Bismuth-containing coated silicon-carbon negative electrode material and preparation method and application thereof

Abstract

The invention provides a bismuth-containing coated silicon-carbon negative electrode material and a preparation method and application thereof, and relates to the technical field of lithium ion battery negative electrode materials, the negative electrode material comprises a silicon-carbon material and a bismuth-containing material coating the silicon-carbon material, the bismuth-containing material includes a first coating layer composed of a bismuth compound and a second coating layer composed of a conductive agent. The preparation method of the negative electrode material comprises the following steps: providing a silicon-carbon negative electrode material; providing a bismuth compound powder; the preparation method comprises the following steps: mixing bismuth compound powder, a silicon-carbon negative electrode material and a binder in a dispersant solution, and carrying out spray drying and curing to form a bismuth compound first coating layer; and then mixing the materials with conductive agent slurry and a binder, and performing spray drying and curing again to form a second coating layer of the conductive agent. By adopting the technical scheme, the advantage that the full-electric voltage platform of the bismuth oxide is about 3.0-3.5 V is utilized, so that the problem that the impedance is sharply increased under low SOC (State of Charge) caused by over-high silicon content in the silicon-carbon negative electrode is solved.

Description

Technical Field

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

[0002] With the rapid development of the new energy industry, the demand for portable, fast-charging, and safe and efficient energy storage devices is gradually increasing. Lithium-ion batteries, with their advantages of fast charging speed, high energy density, long cycle life, and good safety, have been widely used in consumer electronics, electric vehicles, and energy storage systems. Currently, commercial lithium-ion batteries mainly use graphite as the anode material, but its theoretical capacity is only 372 mAh / g, which is close to its theoretical limit, making it difficult to further improve energy density. At the same time, graphite is prone to lithium plating during fast charging, posing a safety hazard. Therefore, developing high-capacity, high-safety alternative anode materials has become a research hotspot in the industry.

[0003] Silicon, as a new generation of high-capacity anode material, boasts a theoretical capacity of up to 4200 mAh / g, approximately 10 times that of graphite, and is considered a highly promising candidate for lithium-ion battery anodes. However, silicon experiences volume expansion of up to approximately 400% during lithium insertion / extraction, leading to material structure pulverization, interface cracking, and severe degradation of cycle performance, thus limiting its commercial application. To mitigate the volume expansion effect of silicon during charge and discharge, the industry has successively developed several generations of silicon-oxygen (SiO2) compounds. X Anode materials. First-generation silicon-oxygen anodes effectively reduced volume expansion and improved structural stability by combining silicon suboxide with graphite. However, the generation of a large amount of irreversible products such as Li₂O during charge and discharge resulted in an initial coulombic efficiency of only about 70%. Second-generation pre-magnesium silicon-oxygen anodes introduced magnesium during preparation to suppress excessive SEI film formation, thereby increasing the initial efficiency to approximately 80%. Third-generation pre-lithiation silicon-oxygen anodes further improved material interface stability through pre-lithiation treatment, increasing the initial efficiency to approximately 85%, while also significantly improving cycle performance and conductivity. However, the aforementioned pre-magnesiation and pre-lithiation processes are complex and costly, increasing the price of the finished product by approximately 100,000 to 200,000 yuan / ton, making large-scale production difficult. Furthermore, significant variations in grain size lead to decreased cycle performance, still presenting significant application limitations. Moreover, the intrinsic electrochemical characteristics of silicon-based materials in actual full-cell systems continue to pose challenges. When silicon or silicon-carbon composite materials are mixed with graphite and used as a negative electrode, its average plateau voltage for full-electric operation is about 3.5V. When paired with ternary positive electrode materials, the operating window is limited to about 2.8~4.25V. In the completely delithiated state, it returns to a state close to silicon, exhibiting a semiconductor / insulator state, which leads to a significant increase in impedance at low SOC.

[0004] In recent years, the preparation of silicon-carbon anode materials by embedding nano-silicon within a porous carbon framework using porous carbon structures and CVD (chemical vapor deposition) technology has become a mainstream approach. These materials can achieve capacities of approximately 2000 mAh / g and a first-cycle coulombic efficiency of approximately 94%, significantly outperforming graphite anodes. The embedded porous structure effectively mitigates volume expansion, reducing the system expansion rate to approximately 80%. However, with increasing silicon doping ratios, problems such as insufficient conductivity, increased structural stress, and poor interfacial bonding in silicon-carbon anodes become increasingly apparent. Furthermore, the complex design and high cost of porous structures and CVD processes hinder stable large-scale applications.

[0005] Therefore, there is an urgent need in this field for a new technical solution that can effectively address the problem of the sharp increase in impedance of silicon-carbon anode materials under deep delithiation (low SOC) while maintaining high capacity, and simultaneously solve the problems of volume expansion, poor conductivity, and high manufacturing cost of silicon-based anode materials, so as to promote their widespread application in high-performance power batteries and consumer batteries. In view of this, the present invention is proposed. Summary of the Invention

[0006] One objective of this invention is to provide a bismuth-coated silicon-carbon anode material to address the problems of rapidly increasing impedance, high volume expansion, and poor conductivity and rate performance of existing silicon-carbon anode materials at low state of charge (SOC). It features a three-layer structure: a silicon-carbon material, a bismuth compound layer, and a conductive agent layer. The bismuth compound layer functions as an active material, provides ion conduction, and acts as a buffer. The outer conductive agent layer constructs an electronic conductivity network and immobilizes the bismuth compound. The two layers work synergistically to give the material high capacity, low expansion, high safety, and excellent rate performance.

[0007] The second objective of this invention is to provide a method for preparing a bismuth-coated silicon-carbon anode material. This method introduces a bismuth compound with high oxygen ion conductivity as a functional coating layer, which contributes to the capacity by utilizing its high theoretical capacity and improves safety by using a high delithiation potential. At the same time, the bismuth compound layer buffers the volume expansion of the silicon-carbon core, promotes lithium-ion transport, and synergistically improves the cycle stability and rate performance of the material.

