Silicon-carbon composite material, preparation method and application thereof

Abstract

This invention provides a silicon-carbon composite material, its preparation method, and its application. The preparation method includes: mixing amino-modified silicon nanowires, sulfonic acid-modified support materials, and a solvent; filtering and drying the mixture through a carbon-based filter membrane to form a loaded layer containing silicon nanowires and support materials, thus obtaining a first composite filter membrane; depositing a carbon source layer on the surface of the loaded layer to obtain a second composite filter membrane; and bonding, compacting, sintering, crushing, and carbon-coating the second and first composite filter membranes to obtain the silicon-carbon composite material. The preparation method of this invention first forms a composite intertwined silicon nanowire / carbon composite material, then passes it through a carbon-based filter membrane, coats it with a carbon source, stacks it, compacts it, and sinters to obtain a layered composite material. Finally, after crushing and re-carbon coating, the resulting silicon-carbon anode material exhibits low volume expansion, high conductivity, high stability, and high overall energy density during charge and discharge processes.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a silicon-carbon composite material, its preparation method, and its application. Background Technology

[0002] The rapid development of electric vehicles and energy storage devices has promoted the widespread application of energy storage technologies such as lithium-ion batteries. Among various lithium-ion battery anode materials, graphite currently dominates the market. However, the theoretical capacity of graphite in lithium-ion batteries is only 372 mAh / g, which can no longer meet the current market demand for high energy density. Therefore, silicon materials with higher theoretical capacity have attracted widespread attention. Silicon-based anodes have advantages such as high energy density, wide distribution of raw materials, and a suitable discharge platform. Moreover, the theoretical specific capacity of elemental silicon anodes is 4200 mAh / g, which is 10 times that of graphite anodes.

[0003] However, during battery charging and lithium intercalation, silicon readily undergoes an alloying reaction with lithium, leading to the loss of active lithium ions. Furthermore, during cycling, the silicon anode experiences significant volume changes, which can easily cause particle breakage, resulting in a significant decrease in product cycle performance. In existing technologies, silicon is typically coated with carbon materials to form silicon-carbon materials to suppress silicon expansion.

[0004] For example, CN 117894951A discloses a silicon-carbon anode material with high conductivity and its preparation method. The preparation method includes: mixing asphalt with porous hard carbon, carbonizing to prepare soft carbon-porous hard carbon powder, embedding silicon particles into porous carbon by vapor deposition, and finally coating the outer layer with another carbon layer to obtain the anode material. However, when depositing silicon particles in porous carbon, the deposition amount is not easy to control, and some silicon particles will not be embedded in porous carbon, which faces problems such as low initial efficiency and high operation difficulty.

[0005] CN 110459757A discloses a negative electrode material for lithium-ion batteries and its fabrication method. The preparation method includes: adding silicon particles to a Na2CO3 solution and stirring, then adding CaCl2 to obtain CaCO3-coated silicon particles, which are then mixed with a carbon source, spray-dried, sintered, and washed with hydrochloric acid to obtain a core-shell structured silicon-carbon negative electrode material. However, when using calcium carbonate for coating, the silicon particles tend to agglomerate, resulting in poor coating effect and affecting the subsequent carbon coating process. Furthermore, the large-scale use of hydrochloric acid and water causes environmental pollution and is environmentally unfriendly; residual calcium and chloride ions also affect battery performance.

[0006] Because silicon nanowires have a large aspect ratio, they can better mitigate lithium intercalation expansion and exhibit superior conductivity compared to silicon particles of the same diameter. Therefore, carbon-coated silicon nanowires can be used to form silicon-carbon anode materials. However, in existing coating methods, depositing silicon nanowires in porous carbon is difficult, as silicon nanowires are more likely to grow outside the pores, increasing the difficulty of subsequent coating. Using template methods to coat silicon nanowires results in poor coating effects due to the relatively long length of the silicon nanowires, and the large amounts of acid or water used also pollute the environment and increase costs. Direct vapor-phase coating, on the other hand, leads to uneven coating and poor uniformity because the silicon nanowires become entangled and aggregated. Summary of the Invention

