3D porous silicon-carbon composite material, preparation method and application thereof

Abstract

The present application relates to a kind of 3D porous silicon-carbon composite material and its preparation method and application.The silicon-carbon composite material described in the present application presents three-dimensional network structure from outside to inside for amorphous carbon layer, silicon layer and nitrogen-doped carbon skeleton wrapping silicon.By the following method: chitin is dissolved in sodium hydroxide urea solution, by coagulation bath and freeze-drying to obtain chitin aerogel, using the pore adsorption effect of chitin aerogel to adsorb the solution containing silicon source inside and surface of chitin aerogel, and by in-situ growth preparation to obtain silica wrapped chitin aerogel composite;The obtained silica wrapped chitin aerogel composite is mixed with magnesium powder, and the silicon layer wrapped nitrogen-doped carbon skeleton coated silicon particles are formed by magnesium thermal reaction;CO2 gas is introduced into the obtained silicon layer wrapped nitrogen-doped carbon skeleton coated silicon particles, and amorphous carbon layer is formed on the surface of the nitrogen-doped carbon skeleton coated silicon particles, i.e. the 3D porous silicon-carbon composite material is obtained.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a 3D porous silicon-carbon composite material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries (LIBs), with their high energy density and relatively fast kinetics, still dominate the energy storage market. Since Sony invented LIBs in 1992, carbon anodes have been the commercially available anode. While graphite now holds the largest market share for LIBs, the theoretical capacity of graphite anodes is only 372 mAh·g. -1 Its low-speed capability limits its application in future high-energy, high-power LIBs.

[0003] Silicon is widely available and has a capacity of 3579 mAh·g -1 Silicon's high theoretical capacity and low operating voltage (below 0.4V) make it a promising anode material for next-generation lithium-ion batteries. However, in practical applications, the dealloying process between silicon and lithium results in significant volume changes (~300%), leading to capacity decay of the silicon anode and even electrode pulverization. Furthermore, low conductivity and the formation of an unstable solid electrolyte interface (SEI) contribute to the instability of silicon's electrochemical performance.

[0004] Carbon materials can prevent the agglomeration of silicon nanoparticles during lithium alloying and act as a buffer host, while their excellent mechanical properties can accommodate the stress generated by silicon expansion. Simultaneously, carbon materials can provide a continuous conductive framework to improve electron and ion transport dynamics, thereby enhancing battery performance. Therefore, designing a rational silicon-carbon material structure is crucial for mitigating the volume expansion effect of silicon anode materials and improving battery cycle performance. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a 3D porous silicon-carbon composite material, its preparation method, and its applications. This invention provides a novel 3D porous silicon-carbon anode material by in-situ growing SiO2 using a three-dimensional chitin aerogel as a framework. Through a magnesothermic reduction reaction, a complex three-dimensional structure is formed, in which chitin-carbon-based aerogel supports and encapsulates Si. This material structure consists of three layers: an amorphous carbon layer, a silicon layer, and a nitrogen-doped carbon framework encapsulating silicon. This rational "network" and "cavity" structure improves the compressive strength of the porous silicon anode material, effectively mitigates the expansion and contraction stress of the electrode material during cycling, controls capacity decay, and ultimately results in high battery capacity retention and stable cycling. Simultaneously, the nitrogen element in the chitin aerogel exists in the form of pyrrole nitrogen (N-5), pyridine nitrogen (N-6), and graphitic carbon (NQ), which effectively improves its conductivity, further enhancing the material's overall conductivity.

[0006] The first objective of this invention is to provide a 3D porous silicon-carbon composite material, which exhibits a three-dimensional network structure from the outside to the inside consisting of an amorphous carbon layer, a silicon layer, and a nitrogen-doped carbon skeleton encapsulating silicon.

[0007] In one embodiment of the present invention, the silicon layer comprises silicon and silicon oxide, wherein the silicon oxide content is greater than or equal to zero, and the silicon oxide content is determined by the degree of magnesothermic reaction.

[0008] In one embodiment of the present invention, the silicon in the silicon layer exhibits a porous structure.

