A kind of bio-carbon loaded silicon nanowire composite material and its preparation method and use

Abstract

The application provides a kind of biomass carbon load silicon nanowire composite material and its preparation method and purposes, the preparation method is by chemical activation method and physical activation method is combined, on the surface and inside of biomass material layer by layer etching, form multilayer biomass porous carbon material of different pore size, effectively improve the problem of incomplete etching or excessive etching of biomass porous carbon prepared by using single activator;The specific surface area of the prepared multilayer porous carbon is large, the void fraction is high, and the metal catalyst particles of different scales can be planted in the interior to play a grading role for large particle catalyst;Silicon nanowires are directionally grown in the carrier by catalytic growth, and the space network structure of this multilayer porous carbon can effectively withstand the volume expansion of silicon nanowires and inhibit the repeated growth of SEI film.

Description

Technical Field

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

[0002] With the vigorous development of a new round of global technological revolution and industrial transformation, new energy vehicles have become the main direction for the transformation and development of the global automotive industry and an important engine for promoting the sustained growth of the world economy. Lithium-ion power batteries with long driving range, high energy density and high safety performance play a crucial role in promoting the high-quality development of new energy vehicles.

[0003] The anode and anode materials have a crucial impact on battery performance and are a key area of ​​battery research and development. Currently, the market primarily uses artificial graphite as an anode material. However, with the graphite industry maturing, its energy density is already close to its theoretical capacity of 372 mAh / g, leaving little room for further improvement. Compared to graphite, silicon-based materials have a theoretical specific capacity nearly ten times that of graphite (4200 mAh / g). As the requirements for battery energy density and driving range increase, silicon-based anodes will undoubtedly become the most important research and application direction. However, silicon materials undergo significant volume expansion during lithium intercalation, and the resulting internal stress can lead to silicon material cracking or even pulverization, damaging the electrode structure and causing a sharp decline in battery capacity.

[0004] To mitigate the volume expansion and reduce the mechanical stress of silicon materials, researchers have proposed silicon-carbon composites as an effective solution. For example, CN101244814A proposes a method for preparing silicon-carbon anode materials for lithium-ion batteries, which involves mixing nano-silicon powder, asphalt solution, and spherical natural graphite, followed by carbonization to obtain the silicon-carbon anode material. However, the interaction between the silicon powder and the carbon source is weak, and volume expansion during lithium intercalation still easily causes electrode structure collapse. The silicon-carbon anode material prepared by this method has an initial efficiency of 80%–85% and a reversible capacity of 420–450 mAh / g, failing to demonstrate the superior properties of silicon. Currently, commercially available silicon-carbon anode materials mainly involve doping graphite powder with a small amount of silicon. Similar to the aforementioned patent, the specific capacity of such commercial graphite / silicon-carbon mixtures is generally below 500 mAh / g, failing to fully utilize the performance advantages of silicon.

[0005] Therefore, it is necessary to continue to research and develop new silicon-carbon anode materials to fully leverage the performance advantages of silicon materials and enable anode materials to effectively improve the electrical performance and stability of batteries. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to provide a bio-carbon supported silicon nanowire composite material, its preparation method and application. The preparation method uses biomass as a carbon source and combines chemical activation and physical activation methods to perform activation etching of different degrees on the surface and inside of the biomass, thereby obtaining a multilayer biomass porous carbon material with multi-level pore size. The biomass is then used as a support for a metal catalyst to grow silicon nanowires, thereby obtaining a silicon-carbon anode material with stable structure and high specific capacity.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a bio-carbon-supported silicon nanowire composite material, the method comprising:

[0009] Biomass raw materials are first chemically activated at least twice, and then physically activated to obtain multilayer porous carbon. A metal catalyst is loaded onto the multilayer porous carbon to obtain a support. The support is catalytically grown with a silicon source to form silicon nanowires, which are simultaneously loaded onto the support to obtain a bio-carbon-supported silicon nanowire composite material (i.e., the support and the silicon nanowires it supports constitute the bio-carbon-supported silicon nanowire composite material).

[0010] This invention combines chemical and physical activation methods to etch layer by layer onto the surface and interior of biomass materials, forming multilayered porous carbon materials with different pore sizes. This effectively improves upon the problems of incomplete or excessive etching that often occur when using a single activator to prepare porous carbon from biomass. The resulting multilayered porous carbon has a large specific surface area and high porosity, enabling the internal loading of metal catalyst particles of different sizes, thus hierarchically classifying large catalyst particles. Subsequently, silicon nanowires are grown from a silicon source using the loaded metal catalyst and in situ loaded onto the multilayered porous carbon material, forming the aforementioned bio-carbon-supported silicon nanowire composite material. The advantage of this multilayered porous carbon lies in providing pores of different sizes, which facilitates the loading of catalysts. Smaller catalyst particles settle in smaller pores, while larger particles settle in larger pores, thus promoting in-situ growth of silicon nanowires and achieving a hierarchical effect. This results in a high silicon wire content and high capacity in the overall product. Simultaneously, the network structure of the multilayered porous carbon acts as a skeletal support, effectively suppressing the volume expansion of silicon nanowires and inhibiting repeated SEI film growth.

