A nano-silicon-carbon material, its preparation method, and its application in lithium-ion batteries.

Abstract

This invention relates to the field of lithium-ion battery technology, specifically disclosing a nano-silicon-carbon material, its preparation method, and its application in lithium-ion batteries. The invention uses industrial waste silicon micropowder as a silicon source, and obtains monodisperse nano-silicon cores through weakly acidic selective etching. These cores are then composited with flexible carbon nanofibers to form a buffer layer. Precursor particles are prepared by mixing these particles with a glucose-biomass coke mixed carbon source and tetraethyl orthosilicate. Finally, low-temperature transient carbonization is used to generate SiO₂-containing particles in situ. x A carbon coating layer in nano-regions is formed, and after carbonization, fluorocarbon vapor is introduced to deposit an SEI precursor film in situ on the material surface, resulting in a nano-silicon-carbon anode material. Lithium-ion batteries using this invention's nano-silicon-carbon material exhibit excellent cycle stability and high initial coulombic efficiency, demonstrating high electrode structural integrity, stable SEI film, and low irreversible lithium loss during cycling. Furthermore, since the anode material uses waste silicon powder as a silicon source, manufacturing costs are significantly reduced, indicating broad application prospects.

Description

Technical Field

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

[0002] Lithium-ion batteries are core energy storage devices for new energy vehicles, large-scale energy storage, and portable electronic devices. Their energy density, cycle life, and production cost directly determine the development of the new energy industry. Silicon-based anode materials have a theoretical specific capacity of 4200 mAh / g, approximately 10 times that of traditional graphite anodes, making them a core candidate material for next-generation high-energy-density lithium-ion battery anodes. However, nano-silicon undergoes a 200%–300% volume expansion during charge and discharge, leading to electrode pulverization and structural damage, resulting in a sharp decline in cycle life. Simultaneously, nano-silicon has high surface activity, making it prone to violent side reactions upon contact with the electrolyte, forming an unstable SEI film. Repeated rupture and regeneration of this film during cycling causes significant irreversible loss of active lithium, typically resulting in an initial coulombic efficiency below 85%, thus limiting the battery's energy utilization efficiency.

[0003] To address the aforementioned issues, the industry commonly employs carbon coating modification technology to modify nano-silicon. The physical support and electronic conduction of the carbon layer mitigate volume expansion and suppress side reactions. Current carbon coating processes include chemical vapor deposition (CVD), high-temperature carbonization, and sol-gel methods. However, all of these processes have significant drawbacks: CVD equipment is expensive and complex to operate, making large-scale production difficult; high-temperature carbonization typically involves prolonged processing at 800–1200°C, resulting in high energy consumption, and nano-silicon is easily oxidized at high temperatures, impairing the material's electrochemical performance; the carbon layer prepared by the sol-gel method lacks sufficient density, limiting the modification effect. Furthermore, existing silicon-carbon materials mostly use commercially available nano-silicon as the silicon source, leading to high costs, and the nano-silicon particles are prone to agglomeration, increasing the difficulty of subsequent homogenization and coating processes and affecting electrode consistency.

[0004] Therefore, there is an urgent need to provide a preparation process for nano-silicon-carbon materials to solve the problems of high silicon source cost, high energy consumption and poor modification effect of carbon coating process, severe material volume expansion, short cycle life and low initial coulombic efficiency caused by SEI film instability in the existing technology. Summary of the Invention

[0005] To address the problems of high silicon source cost, high energy consumption of carbon coating process and limited effect on suppressing volume expansion and interfacial side reactions, unstable SEI film leading to short cycle life and low first coulombic efficiency in existing technologies, this paper provides a nano-silicon-carbon material and its preparation method, as well as the application of the material in lithium-ion batteries.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: In a first aspect, the present invention provides a method for preparing nano-silicon-carbon materials, comprising the following steps: S1, add waste silicon powder to a weakly acidic solution for etching to obtain etched waste silicon powder; S2, disperse carbon nanofibers in water to obtain carbon nanofiber dispersion; add the etched waste silicon powder to the carbon nanofiber dispersion, stir and mix, so that the carbon nanofibers are adsorbed on the surface of the etched waste silicon powder to obtain composite particles. S3, mix the composite particles, carbon source, organosilicon crosslinking precursor and water evenly, and dry to obtain precursor particles; S4. Under an inert atmosphere, the precursor particles are transiently carbonized. After carbonization, fluorocarbonate vapor is introduced into the furnace to deposit an SEI precursor film on the material surface in situ, thus obtaining nano-silicon-carbon material.

