High-capacity nitrogen-doped porous silicon-oxygen-carbon anode materials, their preparation methods and applications

Abstract

This invention discloses a high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material, its preparation method, and its application. The anode material comprises nitrogen-doped carbon material and biomass porous silicon-oxygen material, with the nitrogen-doped carbon material coating the biomass porous silicon-oxygen material. The nitrogen content in the anode material is ≥13 at%. This invention utilizes the crosslinking of amino acid materials with the Si-OH groups on the surface of the biomass porous silicon-oxygen material. Carbonization promotes the polymerization-cyclization-condensation of the amino acid materials to form a high-content nitrogen-doped carbon material that uniformly coats the biomass porous silicon-oxygen material. By optimizing the surface structure of the biomass porous silicon-oxygen material, the polymerization of amino acid materials or pyrolysis products with the biomass porous silicon-oxygen material is promoted, preparing a nitrogen-doped silicon-oxygen-carbon material rich in pores. By optimizing the lithiophilicity of the biomass porous silicon-oxygen material, the prepared nitrogen-doped biomass porous silicon-oxygen-carbon material exhibits excellent electrochemical performance and cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material, its preparation method, and its application. Background Technology

[0002] With the rapid growth in energy demand from applications such as electric vehicles, hybrid vehicles, and portable electronic devices, the development of lithium-ion batteries (LIBs) with high specific capacity and long lifespan has become a research hotspot in recent years. Graphite, due to its low operating potential and high coulombic efficiency, has become the most commonly used anode material for lithium-ion batteries. However, the theoretical capacity of graphite anodes (372 mAh g⁻¹) is limited. -1 The current energy density is far from meeting the rapidly growing demand, especially in large-scale applications such as electric vehicles and energy storage power stations. Therefore, it is necessary to explore novel electrode materials with high reversible capacity and cycle stability. Compared to graphite anodes, abundant and pollution-free silicon-based materials have a higher theoretical specific capacity (4200-1965 mAh g⁻¹). -1 and lower operating potential (<1.0V vs. Li / Li) + It has greater application prospects. Among them, the alloying process of pure silicon materials with lithium will produce a volume expansion of nearly 400%, while the stable silicon-oxygen materials have a smaller volume expansion (<200%) and exhibit longer cycle stability, making them the most promising high-energy-density lithium-ion battery anode materials for commercialization.

[0003] Due to the high oxygen content and intrinsic semiconductor properties of silicon-oxygen materials, the thermodynamics and kinetics of the charge-discharge process are affected, resulting in poor initial coulombic efficiency (20-35%) and rate performance. Therefore, it is urgent to find a method to improve the active silicon exposure and conductivity of silicon-oxygen materials, while simultaneously enhancing their electrochemical performance as much as possible. Summary of the Invention

[0004] This invention aims to address at least one of the aforementioned defects in silicon-oxygen materials in the prior art, thereby alleviating the technical problems of poor initial coulombic efficiency and rate performance in lithium-ion batteries. To this end, this invention proposes a high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material, its preparation method, and its applications. The anode material can effectively mitigate the volume expansion of silicon-oxygen materials during charge and discharge, ensuring the cycle stability and electrochemical performance of the battery.

[0005] To address the aforementioned technical problems, a first aspect of the present invention provides a negative electrode material comprising a nitrogen-doped carbon material and a biomass porous silicon-oxygen material, wherein the nitrogen-doped carbon material coats the biomass porous silicon-oxygen material; and in the negative electrode material, the nitrogen content is ≥13 at%.