[0007] The purpose of this invention is to provide a silicon-carbon composite material, its preparation method, and its application. The preparation method first forms a composite entangled silicon nanowire / carbon composite material by electrostatic adsorption, then coats it with a carbon source after passing it through a carbon-based filter membrane, and then stacks, compacts, and sintersperses the carbon source-coated carbon-based filter membrane loaded only with silicon nanowire / carbon composite material to obtain a stacked C / Si & C / C composite material. Finally, after crushing and re-carbon coating, the resulting silicon-carbon anode material exhibits low volume expansion, high conductivity, high stability, and high overall energy density during charge and discharge processes.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a silicon-carbon composite material, the method comprising the following steps:

[0010] (1) Mix amino-modified silicon nanowires, sulfonic acid-modified support material and solvent. After the mixture is filtered and dried by a carbon-based filter membrane, a load layer loaded with silicon nanowires and support material is formed on the surface of the carbon-based filter membrane to obtain the first composite filter membrane.

[0011] (2) A carbon source layer is provided on the surface of the load layer described in step (1) to obtain a second composite filter membrane. The second composite filter membrane and the first composite filter membrane in step (1) are bonded and compacted to obtain a pre-coated composite material.

[0012] After bonding, the side of the second composite filter membrane with the load material comes into contact with the side of the first composite filter membrane with the load material.

[0013] (3) The pre-coated composite material described in step (2) is subjected to sintering, crushing and carbon coating treatment in sequence to obtain the silicon-carbon composite material.

[0014] In step (1) of this invention, the silicon nanowires are modified to carry a positive charge on their surface, effectively preventing them from agglomerating in water, which is beneficial for subsequent processing. Furthermore, the silicon nanowires are electrostatically attracted to the negatively charged sulfonic acid-modified support material to form an entangled Si&C composite material, enhancing the conductivity of the silicon nanowires and mitigating their expansion. After filtration and drying through a carbon-based filter membrane, the Si&C composite material is loaded onto the surface of the membrane to form a load layer. A carbon source layer is then placed on the surface of the load layer, filling the gaps between the silicon nanowires and the support material, thus forming a layered structure. The silicon nanowires are then bonded, compacted, and sintered with another first composite filter membrane to form a layered C / Si & C / C structure (specifically, carbon layer-silicon nanowires, carbon-carbon layer-silicon nanowires, and carbon-carbon layer structures). This effectively alleviates the expansion of silicon nanowires during lithium intercalation. Simultaneously, this structure results in a more uniform distribution of silicon nanowires, smaller differences in specific capacity among the broken particles, and higher uniformity. Finally, the invention also incorporates a carbon coating process to further improve the carbon coating rate, re-coating the broken and exposed silicon nanowires. This prevents direct contact between the silicon nanowires and the electrolyte, reduces electrolyte consumption, improves initial efficiency, and lowers subsequent costs.

[0015] Preferably, the mass ratio of the amino-modified silicon nanowires to the sulfonic acid-modified support material in step (1) is (1-10):1, for example, it can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] The present invention preferably uses an amino-modified silicon nanowire to a sulfonic acid-modified support material with a mass ratio within a specific range, which can further improve the stability of the network structure formed by the silicon nanowire and the support material, increase the material capacity, and further alleviate the expansion of the silicon nanowire.

[0017] Preferably, the mass ratio of the sulfonic acid-modified support material to the solvent in step (1) is 1:(50-100), for example, it can be 1:50, 1:60, 1:70, 1:80, 1:90 or 1:100, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, the solvent in step (1) includes deionized water.

[0019] Preferably, in step (1), the total mass of amino-modified silicon nanowires and sulfonic acid-modified support material per square centimeter on the surface of the carbon-based filter membrane is 0.01-0.95g, for example, it can be 0.01g, 0.05g, 0.15g, 0.25g, 0.35g, 0.45g, 0.55g, 0.65g, 0.75g, 0.85g or 0.95g, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] The loading amount of the surface loading layer of the carbon-based filter membrane of the present invention also affects the content of silicon nanowires and carbon in the overall silicon-carbon composite material. Therefore, the silicon nanowires and support materials of the present invention are preferably loaded with a specific amount on the carbon-based filter membrane.

[0021] Preferably, the carbon-based filter membrane in step (1) includes a biomass filter membrane.

[0022] Preferably, the thickness of the carbon-based filter membrane in step (1) is 0.01-0.1 mm, for example, it can be 0.01 mm, 0.03 mm, 0.05 mm, 0.07 mm or 0.1 mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the mixing time of the amino-modified silicon nanowires, sulfonic acid-modified support material and solvent in step (1) is 6-12 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the method for preparing the amino-modified silicon nanowires in step (1) includes: mixing the silicon nanowires with an aqueous solution of an ammonium salt-type cationic surfactant, allowing them to stand, washing, and drying.

