A bio-based core-shell carbon-silicon material, an in-situ synthesis method and application thereof

Abstract

The application discloses a kind of biobased core-shell carbon silicon material and its in-situ synthesis method and application, by in-situ method to rice husk as raw material, prepared the core-shell type biobased carbon silicon material, realize the full component utilization of rice husk, its raw material is cheap, easy to get, low energy consumption in preparation process, no toxic gas is generated, green and environmental protection.Carbon silicon in product combination makes the material play the elasticity of carbon material, effectively inhibits the volume expansion of silicon, and carbon layer also better improves the conductivity of material, so that the material has better electrochemical performance.On the other hand, the application uses rice husk as raw material, greatly reduces the cost of raw material, so that the material has better commercial application prospect.

Description

A bio-based core-shell silicon carbide material and its in-situ synthesis method and application Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a bio-based core-shell silicon carbide material and its in-situ synthesis method and application. Background Technology

[0002] In recent years, with the rapid development of the economy and society, the demand for the specific energy density of lithium-ion batteries has been continuously increasing. Graphite anodes, after a long period of development, have reached their capacity limit, but still cannot meet people's needs. Therefore, researchers have explored more materials to investigate whether they can improve battery capacity. As a result, many high-performance anode materials have been developed as new materials for next-generation lithium-ion batteries. Among them, silicon, due to its high theoretical capacity (3590 mAh / g), environmental friendliness, and abundant reserves, has long been considered as a negative electrode material for next-generation high-energy-density lithium-ion batteries.

[0003] However, silicon faces two major challenges in its commercial application. First, the reversible capacity of silicon anode materials during lithium storage is directly proportional to volume expansion. For example, when the capacity of a silicon anode reaches 3590 mAh / g, the particle or grain expansion can reach up to 320%, with a linear relationship between volume change and lithium intercalation capacity. Large volume changes easily lead to electrochemical performance degradation, the active material is prone to detaching from the conductive network, and Si particles may crack and pulverize, severely impacting the cycle performance of silicon-based materials. Another problem is the difficulty in obtaining silicon sources. Currently, most silicon is produced through industrial silicon sources, making silicon expensive. Both of these factors limit the commercial application of silicon anodes.

[0004] Rice husks, a waste product of grain processing, are produced in huge quantities every year. Rice husks are rich in organic matter (cellulose, hemicellulose, and lignin), and their ash contains up to 90% silica. The organic matter and silicon components in rice husks can serve as carbon and silicon sources, respectively. However, there is currently limited research on how to utilize these carbon and silicon sources in the preparation of lithium-ion battery materials. Summary of the Invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a method for preparing core-shell bio-based silicon carbon materials using rice husks as raw materials.

[0006] The second objective of this invention is to provide the application of the above-mentioned core-shell bio-based silicon carbide material in lithium-ion batteries.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a bio-based core-shell silicon carbide material includes the following steps:

[0009] (1) The biomass material is immersed in an acid solution and heated in a water bath. After being taken out, it is filtered and dried.

[0010] (2) The material obtained in step (1) is calcined under an inert atmosphere to obtain biomass powder;

[0011] (3) The biomass powder from step (2) is mixed with calcium hydride (CaH2) and anhydrous aluminum trichloride (AlCl3) and then ball-milled. The mixture is then transferred to a reaction vessel for molten salt thermal reduction reaction.

[0012] (4) After the reaction in step (3) is completed, the product is cooled naturally, soaked in acid, washed and then dried under vacuum.

[0013] Specifically, in step (1), the biomass material is at least one of silicon-containing biomass such as rice husks and straw; the volume concentration of the acid solution is 5-15%, and the water bath temperature is 70-90℃.

[0014] Specifically, the material is calcined in a tube furnace under a nitrogen protective atmosphere. The calcination steps are as follows: the temperature is increased to 650-950°C (preferably 800°C) at a heating rate of 2-10°C (preferably 5°C / min) / min and held for 2-8 hours (preferably 2 hours), and then cooled to room temperature at a cooling rate of 5-10°C / min (preferably 10°C / min).