[0008] The third objective of this invention is to provide a negative electrode that uses the bismuth-coated silicon-carbon negative electrode material as the active material, which has high energy density, excellent structural stability and fast charging capability.

[0009] The fourth objective of this invention is to provide a battery comprising the aforementioned negative electrode, which can achieve high energy density, long cycle life, high safety and excellent fast charging performance, and is suitable for high-end consumer electronics and power battery fields.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: The first aspect of the present invention provides a bismuth-coated silicon-carbon anode material, comprising a silicon-carbon material and a bismuth-containing material coating the silicon-carbon material, wherein the bismuth-containing material comprises a first coating layer composed of a bismuth compound and a second coating layer composed of a conductive agent.

[0011] Furthermore, the bismuth compounds include, but are not limited to, bismuth oxide, bismuth titanate, bismuth silicate, bismuth aluminate, bismuth chloride, and bismuth nitrate.

[0012] Furthermore, the silicon content in the silicon-carbon anode material is 5% to 90% by mass, preferably 30% to 70%; And / or, the specific surface area of ​​the silicon-carbon anode material is 0.5 m². 2 / g ~ 10 m 2 / g; And / or, the bismuth content in the silicon-carbon anode material is 0.9% to 27% by mass, preferably 2% to 10%.

[0013] The second aspect of this invention provides a method for preparing the bismuth-coated silicon-carbon anode material described in the first aspect, comprising the following steps: Step S1: Provide a silicon-carbon anode material, which is obtained by depositing silane in porous carbon and then coating it with carbon. Step S2: Provide bismuth compound powder; Step S3: The bismuth compound powder, the silicon-carbon anode material, and the first binder are added to a solution containing a dispersant and stirred to form a first slurry. Then, a first spray drying and a first curing treatment are performed to obtain a bismuth compound modified silicon-carbon anode material. Step S4: The obtained bismuth compound modified silicon-carbon anode material, conductive agent slurry, and second binder are mixed and stirred in deionized water to form a second slurry. Then, a second spray drying and a second curing treatment are performed to obtain a silicon-carbon anode material with a double layer of conductive agent and bismuth compound coating.

[0014] Further, in step S2, the bismuth compound powder has a particle morphology of spherical, ellipsoidal, or irregular block; and / or, the particle size of the bismuth compound powder is 2 nm to 10 μm, preferably 20 nm to 300 nm; and / or, the dispersant is selected from one or more of polyethylene glycol, paraffin wax, Span-80, Tween-80, polyvinyl alcohol 1788, polyvinyl alcohol 1799, polyvinyl alcohol 2499, sodium dodecyl sulfate, and hexadecyltrimethylammonium bromide; and / or, the concentration of the dispersant in the solution is 0.02% to 5%, preferably 0.03% to 0.08%.

[0015] Further, the first binder and / or the second binder are selected from one or more of polyimide, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, styrene-butadiene rubber, polyethylene oxide, and sodium carboxymethyl cellulose; and / or, the conductive agent is selected from one or more of carbon black, conductive graphite, vapor-grown carbon fiber, carbon nanotubes, graphene, acetylene black, SuperP, superconducting carbon black, graphite microcrystals, single-walled carbon nanotubes, multi-walled carbon nanotubes, and activated carbon fibers.

[0016] Further, the solid content of the conductive agent slurry is 2 wt% to 15 wt%, preferably 4 wt% to 10 wt%; and / or, when the conductive agent is graphene, the number of its layers is 3 to 15, preferably 3 to 5; and / or, the Dv50 particle size distribution of the conductive agent is 1 μm to 15 μm, preferably 2 μm to 13 μm.

[0017] Further, in step S3, the stirring time is 1 to 12 hours, preferably 4 to 6 hours; and / or, the solid content of the first slurry is 5% to 40%, preferably 15% to 25%; and / or, the first curing temperature is 100℃ to 400℃, preferably 200℃ to 300℃, and the curing time is 1 to 12 hours, preferably 3 to 6 hours; In step S4, the stirring time is 1 to 24 hours, preferably 4 to 6 hours; and / or, the solid content of the second slurry is 5% to 40%, preferably 15% to 25%; and / or, the second curing temperature is 100℃ to 400℃, preferably 200℃ to 300℃, and the curing time is 1 to 12 hours, preferably 3 to 6 hours.

[0018] A third aspect of the present invention provides a negative electrode, wherein the negative electrode active material comprises the bismuth-coated silicon-carbon negative electrode material described in the first aspect and the bismuth-coated silicon-carbon negative electrode material obtained by any of the preparation methods in the second aspect.

[0019] A fourth aspect of the present invention provides a battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises a negative electrode active material, and the negative electrode active material comprises the bismuth-coated silicon-carbon negative electrode material described in the first aspect and the bismuth-coated silicon-carbon negative electrode material obtained by any of the preparation methods in the second aspect.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects: The bismuth-coated silicon-carbon anode material provided by this invention possesses a unique synergistic structure of "silicon-carbon core-bismuth compound layer-conductive agent layer." The inner bismuth compound layer, with its high oxygen ion conductivity, acts as an ion conduction enhancement layer and a volume expansion buffer layer, significantly improving the material's rate performance and cycle stability. The outer graphene layer constructs a highly efficient electronic conductivity network and immobilizes the bismuth compound layer, collectively enabling the material to achieve a balance of high capacity, low resistance, long lifetime, and high safety. The bismuth compound in this invention exhibits a plateau voltage of 3.0~3.5V in the all-electric configuration, and can rapidly respond to continue delithiation when the silicon delithiation capacity is nearing its limit, transforming from Bi₂O₃ and Li₂... + When bismuth compounds are converted into Bi and Li2O, compared to the slow, sloping plateau of the single-phase reaction of silicon during discharge, the two-phase coexistence reaction of bismuth compounds provides a completely flat plateau until the delithiation is completed, achieving efficient and stable power output during the discharge process, which greatly expands its application prospects in high-end lithium-ion batteries.

