Silicon-carbon negative electrode slurry, preparation method and application thereof

Abstract

This disclosure pertains to the field of lithium-ion battery technology, providing a silicon-carbon anode slurry, its preparation method, and its applications. The silicon-carbon anode slurry comprises a silicon-based anode material, conductive carbon black, carbon nanotubes, a dispersant, and a composite binder. The composite binder comprises polyacrylic acid (PAA) and flexible rubber. PAA condenses to form a rigid covalent cross-linked network, and the flexible rubber physically penetrates the rigid covalent cross-linked network to form a semi-interpenetrating network. The disclosure also discloses a method for preparing the aforementioned anode slurry and a silicon-carbon anode sheet obtained from the aforementioned anode slurry through coating and heat treatment, including a lithium-ion battery containing the anode sheet. This disclosure, by constructing a rigid-flexible composite binder and synergistically building a stable conductive network with carbon nanotubes, can simultaneously achieve the effects of suppressing electrode structure damage, maintaining stable electrical contact, and reducing interfacial side reactions, ultimately resulting in a significant improvement in the cycle life, coulombic efficiency, and rate performance of the silicon-carbon anode.

Description

Technical Field

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

[0002] Lithium-ion batteries are core energy storage devices in new energy vehicles, energy storage systems, and portable electronic devices. Their energy density, cycle life, and structural stability have become the core research and development directions for the industry. Currently, the graphite anode widely used in commercial lithium-ion batteries has a theoretical specific capacity of only 372 mAh / g, which is insufficient to meet the application requirements of high-energy-density battery systems. Developing high-specific-capacity anode materials has become the key to breaking through the performance bottleneck of lithium-ion batteries.

[0003] Silicon-based anodes, with their theoretical specific capacity of up to 4200 mAh / g, wide availability, and environmental friendliness, have become ideal candidate materials to replace traditional graphite anodes. Silicon-carbon anodes, as composite materials of silicon and carbon, combine the high lithium storage capacity of silicon with the structural stability of carbon, following a dual lithium storage mechanism of silicon-lithium alloying and lithium-carbon intercalation, making them a mainstream research direction for high-energy-density lithium-ion battery anodes. However, silicon-carbon anodes face insurmountable technical bottlenecks in practical applications: the silicon phase undergoes volume expansion and contraction exceeding 300% during lithiation / delithiation. This drastic volume change generates continuous and periodic mechanical stress on the microstructure of the anode sheet, leading not only to silicon particle pulverization and carbon coating layer rupture, but also to electrode structure collapse and conductive network failure. Simultaneously, it causes repeated rupture and reconstruction of the solid electrolyte interphase (SEI) film, exacerbating electrolyte consumption and ultimately resulting in rapid capacity decay and significantly shortened cycle life, becoming a core obstacle to the industrial application of silicon-carbon anodes.

[0004] As a key component of lithium-ion battery electrodes, binders play a crucial role in tightly bonding active materials, conductive agents, and current collectors, maintaining the integrity of the electrode structure, and ensuring the smooth flow of conductive networks and ion transport channels. Their performance directly determines the electrochemical performance and service life of silicon-carbon anodes. For silicon-carbon anode systems with high silicon content (>50%), current commercial binders such as sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and styrene-butadiene rubber (SBR), and their conventional compounding ratios, cannot simultaneously meet the dual requirements of electrode structure bonding and conductivity / ion transport, resulting in an engineering dilemma where binding force and buffering performance cannot be achieved simultaneously. If a high proportion and high modulus binder are used to strengthen structural binding, although it can alleviate the volume expansion of silicon particles to some extent, it will lead to excessive electrode rigidity, which cannot effectively buffer the mechanical stress during cycling. After multiple charge-discharge cycles, electrode cracking is likely to occur, and an excessively thick binder layer will severely hinder the transport of lithium ions and electrons, resulting in increased electrode internal resistance and decreased rate performance. If the binder ratio is reduced or a low modulus flexible binder is used to improve stress buffering capacity, the initial structural strength of the electrode will be insufficient, which cannot effectively bind the active particles. Structural damage and conductive network collapse will occur in the first or early cycles, leading to low initial coulombic efficiency and rapid capacity decay of the battery.

[0005] To address the series of problems caused by the volume expansion of silicon-carbon anodes, industry and academia have successively proposed strategies such as material nanostructuring, carbon coating to construct core-shell structures, conductive network optimization, and the development of novel binders. Among these, the design and development of novel binders has become a key approach to improving the stability of silicon-carbon anodes. Current binder systems or single binder modification schemes can only improve the performance defects of silicon-carbon anodes from a single dimension and cannot systematically solve the synergistic problems of electrode structural stability, conductive network durability, and interface integrity. Therefore, designing a rigid-flexible composite binder system, combined with the construction of a highly stable multi-level conductive network, and optimizing the electrode fabrication process to achieve uniform dispersion of components and interface stability, has become an urgent technical problem to be solved to meet the extreme requirements of silicon-carbon anodes in terms of structure, conductivity, and interface during long-term cycling, and to promote the industrial application of high-energy-density silicon-carbon anode lithium-ion batteries. Summary of the Invention

[0006] This disclosure provides a silicon-carbon anode slurry, its preparation method, and its application, in order to at least solve the above-mentioned technical problems existing in the prior art.

