-pre-crosslinking after the coating operation is completed, the photoinitiator is subjected to an irradiation intensity of 40mW / cm². 2 -60mW / cm 2Under conditions of 20-40 seconds, a small amount of active free radicals are generated, initiating ring-opening reactions of the carboxyl and hydroxyl groups of the active groups in multifunctional epoxy crosslinking agents, polyacrylic acid binders, and elastomer binders. This achieves partial pre-crosslinking of the binders to form a network, effectively increasing the viscosity of the negative electrode slurry. This is beneficial for subsequent drying and deep crosslinking. Under conditions of 75℃-85℃ and 10-20 minutes, the initiator generates a large number of active free radicals, initiating ring-opening reactions of the carboxyl and hydroxyl groups of the active groups in multifunctional epoxy crosslinking agents, polyacrylic acid binders, and elastomer binders. This process achieves deep cross-linking of the binder during drying. On one hand, it forms a highly elastic and tough organic three-dimensional constraint network that can encapsulate and fix the silicon-carbon composite material and the conductive agent, forming the negative electrode active layer. This allows the highly elastic and tough organic three-dimensional constraint network to effectively suppress the expansion of the silicon-carbon composite material, thus better adapting to the application of high-silicon-content negative electrode sheets. On the other hand, since the viscosity of the negative electrode with deep cross-linking during drying will not increase suddenly, it ensures that air bubbles can escape well, effectively avoiding defects such as pinholes and shrinkage cavities in the negative electrode active layer formed after drying. This reduces the probability of defects in the negative electrode active layer and further ensures the stability of the coating process.

[0027] Furthermore, the high-elasticity and tough organic three-dimensional constraint network formed after drying and cross-linking has high bonding strength, which can effectively reduce the total amount of adhesive used, further reduce the viscosity of the negative electrode slurry, and reduce the viscosity of the negative electrode slurry to below 20,000 cP, further reducing the defect probability of the negative electrode active layer, ensuring the stability of the coating process, and also reducing the cost of adhesive use.

[0028] It can also be understood that, since the silicon-carbon composite material includes chemical vapor deposition silicon-carbon material, graphite, and silicon-carbon nanospheres; and the particle size of the graphite is greater than the particle size of the chemical vapor deposition silicon-carbon material, which is greater than the particle size of the silicon-carbon nanospheres, the smaller-sized silicon-carbon nanospheres can be better packed between the larger-sized chemical vapor deposition silicon-carbon material and the larger-sized graphite, thereby increasing the compaction density of the high-silicon-content negative electrode sheet, i.e., the compaction density of the high-silicon-content negative electrode sheet is ≥1.4 g / cm³. 3 This improves the initial coulombic efficiency of lithium-ion batteries, thereby increasing the utilization rate of active materials in high-silicon-content anode sheets. Furthermore, the stacked graphite, together with the highly elastic and tough organic three-dimensional constraint network, forms a dual internal and external suppression system to rapidly transmit and buffer the internal expansion stress of the silicon-carbon composite material, thus better adapting it to the application of high-compact, high-silicon-content anode sheets.

[0029] It should be noted that although some scholars have attempted to achieve a good suppression of silicon expansion by using multiple different types of adhesives in combination, such as patent CN 115954458 B, traditional adhesives mainly rely on physical adsorption—that is, bonding with the silicon particle surface through intermolecular forces between CMC, PAA, and SBR, such as van der Waals forces and hydrogen bonds—rather than forming chemical bonds. This results in an inability to effectively suppress silicon expansion, causing silicon-carbon to easily detach and affecting the cycle performance of lithium-ion batteries. This phenomenon is particularly pronounced in high-silicon-content anode sheets.

[0030] Therefore, in this disclosure, by adding a multifunctional epoxy crosslinking agent and a photoinitiator, the multifunctional epoxy crosslinking agent can provide rigid support for the elastic and tough organic three-dimensional constraint network, and ensure that the ionic cellulose ether binder, polyacrylic acid binder and elastomer binder form chemical bonds through crosslinking reaction, thereby realizing the connection and fixation of different types of adhesives. Furthermore, the carboxyl group of the ionic cellulose ether improves the connection strength with the silicon-carbon composite material, ensuring that the formed elastic and tough organic three-dimensional constraint network has high elasticity and toughness, thereby better suppressing the silicon expansion of the high silicon content negative electrode sheet.

[0031] In one embodiment, the graphite has a particle size of 12μm-15μm to ensure a suitable particle size. This is particularly beneficial when combined with the use of chemical vapor deposition (CVD) silicon carbide material with a particle size of 8μm-12μm and the silicon carbide nanospheres with a particle size of 80nm-100nm. This ensures that the small-sized silicon carbide nanospheres can be well packed between the larger-sized CVD silicon carbide material and the large-sized graphite. This allows the large-sized graphite to provide better structural buffer support for the silicon carbide nanospheres and CVD silicon carbide material, not only providing rapid transfer buffering within the negative electrode active layer but also increasing the compaction density of the high-silicon content negative electrode sheet, achieving a compaction density ≥1.4g / cm³. 3 This improves the initial coulombic efficiency of lithium-ion batteries, thereby increasing the utilization rate of active materials in high-silicon-content anode sheets. Furthermore, the hydroxyl groups (-OH) on the graphite surface can chemically react with the carboxyl groups of polyacrylic binders to form stable COC or amide bonds, thus enhancing the connection strength between graphite and the highly elastic and tough organic three-dimensional constraint network. This ensures that the elastic and tough organic three-dimensional constraint network can effectively suppress the expansion of high-density silicon-carbon composite materials, making it better suited for applications involving high-compact, high-silicon-content anode sheets.

[0032] In one embodiment, the conductive agent includes graphene and single-walled carbon nanotubes to ensure the preparation of a high-silicon-content negative electrode with high conductivity.

[0033] In one embodiment, the graphene has a particle size of 100nm-800nm; the single-walled carbon nanotubes have a particle size of 0.4nm-3nm. This allows the added graphene to have a particle size between that of the chemically vapor-deposited silicon-carbon material and the silicon-carbon nanospheres, while the single-walled carbon nanotubes have a smaller particle size than the silicon-carbon nanospheres. This creates a five-level particle size gradient combination among graphite, chemically vapor-deposited silicon-carbon material, graphene, silicon-carbon nanospheres, and single-walled carbon nanotubes. This optimizes the conductivity distribution, facilitating the preparation of a high-conductivity, high-silicon-content anode sheet. Furthermore, it optimizes the particle size distribution of each material, promoting the formation of a high-density, high-silicon-content anode sheet. It also ensures that the five-level particle size gradient combination can buffer the rapid transmission of internal expansion stress in the silicon-carbon composite material, thus effectively suppressing the high-density, high-silicon-content anode sheet.