[0015] Preferably, in step (3), the mass ratio of biomass powder to calcium hydride is 1:(0.5-5), more preferably 1:1; the mass ratio of anhydrous aluminum trichloride to calcium hydride is 1-10:1, more preferably 5-10:1.

[0016] Preferably, in step (3), a ball mill is used to grind in an air atmosphere for 5 to 30 minutes, preferably 30 minutes; the ball mill speed is controlled to be 200 to 400 r / min.

[0017] Preferably, in step (3), the temperature of the molten salt thermal reduction reaction is 150-400℃, preferably 200℃; and the holding time is 1-10h, preferably 2h.

[0018] Specifically, the metal salts are in a molten state at the reaction temperature, and the reaction needs to be carried out under closed conditions and requires a reaction vessel with a certain mechanical strength, such as a stainless steel reaction vessel or a polytetrafluoroethylene reaction vessel.

[0019] Preferably, in step (4), the product is soaked in hydrochloric acid and hydrofluoric acid in sequence, then washed alternately with deionized water and ethanol, dried under vacuum and then ground into powder.

[0020] Furthermore, the bio-based core-shell silicon carbide material prepared by the above preparation method is also within the scope of protection of this invention.

[0021] Furthermore, the present invention also claims protection for the use of the above-mentioned bio-based core-shell silicon carbide material in the preparation of lithium-ion batteries.

[0022] Furthermore, the present invention also claims a lithium-ion battery whose negative electrode is prepared using the aforementioned bio-based core-shell silicon carbide material.

[0023] Beneficial effects:

[0024] (1) This invention prepares core-shell bio-based carbon silicon materials using rice husks as raw material through an in-situ method, achieving full utilization of rice husk components. The raw material is inexpensive and readily available, and the preparation process is low-energy-consuming and does not produce toxic gases, making it environmentally friendly. The combination of carbon and silicon in the product allows the material to exhibit the elasticity of carbon materials, effectively suppressing the volume expansion of silicon. Simultaneously, the carbon layer also improves the conductivity of the material, resulting in better electrochemical performance. Furthermore, the use of rice husks as raw material significantly reduces the cost of the raw material, thus giving the material better prospects for commercial application.

[0025] (2) The method of this invention is simple and low-cost. By mixing AlCl3 and CaH2 and simultaneously reducing and carbonizing at a relatively low temperature, a well-structured core-shell silicon-carbon material can be directly synthesized in situ. The material has high crystallinity, clear particle edges, and uniform size. This bio-based core-shell silicon-carbon material exhibits high specific capacity and stable cycle charge-discharge performance in lithium-ion battery anode materials. Attached Figure Description

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0027] Figure 1 is a transmission electron microscope image of the core-shell silicon-based anode material prepared in Example 1.

[0028] Figure 2 is an X-ray diffraction pattern of the core-shell silicon-based anode material prepared in Example 1.

[0029] Figure 3 is a linear cyclic voltammetry (CV) curve of the core-shell silicon-based anode material prepared in Example 1 at a scan rate of 0.1 mV / s.

[0030] Figure 4 shows the charge-discharge curves of the lithium-ion battery prepared in Example 1 at a current density of 0.1 A / g for the first 200 cycles.

[0031] Figure 5 is a graph showing the charge-discharge curves of the lithium-ion battery prepared in Example 1 after 300 short cycles at a current density of 0.1 A / g.

[0032] Figure 6 is a specific capacity curve (rate performance) of the lithium-ion battery prepared in Example 1 at different current densities.

[0033] Figure 7 is a graph of the lithium-ion battery prepared in Example 1 after 2000 long-cycle charge-discharge at a current density of 5 A / g. Detailed Implementation

[0034] The present invention can be better understood from the following embodiments.

[0035] Example 1

[0036] Rice husks were heated in an 80°C water bath with a 10% hydrochloric acid solution, then filtered and dried. The biomass rice husks were placed in an alumina crucible and heated from 50°C to 800°C in a nitrogen atmosphere at a rate of 5°C / min, held at this temperature for 2 hours, and then cooled to room temperature at a rate of 10°C / min to obtain biomass powder. The obtained biomass powder was ball-milled with calcium hydride (CaH2) and anhydrous aluminum trichloride (AlCl3) at a mass ratio of 1:1:10 at 200 r / min for 30 minutes. The mixture was then transferred to a reaction vessel, where a molten salt thermal reaction was carried out at 200°C for 2 hours. After natural cooling, the product in the reaction vessel was successively soaked in hydrochloric acid and hydrofluoric acid, washed several times with deionized water and ethanol, and then vacuum dried. Finally, it was ground in an agate mortar to obtain the negative electrode material for lithium-ion batteries (RHs-Si@C).