[0007] According to a first aspect of this disclosure, a silicon-carbon anode slurry is provided, comprising, by weight, 80-96 parts of silicon-based anode material, 0.5-5 parts of conductive carbon black, 0.5-5 parts of carbon nanotubes, 1-5 parts of dispersant, and 1-5 parts of composite binder.

[0008] The composite adhesive includes polyacrylic acid (PAA) and flexible rubber, wherein the flexible rubber is selected from at least one of hydrogenated nitrile butadiene rubber (HNBR) and styrene-butadiene rubber (SBR); the polyacrylic acid undergoes dehydration condensation to form a rigid covalent crosslinked network, and the flexible rubber physically penetrates the rigid covalent crosslinked network to form a semi-interpenetrating network.

[0009] Specifically, this disclosure breaks through the limitations of traditional single binders by using a PAA + flexible rubber (HNBR / SBR) composite binder. The PAA undergoes dehydration and condensation to form a rigid covalent cross-linked network, providing strong mechanical support for the silicon-carbon anode and suppressing the volume expansion of silicon particles during charging and discharging. The flexible rubber is embedded in the rigid network through a physical penetration method, forming a semi-interpenetrating network structure. This retains the structural stability of the rigid network while giving the electrode excellent deformation buffering ability, preventing electrode cracking and pulverization during charge-discharge cycles. Secondly, a two-component conductive agent of conductive carbon black and carbon nanotubes is used. The conductive carbon black provides point-contact conductive pathways, covering the surface of silicon-carbon particles. The carbon nanotubes, as long-range fibrous conductive frameworks, penetrate the interparticle gaps and work synergistically with the conductive carbon black to construct a multi-level conductive network, significantly reducing the internal resistance of the electrode and improving electron transport efficiency. The carbon nanotubes can be firmly anchored by the semi-interpenetrating binder network, maintaining the continuity of the conductive pathway even when the volume of silicon particles changes, thus solving the problem of easy breakage of the conductive network during silicon-carbon anode cycling. In addition, this disclosure strictly controls the mass fraction of each component, ensuring the loading of highly active materials while taking into account conductivity, adhesion and dispersion properties; the ratio of PAA to flexible rubber in the composite binder can be flexibly adjusted to achieve a precise balance between rigid support and flexible buffering, adapting to the expansion requirements of anode materials with different silicon contents; the dispersant is highly compatible with the carbon nanotube and binder system, ensuring uniform and stable slurry, avoiding agglomeration and improving coating processability.

[0010] In the aforementioned negative electrode slurry, PAA undergoes intermolecular dehydration condensation under heat treatment, forming a high-density covalently cross-linked rigid network. This network effectively binds silicon particles, limiting their volume expansion. Flexible rubber, in a linear or branched form, physically intersperses within the rigid network, without participating in covalent cross-linking. It binds to the rigid network only through physical entanglement. When silicon particles expand, it undergoes elastic deformation, absorbing stress and preventing the rigid network from breaking, thus maintaining the integrity of the electrode structure. Conductive carbon black is uniformly dispersed on the surface of silicon-carbon particles in the form of nanoparticles, forming a basic conductive layer. Carbon nanotubes, with their high aspect ratio, form penetrating fibrous conductive pathways inside the electrode, connecting conductive carbon black and silicon-carbon particles in different regions, constructing a point-line-surface multi-level conductive network. This significantly improves the electron transport rate inside the electrode and reduces polarization. The semi-interpenetrating binder network anchors the carbon nanotubes, preventing displacement and aggregation of carbon nanotubes during charge-discharge cycles, ensuring the long-term stability of the conductive network. The dispersant, through electrostatic repulsion and steric hindrance, ensures uniform dispersion of conductive carbon black, carbon nanotubes, and silicon-based anode materials in the aqueous system, preventing particle agglomeration. The semi-interpenetrating network structure of the composite binder forms a three-dimensional colloidal skeleton in the slurry, giving the slurry suitable viscosity and thixotropy, ensuring leveling during coating, preventing sedimentation of active materials, and improving the uniformity and consistency of electrode preparation.

[0011] Specifically, the total mass fraction of silicon-based anode material, conductive carbon black, carbon nanotubes, dispersant, and composite binder is 100 parts.

[0012] In one embodiment, the mass ratio of polyacrylic acid to flexible rubber in the composite adhesive is 0.2~0.8:0.8~0.2.

[0013] In one embodiment, the silicon-based anode material is a silicon-carbon (Si / C) composite anode material, which is a composite system of silicon and carbon materials; the carbon material is selected from at least one of graphite, amorphous carbon, and conductive carbon black.

[0014] Specifically, in the silicon-carbon composite anode material, the silicon content is 50% to 90%.

[0015] Specifically, the silicon source is selected from at least one of nano-silicon, porous silicon, and silicon nanowires.

[0016] In one embodiment, the carbon nanotubes are selected from at least one of single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), and double-walled carbon nanotubes (DWCNTs).

[0017] In a preferred embodiment, the carbon nanotubes are selected from single-walled carbon nanotubes.

[0018] In one embodiment, the dispersant is selected from at least one of sodium carboxymethyl cellulose (CMC), polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), sodium polyacrylate (PAAS), sodium carboxymethyl starch (CMS), and hydroxyethyl cellulose (HEC).

