Biochar-loaded silicon nanowire composite material as well as preparation method and application thereof

Abstract

The invention provides a biochar-loaded silicon nanowire composite material and a preparation method and application thereof.The preparation method comprises the steps that a chemical activation method and a physical activation method are combined, the surface and the interior of a biomass material are etched layer by layer, and multiple layers of biomass porous carbon materials with different pore diameters are formed; the problem that etching is not thorough or excessive when a single activating agent is used for preparing biomass porous carbon is effectively solved; the prepared multi-layer porous carbon is large in specific surface area and high in void ratio, metal catalyst particles with different sizes can be planted and loaded in the multi-layer porous carbon, and a grading effect on a large-particle catalyst is achieved; silicon nanowires grow in the load body in an oriented mode through catalytic growth, the spatial network structure of the multi-layer porous carbon can effectively bear volume expansion of the silicon nanowires, and repeated growth of the SEI film is restrained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and relates to a biocarbon-loaded silicon nanowire composite material and a preparation method and application thereof. BACKGROUND

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

[0003] The anode and anode material have a crucial influence on the performance of the battery and are a key field of battery research and development. At present, the anode material is mainly artificial graphite. With the maturation of the graphite industry, the energy density of the artificial graphite has approached the theoretical capacity of 372 mAh / g, and the space for improvement is small. Compared with the graphite, the theoretical specific capacity of the silicon-based material is close to ten times that of the graphite (4200 mAh / g). With the increasing requirements for the energy density and the endurance mileage of the battery, the silicon-based anode will undoubtedly become the most important research and application direction of the anode. However, the silicon material will produce a huge volume expansion in the lithium intercalation process, and the internal stress generated thereby will cause the silicon material to break and even pulverize, the electrode structure is damaged, and the capacity of the battery is sharply reduced.

[0004] In order to alleviate the volume expansion of the silicon material and reduce the mechanical stress of the silicon material, researchers have proposed an effective solution, which is silicon-carbon compounding. For example, CN101244814A proposes a preparation method of a lithium battery silicon-carbon anode material. The nanosilicon powder, pitch solution and spherical natural graphite are mixed and carbonized to obtain a silicon-carbon anode material. However, the interaction between the silicon powder and the carbon source is weak, and the volume expansion in the lithium intercalation process still easily causes the collapse of the electrode structure. The silicon-carbon anode material prepared by the method has a first efficiency of 80% to 85% and a reversible capacity of 420 to 450 mAh / g, and fails to reflect the superior properties of the silicon material. At present, the commercially applied silicon-carbon anode material is mainly a small amount of silicon doped in the graphite powder. Similar to the above patent, the specific capacity of the commercial graphite / silicon-carbon mixture is generally below 500 mAh / g, and the performance advantages of the silicon material are not fully utilized.

[0005] Therefore, it is necessary to continue to research and develop new silicon-carbon anode materials to fully utilize the performance advantages of the silicon material and effectively improve the electrical performance and stability of the anode material. SUMMARY

[0006] In view of the problems in the prior art, the purpose of the present application is to provide a biomass carbon loaded silicon nanowire composite material and a preparation method and use thereof, the preparation method uses biomass as a carbon source, combines chemical activation and physical activation methods, and performs activation etching on the surface and inside of the biomass to different degrees, thereby obtaining a biomass porous carbon material with multiple layers and multiple pore sizes, and using the same as a carrier of a metal catalyst to grow silicon nanowires, thereby obtaining a silicon-carbon negative electrode material with stable structure and high capacity.

[0007] To achieve this purpose, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a preparation method of a biomass carbon loaded silicon nanowire composite material, the preparation method comprising:

[0009] The biomass raw material is first subjected to chemical activation at least twice and then subjected to physical activation to obtain a multi-layered porous carbon; a metal catalyst is loaded in the multi-layered porous carbon to obtain a carrier; and the carrier is subjected to a catalytic growth reaction with a silicon source to form silicon nanowires and simultaneously load the silicon nanowires in the carrier, thereby obtaining a biomass carbon loaded silicon nanowire composite material (i.e., the carrier and the silicon nanowires loaded therein constitute the biomass carbon loaded silicon nanowire composite material).