[0007] Compared with existing technologies, the preparation method of nano-silicon carbon materials provided by this invention has the following advantages: (1) Using industrial waste silicon powder as silicon source, the grain boundary defects of waste silicon powder are selectively etched by weak acid solution, so that waste silicon is pyrolyzed in situ to form monodisperse nano silicon. This not only realizes the high-value utilization of industrial solid waste and greatly reduces the cost of silicon source, but also avoids the problems of severe agglomeration and uneven particle size distribution in the traditional ball milling method for preparing nano silicon. Moreover, the surface of nano silicon after etching has abundant active sites, which provides good interface conditions for the uniform adsorption of carbon nanofibers. (2) By first dispersing carbon nanofibers and then mixing them with etched waste silicon powder, the carbon nanofibers are preferentially wrapped and adsorbed on the surface of the silicon core to form the first flexible buffer layer, which lays the foundation for the initial absorption of volume expansion stress during subsequent charging and discharging. (3) Introducing an organosilicon crosslinking precursor and a carbon source to co-coat the composite particles, and after drying, forming a uniform precursor layer, which serves as the SiO2 layer for subsequent carbonization. x The in-situ generation and diffuse distribution of nanoscale micro-regions provide a material basis; (4) In the carbonization stage, transient carbonization process is used to replace traditional long-term high-temperature carbonization, which completes the carbonization of carbon source and the in-situ conversion of crosslinking precursor in a short time. This not only significantly reduces production energy consumption and time costs, but also effectively inhibits the oxidation and grain growth of nano-silicon at high temperatures, and simultaneously forms SiO2. x A dense carbon coating layer with uniformly dispersed nano-regions; the generated SiO xUnlike conventional physical doping methods, the nano-regions are generated in situ through the reaction of organosilicon precursors during transient carbonization. They form stable chemical bonds with the carbon-coated matrix and the surface of the nano-silicon cores, significantly enhancing the interfacial bonding between the carbon layer and the silicon core. Furthermore, nanoscale stress buffer nodes are constructed within the carbon layer, further strengthening its resistance to deformation. Simultaneously, SiO₂… x The highly active surface of the nanoscale region can actively capture free lithium generated during charging and discharging, participate in the construction of a uniform and dense SEI film, inhibit the repeated rupture and regeneration of the SEI film, significantly reduce irreversible lithium loss, and thus improve the material's first coulombic efficiency and long-term cycling stability. (5) After carbonization, fluorocarbonate vapor is directly introduced into the furnace for in-situ deposition, forming a uniform and stable SEI precursor film on the material surface in one step, effectively suppressing direct contact and side reactions between the electrolyte and the active material.

[0008] Furthermore, in S1, the particle size of the waste silicon powder is 1μm~5μm.

[0009] Further, in S1, the weakly acidic solution is a mixed aqueous solution of citric acid and oxalic acid in a mass ratio of 2:1 to 3:1, and the total mass concentration of citric acid and oxalic acid in the weakly acidic solution is 5% to 10%.

[0010] Using the aforementioned weakly acidic solution, in-situ controllable pyrolysis of waste silicon micropowder along grain boundary defects can be achieved, yielding monodisperse silicon nanoparticles with uniform particle size. Furthermore, the oxygen-containing functional groups remaining on the surface of the silicon particles after etching are beneficial for the subsequent adsorption and recombination of carbon nanofibers, improving the uniformity of interfacial bonding.

[0011] Furthermore, in S1, the mass-to-volume ratio of the waste silicon powder to the weakly acidic solution is 1 g: (3~8) mL.

[0012] Furthermore, in S1, the etching temperature is 40℃~60℃, and the etching time is 30min~60min.

[0013] The etching temperature and time specified above can prevent the etching rate from being too slow, resulting in insufficient grain boundary cleavage and difficulty in obtaining monodisperse silicon nanoparticles, or the etching rate from being too fast, leading to excessive dissolution of silicon particles and excessive surface roughness, which would affect the uniformity of subsequent carbon coating. Controlling the etching temperature and time within the above range is beneficial for the uniform adsorption of carbon nanofibers and the tight bonding of the carbon coating layer.

[0014] Furthermore, in S1, the particle size of the etched waste silicon powder is 50nm~100nm.

[0015] Specifically, after etching is completed in step S1, the etching product is washed with deionized water until neutral, and then vacuum dried to obtain etched waste silicon powder.

[0016] Furthermore, in S2, the carbon nanofibers have a diameter of 10nm~20nm and a length of 1μm~5μm.

[0017] Specifically, the carbon nanofibers are biomass flexible carbon nanofibers.

[0018] In some embodiments of the present invention, the carbon nanofibers may be selected from the pyrolysis products of straw or wood chips. Compared with rigid carbon nanotubes or vapor-grown carbon fibers prepared by traditional chemical vapor deposition, the surface of biomass pyrolysis carbon nanofibers is rich in oxygen-containing functional groups such as hydroxyl and carboxyl groups, making them easy to disperse in aqueous systems and readily forming uniform and stable carbon nanofiber dispersions.

[0019] In step S2, when the etched waste silicon micro powder is added to the above dispersion and stirred, the biomass carbon nanofibers spontaneously and uniformly wrap around and adsorb onto the surface of the silicon particles through hydrogen bonding and electrostatic interaction between the oxygen-containing functional groups on their surface and the hydroxyl groups on the surface of the etched silicon particles, forming a flexible buffer pre-coating layer.

[0020] Furthermore, in S2, the mass concentration of the carbon nanofiber dispersion is 0.5%~1%.

[0021] Furthermore, in S2, the mass ratio of the etched waste silicon micro powder to carbon nanofibers is 100:(1~2).

[0022] The carbon nanofibers in this ratio can form an appropriate and uniform fiber adsorption layer on the surface of the silicon core, avoiding insufficient buffering effect caused by insufficient fiber content, and also preventing agglomeration and dispersion difficulties caused by excessive fiber content.

[0023] Furthermore, in S2, the stirring and mixing time is 1h to 2h.

[0024] Further, in S3, the carbon source is a mixture of glucose and biochar in a mass ratio of 1:(0.5~1.5).

[0025] During transient carbonization, glucose rapidly pyrolyzes to form a continuous and dense carbon matrix, ensuring the integrity of the carbon coating and its electronic conductivity. Biomass coke, with its naturally porous structure and flexibility, further buffers volume expansion and provides channels for lithium-ion transport. Within this ratio range, the carbon coating constructed by the synergistic use of the two carbon sources exhibits both density and hierarchical porosity, effectively constraining silicon core volume expansion while also facilitating electrolyte wetting and ion diffusion.