[0009] The second objective of this invention is to provide a method for preparing a 3D porous silicon-carbon composite material, comprising the following steps:

[0010] (1) Chitin was dissolved in sodium hydroxide urea solution and obtained by coagulation bath and freeze drying. Chitin aerogel was placed in a solution containing silicon source and the solution containing silicon source was adsorbed inside and on the surface of the chitin aerogel by the pore adsorption of the chitin aerogel. The silica-encapsulated chitin aerogel composite was prepared by in-situ growth by precipitation method.

[0011] (2) The chitin aerogel complex wrapped with silica obtained in step (1) is mixed with magnesium powder and magnesium dioxide, and heated in an inert gas atmosphere to form a silicon-coated nitrogen-doped carbon skeleton silicon particles wrapped with a silicon layer by combining the magnesium thermal reaction.

[0012] (3) Introduce CO2 gas into the nitrogen-doped carbon skeleton-coated silicon particles wrapped with silicon layer obtained in step (2). The CO2 gas reacts with magnesium powder to form an amorphous carbon layer on the surface of the nitrogen-doped carbon skeleton-coated silicon particles, thus obtaining the 3D porous silicon-carbon composite material.

[0013] In one embodiment of the present invention, in step (1), the chitin accounts for 3wt%-7wt% of the mass of the sodium hydroxide urea solution; the mass ratio of sodium hydroxide, urea and water in the sodium hydroxide urea solution is 11:4:85.

[0014] In one embodiment of the present invention, in step (1), the coagulation bath is one or more of water, ethanol and sulfuric acid solution.

[0015] In one embodiment of the present invention, in step (1), the silicon source is selected from one or more of tetraethyl orthosilicate, sodium silicate, silicon tetrachloride and tetramethoxysilane.

[0016] In one embodiment of the present invention, when the silicon source-containing solution is sodium silicate, the concentration of the sodium silicate solution is 20wt%-40wt%. Specifically, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt%, 33wt%, 34wt%, 35wt%, 36wt%, 37wt%, 38wt%, 39wt%, 40wt%, or any value between any two concentrations.

[0017] In one embodiment of the present invention, in step (1), the solution containing the silicon source further includes ethanol and water; the volume ratio of the silicon source, ethanol and water is 1:1:1.1-1:1:2.

[0018] In one embodiment of the present invention, in step (1), the in-situ growth by precipitation is achieved by the following method: after the chitin aerogel is taken out from a solution containing a silicon source, it is immersed in an acidic or alkaline solution to react and obtain a chitin aerogel complex encapsulated in silica. Specifically, after the chitin aerogel is immersed in the silicon source, a portion of the silicon source enters the interior of the chitin aerogel, while another portion adheres to the surface of the chitin aerogel. Subsequently, the silicon source reacts under acidic or alkaline conditions to obtain the chitin aerogel complex encapsulated in silica, and the silicon source inside the silica-encapsulated chitin aerogel complex also reacts to obtain silica.

[0019] In one embodiment of the present invention, the acid in the acid solution is selected from at least one of sulfuric acid and hydrochloric acid; the concentration of the acid solution is 20wt%-25wt%; the alkaline solution is a conventional alkaline solution in the art, which is not specifically limited here, and is preferably ammonia water.

[0020] In one embodiment of the present invention, in step (2), the mass ratio of the silica-encapsulated chitin aerogel complex, magnesium powder, and magnesium dioxide is 1:1 to 1.8:1. Magnesium dioxide serves as a reaction template.

[0021] In one embodiment of the present invention, step (2) further includes drying the obtained silica-encapsulated chitin aerogel composite by at least one of natural drying, vacuum drying and freeze drying.

[0022] In one embodiment of the present invention, in step (2), during the magnesian reduction process, Mg vapor reacts with SiO2 to generate Si crystals, MgO nuclei, and the byproduct Mg2Si. By introducing carbon dioxide gas to react with Mg, a new amorphous carbon layer is generated on the solid surface, which induces Mg2Si to convert into Si and Mg during the magnesian reduction process. At the same time, the newly generated Mg reacts with CO2 gas to form a new amorphous carbon layer on the surface of the material, while the incompletely reduced silicon dioxide continues to exist in the form of silicon oxide. Furthermore, after removing MgO and excess Mg with acids such as HCl, a cavity structure is formed.

[0023] In one embodiment of the present invention, in step (2), the inert gas is argon and / or helium.