[0021] The method for preparing bismuth-coated silicon-carbon anode material provided by the present invention constructs a bismuth compound functional layer and a graphene conductive layer sequentially through spray drying and curing processes. This solves the technical problem of the difficulty in uniformly and firmly bonding the functional layer and the conductive layer in a multilayer coated structure, and provides a reliable method for the large-scale preparation of composite anode materials with consistent structures. Attached Figure Description

[0022] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 SEM image of the bismuth compound-modified silicon-carbon anode material obtained in Example 1; Figure 2 SEM image of the bismuth-coated silicon-carbon anode material obtained in Example 1; Figure 3 This is a SEM image of bismuth oxide used in Example 5; Figure 4 For reference, the dQ / dV curve of bismuth oxide; Figure 5 The graph shows the dQ / dV curve of the silicon-carbon anode material obtained in Example 1. Figure 6 The dQ / dV curve of the silicon-carbon anode material obtained in Comparative Example 1 is shown. Figure 7The charge-discharge curves of the silicon-carbon anode materials obtained in Example 1 and Comparative Example 1 are compared. Detailed Implementation

[0024] The embodiments and examples of the present invention will be described in detail below with reference to the implementation methods and examples. However, those skilled in the art will understand that the following implementation methods and examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The present invention provides a bismuth-coated silicon-carbon anode material, comprising a silicon-carbon material and a bismuth-containing material coating the silicon-carbon material. The bismuth-containing material comprises a first coating layer composed of a bismuth compound and a second coating layer composed of a conductive agent. The bismuth-containing compound includes, but is not limited to, bismuth oxide, bismuth titanate, bismuth silicate, bismuth aluminate, bismuth chloride, and bismuth nitrate.

[0026] In some preferred embodiments, the silicon content in the silicon-carbon anode material is 5% to 90% by mass, more preferably 30% to 70%; and / or, the specific surface area of ​​the silicon-carbon anode material is 0.5 m². 2 / g ~ 10 m 2 / g; and / or, the bismuth content in the silicon-carbon anode material is 0.9% to 27% by mass, and more preferably 2% to 10%. In this technical solution, the bismuth compound layer provides high ionic conductivity and volume buffering effect, and the conductive agent layer provides excellent electronic conduction path, synergistically improving the overall electrochemical performance of the material.

[0027] This invention provides a method for preparing the above-mentioned bismuth-coated silicon-carbon anode material, comprising the following steps: Step S1: Provide a silicon-carbon anode material, which is obtained by depositing silane in porous carbon and then coating it with carbon.

[0028] Step S2: Provide bismuth compound powder. The particle morphology of the bismuth compound powder can be spherical, ellipsoidal, irregular block, flake, rod, etc. Among them, the spherical and ellipsoidal particles are obtained by sand milling the purchased bismuth compound, with a size of 30~3000nm. It has the advantages of low cost and simple post-processing. The irregular block, flake, and rod particles are prepared by hydrothermal method, with a nanoscale size of 2~400nm. They have the advantages of large specific surface area and small volume.

[0029] Step S3: The bismuth compound powder, the silicon-carbon anode material, and the first binder are added to a solution containing a dispersant, stirred to form a first slurry, and then subjected to a first spray drying and a first curing treatment to obtain a bismuth compound-modified silicon-carbon anode material. The dispersant is selected from one or more of polyethylene glycol, polyvinyl alcohol 1788, polyvinyl alcohol 1799, and sodium dodecyl sulfate, and its concentration in the solution is 0.02% to 5%, more preferably 0.03% to 0.08%. The first binder is selected from one or more of polyimide, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, styrene-butadiene rubber, polyethylene oxide, and sodium carboxymethyl cellulose. In this step, by optimizing the selection of the dispersant and binder, the uniformity and stability of the slurry can be improved, ensuring uniform coating of the bismuth compound on the surface of the silicon-carbon material.

[0030] Step S4: The obtained bismuth compound-modified silicon-carbon anode material, conductive agent slurry, and second binder are mixed and stirred in deionized water to form a second slurry. This slurry is then subjected to a second spray drying and a second curing treatment to obtain a silicon-carbon anode material with a double-layer coating of conductive agent and bismuth compound. The conductive agent is selected from one or more of carbon black, conductive graphite, vapor-grown carbon fibers, carbon nanotubes, graphene, acetylene black, SuperP, highly conductive carbon black, graphite microcrystals, single-walled carbon nanotubes, multi-walled carbon nanotubes, and activated carbon fibers. When the conductive agent is graphene, it has 3 to 15 layers, preferably 3 to 5 layers. The second binder is consistent with the first binder and can be selected from one or more of polyimide, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, styrene-butadiene rubber, polyethylene oxide, and sodium carboxymethyl cellulose. In this step, the outer layer coating with the conductive agent can construct a three-dimensional conductive network, thereby significantly improving the electronic conductivity of the material, while simultaneously fixing the inner bismuth compound particles and preventing them from falling off during cycling.

[0031] In some preferred embodiments, the particle size of the bismuth compound powder in step S2 is 2 nm to 10 μm, and more preferably 20 nm to 300 nm. When the particle size is above 300 nm, the coefficient of expansion is high. As the bismuth compound transforms into metallic bismuth with increasing cycle count, the particles fuse together into micron-sized spheres, further worsening the expansion. In addition, the specific surface area of ​​large particles decreases, reducing the conductive contact area and increasing the risk of disconnection from the conductive agent. Furthermore, the coating difficulty increases, and the particles are prone to detachment. By limiting the size to hundreds of nanometers, the expansion caused by the charge-discharge process can be reduced, improving the cycle performance of the bismuth compound. Simultaneously, small bismuth compound particles can be stably embedded between silicon carbon particles and graphene layers, completing electron and ion transport in a surface-to-point-to-surface manner.