[0025] Preferably, the length of the silicon nanowire is 1-20 μm, for example, it can be 1 μm, 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm or 20 μm, and the diameter is 50-300 nm, for example, it can be 50 nm, 100 nm, 150 nm, 200 nm, 250 nm or 300 nm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0026] Preferably, the solute content in the aqueous solution of the ammonium salt cationic surfactant is 5-20 wt%, for example, it can be 5 wt%, 10 wt%, 15 wt% or 20 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the aqueous solution of the ammonium salt cationic surfactant includes any one or a combination of at least two of dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, polydienedimethylammonium chloride, or dioctadecyldimethylammonium chloride.

[0028] Preferably, the mass ratio of the silicon nanowires to the aqueous solution of the ammonium salt cationic surfactant is (1-10):100, for example, it can be 1:100, 3:100, 5:100, 7:100, 9:100 or 10:100, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the method of mixing the silicon nanowires with the aqueous solution of the ammonium salt cationic surfactant includes ultrasonic treatment.

[0030] Preferably, after mixing the silicon nanowires with the aqueous solution of the ammonium salt cationic surfactant, the temperature for standing is 20-30°C, for example, 20°C, 25°C or 30°C, and the time is 11-13h, for example, 11h, 12h or 13h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, after mixing and allowing the silicon nanowires to stand with an aqueous solution of an ammonium salt-type cationic surfactant, the mixture is washed with deionized water 1-3 times, for example, once, twice or three times, and then dried at 60-80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C for 5-10 hours, for example, 5 hours, 7 hours, 9 hours or 10 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the method for preparing the sulfonic acid-modified support material in step (1) includes: mixing the support material with an aqueous solution of a sulfonic acid-type anionic surfactant, allowing it to stand, washing, and drying.

[0033] Preferably, the support material includes carbon support material and / or metal support material.

[0034] Preferably, the carbon support material includes any one or a combination of at least two of carbon nanotubes, carbon nanofibers, or graphene.

[0035] Preferably, the metal support material includes copper nanowires and / or silver nanowires.

[0036] Preferably, the solute content in the aqueous solution of the sulfonic acid anionic surfactant is 5-20 wt%, for example, it can be 5 wt%, 10 wt%, 15 wt% or 20 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the aqueous solution of the sulfonic acid anionic surfactant includes any one or a combination of at least two of sodium undecylbenzenesulfonate, sodium dodecylbenzenesulfonate, or sodium dodecylbenzenesulfonate.

[0038] Preferably, the mass ratio of the supporting material to the aqueous solution of the sulfonic acid anionic surfactant is (1-10):100, for example, it can be 1:50, 1:60, 1:70, 1:80, 1:90 or 1:100, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the method of mixing the support material with the aqueous solution of the sulfonic acid anionic surfactant includes ultrasonic treatment.

[0040] Preferably, after mixing the support material with the aqueous solution of sulfonic acid anionic surfactant, the standing temperature is 20-30°C, for example, 20°C, 25°C or 30°C, and the time is 11-13h, for example, 11h, 12h or 13h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] Preferably, after mixing and allowing the support material to stand with an aqueous solution of sulfonic acid-type anionic surfactant, it is washed with deionized water 1-3 times, for example, once, twice or three times, and then dried at 60-80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C for 5-10 hours, for example, 5 hours, 7 hours, 9 hours or 10 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, in step (2), the mass of the carbon source layer in the second composite filter membrane is 1-5 times the mass of the amino-modified silicon nanowires, for example, it can be 1, 2, 3, 4 or 5 times, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the method of setting the carbon source layer in step (2) includes any one or a combination of at least two of coating, adsorption, compaction or bonding.

[0044] Preferably, the carbon source layer in step (2) includes any one or a combination of at least two of glucose, chitosan, gelatin, asphalt, tannic acid or citric acid.

[0045] Preferably, the compaction method in step (2) includes roller compaction and / or flat compaction.

[0046] Preferably, the compaction pressure in step (2) is 1-10 MPa, for example, it can be 1 MPa, 3 MPa, 5 MPa, 7 MPa, 9 MPa or 10 MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, the heating rate of the sintering in step (3) is 5-10℃ / min, for example, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, the holding temperature is 800-1000℃, for example, 800℃, 900℃ or 1000℃, and the holding time is 6-12h, for example, 6h, 8h, 10h or 12h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] Preferably, the sintering atmosphere in step (3) includes an inert gas.