[0010] The present application combines chemical activation and physical activation methods to etch layer by layer on the surface and inside of the biomass material, thereby forming a biomass porous carbon material with multiple layers and different pore sizes, effectively improving the problem of incomplete etching or excessive etching when using a single activator to prepare a biomass porous carbon; the multi-layered porous carbon has a large specific surface area and high porosity, and can plant metal catalyst particles of different sizes inside, thereby playing a grading role for large catalyst particles; and subsequently, the silicon nanowires are grown by loading a metal catalyst to catalyze a silicon source and are in-situ loaded in the multi-layered porous carbon material, thereby constituting the biomass carbon loaded silicon nanowire composite material. The multi-layered porous carbon has the advantage of providing pores of different sizes, which can provide conditions for the subsequent catalyst loading, the small catalyst particles are deposited in small-pore pores, and the large catalyst particles are deposited in large-pore pores, thereby facilitating the in-situ growth of silicon nanowires, playing a grading role, making the content of silicon wires in the overall product high, and the capacity high, and the multi-layered porous carbon with a network structure plays a role of skeleton support, which can effectively inhibit the volume expansion of the silicon nanowires and inhibit the repeated growth of the SEI film.

[0011] The following is a preferred technical solution of the present application, but is not a limitation of the technical solutions provided by the present application. Through the following technical solution, the technical purpose and beneficial effects of the present application can be better achieved and implemented.

[0012] As a preferred technical solution of the present application, the biomass raw material comprises at least one of pine cones, corn cobs, corn stalks, coconut shells or peanut shells, such as typical but non-limiting examples including a combination of pine cones and corn cobs, a combination of pine cones and corn stalks, a combination of pine cones and coconut shells, or a combination of pine cones and peanut shells, etc.

[0013] Preferably, the biomass raw material is pre-dried to remove moisture, and is crushed, ground and sieved to obtain biomass raw material powder. The biomass raw material powder is subjected to the chemical activation, and the particle size of the biomass raw material powder is 150-600 μm, such as 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, etc., but not limited to the listed values, and other values not listed in the above value range are also applicable.

[0014] As a preferred technical solution of the present application, the method of chemical activation comprises mixing the biomass raw material or the biomass raw material after chemical activation with a chemical activation agent and sintering.

[0015] Preferably, the number of chemical activation is twice.

[0016] Preferably, the method of twice chemical activation of the biomass raw material comprises:

[0017] The biomass raw material is mixed with a first activation agent for a first time, and is subjected to first sintering to obtain first porous carbon with primary pores; the first porous carbon is mixed with a second activation agent for a second time, and is subjected to second sintering to form secondary pores in the primary pores, thereby obtaining second porous carbon, and the second porous carbon is subjected to physical activation.

[0018] The preparation method of the present application preferably uses a first activation agent with strong etching effect to perform chemical activation to etch the surface layer of the biomass carbon to form large-pore pores (i.e. the primary pores, preferably with a pore size of 1-3 μm) to obtain first porous carbon; then a relatively mild second activation agent is used to further etch the inside of the large-pore pores of the first porous carbon to form small pores (i.e. the secondary pores, preferably with a pore size of 500-900 nm) by chemical activation, so that the biomass carbon obtains a structure with multi-level pore distribution; when subsequent physical activation is performed using a physical activation agent, tertiary pores (preferably with a pore size of <500 nm) can be formed in the primary pores and the secondary pores, thereby constructing the multi-layer porous carbon material, and loading a metal catalyst thereon (i.e. obtaining the support).

[0019] As a preferred technical solution of the present invention, the first activator includes at least one of potassium carbonate, sodium carbonate, potassium hydroxide or sodium hydroxide. For example, typical but non-limiting combination examples include a combination of potassium carbonate and potassium hydroxide, a combination of potassium carbonate and sodium hydroxide, or a combination of potassium hydroxide and sodium hydroxide.

[0020] In the existing process of synthesizing porous carbon using biomass raw materials, a single activator is usually used, which results in incomplete etching and excessive etching, which in turn leads to a low surface area of ​​the porous carbon and a broken porous carbon structure. The present invention combines the characteristics of each active agent, uses a variety of activators and activation methods, and further controls the sintering temperature and sintering time to obtain a biocarbon material with a complete structure, multiple layers and multi-level pore size distribution. In the preparation method of the present invention, the degree of activation can be adjusted by reasonably adjusting the amount of activator, the temperature during activation (sintering process) and the time, thereby controlling the stability of the overall structure of the multilayer porous carbon and avoiding excessive etching caused by structural collapse.