[0026] In this invention, the biomass char refers to a carbon-rich solid product obtained by low-temperature pyrolysis of biomass raw materials under oxygen-limited or oxygen-deficient conditions. At least one of the pyrolysis products of agricultural and forestry wastes, such as straw char, sawdust char, rice husk char, and bamboo char, can be selected.

[0027] Furthermore, in S3, the organosilicon crosslinking precursor is tetraethyl orthosilicate.

[0028] Utilizing the hydrolysis-condensation reaction characteristics of tetraethyl orthosilicate, a pre-crosslinked structure is formed with hydroxyl groups on the silicon core surface and oxygen-containing functional groups of the carbon source before carbonization. During transient carbonization, tetraethyl orthosilicate is converted in situ to SiO2. x Nanoscale microdomains form stable chemical bonds with the carbon-coated matrix and the nanoscale silicon core, enabling SiO2 to... x Uniformly dispersed in the carbon layer at nanoscale size, avoiding physical doping of SiO x The problem of powder agglomeration and weak interfacial bonding.

[0029] Furthermore, in S3, the mass ratio of the composite particles to the carbon source is 100:(30~80).

[0030] Furthermore, in S3, the amount of the organosilicon crosslinking precursor added is 5% to 10% of the mass of the composite particles.

[0031] The optimal proportion of tetraethyl orthosilicate added ensures both the SiO₂ content and the desired SiO₂ content. x The carbon layer and the substrate are fully cross-linked and anchored, while maintaining the structural integrity and conductivity of the carbon coating layer, thus achieving a balance between stress buffering, lithium locking and electronic conduction.

[0032] Furthermore, in S3, the mass-volume ratio of the composite particles to water is 1 g: (100~500) mL.

[0033] In some specific embodiments of the present invention, in S3, the drying is carried out by vacuum drying, with an inlet air temperature of 180℃~200℃ and an outlet air temperature of 80℃~100℃.

[0034] Furthermore, in S4, the transient carbonization temperature is 400℃~800℃, and the holding time is 5s~20s.

[0035] Within the aforementioned temperature and time range, the transient carbonization process can effectively suppress high-temperature oxidation and grain coarsening of nano-silicon while ensuring the quality of the carbon layer and the cross-linking effect, thus maximizing the retention of the lithium storage capacity of nano-silicon and significantly reducing production energy consumption and time costs, meeting the needs of large-scale preparation.

[0036] In some specific embodiments of the present invention, the transient carbonization treatment described in S4 can be carried out using a transient flash carbonization furnace.

[0037] Compared to traditional tube furnaces or box furnaces with prolonged high-temperature carbonization processes, transient flash carbonization furnaces utilize rapid thermal shock to complete the pyrolysis and carbonization of the carbon source in an extremely short time. This results in a rapid and dense carbon coating layer formation, effectively preventing the growth of nano-silicon grains and surface oxidation caused by prolonged heating. Furthermore, transient flash carbonization furnaces allow for continuous feeding and discharging, achieving significantly higher production efficiency than batch high-temperature furnaces. The equipment structure is also relatively simple, making it easy to scale up.

[0038] It should be noted that the inert atmosphere mentioned in this invention refers to a high-purity protective gas environment that does not chemically react with the materials, preferably high-purity nitrogen or high-purity argon with a purity of not less than 99.99%. Before the S4 transient carbonization treatment, inert gas must be continuously introduced into the furnace to replace the air inside the furnace, ensuring that the oxygen content inside the furnace drops below 50 ppm before heating. During the carbonization process, inert gas continues to be introduced to maintain a slightly positive pressure state inside the furnace to prevent outside air from seeping in.

[0039] Furthermore, in S4, the fluorocarbonate compound is trifluoromethyl ethylene carbonate.

[0040] Furthermore, in S4, the temperature for in-situ deposition of the SEI precursor film is 150℃~200℃, and the deposition time is 30min~60min.

[0041] The optimal deposition temperature and time enable fluorocarbonate vapors to be fully adsorbed and uniformly deposited on the carbon coating surface, forming a continuous and dense SEI precursor film.

[0042] Furthermore, in S4, the fluorocarbonate compound vapor is a mixture of fluorocarbonate compound and high-purity nitrogen, wherein the concentration of the fluorocarbonate compound is 5% to 10%.

[0043] Specifically, the flow rate of the fluorocarbonate compound vapor is 30 L / min to 80 L / min.

[0044] Secondly, the present invention provides a nano-silicon-carbon material, which is prepared by the above-mentioned method for preparing nano-silicon-carbon materials.

[0045] Specifically, the nano-silicon-carbon material includes: Nano-silicon core; A carbon coating layer is applied to the outside of the nano-silicon core, and in-situ generated SiO is dispersed in the carbon coating layer. x Nanoscale micro-regions; Carbon nanofibers, some of which are located in the carbon coating layer and some of which are located at the interface between the nano-silicon core and the carbon coating layer; And a fluorine-containing deposited film covering the surface of the carbon coating layer.

[0046] The nano-silicon-carbon material provided by this invention is achieved by constructing a SiO2-containing structure on the outside of a nano-silicon core. x The carbon coating layer of the nano-micro region introduces carbon nanofibers at the interface between the nano-silicon core and the carbon coating layer and inside the carbon coating layer, and coats the surface of the carbon coating layer with a fluorocarbonate layer, which effectively solves the problems of severe volume expansion, poor cycle stability and low initial coulombic efficiency of existing silicon-carbon materials.

