A rice hull derived carbon@silica composite

Abstract

The present application provides a rice husk-derived carbon@silica composite material, which uses rice husk as raw material, and after pretreatment, is calcined under the protection of inert gas to obtain the rice husk-derived carbon@silica composite material. The rice husk-derived carbon@silica composite material provided in the present application has abundant raw material sources and low costs, and realizes waste recycling; its preparation method is simple and easy, green and environmentally friendly, and suitable for large-scale production. The rice husk-derived carbon@silica composite material provided in the present application has a hierarchical porous structure, which is not only conducive to the formation of a stable solid electrolyte interface film to inhibit side reactions, but also can improve the negative effects caused by the poor conductivity and volume change effect of the silica negative electrode material, thereby having good cycle stability. Using the rice husk-derived carbon@silica composite material provided in the present application as a negative electrode material for lithium-ion batteries is beneficial to improving the cycle stability and rate performance of lithium-ion batteries.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of battery negative electrode material preparation, in particular to a rice hull derived carbon@silicon dioxide composite material. BACKGROUND

[0002] Rice hull, as one of the main by-products of rice processing, accounts for about one fifth of the rice yield, and has a high yield. At present, the main treatment method for rice hull is to burn it on the spot or to bury it, and the generated rice hull ash will pollute the environment if not treated. Therefore, how to more effectively utilize the rice hull or the rice hull ash has important significance for environmental protection and energy utilization.

[0003] The main components of rice hull are about 40% cellulose, about 20% lignin, about 20% hemicellulose, about 20% silicon dioxide and ash. The silicon dioxide content in rice hull is high, and the roots of rice can absorb soluble silicon dioxide or water-silicic acid from the soil and then convert them into hydrated silicon dioxide (SiO2·nH2O). The silicon dioxide in rice hull exists in the form of nanoparticles, so that the rice hull derived silicon dioxide material is expected to become a negative electrode material of a lithium ion battery. In the prior art, rice hull is usually used as a precursor of a silicon-based negative electrode material, and the silicon dioxide in the rice hull is reduced to porous silicon for use as a negative electrode material of a lithium ion battery, which is relatively complex in technology and has a high reduction cost. SUMMARY

[0004] The application aims to provide a rice hull derived carbon@silicon dioxide composite material, so as to provide a negative electrode material which is simple and easy to prepare and low in cost. The specific technical scheme is as follows:

[0005] The first aspect of the application provides a rice hull derived carbon@silicon dioxide composite material, which is prepared by the following process:

[0006] (1) washing and drying rice hull, then adding a citric acid solution for acid washing, and then washing and drying to obtain pretreated rice hull; wherein the mass ratio of the rice hull to the solute in the citric acid solution is 1:0.6-1:2.4;

[0007] (2) calcining the pretreated rice hull under the protection of an inert gas to obtain the rice hull derived carbon@silicon dioxide composite material, wherein the calcination temperature is 600-800 DEG C, the time is 1-3 h, and the heating rate is 3-7 DEG C / min.

[0008] The second aspect of the application provides a rice hull derived carbon@silicon dioxide composite material, which is prepared by the following process:

[0009] (1) washing and drying rice husks, then adding a citric acid solution to perform acid washing, then washing and drying to obtain pretreated rice husks; wherein the mass ratio of the rice husks to the solute in the citric acid solution is 1:0.6-1:2.4;

[0010] (2) mixing the pretreated rice husks with a dilute sulfuric acid solution, refluxing at 100-110°C for 3-5h, then washing and drying to obtain rice husks without hemicellulose; wherein the mass ratio of the rice husks to the dilute sulfuric acid solution is 1:6-1:10, and the concentration of the dilute sulfuric acid solution is 1wt%-1.5wt%;

[0011] (3) calcining the rice husks without hemicellulose under inert gas protection to obtain the rice husk-derived carbon@silicon dioxide composite material, wherein the calcination temperature is 600-800°C, the time is 1-3h, and the heating rate is 3-7°C / min.

[0012] The third aspect of the present application provides a rice husk-derived carbon@silicon dioxide composite material, which is prepared by the following process:

[0013] (1) washing and drying rice husks, then adding a citric acid solution to perform acid washing, then washing and drying to obtain pretreated rice husks; wherein the mass ratio of the rice husks to the solute in the citric acid solution is 1:0.6-1:2.4;

[0014] (2) mixing the pretreated rice husks with a dilute sulfuric acid solution, refluxing at 100-110°C for 3-5h, then washing and drying to obtain rice husks without hemicellulose; wherein the mass ratio of the rice husks to the dilute sulfuric acid solution is 1:6-1:10, and the concentration of the dilute sulfuric acid solution is 1wt%-1.5wt%;

[0015] (3) mixing the rice husks without hemicellulose with a concentrated sulfuric acid solution according to a mass ratio of 1:8-1:12 to perform a hydrothermal reaction, then washing and drying after the reaction to obtain rice husks containing lignin; wherein the reaction temperature of the hydrothermal synthesis reaction is 120-140°C, the reaction time is 5-8h, and the concentration of the concentrated sulfuric acid solution is 30wt%-35wt%;

[0016] (4) calcining the rice husks containing lignin under inert gas protection to obtain a rice husk-derived carbon@silicon dioxide composite material, wherein the calcination temperature is 600-800°C, the time is 1-3h, and the heating rate is 3-7°C / min.

[0017] The fourth aspect of the present application provides a rice husk-derived carbon@silicon dioxide composite material, which is prepared by the following process:

[0018] (1) washing, drying rice husks, and then adding a citric acid solution to perform acid washing, and then washing and drying to obtain pretreated rice husks; wherein the mass ratio of the rice husks to the solute in the citric acid solution is 1:0.6-1:2.4;

[0019] (2) mixing the pretreated rice husks with a dilute sulfuric acid solution, refluxing at 100℃-110℃ for 3h-5h, and then washing and drying to obtain rice husks free of hemicellulose; wherein the mass ratio of the rice husks to the dilute sulfuric acid solution is 1:6-1:10, and the concentration of the dilute sulfuric acid solution is 1wt%-1.5wt%;

[0020] (3) mixing the rice husks free of hemicellulose with an ethylene glycol aqueous solution according to a mass ratio of 1:5-1:9 to perform a hydrothermal reaction, washing and drying after the reaction is completed to obtain rice husks containing cellulose, wherein the reaction temperature of the hydrothermal synthesis reaction is 180℃-220℃, the reaction time is 3h-5h, and the concentration of the ethylene glycol aqueous solution is 75wt%-85wt%;

[0021] (4) calcining the rice husks containing cellulose under protection of an inert gas to obtain a rice husk-derived carbon@silicon dioxide composite material, wherein the calcination temperature is 600℃-800℃, the time is 1h-3h, and the heating rate is 3℃ / min-7℃ / min.