[0021] Preferably, the first mixing method comprises solid phase mechanical milling.

[0022] Preferably, the mass ratio of the biomass raw material to the first activating agent is 1:(0.5-4), for example, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5 or 1:4, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0023] In the present invention, when other conditions are the same, using too much of the first activator can easily lead to excessive material etching, collapse of the pore structure, and low yield; using too little can easily lead to inadequate etching, resulting in a reduction in the subsequent loading capacity.

[0024] Preferably, the temperature of the first sintering is 700-900°C, for example, 700°C, 730°C, 750°C, 780°C, 800°C, 830°C, 850°C, 880°C or 900°C, and the time is 2-4h, for example, 2h, 2.3h, 2.5h, 2.8h, 3h, 3.3h, 3.5h or 4h, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0025] In the present invention, under the condition that other conditions are the same, 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 pore structure; if the temperature is too low or the time is too short, it will easily lead to incomplete etching.

[0026] As a preferred technical solution 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 activating agent 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, etc., but not limited to the listed values, and other values not listed in the above numerical range are also applicable.

[0028] In the present application, under the same conditions, excessive use of the second activating agent can easily cause the secondary pores of the second layer to be too large, which can easily lead to structural collapse; and insufficient use can easily fail to achieve the design target of the pore structure.

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

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

[0031] In the present application, under the same conditions, excessive temperature or time of the second sintering can easily cause the secondary pores of the second layer to be too large, which can easily lead to structural collapse; and insufficient temperature or time can easily fail to achieve the design target of the pore structure.

[0032] As a preferred technical solution of the present application, the method of physical activation comprises third sintering of the biomass raw material that has been chemically activated with a physical activating agent to obtain a multi-layered porous carbon.

[0033] Preferably, the physical activating agent comprises water vapor and / or carbon dioxide.

[0034] Preferably, the flow rate of the physical activating agent is 50-100sccm, such as 50sccm, 60sccm, 70sccm, 80sccm, 90sccm, or 100sccm, etc., but not limited to the listed values, and other values not listed in the above numerical range are also applicable.

[0035] In the present application, under the same conditions, excessive use of the physical activating agent can easily cause the tertiary pores of the third layer to be too large, which can easily lead to structural collapse; and insufficient use can easily fail to achieve the design target of the pore structure.

[0036] Preferably, the third sintering is performed at a temperature of 700-1000°C, such as 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, or 1000°C, and for a time period of 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 not limited to the listed values, and other values within the above ranges are also applicable.

[0037] In the present application, under other conditions being the same, the temperature of the third sintering is too high or the time is too long, which can easily cause the third layer to have a too large third-level pore, and can easily lead to structural collapse; the temperature is too low or the time is too short, which can easily fail to achieve the design goal of the pore structure.

[0038] Preferably, the temperature rising stage and the temperature falling stage of the third sintering in the physical activation are performed under the protection of inert gas, and the temperature holding stage of the third sintering is performed in the atmosphere of the physical activator.

[0039] As a preferred technical solution of the present application, the method for loading a metal catalyst into the multi-layered porous carbon comprises: performing a reduction reaction on the multi-layered porous carbon with a metal catalyst raw material and a reducing agent, forming a metal catalyst and simultaneously loading the metal catalyst into the multi-layered porous carbon, and obtaining a carrier.

[0040] Preferably, the metal catalyst raw material comprises at least one of CuCl, CuCl2, FeCl3, CoCl2, HAuCl4, or SnCl2, such as typical but non-limiting examples including a combination of CuCl and CuCl2, a combination of CuCl and FeCl3, a combination of CuCl and CoCl2, a combination of CuCl and HAuCl4, a combination of CuCl and SnCl2, a combination of CuCl2 and FeCl3, a combination of CoCl2 and HAuCl4, or a combination of CoCl2 and SnCl2, etc.

[0041] Preferably, the reducing agent comprises at least one of NaBH4, B2H6, or LiBH4, such as typical but non-limiting combination examples including a combination of NaBH4 and B2H6, a combination of NaBH4 and LiBH4, or a combination of B2H6 and LiBH4, etc.

[0042] Preferably, the reduction reaction is performed at a temperature of 25-80°C, such as 25°C, 35°C, 45°C, 55°C, 65°C, 73°C, or 80°C, and for a time period of 12-24h, such as 12h, 14h, 16h, 18h, 20h, 22h, or 24h, but not limited to the listed values, and other values within the above ranges are also applicable.