[0024] In one embodiment of the present invention, in step (2), the total reaction time is 7h-10h, and the CO2 gas is introduced for 2h-6h.

[0025] In one embodiment of the present invention, in step (2), at least one of the following conditions is satisfied:

[0026] 1) The heating temperature is not lower than 600℃; the heating rate is 2℃ / min-5℃ / min.

[0027] 2) The flow rate of the inert gas is 40 mL / min - 80 mL / min;

[0028] 3) The flow rate of the CO2 gas is 20 mL / min-30 mL / min.

[0029] In one embodiment of the present invention, in steps (2) and (3), the volume ratio of the inert gas to the CO2 gas is 3-1.5:1.

[0030] In one embodiment of the present invention, step (3) further includes acid washing and drying of the 3D porous silicon-carbon composite material; the acid used in the acid washing is one or more of hydrochloric acid, nitric acid and sulfuric acid.

[0031] Furthermore, the concentration of the acid solution in the pickling process is 0.1M-1M.

[0032] In one embodiment of the present invention, the pickling solution is a mixed solution of acid, ethanol and water, wherein the volume ratio of acid, ethanol and water is 1:0.2-1:0.2-1.

[0033] A third objective of the present invention is to provide a lithium-ion battery comprising the aforementioned 3D porous silicon-carbon composite material.

[0034] The technical solution of the present invention has the following advantages compared with the prior art:

[0035] Chitin aerogel, with its abundant hydroxyl groups on the surface, exhibits good hydrophilicity, which is beneficial for the in-situ growth of SiO2. The interwoven fibers of this aerogel form numerous pores, resulting in a three-dimensional honeycomb structure with excellent mechanical properties. Through in-situ growth, SiO2 is uniformly distributed on the chitin aerogel, exhibiting consistent size. After magnesothermic reduction, this silicon-carbon composite material displays a clear 3D porous structure with channels conducive to continuous electron transport. The nitrogen-doped carbon framework prevents direct contact between Si and the electrolyte, effectively reducing the volume effect of silicon, alleviating internal stress, and forming a stable SEI film. Furthermore, the excellent mechanical properties of the chitin-carbon aerogel prevent structural collapse due to Si volume expansion, improving the cycling stability of Si.

[0036] Chitin is a natural linear polymer composed of N-acetyl-2-amino-D-glucose unit structures linked by β-1,4 glycosidic bonds, containing a large amount of nitrogen (N). In chitin carbon-based aerogels, N exists in the form of pyrrole nitrogen (N-5), pyridine nitrogen (N-6), and graphitic carbon (NQ), which can effectively improve its conductivity and further enhance the conductivity of Si.

[0037] This invention incorporates chitosan to form a nitrogen-doped carbon framework. The silicon on the surface of this nitrogen-doped carbon framework exhibits a cavity structure. The introduction of CO2 gas causes an amorphous carbon layer to form on the Si surface, preventing direct contact between the silicon and the electrolyte and facilitating the formation of a stable SEI film. Simultaneously, the cavity structure increases the specific surface area of ​​the composite material, providing channels for electrolyte penetration and rapid transport, as well as space for silicon volume expansion, thus contributing to excellent electrochemical stability. Attached Figure Description

[0038] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0039] Figure 1 These are the XRD patterns of the 3D porous silicon-carbon composite materials obtained in Examples 1-4 of this invention;

[0040] Figure 2 This is the XRD pattern of the 3D porous silicon-carbon composite material obtained in Comparative Example 1 of this invention;

[0041] Figure 3 This is a SEM image of the 3D porous silicon-carbon composite material obtained in Example 1 of this invention;

[0042] Figure 4Here is a SEM image of the 3D porous silicon-carbon composite material obtained in Example 2 of this invention;

[0043] Figure 5 Here is a SEM image of the 3D porous silicon-carbon composite material obtained in Example 3 of this invention;

[0044] Figure 6 Here is a SEM image of the 3D porous silicon-carbon composite material obtained in Example 4 of this invention;

[0045] Figure 7 This is a SEM image of the 3D porous silicon-carbon composite material obtained in Comparative Example 1 of this invention.