[0022] In some embodiments of the present application, the step of acid washing comprises washing with a citric acid solution at 70℃-90℃ for 10min-30min, and the concentration of the citric acid solution is 3wt%-8wt%.

[0023] In some embodiments of the present application, the specific surface area of the rice husk-derived carbon@silicon dioxide composite material is 230m 2 g -1 -280m 2 g -1 , and the pore size is 1nm-15nm.

[0024] A fifth aspect of the present application provides a negative electrode tab, comprising a negative electrode material layer, wherein the negative electrode material layer comprises the rice husk-derived carbon@silicon dioxide composite material provided in any one of the first aspect, the second aspect, the third aspect or the fourth aspect of the present application.

[0025] In some embodiments of the present application, the mass percentage content of the rice husk-derived carbon@silicon dioxide composite material is 1%-99%, based on the total mass of the negative electrode material layer.

[0026] The sixth aspect of the present application provides a lithium ion battery comprising the negative electrode sheet provided by the fifth aspect of the present application.

[0027] The beneficial effects of the present application are as follows:

[0028] The present application provides a rice husk-derived carbon@silicon dioxide composite material, which is prepared by using rice husk as raw material, pre-treating the rice husk, and calcining the pre-treated rice husk under the protection of inert gas. The rice husk-derived carbon@silicon dioxide composite material provided by the present application has abundant raw material source and low cost, realizes waste recycling, and has simple and easy-to-operate preparation method, is green and environmentally friendly, and is suitable for large-scale production. The rice husk-derived carbon@silicon dioxide composite material provided by the present application has hierarchical porous structure and low charge transfer resistance, which is not only beneficial to form stable solid electrolyte interface film to inhibit side reactions, but also can improve the negative effects of poor conductivity of silicon dioxide negative electrode material and volume change effect, thereby having good cycle stability. Using the rice husk-derived carbon@silicon dioxide composite material provided by the present application as negative electrode material of lithium ion battery is beneficial to improve the cycle stability and rate performance of lithium ion battery.

[0029] Of course, implementing any product or method of the present application does not necessarily require achieving all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art according to these drawings.

[0031] Figure 1 The infrared spectrum of the rice husk-derived material before calcination in Examples 1-4;

[0032] Figure 2 The nitrogen adsorption-desorption curve of the rice husk-derived carbon@silicon dioxide composite material prepared in Examples 1-4;

[0033] Figure 3 The pore size distribution graph of the rice husk-derived carbon@silicon dioxide composite material prepared in Examples 1-4;

[0034] Figure 4 The nitrogen adsorption-desorption curve of the intermediate product rice husk-derived silicon dioxide material (RH-SiO2) in Example 1;

[0035] Figure 5 The pore size distribution graph of the intermediate product RH-SiO2 in Example 1;

[0036] Figure 6 This is a scanning electron microscope (SEM) photograph of the intermediate product RH-SiO2 in Example 1;

[0037] Figure 7 This is a SEM photo of the intermediate product RH-SiO2 in Example 1;

[0038] Figure 8 This is a SEM photo of the intermediate product RH-SiO2 in Example 1;

[0039] Figure 9a This is a high-angle annular dark field scanning transmission electron microscopy (STEM-HAADF) image of the rice husk-derived carbon@silica composite material in Example 1;

[0040] Figure 9b for Figure 9a Elemental energy dispersive X-ray spectroscopy mapping distribution of O element in rice husk derived carbon@silica composites;

[0041] Figure 9c for Figure 9a Elemental energy dispersive X-ray spectroscopy mapping distribution of Si element in rice husk derived carbon@silica composites;

[0042] Figure 9d for Figure 9a Elemental energy dispersive X-ray spectroscopy mapping distribution of C element in rice husk derived carbon@silica composites;

[0043] Figure 10 for Figure 9a Elemental X-ray energy dispersive (EDS) patterns of the rice husk derived carbon@silica composites;

[0044] Figure 11 Graphs showing the rate performance of the rice husk-derived carbon@silica composites at different current densities in Examples 1-4;

[0045] Figure 12a The lithium ion battery prepared in Example 1-4 was subjected to a load of 400 mA·g -1 Specific capacity change diagram after 200 cycles at different current densities;

[0046] Figure 12b The lithium ion battery prepared in Example 1-4 was subjected to a load of 400 mA·g -1 Coulombic efficiency change diagram after 200 cycles at different current densities;

[0047] Figure 13 This is a long-term cycle performance diagram of the lithium-ion battery prepared in Example 3;

[0048] Figure 14A graph of the long-term cycling performance of a lithium-ion battery prepared for Example 4. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art based on the present application belong to the scope of protection of the present application.

[0050] The inventors found that the natural vascular bundle structure in rice husks makes large pores naturally exist in the rice husks. The organic carbon components in the rice husks include cellulose, hemicellulose and lignin. The three natural biomasses have different composition structures and different physicochemical properties. In the hierarchical porous carbon electrode material for energy storage, the hierarchical porous structure of the hierarchical porous carbon is closely related to the different components in the rice husks and can be adjusted through carbonization, desiliconization and activation. The pores of 3 nm-50 nm are mainly formed in the carbonization and desiliconization process of the rice husks, and the micropores (<2 nm) and the small-sized mesopores (2 nm-3 nm) are mainly formed in the activation process of the rice husks. Among the organic carbon components in the rice husks, lignin is the main contributor of the micropores, and lignin is crucial to the high specific capacitance and excellent rate performance of the hierarchical porous carbon electrode material; cellulose has good electrical conductivity, and in combination with the stable carbon skeleton of the hierarchical porous carbon, the hierarchical porous carbon electrode material has excellent cycle stability; and hemicellulose helps the hierarchical porous carbon electrode material to have high specific capacitance and low charge transfer resistance.

[0051] Therefore, the first aspect of the present application provides a rice husk-derived carbon@silicon dioxide composite material, which is prepared by the following process:

[0052] (1) washing and drying the rice husks, then adding a citric acid solution for acid washing, and then washing and drying to obtain pretreated rice husks; wherein the mass ratio of the rice husks to the solute in the citric acid solution is 1:0.6-1:2.4;

[0053] (2) calcining the pretreated rice husks under the protection of an inert gas to obtain the rice husk-derived carbon@silicon dioxide composite material, wherein the calcination temperature is 600°C-800°C, the time is 1h-3h, and the heating rate is 3°C / min-7°C / min.