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

[0044] Preferably, the temperature of the catalytic growth reaction is 600-1000°C, for example, 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 values ​​not listed within the above numerical range are also applicable.

[0045] The second mixing step of the present invention is preferably carried out in the liquid phase, that is, preferably using an in-situ impregnation reduction method to evenly distribute the metal catalyst within the pores of the multilayer porous carbon. The catalytic growth reaction is then preferably carried out using a VLS catalytic method to directionally grow silicon nanowires to form 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 the volume expansion and crushing of the negative electrode material. Compared to the prior art method of loading silicon particles onto a carrier using CVD, the capacity and stability of the silicon nanowires obtained by the present invention are significantly 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, and the drying temperature is 80-120°C, for example, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C, etc. The washing method includes first washing with 1M hydrochloric acid and then washing with deionized water until neutral, but is not limited to the listed values, and other values ​​not listed within the above numerical 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, and the inert gas includes nitrogen and / or argon. The flow rate of the inert gas is 500 to 1000 sccm, for example, 500 sccm, 600 sccm, 700 sccm, 800 sccm, 900 sccm or 1000 sccm, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

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

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

[0050] (1) drying the biomass raw material at 80-120° C. to remove moisture, crushing, grinding, and sieving to obtain a biomass raw material powder of 50-600 μm;

[0051] (2) mixing the biomass raw material powder and the first activator in a mass ratio of 1:(0.5-4), performing solid-phase mechanical ball milling, and then performing a first sintering at 700-900° C. for 2-4 h under the protection of an inert gas with a flow rate of 500-1000 sccm. After washing and drying the sample, a first porous carbon with primary pores is obtained;

[0052] (3) Mixing the first porous carbon and the second activator in an aqueous phase at a mass ratio of 1:(0.5-3), setting the magnetic stirring speed to 100-300 rpm, drying the sample in an oven at 100-150°C to remove moisture, and then performing a second sintering 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, and then washing the sample with 1M hydrochloric acid and then with deionized water until neutral, and drying at 80-100°C to obtain a second porous carbon;

[0053] (4) placing the second porous carbon in a quartz tube furnace, heating the temperature 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; stopping the introduction of the inert gas, introducing a physical activator at a flow rate of 50-100 sccm, and performing a third sintering for 1-2 hours, stopping the introduction of the physical activator, resuming the introduction of the inert gas, and cooling the temperature at a cooling rate of 1-10° C. / min to obtain a multilayer porous carbon;

[0054] (5) preparing a solution containing a metal catalyst raw material and a reducing agent, adding the multilayer porous carbon, and performing a reduction reaction at 25 to 80° C. for 12 to 24 hours to form a metal catalyst and simultaneously load it into the multilayer porous carbon to obtain a support;

[0055] (6) The support is placed in a vacuum tube furnace, an inert gas is used as a carrier gas to introduce a silicon source, and a catalytic growth reaction is performed at 600-1000° C. to form silicon nanowires and simultaneously load them in the support, thereby obtaining a biocarbon-loaded silicon nanowire composite material.

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

[0057] In a third aspect, the present invention provides a negative electrode plate, wherein the negative electrode plate contains the biocarbon-loaded silicon nanowire composite material described in the second aspect.

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

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

[0060] The present invention combines chemical activation with physical activation to etch the surface and interior of a biomass material layer by layer to form multi-layer biomass porous carbon materials with different pore sizes, effectively improving the problem of incomplete or excessive etching when using a single activator to prepare biomass porous carbon. The prepared multi-layer porous carbon has a large specific surface area and a high porosity, and can be planted with metal catalyst particles of different sizes to grade large-particle catalysts. Silicon nanowires are directionally grown in the support through catalytic growth, and the spatial network structure of the multi-layer porous carbon can effectively withstand the volume expansion of the silicon nanowires and inhibit the repeated growth of the SEI film. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0063] Figure 3 This is the SEM test image of the biochar material obtained in Comparative Example 2;

[0064] Figure 4 This is the SEM test image of the biocarbon material obtained in Comparative Example 4. DETAILED DESCRIPTION

[0065] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0066] It should be apparent to those skilled in the art that the embodiments are only intended to help understand the present invention and should not be considered as specific limitations of the present invention.