[0049] Preferably, the carbon coating method in step (3) includes gas phase carbon coating.

[0050] Preferably, the gaseous carbon coating is heated at a rate of 5-10℃ / min, for example, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, to 600-800℃, for example, 600℃, 700℃ or 800℃, and a gaseous carbon source is introduced and kept at that temperature for 1-3 hours, for example, 1 hour, 2 hours or 3 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] Preferably, the gaseous carbon source includes methane or acetylene.

[0052] In a second aspect, the present invention provides a silicon-carbon composite material, which is prepared by the preparation method described in the first aspect.

[0053] Thirdly, the present invention provides a lithium-ion battery comprising the silicon-carbon composite material as described in the second aspect.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] The modified silicon nanowires and supporting materials of this invention form a relatively stable structure through electrostatic attraction, which can alleviate carbon layer cracking and enhance the conductivity of silicon nanowires. At the same time, by preparing a C / Si & C / C stacked structure, compared with a disordered structure, this invention can effectively alleviate the volume expansion of silicon nanowires during charge and discharge, improve conductivity, enhance cycle stability, improve thermal stability and mechanical strength. Furthermore, the silicon nanowires are more uniformly distributed in the carbon layer, and the uniformity of each particle is better, which improves the overall energy density of the material. Attached Figure Description

[0056] Figure 1 This is a flowchart of the preparation method described in Example 1 of the present invention;

[0057] Figure 2 The image shown is an electron microscope image of the silicon-carbon composite material obtained by the preparation method described in Example 3 of this invention.

[0058] Figure 3 The image shown is an electron microscope image of the silicon-carbon composite material obtained by the preparation method described in Comparative Example 1 of this invention. Detailed Implementation

[0059] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0060] Example 1

[0061] This embodiment provides a method for preparing silicon-carbon composite materials, the flowchart of which is shown below. Figure 1 As shown, the preparation method includes the following steps:

[0062] (1) 10g of silicon nanowires were dispersed in 200mL of an aqueous solution containing 10wt% hexadecyltrimethylammonium chloride. After sonication for 30min, the solution was allowed to stand at 25℃ for 12h. Then, the solution was washed and filtered three times with deionized water and dried under vacuum at 80℃ for 8h to obtain amino-modified silicon nanowires. The length of the silicon nanowires was 10μm and the diameter was 150nm. The mass ratio of the silicon nanowires to the aqueous solution of the ammonium salt cationic surfactant was 5:100.

[0063] 10g of carbon nanofiber powder was dispersed in 200mL of an aqueous solution containing 10% sodium dodecylbenzenesulfonate, sonicated for 30min, and allowed to stand at 25℃ for 12h. After washing and filtering with deionized water three times, the nanofiber was dried under vacuum at 80℃ for 8h to obtain sulfonic acid modified carbon nanofiber.

[0064] (2) Disperse 0.5g of amino-modified silicon nanowires and 0.1g of sulfonic acid-modified carbon nanofibers in 50mL of deionized water, wherein the mass ratio of amino-modified silicon nanowires to sulfonic acid-modified carbon nanofibers is 5:1. Stir for 6h, filter through a biomass filter membrane, and dry at 80℃ for 8h for later use to obtain a biomass filter membrane loaded with Si / C composite.

[0065] The biomass filter membrane has a thickness of 0.1 mm and a total mass of the load per square centimeter on the surface of the biomass filter membrane is 0.25 g.

[0066] (3) After melting 3g of glucose, coat it onto the surface of the Si / C composite loaded on the biomass filter membrane described in step (2), and attach it to another biomass filter membrane loaded with Si / C composite in step (2) (the loaded Si / C composite faces the carbon layer after glucose coating). Compact it with a roller at a pressure of 5MPa to obtain the pre-coated silicon-carbon material.

[0067] (4) The pre-coated silicon-carbon material described in step (3) is placed in a sintering furnace and heated to 800°C at a heating rate of 5°C / min under argon protection. The temperature is then maintained for 8 hours, cooled, ground, and crushed to obtain a one-time coated silicon-carbon anode material.