[0047] The carbon coating can physically constrain the nano-silicon core, suppressing its volume expansion during charging and discharging; the SiO₂ dispersed in the carbon coating... x The nano-regions are tightly integrated with the carbon-coated matrix and the nano-silicon core. On the one hand, they further buffer volume changes; on the other hand, they actively capture free lithium generated during charging and discharging, participating in the formation of a stable SEI film, inhibiting repeated SEI film rupture and regeneration, and reducing irreversible lithium loss. Carbon nanofibers are distributed in two forms within the material: some are wound around the outer surface of the nano-silicon core, forming a flexible buffer layer between the silicon core and the carbon-coated layer, mitigating the impact of volume expansion on the carbon layer; the other part is dispersed and embedded within the carbon-coated layer, giving the carbon layer both rigid support and flexible buffering functions, while simultaneously enhancing the interfacial bonding between the silicon core and the carbon layer, preventing core-shell structure delamination during charging and discharging. Furthermore, the two types of carbon nanofibers together form a continuous conductive network within the material, improving electron conduction efficiency. The fluorocarbonate layer on the surface of the carbon-coated layer preferentially forms a uniform and stable fluorine-rich SEI film on the material surface before electrolyte decomposition, inhibiting direct contact between the electrolyte and active materials, reducing side reactions, and further improving the material's initial coulombic efficiency and cycle life. The synergistic effect of the above structures enables this nano-silicon-carbon material to possess both high structural stability and excellent electrochemical performance.

[0048] Furthermore, the nano-silicon core is formed by etching waste silicon micropowder with a weakly acidic solution, and the particle size of the nano-silicon core is 50nm~100nm.

[0049] The formation of nano-silicon cores by etching waste silicon micropowder with a weakly acidic solution not only significantly reduces raw material costs and realizes the resource utilization of industrial waste, but also allows the etching process to selectively target grain boundary defects in the waste silicon, causing the micropowder to break down into monodisperse nano-silicon particles in situ. This avoids the particle size inconsistencies and agglomeration problems associated with conventional ball milling processes. Controlling the particle size to 50nm~100nm effectively mitigates the volume expansion effect during lithium insertion / extraction and facilitates the uniform composite of subsequent carbon coating layers and carbon nanofibers, improving the structural integrity and cycle stability of the material.

[0050] In this invention, the waste silicon powder is selected from at least one of photovoltaic cutting waste silicon powder or industrial silicon slag.

[0051] Furthermore, the SiO xThe size of the nanoscale regions is 2nm~5nm.

[0052] SiO x The size of the nano-regions is controlled within the range of 2nm to 5nm, avoiding localized stress concentration or carbon layer structure damage caused by excessively large micro-region sizes. Simultaneously, SiO₂ within this size range... x The nanoscale micro-regions have a high specific surface area and abundant active sites, which can efficiently capture free lithium generated during charging and discharging, participate in the formation of a uniform and stable SEI film, further suppress irreversible lithium loss, and improve the material's first coulombic efficiency and cycle stability.

[0053] Furthermore, the carbon nanofibers have a diameter of 10 nm to 20 nm and a length of 1 μm to 5 μm.

[0054] The carbon nanofibers are controlled in diameter (10 nm–20 nm) and length (1 μm–5 μm), giving them both a high specific surface area at the nanoscale and long-range bridging capability at the microscale. At this size, the fibers can tightly wrap around the surface of the silicon nanoparticles to form a flexible buffer layer, effectively absorbing volume change stress during charging and discharging. Simultaneously, the fiber length is greater than the silicon core particle size, enabling bridging and interconnection between multiple silicon particles. Together with the fiber segments embedded in the carbon coating layer, they construct a continuous cross-particle conductive network, reducing electrode internal resistance and improving electron conduction efficiency. Furthermore, the high aspect ratio of the fibers allows them to act as microfiber toughening agents within the carbon layer, enhancing the crack resistance of the carbon coating layer and preventing carbon layer fragmentation and failure during cycling.

[0055] Thirdly, the present invention also provides a negative electrode comprising the aforementioned nano-silicon-carbon material.

[0056] Specifically, the negative electrode includes a negative electrode active material, a conductive agent, a binder, and a current collector, wherein the negative electrode active material comprises the nano-silicon-carbon material described in the first aspect of the present invention, or the nano-silicon-carbon material prepared by the preparation method described in the second aspect of the present invention.

[0057] The conductive agent can be one or more conventional conductive agents in the art, such as Super P, acetylene black, Ketjen black, carbon nanotubes, and graphene. The binder can be one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA). The current collector is typically copper foil, preferably with a thickness of 6-15 μm.

[0058] The negative electrode can be prepared using a conventional slurry coating process in the art: the nano-silicon carbon material is mixed with a conductive agent and a binder, and a solvent is added and stirred to form a uniform slurry; the slurry is coated on the surface of a copper foil current collector, and after vacuum drying to remove the solvent, it is rolled and cut to obtain the negative electrode sheet.

[0059] Specifically, the solvent is N-methylpyrrolidone.

[0060] Fourthly, the present invention provides the application of the above-mentioned nano-silicon-carbon material or the aforementioned negative electrode in the preparation of lithium-ion batteries.

[0061] Fifthly, the present invention also provides a lithium-ion battery comprising the above-mentioned nano-silicon-carbon material or the above-mentioned negative electrode.

[0062] Specifically, the lithium-ion battery includes a positive electrode, a negative electrode, a separator, an electrolyte, and a casing, wherein the negative electrode is the negative electrode containing nano-silicon-carbon material as described in this invention. The positive electrode can be a conventional lithium-ion battery positive electrode material in the art, such as lithium iron phosphate, lithium nickel cobalt manganese oxide ternary materials, lithium cobalt oxide, or lithium manganese oxide. The electrolyte can be a carbonate electrolyte containing LiPF6, and the separator can be a polypropylene or polyethylene porous membrane.