[0054] The preparation method of the rice husk-derived carbon@silica composite material provided in the first aspect of the present application comprises the following steps: firstly, the rice husk is cleaned with tap water and deionized water to remove dust and other impurities on the surface of the rice husk; then the rice husk is pickled with a citric acid solution to remove as much as possible metal impurities (such as sodium ions, potassium ions, iron ions and magnesium ions) in the rice husk; and then the rice husk is calcined under the protection of an inert gas to carbonize the organic carbon components (cellulose, hemicellulose and lignin) in the rice husk, thereby obtaining the rice husk-derived carbon@silica composite material.

[0055] The second aspect of the present application provides a rice husk-derived carbon@silica composite material prepared by the following process:

[0056] (1) The rice husk is cleaned, dried, then added into a citric acid solution for pickling, then cleaned and dried to obtain pretreated rice husk; wherein the mass ratio of the rice husk to the solute in the citric acid solution is 1:0.6-1:2.4;

[0057] (2) The pretreated rice husk is mixed with a dilute sulfuric acid solution, and then refluxed at 100-110℃ for 3-5h, and then cleaned and dried to obtain rice husk without hemicellulose; wherein the mass ratio of the rice husk to the dilute sulfuric acid solution is 1:6-1:10, and the concentration of the dilute sulfuric acid solution is 1wt%-1.5wt%;

[0058] (3) The rice husk without hemicellulose is calcined under the protection of an inert gas to obtain the rice husk-derived carbon@silica composite material, wherein the calcination temperature is 600-800℃, the calcination time is 1-3h, and the heating rate is 3-7℃ / min.

[0059] The preparation method of the rice husk-derived carbon@silica composite material provided in the second aspect of the present application comprises the following steps: firstly, the rice husk is cleaned with tap water and deionized water to remove dust and other impurities on the surface of the rice husk; then the rice husk is pickled with a citric acid solution to remove as much as possible metal impurities (such as sodium ions, potassium ions, iron ions and magnesium ions) in the rice husk; and then the rice husk is calcined under the protection of an inert gas to carbonize the organic carbon components (cellulose, hemicellulose and lignin) in the rice husk, thereby obtaining the rice husk-derived carbon@silica composite material.

[0060] The third aspect of the present application provides a rice husk-derived carbon@silica composite material prepared by the following process:

[0061] (1) washing, drying rice husks, and then adding a citric acid solution to perform acid washing, and then washing and drying to obtain pretreated rice husks; wherein the mass ratio of the rice husks to the solute in the citric acid solution is 1:0.6-1:2.4;

[0062] (2) mixing the pretreated rice husks with a dilute sulfuric acid solution, refluxing at 100-110°C for 3-5h, and then washing and drying to obtain rice husks without hemicellulose; wherein the mass ratio of the rice husks to the dilute sulfuric acid solution is 1:6-1:10, and the concentration of the dilute sulfuric acid solution is 1wt%-1.5wt%;

[0063] (3) mixing rice husks without hemicellulose with a concentrated sulfuric acid solution according to a mass ratio of 1:8-1:12 to perform hydrothermal reaction, washing and drying after the reaction is completed to obtain rice husks containing lignin; wherein the reaction temperature of the hydrothermal synthesis reaction is 120-140°C, the reaction time is 5-8h, and the concentration of the concentrated sulfuric acid solution is 30wt%-35wt%;

[0064] (4) calcining the rice husks containing lignin under the protection of an inert gas to obtain rice husk-derived carbon@silicon dioxide composite materials, wherein the calcination temperature is 600-800°C, the time is 1-3h, and the heating rate is 3-7°C / min.

[0065] In the preparation method of the rice husk-derived carbon@silicon dioxide composite material provided in the third aspect of the present application, the rice husks are first washed by tap water and deionized water to remove dust and other impurities on the surface of the rice husks; then the rice husks are acid washed by a citric acid solution to remove metal impurities (such as sodium ions, potassium ions, iron ions, and magnesium ions) in the rice husks as much as possible; then the hemicellulose component in the rice husks is removed by acid washing treatment with a dilute sulfuric acid solution without damaging the original structure of the organic carbon component as much as possible to obtain rice husks without hemicellulose; then the cellulose in the rice husks is removed by hydrothermal reaction with a concentrated sulfuric acid solution to obtain rice husks containing lignin; and finally, the lignin carbonization of the organic carbon component in the rice husks is performed by calcining the rice husks containing lignin under the protection of an inert gas to obtain rice husk-derived carbon@silicon dioxide composite materials.

[0066] The fourth aspect of the present application provides a rice husk-derived carbon@silicon dioxide composite material, which is prepared by the following process:

[0067] (1) washing, drying rice husks, and then adding a citric acid solution to perform acid washing, and then washing and drying to obtain pretreated rice husks; wherein the mass ratio of the rice husks to the solute in the citric acid solution is 1:0.6-1:2.4;

[0068] (2) mixing the pretreated rice husk with a dilute sulfuric acid solution, refluxing at 100-110°C for 3-5h, and then washing and drying to obtain the rice husk without hemicellulose; wherein the mass ratio of the rice husk to the dilute sulfuric acid solution is 1:6-1:10, and the concentration of the dilute sulfuric acid solution is 1wt%-1.5wt%;

[0069] (3) mixing the rice husk without hemicellulose with an aqueous ethylene glycol solution according to a mass ratio of 1:5-1:9, and then performing a hydrothermal reaction, washing and drying after the reaction to obtain the rice husk containing cellulose; wherein the reaction temperature of the hydrothermal synthesis reaction is 180-220°C, the reaction time is 3-5h, and the concentration of the aqueous ethylene glycol solution is 75wt%-85wt%;

[0070] (4) calcining the rice husk containing cellulose under the protection of an inert gas to obtain the rice husk-derived carbon@silicon dioxide composite material; wherein the calcination temperature is 600-800°C, the time is 1-3h, and the heating rate is 3-7°C / min.

[0071] In the preparation method of the rice husk-derived carbon@silicon dioxide composite material provided in the fourth aspect of the present application, the rice husk is first cleaned with tap water and deionized water to remove dust and other impurities on the surface of the rice husk; then the rice husk is pickled with a citric acid solution to remove as much as possible metal impurities (such as sodium ions, potassium ions, iron ions and magnesium ions, etc.) in the rice husk; then the hemicellulose component in the rice husk is removed by acid washing treatment with a dilute sulfuric acid solution without damaging as much as possible the original structure of the organic carbon component, to obtain the rice husk without hemicellulose; then the aqueous ethylene glycol solution is added to perform a hydrothermal reaction to remove the lignin in the rice husk, to obtain the rice husk containing cellulose; and finally the rice husk containing lignin is calcined under the protection of an inert gas to carbonize the cellulose in the rice husk, to obtain the rice husk-derived carbon@silicon dioxide composite material.