[0032] In some preferred embodiments, the solid content of the conductive agent slurry is 2 wt% to 15 wt%, and its typical but non-limiting solid content can be, for example: 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, and is more preferably 4 wt% to 10 wt%; when the conductive agent is graphene, its number of layers is 3 to 15, and is more preferably 3 to 5; and / or, the Dv50 particle size distribution of the conductive agent is 1 μm to 15 μm, and its typical but non-limiting Dv50 particle size can be, for example: 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, and is more preferably 2 μm to 13 μm.

[0033] In some preferred embodiments, the stirring time in step S3 is 1 to 12 hours, more preferably 4 to 6 hours; and / or, the solid content of the first slurry is 5% to 40%, more preferably 15% to 25%; and / or, the first curing temperature is 100°C to 400°C, more preferably 200°C to 300°C, and the curing time is 1 to 12 hours, more preferably 3 to 6 hours. The stirring time in step S4 is 1 to 24 hours, more preferably 4 to 6 hours; and / or, the solid content of the second slurry is 5% to 40%, more preferably 15% to 25%; and / or, the second curing temperature is 100℃ to 400℃, more preferably 200℃ to 300℃, and the curing time is 1 to 12 hours, more preferably 3 to 6 hours.

[0034] This invention also provides a negative electrode comprising a negative electrode active material, wherein the negative electrode active material comprises the aforementioned bismuth-coated silicon-carbon negative electrode material and the bismuth-coated silicon-carbon negative electrode material obtained by the aforementioned preparation method. A battery is also provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises the aforementioned negative electrode active material. Batteries prepared using the negative electrode material of this invention exhibit high energy density, excellent rate performance, and cycle stability, meeting the application requirements of high-end consumer electronics and power batteries.

[0035] The present invention is further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for illustrative purposes and should not be construed as limiting the invention in any way. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present invention were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0036] Example 1 This embodiment provides a bismuth-coated silicon-carbon anode material, and the preparation method is as follows: Step S1: Provide porous carbon material (the raw material properties of the porous carbon material, such as pore volume and specific surface area data, are shown in Table 1, and the subsequent embodiments and comparative examples are consistent). Place the material in a tube furnace and heat it to 580°C at 5°C / min under a N2 atmosphere. Then, introduce a 25% SiH4-N2 mixed gas and maintain it at 580°C for 18 hours. Change the atmosphere to N2 and place the substrate in the tube furnace again to heat it to 650°C. Introduce methane gas for carbon coating for 2 hours to obtain the silicon-carbon anode material. The silicon content and specific surface area are shown in Table 2.

[0037] Step S2: Bismuth oxide powder (Dv50 of 300nm) was dispersed in water as a dispersion medium, with the solid content controlled at 15%, and ball-milled for 3 hours. After drying, bismuth oxide powder with Dv50 of 30nm was obtained.

[0038] Step S3: Weigh 2g of sodium carboxymethyl cellulose, dissolve it in 900g of deionized water, and cool to room temperature. Then add 25g of the above-mentioned bismuth oxide powder and stir for 10 hours. Add 400g of the silicon-carbon anode material powder obtained in Step S1 and continue stirring for 4 hours. Add 60g of molten PI binder (60℃) and continue stirring for 3 hours to obtain a first slurry with a solid content of 20%. Spray dry the slurry at an outlet temperature of 100℃ to obtain powder, and then cure it at 200℃ for 4 hours to obtain the bismuth oxide modified silicon-carbon anode material, as shown below. Figure 1 As shown.

[0039] Step S4: Mix 1100g of deionized water with 1000g of graphene slurry with a solid content of 2% and stir for 1 hour. Add 400g of the bismuth oxide-modified silicon-carbon anode material obtained in Step S3 and continue stirring for 4 hours. Add 60g of molten PI binder (60℃) and continue stirring for 3 hours to obtain a second slurry with a solid content of 20%. Spray dry the slurry at an outlet temperature of 100℃ to obtain powder, then cure it at 200℃ for 4 hours to obtain the final product, namely, bismuth-coated silicon-carbon anode material, such as... Figure 2 As shown, the electrochemical performance of this silicon-carbon anode material was tested, and the coin cell data are as follows: Figure 5 As shown.

[0040] Example 2 This embodiment provides a bismuth-coated silicon-carbon anode material. The preparation method differs from that in Embodiment 1 in that: in step S3, the amount of deionized water is 1000g and the amount of bismuth titanate powder is 25g. Specifically, 2g of sodium carboxymethyl cellulose is weighed, dissolved in 1000g of deionized water and cooled to room temperature, and then 25g of the above-mentioned bismuth oxide powder is added and stirred for 10 hours.

[0041] Example 3 This embodiment provides a bismuth-coated silicon-carbon anode material. The preparation method differs from that in Embodiment 1 in that: in step S3, the amount of deionized water is 1200g and the amount of bismuth silicate powder is 25g. Specifically, 2g of sodium carboxymethyl cellulose is weighed, dissolved in 1200g of deionized water and cooled to room temperature, and then 100g of the above-mentioned bismuth oxide powder is added and stirred for 10 hours.

[0042] Example 4 This embodiment provides a bismuth-coated silicon-carbon anode material, the preparation method of which differs from that of Embodiment 1 in that: in step S4, the amount of graphene slurry used is 2000g, specifically, 1100g of deionized water is mixed with 2000g of graphene slurry with a solid content of 2%, and stirred for 1 hour.