[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following technical solutions.

[0012] As a preferred technical solution of the present invention, the biomass raw materials include at least one of pine cones, corn cobs, corn stalks, coconut shells or peanut shells. Typical but non-limiting examples include combinations of pine cones and corn cobs, combinations of pine cones and corn stalks, combinations of pine cones and coconut shells, or combinations of pine cones and peanut shells.

[0013] Preferably, the biomass raw material is pre-dried to remove moisture, and then crushed, ground, and sieved to obtain biomass raw material powder. The biomass raw material powder is then chemically activated. The particle size of the biomass raw material powder is 150–600 μm, for example, 150 μm, 180 μm, 200 μm, 230 μm, 250 μm, 280 μm, 300 μm, 330 μm, 350 μm, 380 μm, 400 μm, 430 μm, 450 μm, 480 μm, 500 μm, 430 μm, 550 μm, 580 μm, or 600 μm, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0014] As a preferred technical solution of the present invention, the chemical activation method includes mixing biomass raw materials or chemically activated biomass raw materials with a chemical activator and sintering them.

[0015] Preferably, the chemical activation is performed twice.

[0016] Preferably, the method for chemically activating biomass raw materials twice includes:

[0017] Biomass raw materials are first mixed with a first activator and then sintered to obtain a first porous carbon with primary pores; the first porous carbon is second mixed with a second activator and then sintered to form secondary pores in the primary pores to obtain a second porous carbon; the second porous carbon is then physically activated.

[0018] The preparation method of the present invention preferably uses a first activator with strong etching effect to chemically activate the biomass carbon to form large-pore pores (i.e., primary pores, preferably with a pore size of 1-3 μm) on the surface, thus obtaining a first porous carbon. Then, a relatively mild second activator is used to chemically activate the biomass carbon to further etch small pores (i.e., secondary pores, preferably with a pore size of 500-900 nm) inside the large-pore pores, so that the biomass carbon obtains a multi-level pore distribution structure. When further physical activation is performed using a physical activator, tertiary pores (preferably with a pore size <500 nm) can be formed in the primary and secondary pores, thereby constructing the multilayer porous carbon material, which is then loaded with a metal catalyst (i.e., the supported body is obtained).

[0019] As a preferred embodiment of the present invention, the first activator includes at least one of potassium carbonate, sodium carbonate, potassium hydroxide, or sodium hydroxide. Typical but non-limiting examples of combinations include combinations of potassium carbonate and potassium hydroxide, combinations of potassium carbonate and sodium hydroxide, or combinations of potassium hydroxide and sodium hydroxide.

[0020] In existing processes for synthesizing porous carbon from biomass raw materials, a single activator is typically used, leading to incomplete or excessive etching. This results in low surface area and fragmented porous carbon structures. This invention combines the characteristics of various activators, using multiple activators and activation methods in combination. Furthermore, by controlling the sintering temperature and time, a biocarbon material with a complete structure, multiple layers, and a multi-level pore size distribution can be obtained. In the preparation method described in this invention, the degree of activation can be adjusted by reasonably modifying the amount of activator, the temperature during activation (sintering process), and the time, thereby controlling the stability of the overall structure of the multi-layered porous carbon and avoiding structural collapse that could lead to excessive etching.

[0021] Preferably, the first mixing method includes solid-phase mechanical ball milling.

[0022] Preferably, the mass ratio of the biomass raw material to the first activator is 1:(0.5-4), such as 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5 or 1:4, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0023] In this invention, under otherwise identical conditions, excessive use of the first activator can easily lead to over-etching of the material, collapse of the pore structure, and low yield; while insufficient use can easily lead to incomplete etching, resulting in a reduced loading capacity in the later stages.

[0024] Preferably, the temperature of the first sintering is 700-900℃, such as 700℃, 730℃, 750℃, 780℃, 800℃, 830℃, 850℃, 880℃ or 900℃, and the time is 2-4h, such as 2h, 2.3h, 2.5h, 2.8h, 3h, 3.3h, 3.5h or 4h, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0025] In this invention, under the same conditions, if the temperature of the first sintering is too high or the time is too long, it will easily lead to over-etching and cause the collapse of the hole structure; if the temperature is too low or the time is too short, it will easily lead to incomplete etching.

[0026] As a preferred embodiment of the present invention, the second activator includes zinc chloride and / or phosphoric acid.

[0027] Preferably, the mass ratio of the first porous carbon to the second activator is 1:(0.5-3), such as 1:0.5, 1:0.8, 1:1, 1:1.3, 1:1.5, 1:1.8, 1:2, 1:2.5, 1:2.8 or 1:3, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0028] In this invention, under otherwise identical conditions, if the amount of the second activator is too large, it will easily cause the secondary pores of the second layer to be too large, which will easily lead to structural collapse; if the amount is too small, it will easily lead to failure to achieve the design target of the pore structure.