[0034] In one embodiment, the particle size of graphite is greater than that of chemically vapor-deposited silicon-carbon material, which is greater than that of graphene, which is greater than that of silicon-carbon nanospheres, which is greater than that of single-walled carbon nanotubes, to ensure the construction of a five-level particle size gradient combination.

[0035] In one embodiment, the graphene is nitrogen-doped graphene. Because the nitrogen atoms introduced by the nitrogen-doped graphene can form hydrogen bonds or coordination bonds with the hydroxyl groups on the surface of the silicon-carbon composite material, the interfacial bonding force between the nitrogen-doped graphene and the silicon-carbon particles is enhanced. This not only reduces the peeling of the elastic-tough organic three-dimensional constraint network caused by volume expansion during cycling, but also reduces the sedimentation rate of the negative electrode slurry. Furthermore, the nitrogen-doped sites can serve as active centers for lithium-ion adsorption, lowering the lithium-ion diffusion barrier and increasing the ion transport rate of the high-silicon-content negative electrode, thus better adapting to the conductivity of the high-compact, high-silicon-content negative electrode.

[0036] In one embodiment, the single-walled carbon nanotubes are carboxylated single-walled carbon nanotubes. The introduced carboxyl groups improve the dispersibility of the single-walled carbon nanotubes, preventing agglomeration and thus reducing the sedimentation rate of the negative electrode slurry. Furthermore, the introduced carboxyl groups can undergo esterification with the hydroxyl groups of the binder, participating in the construction of a highly elastic and tough organic three-dimensional constraint network, enhancing the continuity strength between the carboxylated single-walled carbon nanotubes and the binder, thereby reducing the peeling rate of the carboxylated single-walled carbon nanotubes during cycling. In addition, the flexible segments of the carboxylated single-walled carbon nanotubes can absorb the expansion stress of silicon-carbon through deformation, and their tubular structure can interpenetrate the gaps in the silicon-carbon composite material to better suppress the relative displacement of the silicon-carbon composite material.

[0037] In one embodiment, the nitrogen atom doping amount of nitrogen-doped graphene is 4%-6%, especially when combined with the carboxyl group content of carboxylated single-walled carbon nanotubes of 1%-2%, to ensure that the nitrogen atom doping amount of nitrogen-doped graphene and the carboxyl group content of carboxylated single-walled carbon nanotubes are suitable. In this way, the interfacial bonding force between nitrogen-doped graphene, carboxylated single-walled carbon nanotubes and silicon carbon particles is improved, the peeling of the elastic and tough organic three-dimensional constraint network caused by volume expansion during cycling is reduced, the sedimentation rate of negative electrode slurry is reduced, and the ion transport rate of high silicon content negative electrode sheet is improved.

[0038] In one embodiment, the polyacrylic adhesive includes at least one selected from polyacrylic acid, sodium polyacrylate, and lithium-ionized polyacrylic acid. Further, the polyacrylic adhesive is polyacrylic acid.

[0039] In a preferred embodiment, the polyacrylic acid is lithium-ionized polyacrylic acid.

[0040] In one embodiment, the ionic cellulose ether binder comprises at least one selected from sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and carboxymethyl hydroxyethyl cellulose. Further, the ionic cellulose ether binder is lithium carboxymethyl cellulose.

[0041] In one embodiment, the elastomeric binder comprises at least one of styrene-butadiene rubber and nitrile rubber. Further, in one embodiment, the elastomeric binder is styrene-butadiene rubber.

[0042] In one embodiment, the compaction density of the high-silicon content negative electrode is 1.7 g / cm³. 3 -1.8g / cm 3 Since high compaction density means that more silicon-carbon composite material can be accommodated per unit volume, the active material content of high-silicon-content anode sheets can be increased, thereby improving the first coulombic efficiency of lithium-ion batteries; and in turn, improving the utilization rate of active material in high-silicon-content anode sheets.

[0043] It is understandable that if only one type of adhesive is used, the amount of adhesive required for traditional high-silicon content anode sheets is 3-4 parts. This excessive amount of adhesive can affect the compaction density of the high-silicon content anode sheet, and a single adhesive cannot effectively suppress silicon expansion. Therefore, in one embodiment, the ionic cellulose ether binder is used in combination at a ratio of 0.3-0.5 parts by weight, the polyacrylic acid binder at a ratio of 1.0-2.0 parts, and the elastomer binder at a ratio of 0.5-1.0 parts. This combination allows the three to exert a good synergistic effect, effectively reducing the total amount of adhesive used (ensuring a total adhesive usage of 1.8-3.5 parts), which is beneficial for preparing high-silicon content anode sheets with high compaction density. Furthermore, it effectively suppresses silicon expansion in the high-silicon content anode sheet.

[0044] It should be noted that some patents, such as patent CN 115954458 B, address the low compaction density and poor suppression effect of high-silicon content negative electrode sheets by using a combination of various adhesives. However, reducing the amount of adhesive weakens its own adhesion and stability. Therefore, in this disclosure, by using lithium-ionized polyacrylic acid and lithium carboxymethyl cellulose in combination, the carboxymethyl groups of lithium carboxymethyl cellulose can improve the dispersibility of graphite and conductive agents, thereby reducing the sedimentation of the negative electrode slurry. Furthermore, the three-dimensional network formed by lithium-ionized polyacrylic acid and lithium carboxymethyl cellulose through hydrogen bonds can better encapsulate graphite and conductive agents, further suppressing the sedimentation of the negative electrode slurry and ensuring its stability. In addition, the hydrogen bonds formed between lithium-ionized polyacrylic acid and lithium carboxymethyl cellulose can enhance the overall adhesion, compensating for the poor adhesion caused by the reduction in the amount of adhesive.

[0045] It should be noted that although compounding lithium-ion polyacrylic acid with lithium carboxymethyl cellulose can effectively solve the problem of reduced adhesive strength and stability due to reduced adhesive dosage, if the molecular weight of the added lithium-ion polyacrylic acid and lithium carboxymethyl cellulose is too high, the molecular chains of lithium-ion polyacrylic acid and lithium carboxymethyl cellulose will become too long, causing a significant increase in the viscosity of the negative electrode slurry, thus ensuring that the viscosity of the negative electrode slurry can be reduced to below 20,000 cP. If the molecular weight of the added lithium-ion polyacrylic acid and lithium carboxymethyl cellulose is too low, it will affect the strength and toughness of the final high-elasticity and tough organic three-dimensional constraint network, and will not be able to effectively suppress the silicon expansion problem of the high-compact, high-silicon-content negative electrode sheet, making it prone to delamination.