[0072] The rice husk-derived carbon@silicon dioxide composite material provided in the present application has abundant raw material sources and low cost, and realizes waste recycling; the preparation method is simple and easy to implement, green and environmentally friendly, and suitable for large-scale production. The rice husk-derived carbon@silicon dioxide composite material has a hierarchical porous structure and a low charge transfer resistance, which is not only beneficial to the formation of a stable solid electrolyte interface film to inhibit side reactions, but also can improve the negative effects of poor conductivity of the silicon dioxide negative electrode material and volume change effect, thereby having good cycle stability.

[0073] In some embodiments of the present application, the step of acid washing comprises: cleaning with a citric acid solution at 70-90°C for 10-30 min, the concentration of the citric acid solution being 3-8 wt%. In the present application, the metal impurities in the rice husk can be removed as much as possible by acid washing. The operation steps of acid washing in the present application are not particularly limited as long as the purpose of the present application can be achieved. For example, the cleaned rice husk is added into a 3-8 wt% citric acid solution, and acid washing is carried out by magnetic stirring in an oil bath at 70-90°C for 10-30 min.

[0074] In the present application, the rice husk-derived carbon@silica composite material is obtained by carbonizing the rice husk-derived silica material through calcination. The temperature of calcination can be 600°C, 650°C, 700°C, 750°C, 800°C, or a range formed by any two of the above values. The time of calcination can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, or a range formed by any two of the above values. The heating rate can be 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, or a range formed by any two of the above values. By adjusting the temperature, time, and heating rate of calcination within the above ranges, the organic carbon components in the rice husk can be fully decomposed and carbonized, and the rice husk-derived carbon@silica composite material prepared has good electrical conductivity.

[0075] Generally, the specific surface area and pore size of the rice husk-derived carbon@silica composite material can be regulated by changing the temperature, time, and heating rate of calcination. For example, increasing the temperature of calcination, the specific surface area and pore size of the rice husk-derived carbon@silica composite material will decrease. Decreasing the temperature of calcination, the specific surface area and pore size of the rice husk-derived carbon@silica composite material will increase. Prolonging the time of calcination, the specific surface area and pore size of the rice husk-derived carbon@silica composite material will decrease. Shortening the time of calcination, the specific surface area and pore size of the rice husk-derived carbon@silica composite material will increase. Increasing the heating rate of calcination, the specific surface area and pore size of the rice husk-derived carbon@silica composite material will decrease. Decreasing the heating rate of calcination, the specific surface area and pore size of the rice husk-derived carbon@silica composite material will increase.

[0076] In some embodiments of the present application, the specific surface area of the rice husk-derived carbon@silica composite material is 230 m 2 g -1 -280 m 2 g -1 , and the pore size is 1-15 nm. For example, the specific surface area of the rice husk-derived carbon@silica composite material can be 230 m 2 g -1 , 240 m 2 g-1 250 m 2 g -1 260 m 2 g -1 270 m 2 g -1 280 m 2 g -1 or a range of any two of the values, by regulating the specific surface area of the rice husk-derived carbon@silica composite material within the above range, it is beneficial to increase the contact area of the rice husk-derived carbon@silica composite material with the electrolyte, improve the transmission capacity of lithium ions, and at the same time, it is beneficial to form a stable solid electrolyte interface film (SEI film) to inhibit the side reaction between the rice husk-derived carbon@silica composite material and the electrolyte, thereby improving the electrochemical performance of the lithium ion battery. The pore size of the rice husk-derived carbon@silica composite material can be 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, or a range of any two of the values. By regulating the pore size of the rice husk-derived carbon@silica composite material within the above range, it is beneficial to improve the specific capacity of the rice husk-derived carbon@silica composite material, provide a fast transport channel for lithium ions, improve the transmission capacity of lithium ions, and thereby improve the electrochemical performance of the lithium ion battery.

[0077] In the present application, "@" represents the combination of carbon and silica, and the combination method is not particularly limited. For example, the original microstructure of the solid product obtained by carbonizing the treated rice husk in an inert gas after calcination.

[0078] In the present application, the cleaning and drying process can be selected according to the actual situation, and the present application does not have a particular limitation as long as the purpose of the present application can be achieved. For example, the cleaning and drying steps of the rice husk can include but are not limited to: washing the rice husk with tap water for 3 times, then washing with deionized water for 3 times, filtering, and then drying at 100-120°C for 10-16h. By cleaning the rice husk through the above process, dust and other impurities on the surface of the rice husk can be removed. The cleaning and drying steps of the solid product after the pretreated rice husk is treated with a dilute sulfuric acid solution can include but are not limited to: washing the solid product with deionized water to neutral, and drying at 70-90°C for 10-16h. The solid product obtained by hydrothermal reaction is washed with deionized water to neutral, and dried at 70-90°C for 10-16h. The solid product obtained by the above hydrothermal reaction is preferably washed with deionized water at 1-60°C.

[0079] The fifth aspect of the present application provides a negative electrode sheet, comprising a negative electrode material layer, wherein the negative electrode material layer comprises the rice husk-derived carbon@silicon dioxide composite material provided in any one of the first aspect, the second aspect, the third aspect, or the fourth aspect of the present application, which is beneficial to improve the specific capacity of the negative electrode sheet and improve the cycle stability of the negative electrode sheet.

[0080] In some embodiments of the present application, the mass percentage of the rice husk-derived carbon@silicon dioxide composite material is 1% to 99%, preferably 70% to 95%, based on the total mass of the negative electrode material layer. For example, the mass percentage of the rice husk-derived carbon@silicon dioxide composite material can be 1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 99%, or a range between any two of the above values. By adjusting the mass percentage of the rice husk-derived carbon@silicon dioxide composite material in the negative electrode material layer within the above range, a negative electrode sheet with high specific capacity and excellent cycle stability performance can be obtained, thereby improving the cycle stability and rate performance of the lithium ion battery.

[0081] In the present application, the negative electrode material layer can further comprise a conductive agent and a binder, which can be known in the art and are not limited in the present application. In the present application, the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along the thickness direction of the negative electrode current collector, or can be disposed on two surfaces of the negative electrode current collector along the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the negative electrode current collector, or can be a partial area of the negative electrode current collector, which is not particularly limited in the present application as long as the purpose of the present application can be achieved. The above-mentioned negative electrode current collector can be known in the art and is not limited in the present application.

[0082] The sixth aspect of the present application provides a lithium ion battery, comprising a positive electrode sheet, an electrolyte, a separator, and the negative electrode sheet of any one of the above-mentioned embodiments of the present application. The lithium ion battery provided in the present application has good cycle stability and rate performance. The above-mentioned positive electrode sheet, electrolyte, and separator can be known in the art and are not limited in the present application. The preparation process of the lithium ion battery of the present application is known to those skilled in the art, and is not limited in the present application.