[0029] Preferably, the second mixing method is liquid-phase magnetic stirring and / or liquid-phase ultrasonic mixing.

[0030] Preferably, the second sintering temperature is 600-800℃, such as 600℃, 630℃, 650℃, 680℃, 700℃, 730℃, 750℃, 780℃ or 800℃, and the time is 1-3h, such as 1h, 1.3h, 1.5h, 1.8h, 2h, 2.3h, 2.5h, 2.8h or 3h, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0031] In this invention, under otherwise identical conditions, if the second sintering temperature is too high or the time is too long, the secondary pores in the second layer will be too large, which may lead to structural collapse; if the temperature is too low or the time is too short, the design target of the pore structure may not be achieved.

[0032] As a preferred technical solution of the present invention, the physical activation method includes subjecting the chemically activated biomass raw material to a third sintering with a physical activator to obtain multilayer porous carbon.

[0033] Preferably, the physical activator includes water vapor and / or carbon dioxide.

[0034] Preferably, the flow rate of the physical activator is 50 to 100 sccm, such as 50 sccm, 60 sccm, 70 sccm, 80 sccm, 90 sccm or 100 sccm, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0035] In this invention, under otherwise identical conditions, excessive use of physical activator can easily lead to excessively large tertiary pores in the third layer, which can easily cause structural collapse; while insufficient use can easily lead to failure to achieve the design target of the pore structure.

[0036] Preferably, the temperature of the third sintering is 700-1000℃, such as 700℃, 750℃, 800℃, 850℃, 900℃, 950℃ or 1000℃, and the time is 1-2h, such as 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2h, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0037] In this invention, under the same conditions, if the temperature of the third sintering is too high or the time is too long, the tertiary pores of the third layer will be too large, which will easily lead to structural collapse; if the temperature is too low or the time is too short, the design target of the pore structure will not be achieved.

[0038] Preferably, the heating and cooling stages of the third sintering in the physical activation are carried out under the protection of an inert gas, and the heat holding stage of the third sintering is carried out in the atmosphere of the physical activator.

[0039] As a preferred technical solution of the present invention, the method of loading a metal catalyst into the multilayer porous carbon includes: subjecting the multilayer porous carbon to a reduction reaction with a metal catalyst raw material and a reducing agent to form a metal catalyst, which is then loaded into the multilayer porous carbon to obtain a supported body.

[0040] Preferably, the raw materials for the metal catalyst include at least one of CuCl, CuCl2, FeCl3, CoCl2, HAuCl4, or SnCl2. Typical but non-limiting examples include combinations of CuCl and CuCl2, CuCl and FeCl3, CuCl and CoCl2, CuCl and HAuCl4, CuCl and SnCl2, CuCl2 and FeCl3, CoCl2 and HAuCl4, or CoCl2 and SnCl2, etc.

[0041] Preferably, the reducing agent includes at least one of NaBH4, B2H6, or LiBH4. Typical but non-limiting examples of combinations include combinations of NaBH4 and B2H6, combinations of NaBH4 and LiBH4, or combinations of B2H6 and LiBH4.

[0042] Preferably, the temperature of the reduction reaction is 25 to 80°C, such as 25°C, 35°C, 45°C, 55°C, 65°C, 73°C, or 80°C, and the time is 12 to 24 hours, such as 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0043] Preferably, the silicon source comprises a gaseous silicon compound, which includes silane and / or silane.

[0044] Preferably, the temperature of the catalytic growth reaction is 600 to 1000°C, such as 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, or 1000°C, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0045] The second mixing in this invention is preferably carried out in the liquid phase, specifically using an in-situ impregnation reduction method to uniformly distribute the metal catalyst within the pores of multiple layers of porous carbon. Subsequently, the catalytic growth reaction is preferably carried out using VLS catalysis to directionally grow silicon nanowires, forming a network structure. Compared to traditional in-situ loading of silicon particles or mechanical mixing loading of silicon nanowires, this composite spatial network structure can effectively suppress volume expansion and fragmentation of the negative electrode material. Compared to the prior art using CVD to load silicon particles onto a support, the capacity and stability of the silicon nanowires obtained in this invention are effectively improved.

[0046] As a preferred technical solution of the present invention, the preparation method includes washing and drying the obtained sample after each chemical activation. The drying temperature is 80-120°C, such as 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, or 120°C. The washing method includes washing with 1M hydrochloric acid first, and then washing with deionized water until neutral, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0047] Preferably, the chemical activation, the physical activation, and the catalytic growth reaction are all carried out under an inert gas, which includes nitrogen and / or argon, and the flow rate of the inert gas is 500 to 1000 sccm, such as 500 sccm, 600 sccm, 700 sccm, 800 sccm, 900 sccm, or 1000 sccm, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0048] Preferably, the inert gas in the catalytic growth reaction serves as the carrier gas for the silicon source.

[0049] As a preferred technical solution of the present invention, the preparation method includes:

[0050] (1) The biomass raw material is dried at 80-120℃ to remove moisture, and then crushed, ground and sieved to obtain biomass raw material powder of 50-600μm.