[0046] Therefore, in one embodiment, by controlling the molecular weight of lithium-ion polyacrylic acid to be 50kDa-100kDa and the molecular weight of lithium carboxymethyl cellulose to be 200kDa-250kDa, it is ensured that the molecular weights of the added lithium-ion polyacrylic acid and lithium carboxymethyl cellulose are suitable. In this way, while ensuring that the added lithium-ion polyacrylic acid and lithium carboxymethyl cellulose do not cause a significant increase in the viscosity of the negative electrode slurry, it is also ensured that the formed high-elasticity and tough organic three-dimensional constraint network has high strength and toughness, so as to better suppress the silicon expansion problem of the high-compact high-silicon content negative electrode sheet and reduce the peeling rate of the high-elasticity and tough organic three-dimensional constraint network.

[0047] In one embodiment, the multifunctional epoxy crosslinking agent includes at least one of the following: trimethylolpropane triglycidyl ether solution, polyethylene glycol diglycidyl ether solution, glycerol triglycidyl ether solution, trimethylolpropane tri(3-mercaptopropionate) solution, pentaerythritol tetramercaptoacetate solution, and pentaerythritol tetraglycidyl ether solution.

[0048] In one embodiment, the multifunctional epoxy crosslinking agent is trimethylolpropane tris(3-mercaptopropionate).

[0049] In one embodiment, the photoinitiator includes at least one of 2-hydroxy-2-methylphenylacetone, 1-hydroxycyclohexylphenylacetone, and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone.

[0050] In one embodiment, the amount of the multifunctional epoxy crosslinking agent used is 0.3-0.9 parts by weight; particularly, the amount of the photoinitiator used is 1.0-2.0 parts; to ensure that the added multifunctional epoxy crosslinking agent and photoinitiator do not affect the electrochemical performance of the lithium-ion battery.

[0051] In one embodiment, by using 30-35 parts by weight of the chemical vapor deposition silicon carbide material, 40-50 parts by weight of the graphite and 10-15 parts by weight of the nano-silicon carbide spheres, a high silicon content negative electrode sheet is finally prepared, wherein the silicon content of the high silicon content negative electrode sheet is 25%-35%.

[0052] In one embodiment, the surface of the chemical vapor deposition silicon-carbon material is coated with a porous carbon layer with a thickness of 100nm-200nm. This ensures that the added porous carbon layer can effectively buffer the huge volume expansion of silicon during lithium intercalation, reduce the direct contact between silicon and electrolyte, suppress the breakage and regeneration of SEI film caused by silicon expansion, and improve the uniformity of the particle size of the chemical vapor deposition silicon-carbon material, which is beneficial for constructing a five-level particle size gradient combination.

[0053] In one embodiment, the graphite is artificial graphite.

[0054] In one embodiment, the amount of nitrogen-doped graphene used is 2.0-5.0 parts by mass, and the amount of carboxylated single-walled carbon nanotubes used is 1.5-2.0 parts, to ensure the preparation of a highly conductive, elastic, and tough organic three-dimensional confinement network.

[0055] In one embodiment, the nano-silicon-carbon spheres include a silicon dioxide core and an amorphous carbon shell. The thickness of the amorphous carbon shell is 5nm-10nm to ensure that the added amorphous carbon shell can effectively buffer the huge volume expansion of silicon during the lithium intercalation process, reduce the direct contact between silicon and electrolyte, suppress the breakage and regeneration of SEI film caused by silicon expansion, and improve the uniformity of the nano-silicon-carbon sphere particle size, which is beneficial to constructing a five-level particle size gradient combination.

[0056] In one embodiment, the porosity of the silica core is 30%-40% to ensure that the pore structure of the silica core is stable and appropriate, which is conducive to the construction of a five-level particle size gradient combination and effectively avoids the low mechanical strength caused by excessively high silica porosity, which would make it easy to break during subsequent rolling.

[0057] In one embodiment, the solvent includes at least one of water and ethanol.

[0058] In one embodiment, the solvent is a mixture of water and ethanol.

[0059] In one embodiment, the volume ratio of water to ethanol is (6-8)-(4-2). The mixing of ethanol and water reduces the surface tension of the solvent and breaks the hydrogen bond structure, thereby reducing the viscosity of the mixed system. At the same time, the weak alkalinity neutralizes the acidic sites generated by the oxidation of silicon surface to neutralize the pH value, thereby ensuring the stability of the negative electrode slurry system.

[0060] In one embodiment, the amount of solvent used is 52-60 parts by weight.

[0061] In one embodiment, the solid content of the negative electrode slurry is 40%-48%. It is understood that in this disclosure, 0.3-0.5 parts of ionic cellulose ether binder, 1.0-2.0 parts of polyacrylic acid binder, 0.5-1.0 parts of elastomer binder, 0.3-0.9 parts of multifunctional epoxy crosslinking agent, and 1.0-2.0 parts of photoinitiator are used in combination, especially in conjunction with 40-50 parts of graphite, 30-35 parts of chemical vapor deposition silicon carbide material, 2.0-5.0 parts of graphene, and 10-1... A five-level particle size gradient combination of 5 parts nano-silicon carbide spheres and 1.5-2.0 parts single-walled carbon nanotubes ensures that the viscosity of the negative electrode slurry is reduced while reducing the total amount of binder. This ensures that the viscosity of the negative electrode slurry is reduced to below 20,000 cP, thereby reducing the defect probability of the negative electrode active layer, ensuring the stability of the coating process, and reducing the cost of binder. It also increases the solid content of the negative electrode slurry, ensuring that the solid content of the negative electrode slurry can be maintained within 40%-48%.

[0062] In one embodiment, the viscosity of the negative electrode slurry before light irradiation is 8200 cP-10000 cP; the viscosity increase rate after light irradiation is 22%-30%.

[0063] It should be noted that the preparation of negative electrode slurry currently generally adopts a dry mixing method, such as patent CN 115954458 B. This involves first mixing silicon-based materials with single-walled carbon nanotubes and conductive carbon black under vacuum stirring, then adding sodium carboxymethyl cellulose and stirring until homogeneous to obtain a first slurry. Then, single-walled carbon nanotubes are added and mixed, followed by the addition of sodium carboxymethyl cellulose for dry mixing to obtain the first slurry. However, the dry mixing method easily leads to agglomeration of the silicon-carbon composite material and the conductive agent, making it impossible to form a highly conductive, elastic, and tough organic three-dimensional constraint network. At this point, some researchers have attempted to use a preparation method such as patent CN105869709A, where acrylic acid, cellulose, and water are stirred evenly to form a glue solution; then, silicon-carbon composite material, glue solution, binder, and water are added and stirred evenly, followed by adjusting the pH with an organic acid and stirring until homogeneous to form an electrode slurry. Although the aforementioned patent achieves pre-dispersion mixing of the binder, if the silicon-carbon composite material is added all at once, the problem of silicon-carbon composite material agglomeration still exists, making it impossible to prepare a uniformly conductive and continuous highly elastic and tough organic three-dimensional constraint network, which is unsuitable for applications with high silicon content negative electrode sheets.