[0019] In a preferred embodiment, the dispersant is selected from sodium carboxymethyl cellulose, with a degree of polymerization n > 200.

[0020] In one embodiment, the silicon-carbon anode slurry further includes 100 to 300 parts of water.

[0021] According to a second aspect of this disclosure, a method for preparing the aforementioned silicon-carbon anode slurry is provided, comprising the following steps: S1: Carbon nanotubes are added to a dispersant solution and ultrasonically treated to obtain a carbon nanotube dispersion slurry; S2: Add polyacrylic acid to the carbon nanotube dispersion slurry described in step S1, mix and adjust the pH to 6-8 to obtain a mixed slurry; S3: Add flexible rubber to the mixed slurry described in step S2 to obtain a composite conductive adhesive slurry; S4: Mix the silicon-based anode material with conductive carbon black and add it to the composite conductive binder slurry described in step S3 to obtain the silicon-carbon anode slurry.

[0022] In one embodiment, step S1 first prepares the dispersant solution, including the following steps: adding the dispersant to the solvent and mixing at 200~500 rpm for 1~4 h to obtain the dispersant solution.

[0023] Specifically, the solvent is selected from water or a mixture of water and a hydrophilic organic solvent, wherein the mass percentage of water in the mixed solvent is ≥80%, and the hydrophilic organic solvent is selected from at least one of ethylene glycol, propylene glycol, and isopropanol.

[0024] In one embodiment, the ultrasonic treatment in step S1 has a power of 300~800W and a duration of 20~60min, and the ultrasonic treatment is intermittent ultrasonic treatment.

[0025] In one embodiment, the mixing speed in step S2 is 200~500 rpm and the time is 30~60 min.

[0026] In one embodiment, step S2 involves adjusting the pH to 6-8 using a dilute acid or a dilute alkali, wherein the dilute acid is selected from any one of 5-10 wt% acetic acid or 1-3 wt% dilute hydrochloric acid, and the dilute alkali is selected from any one of 5-10 wt% ammonia, 1-5 wt% sodium hydroxide, or 1-5 wt% potassium hydroxide.

[0027] In one embodiment, the mixing speed in step S3 is 200~500 rpm and the time is 30~90 min.

[0028] In one embodiment, in step S4, the silicon-based anode material is mixed with conductive carbon black for 10-30 minutes and then added to the composite conductive binder slurry described in step S3. The mixture is then mixed at 1000-2000 rpm for 60-120 minutes under vacuum to obtain the silicon-carbon anode slurry.

[0029] Specifically, in step S4, the silicon-based negative electrode material is mixed with conductive carbon black and then added to the composite conductive adhesive slurry described in step S3. A small amount of dispersant solution can be added to adjust the viscosity.

[0030] According to a third aspect of this disclosure, a silicon-carbon anode sheet is provided, which is obtained by coating, step drying and compaction of the above-mentioned silicon-carbon anode slurry; the step drying includes: baking at 80~100℃ for 2~4h, and then heat-treating at 130~170℃ for 0.5~2h.

[0031] Specifically, baking at 80~100℃ is to remove the solvent, and heat treatment at 130~170℃ is to trigger the dehydration condensation of polyacrylic acid to form a rigid covalent cross-linked network.

[0032] According to a fourth aspect of this disclosure, a lithium-ion battery is provided, comprising the aforementioned silicon-carbon negative electrode sheet.

[0033] According to one possible implementation of this disclosure, at least the following beneficial effects are achieved: 1. This disclosure employs a composite binder composed of PAA and HNBR / SBR. After heat treatment, a semi-interpenetrating network structure is formed, with a rigid covalent cross-linked PAA network as the macroscopic framework and flexible rubber physically penetrating within it. This achieves a balance of rigidity and flexibility in mechanical properties: the rigid PAA network effectively resists macroscopic deformation caused by the volume expansion of silicon particles, preventing electrode cracking; the flexible rubber can efficiently stretch and buffer the microscopic mechanical stress generated during silicon-lithium alloying, avoiding brittle fracture of the binder network. This structure can firmly bind the active particles, conductive agent, and current collector, effectively inhibiting active material shedding and electrode pulverization, and significantly improving the long-term cycle stability of the silicon-carbon anode. Furthermore, the point contact of conductive carbon black and the long-range fiber conductivity of carbon nanotubes form a synergy, and the carbon nanotubes are firmly fixed in the semi-interpenetrating binder network. During charging and discharging, they deform with the network without breaking, maintaining the continuity and integrity of the conductive path like an elastic steel bar, solving the problem of traditional conductive networks easily collapsing with electrode expansion. Meanwhile, the composite binder system avoids the problems of excessive electrode rigidity and obstructed ion / electron transport caused by high proportions of binders. After optimization, it significantly reduces the internal resistance of the electrode, ensuring that all active materials maintain efficient electrical contact at all times, laying the foundation for improving the rate performance of the battery. Moreover, the conductive agent is a combination of conductive carbon black and carbon nanotubes with a controllable total proportion. The carbon nanotubes can be SWCNT, MWCNT, DWCNT, or their blends. High-flexibility SWCNT or low-cost MWCNT can be selected according to performance requirements. The mass ratio of PAA to flexible rubber in the composite binder can be adjusted within the range of 0.2~0.8:0.8~0.2. The flexible rubber can be HNBR / SBR alone or a blend of the two, achieving flexible adaptation for performance-first or cost-first needs. While ensuring core performance, it provides more options for cost control in industrial production.