[0051] (2) The biomass raw material powder is mixed with the first activator at a mass ratio of 1:(0.5-4), and solid-phase mechanical ball milling is performed. Then, under the protection of an inert gas with a flow rate of 500-1000 sccm, the first sintering is carried out at 700-900℃ for 2-4 hours. After washing and drying the sample, the first porous carbon with primary pores is obtained.

[0052] (3) The first porous carbon and the second activator are mixed in an aqueous phase at a mass ratio of 1:(0.5-3). The magnetic stirring speed is set to 100-300 rpm. After drying the sample in an oven at 100-150°C to remove moisture, it is sintered at 600-800°C for 1-3 hours under the protection of an inert gas with a flow rate of 500-1000 sccm to form secondary pores in the primary pores. Then the sample is washed with 1M hydrochloric acid and then washed with deionized water until neutral. After drying at 80-100°C, the second porous carbon is obtained.

[0053] (4) The second porous carbon is placed in a quartz tube furnace and heated to 700-1000°C at a heating rate of 1-10°C / min under the protection of an inert gas with a flow rate of 500-1000 sccm. The inert gas is stopped, and a physical activator is introduced at a flow rate of 50-100 sccm. After the third sintering is carried out for 1-2 hours, the physical activator is stopped, the inert gas is resumed, and the temperature is lowered at a cooling rate of 1-10°C / min to obtain multilayer porous carbon.

[0054] (5) Prepare a solution containing metal catalyst raw material and reducing agent, add the multilayer porous carbon, and carry out a reduction reaction at 25-80°C for 12-24 hours to form a metal catalyst and simultaneously load it in the multilayer porous carbon to obtain a supported body;

[0055] (6) The support is placed in a vacuum tube furnace, and an inert gas is introduced into the silicon source as a carrier gas. A catalytic growth reaction is carried out at 600-1000°C to form silicon nanowires, which are simultaneously loaded into the support to obtain a bio-carbon supported silicon nanowire composite material.

[0056] In a second aspect, the present invention provides a bio-carbon-supported silicon nanowire composite material, obtained according to the preparation method described in the first aspect.

[0057] Thirdly, the present invention provides a negative electrode sheet containing the bio-carbon-supported silicon nanowire composite material described in the second aspect.

[0058] Fourthly, the present invention provides a lithium-ion battery comprising the negative electrode sheet described in the third aspect.

[0059] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0060] This invention combines chemical and physical activation methods to etch layer by layer onto the surface and interior of biomass materials, forming multilayer porous carbon materials with different pore sizes. This effectively improves the problem of incomplete or excessive etching that occurs when using a single activator to prepare porous carbon from biomass. The resulting multilayer porous carbon has a large specific surface area and high porosity, enabling the internal loading of metal catalyst particles of different sizes, thus playing a role in the classification of large catalyst particles. By catalytically growing silicon nanowires directionally within the support, the spatial network structure of this multilayer porous carbon can effectively withstand the volume expansion of silicon nanowires and inhibit the repeated growth of SEI films. Attached Figure Description

[0061] Figure 1 This is a SEM image of the multilayer porous carbon obtained in Example 1;

[0062] Figure 2 This is a SEM image of the bio-carbon-supported silicon nanowire composite material obtained in Example 1;

[0063] Figure 3 The image shows the SEM test results of the biocarbon material obtained in Comparative Example 2.

[0064] Figure 4 This is a SEM image of the biocarbon material obtained in Comparative Example 4. Detailed Implementation

[0065] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0066] Those skilled in the art will understand that the embodiments described are merely illustrative of the invention and should not be construed as limiting the invention.

[0067] Example 1

[0068] This embodiment provides a method for preparing a bio-carbon-supported silicon nanowire composite material, the method comprising:

[0069] (1) The biomass raw material pine cones were dried at 100°C to remove moisture, and then crushed, ground and sieved to obtain biomass raw material powder with a thickness of 260μm.

[0070] (2) The biomass raw material powder was mixed with potassium hydroxide as the first activator at a mass ratio of 1:1.8 and subjected to solid-phase mechanical ball milling. Then, under the protection of an inert gas with a flow rate of 800 sccm, the mixture was subjected to first sintering at 900°C for 1.5 h. After washing and drying the sample, the first porous carbon with primary pores was obtained.

[0071] (3) The first porous carbon and the second activator phosphoric acid were mixed in an aqueous phase at a mass ratio of 1:1.5. The magnetic stirring speed was set to 200 rpm. After drying the sample in an oven at 120°C to remove moisture, it was sintered at 700°C for 2 hours under the protection of an inert gas with a flow rate of 800 sccm to form secondary pores in the primary pores. The sample was then washed with 1M hydrochloric acid and then washed with deionized water until neutral. After drying at 90°C, the second porous carbon was obtained.