[0083] Examples

[0084] Hereinafter, examples and comparative examples are given to more specifically explain the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are mass-based.

[0085] Test method and equipment:

[0086] The micro-morphology of the rice husk-derived carbon@silica composite material and the rice husk-derived silica material in the examples was observed by scanning electron microscopy, and scanning electron microscope (SEM) photos were taken.

[0087] The micro-morphology of the rice husk-derived carbon@silica composite material was observed by transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy (STEM-HAADF) images were taken, and element energy dispersive X-ray spectroscopy mapping tests were performed.

[0088] Test of specific surface area:

[0089] The nitrogen adsorption-desorption curves of the rice husk-derived carbon@silica composite material and the rice husk-derived silica material in the examples were tested using a full-automatic nitrogen adsorption micropore distribution tester (model QUADRASORB SI), so as to obtain the specific surface area of the rice husk-derived carbon@silica composite material and the rice husk-derived silica material in the examples.

[0090] Test of pore size distribution:

[0091] The pore size distribution of the rice husk-derived carbon@silica composite material and the rice husk-derived silica material in the examples was tested using a full-automatic nitrogen adsorption micropore distribution tester (model QUADRASORB SI).

[0092] Cycling performance test

[0093] In an environment of 25°C, the lithium ion battery was charged at 400 mAg to 1.5 V at a constant current, rested for 10 seconds, discharged to 0.01 V at 400 mA / g, rested for 10 seconds, and ended one cycle of circulation. The lithium ion batteries prepared in Examples 1-4 were cycled according to the above charging / discharging steps for 500 cycles, and the charging capacity and discharging capacity of each cycle were recorded. The coulombic efficiency and specific capacity were calculated according to the following formula.

[0094] Coulombic efficiency = charging capacity / discharge capacity x 100%.

[0095] The specific capacity of the rice husk-derived carbon@silica composite material = discharge capacity / mass of the rice husk-derived carbon@silica composite material, and the specific capacity unit is mAh·g -1 .

[0096] Rate performance test

[0097] In an environment of 25°C, the lithium ion batteries prepared in Examples 1-4 were charged at 100 mA·g -1The charge / discharge cycle was carried out according to the cycle steps in the cycle test at a current density of 100 mA g. Then the current density was increased to 200 mA g. -1 , 400mA·g -1 , 800mA·g -1 , 1000mA·g -1 , 1200mA·g -1 and 1500mA·g -1 , 10 cycles at each current density; at 1500mA·g -1 After the next cycle is completed, the current density is increased from 1500mAg -1 Reduced to 100mAg -1 , cycle 10 times. Record the discharge capacity for each cycle. Then calculate the specific capacity using the formula in the cycle test above.

[0098] Example 1

[0099] <Preparation of Rice Husk-Derived Carbon@Silica Composites>

[0100] The rice husks were rinsed three times with tap water and then three times with deionized water, filtered, and dried overnight at 110°C for 12 hours to remove dust and other impurities from the surface. The washed rice husks were added to a 5% citric acid solution at a solid-to-liquid ratio of 1:25. The mixture was magnetically stirred in an 80°C oil bath for 15 minutes, and then filtered to collect the solid product. The solid product was washed with deionized water until neutral and dried at 80°C for 12 hours to obtain the pretreated rice husk (RH).

[0101] The above RH was placed in a quartz boat, and then placed in a tube furnace with a heating rate of 5°C·min -1 , and calcined at 700 °C in argon atmosphere for 2 h to obtain rice husk-derived carbon@silica composite material after carbonization, which was denoted as C@SiO2-RH.

[0102] <Preparation of negative electrode sheet>

[0103] The C@SiO2-RH, conductive carbon black, and polyvinylidene fluoride prepared above were mixed in a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 30wt%. After stirring evenly with a vacuum mixer, a negative electrode slurry was obtained. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 18μm, and dried under vacuum at 70℃ to obtain a negative electrode sheet with a coating thickness of 100μm and a single-sided negative electrode active material layer. The negative electrode sheet was cut into 1.13cm pieces using a battery sheet slicer. 2 The negative electrode is spare.

[0104] <Lithium Tablets>

[0105] A lithium sheet (provided by Xinghua Muxin New Energy Materials Co., Ltd.) with an area of 1.91 cm 2

[0106] <Preparation of electrolyte>

[0107] In a dry argon glove box, organic solvents dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylene carbonate (EC) were mixed in a volume ratio of 1:1:1, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the organic solvent to dissolve and mix uniformly, to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0108] <Separator>

[0109] A porous polyethylene film (provided by Celgard, Celgard 2400) with a thickness of 14 μm was used.

[0110] <Preparation of lithium ion battery>

[0111] The seasoning box containing the weighing bottle, dust-free paper and filter paper, and the battery shell were placed in the glove box small transition bin, and the gas was pumped and charged more than three times. The filter paper was laid flat in front of the sealing machine, and the negative electrode shell (CR2032) was placed on the dust-free paper with the opening facing up, and a spring was placed in each negative electrode shell. Take a clean self-sealing bag, put the gasket and lithium sheet on the self-sealing bag; select the brighter side of the lithium sheet downward, and use tweezers to press the gasket and lithium sheet together (the gasket and lithium sheet are aligned). Drop three drops of electrolyte in the center of the spring, and place the gasket and lithium sheet (lithium sheet facing up) on the spring in the negative electrode shell, and drop two drops of electrolyte; cover the lithium sheet in the center of the negative electrode shell with the separator and soak it thoroughly; drop two drops of electrolyte, and place the negative electrode sheet, and use an insulated tweezer to cover the positive electrode shell (CR2032). Turn the battery over and place it on the dust-free paper, and when the dust-free paper has absorbed the excess electrolyte, use a battery packaging machine (provided by Hefei Kexin Co., Ltd.) to package the battery at a pressure of 12.6 MPa. The positive electrode shell, gasket, spring and negative electrode shell are all provided by Keluode Company.

[0112] Example 2

[0113] Except that the rice husk-derived carbon@silicon dioxide composite material prepared in the following <Preparation of rice husk-derived carbon@silicon dioxide composite material> was used, the rest was the same as in Example 1.

[0114] <Preparation of rice husk-derived carbon@silicon dioxide composite material>

[0115] ​The rice husk was washed with tap water for 3 times, then washed with deionized water for 3 times, filtered, and dried at 110℃ for 12h to remove the dust and other impurities on the surface of the rice husk. The washed rice husk was added to a 5wt% citric acid solution at a mass ratio of 1:25, and stirred magnetically in an 80℃ oil bath for 15min, then filtered to collect the solid product. The solid product was washed with deionized water until neutral, and dried at 80℃ for 12h to obtain RH.