[0034] 2. This disclosure utilizes a specific preparation process. First, carbon nanotubes are dispersed with a dispersant to ensure nanoscale, agglomerated dispersion. Then, PAA is introduced and the pH is adjusted to a neutral range of 6-8 before adding flexible rubber. This effectively optimizes the dispersion uniformity of each component and avoids interfacial defects caused by nanomaterial agglomeration. Simultaneously, the uniform and dense electrode coating promotes the formation of a stable solid electrolyte interphase (SEI) film, reducing side reactions between the electrolyte and active materials and lowering irreversible lithium-ion consumption. The silicon-carbon anode slurry prepared by this disclosure exhibits stable initial coulombic efficiency, achieving high capacity while maintaining excellent initial electrochemical efficiency, thus improving the actual energy density of the battery.

[0035] 3. The preparation process disclosed herein achieves uniform dispersion of silicon-based anode materials, conductive agents, binders, and other components in an aqueous solution through precise control of the feeding sequence, dispersion parameters, and stirring process. The prepared silicon-carbon anode slurry is free of particles and bubbles, has uniform viscosity, and does not settle after standing. At the same time, the equipment used in the process is conventional equipment used in lithium-ion battery production. The operation steps are clear, the parameters are controllable, no additional special equipment is required, and the ratio range of each raw material is wide. The core parameters have clear optimal ranges, the process has good reproducibility, is easy to scale up for mass production, and is suitable for the actual needs of industrial production.

[0036] 4. The silicon-carbon anode sheet prepared from the silicon-carbon anode slurry of this disclosure has the characteristics of low expansion, low internal resistance, high cycle retention rate and high first-time efficiency. When applied to lithium-ion batteries, it can effectively improve the energy density, cycle life and rate performance of the battery, solve the problem of low theoretical specific capacity of traditional graphite anodes, and overcome the core technical obstacles to the commercial application of silicon-carbon anodes. It provides key technical support for the widespread application of high-energy-density lithium-ion batteries in new energy vehicles, energy storage equipment, portable electronic devices and other fields, and has significant industrial application value and market prospects.

[0037] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0038] The above and other objects, features, and advantages of this disclosure will become readily apparent from the following detailed description of exemplary embodiments, taken in conjunction with the accompanying drawings. Several embodiments of this disclosure are illustrated in the drawings by way of example and not limitation, in which: In the accompanying drawings, the same or corresponding reference numerals indicate the same or corresponding parts.

[0039] Figure 1 The diagram shows a comparison of the long-cycle performance of the silicon-carbon anode materials of Comparative Examples 1, 2, 5 and 2 of this disclosure at a rate of 0.5C. Figure 2 The diagram shows a comparison of the long-cycle performance of the silicon-carbon anode materials of Comparative Examples 3, 4 and 2 of this disclosure at a rate of 0.5C. Figure 3 The diagram shows a comparison of the long-cycle performance of the silicon-carbon anode materials of Examples 2, 5, and 6 of this disclosure at a rate of 0.5C. Figure 4SEM images of the silicon-carbon anode plates of Comparative Example 1 and Example 2 of this disclosure are shown; wherein, a is a surface SEM image of the electrode plate of Comparative Example 1 after 300 cycles, b is a surface SEM image of the electrode plate of Example 2 after 300 cycles, c is a cross-sectional SEM image of the electrode plate of Example 2 before 300 cycles, and d is a cross-sectional SEM image of the electrode plate of Example 2 after 300 cycles. Detailed Implementation

[0040] To make the objectives, features, and advantages of this disclosure more apparent and understandable, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0041] Example 1 This embodiment prepares a silicon-carbon anode slurry, a corresponding anode sheet, and a lithium-ion battery, as detailed below: The formulation of silicon-carbon anode slurry is: Si / C: Super P: SWCNT: CMC: SBR: PAA = 94: 3.5: 0.5: 1: 0.5: 0.5.

[0042] (1) Slowly add CMC powder to deionized water and mechanically stir at 300 rpm for 2 hours at room temperature until a completely dissolved, homogeneous, and transparent CMC aqueous solution is formed. Slowly add SWCNT powder to the CMC aqueous solution and use a probe-type ultrasonic cell disruptor to perform intermittent ultrasonic treatment under ice-water bath cooling conditions. The ultrasonic treatment lasts for 2 seconds, followed by a 1-second pause. The ultrasonic power is 500W, and the total treatment time is 40 minutes until a homogeneous, black, and stable SWCNT dispersion slurry without visible particles is formed.

[0043] (2) Add the PAA aqueous solution to the SWCNT dispersion slurry obtained in step (1) while stirring at 300 rpm, and continue stirring for 45 min to make it evenly mixed. Then, adjust the pH of the mixture to a neutral range of 6-8 using 2 wt% dilute hydrochloric acid or 3 wt% sodium hydroxide to obtain the mixed slurry.