[0064] Therefore, this disclosure also provides a method for preparing a high-silicon-content negative electrode, comprising the following steps: First, dissolving an ionic cellulose ether binder in a solvent to obtain a cellulose adhesive; then, adding a conductive agent to the cellulose adhesive to obtain a conductive slurry; next, adding a silicon-carbon composite material in batches to the conductive slurry for kneading to obtain a primary mixed slurry; subsequently, adding a polyacrylic acid binder to the primary mixed slurry to obtain a secondary mixed slurry; next, adding a multifunctional epoxy crosslinking agent and a photoinitiator to the secondary mixed slurry to obtain a tertiary mixed slurry; immediately following, adding an elastomer binder to the tertiary mixed slurry to obtain a negative electrode slurry; then, coating the negative electrode slurry onto the current collector to obtain a negative electrode precursor; finally, sequentially performing photo-pre-crosslinking and drying-deep crosslinking on the negative electrode precursor to obtain the high-silicon-content negative electrode as described in any of the above embodiments.

[0065] The aforementioned preparation method, by introducing multifunctional epoxy crosslinking agents and photoinitiators, especially in conjunction with photo-induced pre-crosslinking, achieves partial pre-crosslinking of the binder, thereby reducing the concentration of polyacrylic acid binders and consequently lowering the viscosity of the negative electrode slurry. This ensures that the viscosity of the negative electrode slurry does not increase sharply during subsequent deep crosslinking during drying, guaranteeing the stability of the coating process. It also ensures the formation of a conductive, uniform, and continuous highly elastic and tough organic three-dimensional constraint network during deep crosslinking, effectively suppressing the expansion of the silicon-carbon composite material and better adapting it to the application of high-pressure, high-silicon-content negative electrode sheets. Furthermore, it reduces the total amount of binder used, while simultaneously improving the bonding strength of the highly elastic and tough organic three-dimensional constraint network and reducing the sedimentation of the negative electrode slurry.

[0066] One embodiment of a method for preparing a high-silicon-content negative electrode includes some or all of the following steps: S101. The ionic cellulose ether binder is dissolved in a solvent to obtain a cellulose gel. This allows the ionic cellulose ether binder to pre-form a stable cellulose gel, providing a better dispersion medium for subsequent conductive agents, silicon-carbon composites, polyacrylic binders, multifunctional epoxy crosslinking agents, photoinitiators, and elastomer binders, effectively preventing the agglomeration of conductive agents. Furthermore, the carboxyl and hydroxyl groups of the ionic cellulose ether binder can initially stabilize the system through hydrogen bonding, preventing subsequent sedimentation of the negative electrode slurry.

[0067] In one embodiment, the ionic cellulose ether binder and solvent are mixed using a vacuum double planetary mixer, with the revolution speed controlled at 20 r / min-30 r / min and the rotation speed controlled at 1000 r / min-1500 r / min for 180 min-300 min, to obtain a uniform and stable cellulose adhesive.

[0068] S102. Add a conductive agent to the cellulose adhesive to obtain a conductive slurry, which makes the conductive agent, such as graphene and carbon nanotubes, uniformly dispersed, effectively avoiding the problem of graphene and carbon nanotubes agglomeration, which helps to build a uniform and continuous conductive network, and ensures that the subsequently added silicon-carbon composite material can be "embedded" in the gaps of the conductive network, improving the interfacial contact between the silicon-carbon composite material and the conductive agent, thereby reducing the resistance of the high elastic and tough organic three-dimensional constraint network.

[0069] In one embodiment, since the conductive agent is a mixture of nitrogen-doped graphene and carboxymethylated single-walled carbon nanotubes, and since the particle size of nitrogen-doped graphene is 100nm-800nm ​​and the particle size of carboxymethylated single-walled carbon nanotubes is 0.4nm-3nm, it is beneficial to form a uniform and continuous conductive network.

[0070] In one embodiment, the carboxymethylated single-walled carbon nanotubes are a dispersion of carboxymethylated single-walled carbon nanotubes, which are dispersed in a carboxymethyl cellulose solution to obtain the dispersion of carboxymethylated single-walled carbon nanotubes.

[0071] In one embodiment, the concentration of the carboxymethylated carbon nanotube dispersion is 0.4%-0.6%.

[0072] S103. The silicon-carbon composite material is added to the conductive slurry in batches and kneaded to obtain a primary mixed slurry.

[0073] It should be noted that, to ensure uniform dispersion of silicon-carbon composite materials, most researchers typically employ batch addition. While batch addition addresses the issue of agglomeration in silicon-carbon composites, the significant size differences between the graphite, chemically vapor-deposited silicon-carbon material, and silicon-carbon nanospheres make it difficult to overcome the van der Waals forces between particles through stirring alone. In particular, the high surface energy of silicon-carbon nanospheres makes them prone to agglomeration, forming micron-sized secondary particles that fail to fill the gaps between the large-particle graphite and silicon-carbon materials. This results in a non-uniform structure of "large particle gap vacancy + small particle local agglomeration," causing the bulk density to decrease to 1.4 g / cm³. 3 the following.

[0074] Therefore, in this disclosure, by adding silicon-carbon composite materials in batches to the conductive slurry for kneading, the graphite, chemical vapor-deposited silicon-carbon material, and nano-silicon-carbon spheres of the silicon-carbon composite material with large particle size differences can be better deposited on nitrogen-doped graphene and carboxylated single-walled carbon nanotubes under the action of kneading. This helps to construct a five-level particle size gradient combination, which is beneficial to the preparation of high-pressure, high-silicon-content anode sheets, thus laying the foundation for subsequent high-pressure, high-silicon-content anode sheets.

[0075] In one embodiment, the step of adding the silicon-carbon composite material to the conductive slurry in batches for kneading includes the following specific steps: first, the chemical vapor deposition silicon-carbon material, graphite, and nano-silicon-carbon spheres are dry-mixed, and then added to the conductive slurry in 3-5 batches for kneading. The kneading conditions are controlled as follows: dual planetary mixer, stirring for 35-45 minutes, and stirring speed of 20-50 r / min. This allows the chemical vapor deposition silicon-carbon material, graphite, and nano-silicon-carbon spheres to achieve effective particle size gradient stacking with nitrogen-doped graphene and carboxymethylated single-walled carbon nanotubes, which is beneficial for preparing high-pressure, high-silicon-content negative electrode sheets.