[0068] (5) The silicon-carbon anode material coated in step (4) is placed in a gas phase coating furnace and heated to 700°C at a heating rate of 5°C / min under argon protection. Acetylene is introduced and kept at the temperature for 2 hours. After cooling, the silicon-carbon composite material with a sandwich structure is obtained.

[0069] Example 2

[0070] This embodiment provides a method for preparing a silicon-carbon composite material. The preparation method is the same as in Example 1, except that 1g of amino-modified silicon nanowires and 0.1g of sulfonic acid-modified carbon nanofibers described in step (1) are dispersed in 50mL of deionized water, and 3g of chitosan is melted and coated in step (3).

[0071] In this embodiment, the mass ratio of amino-modified silicon nanowires to sulfonic acid-modified carbon nanofibers in step (2) is 10:1, and the total mass of the load per square centimeter on the surface of the biomass filter membrane is 0.35g.

[0072] Example 3

[0073] This embodiment provides a method for preparing a silicon-carbon composite material. The preparation method is the same as in Example 1, except that 1g of amino-modified silicon nanowires and 0.5g of sulfonic acid-modified carbon nanofibers described in step (1) are dispersed in 50mL of deionized water, and 3g of gelatin is melted and coated in step (3).

[0074] In this embodiment, the mass ratio of amino-modified silicon nanowires to sulfonic acid-modified carbon nanofibers in step (2) is 2:1, and the total mass of the load per square centimeter on the surface of the biomass filter membrane is 0.45g.

[0075] The electron microscope image of the silicon-carbon composite material obtained in this embodiment is as follows: Figure 2 As shown.

[0076] Example 4

[0077] This embodiment provides a method for preparing a silicon-carbon composite material. The preparation method is the same as in Example 1, except that 2g of amino-modified silicon nanowires and 1g of sulfonic acid-modified carbon nanofibers described in step (1) are dispersed in 50mL of deionized water, and 3g of citric acid is melted and coated in step (3).

[0078] In this embodiment, the mass ratio of amino-modified silicon nanowires to sulfonic acid-modified carbon nanofibers in step (2) is 2:1, and the total mass of the load per square centimeter on the surface of the biomass filter membrane is 0.95g.

[0079] Example 5

[0080] This embodiment provides a method for preparing a silicon-carbon composite material, the method comprising the following steps:

[0081] (1) 10g of silicon nanowires were dispersed in 100mL of an aqueous solution containing 5wt% cetyltrimethylammonium chloride. After sonication for 30min, the mixture was allowed to stand at 30℃ for 11h. Then, the mixture was washed and filtered three times with deionized water and dried under vacuum at 70℃ for 8h to obtain amino-modified silicon nanowires. The length of the silicon nanowires was 5μm and the diameter was 50nm.

[0082] 10g of carbon nanofiber powder was dispersed in 100mL of an aqueous solution containing 5wt% sodium dodecylbenzenesulfonate, sonicated for 30min, and allowed to stand at 30℃ for 11h. After washing and filtering with deionized water three times, the nanofiber was dried under vacuum at 70℃ for 8h to obtain sulfonic acid modified carbon nanofiber.

[0083] (2) Disperse 1g of amino-modified silicon nanowires and 0.5g of sulfonic acid-modified carbon nanofibers described in step (1) in 50mL of deionized water, stir for 10h, filter through a biomass filter membrane, dry at 80℃ for 8h and use for later use to obtain a biomass filter membrane loaded with Si / C composite.

[0084] The biomass filter membrane has a thickness of 0.1 mm and a total mass of the load per square centimeter on the surface of the biomass filter membrane is 0.45 g.

[0085] (3) After melting 3g of glucose, coat it onto the surface of the Si / C composite loaded on the biomass filter membrane described in step (2), and attach it to another biomass filter membrane loaded with Si / C composite in step (2) (the loaded Si / C composite faces the carbon layer after glucose coating). Compact it with a roller at a pressure of 10MPa to obtain the pre-coated silicon-carbon material.

[0086] (4) The pre-coated silicon-carbon material described in step (3) is placed in a sintering furnace and heated to 1000°C at a heating rate of 10°C / min under argon protection. The temperature is held for 6 hours, then cooled and ground to obtain a one-time coated silicon-carbon anode material.

[0087] (5) The silicon-carbon anode material coated in step (4) is placed in a gas phase coating furnace and heated to 800°C at a heating rate of 10°C / min under argon protection. Acetylene is introduced and kept at the temperature for 3 hours. After cooling, the silicon-carbon composite material with a sandwich structure is obtained.