[0044] (3) While stirring at 300 rpm, the SBR emulsion diluted with deionized water was slowly added dropwise to the mixed slurry obtained in step (2). After the addition was completed, stirring was continued at 300 rpm for 60 min to obtain a composite conductive adhesive slurry with consistent flowability.

[0045] (4) Place Si / C (a composite material of graphite and nano-silicon with a silicon content of 60%) and Super P (conductive carbon black) in a mixing container according to the designed mass ratio, and perform physical premixing using a dry powder mixer for 20 minutes to ensure that the powder is macroscopically uniformly mixed to obtain a premix. Add the premix to the composite conductive bonding slurry obtained in step (3), add deionized water, and use a planetary mixer to stir at a speed of 1500 rpm for 80 minutes in a vacuum environment until a silicon-carbon anode slurry with uniform viscosity, no bubbles, and no particles is obtained.

[0046] (5) The silicon-carbon negative electrode slurry obtained in step (4) is uniformly coated onto the copper foil current collector by a doctor blade coating method, and then subjected to step drying: firstly, it is baked at 90°C for 3 hours to remove the solvent, and then heat-treated at 150°C for 1 hour to promote the dehydration condensation crosslinking reaction of the PAA component. The dried electrode sheet is compacted by a roller press and then cut into the required size to obtain the silicon-carbon negative electrode sheet.

[0047] (6) In a glove box filled with argon, the silicon-carbon negative electrode obtained in step (5) is used as the working electrode and the lithium metal sheet is used as the counter / reference electrode to assemble a CR2025 coin cell.

[0048] Example 2 In this embodiment, a silicon-carbon anode slurry and the corresponding anode sheet and lithium-ion battery were prepared. The formulation of the silicon-carbon anode slurry is: Si / C: Super P: SWCNT: CMC: HNBR: PAA = 94: 3.5: 0.5: 1: 0.5: 0.5.

[0049] In this embodiment, the SBR in embodiment 1 is replaced with HNBR in step (3), and the remaining steps are the same as in embodiment 1, which will not be repeated here.

[0050] Example 3 In this embodiment, a silicon-carbon anode slurry and the corresponding anode sheet and lithium-ion battery were prepared. The formulation of the silicon-carbon anode slurry is: Si / C: Super P: SWCNT: CMC: HNBR: PAA = 94: 3.5: 0.5: 1: 0.8: 0.2.

[0051] In this embodiment, the SBR in embodiment 1 is replaced with HNBR in step (3), and the remaining steps are the same as in embodiment 1, which will not be repeated here.

[0052] Example 4 In this embodiment, a silicon-carbon anode slurry and the corresponding anode sheet and lithium-ion battery were prepared. The formulation of the silicon-carbon anode slurry is: Si / C: Super P: SWCNT: CMC: HNBR: PAA = 94: 3.5: 0.5: 1: 0.2: 0.8.

[0053] In this embodiment, the SBR in embodiment 1 is replaced with HNBR in step (3), and the remaining steps are the same as in embodiment 1, which will not be repeated here.

[0054] Example 5 In this embodiment, a silicon-carbon anode slurry and the corresponding anode sheet and lithium-ion battery were prepared. The formulation of the silicon-carbon anode slurry is: Si / C: Super P: SWCNT: CMC: HNBR: PAA = 94: 3.5: 0.5: 1: 0.5: 0.5.

[0055] In this embodiment, HNBR is used to replace SBR in Example 1 in step (3), and the heat treatment temperature in step (5) is 130°C. The remaining steps are the same as in Example 1, and will not be repeated here.

[0056] Example 6 In this embodiment, a silicon-carbon anode slurry and the corresponding anode sheet and lithium-ion battery were prepared. The formulation of the silicon-carbon anode slurry is: Si / C: Super P: SWCNT: CMC: HNBR: PAA = 94: 3.5: 0.5: 1: 0.5: 0.5.

[0057] In this embodiment, HNBR is used to replace SBR in Example 1 in step (3), and the heat treatment temperature in step (5) is 170°C. The remaining steps are the same as in Example 1, and will not be repeated here.

[0058] Comparative Example 1 This comparative example prepared a silicon-carbon anode slurry and the corresponding anode sheet and lithium-ion battery. The formulation of the silicon-carbon anode slurry is: Si / C: Super P: SWCNT: CMC: SBR = 94: 3.5: 0.5: 1: 1.

[0059] Unlike Example 1, this comparative example did not introduce PAA and adjust the pH, but instead directly added SBR emulsion (i.e., no step (2)); and there was no heat treatment step in step (5), only baking at 90°C for 3 hours to remove the solvent, and then compacting and cutting to obtain the silicon-carbon negative electrode sheet. The remaining steps are the same as in Example 1, and will not be repeated here.

[0060] Comparative Example 2 This comparative example prepared a silicon-carbon anode slurry and the corresponding anode sheet and lithium-ion battery. The formulation of the silicon-carbon anode slurry is: Si / C: Super P: SWCNT: CMC: PAA = 94: 3.5: 0.5: 1: 1.

[0061] Unlike Example 1, this comparative example did not introduce SBR emulsion, but instead directly added PAA and adjusted the pH (i.e., step (3) was omitted). The remaining steps were the same as in Example 1, and will not be repeated here.