[0006] Specifically, the negative electrode material of this invention, by introducing nitrogen-doped carbon material to coat biomass porous silicon-oxygen material, can reduce the internal resistance of the porous silicon-oxygen negative electrode, enhance the interfacial bonding force between the carbon material and the porous silicon-oxygen material, and construct a flexible coating layer on the porous structure of the biomass silicon-oxygen material to buffer the mechanical stress of phase transition during the alloying process, thereby enhancing the cycle stability of the electrode material. Simultaneously, the nitrogen-containing polar groups on the surface of the nitrogen-doped carbon are beneficial for increasing the adsorption capacity of lithium ions and promoting the diffusion rate of lithium ions, thereby improving the reversible specific capacity of the porous silicon-oxygen material. Furthermore, silicon-oxygen material undergoes numerous side reactions with the electrolyte during the first discharge, thus consuming the lithium source in the electrolyte and reducing the charge-discharge coulombic efficiency of the battery. The nitrogen-doped carbon layer coating acts as a physical barrier to reduce direct contact between the electrolyte and the silicon-oxygen material, forming a stable solid electrolyte film, thereby suppressing the occurrence of side reactions and improving the coulombic efficiency and cycle stability of the lithium-ion battery. Therefore, the high-nitrogen capacity anode material of the present invention not only enhances the stability of the electrode material, but also improves the reversible specific capacity of the material, thereby improving the coulombic efficiency and cycle stability of lithium-ion batteries.

[0007] In some embodiments of the present invention, the nitrogen content in the negative electrode material is 13.12-20.27 at%.

[0008] In some embodiments of the present invention, the negative electrode material has a hierarchical porous structure, including micropores, mesopores and macropores, and the proportion of micropores is greater than 80%.

[0009] In some embodiments of the present invention, the proportions of micropores, mesopores and macropores are 80-85%, 12-18% and 1-5%, respectively.

[0010] In some embodiments of the present invention, the pore size of the micropores is 0.35-2 nm, the pore size of the mesopores is 2-50 nm, and the pore size of the macropores is 50-200 nm.

[0011] In some embodiments of the present invention, the specific surface area of ​​the negative electrode material is 160-360 m². 2 / g.

[0012] Specifically, the high specific surface area and hierarchical pore distribution of the negative electrode material of this invention can significantly shorten the diffusion path of lithium ions, accelerate the migration rate of lithium ions, promote the uniform deposition of the solid electrolyte membrane, and reduce material cracking caused by local polarization. At the same time, the presence of a large number of microporous structures can not only expose more active sites, but also limit the excessive penetration of electrolyte, reduce electrolyte decomposition, and effectively improve the reversible capacity of silicon-oxygen materials.

[0013] In some embodiments of the present invention, the raw materials for preparing the negative electrode material include biomass porous silica materials and amino acid materials.

[0014] Specifically, the anode material of this invention uses biomass porous silica materials and amino acid-based materials as raw materials. Due to the well-developed three-dimensional porous structure of the biomass porous silica materials, by controlling the carbonization temperature and time, the resulting nitrogen-doped carbon-coated biomass silica materials can exhibit a high degree of disorder. Simultaneously, the abundant Si-OH surface of the biomass porous silica materials can effectively crosslink the amino acid-based materials, reducing the loss of the amino acid-based materials during high-temperature pyrolysis, forming a structurally stable nitrogen-doped carbon coating on the biomass porous silica materials, and increasing the nitrogen content in the anode material. Furthermore, the decomposition of amino acid-based materials under high-temperature conditions generates gases such as NH3, HCNO, and HCN, which helps optimize the pore and surface structures of the biomass porous silica materials, further improving the affinity of the anode material for lithium ions.

[0015] In some embodiments of the present invention, the mass ratio of the biomass porous silica material to the amino acid material is 1:(0.5-5); such as 1:0.5, 1:1, 1:2, 1:3, 1:4 or 1:5, etc., including but not limited to the listed values. At the same time, other unlisted values ​​within the range are also applicable.

[0016] In some embodiments of the present invention, the mass ratio of the biomass porous silica material to the amino acid material is 1:(2-4).

[0017] Studies have found that when the amino acid content is too low, the biomass porous silica material is not sufficiently coated with nitrogen-doped carbon material, resulting in a poorly stable conductive network. When the amino acid content is too high, excessive nitrogen defects easily form on the surface of the biomass porous silica material, causing irreversible capacity. Therefore, this invention controls the mass ratio of biomass porous silica material to amino acid-based materials to promote good bonding between the biomass porous silica material and the amino acid-based material matrix, forming a uniform and dense network structure. This allows the biomass porous silica material, after carbon coating, to be suitable for lithium-ion reaction while ensuring structural stability during cycling.

[0018] In some embodiments of the present invention, the biomass porous silica material includes diatoms, wherein the diatoms are selected from at least one of round diatoms and boat-shaped diatoms.