[0088] Example 6

[0089] This embodiment provides a method for preparing a silicon-carbon composite material, the method comprising the following steps:

[0090] (1) 10g of silicon nanowires were dispersed in 200mL of an aqueous solution containing 20wt% cetyltrimethylammonium chloride. After sonication for 30min, the mixture was allowed to stand at 20℃ for 13h. Then, the mixture was washed and filtered once with deionized water and dried under vacuum at 60℃ for 10h to obtain amino-modified silicon nanowires. The length of the silicon nanowires was 20μm and the diameter was 300nm.

[0091] 10g of carbon nanofiber powder was dispersed in 200mL of an aqueous solution containing 20wt% sodium dodecylbenzenesulfonate, sonicated for 30min, and allowed to stand at 20℃ for 13h. After washing and filtering once with deionized water, the nanofiber was dried under vacuum at 60℃ for 10h to obtain sulfonic acid modified carbon nanofiber.

[0092] (2) Disperse 1g of amino-modified silicon nanowires and 0.5g of sulfonic acid-modified carbon nanofibers described in step (1) in 50mL of deionized water, stir for 12h, filter through a biomass filter membrane, dry at 80℃ for 8h and use for later use to obtain a biomass filter membrane loaded with Si / C composite.

[0093] The biomass filter membrane has a thickness of 0.1 mm and a total mass of the load per square centimeter on the surface of the biomass filter membrane is 0.45 g.

[0094] (3) After melting 3g of glucose, coat it onto the surface of the Si / C composite loaded on the biomass filter membrane described in step (2), and attach it to another biomass filter membrane loaded with Si / C composite in step (2) (the loaded Si / C composite faces the carbon layer after glucose coating). Compact it with a roller at a pressure of 1MPa to obtain the pre-coated silicon-carbon material.

[0095] (4) The pre-coated silicon-carbon material described in step (3) is placed in a sintering furnace and heated to 800°C at a heating rate of 5°C / min under argon protection. The temperature is then maintained for 6 hours, cooled, ground and crushed to obtain a one-time coated silicon-carbon anode material.

[0096] (5) The silicon-carbon anode material coated in step (4) is placed in a gas phase coating furnace and heated to 600°C at a heating rate of 5°C / min under argon protection. Acetylene is introduced and kept at the temperature for 1 hour. After cooling, the silicon-carbon composite material with a sandwich structure is obtained.

[0097] Example 7

[0098] This embodiment provides a method for preparing a silicon-carbon composite material. The preparation method is the same as in Example 1, except that 1g of amino-modified silicon nanowires and 1g of sulfonic acid-modified carbon nanofibers described in step (1) are dispersed in 50mL of deionized water.

[0099] In this embodiment, the mass ratio of amino-modified silicon nanowires and sulfonic acid-modified carbon nanofibers in step (2) is 1:1, and the total mass of the load per square centimeter on the surface of the biomass filter membrane is 0.65g.

[0100] Example 8

[0101] This embodiment provides a method for preparing a silicon-carbon composite material. Except for step (2), in which 0.8g of the amino-modified silicon nanowires and 1g of the sulfonic acid-modified carbon nanofibers described in step (1) are dispersed in 50mL of deionized water, the preparation method is the same as in Example 1.

[0102] In this embodiment, the mass ratio of amino-modified silicon nanowires to sulfonic acid-modified carbon nanofibers in step (2) is 0.8:1, and the total mass of the load per square centimeter on the surface of the biomass filter membrane is 0.55g.

[0103] Example 9

[0104] This embodiment provides a method for preparing a silicon-carbon composite material. Except for step (2), in which 1.2g of the amino-modified silicon nanowires and 0.1g of the sulfonic acid-modified carbon nanofibers described in step (1) are dispersed in 50mL of deionized water, the preparation method is the same as in Example 1.

[0105] In this embodiment, the mass ratio of amino-modified silicon nanowires to sulfonic acid-modified carbon nanofibers in step (2) is 12:1, and the total mass of the load per square centimeter on the surface of the biomass filter membrane is 0.45g.