[0063] The lithium-ion battery using the nano-silicon-carbon material of this invention exhibits excellent cycle stability and high initial coulombic efficiency, characterized by high electrode structure integrity, stable SEI film, and low irreversible lithium loss during cycling. Furthermore, since the core anode material uses waste silicon micropowder as the silicon source, the overall manufacturing cost is significantly reduced, making it a promising candidate for applications in power batteries, energy storage batteries, and consumer electronics batteries.

[0064] In a sixth aspect, the present invention also provides a battery module including the lithium-ion battery described above.

[0065] In summary, this invention uses industrial waste silicon micropowder as the silicon source, and obtains monodisperse nano-silicon cores through weakly acidic selective etching. These cores are then composited with flexible carbon nanofibers, causing the fibers to entangle and adsorb onto the surface of the silicon cores to form a first-layer buffer. Precursor particles are then prepared by mixing these particles with a glucose-biomass coke mixed carbon source and a tetraethyl orthosilicate organosilicon precursor. Finally, low-temperature transient carbonization is used to generate SiO2-containing particles in situ. x After carbonization of the carbon-coated nano-regions, fluorocarbonate solvent vapor is directly introduced to deposit an SEI precursor film in situ on the material surface, ultimately yielding a nano-silicon-carbon anode material. This invention achieves high-value utilization of industrial solid waste through in-situ etching technology, significantly reducing silicon source costs. Simultaneously, a multi-level stress buffer system is constructed through the two-level distribution of carbon nanofibers on the silicon core surface and within the carbon layer. In-situ reaction of tetraethyl orthosilicate generates SiO₂ that forms chemical bonds with both the nano-silicon core and the carbon coating layer. xNano-rivets significantly enhance the stability of the carbon layer structure and the lithium-locking capability of the material. A transient carbonization process replaces the traditional long-term high-temperature carbonization, greatly reducing production energy consumption and effectively suppressing the oxidation and grain growth of nano-silicon. Combined with in-situ SEI precursor film deposition technology, side reactions between the electrolyte and active materials are reduced, solving the technical challenges of severe volume expansion, short cycle life, and low initial coulombic efficiency in silicon-based anode materials. This preparation method is simple and controllable, requires no complex equipment, and is suitable for continuous large-scale production. The resulting nano-silicon-carbon material can be widely used in high-energy-density lithium-ion batteries for new energy vehicles, large-scale energy storage, and other fields, showing promising prospects for industrial application. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0067] To better illustrate the present invention, further examples are provided below.

[0068] Example 1 This embodiment provides a method for preparing nano-silicon carbon materials, including the following steps: S1. Take 100g of photovoltaic cutting waste silicon micro powder (particle size 1~5μm), add it to 500mL of 7% citric acid-oxalic acid mixed aqueous solution (citric acid to oxalic acid mass ratio 2:1), stir and etch for 40min at 40℃ and 200r / min, filter, wash with deionized water until neutral, and dry at 80℃ and -0.08MPa for 3h to obtain monodisperse nano silicon with a particle size of 50~100nm; S2, take 1.2g of flexible carbon nanofibers (diameter 10~20nm, length 1~5μm) prepared by straw pyrolysis, add to 200mL of deionized water, ultrasonically disperse at 250W for 25min, add the monodisperse nano-silicon prepared above, stir at 45℃ and 200r / min for 1.5h, filter, vacuum dry at 80℃ for 2.5h to obtain composite particles; S3, take 100g of the above-prepared composite particles, 55g of glucose-biomass coke mixture with a mass ratio of 1:1, and 7g of tetraethyl orthosilicate, add them to 320mL of deionized water, stir at 1200r / min for 1.5h, spray dry, with inlet air temperature of 190℃, outlet air temperature of 90℃, and feed rate of 12L / min to obtain precursor particles. S4. The above precursor particles are fed into a transient flash carbonization furnace, nitrogen is introduced to replace the air in the furnace, and then the temperature is raised to 700℃ within 10s, held for 15s, and naturally cooled to 160℃. A mixed gas of 5% trifluoromethyl ethylene carbonate and nitrogen is introduced at a flow rate of 40L / min for 45min. After cooling to room temperature, the mixture is pulverized through a 250-mesh sieve to obtain nano-silicon carbon material.

[0069] Example 2 This embodiment provides a method for preparing nano-silicon carbon materials, including the following steps: S1. Take 100g of photovoltaic cutting waste silicon micro powder (particle size 1~5μm), add it to 300mL of 10% citric acid-oxalic acid mixed aqueous solution (citric acid to oxalic acid mass ratio 3:1), stir and etch for 30min at 45℃ and 200r / min, filter, wash with deionized water until neutral, and dry at 80℃ and -0.08MPa for 4h to obtain monodisperse nano silicon with a particle size of 50~100nm; S2, take 1.0g of flexible carbon nanofibers (diameter 10~20nm, length 1~5μm) prepared by straw pyrolysis, add to 190mL of deionized water, ultrasonically disperse at 250W for 20min, add the monodisperse nano-silicon prepared above, stir at 45℃ and 200r / min for 1h, filter, vacuum dry at 80℃ for 2.5h to obtain composite particles; S3, take 100g of the composite particles prepared above, 30g of glucose-biomass coke mixture with a mass ratio of 1:1.3, and 5g of tetraethyl orthosilicate, add them to 300mL of deionized water, stir at 1200r / min for 2h, spray dry, with inlet air temperature of 180℃, outlet air temperature of 80℃, and feed rate of 12L / min to obtain precursor particles. S4. The above precursor particles are fed into a transient flash carbonization furnace, nitrogen is introduced to replace the air in the furnace, and then the temperature is raised to 800°C within 10 seconds, held for 5 seconds, and then naturally cooled to 200°C. A mixed gas of 5% trifluoromethyl ethylene carbonate and nitrogen is introduced at a flow rate of 60 L / min for 30 minutes. After cooling to room temperature, the mixture is pulverized through a 250-mesh sieve to obtain nano-silicon carbon material.