[0067] Example 1

[0068] This embodiment provides a method for preparing a biochar-loaded silicon nanowire composite material, the preparation method comprising:

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

[0070] (2) mixing the biomass raw material powder with a first activator, potassium hydroxide, in a mass ratio of 1:1.8, performing solid-phase mechanical ball milling, and then performing a first sintering at 900° C. for 1.5 h under the protection of an inert gas with a flow rate of 800 sccm. After washing and drying the sample, a first porous carbon having primary pores is 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, the sample was dried in an oven at 120 ° C to remove moisture, and then a second sintering was performed at 700 ° C for 2 h 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 1 M hydrochloric acid and then washed with deionized water until neutral, and dried at 90 ° C to obtain a second porous carbon;

[0072] (4) placing the second porous carbon in a quartz tube furnace, and heating the furnace to 850°C at a heating rate of 5°C / min under the protection of an inert gas with a flow rate of 800 sccm; stopping the introduction of the inert gas, and introducing water vapor as a physical activator at a flow rate of 70 sccm. After the third sintering for 1.5 hours, stopping the introduction of the physical activator, resuming the introduction of the inert gas, and cooling the furnace at a cooling rate of 5°C / min to obtain a multilayer porous carbon;

[0073] (5) preparing a solution containing a metal catalyst raw material CuCl2 and a reducing agent NaBH4, adding the multilayer porous carbon, and performing a reduction reaction at 60°C for 18 hours to form a metal catalyst and simultaneously load it in the multilayer porous carbon to obtain a support;

[0074] (6) The support is placed in a vacuum tube furnace, and silicon source silane is introduced using an inert gas as a carrier gas to perform a catalytic growth reaction at 800° C. to form silicon nanowires and simultaneously load them in the support, thereby obtaining a biocarbon-loaded silicon nanowire composite material.

[0075] Example 2

[0076] This embodiment provides a method for preparing a biochar-loaded silicon nanowire composite material, the preparation method comprising:

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

[0078] (2) mixing the biomass raw material powder and the first activator potassium carbonate in a mass ratio of 1:2, performing solid-phase mechanical ball milling, and then performing a first sintering at 800° C. for 2 h under the protection of an inert gas with a flow rate of 500 sccm. After washing and drying the sample, a 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, the sample was dried in an oven at 100 ° C to remove moisture, and then a second sintering was performed at 750 ° C for 2 h 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 1 M hydrochloric acid and then washed with deionized water until neutral, and dried at 80 ° C to obtain a second porous carbon;

[0080] (4) placing the second porous carbon in a quartz tube furnace, heating the temperature 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; stopping the introduction of the inert gas, introducing a physical activator, carbon dioxide, at a flow rate of 50 sccm, and performing a third sintering for 2 hours, then stopping the introduction of the physical activator, resuming the introduction of the inert gas, and cooling the temperature at a cooling rate of 2°C / min to obtain a multilayer porous carbon;

[0081] (5) preparing a solution containing a metal catalyst raw material HAuCl4 and a reducing agent LiBH4, adding the multilayer porous carbon, and performing 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 support;

[0082] (6) The support is placed in a vacuum tube furnace, and silicon source silane is introduced using an inert gas as a carrier gas to perform a catalytic growth reaction at 600° C. to form silicon nanowires and simultaneously load them in the support, thereby obtaining a biocarbon-loaded silicon nanowire composite material.

[0083] Example 3

[0084] This embodiment provides a method for preparing a biochar-loaded silicon nanowire composite material, the preparation method comprising:

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

[0086] (2) mixing the biomass raw material powder and the first activator sodium hydroxide in a mass ratio of 1:0.5, performing solid-phase mechanical ball milling, and then performing a first sintering at 900° C. for 2 h under the protection of an inert gas with a flow rate of 1000 sccm. After washing and drying the sample, a 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, the sample was dried in an oven at 150 ° C to remove moisture, and then a second sintering was performed 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 1 M hydrochloric acid and then washed with deionized water until neutral, and dried at 100 ° C to obtain a second porous carbon;

[0088] (4) placing the second porous carbon in a quartz tube furnace, heating the temperature to 800°C at a heating rate of 8°C / min under the protection of an inert gas with a flow rate of 1000 sccm; stopping the introduction of the inert gas, introducing water vapor as a physical activator at a flow rate of 100 sccm, and performing a third sintering for 1 hour, stopping the introduction of the physical activator, resuming the introduction of the inert gas, and cooling the temperature at a cooling rate of 8°C / min to obtain a multilayer porous carbon;

[0089] (5) preparing a solution containing a metal catalyst raw material CoCl2 and a reducing agent NaBH4, adding the multilayer porous carbon, and performing 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 support;

[0090] (6) The support is placed in a vacuum tube furnace, and silicon source silane is introduced using an inert gas as a carrier gas to perform a catalytic growth reaction at 850° C. to form silicon nanowires and simultaneously load them in the support, thereby obtaining a biocarbon-loaded silicon nanowire composite material.