[0019] In some embodiments of the present invention, the amino acid material is selected from at least one of glutamic acid, proline, cysteine, glycine, and alanine.

[0020] A second aspect of the present invention provides a method for preparing the above-mentioned negative electrode material, comprising the following steps:

[0021] (1) Mix biomass porous silica materials with amino acid materials to obtain a mixed material;

[0022] (2) The mixed material is annealed under an inert atmosphere to obtain the negative electrode material.

[0023] In some embodiments of the present invention, the annealing temperature regime is as follows: the temperature is increased to 400-800°C at a rate of 3-10°C / min, and then held at that temperature for 2-4 hours.

[0024] Specifically, this invention controls the annealing temperature regime, namely the carbonization temperature and carbonization time, to ensure stable bonding between amino acids and the surface of biomass porous silica-oxygen materials. It also controls the optimal nitrogen content and the area of ​​nitrogen-doped carbon material covering the porous silica-oxygen materials, thereby obtaining nitrogen-doped biomass porous silica-oxygen carbon materials with high disorder and high nitrogen content. When used as a negative electrode material for lithium-ion batteries, these materials can adsorb more lithium ions, thereby greatly improving the energy density of the batteries.

[0025] In some embodiments of the present invention, the inert atmosphere is an atmosphere of at least one of nitrogen, argon, and nitrogen and argon.

[0026] In some embodiments of the present invention, the biomass porous silica material further includes a grinding step before being mixed with the amino acid-based material. The grinding process conditions are as follows: using grinding balls with a particle size of 1-10 mm (such as zirconia balls, alumina balls, agate balls, etc.), and ball milling at a speed of 200-600 rpm for 3-48 hours. For example, ball milling can be performed for 3 hours, 6 hours, 12 hours, 28 hours, 24 hours, 30 hours, 36 hours, 42 hours, or 48 hours at this particle size and speed, including but not limited to the listed values. Other unlisted values ​​within the same range are also applicable.

[0027] In some embodiments of the present invention, the grinding process conditions are as follows: using grinding balls with a particle size of 1-10 mm, and grinding at a speed of 200-600 rpm for 3-12 hours.

[0028] Studies have found that the ball milling time of biomass porous silica materials affects their particle size, and consequently, their electrochemical performance. If the ball milling time is too short, the biomass porous silica materials are at the micron level, forming an unstable solid electrolyte interphase (SEI) membrane, which is detrimental to subsequent carbonization. If the ball milling time is too long, the pore structure of the biomass porous silica materials is easily destroyed, hindering lithium-ion transport and diffusion, resulting in irreversible capacity buildup. Therefore, this invention promotes a good bond between amino acid-based materials and the biomass porous silica material matrix by controlling the ball milling time of the biomass porous silica materials, forming a uniform and dense carbon layer network structure. This allows the mixed material to adapt to lithium-ion reaction and diffusion after carbonization, and ensures structural stability during cycling.

[0029] A third aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising the above-described negative electrode material, or comprising a negative electrode material prepared by the above-described preparation method.

[0030] In some embodiments of the present invention, the method for preparing the negative electrode sheet includes the following steps:

[0031] 1) Mix the negative electrode material, conductive agent and binder in a certain proportion to obtain the negative electrode slurry;

[0032] 2) Coat the negative electrode slurry onto the current collector and dry it to obtain the negative electrode sheet.

[0033] In some embodiments of the present invention, the conductive agent can be a conventional negative electrode conductive agent, preferably conductive carbon black.

[0034] In some embodiments of the present invention, the binder may be a conventional negative electrode binder, such as polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), sodium alginate, etc.; PAA is preferred. Water is used as the solvent for the binder.

[0035] In some embodiments of the present invention, the mass ratio of the negative electrode material, the conductive agent and the binder is (7-8):(2-1):1, for example, it can be 7:2:1 or 8:1:1, etc.

[0036] In some embodiments of the present invention, the current collector is a copper foil or an aluminum foil; preferably a copper foil.

[0037] In some embodiments of the present invention, the drying temperature is 60-120°C and the drying time is 12-24 hours.