[0043] Example 5 This embodiment provides a bismuth-coated silicon-carbon anode material, the preparation method of which differs from that of Example 1 in that: 1200g of deionized water is used in step S3, and the bismuth oxide powder used in step S3 is commercially available. The SEM image of the bismuth oxide is attached. Figure 3 As shown, the Dv50 particle size of its powder is approximately 300 nm.

[0044] Example 6 This embodiment provides a bismuth-coated silicon-carbon anode material, the preparation method of which differs from that of Embodiment 1 in that: in step S2, bismuth oxide powder is prepared by a hydrothermal method, specifically including dissolving 10g of bismuth nitrate pentahydrate Bi(NO3)3·5H2O in 50g of 2mol / L dilute nitric acid solution, slowly adding 2mol / L sodium hydroxide to adjust the pH to 9, and stirring for 1 hour. Then, 500ml of 2% CTAB solution is added, and the mixture is stirred at room temperature for 3 hours. The mixture is then transferred to a hydrothermal reactor and reacted at 150℃ for 2 hours. Nanoparticles are obtained by centrifugation, washed three times with deionized water, dried at 80℃ to obtain nanoparticle powder, and calcined at 800℃ for 2 hours to obtain bismuth oxide powder with a Dv50 particle size of 3nm. In step S4, the amount of graphene slurry used is 2000g, specifically by mixing 1100g of deionized water with 2000g of graphene slurry with a solid content of 2%, and stirring for 1 hour.

[0045] Example 7 This embodiment provides a bismuth-coated silicon-carbon anode material, and the preparation method is as follows: Step S1: Provide porous carbon material (the raw material properties of porous carbon material, such as pore volume and specific surface area, are shown in Table 1). Place the material in a tube furnace and heat it to 580°C at 5°C / min under a N2 atmosphere. Then, introduce a 25% SiH4-N2 mixed gas and maintain the temperature at 580°C for 20 hours. Change the atmosphere to N2 and place the substrate in the tube furnace again, heating it to 650°C. Introduce methane gas for carbon coating for 2 hours. Change the atmosphere back to N2 and cool it to room temperature to obtain the silicon-carbon anode material.

[0046] Step S2: Weigh 2g of sodium carboxymethyl cellulose, dissolve it in 1200g of deionized water, and cool to room temperature. Then add 25g of bismuth oxide powder (this bismuth oxide powder is commercially available, unlike the ball milling method in Example 1, and its Dv50 particle size is 3000nm), and stir for 10 hours. Add 400g of the silicon-carbon anode material powder obtained in Step S1, and continue stirring for 4 hours. Add 60g of molten PI binder (60℃), and continue stirring for 3 hours to obtain the first slurry. Spray dry the slurry at an outlet temperature of 100℃, and then cure the powder at 200℃ for 4 hours to obtain the bismuth oxide-modified silicon-carbon anode material.

[0047] Step S3: Mix 1100g of deionized water with 333g of graphene slurry with a solid content of 12% and stir for 1 hour. Add 400g of the bismuth oxide-modified silicon-carbon anode material obtained in Step S2 and continue stirring for 4 hours. Add 60g of molten PI binder (60℃) and continue stirring for 3 hours to obtain a second slurry. Spray dry the slurry at an outlet temperature of 100℃ to obtain powder, and then cure it at 200℃ for 4 hours to obtain bismuth-coated silicon-carbon anode material.

[0048] Example 8 This embodiment provides a bismuth-coated silicon-carbon anode material. The preparation method differs from that of Example 1 in that the concentration of the SiH4-N2 mixed gas in step S1 is 5%, the reaction time is 4 hours, and a silicon-carbon anode substrate is obtained. The silicon content and specific surface area are shown in Table 2. The carbon coating process is the same as that in Example 1.

[0049] Example 9 This embodiment provides a bismuth-coated silicon-carbon anode material. The preparation method differs from that of Example 1 in that the concentration of the SiH4-N2 mixed gas in step S1 is 30%, the reaction temperature is 600℃, and the reaction time is 30 hours, resulting in a silicon-carbon anode substrate. The silicon content and specific surface area are shown in Table 2. The carbon coating process is consistent with that of Example 1.

[0050] Example 10 This embodiment provides a bismuth-coated silicon-carbon anode material, the preparation method of which differs from that of Embodiment 1 in that: in step S3, the bismuth oxide powder is 225g, specifically, 2g of sodium carboxymethyl cellulose is weighed, dissolved in 900g of deionized water and cooled to room temperature, and then 225g of the above bismuth oxide powder is added and stirred for 10 hours.

[0051] Example 11 This embodiment provides a bismuth-coated silicon-carbon anode material. The preparation method differs from that of Embodiment 1 in that: in step S3, the amount of deionized water is changed from 900g to 400g; in step S4, 1000g of graphene slurry with a solid content of 2% is replaced with 500g of carbon nanotube slurry with a solid content of 1%, while the rest remains unchanged.

[0052] Comparative Example 1 This comparative example provides a silicon-carbon anode material, and the preparation method is as follows: Porous carbon material was provided (the raw material properties of the porous carbon material, such as pore volume and specific surface area, are shown in Table 1). This material was placed in a tube furnace and heated to 580°C at a rate of 5°C / min under a N2 atmosphere. Then, a 25% SiH4-N2 mixture was introduced, and the temperature was maintained at 580°C for 18 hours. The atmosphere was then changed to N2, and the substrate was placed back in the tube furnace and heated to 650°C. Methane gas was introduced for carbon coating for 2 hours. The atmosphere was then changed back to N2, and the material was cooled to room temperature to obtain a silicon-carbon anode material. The electrochemical performance of this silicon-carbon anode material was tested, and the coin cell data are as follows: Figure 6 As shown. Furthermore, the charge-discharge curves of this comparative example and the silicon-carbon anode material obtained in Example 1 are compared, as shown in the attached figure. Figure 7 As shown.