[0072] (4) The second porous carbon is placed in a quartz tube furnace and heated to 850°C at a heating rate of 5°C / min under the protection of an inert gas with a flow rate of 800 scc. The inert gas is stopped, and physical activator water vapor is introduced at a flow rate of 70 sccm. After the third sintering for 1.5 h, the physical activator is stopped, the inert gas is resumed, and the temperature is lowered at a cooling rate of 5°C / min to obtain multilayer porous carbon.

[0073] (5) Prepare a solution containing metal catalyst raw material CuCl2 and reducing agent NaBH4, add the multilayer porous carbon, and carry out a reduction reaction at 60°C for 18h to form a metal catalyst and simultaneously load it in the multilayer porous carbon to obtain a supported body.

[0074] (6) The support is placed in a vacuum tube furnace, and an inert gas is used as a carrier gas to introduce silicon source silane. A catalytic growth reaction is carried out at 800°C to form silicon nanowires, which are simultaneously loaded into the support to obtain a bio-carbon supported silicon nanowire composite material.

[0075] Example 2

[0076] This embodiment provides a method for preparing a bio-carbon-supported silicon nanowire composite material, the method comprising:

[0077] (1) The biomass raw material coconut shell is dried at 80°C to remove moisture, and then crushed, ground and sieved to obtain 150μm biomass raw material powder.

[0078] (2) The biomass raw material powder is mixed with the first activator potassium carbonate at a mass ratio of 1:2, and solid-phase mechanical ball milling is performed. Then, under the protection of inert gas with a flow rate of 500 sccm, the first sintering is carried out at 800°C for 2 hours. After washing the sample with water and drying it, the first porous carbon with primary pores is obtained.

[0079] (3) The first porous carbon and the second activator zinc chloride were mixed in an aqueous phase at a mass ratio of 1:1. The magnetic stirring speed was set to 100 rpm. After drying the sample in an oven at 100°C to remove moisture, it was sintered at 750°C for 2 hours under the protection of an inert gas with a flow rate of 500 sccm to form secondary pores in the primary pores. The sample was then washed with 1M hydrochloric acid and then washed with deionized water until neutral. After drying at 80°C, the second porous carbon was obtained.

[0080] (4) The second porous carbon is placed in a quartz tube furnace and heated to 700°C at a heating rate of 2°C / min under the protection of an inert gas with a flow rate of 500 sccm. The inert gas is stopped, and a physical activator, carbon dioxide, is introduced at a flow rate of 50 sccm. After the third sintering for 2 hours, the physical activator is stopped, the inert gas is resumed, and the temperature is lowered at a cooling rate of 2°C / min to obtain multilayer porous carbon.

[0081] (5) Prepare a solution containing metal catalyst raw material HAuCl4 and reducing agent LiBH4, add the multilayer porous carbon, and carry out a reduction reaction at 35°C for 24 hours to form a metal catalyst and simultaneously load it in the multilayer porous carbon to obtain a supported body.

[0082] (6) The support is placed in a vacuum tube furnace, and an inert gas is used as the carrier gas to introduce silicon ethylene source. A catalytic growth reaction is carried out at 600°C to form silicon nanowires, which are simultaneously loaded into the support to obtain a bio-carbon supported silicon nanowire composite material.

[0083] Example 3

[0084] This embodiment provides a method for preparing a bio-carbon-supported silicon nanowire composite material, the method comprising:

[0085] (1) The biomass raw material corn cob was dried at 120°C to remove moisture, and then crushed, ground and sieved to obtain 600μm biomass raw material powder.

[0086] (2) The biomass raw material powder is mixed with the first activator sodium hydroxide at a mass ratio of 1:0.5, and then subjected to solid-phase mechanical ball milling. Under the protection of inert gas with a flow rate of 1000 sccm, the first sintering is carried out at 900°C for 2 hours. After washing and drying the sample, the first porous carbon with primary pores is obtained.

[0087] (3) The first porous carbon and the second activator phosphoric acid were mixed in an aqueous phase at a mass ratio of 1:3. The magnetic stirring speed was set to 300 rpm. After drying the sample in an oven at 150°C to remove moisture, it was sintered at 800°C for 1 hour under the protection of an inert gas with a flow rate of 1000 sccm to form secondary pores in the primary pores. The sample was then washed with 1M hydrochloric acid and then washed with deionized water until neutral. After drying at 100°C, the second porous carbon was obtained.

[0088] (4) The second porous carbon is placed in a quartz tube furnace and heated to 800°C at a heating rate of 8°C / min under the protection of inert gas with a flow rate of 1000 sccm. The inert gas is stopped, and physical activator water vapor is introduced at a flow rate of 100 sccm. After the third sintering for 1 hour, the physical activator is stopped, the inert gas is resumed, and the temperature is lowered at a cooling rate of 8°C / min to obtain multilayer porous carbon.

[0089] (5) Prepare a solution containing metal catalyst raw material CoCl2 and reducing agent NaBH4, add the multilayer porous carbon, and carry out a reduction reaction at 80°C for 12 hours to form a metal catalyst and simultaneously load it in the multilayer porous carbon to obtain a supported body.