[0062] Comparative Example 3 This comparative example prepared a silicon-carbon anode slurry and the corresponding anode sheet and lithium-ion battery. The formulation of the silicon-carbon anode slurry is: Si / C: Super P: SWCNT: CMC: HNBR: PAA = 94: 3.5: 0.5: 1: 0.5: 0.5.

[0063] Unlike Example 1, in this comparative example, HNBR is used instead of SBR in Example 1; and the order of introducing PAA and adjusting pH (step (2)) and introducing HNBR emulsion (step (3)) is reversed, that is, HNBR emulsion is introduced first, followed by PAA and pH adjustment. The remaining steps are the same as in Example 1, and will not be repeated here.

[0064] Comparative Example 4 This comparative example prepared a silicon-carbon anode slurry and the corresponding anode sheet and lithium-ion battery. The formulation of the silicon-carbon anode slurry is: Si / C: Super P: SWCNT: CMC: HNBR: PAA = 94: 3.5: 0.5: 1: 0.5: 0.5.

[0065] Unlike Example 1, this comparative example uses HNBR instead of SBR; and no pH adjustment was performed after adding PAA. The remaining steps are the same as in Example 1, and will not be repeated here.

[0066] Comparative Example 5 This comparative example prepared a silicon-carbon anode slurry and the corresponding anode sheet and lithium-ion battery. The formulation of the silicon-carbon anode slurry is: Si / C: Super P: SWCNT: CMC: HNBR: PAA = 94: 3.5: 0.5: 1: 0.5: 0.5.

[0067] Unlike Example 1, this comparative example uses HNBR instead of SBR in Example 1; and there is no heat treatment step in step (5), but instead the sample is directly baked at 90°C for 3 hours to remove the solvent, and then compacted and cut to obtain a silicon-carbon negative electrode sheet. The remaining steps are the same as in Example 1, and will not be repeated here.

[0068] Comparative Example 6 This comparative example prepared a silicon-carbon anode slurry and the corresponding anode sheet and lithium-ion battery. The formulation of the silicon-carbon anode slurry is: Si / C: Super P: SWCNT: CMC: HNBR = 94: 3.5: 0.5: 1: 1.

[0069] Unlike Example 1, this comparative example uses HNBR instead of SBR in Example 1; and PAA is not introduced and pH is not adjusted (i.e., step (2) is omitted); there is no heat treatment step in step (5), but instead the sample is directly baked at 90°C for 3 hours to remove the solvent, and then compacted and cut to obtain the silicon-carbon negative electrode sheet. The remaining steps are the same as in Example 1, and will not be repeated here.

[0070] Test case 1. Electrochemical performance tests, such as constant current charge-discharge, were performed on the coin cells of the examples and comparative examples using a battery testing system. The results are shown in Table 1.

[0071] Table 1

[0072] Table 1 shows that the initial discharge capacity of all tested samples ranged from 1911.90 to 1980.41 mAh / g, the initial charge capacity ranged from 1788.01 to 1848.71 mAh / g, and the initial efficiency remained stable at 93.00% to 93.62%, with minimal overall difference. This indicates that the optimization methods disclosed in this paper, such as formulation design, preparation process, and heat treatment, improved other performance characteristics of the anode without sacrificing the high specific capacity of the carbon anode, and maintained a stable initial coulombic efficiency, effectively ensuring the actual energy density of the battery and avoiding a significant increase in irreversible lithium-ion consumption.

[0073] Regarding cycle retention, Comparative Example 1 (SBR only), Comparative Example 2 (PAA only), and Comparative Example 6 (HNBR only) had cycle retention rates of 5.15%, 2.57%, and 3.60%, respectively, almost completely losing capacity. This demonstrates that a single binder cannot solve the structural collapse problem caused by the volume expansion of silicon-carbon anodes, and neither rigidity nor flexibility alone can meet the cycling requirements of silicon-carbon anodes. Comparative Example 3 (reversed feeding order), Comparative Example 4 (unadjusted pH), and Comparative Example 5 (no heat treatment), although using PAA+HNBR composite binder, had cycle retention rates of only 18.50%~45.30%, far lower than those of Examples 2, 5, and 6. This proves that the performance of composite binders depends on precise preparation processes; feeding order, pH adjustment, and stepped heat treatment are necessary conditions for achieving a semi-interpenetrating network structure. Example 1 (PAA+SBR) had a cycle retention rate of only 25.48%, and Example 2 (same proportion P) The AA+HNBR ratio directly increased to 79.72%, proving that HNBR, as a flexible rubber component, forms a semi-interpenetrating network with PAA, which significantly outperforms SBR in terms of stress buffering and structural stability. In Examples 2 (PAA:HNBR=0.5:0.5), 3 (PAA:HNBR=0.2:0.8), and 4 (PAA:HNBR=0.8:0.2), the cycle retention rate was optimal when the ratios were equal. Excessive flexibility or rigidity would lead to a decrease in cycle retention rate, proving that the balance between rigidity and flexibility is the core design principle of composite adhesives. The cycle retention rates of Examples 2 (heat treatment temperature 150℃), 5 (heat treatment temperature 130℃), and 6 (heat treatment temperature 170℃) were all above 56.80%, with 150℃ being the optimal temperature. Good cycle stability could be achieved in the 130~170℃ range, providing flexible space for parameter adjustment in industrial production.