[0076] It is also understandable that if the kneading speed is too high, the excessively high shear force will cause the graphite and chemical vapor deposition silicon carbide materials to break down, which is not conducive to constructing a five-level particle size gradient combination. If the kneading speed is too low, the insufficient shear force will not be able to complete the stacking of the five-level effective particle size gradient. Therefore, in this disclosure, the five-level effective particle size gradient stacking is achieved by controlling the stirring speed to 20 r / min-50 r / min.

[0077] S104. Add the polyacrylic adhesive to the primary mixed slurry to obtain the secondary mixed slurry, so as to ensure that the polyacrylic adhesive can be uniformly dispersed in the primary mixed slurry.

[0078] S105. The multifunctional epoxy crosslinking agent and photoinitiator are added to the secondary mixed slurry so that the multifunctional epoxy crosslinking agent and photoinitiator can be uniformly dispersed in the secondary mixed slurry to obtain the tertiary mixed slurry.

[0079] In one embodiment, the multifunctional epoxy crosslinking agent is a trimethylolpropane triglycidyl ether solution.

[0080] In one embodiment, trimethylolpropane triglycidyl ether is dissolved in anhydrous ethanol to obtain a trimethylolpropane triglycidyl ether solution. Further, the concentration of trimethylolpropane triglycidyl ether is 10%-20%.

[0081] S106. Add an elastomer binder to the three-stage mixed slurry to obtain a negative electrode slurry; It is understandable that if the elastomeric binder is added before the multifunctional epoxy crosslinking agent and photoinitiator, the earlier addition of the elastomeric binder will affect the mixing uniformity of the multifunctional epoxy crosslinking agent and photoinitiator with the polyacrylic binder, making it impossible to ensure the effectiveness of subsequent photo-induced pre-crosslinking and drying-induced deep crosslinking, thereby affecting the bonding strength and elasticity of the high-elasticity and toughness organic three-dimensional constraint network. Therefore, in this disclosure, by setting the addition order of the functional group epoxy crosslinking agent and photoinitiator after the polyacrylic binder, the mixing uniformity of the added multifunctional epoxy crosslinking agent and photoinitiator with the polyacrylic binder is ensured, and the elastomeric binder is added last, thereby ensuring the preparation of a conductive, uniform, and continuous high-elasticity and toughness organic three-dimensional constraint network.

[0082] In one embodiment, the elastomeric binder is a styrene-butadiene rubber latex.

[0083] S107. The negative electrode slurry is coated onto the current collector to obtain the negative electrode precursor.

[0084] In one embodiment, the thickness of the negative electrode slurry coated on the current collector is 200um-300um.

[0085] S108. The negative electrode precursor is subjected to photo-pre-crosslinking and drying deep crosslinking in sequence to obtain the high silicon content negative electrode as described in any of the above embodiments.

[0086] It is understandable that by performing photo-pre-crosslinking on the negative electrode precursor, the photoinitiator can be subjected to an irradiation intensity of 40 mW / cm². 2 -60mW / cm 2 Under conditions of 20-40 seconds, a small amount of active free radicals are generated, initiating ring-opening reactions of the carboxyl and hydroxyl groups of the active groups in multifunctional epoxy crosslinking agents, polyacrylic acid binders, and elastomer binders. This achieves partial pre-crosslinking of the binders to form a network, effectively increasing the viscosity of the negative electrode slurry. This is beneficial for subsequent drying and deep crosslinking. Under conditions of 75℃-85℃ and 10-20 minutes, the photoinitiator generates a large number of active free radicals, initiating ring-opening reactions of the carboxyl and hydroxyl groups of the active groups in multifunctional epoxy crosslinking agents, polyacrylic acid binders, and elastomer binders. The reaction achieves deep cross-linking of the binder during drying. On the one hand, it forms a highly elastic and tough organic three-dimensional constraint network that can encapsulate and fix the silicon-carbon composite material and the conductive agent, forming a negative electrode active layer. This allows the highly elastic and tough organic three-dimensional constraint network to effectively suppress the expansion of the silicon-carbon composite material, thus better adapting to the application of high-silicon-content negative electrode sheets. On the other hand, since the viscosity of the negative electrode with deep cross-linking during drying will not increase suddenly, it ensures that air bubbles can escape well, effectively avoiding defects such as pinholes and shrinkage cavities in the negative electrode active layer formed after drying. This reduces the probability of defects in the negative electrode active layer and ensures the stability of the coating process.

[0087] In one embodiment, the wavelength of the light-induced pre-crosslinking is an ultraviolet wavelength of 365 nm.

[0088] Furthermore, due to the high bonding strength of the formed highly elastic and tough organic three-dimensional constraint network, the total amount of adhesive used can be effectively reduced, further reducing the viscosity of the negative electrode slurry to below 20,000 cP, which further reduces the defect probability of the negative electrode active layer, ensures the stability of the coating process, and also reduces the cost of adhesive use.

[0089] In one embodiment, the negative electrode precursor is subjected to photo-pre-crosslinking and drying-deep crosslinking in sequence, and the negative electrode precursor is also subjected to roll pressing to prepare a high-pressure, high-silicon-content negative electrode.

[0090] In one embodiment, the rolling conditions were 6.5 MPa-8 MPa to obtain a compacted density of 1.7 g / cm³. 3 -1.8g / cm 3 High silicon content negative electrode.

[0091] This disclosure also provides a lithium-ion battery including the high-silicon-content negative electrode sheet described in any of the above embodiments. This ensures that the use of the high-silicon-content negative electrode sheet of this disclosure reduces the total amount of binder used, while also improving the bonding strength of the high-elasticity and tough organic three-dimensional constraint network, and reducing the sedimentation of the negative electrode slurry. This ensures the stability of the coating process, thereby achieving good suppression of silicon expansion of the high-silicon-content negative electrode sheet under high pressure compaction, and thus improving the cycle performance and first coulombic efficiency of the lithium-ion battery.

[0092] The following are some specific examples. When %, it refers to a percentage by weight. It should be noted that the following examples do not exhaustively list all possible scenarios, and unless otherwise specified, the materials used in the examples are commercially available.

[0093] Understandably, the lithium carboxymethyl cellulose used in this disclosure was provided by Chongqing Lihong Fine Chemical Co., Ltd.; the nitrogen-doped graphene was provided by Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.; the carboxylated single-walled carbon nanotubes were provided by OCSiAl; and the lithium-ionized polyacrylic acid was provided by Fujian Blue Ocean Blackstone New Material Technology Co., Ltd.