[0070] Example 3 This embodiment provides a method for preparing nano-silicon carbon materials, including the following steps: S1. Take 100g of photovoltaic cutting waste silicon micro powder (particle size 1~5μm), add it to 800mL of 5% (mass concentration) mixed aqueous solution of citric acid and oxalic acid (mass ratio of citric acid to oxalic acid 2.5:1), stir and etch for 60min at 60℃ and 200r / min, filter, wash with deionized water until neutral, and dry at 100℃ and -0.08MPa for 2h to obtain monodisperse nano-silicon with a particle size of 50~100nm; S2, take 1.5g of flexible carbon nanofibers (diameter 10~20nm, length 1~5μm) prepared by straw pyrolysis, add to 200mL of deionized water, ultrasonically disperse at 250W for 25min, add the monodisperse nano-silicon prepared above, stir at 45℃ and 200r / min for 2h, filter, vacuum dry at 80℃ for 2.5h to obtain composite particles; S3, take 100g of the composite particles prepared above, 70g of glucose-biomass coke mixture with a mass ratio of 1:1.5, and 8g of tetraethyl orthosilicate, add them to 150mL of deionized water, stir at 1200r / min for 3h, spray dry, with inlet air temperature of 200℃, outlet air temperature of 100℃, and feed rate of 12L / min to obtain precursor particles; S4. The above precursor particles are fed into a transient flash carbonization furnace, nitrogen is introduced to replace the air in the furnace, and then the temperature is raised to 500℃ within 10s, held for 15s, and naturally cooled to 160℃. A mixed gas of 5% trifluoromethyl ethylene carbonate and nitrogen is introduced at a flow rate of 50L / min for 50min. After cooling to room temperature, the mixture is pulverized through a 250-mesh sieve to obtain nano-silicon carbon material.

[0071] Example 4 This embodiment provides a method for preparing nano-silicon carbon materials, including the following steps: S1. Take 100g of photovoltaic cutting waste silicon micro powder (particle size 1~5μm), add it to 600mL of 6% (mass concentration) mixed aqueous solution of citric acid and oxalic acid (mass ratio of citric acid to oxalic acid 3:1), stir and etch for 50min at 50℃ and 200r / min, filter, wash with deionized water until neutral, and dry at 90℃ and -0.08MPa for 2h to obtain monodisperse nano-silicon with a particle size of 50~100nm; S2, take 2.0g of flexible carbon nanofibers (diameter 10~20nm, length 1~5μm) prepared by straw pyrolysis, add to 200mL of deionized water, ultrasonically disperse at 250W for 30min, add the monodisperse nano-silicon prepared above, stir at 45℃ and 200r / min for 2h, filter, vacuum dry at 80℃ for 2.5h to obtain composite particles; S3, take 100g of the above-prepared composite particles, 80g of glucose-biomass coke mixture with a mass ratio of 1:0.5, and 10g of tetraethyl orthosilicate, add them to 500mL of deionized water, stir at 1200r / min for 1h, spray dry, with an inlet air temperature of 190℃, an outlet air temperature of 90℃, and a feed rate of 12L / min to obtain precursor particles; S4. The above precursor particles are fed into a transient flash carbonization furnace, nitrogen is introduced to replace the air in the furnace, and then the temperature is raised to 400°C within 8 seconds, held for 20 seconds, and then naturally cooled to 150°C. A mixed gas of 10% trifluoromethyl ethylene carbonate and nitrogen is introduced at a flow rate of 80 L / min for 60 min. After cooling to room temperature, the mixture is pulverized through a 250-mesh sieve to obtain nano-silicon carbon material.

[0072] Comparative Example 1 This comparative example provides a method for preparing nano-silicon-carbon materials. The only difference from Example 1 is the use of commercially available nano-silicon and a traditional high-temperature carbonization process. The remaining steps are exactly the same, and the specific steps are as follows: S1, take 100g of commercial nano-silicon (particle size 50~100nm) and 4g of dispersant (40% solid content, mass ratio 1:1 BYK-190 and PEG4000), add to 200mL of water, and ultrasonically disperse at 250W for 30min to obtain nano-silicon dispersion. S2~S3, same as in Example 1; S4. The precursor particles are fed into a high-temperature carbonization furnace, nitrogen is introduced to replace the air in the furnace, and then the temperature is raised to 800°C at a rate of 5°C / min, held for 30 min, and then naturally cooled to room temperature. The particles are then pulverized through a 250-mesh sieve to obtain nano-silicon-carbon materials.

[0073] The nano-silicon-carbon material obtained in S4 was used as the electrode active material, and the battery was assembled according to the same coin cell manufacturing process as in the example. Fluorinated ethylene carbonate (FEC) was added to the electrolyte as a fluorinated additive at a concentration of 5% of the total electrolyte mass. After coin cell assembly, the cells were allowed to stand at 25°C for 12 hours to activate, allowing the fluorinated additive to decompose on the electrode surface during the first charge-discharge process to form an SEI film.