[0116] The above RH was stirred with a 1.2wt% dilute sulfuric acid solution at a mass ratio of 1:8 in a 105℃ oil bath for 4h, and filtered while hot to collect the solid product. The solid product was washed with deionized water until neutral, and dried at 80℃ for 12h to obtain RH-L+X.

[0117] The above RH-L+X was placed in a quartz boat, which was then placed in a tube furnace, and heated at a rate of 5℃·min -1 in an argon atmosphere at 700℃ for 2h to obtain a rice husk-derived carbon@silica composite material, denoted as C@SiO2-L+X.

[0118] Example 3

[0119] The same as Example 1, except that the rice husk-derived carbon@silica composite material was prepared according to the following <Preparation of a rice husk-derived carbon@silica composite material>.

[0120] <Preparation of a rice husk-derived carbon@silica composite material>

[0121] The rice husk was washed with tap water for 3 times, then washed with deionized water for 3 times, filtered, and dried at 110℃ overnight (12h) to remove the dust and other impurities on the surface of the rice husk. The washed rice husk was added to a 5wt% citric acid solution at a solid-liquid ratio of 1:25, and stirred magnetically in an 80℃ oil bath for 15min, then filtered to collect the solid product. The solid product was washed with deionized water until neutral, and dried at 80℃ for 12h to obtain RH.

[0122] The above RH was stirred with a 1.2wt% dilute sulfuric acid solution at a mass ratio of 1:8 in a 105℃ oil bath for 4h, and filtered while hot to collect the solid product. The solid product was washed with deionized water until neutral, and dried at 80℃ for 12h to obtain RH-L+X.

[0123] The above RH-L+X was mixed with 32wt% concentrated sulfuric acid solution according to a mass ratio of 1:10, added to a polytetrafluoroethylene (PTFE) liner, and then placed in a stainless steel reactor for hydrothermal reaction at 130°C for 6h. Then filtration was performed, and the solid product was collected. The solid product was washed with deionized water until neutral, and dried at 80°C for 12h to obtain the rice husk (RH-L) containing lignin.

[0124] The above RH-L was placed in a quartz boat, and then placed in a tube furnace, with a heating rate of 5°C·min -1 , calcined in an argon atmosphere at 700°C for 2h, and carbonized to obtain a rice husk-derived carbon@silica composite material, denoted as C@SiO2-L.

[0125] Example 4

[0126] Except that the rice husk-derived carbon@silica composite material was prepared by the following <Preparation of a rice husk-derived carbon@silica composite material>, the rest was the same as Example 1.

[0127] <Preparation of a rice husk-derived carbon@silica composite material>

[0128] The rice husk was washed with tap water for 3 times, and then washed with deionized water for 3 times, filtered, and oven-dried at 110°C overnight (12h) to remove dust and other impurities on the surface of the rice husk. The washed rice husk was added to a 5% mass fraction citric acid solution at a solid-liquid ratio of 1:25, and stirred in a 80°C oil bath for 15min, and then filtered to collect the solid product. The solid product was washed with deionized water until neutral, and dried at 80°C for 12h to obtain RH.

[0129] The above RH was stirred with 1.2wt% dilute sulfuric acid solution at a mass ratio of 1:8 in a 105°C oil bath for 4h, and then filtered while hot to collect the solid product. The solid product was washed with deionized water until neutral, and dried at 80°C for 12h to obtain RH-L+X.

[0130] The above RH-L+X was mixed with 80wt% ethylene glycol aqueous solution according to a mass ratio of 1:7, added to a polytetrafluoroethylene (PTFE) liner, and then placed in a stainless steel reactor for hydrothermal reaction at 200°C for 4h. Then filtration was performed, and the solid product was collected. The solid product was washed with deionized water until neutral, and dried at 80°C for 12h to obtain the rice husk (RH-X) containing cellulose.

[0131] The above RH-X was placed in a quartz boat, and then placed in a tube furnace, with a heating rate of 5°C·min -1 , calcined in an argon atmosphere at 700°C for 2h, and carbonized to obtain a rice husk-derived carbon@silica composite material, denoted as C@SiO2-X.

[0132] The rice husk derived materials before calcination in Examples 1-4 are: RH, RH-L+X, RH-L, RH-X, Figure 1 The infrared spectra of the four rice husk derived materials are shown in Figure 2. Figure 1 As shown, it appears at 1220 cm -1 The shoulder peak is the asymmetric stretching vibration peak of Si-OC, which appears at 1095 cm -1 The strong band is the asymmetric stretching vibration peak of Si-O-Si; the symmetric stretching vibration peak of Si-O-Si appears at 815cm -1 , the stretching vibration peak of Si-O appears at 580 cm -1 The bending vibration peak of Si-O appears at 467 cm -1 , the above peaks correspond to SiO2 components. In addition, the infrared spectra of the four rice husk derived materials are shown at 1700 cm -1 Up to 1300cm -1 There are a series of absorption peaks in the range of 1710cm -1 The wave number at 1500 cm corresponds to the C=O group. -1 -1520cm -1 and 1600cm -1 -1610cm -1 The vibration absorption peak of 1400 cm -1 -1460cm -1 The spectral bands are related to the aromatic ring vibration and methyl and methylene CH deformation in lignin, indicating that RH-L contains lignin.

[0133] Figure 2 The nitrogen adsorption-desorption curves of the rice husk-derived carbon@silica composite materials prepared in Examples 1-4 show the porosity characteristics of the rice husk-derived carbon@silica composite materials prepared in Examples 1-4. The natural vascular bundle structure in the rice husk causes large pores to naturally exist in the rice husk, and these pores can be retained after carbonization. The nitrogen adsorption-desorption curves of the three materials C@SiO2-RH, C@SiO2-L+X and C@SiO2-X are type IV, with H4 type hysteresis loops, indicating that the structure of the pores in the material is mainly slit-shaped pores. The nitrogen adsorption-desorption curve of C@SiO2-L is also type IV, with an H3 type hysteresis loop, which also indicates that slit-shaped pores mainly exist in the material. From Figure 3 It can also be seen that C@SiO2-L and C@SiO2-X have hierarchical porous structures and a wide range of pore size distribution, especially the presence of mesopores in the range of 5nm-15nm. C@SiO2-X has the largest small mesopores (2nm-5nm), and C@SiO2-L has a high content of 5nm-15nm mesopores. Figure 2 、Figure 3 As can be seen from Table 1, the specific surface area and pore volume of the material C@SiO2-L+X obtained by removing hemicellulose are slightly lower than those of C@SiO2-RH, indicating that the presence of hemicellulose contributes to the porosity and pore distribution of the material but has little effect.