[0091] Example 4

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

[0093] Example 5

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

[0095] Example 6

[0096] The present example provides a preparation method of a bio-carbon loaded silicon nanowire composite material, wherein the mass ratio of the biomass raw material powder to the first activating agent in step (2) is adjusted from 1:1.8 to 1:2.5, and other conditions are the same as those in Example 1.

[0097] Example 7

[0098] The present example provides a preparation method of a bio-carbon loaded silicon nanowire composite material, wherein the mass ratio of the biomass raw material powder to the first activating agent in step (2) is adjusted from 1:1.8 to 1:4, and other conditions are the same as those in Example 1.

[0099] Example 8

[0100] The present example provides a preparation method of a bio-carbon loaded silicon nanowire composite material, wherein the temperature of the first sintering in step (2) is adjusted from 800℃ to 650℃, and other conditions are the same as those in Example 1.

[0101] Example 9

[0102] The present example provides a preparation method of a bio-carbon loaded silicon nanowire composite material, wherein the temperature of the first sintering in step (2) is adjusted from 800℃ to 700℃, and other conditions are the same as those in Example 1.

[0103] Example 10

[0104] The present example provides a preparation method of a bio-carbon loaded silicon nanowire composite material, wherein the temperature of the first sintering in step (2) is adjusted from 800℃ to 900℃, and other conditions are the same as those in Example 1.

[0105] Example 11

[0106] The present example provides a preparation method of a bio-carbon loaded silicon nanowire composite material, wherein the temperature of the first sintering in step (2) is adjusted from 800℃ to 950℃, and other conditions are the same as those in Example 1.

[0107] Comparative Example 1

[0108] The present comparative example provides a preparation method of a bio-carbon loaded silicon nanowire composite material, wherein steps (3) and (4) are not performed, and the first porous carbon obtained in step (2) is used in step (5) instead of the multi-layered porous carbon, and other conditions are the same as those in Example 1.

[0109] Comparative Example 2

[0110] This comparative example provides a method for preparing a biochar-loaded silicon nanowire composite material. The preparation method does not perform steps (3) and (4), and adjusts step (2) to:

[0111] The biomass raw material powder and the first activator are mixed in a mass ratio of 1:4, solid-phase mechanical ball milling is performed, and then a first sintering is performed at 950° C. for 3 h under the protection of an inert gas with a flow rate of 1000 sccm. The sample is washed with water and dried to obtain a biocarbon material; the first porous carbon obtained in step (2) is used in step (5) to replace the multilayer porous carbon;

[0112] Except for the above, other conditions are exactly the same as those in Example 1.

[0113] Comparative Example 3

[0114] This comparative example provides a method for preparing a biochar-loaded 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) instead of the first porous carbon to obtain a biochar material and use it in step (5). Except for the above, other conditions are exactly the same as those in Example 1.

[0115] Comparative Example 4

[0116] This comparative example provides a method for preparing a biochar-loaded 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) instead of the second porous carbon to obtain a biochar material and use it in step (5). Except for the above, other conditions are exactly the same as those in Example 1.

[0117] Comparative Example 5

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

[0119] Comparative Example 6

[0120] This comparative example provides a method for preparing a biochar-loaded silicon nanowire composite material. The preparation method does not perform step (3), and the first porous carbon obtained in step (2) is used in step (4) instead of the second porous carbon. Except for the above, other conditions are exactly the same as those in Example 1.

[0121] Comparative Example 7

[0122] This comparative example provides a method for preparing a biochar-loaded silicon nanowire composite material. The preparation method does not perform step (4), and the second porous carbon obtained in step (3) is used in step (5) instead of the multilayer porous carbon. Except for the above, other conditions are exactly the same as those in Example 1.

[0123] Control group 1

[0124] The control group used the multilayer porous carbon obtained in step (4) of Example 1, and loaded thereon the silicon nanoparticle material in the same amount as the silicon nanowire loading in Example 1.