[0046] Figure 8 This is a SEM image of the 3D porous silicon-carbon composite material obtained in Example 2 of the present invention; A and B in the figure are SEM images of the obtained 3D porous silicon-carbon composite material, and C and D in the figure correspond to the magnified structural images of B in the figure. Detailed Implementation

[0047] The present invention will be further described below with reference to the accompanying drawings and specific examples, so that those skilled in the art can better understand and implement the present invention, but the examples given are not intended to limit the present invention.

[0048] Example 1

[0049] This invention provides a method for preparing a 3D porous silicon-carbon composite material, as detailed below:

[0050] (1) 6g of chitin powder was uniformly dispersed in a sodium hydroxide urea aqueous solution (NaOH: urea: H2O = 11:4:85; w / w), and frozen in a -30℃ refrigerator for 4 hours. Afterward, it was removed and allowed to thaw, with continuous stirring using a glass rod. This dissolution-thawing cycle was repeated three times to obtain a homogeneous and transparent solution. After centrifugation and defoaming, the alkali was replaced using a water coagulation bath to obtain chitin hydrogel. The water was changed multiple times until no more alkali precipitated. The hydrogel was then cut into 0.5cm thin slices and freeze-dried to obtain chitin aerogel.

[0051] (2) First, prepare a mixed solution of tetraethyl orthosilicate (TOES), ethanol and water in a volume ratio of 1:1:2. Immerse the chitin aerogel obtained in step (1) in the above mixed solution. After 12 hours, remove it and use clean paper to absorb the excess solution on the surface of the chitin aerogel. Then, soak it in ammonia water for 12 hours. After removing it, use clean paper to absorb the excess solution on the surface of the chitin aerogel. Freeze-dry to obtain a chitin aerogel composite coated with silica.

[0052] (3) The silica-encapsulated chitin aerogel composite obtained in step (2), magnesium powder, and magnesium oxide were mixed evenly in a mass ratio of 1:1.5:2 and placed in a ceramic boat. Then, the boat was placed in a tube furnace and heated to 750°C at a heating rate of 5°C / min under an argon atmosphere and held for 8 hours. During the holding period, carbon dioxide gas (carbon dioxide gas flow rate: 30 mL / min; argon to carbon dioxide volume ratio: 2:1; v / v) was introduced into an argon atmosphere (gas flow rate: 60 mL / min). The resulting product was washed with 1M hydrochloric acid, water, and alcohol, dried, and passed through a 300-mesh sieve. It was then placed in an oven for later use to obtain a 3D porous silicon-carbon composite material.

[0053] Example 2

[0054] This invention provides a method for preparing a 3D porous silicon-carbon composite material, as detailed below:

[0055] (1) Disperse 5g of chitin powder evenly in a sodium hydroxide urea aqueous solution (NaOH:urea:H2O = 11:4:85; w / w), freeze in a -30℃ refrigerator for 4 hours, then remove and allow to thaw, stirring constantly with a glass rod. Repeat this cycle three times to obtain a homogeneous and transparent solution. After centrifugation and defoaming, replace the alkali with a water coagulation bath to obtain chitin hydrogel. Change the water several times until no more alkali precipitates. Cut the hydrogel into 0.5cm thin slices with a blade and freeze-dry to obtain chitin aerogel.

[0056] (2) First, prepare a mixed solution of tetraethyl orthosilicate (TOES), ethanol and water in a volume ratio of 1:1:1.5. Immerse the chitin aerogel obtained in step (1) in the above mixed solution. After 12 hours, remove it and use clean paper to absorb the excess solution on the surface of the chitin aerogel. Then, soak it in ammonia water for 12 hours. After removing it, use clean paper to absorb the excess solution on the surface of the chitin aerogel. Freeze-dry to obtain a chitin aerogel composite coated with silica.

[0057] (3) The silica-encapsulated chitin aerogel composite obtained in step (2), magnesium powder, and magnesium oxide were mixed evenly in a mass ratio of 1:1.2:2 and placed in a ceramic boat. Then, the boat was placed in a tube furnace and heated to 750°C at a heating rate of 5°C / min under an argon atmosphere and held for 8 hours. During the 4-hour holding period, carbon dioxide gas (carbon dioxide gas flow rate: 30 mL / min; argon to carbon dioxide volume ratio: 2:1; v / v) was introduced into an argon atmosphere (gas flow rate: 60 mL / min). The resulting product was washed with 1M hydrochloric acid, water, and alcohol, dried, and passed through a 300-mesh sieve. It was then placed in an oven for later use to obtain a 3D porous silicon-carbon composite material.