[0090] (6) The support is placed in a vacuum tube furnace, and an inert gas is used as a carrier gas to introduce silicon source silane. A catalytic growth reaction is carried out at 850°C to form silicon nanowires, which are simultaneously loaded into the support to obtain a bio-carbon supported silicon nanowire composite material.

[0091] Example 4

[0092] This embodiment provides a method for preparing a bio-carbon-supported silicon nanowire composite material. In step (2), the mass ratio of biomass raw material powder to the first activator is adjusted from 1:1.8 to 1:0.5. Except for the above, the other conditions are exactly the same as in Example 1.

[0093] Example 5

[0094] This embodiment provides a method for preparing a bio-carbon-supported silicon nanowire composite material. In step (2), the mass ratio of biomass raw material powder to the first activator is adjusted from 1:1.8 to 1:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0095] Example 6

[0096] This embodiment provides a method for preparing a bio-carbon-supported silicon nanowire composite material. In step (2), the mass ratio of biomass raw material powder to the first activator is adjusted from 1:1.8 to 1:2.5. Except for the above, the other conditions are exactly the same as in Example 1.

[0097] Example 7

[0098] This embodiment provides a method for preparing a bio-carbon-supported silicon nanowire composite material. In step (2), the mass ratio of biomass raw material powder to the first activator is adjusted from 1:1.8 to 1:4. Except for the above, the other conditions are exactly the same as in Example 1.

[0099] Example 8

[0100] This embodiment provides a method for preparing a bio-carbon-supported silicon nanowire composite material. In step (2), the temperature of the first sintering is adjusted from 800°C to 650°C. Except for the above, the other conditions are exactly the same as in Example 1.

[0101] Example 9

[0102] This embodiment provides a method for preparing a bio-carbon supported silicon nanowire composite material. In step (2), the temperature of the first sintering is adjusted from 800°C to 700°C. Except for the above, the other conditions are exactly the same as in Example 1.

[0103] Example 10

[0104] This embodiment provides a method for preparing a bio-carbon supported silicon nanowire composite material. In step (2), the temperature of the first sintering is adjusted from 800°C to 900°C. Except for the above, the other conditions are exactly the same as in Example 1.

[0105] Example 11

[0106] This embodiment provides a method for preparing a bio-carbon-supported silicon nanowire composite material. In step (2), the temperature of the first sintering is adjusted from 800°C to 950°C. Except for the above, the other conditions are exactly the same as in Example 1.

[0107] Comparative Example 1

[0108] This comparative example provides a method for preparing a bio-carbon-supported silicon nanowire composite material. The preparation method does not include steps (3) and (4). The first porous carbon obtained in step (2) is used in step (5) to replace the multilayer porous carbon. Except for the above, the other conditions are exactly the same as in Example 1.

[0109] Comparative Example 2

[0110] This comparative example provides a method for preparing a bio-carbon-supported silicon nanowire composite material, wherein the preparation method omits steps (3) and (4), and steps (2) are adjusted as follows:

[0111] The biomass raw material powder was mixed with the first activator at a mass ratio of 1:4, and then subjected to solid-phase mechanical ball milling. Under the protection of an inert gas with a flow rate of 1000 sccm, the mixture was sintered at 950°C for 3 hours. After washing and drying the sample, biochar material was obtained. The first porous carbon obtained in step (2) was used in step (5) to replace the multilayer porous carbon.

[0112] Apart from the above, all other conditions are exactly the same as in Example 1.

[0113] Comparative Example 3

[0114] This comparative example provides a method for preparing a bio-carbon-supported silicon nanowire composite material. The preparation method does not perform steps (2) and (4). The biomass raw material powder obtained in step (1) is used in step (3) to replace the first porous carbon to obtain bio-carbon material, which is then used in step (5). Except for the above, the other conditions are exactly the same as in Example 1.

[0115] Comparative Example 4

[0116] This comparative example provides a method for preparing a bio-carbon-supported silicon nanowire composite material. The preparation method does not perform steps (2) and (3). The biomass raw material powder obtained in step (1) is used in step (4) to replace the second porous carbon to obtain bio-carbon material, which is then used in step (5). Except for the above, the other conditions are exactly the same as in Example 1.

[0117] Comparative Example 5

[0118] This comparative example provides a method for preparing a bio-carbon-supported silicon nanowire composite material. The preparation method does not include step (2). The biomass raw material powder obtained in step (1) is used in step (3) to replace the first porous carbon. Except for the above, the other conditions are exactly the same as in Example 1.

[0119] Comparative Example 6

[0120] This comparative example provides a method for preparing a bio-carbon-supported silicon nanowire composite material. The preparation method does not include step (3). The first porous carbon obtained in step (2) is used in step (4) to replace the second porous carbon. Except for the above, the other conditions are exactly the same as in Example 1.

[0121] Comparative Example 7

[0122] This comparative example provides a method for preparing a bio-carbon-supported silicon nanowire composite material. The preparation method does not include step (4). The second porous carbon obtained in step (3) is used in step (5) to replace the multilayer porous carbon. Except for the above, the other conditions are exactly the same as in Example 1.