[0125] Control group 2

[0126] The control group used commercially available porous carbon, which was used to replace the multilayer porous carbon in steps (5) and (6) to load silicon nanowires.

[0127] Ⅰ. Morphological characterization:

[0128] Figure 1 This is a SEM test 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, has large pores on the surface, and contains small pores within the large pores, and has a complete overall structure. Figure 2 is a SEM image of the biochar-loaded silicon nanowire composite material obtained in Example 1, showing that silicon nanowires are successfully generated and loaded within the pores of the multilayer porous carbon; Figure 3 This is a SEM test image of the biochar material obtained in Comparative Example 2. Comparative Example 2 is the biochar obtained by directly using KOH to activate biomass. Due to the strong etching ability of KOH, the activation etching is excessive, resulting in a large distribution of macropores (greater than 1 μm). Although some small pores are also contained in the surface macropores, the original porous carbon network structure collapses, the overall morphology is broken, and the particle size is about 1 to 10 μm, which is not conducive to being used as a carrier for silicon nanowires; Figure 4 This is an SEM test image of the biochar material obtained in Example 4. Comparative Example 4 is the biochar obtained by activating the biomass raw material only by a physical activator. Its overall pore size is small, and only the surface layer is etched. No other small pores are formed in the pores. There is also an uneven pore distribution, and some areas do not have pores. Using it as a carrier for silicon nanowires only grows silicon wires on the outer surface of the porous carbon, and cannot improve the current situation of volume expansion, breakage, and repeated growth of the SEI film of the silicon nanowires.

[0129] II. Battery test:

[0130] The material obtained in the examples, comparative examples and control group was used as a negative electrode active material. The above negative electrode active material, a conductive agent and a binder were prepared into a slurry with deionized water in a corresponding proportion, and were continuously grinded until uniform. The slurry was uniformly coated on a copper foil as a current collector by using a 250 μm doctor blade, and then was placed in a vacuum oven at 80°C for drying for 12 h. After that, the electrode was formed by compression molding through a roll press, and was punched into a circular electrode sheet with a diameter of 12 mm. The electrode sheet was placed in an Ar-filled glove box, and then a coin-type battery was assembled in the order of the electrode sheet, a separator, an electrolyte, a lithium sheet, a gasket and a spring.

[0131] The obtained battery was tested. The assembled half battery was subjected to charge-discharge test and rate performance test by using a new CT / CTE-4000 series multi-channel battery test system. The test temperature was 30°C, and the test voltage range was 0.01-1.5 V. The obtained results are recorded in Table 1.

[0132] Table 1

[0133]

[0134]

[0135] As can be seen from Table 1, the type and amount of activator, activation temperature and activation time can affect the apparent morphology of the multi-layered porous carbon, and then affect the loading of the catalyst, and finally affect the capacity and cycle number of the negative electrode material. The type of activation is crucial to the apparent morphology of the porous carbon. For example, the capacity and cycle parameters of the samples using the first activator, the second activator and the third activator in Comparative Example 1, Comparative Example 3 and Comparative Example 4 are quite different. 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 the porous carbon, a lower loading amount, a lower capacity and the growth of silicon nanowires on the surface of the porous carbon. The spatial network structure of the porous carbon does not play a supporting role, and thus the cycle performance is poor. For example, the lower the concentration of the activator in Example 4, Example 5, Example 6 and Example 7, the lower the loading amount of the silicon nanowires and the capacity of the material due to the incomplete activation of the porous carbon. The higher the concentration of the activator, the more likely the over-activation of the porous carbon. The spatial network structure of the porous carbon is not enough to support the volume expansion of the silicon nanowires, resulting in poor cycle performance of the material. The activation temperature and activation time have a similar effect on the apparent morphology of the porous carbon. The higher the activation temperature and the longer the activation time, the more likely the over-activation of the porous carbon, and the lower the strength, which is not enough to support the volume expansion of the silicon nanowires. The lower the activation temperature and the shorter the activation time, the lower the loading amount and the capacity of the material due to the incomplete activation of the porous carbon.