[0058] Example 3

[0059] This invention provides a method for preparing a 3D porous silicon-carbon composite material, as detailed below:

[0060] (1) Disperse 6g of chitin powder evenly in a sodium hydroxide urea aqueous solution (NaOH:urea:H2O = 11:4:85; w / w), freeze in a -30℃ refrigerator for 4 hours, then remove and allow to thaw, stirring constantly with a glass rod. Repeat this cycle three times to obtain a homogeneous and transparent solution. After centrifugation and defoaming, replace the alkali with a water coagulation bath to obtain chitin hydrogel. Change the water several times until no more alkali precipitates. Cut the hydrogel into 0.5cm thin slices with a blade and freeze-dry to obtain chitin aerogel.

[0061] (2) First, prepare an aqueous solution of sodium silicate with a mass fraction of 30%. Immerse the chitin aerogel obtained in step (1) in the mixed solution. After 12 hours, remove it and use a clean paper to absorb the excess solution on the surface of the chitin aerogel. Then, immerse it in 25 wt% sulfuric acid for 12 hours. After removing it, use a clean paper to absorb the excess solution on the surface of the chitin aerogel. Freeze-dry to obtain a chitin aerogel composite coated with silica.

[0062] (3) The silica-encapsulated chitin aerogel composite obtained in step (2), magnesium powder, and magnesium oxide were mixed evenly in a mass ratio of 1:1.5:2 and placed in a ceramic boat. Then, the boat was placed in a tube furnace and heated to 750°C at a heating rate of 5°C / min under an argon atmosphere and held for 8 hours. During the holding period, carbon dioxide gas (carbon dioxide gas flow rate: 30 mL / min; argon to carbon dioxide volume ratio: 2:1; v / v) was introduced into an argon atmosphere (gas flow rate: 60 mL / min). The resulting product was acid-washed with 1M hydrochloric acid, washed with water, washed with alcohol, dried, and passed through a 300-mesh sieve. It was then placed in an oven for later use to obtain a 3D porous silicon-carbon composite material.

[0063] Example 4

[0064] This invention provides a method for preparing a 3D porous silicon-carbon composite material, as detailed below:

[0065] (1) Disperse 4g of chitin powder evenly in a sodium hydroxide urea aqueous solution (NaOH: urea: H2O = 11:4:85; w / w), freeze in a -30℃ refrigerator for 4 hours, then remove and allow to thaw, stirring constantly with a glass rod. Repeat this cycle three times to obtain a homogeneous and transparent solution. After centrifugation and defoaming, replace the alkali with a water coagulation bath to obtain chitin hydrogel. Change the water several times until no more alkali precipitates. Cut the hydrogel into 0.5cm thin slices with a blade and freeze-dry to obtain chitin aerogel.

[0066] (2) First, prepare an aqueous solution of sodium silicate with a mass fraction of 25%. Immerse the chitin aerogel obtained in step (1) in the mixed solution. After 12 hours, remove it and use a clean paper to absorb the excess solution on the surface of the chitin aerogel. Then, immerse it in 25 wt% hydrochloric acid for 12 hours. After removing it, use a clean paper to absorb the excess solution on the surface of the chitin aerogel. Freeze-dry to obtain a chitin aerogel composite coated with silica.

[0067] (3) First, the silica-encapsulated chitin aerogel composite obtained in step (2), magnesium powder, and magnesium oxide are mixed evenly in a mass ratio of 1:1.5:2 and placed in a ceramic boat. Then, the boat is placed in a tube furnace and heated to 750°C at a heating rate of 5°C / min under an argon atmosphere and held for 8 hours. During this period, after holding for 3 hours, carbon dioxide gas (carbon dioxide gas flow rate: 30 mL / min; argon to carbon dioxide volume ratio: 2:1; v / v) is introduced into an argon atmosphere (gas flow rate: 40 mL / min). The resulting product is then acid-washed with 1M sulfuric acid and hydrochloric acid, washed with water, and washed with alcohol. After drying, it is passed through a 300-mesh sieve and placed in an oven for later use to obtain a 3D porous silicon-carbon composite material.