[0074] Comparative Example 2 This comparative example provides a method for preparing nano-silicon-carbon materials. The only difference from Example 1 is that the waste silicon powder is treated by a traditional ball milling method and a traditional low-temperature carbonization process is used. The other steps are exactly the same, and the specific steps are as follows: S1, take 100g of photovoltaic cutting waste silicon micro powder and 3g of dispersant (40% solid content, mass ratio of BYK-190 and PEG4000 1:1), add to 200mL of water, mechanically grind at 300r / min for 60min, filter, and dry at 80℃ and -0.08MPa for 3h to obtain nano-silicon with a particle size of 100nm~150nm; S2~S3, same as in Example 1; S4. The above precursor particles are fed into a carbonization furnace, nitrogen is introduced to replace the air in the furnace, and then the temperature is raised to 600°C at a rate of 5°C / min and held for 20 min. The temperature is then naturally cooled to 160°C, and a mixed gas of 5% trifluoromethyl ethylene carbonate and nitrogen is introduced at a flow rate of 40 L / min for 45 min. The temperature is then cooled to room temperature, pulverized and passed through a 250-mesh sieve to obtain nano-silicon carbon material.

[0075] Comparative Example 3 This comparative example provides a method for preparing nano-silicon-carbon materials, which differs from Example 1 only in that step S2 is omitted. The specific steps are as follows: S1. Take 100g of photovoltaic cutting waste silicon micro powder (particle size 1~5μm), add it to 500mL of 7% citric acid-oxalic acid mixed aqueous solution (citric acid to oxalic acid mass ratio 2:1), stir and etch for 40min at 40℃ and 200r / min, filter, wash with deionized water until neutral, and dry at 80℃ and -0.08MPa for 3h to obtain monodisperse nano silicon with a particle size of 50~100nm; S2, take 100g of the monodisperse nano-silicon prepared above, 55g of glucose-biomass coke mixture with a mass ratio of 1:1, and 7g of tetraethyl orthosilicate, add them to 320mL of deionized water, stir at 1200r / min for 1.5h, spray dry, with inlet air temperature of 190℃, outlet air temperature of 90℃, and feed rate of 12L / min to obtain precursor particles; S3. The above precursor particles are fed into a transient flash carbonization furnace, nitrogen is introduced to replace the air in the furnace, and then the temperature is raised to 700℃ within 10s, held for 15s, and naturally cooled to 160℃. A mixed gas of 5% trifluoromethyl ethylene carbonate and nitrogen is introduced at a flow rate of 40L / min for 45min. After cooling to room temperature, the mixture is pulverized through a 250-mesh sieve to obtain nano-silicon carbon material.

[0076] Comparative Example 4 This comparative example provides a method for preparing nano-silicon-carbon materials. The only difference from Example 1 is that tetraethyl orthosilicate is not added in S3, but nano-SiO2 powder (particle size 20~50nm) is added after carbonization in S4. The specific steps are as follows: S1~S2, same as in Example 1; S3, take 100g of the above-prepared composite particles and 55g of glucose-biomass char mixture with a mass ratio of 1:1, add them to 320mL of deionized water, stir at 1200r / min for 1.5h, spray dry, with inlet air temperature of 190℃, outlet air temperature of 90℃, and feed rate of 12L / min to obtain precursor particles. S4. The above precursor particles are fed into a transient flash carbonization furnace, nitrogen is introduced to replace the air in the furnace, and then the temperature is raised to 700℃ within 10s, held for 15s, and naturally cooled to room temperature. The particles are then removed, 5g of nano-SiO2 powder is added, and the mixture is stirred and mixed at 1500r / min for 30min. The mixture is then placed in a tube furnace, heated to 160℃, and a mixed gas of 5% trifluoromethyl ethylene carbonate and nitrogen is introduced at a flow rate of 40L / min for 45min. The mixture is then cooled to room temperature, pulverized through a 250-mesh sieve, and nano-silicon carbon material is obtained.

[0077] Comparative Example 5 This comparative example provides a method for preparing nano-silicon-carbon materials. The only difference from Example 1 is that the vapor deposition step in step S4 is replaced by a conventional SEI film modification method. The specific steps are as follows: S1~S3, same as in Example 1; S4. The above precursor particles are fed into a transient flash carbonization furnace, nitrogen is introduced to replace the air in the furnace, and then the temperature is raised to 700°C within 10 seconds, held for 15 seconds, and naturally cooled to room temperature. The particles are then removed, soaked in a fluorine-containing electrolyte, soaked at room temperature for 30 minutes, vacuum dried, and pulverized through a 250-mesh sieve to obtain nano-silicon-carbon materials.

[0078] The specific composition of the fluorinated electrolyte is as follows: 1 mol / L LiPF6 dissolved in a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1:1), and 5% fluoroethylene carbonate (FEC) is added.

[0079] Application Examples The electrochemical and physical properties of the nano-silicon carbon materials obtained in the examples and comparative examples were tested according to the following standards and methods: (1) Preparation of button cells Nano-silicon carbon material was used as the sole negative electrode active material. The negative electrode active material was mixed with conductive agent Super P, binder sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) at a mass ratio of 70:20:5:5. Deionized water was used as the solvent to form a uniform slurry, which was then coated onto the surface of a copper foil current collector, achieving a coating density of 1.2 mg / cm³. 2 The electrode was vacuum dried at 80℃ for 12 hours, then rolled and cut into 14mm diameter pieces to serve as working electrodes.

[0080] CR2032 coin cells were assembled in an Ar-filled glove box using lithium metal sheets as the counter electrode and Celgard 2500 as the separator. The electrolyte was a 1 mol / L LiPF6 solution dissolved in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (volume ratio 1:1:1). 40 μL of electrolyte was injected into each cell. The CR2032 coin cells were assembled in an argon-filled glove box with water and oxygen content both below 0.1 ppm. Electrochemical performance was tested after standing for 12 hours.