[0134] Table 1

[0135]

[0136]

[0137] Figure 3 The pore volume distribution graphs further demonstrate that C@SiO2-RH, C@SiO2-L+X, C@SiO2-L and C@SiO2-X are mesoporous materials. Specifically, they belong to materials mainly with mesopores and coexisting mesopores and micropores. As can be seen from the statistical results in Table 1, the average pore diameter of C@SiO2-RH, C@SiO2-L+X and C@SiO2-X is less than 2 nm, and the proportion of micropores is relatively high. The average pore diameter of C@SiO2-L is greater than 4 nm, because it has a relatively high content of mesopores of 5 nm-15 nm.

[0138] The inventors found that calcining RH in Example 1 of the present application in air, most of the carbon component escapes with gas molecules such as CO and CO2, and SiO2 remains, obtaining a rice husk-derived silica material (RH-SiO2), which is white, and the RH-SiO2 still maintains the original micro morphology of the rice husk. Figure 4 is a nitrogen adsorption-desorption curve of RH-SiO2, which shows that the RH-SiO2 material is also a mesoporous material. The pore size distribution graph of RH-SiO2 is shown in Figure 5 , which has the maximum pore volume distribution fraction at 2.5 nm-5 nm, and the statistical results show that the average pore diameter is 3.726 nm, which is consistent with the results of the nitrogen adsorption-desorption curve. RH-SiO2 has a H3 type hysteresis loop, indicating that there are mainly crack-like pores in RH-SiO2. In addition, RH-SiO2 has two kinds of pores, one is a micron-scale (about 10 μm) honeycomb hole formed by the interlaced RH-SiO2 plates as the rice husk skeleton and maintaining the morphology of the rice husk, as shown in Figure 6 ; the other is a nanometer-scale (<50 nm) interstitial pore of SiO2 particles formed by non-tightly aggregated SiO2 gel particles aggregated into plate-like, as shown in Figure 8 ; the black area between SiO2 particles is an interstitial pore, also known as a stacking pore. The above two kinds of pores are the source of crack-like mesopores. Therefore, the nanometer-scale SiO2 is loosely aggregated into a network in the rice husk, thereby resulting in a relatively large specific surface area (248.837 m 2 ·g-1 ) and pore volume (0.358 cm 3 ·g -1 ).

[0139] The above results also show that, compared with RH-SiO2, the rice husk derived carbon@silica composite material provided in the application has a hierarchical porous structure. The combination of carbon narrows the pore size and reduces the pore volume, but does not completely block the mesopores. Moreover, the introduction of carbon increases the content of micropores in the material, thereby increasing the specific surface area of the material. Studies have shown that the presence of a hierarchical porous structure is beneficial to improving the specific capacity of the material. Large pores (> 50 nm) always play a role in storing electrolyte ions, mesopores (5-15 nm) are usually channels for lithium ion transmission, and micropores (< 2 nm) provide a place for electrolyte ion adsorption. Therefore, the difference in pore structure will directly affect the electrochemical performance of the material. The rice husk derived carbon@silica composite material provided in the application can maintain the original microstructure of the rice husk and has a hierarchical porous structure, which is beneficial to increasing the specific surface area of the material and forming a stable solid electrolyte interface film to inhibit side reactions, and has a high specific capacity and good cycle stability.

[0140] Figure 6 The SEM photo of RH-SiO2 is shown, and it can be seen that the SiO2 in the rice husk can play a supporting role for the skeleton of the rice husk. The SiO2 in RH-SiO2 is mainly distributed on the inner and outer surfaces of the rice husk, and the thinnest part reaches 13.80 μm, and the thickness of the raised part is about 28.87 μm. Figure 7 The SEM photo of RH-SiO2 is shown, and it can be seen that the SiO2 in the rice husk can play a supporting role for the skeleton of the rice husk. The SiO2 in RH-SiO2 is mainly distributed on the inner and outer surfaces of the rice husk, and the thinnest part reaches 13.80 μm, and the thickness of the raised part is about 28.87 μm. Figure 8 The SEM photo of RH-SiO2 is shown, and it can be seen that the SiO2 in the rice husk can play a supporting role for the skeleton of the rice husk. The SiO2 in RH-SiO2 is mainly distributed on the inner and outer surfaces of the rice husk, and the thinnest part reaches 13.80 μm, and the thickness of the raised part is about 28.87 μm. Figure 7 The SEM photo of RH-SiO2 is shown, and it can be seen that the SiO2 in the rice husk can play a supporting role for the skeleton of the rice husk. The SiO2 in RH-SiO2 is mainly distributed on the inner and outer surfaces of the rice husk, and the thinnest part reaches 13.80 μm, and the thickness of the raised part is about 28.87 μm. Figure 8 The SEM photo of RH-SiO2 is shown, and it can be seen that the SiO2 in the rice husk can play a supporting role for the skeleton of the rice husk. The SiO2 in RH-SiO2 is mainly distributed on the inner and outer surfaces of the rice husk, and the thinnest part reaches 13.80 μm, and the thickness of the raised part is about 28.87 μm.

[0141] Figure 9a The STEM-HAADF photo of C@SiO2-RH in Example 1 is shown, Figure 9b , Figure 9c , Figure 9d The element energy dispersive X-ray spectroscopy mapping of O element, Si element and C element, respectively. From Figures 9b-9d it can be seen that C, O and Si elements are uniformly distributed on the slice. Figure 9a It can also be further proved that the SiO2 in the rice husk derived carbon@silica composite material can still maintain the surface morphology and skeleton of the rice husk without collapse. Figure 10 is the EDS spectrum of C@SiO2-RH, fromFigure 10 It can be seen that almost no metal impurities were detected, indicating that the organic matter was retained during the washing process and the metal ions in the rice husk were effectively removed.

[0142] Figure 11 The specific capacities of the rice husk-derived carbon@silica composites in Examples 1-4 at different current densities are shown. -1 , 200mA·g -1 , 400mA·g -1 , 800mA·g -1 , 1000mA·g -1 , 1200mA·g -1 and 1500mA·g -1 The specific capacities at current densities (tested 10 times at each current density) were 482.3 mAh g -1 , 426.4mAh·g -1 、346.2mAh·g -1 , 278.9mAh·g -1 , 265.8mAh·g -1 , 252.2mAh·g -1 and 220.8mAh·g -1 After testing 1500mA·g -1 After the specific capacity is reduced, the current density is increased from 1500mAg -1 Reduced to 100mAg -1 , the discharge capacity recovered and was higher than the initial value, which was 506.8mAhg -1 This indicates that the rice husk-derived carbon@silica composite material provided in this application is applied to the negative electrode material of a lithium-ion battery, and the lithium-ion battery prepared has excellent rate performance.