[0068] Comparative Example 1

[0069] The present invention provides a comparative example of a method for preparing a silicon-carbon composite material, as detailed below:

[0070] (1) Disperse 6g of chitin powder evenly in a sodium hydroxide urea aqueous solution (NaOH: urea: H2O = 11:4:85; w / w), freeze in a -30℃ refrigerator for 4 hours, then remove and allow to thaw, stirring constantly with a glass rod. Repeat this cycle three times to obtain a homogeneous and transparent solution. After centrifugation and defoaming, replace the alkali with a water coagulation bath to obtain chitin hydrogel. Change the water several times until no more alkali precipitates. Cut the hydrogel into 0.5cm thin slices with a blade and freeze-dry to obtain chitin aerogel.

[0071] (2) Prepare a mixed solution of tetraethyl orthosilicate (TOES), ethanol and water in a volume ratio of 2:1:2, then add ammonia and stir for 12 h. Filter and wash the resulting mixed solution until neutral, then freeze-dry to obtain silica nanoparticles.

[0072] (3) The silica particles and chitin aerogel obtained in step (2) were mixed evenly at a mass ratio of 1:5. The resulting mixture, magnesium powder, and magnesium oxide were mixed evenly at a mass ratio of 1:1.5:2 and placed in a ceramic boat. The boat was then placed in a tube furnace and heated to 750°C at a heating rate of 5°C / min under an argon atmosphere and held for 8 hours. After holding for 4 hours, carbon dioxide gas was introduced into the argon atmosphere (the volume ratio of argon to carbon dioxide was 2:1; v / v). The resulting product was acid-washed with 1M hydrochloric acid, washed with water, and washed with alcohol. After drying, it was passed through a 300-mesh sieve and placed in an oven for later use to obtain the silicon-carbon composite material.

[0073] Performance testing

[0074] (1) X-ray diffraction analysis (XRD)

[0075] X-ray diffraction was performed on a Model 6100 X-ray diffractometer (Shimadzu Corporation, Japan) to determine the aggregation morphology of the samples. Copper was used as the target source (λ = 1.5406), the operating voltage and current were 40 kV and 30 mA, respectively, the scanning speed was 5° / min, and the scanning range was 10°–80°. X-ray diffraction analysis was performed on the 3D porous silicon-carbon composite materials prepared in Examples 1–4 and the silicon-carbon composite material prepared in Comparative Example 1. The results are shown in [Figure 1]. Figure 1 and Figure 2 .

[0076] Figure 1 X-ray diffraction patterns of the 3D porous silicon-carbon composite materials prepared in Examples 1-4 are shown, with the vertical axis representing the intensity of the X-ray diffraction and the horizontal axis representing the scanning angle of the X-rays. Distinct characteristic peaks are observed at 2θ of 28.4°, 47.3°, 56.1°, 69.1°, 76.4°, and 88.0°, consistent with the standard card for Si (PDF#27-1402), corresponding to the (111), (220), (311), (400), (331), and (422) crystal planes of crystalline silicon, respectively, indicating the formation of silicon.

[0077] Figure 2 The X-ray diffraction pattern of the silicon-carbon composite material prepared in Comparative Example 1 is shown, with the vertical axis representing the intensity of the X-ray diffraction and the horizontal axis representing the scanning angle of the X-rays. Distinct characteristic peaks are observed at 2θ of 28.4°, 47.3°, 56.1°, 69.1°, 76.4°, and 88.0°, consistent with the standard card for Si (PDF#27-1402), corresponding to the (111), (220), (311), (400), (331), and (422) crystal planes of crystalline silicon, respectively, indicating the formation of silicon.

[0078] (2) Morphology and microstructure analysis (SEM)

[0079] The morphology and microstructure of all samples of the 3D porous silicon-carbon composite materials obtained in Examples 1-4 and the silicon-carbon composite material obtained in Comparative Example 1 were analyzed by scanning electron microscopy (SEM). The results are shown below. Figures 3-7 .

[0080] Figure 3 The image shows a scanning electron microscope (SEM) image of the 3D porous silicon-carbon composite material prepared in Example 1. It is clearly visible that the material exhibits a complex three-dimensional structure in which Si is supported and encapsulated by chitin-based carbon aerogel.