[0106] Comparative Example 1

[0107] This comparative example provides a method for preparing a silicon-carbon composite material, the method comprising the following steps:

[0108] (1) Disperse 1g of silicon nanowires (the length and diameter of the silicon nanowires are the same as in Example 1) and 0.5g of carbon nanofibers in 100mL of deionized water, add 3g of glucose and stir for 6h, and then dry at 80℃ to obtain the pre-coated material;

[0109] (2) The pre-coated material described in step (1) is placed in a sintering furnace and heated to 800°C for 8 hours under argon protection at a heating rate of 5°C / min. After cooling, the silicon-carbon composite material is obtained by grinding and crushing.

[0110] The electron microscope image of the silicon-carbon composite material obtained in this comparative example is as follows: Figure 3 As shown, by Figure 2 and Figure 3 The comparison shows that Figure 2 The encapsulation properties of silicon nanowires are relatively good, with fewer exposed silicon nanowires that are not encapsulated by carbon. Figure 3 The coating properties of silicon nanowires are poor, with a large number of silicon nanowires exposed and not coated with carbon.

[0111] Comparative Example 2

[0112] This comparative example provides a method for preparing a silicon-carbon composite material, the method comprising the following steps:

[0113] (1) Take 1g of amino-modified silicon nanowires from Example 1 and 0.5g of sulfonic acid-modified carbon nanofibers from Example 1 and disperse them in 50mL of deionized water. Add 3g of glucose, stir for 6h, and then dry to obtain the pre-coated material.

[0114] (2) The pre-coated material described in step (1) is placed in a sintering furnace and heated to 800°C for 8 hours under argon protection at a heating rate of 5°C / min. After cooling and grinding, the silicon-carbon anode material is obtained after one-time coating.

[0115] (3) The silicon-carbon anode material coated in step (2) is placed in a gas phase coating furnace and heated to 700°C at a heating rate of 5°C / min under argon protection. Acetylene is introduced and kept at the temperature for 2 hours. After cooling, the silicon-carbon composite material is obtained.

[0116] Comparative Example 3

[0117] This comparative example provides a method for preparing a silicon-carbon composite material. The preparation method is the same as that in Example 3 except that the vapor phase coating step (5) is not performed.

[0118] The silicon-carbon composite materials obtained in the above examples and comparative examples were used to fabricate coin half-cells with conductive agents and binders at a mass ratio of 8:1:1. The cell performance was tested at 0.5C, and the test results are shown in Table 1.

[0119] Table 1

[0120]

[0121] As can be seen from Table 1:

[0122] (1) As can be seen from Examples 1-4 and Comparative Example 1, the coating effect of silicon nanowires using conventional methods is poor. Direct contact between silicon nanowires and electrolyte will consume electrolyte, and there is no effective structure to alleviate the expansion of silicon nanowires, so the cycle performance is the worst. As can be seen from Examples 1-4 and Comparative Example 2, after the mixed solution in Comparative Example 2 is dried, the distribution of silicon nanowires and carbon source is uneven, and carbon layer-silicon nanowire, carbon-carbon layer-silicon nanowire, and carbon-carbon layer structures are not formed. During the cycle, the expansion of silicon nanowires cannot be effectively alleviated, and the cycle performance is poor. As can be seen from Examples 3 and Comparative Example 3, although Comparative Example 3 forms a good structure, some silicon nanowires are exposed after breakage, which affects the overall performance.

[0123] (2) As can be seen from Examples 1-4, the amount of silicon nanowires added in Example 1 is relatively small, resulting in a high carbon content in the silicon-carbon composite material and a low battery capacity. In Example 2, the silicon nanowire content is increased, which increases the battery capacity. In Example 3, the ratio of silicon nanowires to carbon nanofibers is more suitable. The network structure formed and the nitrogen doping in the gelatin improve the conductivity. At the same time, the layered C / Si & C / C structure also alleviates the expansion of silicon nanowires during cycling. In Example 4, silicon nanowires and carbon nanofibers are further increased, but the carbon content is low, resulting in a decrease in the coating rate and a slight decrease in the battery's first efficiency and cycle performance. As can be seen from Examples 1 and Examples 7-9, the amount of silicon nanowires, support materials and carbon source layer in this invention is preferably within a specific range, which can further ensure that the silicon-carbon composite material contains an appropriate amount of silicon nanowires and carbon materials, thereby ensuring the battery's capacity, first efficiency and cycle performance at the same time.