[0143] from Figure 11 It can also be seen that the theoretical specific capacity of C@SiO2-L and C@SiO2-X prepared in Example 3-4 is significantly better than that of C@SiO2-RH and C@SiO2-L+X prepared in Example 1-2. The inventor speculates that the reasons can be mainly attributed to two aspects. First, the contribution of SiO2 to the specific capacity of lithium-ion batteries is much higher than that of carbon. The SiO2 content in C@SiO2-L and C@SiO2-X is higher, which makes the lithium-ion battery prepared in Example 3-4 have a higher specific capacity. Secondly, C@SiO2-L and C@SiO2-X in Example 3-4, especially C@SiO2-L, have the largest average pore size and a more uniform pore size distribution, which is more conducive to improving the electrochemical properties of the material, thereby making the lithium-ion battery prepared in Example 3-4 have better rate performance.

[0144] Figure 12a and Figure 12b The lithium ion batteries prepared in Examples 1-4 are shown in FIG. -1 The specific capacity and coulombic efficiency of the battery were measured after 200 cycles. Figure 12a It can be seen that after 200 cycles, the specific capacities of the rice husk-derived carbon@silica composites in Examples 3-4 were 380.3 mAh·g -1 and 378.8mAh·g -1 , higher than the specific capacity of the rice husk-derived carbon@silica composite material of Examples 1-2, and also higher than the theoretical specific capacity of commercial graphite anode materials. The capacity of the C@SiO2-L and C@SiO2-X materials continues to increase after the start of cycling. This is because the SEI film becomes increasingly uniformly coated on the anode surface, enhancing the stability of the anode material. The SiO2 lithiation process is as follows:

[0145] SiO2 + 4Li + + 4e - → 2Li2O + Si (1)

[0146] 2SiO2 + 4Li + + 4e - → Li4SiO4+ Si (2)

[0147]

[0148]

[0149] Among them, 0<x≤4.4, finally Li is generated x Si, it can be inferred that active material silicon with high theoretical specific capacity contribution value will continue to be produced in this process. Figure 12b It can be seen that the coulombic efficiency of the lithium ion batteries prepared in Examples 1-4 tends to be stable after 25 cycles and is close to 100%, indicating that the lithium ion batteries prepared in Examples 1-4 all have excellent cycle performance.

[0150] Figure 13 Shown at 400mA·g -1 The specific capacity of C@SiO2-L after 500 cycles and the coulombic efficiency of the lithium ion battery prepared in Example 3 are shown in FIG. Figure 14 Shown at 400mA·g -1 The specific capacity of C@SiO2-X after 500 cycles and the coulombic efficiency of the lithium-ion battery prepared in Example 4. After 5 cycles, the specific capacity of C@SiO2-L in Example 3 and C@SiO2-X in Example 4 were 261.8 mAh·g -1 and 290.3 mAh g-1 After 500 cycles, its specific capacity still remained 486.9 mAh·g -1 and 473.5 mAh·g -1 and still showed a rising trend, proving that the rice husk derived carbon@silicon dioxide composite material in Example 3-4 had excellent cycle stability, so that the lithium ion battery prepared in Example 3-4 had excellent cycle stability.

[0151] In summary, the rice husk derived carbon@silicon dioxide composite material provided in the present application has abundant raw material sources and low cost, realizing waste recycling; its preparation method is simple and easy to operate, green and environmentally friendly, and is suitable for large-scale production. The rice husk derived carbon@silicon dioxide composite material provided in the present application has a hierarchical porous structure and a low charge transfer resistance, which not only helps to form a stable solid electrolyte interface film to inhibit side reactions, but also can improve the negative effects of poor conductivity of silicon dioxide negative electrode material and volume change effect, thereby having good cycle stability. Using the rice husk derived carbon@silicon dioxide composite material provided in the present application as the negative electrode material of the lithium ion battery is conducive to improving the cycle stability and rate performance of the lithium ion battery.

[0152] It should be noted that the terms "comprising", "containing", or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or inherent to such a process, method or article.

[0153] Each embodiment in the specification is described in a relevant manner, and the same and similar parts between each embodiment can be referred to each other, and each embodiment focuses on the difference from other embodiments.

[0154] The above only describes the preferred embodiments of the present application, and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A rice husk-derived carbon@silica composite material prepared by the following process: (1) washing and drying the rice husks, then adding them to a citric acid solution for pickling, and then washing and drying them to obtain pretreated rice husks; wherein, The mass ratio of the rice husk to the solute in the citric acid solution is 1:0.6-1:2.4; (2) mixing the pretreated rice husks with a dilute sulfuric acid solution, reflux-treating at 100° C.-110° C. for 3 h-5 h, and then washing and drying to obtain rice husks free of hemicellulose; wherein the mass ratio of the rice husks to the dilute sulfuric acid solution is 1:6-1:10, and the concentration of the dilute sulfuric acid solution is 1 wt%-1.5 wt%; (3) mixing the rice husks free of hemicellulose with a concentrated sulfuric acid solution in a mass ratio of 1:8-1:12, performing a hydrothermal reaction, and washing and drying after the reaction to obtain the rice husks containing lignin; wherein the reaction temperature of the hydrothermal synthesis reaction is 120° C.-140° C., the reaction time is 5 h-8 h, and the concentration of the concentrated sulfuric acid solution is 30 wt%-35 wt%; (4) calcining the lignin-containing rice husk under inert gas protection to obtain a rice husk-derived carbon@silica composite material, wherein the calcination temperature is 600°C-800°C, the time is 1 hour-3 hours, and the heating rate is 3°C / min-7°C / min.

2. The rice husk-derived carbon@silica composite material according to claim 1, wherein The pickling step comprises: washing with a citric acid solution at 70° C.-90° C. for 10 min-30 min, wherein the concentration of the citric acid solution is 3 wt %-8 wt %.

3. The rice husk-derived carbon@silica composite material according to claim 1, having a specific surface area of ​​230 m 2 g -1 -280m 2 g -1 , pore size is 1nm-15nm.

4. A negative electrode sheet comprising a negative electrode material layer, wherein the negative electrode material layer comprises the rice husk-derived carbon@silicon dioxide composite material according to any one of claims 1 to 3.

5. The negative electrode sheet according to claim 4, wherein: Based on the total mass of the negative electrode material layer, the mass percentage of the rice husk-derived carbon@silicon dioxide composite material is 1%-99%.

6. A lithium-ion battery comprising the negative electrode sheet according to claim 4 or 5.

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