[0094] Example 1 1) Add 0.3 kg of lithium carboxymethyl cellulose with a molecular weight of 250 kDa and 20 kg of deionized water and ethanol mixed solvent in a volume ratio of 7:3 to a vacuum double planetary mixer and stir and mix. Control the vacuum double planetary mixer to revolve at 20 r / min and rotate at 1000 r / min for 240 min to obtain cellulose gel solution. 2) Add 2 kg of nitrogen-doped graphene with a particle size of 800 nm and a nitrogen atom doping amount of 4% and 25 kg of carboxylated single-walled carbon nanotube dispersion with a particle size of 3 nm, a concentration of 0.4%, and a carboxyl content of 1%, and stir and mix for 60 min to obtain a conductive slurry. 3) Dry mix 35 kg of silicon carbide material with a particle size of 12 μm, 15 kg of silicon carbide nanospheres with a particle size of 100 nm, and 47.5 kg of artificial graphite with a particle size of 15 μm, and add them in three batches. Control the speed of the double planetary mixer blades to revolve at 30 r / min and rotate at 1200 r / min, knead for 120 min to obtain the primary mixed slurry. 4) Add 14 kg of lithium-ion polyacrylic acid adhesive with a concentration of 7% and a molecular weight of 80 kDa, and stir for 30 min at a speed of 45 r / min to obtain a secondary mixed slurry; 5) Inject 2 kg of photoinitiator and 2 kg of 15% trimethylolpropane triglycidyl ether solution and stir to obtain a three-stage mixed slurry; 6) Add 1 kg of 50% styrene-butadiene rubber latex, stir and mix to obtain the negative electrode slurry; 7) The negative electrode slurry is coated onto a current collector with a thickness of 260 μm to obtain the negative electrode precursor; 8) Using a 365nm wavelength ultraviolet light source with an irradiance of 50mW / cm² 2 The negative electrode precursor was continuously irradiated for 30 seconds; then dried at 80℃ for 20 minutes, followed by rolling under 6.5 MPa-7.0 MPa conditions to obtain a compacted density of 1.7 g / cm³. 3 High-silicon-content negative electrode sheet with a silicon content of 35%.

[0095] Example 2: 1) Add 0.4 kg of lithium carboxymethyl cellulose with a molecular weight of 220 kDa and 20 kg of deionized water and ethanol mixed solvent in a volume ratio of 8:2 to a vacuum double planetary mixer and stir and mix. Control the vacuum double planetary mixer to revolve at 20 r / min and rotate at 1000 r / min for 240 min to obtain cellulose gel solution. 2) Add 3 kg of nitrogen-doped graphene with a particle size of 500 nm and a nitrogen atom doping amount of 5% and 30 kg of carboxylated single-walled carbon nanotube dispersion with a particle size of 1.2 nm, a concentration of 0.4%, and a carboxyl group content of 1.5%, and stir and mix for 60 min to obtain a conductive slurry. 3) Dry mix 30 kg of silicon carbide material with a particle size of 10 μm, 12 kg of silicon carbide nanospheres with a particle size of 90 nm, and 45 kg of artificial graphite with a particle size of 13 μm, and add them in three batches. Control the speed of the double planetary mixer blades at 30 r / min and the rotation speed at 1200 r / min, knead for 120 min to obtain the primary mixed slurry. 4) Add 21.5 kg of lithium-ion polyacrylic acid adhesive with a concentration of 7% and a molecular weight of 50 kDa, and stir to mix (45 r / min for 30 min) to obtain a secondary mixed slurry; 5) Inject 1.5 kg of photoinitiator and 1.5 kg of 20% trimethylolpropane triglycidyl ether solution and stir to obtain a three-stage mixed slurry; 6) Add 1.4 kg of styrene-butadiene rubber latex with a concentration of 50%, stir and mix to obtain the negative electrode slurry; 7) The negative electrode slurry is coated onto the current collector with a thickness of 6 μm to obtain the negative electrode precursor; 8) The negative electrode precursor is irradiated with a 365nm wavelength ultraviolet light source with an intensity of 60mW / cm². 2 Irradiate for 20 seconds; then dry at 85℃ for 10 minutes, followed by roller pressing under 7.0 MPa-7.5 MPa conditions to obtain a compacted density of 1.72 g / cm³. 3 A negative electrode sheet with a silicon content of 30%.

[0096] Example 3 1) Add 0.5 kg of lithium carboxymethyl cellulose with a molecular weight of 200 kDa and 20 kg of deionized water and ethanol mixed solvent in a volume ratio of 6:4 to a vacuum double planetary mixer and stir and mix. Control the vacuum double planetary mixer to revolve at 20 r / min and rotate at 1000 r / min for 240 min to obtain cellulose gel solution. 2) Add 5 kg of nitrogen-doped graphene with a particle size of 100 nm and a nitrogen atom doping amount of 6% and 35 kg of carboxylated single-walled carbon nanotube dispersion with a particle size of 0.4 nm, a concentration of 0.4%, and a carboxyl group content of 2%, and stir and mix for 60 min to obtain a conductive slurry; 3) 25 kg of silicon carbide material with a particle size of 8 μm, 10 kg of silicon carbide nanospheres with a particle size of 80 nm and 50 kg of artificial graphite with a particle size of 12 μm were dry-mixed and added in three batches. The speed of the blades of the double planetary mixer was controlled at 30 r / min and the rotation speed was 1200 r / min. The mixture was kneaded for 120 min to obtain the primary mixed slurry. 4) Add 28.5 kg of lithium-ion polyacrylic acid adhesive with a concentration of 7% and a molecular weight of 100 kDa, and stir and mix at a speed of 45 r / min for 30 min to obtain a secondary mixed slurry; 5) Inject 1 kg of photoinitiator and 1 kg of 10% trimethylolpropane triglycidyl ether solution and stir to obtain a three-stage mixed slurry; 6) Add 2 kg of 50% styrene-butadiene rubber latex, stir and mix to obtain the negative electrode slurry; 7) The negative electrode slurry is coated onto the current collector with a thickness of 6 μm to obtain the negative electrode precursor; 8) Using a 365nm wavelength ultraviolet light source, with an irradiance of 60mW / cm². 2 The negative electrode precursor was continuously irradiated for 20 seconds; then dried at 85°C for 10 minutes, followed by rolling under 7.5 MPa-8.0 MPa conditions to obtain a compacted density of 1.75 g / cm³. 3 A negative electrode sheet with a silicon content of 20%.