[0123] Control group 1

[0124] This control group uses the multilayer porous carbon obtained in step (4) of Example 1, and loads silicon nanoparticles on it with the same loading amount as silicon nanowires in Example 1.

[0125] Control group 2

[0126] This control group uses commercially available porous carbon to replace the multilayer porous carbon in steps (5) and (6) for loading silicon nanowires.

[0127] I. Morphological characteristics:

[0128] Figure 1 The image shows a SEM image of the multilayer porous carbon obtained in Example 1. The image shows that the multilayer porous carbon obtained in Example 1 has a uniform pore size distribution, large pores on the surface, and small pores inside the large pores, with an overall complete structure. Figure 2 The image shows a SEM image of the bio-carbon-supported silicon nanowire composite material obtained in Example 1. The image shows that silicon nanowires were successfully generated and loaded in the pores of the multilayer porous carbon. Figure 3 The image shows the SEM test results of the biochar material obtained in Comparative Example 2. Comparative Example 2 is biochar obtained by directly activating biomass with KOH. Due to the excessive etching ability of KOH, the activation and etching were overdone, resulting in a large number of macropores (greater than 1 μm). Although some micropores are also present in the macropores on the surface, the original porous carbon network structure collapsed, the overall morphology was broken, and the particle size was about 1 to 10 μm, which is not conducive to its use as a carrier for silicon nanowires. Figure 4 The image shows the SEM test results of the biochar material obtained in Comparative Example 4. Comparative Example 4 is biochar obtained by activating biomass raw materials only through physical activators. Its overall pore size is relatively small, and only the surface layer is etched. No other small pores are formed inside the pores. Furthermore, there is an uneven distribution of pores, and some areas do not have pores. Using it as a carrier for silicon nanowires only results in the growth of silicon wires on the outer surface of porous carbon. It cannot improve the current situation of silicon nanowire volume expansion, breakage, and repeated growth of SEI film.

[0129] II. Battery Testing:

[0130] The materials obtained from the examples, comparative examples, and control groups were used as negative electrode active materials. The above negative electrode active materials, conductive agents, and binders were mixed with deionized water in the corresponding proportions to form a slurry. The slurry was continuously ground until uniform. The slurry was uniformly coated onto copper foil, which served as the current collector, using a 250 μm scraper. After drying in a vacuum oven at 80°C for 12 hours, the electrode was pressed into a circular electrode sheet with a diameter of 12 mm by a roller press. The electrode sheet was then placed in a glove box filled with Ar. Subsequently, the button cell was assembled in the order of electrode sheet, separator, electrolyte, lithium sheet, gasket, and spring sheet.

[0131] The obtained batteries were tested using the Xinwei CT / CTE-4000 series multi-channel battery testing system to perform charge-discharge tests and rate performance tests on the assembled half-cells. The test temperature was 30℃, and the test voltage range was 0.01~1.5V. The results are recorded in Table 1.

[0132] Table 1

[0133]

[0134]

[0135] As shown in Table 1, the type and amount of activator, activation temperature, and activation time affect the morphology of multilayer porous carbon, which in turn affects the supported catalyst and ultimately the performance indicators such as the capacity and cycle number of the anode material. The type of activator is crucial to the morphology of porous carbon. Taking Comparative Examples 1, 3, and 4 as examples, the capacity and cycle parameters of the samples using the first, second, and third activators, respectively, differ significantly. The sample using only the first activator has a higher capacity but poorer cycle performance. The sample using only the third activator has uneven etching of porous carbon, lower loading, lower capacity, and silicon nanowires growing on the surface of porous carbon. The spatial network structure of porous carbon does not provide support, resulting in poor cycle performance. Taking Examples 4, 5, 6, and 7 as examples, the activation... The lower the concentration of the activator, the less effective the activation of porous carbon, resulting in a lower loading of silicon nanowires and a lower capacity. The higher the concentration of the activator, the more likely the porous carbon is to be over-activated, and the spatial network structure of the porous carbon is insufficient to support the volume expansion of the silicon nanowires, resulting in poor cycling performance. The activation temperature and activation time have similar effects on the appearance morphology of porous carbon. The higher the activation temperature and the longer the activation time, the more likely the porous carbon is to be over-activated, resulting in lower strength and insufficient strength to support the volume expansion of the silicon nanowires. The lower the activation temperature and the shorter the activation time, the more likely the porous carbon is to be under-activated, resulting in insufficient loading and ultimately a lower material capacity.

[0136] This invention illustrates the detailed process equipment and process flow through the above embodiments. However, this invention is not limited to the detailed process equipment and process flow described above, meaning that this invention does not necessarily depend on the detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, additions of auxiliary components, and selection of specific methods, all fall within the protection scope and disclosure scope of this invention.