[0136] While the present invention uses the above-described embodiments to illustrate the detailed process equipment and process flow of the present invention, the present invention is not limited to the above-described detailed process equipment and process flow, and does not necessarily rely on the above-described detailed process equipment and process flow for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent replacements for raw materials in the products of the present invention, additions of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

[0137] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within 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 scope of protection 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 appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0139] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing a biocarbon-loaded silicon nanowire composite material, characterized in that: The preparation method comprises: The biomass raw material is 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 body; the support body is subjected to a catalytic growth reaction with a silicon source to form silicon nanowires which are simultaneously loaded into the support body to obtain a biocarbon-loaded silicon nanowire composite material.

2. The preparation method according to claim 1, characterized in that The biomass raw material comprises at least one of pine cones, corn cobs, corn stalks, coconut shells or peanut shells; Preferably, the biomass raw material is dried in advance to remove moisture, and is crushed, ground and sieved to obtain biomass raw material powder, which is then chemically activated. The particle size of the biomass raw material powder is 150 to 600 μm.

3. The preparation method according to claim 1 or 2, characterized in that The chemical activation method includes mixing the biomass raw material or the chemically activated biomass raw material with a chemical activator and sintering the mixture; Preferably, the chemical activation is performed twice; Preferably, the method of chemically activating the biomass raw material twice comprises: The biomass raw material is first mixed with a first activating agent, and then first sintered to obtain a first porous carbon having primary pores; The first porous carbon is mixed with a second activator for a second time, and then sintered for a second time to form secondary pores in the primary pores to obtain second porous carbon, and the second porous carbon is physically activated.

4. The preparation method according to claim 3, characterized in that The first activator includes at least one of potassium carbonate, potassium hydroxide or sodium hydroxide; Preferably, the first mixing method comprises solid phase mechanical ball milling; Preferably, the mass ratio of the biomass raw material to the first activating agent is 1:(0.5-4); Preferably, the temperature of the first sintering is 700-900°C and the time is 2-4 hours; Preferably, the second activator comprises zinc chloride and / or phosphoric acid; Preferably, the mass ratio of the first porous carbon to the second activator is 1:(0.5-3); Preferably, the second mixing method is liquid phase magnetic stirring and / or liquid phase ultrasonic mixing; Preferably, the second sintering temperature is 600-800° C., and the time is 1-3 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that The physical activation method includes performing a third sintering of the chemically activated biomass raw material with a physical activating agent to obtain multilayer porous carbon; Preferably, the physical activator comprises water vapor and / or carbon dioxide; Preferably, the flow rate of the physical activator is 50 to 100 sccm; Preferably, the temperature of the third sintering is 700-1000° C., and the time is 1-2 hours; Preferably, the temperature rising stage and the temperature falling stage of the third sintering in the physical activation are carried out under the protection of an inert gas, and the heat keeping stage of the third sintering is carried out in the atmosphere of the physical activating agent.

6. The preparation method according to any one of claims 1 to 5, characterized in that The method for loading the metal catalyst in the multilayer porous carbon comprises: subjecting the multilayer porous carbon to a reduction reaction with a metal catalyst raw material and a reducing agent to form a metal catalyst and simultaneously loading the metal catalyst in the multilayer porous carbon to obtain a support; Preferably, the raw material of the metal catalyst includes at least one of CuCl, CuCl2, FeCl3, CoCl2, HAuCl4 or SnCl2; Preferably, the reducing agent comprises at least one of NaBH4, B2H6 or LiBH4; Preferably, the reduction reaction temperature is 25 to 80° C. and the time is 12 to 24 hours; Preferably, the silicon source comprises a gaseous silicon compound, and the gaseous silicon compound comprises silane and / or silane; Preferably, the temperature of the catalytic growth reaction is 600-1000°C.

7. The preparation method according to any one of claims 1 to 6, characterized in that The preparation method includes washing and drying the obtained sample after each chemical activation, wherein the drying temperature is 80-120° C.; the washing method includes first washing with 1M hydrochloric acid and then washing with deionized water until neutral; Preferably, the chemical activation, the physical activation and the catalytic growth reaction are all carried out under an inert gas, wherein the inert gas includes nitrogen and / or argon, and the flow rate of the inert gas is 500 to 1000 sccm; Preferably, the inert gas is used as a carrier gas for the silicon source in the catalytic growth reaction.

8. A biocarbon-supported silicon nanowire composite material, characterized in that: Obtained according to the preparation method according to any one of claims 1 to 7.

9. A negative electrode plate, characterized in that: The negative electrode plate contains the biocarbon-loaded silicon nanowire composite material according to claim 8.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode sheet according to claim 9.

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