[0074] Regarding electrode sheet resistance, in the single binder system, the flexible binder (Comparative Example 1 / 6) has a low sheet resistance but extremely poor cycle retention; the rigid binder (Comparative Example 2) has a sheet resistance as high as 158.6 Ω / □, hindering electron transport; in the composite binder system, the sheet resistance of Comparative Examples 3 / 4 / 5 is 125.6~145.0 Ω / □, higher than that of Examples 2 / 5 / 6, proving that the process disclosed in this paper can achieve the anchoring and bonding of the conductive carbon black + carbon nanotube multi-level conductive network with the semi-interpenetrating binder network, avoiding conductive agent displacement / agglomeration during cycling, maintaining the continuity of the conductive path, and thus reducing electrode sheet resistance. In the PAA to HNBR ratio, Example 4 (0.8:0.2), with slightly higher rigidity, has the lowest sheet resistance (96.3 Ω / □), but the cycle retention rate decreases, indicating that increasing the rigidity of the binder can reduce the sheet resistance to a certain extent, but a balance between rigidity and flexibility is required.

[0075] Regarding electrode expansion rate, Comparative Example 1 (SBR only) showed an expansion rate as high as 42.39%, nearly three times that of Example 2, demonstrating that the rigid covalent cross-linked network formed by PAA can effectively bind silicon particles and limit volume expansion. The expansion rate of Comparative Example 5 was 35.40%, much higher than the 14.87% of Example 2, proving that stepped heat treatment is the key to the formation of a rigid cross-linked network in PAA, and volume expansion suppression cannot be achieved without heat treatment. The expansion rate of the PAA+HNBR system was much lower than that of the PAA+SBR system (33.12% in Example 1 vs. 14.87% in Example 2), further verifying the excellent performance of HNBR in structural stability.

[0076] Regarding the electrode swelling rate, Comparative Example 1 showed the highest swelling rate, indicating that the composite binder system can reduce side reactions between the electrode and the electrolyte, forming a more stable solid electrolyte interphase (SEI) film. In all examples of the PAA+HNBR composite system, the swelling rate was less than 5%, proving that HNBR has better electrolyte resistance than SBR, and that the semi-interpenetrating network structure can effectively block electrolyte intrusion and reduce electrode swelling.

[0077] In addition, the performance of the silicon-carbon anode materials of Comparative Examples 1, 2, 5, and 2 in long-cycle testing (0-300 cycles) at 0.5C rate was compared, and the results are as follows: Figure 1 As shown. Figure 1 The results show that the first-cycle specific capacity of Example 2 is at the highest level, indicating that the formulation of Example 2 can effectively suppress the capacity decay caused by the volume expansion of silicon particles, and the cycle stability is far superior to other comparative samples; Comparative Example 1 / 2 proves that a single binder system cannot solve the problem of silicon anode pulverization; Comparative Example 5 proves that the lack of conductive network or binder structure will lead to a sharp drop in capacity in the later stage.

[0078] The performance of the silicon-carbon anode materials of Comparative Examples 3, 4, and 2 was compared during long-cycle testing (0-300 cycles) at 0.5C rate. The results are as follows: Figure 2 As shown. Figure 2 The results show that Example 2 has the highest specific capacity in the first cycle, indicating that the synergistic structure of the semi-interpenetrating binder network and carbon nanotube conductive network in Example 2 can effectively suppress silicon volume expansion, maintain the integrity of the electrode structure, and has a cycle stability far superior to the comparative examples. Comparative examples 3 and 4 respectively demonstrate that when the binder system is single or lacks key synergistic structures, it cannot effectively buffer mechanical stress and maintain the conductive path, resulting in rapid capacity decay.

[0079] The performance of the silicon-carbon anode materials in Examples 2, 5, and 6 under long-cycle conditions (0-300 cycles) at 0.5C rate was compared, and the results are as follows: Figure 3 As shown. Figure 3The results show that all three embodiments exhibit significantly better cycle performance than conventional silicon-carbon anodes, confirming the technical effectiveness of this disclosure in solving the silicon anode pulverization problem through the synergistic design of composite binders and conductive agents.

[0080] 2. The microstructure of the silicon-carbon anode sheets in Comparative Example 1 and Example 2 was tested, and the results are as follows: Figure 4 As shown. Figure 4 The results show that after 300 cycles, the electrode of Comparative Example 1 exhibited severe breakage and agglomerate detachment. Silicon particles underwent significant volume expansion and then fractured, with irregular cracks appearing at the particle edges. Numerous fine particles detached and scattered from the main structure. The overall surface roughness was uneven, and continuity was disrupted, resulting in a fragmented distribution. This corresponds to the core reason for the low cycle retention rate of Comparative Example 1 (5.15%) in Table 1: the mechanical stress caused by silicon particle expansion cannot be buffered by a single binder system, leading to electrode layer instability, eventual pulverization and detachment, and rapid capacity decay. In contrast, after 300 cycles, the electrode of Example 2 maintained a continuous and dense surface. Although the silicon particles showed some morphological changes, there was no significant breakage or detachment. The particles remained tightly bonded by the binder. The surface showed no obvious pores or cracks, and the overall structural integrity was significantly better than that of Comparative Example 1. This feature confirms the role of the PAA+HNBR composite binder: the rigid PAA network confines the volume expansion of silicon particles, while the flexible HNBR network buffers cyclic stress. Together, they maintain the structural stability of the electrode surface, prevent pulverization and detachment, and support a high cycle retention rate of 79.72%.