[0081] Figure 4 The image shows a scanning electron microscope (SEM) image of the 3D porous silicon-carbon composite material prepared in Example 2. It is clearly visible that the material exhibits a complex three-dimensional structure in which Si is supported and encapsulated by chitin-based carbon aerogel.

[0082] Figure 5 This is a scanning electron microscope image of the 3D porous silicon-carbon composite material prepared in Example 3. It is clearly visible that the material exhibits a complex three-dimensional structure in which Si is supported and encapsulated by chitin-based carbon aerogel.

[0083] Figure 6 This is a scanning electron microscope image of the 3D porous silicon-carbon composite material prepared in Example 4. It is clearly visible that the material exhibits a complex three-dimensional structure in which Si is supported and encapsulated by chitin-based carbon aerogel.

[0084] Figure 7 This is a scanning electron microscope image of the silicon-carbon composite material prepared in Comparative Example 1. It is clearly visible that the material exhibits a bulk, aggregated structure.

[0085] Figure 8 The image shows the SEM image of the 3D porous silicon-carbon composite material obtained in Example 2. It can be clearly seen that the silicon-carbon composite material exhibits a complex three-dimensional network structure from the outside to the inside, consisting of an amorphous carbon layer, a silicon layer, and a nitrogen-doped carbon skeleton encapsulating silicon. The silicon in the silicon layer also exhibits a porous cavity structure.

[0086] (3) Powder resistance test

[0087] The powder resistance of the 3D porous silicon-carbon composite materials prepared in Examples 1-4 and the silicon-carbon composite material in Comparative Example 1 was measured using a PR510 powder resistance tester from Chuanyuan Technology. The test results are shown in Table 1. Table 1 shows that the powder resistance of the 3D porous silicon-carbon composite materials prepared in Examples 1-4 is lower than that of Comparative Example 1, indicating better conductivity. The amorphous carbon and silicon layers, and the nitrogen-doped carbon framework encapsulating silicon structure exhibited in the silicon-carbon composite materials prepared in Examples 1-4 and Comparative Example 1, contribute to the higher conductivity of the silicon-carbon materials.

[0088] Table 1 shows the powder resistance of the silicon-carbon composite electrode materials in Examples 1-4 and Comparative Example 1.

[0089] Powder resistance / mΩ Example 1 12.7 Example 2 14.2 Example 3 15.0 Example 4 14.9 Comparative Example 1 20.4

[0090] (4) Battery performance test

[0091] 1) Using the 3D porous silicon-carbon composite anode materials prepared in Examples 1-4 and the silicon-carbon composite material prepared in Comparative Example 1 as anodes, and lithium metal sheets as cathodes, CR2032 button cells were assembled in an argon glove box using 1.0 mol / L LiPF6 solution as the electrolyte. The electrolyte solvent consisted of EC (ethylene carbonate), DMC (dimethyl carbonate), and FEC (fluoroethylene carbonate) (where the volume ratio of EC, DMC, and FEC was 4.5:4.5:1). GCD was tested using a Land battery testing system within a voltage window of 0.01V-2.5V. The test conditions and results are as follows:

[0092] The button cells were subjected to constant current charge-discharge tests at current densities of 100 mA / g, 200 mA / g, 500 mA / g, 1000 mA / g, 1500 mA / g, and 100 mA / g, with a voltage range of 0V-1.5V. The experimental results are shown in Tables 2 and 3. Table 2 shows that the 3D porous silicon-carbon composite coin cells prepared in Examples 1-4 all exhibited high initial discharge capacity (over 12500 mAh / g) and initial coulombic efficiency exceeding 58%, while Comparative Example 1 had a lower initial discharge capacity (1178.3 mAh / g) and an initial coulombic efficiency of 52.32%. Table 3 shows that the 3D porous silicon-carbon composite coin cells prepared in Examples 1-4 exhibited high capacity at different current densities and could recover to near-initial capacity after high-current charge-discharge, demonstrating excellent rate performance. The silicon-carbon composite material obtained in Comparative Example 1 exhibited poor rate cycling performance and low discharge capacity in its coin cell test.

[0093] Table 2 shows the initial discharge capacity and initial coulombic efficiency of the silicon-carbon composite electrode materials used in Examples 1-4 and Comparative Example 1 for coin half-cells.