[0137] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0138] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0139] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a bio-carbon-supported silicon nanowire composite material, characterized in that, The preparation method includes: Biomass raw materials are first chemically activated at least twice, and then physically activated to obtain multilayer porous carbon; a metal catalyst is loaded into the multilayer porous carbon to obtain a support; the support is subjected to a catalytic growth reaction with a silicon source to form silicon nanowires, which are simultaneously loaded into the support to obtain a bio-carbon-supported silicon nanowire composite material. The chemical activation method includes mixing biomass raw materials or chemically activated biomass raw materials with a chemical activator and sintering them.

2. The preparation method according to claim 1, characterized in that, The biomass raw materials include at least one of pine cones, corn cobs, corn stalks, coconut shells, or peanut shells.

3. The preparation method according to claim 1, characterized in that, The biomass raw material is pre-dried to remove moisture, and then crushed, ground and sieved to obtain biomass raw material powder. The biomass raw material powder is then chemically activated, and the particle size of the biomass raw material powder is 150~600μm.

4. The preparation method according to claim 1, characterized in that, The chemical activation is performed twice.

5. The preparation method according to claim 4, characterized in that, Methods for chemically activating biomass raw materials twice include: Biomass raw materials are first mixed with a first activator and then sintered to obtain a first porous carbon with primary pores; the first porous carbon is second mixed with a second activator and then sintered to form secondary pores in the primary pores to obtain a second porous carbon; the second porous carbon is then physically activated.

6. The preparation method according to claim 5, characterized in that, The first activator includes at least one of potassium carbonate, potassium hydroxide, or sodium hydroxide.

7. The preparation method according to claim 5, characterized in that, The first mixing method includes solid-phase mechanical ball milling.

8. The preparation method according to claim 5, characterized in that, The mass ratio of the biomass raw material to the first activator is 1:(0.5~4).

9. The preparation method according to claim 5, characterized in that, The first sintering temperature is 700~900℃ and the time is 2~4h.

10. The preparation method according to claim 5, characterized in that, The second activator includes zinc chloride and / or phosphoric acid.

11. The preparation method according to claim 5, characterized in that, The mass ratio of the first porous carbon to the second activator is 1:(0.5~3).

12. The preparation method according to claim 5, characterized in that, The second mixing method is liquid-phase magnetic stirring and / or liquid-phase ultrasonic mixing.

13. The preparation method according to claim 5, characterized in that, The second sintering temperature is 600~800℃, and the time is 1~3h.

14. The preparation method according to claim 1, characterized in that, The physical activation method includes a third sintering of the chemically activated biomass raw material with a physical activator to obtain multilayer porous carbon.

15. The preparation method according to claim 14, characterized in that, The physical activator includes water vapor and / or carbon dioxide.

16. The preparation method according to claim 14, characterized in that, The flow rate of the physical activator is 50~100 sccm.

17. The preparation method according to claim 14, characterized in that, The third sintering temperature is 700~1000℃, and the time is 1~2h.

18. The preparation method according to claim 14, characterized in that, The heating and cooling stages of the third sintering in the physical activation process are carried out under the protection of an inert gas, and the heat holding stage of the third sintering is carried out in the atmosphere of the physical activator.

19. The preparation method according to claim 1, characterized in that, The method of loading a metal catalyst onto the multilayer porous carbon includes reacting the multilayer porous carbon with a metal catalyst raw material and a reducing agent to form a metal catalyst, which is then loaded onto the multilayer porous carbon to obtain a supported medium.

20. The preparation method according to claim 19, characterized in that, The raw materials for the metal catalyst include at least one of CuCl, CuCl2, FeCl3, CoCl2, HAuCl4, or SnCl2.

21. The preparation method according to claim 19, characterized in that, The reducing agent includes at least one of NaBH4, B2H6, or LiBH4.

22. The preparation method according to claim 19, characterized in that, The reduction reaction is carried out at a temperature of 25~80℃ for 12~24h.

23. The preparation method according to claim 1, characterized in that, The silicon source includes gaseous silicon compounds, which include silanes and / or silanes.

24. The preparation method according to claim 1, characterized in that, The temperature of the catalytic growth reaction is 600~1000℃.

25. The preparation method according to claim 1, characterized in that, The preparation method includes washing and drying the obtained sample after each chemical activation, wherein the drying temperature is 80~120℃; the washing method includes washing with 1M hydrochloric acid first, and then washing with deionized water until neutral.

26. The preparation method according to claim 1, characterized in that, The chemical activation, physical activation, and catalytic growth reactions are all carried out under an inert gas, which includes nitrogen and / or argon, and the flow rate of the inert gas is 500~1000 sccm.

27. The preparation method according to claim 26, characterized in that, In the catalytic growth reaction, the inert gas serves as the carrier gas for the silicon source.

28. A bio-carbon-supported silicon nanowire composite material, characterized in that, The preparation method according to any one of claims 1-27 is obtained.

29. A negative electrode sheet, characterized in that, The negative electrode contains the bio-carbon-supported silicon nanowire composite material as described in claim 28.

30. A lithium-ion battery, characterized in that, The lithium-ion battery contains the negative electrode sheet as described in claim 29.

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