[0037] Example 2

[0038] Rice husks were heated in an 80°C water bath with a 10% hydrochloric acid solution, then filtered and dried. The biomass rice husks were placed in an alumina crucible and heated from 50°C to 650°C in a nitrogen atmosphere at a rate of 5°C / min, held at this temperature for 8 hours, and then cooled to room temperature at a rate of 10°C / min to obtain biomass powder. The obtained biomass powder was ball-milled with calcium hydride (CaH2) and anhydrous aluminum trichloride (AlCl3) at a mass ratio of 1:0.5:5 at 200 r / min for 30 minutes. The mixture was then transferred to a reaction vessel, where a molten salt thermal reaction was carried out at 150°C for 10 hours. After natural cooling, the product in the reaction vessel was successively soaked in hydrochloric acid and hydrofluoric acid, washed several times with deionized water and ethanol, and then vacuum dried. Finally, it was ground in an agate mortar to obtain the negative electrode material (Si / C-1) for lithium-ion batteries.

[0039] Example 3

[0040] Rice husks were heated in an 80°C water bath with a 10% hydrochloric acid solution, then filtered and dried. The biomass rice husks were placed in an alumina crucible and heated from 50°C to 900°C in a nitrogen atmosphere at a rate of 10°C / min, held at this temperature for 2 hours, and then cooled to room temperature at a rate of 5°C / min to obtain biomass powder. The obtained biomass powder was ball-milled with calcium hydride (CaH2) and anhydrous aluminum trichloride (AlCl3) at a mass ratio of 1:3:15 at 200 r / min for 30 minutes. The mixture was then transferred to a reaction vessel, where a molten salt thermal reaction was carried out at 400°C for 1 hour. After natural cooling, the product in the reaction vessel was successively soaked in hydrochloric acid and hydrofluoric acid, washed several times with deionized water and ethanol, and then vacuum dried. Finally, it was ground in an agate mortar to obtain the negative electrode material (Si / C-2) for lithium-ion batteries.

[0041] Example 4

[0042] Straw was heated in an 80°C water bath with a 10% hydrochloric acid solution, then filtered and dried. Biomass rice husks were placed in an alumina crucible and heated from 50°C to 800°C in a nitrogen atmosphere at a rate of 2°C / min, held at this temperature for 6 hours, and then cooled to room temperature at a rate of 10°C / min to obtain biomass powder. The obtained biomass powder was ball-milled with calcium hydride (CaH2) and anhydrous aluminum trichloride (AlCl3) at a mass ratio of 1:5:50 at 200 r / min for 30 minutes. The mixture was then transferred to a reaction vessel, where a molten salt thermal reaction was carried out at 200°C for 2 hours. After natural cooling, the product in the reaction vessel was successively soaked in hydrochloric acid and hydrofluoric acid, washed several times with deionized water and ethanol, and then vacuum dried. Finally, it was ground in an agate mortar to obtain the negative electrode material (Si / C-3) for lithium-ion batteries.

[0043] Example 5

[0044] The lithium-ion battery negative electrode materials prepared in Examples 1-4 were mixed with conductive agents acetylene black and sodium alginate in a mass ratio of 6:2:2. The mixture was then prepared into a slurry with deionized water and coated onto copper foil. The resulting slurry coating was placed in a vacuum drying oven and dried at 80°C for 10 hours. A circular electrode sheet with a diameter of 12 mm was pressed out using a pressing machine to obtain the experimental battery negative electrode. A lithium foil was used as the counter electrode, a porous polypropylene membrane as the separator, and an organic solution of lithium hexafluorophosphate as the electrolyte. Springs and gaskets were added, and the mixture was assembled into a 2032 model button cell in a glove box.