[0053] Comparative Example 2 This comparative example provides a silicon-carbon anode material with only a bismuth oxide inner layer coating, and the preparation method is as follows: Step S1: Provide a porous carbon material, place the porous carbon material in a tube furnace, heat it to 580°C at 5°C / min under N2 atmosphere, then introduce a 25% SiH4-N2 mixed gas, maintain at 580°C for 20 hours, change the atmosphere to N2, and cool to room temperature to obtain a silicon-carbon anode material.

[0054] Step S2: Weigh 2g of sodium carboxymethyl cellulose and dissolve it in 1200g of deionized water. Add 25g of bismuth oxide powder (Dv50=300nm) and stir for 10 hours. Add 400g of the silicon-carbon anode material obtained in Step S1 and continue stirring for 4 hours. Add 60g of molten PI binder (60℃) and continue stirring for 3 hours to obtain a slurry with a solid content of 16%. Perform spray drying at an outlet temperature of 100℃. After obtaining the powder, cure it at 200℃ for 4 hours to obtain a bismuth oxide monolayer coated silicon-carbon anode material.

[0055] Comparative Example 3 This comparative example provides a silicon-carbon anode material with only a graphene outer layer, and the preparation method is as follows: Step S1: Provide a porous carbon material, place the porous carbon material in a tube furnace, heat it to 580°C at 5°C / min under N2 atmosphere, then introduce a 25% SiH4-N2 mixed gas, maintain at 580°C for 20 hours, change the atmosphere to N2, and cool to room temperature to obtain a silicon-carbon anode material.

[0056] Step S2: Mix 1100g of deionized water with 2000g of graphene slurry with a solid content of 2% and stir for 1 hour. Add 400g of the silicon-carbon anode material obtained in Step S1 and continue stirring for 4 hours. Add 60g of molten PI binder (60℃) and continue stirring for 3 hours to obtain a slurry with a solid content of 18%. Perform spray drying at an outlet temperature of 100℃ to obtain powder, and then cure at 200℃ for 4 hours to obtain a graphene monolayer coated silicon-carbon anode material.

[0057] Reference Example This reference example uses commercially sourced bismuth oxide from Example 5 and directly tests its electrochemical performance; its coin cell data is as follows: Figure 4 As shown in the example, this reference example primarily provides a characteristic voltage reference for identifying the electrochemical contribution of bismuth compounds in composite anode materials. It aims to pinpoint the characteristic voltage position of the intrinsic reaction of bismuth oxide. However, due to the poor conductivity and large volume change of bismuth oxide itself, this electrode configuration is not an optimized anode material, and its cycle performance and rate performance are not within the scope of this patent. The core of this technical solution lies in the innovative structure shown in the above embodiment, which uses a bismuth compound with this characteristic activity as a functional coating layer, combined with a silicon-carbon matrix and a conductive network.

[0058] Electrode and half-cell preparation and electrochemical performance testing Using the silicon-carbon anode materials prepared in the above embodiments and comparative examples as the anode active materials, anode sheets were prepared and CR2032 coin cell half-cells were assembled for electrochemical performance testing. The specific steps are as follows: (1) Half-cell assembly: CR2032 coin cells were assembled in a glove box, with lithium metal sheets as the counter electrode, polypropylene microporous membranes as the separator, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC=1:1), where the LiPF6 concentration was 1 mol / L. The cells were charged and discharged using a LAND battery testing system.

[0059] (2) Cyclic specific capacity and initial efficiency test: After the CR2032 button cell was left to stand for 6 hours, it was discharged at 0.1C to 0.005V and the capacity was recorded as Q1; then it was discharged at a constant voltage of 0.005V until the current was cut off at 0.01C and the total capacity was recorded as Q2; after standing for 5 minutes, it was charged at a constant current of 0.1C to 1.5V; the initial delithiation specific capacity is the specific capacity (or mass specific capacity) of the electrode material, and the ratio of the initial delithiation capacity to the initial lithium insertion capacity is the initial coulombic efficiency of the battery.

[0060] The porous carbon raw material property data provided in the above embodiments and comparative examples are shown in Table 1. The physical performance characterization results of the negative electrode materials obtained in each embodiment and comparative example are shown in Table 2. The electrochemical cycle performance test results are shown in Table 3. The charge-discharge rate performance test results are shown in Table 4. Tables 2, 3 and 4 include the physical performance characterization results, electrochemical cycle performance test results and charge-discharge rate performance test results of bismuth oxide in the reference example.