[0081] As can be seen from the cross-sectional diagram of the electrode in Example 2, before 300 cycles, the electrode cross-section exhibits a uniform layered structure with an active material layer thickness of 6.11 μm. The active material layer is clearly bonded to the current collector interface without any obvious gaps, and the active material particles are densely packed. The conductive network and binder network are seamlessly connected, providing a stable pathway for ion / electron transport. After 300 cycles, the electrode cross-section structure shrinks but does not peel off. The thickness is reasonably controlled, with the active material layer thickness at 6.70 μm. Compared to the 6.11 μm before cycling, there is only a slight increase (the silicon-carbon anode undergoes an alternating process of volume expansion and contraction during cycling; this slight increase is consistent with the volume change characteristics of lithium insertion / extraction in silicon particles). Furthermore, the active material layer and the current collector interface remain tightly bonded, without delamination, peeling, or cracking. The reasonable thickness change of the electrode in Example 2 after cycling indicates that there was neither excessive expansion leading to electrode bulging nor irregular shrinkage, which is suitable for the stress release caused by volume changes during silicon-carbon anode cycling; the absence of interface peeling proves that the adhesive system has extremely strong adhesion to the current collector and active material, and no interface failure occurred during cycling, ensuring the stability of the electrode during long-term operation.

[0082] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this disclosure can be achieved, and this is not limited herein.

[0083] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means two or more, unless otherwise explicitly specified.

[0084] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A silicon-carbon anode slurry, characterized in that, The silicon-carbon anode slurry comprises, by weight, 80-96 parts silicon-based anode material, 0.5-5 parts conductive carbon black, 0.5-5 parts carbon nanotubes, 1-5 parts dispersant, and 1-5 parts composite binder. The composite adhesive includes polyacrylic acid and flexible rubber, wherein the flexible rubber is selected from at least one of hydrogenated nitrile rubber and styrene-butadiene rubber; the polyacrylic acid undergoes dehydration condensation to form a rigid covalent crosslinked network, and the flexible rubber physically penetrates the rigid covalent crosslinked network to form a semi-interpenetrating network.

2. The silicon-carbon anode slurry according to claim 1, characterized in that, In the composite adhesive, the mass ratio of polyacrylic acid to flexible rubber is 0.2~0.8:0.8~0.

2.

3. The silicon-carbon anode slurry according to claim 1, characterized in that, In the silicon-carbon anode slurry, the carbon nanotubes are selected from at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and double-walled carbon nanotubes. The dispersant is selected from at least one of sodium carboxymethyl cellulose, polyethylene glycol, polyvinylpyrrolidone, sodium polyacrylate, sodium carboxymethyl starch, and hydroxyethyl cellulose.

4. The method for preparing the silicon-carbon anode slurry according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Carbon nanotubes are added to a dispersant solution and ultrasonically treated to obtain a carbon nanotube dispersion slurry; S2: Add polyacrylic acid to the carbon nanotube dispersion slurry described in step S1, mix and adjust the pH to 6-8 to obtain a mixed slurry; S3: Add flexible rubber to the mixed slurry described in step S2 to obtain a composite conductive adhesive slurry; S4: Mix the silicon-based anode material with conductive carbon black and add it to the composite conductive binder slurry described in step S3 to obtain the silicon-carbon anode slurry.

5. The preparation method according to claim 4, characterized in that, Step S1 involves preparing the dispersant solution, including the following steps: adding the dispersant to the solvent and mixing at 200-500 rpm for 1-4 hours to obtain the dispersant solution; The ultrasonic treatment in step S1 has a power of 300~800W and a duration of 20~60min, and the ultrasonic treatment is intermittent ultrasonic treatment.

6. The preparation method according to claim 4, characterized in that, In step S2, the mixing speed is 200~500 rpm and the time is 30~60 min; The pH is adjusted to 6-8 using a dilute acid or dilute alkali, wherein the dilute acid is selected from any one of 5-10 wt% acetic acid or 1-3 wt% dilute hydrochloric acid, and the dilute alkali is selected from any one of 5-10 wt% ammonia, 1-5 wt% sodium hydroxide, or 1-5 wt% potassium hydroxide.

7. The preparation method according to claim 4, characterized in that, The mixing speed in step S3 is 200~500 rpm, and the time is 30~90 min.

8. The preparation method according to claim 4, characterized in that, In step S4, the silicon-based anode material is mixed with conductive carbon black for 10-30 minutes and then added to the composite conductive binder slurry described in step S3. The mixture is then mixed at 1000-2000 rpm for 60-120 minutes under vacuum to obtain the silicon-carbon anode slurry.

9. A silicon-carbon negative electrode sheet, characterized in that, The silicon-carbon anode sheet is prepared by coating, step drying and compaction of the silicon-carbon anode slurry according to any one of claims 1 to 3; the step drying includes: baking at 80 to 100°C for 2 to 4 hours, and then heat-treating at 130 to 170°C for 0.5 to 2 hours.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the silicon-carbon negative electrode sheet as described in claim 9.

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