[0081] 1.2 Electrochemical performance testing Specific capacity and initial coulombic efficiency testing: Based on the standards "Specific Capacity Test Method for Anode Materials of Lithium-ion Batteries" (GB / T 33821-2017) and "Coulombic Efficiency Test Method for Electrode Materials of Lithium-ion Batteries" (GB / T 38812-2020), the Blue Battery testing system was used, with a charge / discharge voltage range of 0.01V~2.0V. First, the battery was discharged at a constant current rate of 0.1C to 0.01V, then charged at a constant current rate of 0.1C to 2.0V, and finally charged at a constant voltage until the current was less than 0.02C. The initial discharge capacity and initial charge capacity were recorded, and the initial coulombic efficiency was calculated. Three batteries were tested in parallel for each sample, and the average value was taken as the test result.

[0082] Initial coulombic efficiency = (Initial charge capacity / Initial discharge capacity) × 100% Cyclic performance testing: According to the "Test Method for Cycle Life of Lithium-ion Batteries" (GB / T 31484-2015), within the above-mentioned charge and discharge voltage range, the batteries were first activated by charging and discharging twice at a rate of 0.1C, followed by constant current charge and discharge cycles at a rate of 0.5C. The discharge capacity of the 200th cycle was recorded, and the capacity retention rate after 200 cycles was calculated. Three batteries were tested in parallel for each sample, and the average value was taken as the test result.

[0083] 200-cycle capacity retention = (200th discharge capacity / First discharge capacity) × 100% 1.3 Volumetric expansion rate test According to the "Test Method for Volume Expansion Rate of Lithium-ion Battery Electrode Materials" (QB / T 5581-2021), the cross-sectional thickness of the negative electrode sheet was measured using a scanning electron microscope (SEM) before cycling and after 100 cycles at a 0.5C rate. Five different points were selected for testing each electrode sheet, and the average value was used to calculate the volume expansion rate. Volumetric expansion rate (%) = (Average thickness after cycling - Average thickness before cycling) / Average thickness before cycling × 100% The results are shown in Table 1.

[0084] Table 1

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing nano-silicon-carbon materials, characterized in that, Includes the following steps: S1, add waste silicon powder to a weakly acidic solution for etching to obtain etched waste silicon powder; S2, disperse carbon nanofibers in water to obtain carbon nanofiber dispersion; add the etched waste silicon powder to the carbon nanofiber dispersion, stir and mix, so that the carbon nanofibers are adsorbed on the surface of the etched waste silicon powder to obtain composite particles. S3, mix the composite particles, carbon source, organosilicon crosslinking precursor and water evenly, and dry to obtain precursor particles; S4. Under an inert atmosphere, the precursor particles are transiently carbonized. After carbonization, fluorocarbonate vapor is introduced into the furnace to deposit an SEI precursor film on the material surface in situ, thus obtaining nano-silicon-carbon material.

2. The method for preparing nano-silicon-carbon materials as described in claim 1, characterized in that, In S1, the particle size of the waste silicon powder is 1μm~5μm; and / or In S1, the weakly acidic solution is a mixed aqueous solution of citric acid and oxalic acid in a mass ratio of 2:1 to 3:1, and the total mass concentration of citric acid and oxalic acid in the weakly acidic solution is 5% to 10%; and / or In S1, the mass-to-volume ratio of the waste silica powder to the weakly acidic solution is 1 g: (3~8) mL; and / or In S1, the etching temperature is 40℃~60℃, and the etching time is 30min~60min; and / or In S1, the particle size of the etched waste silicon powder is 50nm~100nm.

3. The method for preparing nano-silicon-carbon materials as described in claim 1, characterized in that, In S2, the carbon nanofibers are biomass flexible carbon nanofibers with a diameter of 10nm~20nm and a length of 1μm~5μm; and / or In S2, the mass concentration of the carbon nanofiber dispersion is 0.5%~1%; and / or In S2, the mass ratio of the etched waste silicon micropowder to carbon nanofibers is 100:(1~2); and / or In S2, the stirring and mixing time is 1h to 2h.

4. The method for preparing nano-silicon-carbon materials as described in claim 1, characterized in that, In S3, the carbon source is a mixture of glucose and biochar at a mass ratio of 1:(0.5~1.5); and / or In S3, the organosilicon crosslinking precursor is tetraethyl orthosilicate; and / or In S3, the mass ratio of the composite particles to the carbon source is 100:(30~80); and / or In S3, the amount of the organosilicon crosslinking precursor added is 5% to 10% of the mass of the composite particles; and / or In S3, the mass-volume ratio of the composite particles to water is 1 g: (100~500) mL.

5. The method for preparing nano-silicon-carbon materials as described in claim 1, characterized in that, In S4, the transient carbonization temperature is 400℃~800℃, and the holding time is 5s~20s; and / or In S4, the fluorocarbonate compound is trifluoromethyl ethylene carbonate; and / or In S4, the temperature for in-situ deposition of the SEI precursor film is 150℃~200℃, and the deposition time is 30min~60min.

6. A nano-silicon-carbon material, characterized in that, It is prepared by the method for preparing nano-silicon-carbon materials according to any one of claims 1 to 5.

7. A negative electrode, characterized in that, Including the nano-silicon-carbon material as described in claim 6.

8. The application of the nano-silicon-carbon material of claim 6 or the negative electrode of claim 7 in the preparation of lithium-ion batteries.

9. A lithium-ion battery, characterized in that, It includes the nano-silicon-carbon material as described in claim 6 or the negative electrode as described in claim 7.

10. A battery module, characterized in that, Including the lithium-ion battery as described in claim 9.

Images