[0061] Table 1 Properties of Porous Carbon Raw Materials Material type Dv10 Dv50 Dv90 Concentration <![CDATA[Pore volume (cm 3 / g)]]> <![CDATA[Specific surface area (m 2 / g)]]> Average pore size (nm) Micropore percentage (%) Porous carbon 5.21 7.53 12.63 0.99 0.91 1956 1.85 95% Table 2 Characterization of Physical Properties of Anode Materials experiment Dv10 Dv50 Dv90 Concentration Bismuth content (%) Silicon content (%) <![CDATA[Specific surface area (m 2 / g)]]> Resistivity (4MPa) Example 1 5.4 7.7 13.2 1.0 3.1 47.1 2.8 1.5 Example 2 5.1 7.9 12.9 1.0 5.8 46.3 4.1 2.3 Example 3 5.1 7.6 12.2 0.9 8.7 43.2 2.5 4.5 Example 4 5.2 7.9 12.7 0.9 3.1 47.4 2.9 .0.9 Example 5 5.7 7.9 13.7 1.0 3.2 47.3 3.2 2.1 Example 6 0.2 5.3 14.1 2.6 2.6 46.3 6.9 1.7 Example 7 6.1 13.4 56.7 3.8 3.1 45.1 3.4 3.4 Example 8 4.1 7.8 13.4 1.2 2.9 7.2 6.1 4.9 Example 9 4.3 7.4 12.3 1.1 3.5 81.4 4.3 7.5 Example 10 3.1 8.5 18.7 1.8 23.1 22.1 5.1 13.2 Example 11 4.4 8.4 14.2 1.17 3.3 45.4 4.5 2.8 Comparative Example 1 5.2 7.6 13.4 1.1 0 51.0 2.2 23 Comparative Example 2 5.7 7.6 13.9 1.1 2.7 47.6 2.8 45 Comparative Example 3 5.5 7.6 13.5 1.1 0 48.7 5.1 0.4 Reference Example 0.24 0.30 0.45 0.7 89.7 0 45.1 / Table 3 Test Table of Physicochemical Cyclic Performance of Anode Materials experiment 1.5V capacity (mAh / g) 1.5V First-Effect (%) 1 volt capacity (mAh / g) 1V First Effect (%) 0.9V capacity (mAh / g) 0.9V First-Effect (%) 0.8V capacity (mAh / g) 0.8V First-Effect (%) dQ / dV expansion Example 1 1883.4 93.1% 1806.5 89.3% 1745.8 86.3% 1681.1 83.1% 1.64 45.1% Example 2 1730.0 92.0% 1658.0 88.2% 1613.6 85.8% 1535.2 81.7% 1.68 42.7% Example 3 1664.3 93.5% 1593.1 89.5% 1550.4 87.1% 1484.5 83.4% 1.61 38.9% Example 4 1879.8 93.2% 1803.2 89.4% 1752.8 86.9% 1680.2 83.3% 1.62 49.4% Example 5 1851.1 93.2% 1770.4 89.1% 1722.7 86.7% 1653.2 83.2% 1.61 53.1% Example 6 1790 92.7% 1703.1 88.2% 1595.0 82.6% 1535.1 79.5% 1.59 35.1% Example 7 1831 90.1% 1774.1 87.3% 1696.9 83.5% 1607.5 79.1% 1.53 54.1% Example 8 950.1 60.1% 795.2 50.3% 728.8 46.1% 659.2 41.7% 1.50 20.5% Example 9 2300.3 94.5% 2152.5 90.3% 2114.4 88.7% 2023.8 84.9% 3.17 120.7% Example 10 1007.6 60.3% 763.6 45.7% 721.9 43.2% 646.7 38.7% 0.79 64.1% Example 11 1895.8 91.2% 1838.0 88.5% 1751.8 84.3% 1664.5 80.1% 1.54 53.9% Comparative Example 1 1879.6 94.2% 1798.5 90.1% 1749.5 87.7% 1675.7 84.0% 1.60 71.1% Comparative Example 2 1841.1 92.1% 1761.1 88.1% 1717.1 85.90% 1655.2 82.8% 1.59 50.5% Comparative Example 3 1767.2 93.5% 1691.6 89.5% 1646.2 87.1% 1576.3 83.4% 1.61 60.3% Reference Example 202.37 32.0% 163.80 25.9% 113.64 17.9% 47.97 7.6% / 32.1% Table 4 Test Table of Charge-Discharge Rate Performance of Anode Materials experiment 1C discharge rate 1C charging rate 2C discharge rate 2C charging rate Example 1 52.1% 82.6% 26.9% 92.1% Example 2 53.7% 84.9% 26.7% 93.4% Example 3 55.2% 85.1% 28.1% 94.6% Example 4 54.1% 83.9% 24.7% 91.7% Example 5 53.1% 83.4% 25.1% 92.3% Example 6 53.9% 86.9% 26.7% 93.9% Example 7 52.1% 85.7% 26.1% 93.1% Example 8 25.7% 46.3% 11.6% 79.5% Example 9 40.1% 78.2% 13.3% 83.4% Example 10 26.9% 47.8% 13.9% 79.8% Example 11 51.9% 85.3% 25.9% 93.0% Comparative Example 1 48.2% 87.2% 20.7% 89.1% Comparative Example 2 49.7% 89.6% 22.9% 89.8% Comparative Example 3 49.3% 82.5% 21.7% 88.4% Reference Example 42.1% 47.5% 33.1% 37.4% The experimental data above show that the introduction of bismuth-containing compounds significantly improves the ionic conductivity of the material, which stems from the effect of Bi. 3+ The unique electronic structure of the ions—their easily polarizable lone pairs of electrons and low Bi-O bond energy—effectively promotes oxygen vacancy migration, making δ-Bi₂O₃ a highly efficient ion conduction channel. As shown in Tables 2 and 4, Example 3, while maintaining high capacity, reduced resistivity to 4.5 Ω·cm, achieving discharge efficiencies of 55.2% and 28.1% at 1C and 2C rates, respectively, significantly outperforming the comparative materials and confirming the excellent rate performance of this material.

[0062] The double-layer coating structure of this invention exhibits multiple technical advantages: the outer graphene layer not only constructs a three-dimensional conductive network, significantly reducing the powder resistivity of the material to below 10 Ω·cm, but also effectively fixes the inner bismuth oxide particles through physical anchoring, preventing them from detaching during electrode fabrication. Simultaneously, the bismuth-containing compound (taking bismuth oxide as an example) itself has a theoretical capacity of approximately 600 mAh / g, and its 3-3.5V delithiation potential contributes to capacity while preventing lithium plating, significantly improving battery safety. Figure 4This is a reference example, showing the dQ / dV curve of the coin cell using bismuth oxide as the sole active material. The reaction peak from 0.8 to 1 V represents the delithiation voltage corresponding to the delithiation of bismuth oxide. Figure 5 The figure shows the dQ / dV curve of the silicon-carbon anode material obtained in Example 1. A reaction peak appears between 0.8 and 1 V, and the delithiation reaction plateau of silicon is between 0.2 V and 0.8 V. Figure 6 The figure shows the dQ / dV curve of the pure silicon-carbon anode material in Comparative Example 1. The reaction plateau is only between 0.2 and 0.8 V. The comparison of the three figures shows that the introduction of bismuth compounds into the silicon anode system begins to contribute capacity at around 0.8 to 1 V, effectively extending the plateau voltage width of lithium insertion / extraction. Figure 7 A comparison of the charge-discharge curves of the silicon-carbon materials obtained in Example 1 and Comparative Example 1 shows that for the bismuth-containing silicon-carbon anode material, a voltage plateau appears above 0.8V in its delithiation curve, which is the delithiation plateau of bismuth oxide. As shown in Table 3, Example 1 retains 83.1% of its capacity after cycling at 0.5C, with a volume expansion rate controlled at 45.1%, far lower than the 71.1% expansion rate of Comparative Example 1. This comprehensive performance advantage allows the material to simultaneously meet the requirements of high energy density, excellent rate performance, and long cycle life, providing an ideal anode material solution for developing next-generation high-performance lithium-ion batteries.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A bismuth-coated silicon-carbon anode material, characterized in that, The material includes silicon-carbon material and a bismuth-containing material coating the silicon-carbon material, wherein the bismuth-containing material includes a first coating layer composed of a bismuth compound and a second coating layer composed of a conductive agent.