[0094] Current density 100 mA / g Initial discharge capacity mAh / g First-time coulomb efficiency (%) Example 1 1351.9 58.63 Example 2 1357.0 60.71 Example 3 1302.7 59.47 Example 4 1258.6 60.44 Comparative Example 1 1178.3 52.32

[0095] Table 3 shows the coin half-cell rate cycling capacity of the silicon-carbon composite electrode materials in Examples 1-4 and Comparative Example 1.

[0096]

[0097] 2) Button cells were subjected to constant current charge-discharge tests at a current density of 500 mA / g, with a voltage range of 0V-1.5V. After 200 cycles, the 3D porous silicon-carbon composite coin cells prepared in Examples 1-4 all exhibited high cycle retention rates (greater than 80%) and excellent cycle stability. In contrast, the capacity retention rate of Comparative Example 1 was only 17.1%. Specific values ​​are shown in Table 4.

[0098] Table 4 shows the capacity retention of coin half-cells of silicon-carbon composite electrode materials in Examples 1-4 and Comparative Example 1 after 200 cycles.

[0099] Current density 500 mA / g Capacity retention rate (%) Example 1 82.8 Example 2 85.6 Example 3 80.7 Example 4 84.2 Comparative Example 1 71.1

[0100] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a 3D porous silicon-carbon composite material, characterized in that, Includes the following steps: (1) Chitin was dissolved in sodium hydroxide urea solution, and chitin aerogel was obtained by coagulation bath and freeze drying. The chitin aerogel was placed in a solution containing silicon source, and the solution containing silicon source was adsorbed in the interior and surface of the chitin aerogel by the pore adsorption effect of the chitin aerogel. The silica-encapsulated chitin aerogel composite was prepared by in-situ growth by precipitation method. (2) The chitin aerogel complex encapsulated with silica obtained in step (1) is mixed with magnesium powder and magnesium dioxide, and heated in an inert gas atmosphere to form a silicon-encapsulated nitrogen-doped carbon skeleton-coated silicon particles by combining magnesium thermodynamic reaction. (3) Introduce CO2 gas into the nitrogen-doped carbon skeleton-coated silicon particles wrapped with silicon layer obtained in step (2). The CO2 gas reacts with magnesium powder to form an amorphous carbon layer on the surface of the nitrogen-doped carbon skeleton-coated silicon particles, thus obtaining the 3D porous silicon-carbon composite material.

2. The preparation method according to claim 1, characterized in that, In step (1), the chitin accounts for 3wt%-7wt% of the mass of the sodium hydroxide urea solution.

3. The preparation method according to claim 1, characterized in that, In step (1), the silicon source is selected from one or more of tetraethyl orthosilicate, sodium silicate, silicon tetrachloride and tetramethoxysilane.

4. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the silica-encapsulated chitin aerogel complex, magnesium powder, and magnesium dioxide is 1:1 to 1.8:

1.

5. The preparation method according to claim 1, characterized in that, In steps (2) and (3), at least one of the following conditions must be met: (1) The heating temperature is 600℃-900℃; (2) The flow rate of the inert gas is 40 mL / min-80 mL / min; (3) The flow rate of the CO2 gas is 20 mL / min-30 mL / min.

6. The preparation method according to claim 1, characterized in that, Step (3) also includes pickling and drying the 3D porous silicon-carbon composite material; the acid used in the pickling is one or more of hydrochloric acid, nitric acid and sulfuric acid.

7. A 3D porous silicon-carbon composite material prepared by the preparation method according to any one of claims 1-6, characterized in that, The silicon-carbon composite material exhibits a three-dimensional network structure from the outside to the inside, consisting of an amorphous carbon layer, a silicon layer, and a nitrogen-doped carbon skeleton encapsulating silicon.

8. The 3D porous silicon-carbon composite material according to claim 7, characterized in that, The silicon layer comprises silicon and silicon oxide, wherein the silicon oxide content is greater than or equal to zero.

9. The 3D porous silicon-carbon composite material according to claim 8, characterized in that, The silicon in the silicon layer exhibits a porous structure.

10. A lithium-ion battery, characterized in that, The 3D porous silicon-carbon composite material prepared by the preparation method according to any one of claims 1-6.

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