[0124] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that, The preparation method includes the following steps: (1) Mix amino-modified silicon nanowires, sulfonic acid-modified support material and solvent. After the mixture is filtered and dried by a carbon-based filter membrane, a load layer loaded with silicon nanowires and support material is formed on the surface of the carbon-based filter membrane to obtain the first composite filter membrane. (2) A carbon source layer is provided on the surface of the load layer described in step (1) to obtain a second composite filter membrane. The second composite filter membrane and the first composite filter membrane in step (1) are bonded and compacted to obtain a pre-coated composite material. After bonding, the side of the second composite filter membrane with the load material comes into contact with the side of the first composite filter membrane with the load material. (3) The pre-coated composite material described in step (2) is subjected to sintering, crushing and carbon coating treatment in sequence to obtain the silicon-carbon composite material.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the amino-modified silicon nanowires to the sulfonic acid-modified support material in step (1) is (1-10):1; Preferably, the mass ratio of the sulfonic acid-modified support material to the solvent in step (1) is 1:(50-100).

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the total mass of amino-modified silicon nanowires and sulfonic acid-modified support material per square centimeter on the surface of the carbon-based filter membrane is 0.01-0.95 g; Preferably, the thickness of the carbon-based filter membrane in step (1) is 0.01-0.1 mm; Preferably, the carbon-based filter membrane in step (1) includes a biomass filter membrane; Preferably, the mixing time of the amino-modified silicon nanowires, sulfonic acid-modified support material and solvent in step (1) is 6-12 hours.

4. The preparation method according to any one of claims 1-3, characterized in that, The method for preparing the amino-modified silicon nanowires in step (1) includes: mixing silicon nanowires with an aqueous solution of an ammonium salt cationic surfactant, allowing them to stand, washing, and drying. Preferably, the silicon nanowires have a length of 1-20 μm and a diameter of 50-300 nm; Preferably, the solute content in the aqueous solution of the ammonium salt cationic surfactant is 5-20 wt%. Preferably, the aqueous solution of the ammonium salt-type cationic surfactant includes any one or a combination of at least two of dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, polydienedimethylammonium chloride, or dioctadecyldimethylammonium chloride; Preferably, the mass ratio of the silicon nanowires to the aqueous solution of the ammonium salt cationic surfactant is (1-10):

100.

5. The preparation method according to any one of claims 1-4, characterized in that, The method for preparing the sulfonic acid-modified support material in step (1) includes: mixing the support material with an aqueous solution of a sulfonic acid-type anionic surfactant, allowing it to stand, washing, and drying. Preferably, the support material includes carbon support material and / or metal support material; Preferably, the carbon support material includes any one or a combination of at least two of carbon nanotubes, carbon nanofibers, or graphene. Preferably, the metal support material comprises copper nanowires and / or silver nanowires; Preferably, the solute content in the aqueous solution of the sulfonic acid anionic surfactant is 5-20 wt%. Preferably, the aqueous solution of the sulfonic acid anionic surfactant includes any one or a combination of at least two of sodium undecylbenzenesulfonate, sodium dodecylbenzenesulfonate, or sodium dodecylbenzenesulfonate. Preferably, the mass ratio of the supporting material to the aqueous solution of the sulfonic acid anionic surfactant is (1-10):

100.

6. The preparation method according to any one of claims 1-5, characterized in that, In step (2), the mass of the carbon source layer in the second composite filter membrane is 1-5 times the mass of the amino-modified silicon nanowires; Preferably, the method of setting the carbon source layer in step (2) includes any one or a combination of at least two of coating, adsorption, compaction or bonding; Preferably, the carbon source layer in step (2) includes any one or a combination of at least two of glucose, chitosan, gelatin, asphalt, tannic acid or citric acid.

7. The preparation method according to any one of claims 1-6, characterized in that, The compaction method described in step (2) includes roller pressing and / or flat pressing; Preferably, the compaction pressure in step (2) is 1-10 MPa.

8. The preparation method according to any one of claims 1-7, characterized in that, The heating rate of the sintering in step (3) is 5-10℃ / min, the holding temperature is 800-1000℃, and the holding time is 6-12h. Preferably, the carbon coating method in step (3) includes gas-phase carbon coating; Preferably, the gaseous carbon coating is heated to 600-800°C at a heating rate of 5-10°C / min, and a gaseous carbon source is introduced and kept at that temperature for 1-3 hours. Preferably, the gaseous carbon source includes methane or acetylene.

9. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material is prepared by the preparation method described in any one of claims 1-8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery comprises the silicon-carbon composite material as described in claim 9.

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