[0097] Comparative Example 1 The difference from Example 1 is that steps 5) and 8) are omitted. The negative electrode precursor is irradiated with a 365nm wavelength ultraviolet light source with an intensity of 60mW / cm². 2 The procedure remains the same for 20 seconds of irradiation.

[0098] Comparative Example 2 The difference from Example 1 is that Comparative Example 2 uses a negative electrode slurry composed of a traditional polyacrylic acid binder system and a traditional particle size system. Specifically, it omits the nano-silicon carbon spheres and replaces graphene with conductive carbon black. The particle size system used is: silicon carbon material 12μm, artificial graphite 15μm, conductive carbon black 30nm, and single-walled carbon nanotubes 3nm. The binder is a traditional polyacrylic acid binder system, replacing the styrene-butadiene rubber latex. Steps 5) and 8) are omitted, and the negative electrode precursor is irradiated with a 365nm wavelength ultraviolet light source at an intensity of 60mW / cm². 2 With irradiation for 20 seconds and other parameters remaining unchanged, the compaction density of the high-silicon content negative electrode sheet prepared was 1.40 g / cm³. 3 .

[0099] Comparative Example 3 The difference from Example 1 is that the negative electrode precursor in step 8) is irradiated with a 365nm wavelength ultraviolet light source at an intensity of 60mW / cm². 2 Irradiation for 20 seconds equals 30 mW / cm 2 Irradiate for 45 seconds, with the rest remaining unchanged.

[0100] Comparative Example 4 The difference from Example 1 is that the negative electrode precursor in step 8) is irradiated with a 365nm wavelength ultraviolet light source at an intensity of 60mW / cm². 2 Irradiation for 20 seconds equals 70 mW / cm 2 Irradiate for 15 seconds, with the rest remaining unchanged.

[0101] Comparative Example 5 The difference from Example 1 is that the trimethylolpropane triglycidyl ether solution in step 5) is replaced with polyethylene glycol diglycidyl ether solution and glycerol triglycidyl ether solution, while the rest remain unchanged.

[0102] Comparative Example 6 The difference from Example 1 is that the lithium-ionized polyacrylic acid adhesive in step 4) is replaced with ordinary polyacrylic acid adhesive, while the rest remains the same.

[0103] Comparative Example 7 The difference from Example 1 is that the addition in three batches in step 3) is replaced with the addition in one batch, while the rest remains the same.

[0104] The viscosity, 72-hour sedimentation rate, solid content, and viscosity increase rate after light irradiation of the negative electrode slurries prepared in Examples 1-3 and Comparative Examples 1-7 were tested, and the experimental data are shown in Table 1. Wherein, viscosity increase rate after light irradiation = (viscosity after light irradiation - viscosity before light irradiation) / viscosity before light irradiation * 100%; Table 1 As can be seen from Examples 1-3 and Comparative Example 1 in Table 1 above, the negative electrode slurry formed by the compounding of ionic cellulose ether binder, polyacrylic acid binder, elastomer binder, multifunctional epoxy crosslinking agent, photoinitiator and silicon-carbon composite material in Examples 1-3 is a low viscosity system. On the one hand, it can better meet the stability of the coating process, and on the other hand, it helps to reduce the sedimentation rate of the negative electrode slurry and improve the storage stability of the negative electrode slurry. Furthermore, it ensures that the introduction of photo-pre-crosslinking after coating to form a network effectively increases the viscosity of the negative electrode slurry, which is beneficial to the formation of a highly elastic and tough organic three-dimensional constraint network during subsequent deep crosslinking in drying, so as to achieve the effect of suppressing the expansion of the high silicon content negative electrode sheet. In contrast, Comparative Example 1 did not use photo-pre-crosslinking, so the viscosity of its coated negative electrode slurry did not show an upward trend, thus failing to form a highly elastic and tough organic three-dimensional constraint network. As a result, the comprehensive performance of the lithium-ion battery prepared in Comparative Example 1 is significantly worse than that of Examples 1-3. For details, please refer to the experimental data table in Table 2. Among them, the comprehensive performance of Example 1 is the best.

[0105] As can be seen from the comparison between Example 1 and Comparative Example 2 in Table 1 above, since Comparative Example 2 uses a traditional negative electrode slurry, the viscosity of the negative electrode slurry in Comparative Example 2 increases sharply to over 20,000 cP. This is not only unfavorable for coating, but also increases the sedimentation rate of the negative electrode slurry. As a result, the overall performance of the lithium-ion battery prepared in Comparative Example 2 is significantly worse than that of Example 1. For details, please refer to Table 2.

[0106] Please refer to the details below. Figure 1 and Figure 2 The comparison shows that... Figure 1 After 72 hours of settling, the negative electrode slurry tilted, and the top negative electrode slurry still showed a high-viscosity mixture state, adhering to the inner wall of the reagent bottle, indicating that the negative electrode slurry of Example 1 still maintained good anti-settling performance and did not separate into layers. Figure 2After 72 hours of settling, the negative electrode slurry was tilted, and the top slurry was liquid with low viscosity and showed stratification, indicating that the negative electrode slurry had settled. Among them, Example 1 had the best overall performance.

[0107] As can be seen from the comparison between Example 1 and Comparative Examples 3-4 in Table 1 above, when the irradiation intensity of Example 1 is 40 mW / cm 2 -60mW / cm 2 Within the range of 20S-40S for pre-crosslinking under light irradiation, the overall performance of the lithium-ion battery prepared in Example 1 is significantly better than that of Comparative Examples 3-4. For details, please refer to Table 2.

[0108] As can be seen from the comparison between Example 1 and Comparative Example 5 in Table 1 above, the overall performance of the negative electrode slurry prepared by Example 1 using trimethylolpropane triglycidyl ether solution as a multifunctional epoxy crosslinking agent is significantly better than that of the negative electrode slurry using polyethylene glycol diglycidyl ether solution and glycerol triglycidyl ether solution as multifunctional epoxy crosslinking agents.

[0109] As can be seen from Example 1 and Comparative Example 6 in Table 1 above, the overall performance of the negative electrode slurry prepared by lithium-ionized polyacrylic acid solution in Example 1 is significantly better than that of the negative electrode slurry prepared by lithium-ionized polyacrylic acid solution in Comparative Example 6.

[0110] As can be seen from Example 1 and Comparative Example 7 in Table 1 above, since Example 1 adopts a batch addition operation, it helps to improve the uniform dispersion of each component, making the overall index of Example 1 significantly better than that of Comparative Example 7, which is added in one batch.