[0045] Figure 1 is a transmission electron microscope (TEM) image of the lithium-ion battery anode material prepared in Example 1. It shows that the inner layer of the sample is highly crystalline silicon, and the outer layer is amorphous carbon. During molten salt thermal reduction, not only is silicon dioxide reduced to elemental silicon, but in-situ coating is also achieved, forming a core-shell structured silicon-carbon material. The X-ray diffraction (XRD) pattern in Figure 2 clearly shows that the five peaks of RHs-Si@C at 28.56, 47.44, 56.25, 69.3, and 76.51 correspond to the diffraction peaks of cubic silicon lattice planes 111, 220, 311, 400, and 331. Comparing this with the results in Figure 1, it indicates that elemental silicon is coated within the carbon layer. Figure 3 shows the linear cyclic voltammetry (CV) curve of the prepared lithium-ion battery at a scan rate of 0.1 mV / s. The reduction and oxidation peaks at 0.22 V, 0.33 V, and 0.50 V further illustrate the alloying / dealloying process between lithium ions and silicon.

[0046] As shown in Figure 4, when using the sample from Example 1 as the electrode material, the lithium-ion battery achieved a discharge capacity of 1996.95 mAh / g at a current density of 0.1 A / g, with an initial coulombic efficiency of 73.88%. Figure 5 shows that even after 300 charge-discharge cycles, it still possessed a specific capacity of 1128.36 mAh / g. Figure 6 shows the specific capacity curves of the prepared lithium-ion battery at different current densities. Doubling the current to 20 A / g still retained a specific capacity of 39 mAh / g, and the capacity did not decrease after returning to a lower current, indicating the excellent structural stability of the core-shell structure. Figure 7 shows that after 2000 charge-discharge cycles, the battery still maintained a specific capacity of 387.02 mAh / g at a high current density of 5 A / g, with a capacity retention rate of 90.48%.

[0047] This invention provides a concept and method for the in-situ synthesis and application of a bio-based core-shell silicon carbide material. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing a bio-based core-shell silicon carbide material, characterized in that, The process includes the following steps: (1) Immersing the biomass material in an acid solution for water bath heating, then removing it, filtering, and drying; (2) calcining the material obtained in step (1) under an inert atmosphere to obtain biomass powder; (3) mixing the biomass powder from step (2) with calcium hydride and anhydrous aluminum trichloride, then ball milling, and then transferring it to a reaction vessel for molten salt thermal reduction reaction; (4) after the reaction in step (3) is completed, naturally cooling, soaking the product in acid, washing, and then vacuum drying to obtain the product; the inner layer of the bio-based core-shell carbon silicon material is highly crystalline silicon, and the outer layer is amorphous carbon; in step (2), the material is placed in a tube furnace, Calcination is carried out under a nitrogen protective atmosphere. The calcination steps are as follows: the temperature is raised to 650-950℃ at a heating rate of 2-10℃ / min and held for 2-8h, and then cooled to room temperature at a cooling rate of 5-10℃ / min. In step (3), the mass ratio of biomass powder to calcium hydride is 1:(0.5-5), and the mass ratio of anhydrous aluminum trichloride to calcium hydride is 1-10:

1. In step (3), the ball mill is used to grind in an air atmosphere for 5-30min, and the ball mill speed is controlled at 200-400r / min. In step (3), the temperature of the molten salt thermal reduction reaction is 150-400℃, and the holding time is 1-10h.

2. The method for preparing bio-based core-shell silicon-carbon material according to claim 1, characterized in that, In step (1), the biomass material is at least one of rice husk and straw; the volume concentration of the acid solution is 5-15%, and the water bath temperature is 70-90℃.

3. The method for preparing bio-based core-shell silicon-carbon material according to claim 1, characterized in that, In step (4), the product is soaked in hydrochloric acid and hydrofluoric acid in sequence, then washed alternately with deionized water and ethanol, dried under vacuum and then ground into powder.

4. The bio-based core-shell silicon carbide material prepared by the preparation method according to any one of claims 1 to 3.

5. The application of the bio-based core-shell silicon carbide material of claim 4 in the preparation of lithium-ion batteries.

6. A lithium-ion battery, characterized in that, Its negative electrode is prepared using the bio-based core-shell silicon carbide material described in claim 5.

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