2. The bismuth-coated silicon-carbon anode material according to claim 1, characterized in that, The silicon content in the silicon-carbon anode material is 5% to 90% by mass, preferably 30% to 70%. And / or, the specific surface area of ​​the silicon-carbon anode material is 0.5 m². 2 / g ~ 10 m 2 / g; And / or, the bismuth content in the silicon-carbon anode material is 0.9% to 27% by mass, preferably 2% to 10%.

3. The bismuth-coated silicon-carbon anode material according to claim 1, characterized in that, The bismuth compounds include, but are not limited to, bismuth oxide, bismuth titanate, bismuth silicate, bismuth aluminate, bismuth chloride, and bismuth nitrate.

4. A method for preparing the bismuth-coated silicon-carbon anode material as described in claim 1, characterized in that, Includes the following steps: Step S1: Provide a silicon-carbon anode material, which is obtained by depositing silane in porous carbon and then coating it with carbon. Step S2: Provide bismuth compound powder; Step S3: The bismuth compound powder, the silicon-carbon anode material, and the first binder are added to a solution containing a dispersant and stirred to form a first slurry. Then, a first spray drying and a first curing treatment are performed to obtain a bismuth compound modified silicon-carbon anode material. Step S4: The obtained bismuth compound modified silicon-carbon anode material, conductive agent slurry, and second binder are mixed and stirred in deionized water to form a second slurry. Then, a second spray drying and a second curing treatment are performed to obtain a silicon-carbon anode material with a double layer of conductive agent and bismuth compound coating.

5. The method for preparing the bismuth-coated silicon-carbon anode material according to claim 4, characterized in that, In step S2, the bismuth compound powder has a particle morphology of spheres, ellipsoids, or irregular blocks. And / or, in step S2, the particle size of the bismuth compound powder is 2 nm to 10 μm, preferably 20 nm to 300 nm; And / or, the dispersant in step S3 is selected from one or more of polyethylene glycol, paraffin wax, Span-80, Tween-80, polyvinyl alcohol 1788, polyvinyl alcohol 1799, polyvinyl alcohol 2499, sodium dodecyl sulfate, and hexadecyltrimethylammonium bromide; And / or, the concentration of the dispersant in the solution in step S3 is 0.02% to 5%, preferably 0.03% to 0.08%.

6. The method for preparing the bismuth-coated silicon-carbon anode material according to claim 4, characterized in that, The first binder and / or the second binder are selected from one or more of polyimide, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, styrene-butadiene rubber, polyethylene oxide, and sodium carboxymethyl cellulose; and / or the conductive agent is selected from one or more of carbon black, conductive graphite, vapor-grown carbon fiber, carbon nanotubes, graphene, acetylene black, SuperP, superconducting carbon black, graphite microcrystals, single-walled carbon nanotubes, multi-walled carbon nanotubes, and activated carbon fibers. When the conductive agent is graphene, it has 3 to 15 layers, preferably 3 to 5 layers.

7. The method for preparing the bismuth-coated silicon-carbon anode material according to claim 4, characterized in that, The conductive agent slurry has a solid content of 2 wt% to 15 wt%, preferably 4 wt% to 10 wt%; and / or the conductive agent has a Dv50 particle size distribution of 1 μm to 15 μm, preferably 2 μm to 13 μm.

8. The method for preparing the bismuth-coated silicon-carbon anode material according to claim 4, characterized in that, The stirring time in step S3 is 1 to 12 hours, preferably 4 to 6 hours; and / or, the solid content of the first slurry is 5% to 40%, preferably 15% to 25%; and / or, the first curing temperature is 100℃ to 400℃, preferably 200℃ to 300℃, and the curing time is 1 to 12 hours, preferably 3 to 6 hours. In step S4, the stirring time is 1 to 24 hours, preferably 4 to 6 hours; and / or, the solid content of the second slurry is 5% to 40%, preferably 15% to 25%; and / or, the second curing temperature is 100℃ to 400℃, preferably 200℃ to 300℃, and the curing time is 1 to 12 hours, preferably 3 to 6 hours.

9. A negative electrode comprising a negative electrode active material, characterized in that, The negative electrode active material comprises the bismuth-coated silicon-carbon negative electrode material as described in claims 1-3, wherein the negative electrode active material comprises the bismuth-coated silicon-carbon negative electrode material as described in any one of claims 1-3 and the bismuth-coated silicon-carbon negative electrode material obtained by any one of the preparation methods in claims 4-8.

10. A battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode comprises a negative electrode active material, which comprises the bismuth-coated silicon-carbon negative electrode material according to any one of claims 1-3 and the bismuth-coated silicon-carbon negative electrode material obtained by any one of the preparation methods of claims 4-8.

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