[0111] The high-silicon content negative electrode, lithium cobalt oxide positive electrode, and polyethylene ceramic coated separator prepared in Examples 1-3 and Comparative Examples 1-7 were assembled to form a lithium-ion battery. Then, the lithium-ion battery was subjected to the first coulombic efficiency, capacity retention rate, expansion rate of the high-silicon content negative electrode, and adhesion strength between the active layer and the current collector. The experimental data in Table 2 below were obtained.

[0112] Table 2: As can be seen from the comparison of Examples 1-3 and Comparative Examples 1-7 in Table 2 above, the lithium-ion batteries of Examples 1-3 have significantly better overall performance than those of Comparative Examples 1-7 due to the combined use of multifunctional epoxy crosslinking agents and photoinitiators, photo-induced pre-crosslinking operations, five-level particle size gradient combinations, nitrogen-doped graphene, carboxylated single-walled carbon nanotubes, lithium-ionized polyacrylic acid, and lithium carboxymethyl cellulose. Among them, Example 1 has the best overall performance.

[0113] Furthermore, the appearance of the active layers of the high-silicon-content negative electrode sheets prepared in Examples 1-3 and Comparative Examples 1-7 was examined. Because Examples 1-3 used a combination of multifunctional epoxy crosslinking agents and photoinitiators, photo-pre-crosslinking operation, five-level particle size gradient combination, nitrogen-doped graphene, carboxylated single-walled carbon nanotubes, lithium-ionized polyacrylic acid and lithium carboxymethyl cellulose, the active layers of the high-silicon-content negative electrode sheets in Examples 1-3 had significantly fewer pinholes and shrinkage cavities than those in Comparative Examples 1-7.

[0114] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the disclosed patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A high-silicon-content negative electrode sheet, comprising a current collector and a negative electrode slurry, wherein the negative electrode slurry is coated on at least one side of the current collector, and the negative electrode slurry comprises a silicon-carbon composite material, a binder, a conductive agent, and a solvent, characterized in that, The silicon-carbon composite material includes chemical vapor deposition silicon-carbon material, graphite, and silicon-carbon nanospheres; wherein the particle size of the graphite is greater than the particle size of the chemical vapor deposition silicon-carbon material, which is greater than the particle size of the silicon-carbon nanospheres. The adhesive includes ionic cellulose ether binders, polyacrylic acid binders, and elastomer binders; the negative electrode slurry also includes multifunctional epoxy crosslinking agents and photoinitiators; The negative electrode slurry after coating is subjected to photo-pre-crosslinking to reduce the viscosity of the negative electrode slurry. The pre-crosslinked negative electrode slurry is dried and deeply crosslinked to form a negative electrode active layer with a highly elastic and tough organic three-dimensional constraint network. The conditions for the photo-induced pre-crosslinking are: irradiation intensity 40 mW / cm². 2 -60mW / cm 2 Last 20-40 seconds; The conditions for the drying depth crosslinking are: temperature 75℃-85℃; time 10min-20min.

2. The high-silicon-content negative electrode according to claim 1, characterized in that, The graphite has a particle size of 12μm-15μm; and / or, The particle size of the chemical vapor deposition silicon-carbon material is 8μm-12μm; and / or, The particle size of the nano-silicon carbide spheres is 80nm-100nm.

3. The high-silicon-content negative electrode according to claim 1, characterized in that, The conductive agent includes graphene and single-walled carbon nanotubes.

4. The high-silicon-content negative electrode according to claim 3, characterized in that, The graphene has a particle size of 100nm-800nm; and / or, The single-walled carbon nanotubes have a particle size of 0.4 nm-3 nm; and / or, The graphene is nitrogen-doped graphene; and / or, The single-walled carbon nanotubes are carboxylated single-walled carbon nanotubes; and / or... The amount of graphene used is 2.0-5.0 parts by weight; the amount of single-walled carbon nanotubes used is 1.5-2.0 parts.

5. The high-silicon-content negative electrode according to claim 1, characterized in that, The polyacrylic adhesive includes at least one of polyacrylic acid, sodium polyacrylate, and lithium-ionized polyacrylic acid; and / or, The ionic cellulose ether binder comprises at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and carboxymethyl hydroxyethyl cellulose; and / or, The elastomeric binder includes at least one of styrene-butadiene rubber and nitrile rubber.

6. The high-silicon-content negative electrode according to claim 1, characterized in that, The amount of the ionic cellulose ether binder used, by weight, is 0.3-0.5 parts; and / or, The amount of the polyacrylic adhesive used is 1.0 part to 2.0 parts; and / or, The amount of the elastomeric adhesive used is 0.5 parts to 1.0 parts.

7. The high-silicon-content negative electrode according to claim 1, characterized in that, The multifunctional epoxy crosslinking agent includes at least one of the following: trimethylolpropane triglycidyl ether solution, polyethylene glycol diglycidyl ether solution, glycerol triglycidyl ether solution, trimethylolpropane tris(3-mercaptopropionate) solution, pentaerythritol tetramercaptoacetate solution, and pentaerythritol tetraglycidyl ether solution; and / or, The photoinitiator comprises at least one selected from 2-hydroxy-2-methylphenylacetone, 1-hydroxycyclohexylphenyl ketone, and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone; and / or, The amount of the multifunctional epoxy crosslinking agent used is 0.3-0.9 parts by weight. The amount of photoinitiator used is 1.0 part to 2.0 parts; The amount of the chemical vapor deposition silicon-carbon material used is 30-35 parts; The amount of graphite used is 40-50 parts; The amount of the nano-silicon carbide spheres used is 10-15 parts.

8. The high-silicon-content negative electrode according to claim 1, characterized in that, The solvent includes at least one of water and ethanol.

9. A method for preparing a high-silicon-content negative electrode, characterized in that, Includes the following steps: The ionic cellulose ether binder is dissolved in a solvent to obtain a cellulose adhesive solution; A conductive agent is added to the cellulose adhesive to obtain a conductive slurry; The silicon-carbon composite material is added to the conductive slurry in batches and kneaded to obtain a primary mixed slurry. A polyacrylic acid binder is added to the primary mixed slurry to obtain a secondary mixed slurry; The multifunctional epoxy crosslinking agent and photoinitiator are added to the secondary mixed slurry to obtain the tertiary mixed slurry; An elastomer binder is added to the three-stage mixed slurry to obtain a negative electrode slurry; The negative electrode slurry is coated onto the current collector to obtain a negative electrode precursor. The negative electrode precursor is subjected to photo-pre-crosslinking and dry deep crosslinking in sequence to obtain the high silicon content negative electrode sheet as described in any one of claims 1-8.

10. A lithium-ion battery, characterized in that, The high-silicon-content negative electrode includes any one of claims 1-8.

Images