[0038] A fourth aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising the above-described negative electrode sheet.

[0039] In some embodiments of the present invention, the lithium-ion battery further includes a positive electrode, a separator, and an electrolyte.

[0040] In some embodiments of the present invention, the electrolyte contains lithium salt and a non-aqueous solvent.

[0041] In some embodiments of the present invention, the lithium salt is selected from either LiClO4 or LiPF6.

[0042] In some embodiments of the present invention, the non-aqueous solvent is selected from at least one of ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (DME), and dimethyl carbonate (DMC). When the lithium salt is LiClO4, the non-aqueous solvent is a mixture of EC and DEC in a volume ratio of 1:1; when the lithium salt is LiPF6, the non-aqueous solvent is a mixture of EC, DMC, and DEC in a volume ratio of 1:1:1, or a mixture of EC and DME in a volume ratio of 1:1.

[0043] In some embodiments of the present invention, the concentration of the lithium salt in the electrolyte is 0.8-1.5 mol / L.

[0044] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages:

[0045] (1) The negative electrode material of the present invention is a biomass porous silicon-oxygen material coated with carbon material doped with high nitrogen content (≥13at%). This negative electrode material not only helps to enhance the stability of the electrode material, but also improves the reversible specific capacity of the material, thereby improving the coulombic efficiency and cycle stability of the lithium-ion battery.

[0046] (2) The anode material of this invention uses amino acid-based materials and abundant, widely available, and environmentally friendly biomass porous silica materials as raw materials. This results in low cost and low energy consumption. Furthermore, due to the well-developed three-dimensional pore structure of the biomass porous silica material, by controlling the mass ratio of the two materials, the carbonization temperature, and the carbonization time, the nitrogen-doped carbon material coating the biomass silica material exhibits a highly disordered and nitrogen-rich characteristic. Simultaneously, the abundant Si-OH surface of the biomass porous silica material can effectively crosslink the amino acid-based materials, reducing the loss of the amino acid-based materials during high-temperature pyrolysis, forming a structurally stable nitrogen-doped carbon coating on the biomass porous silica material, and increasing the nitrogen content in the anode material. In addition, the decomposition of the amino acid-based materials under high-temperature conditions helps optimize the pore and surface structure of the biomass porous silica material, further improving the affinity of the anode material for lithium ions.

[0047] (3) The preparation method of the negative electrode material of the present invention is simple to operate and has a short process flow, which is suitable for large-scale industrial production. The nitrogen-doped biomass porous silicon-oxygen-carbon material prepared has a unique multi-level pore structure. Combined with the nitrogen-doped carbon material coating, it promotes the interaction between silicon-oxygen material and lithium ions, while alleviating the volume expansion of silicon-oxygen material during charging and discharging, ensuring the cycle stability of the battery. When applied to lithium-ion batteries, it can ensure the integrity of the electrode and achieve good cycle stability and electrochemical performance of the battery. Attached Figure Description

[0048] Figure 1 The image shows the XRD pattern of the negative electrode material prepared in Example 2 of this invention.

[0049] Figure 2 This is a SEM image of the negative electrode material prepared in Example 2 of the present invention;

[0050] Figure 3 This is a pore size distribution diagram of the negative electrode material prepared in Example 2 of the present invention;

[0051] Figure 4 The charging and discharging diagrams show the lithium-ion batteries assembled from the negative electrode materials prepared in Example 2 and Comparative Example 1 of this invention.

[0052] Figure 5 The graph shows the cycle performance of lithium-ion batteries assembled from the negative electrode materials prepared in Example 2 and Comparative Example 1 of this invention. Detailed Implementation

[0053] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0054] Example 1

[0055] A method for preparing a high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material includes the following steps:

[0056] (1) Place 5g of biomass porous silica material (round diatoms) in a ball mill jar, add 10mL of grinding aid (ethanol) and 50g of ball milling media (zirconia balls with a particle size of 1-10mm), and put it into a ball mill and mill at a speed of 400 rpm for 12 hours. After filtering the ball milling suspension, place it in a forced-air drying oven and dry at 80℃ for 24 hours to obtain small-particle-size biomass porous silica material.

[0057] (2) Weigh 1g of the biomass porous silica material obtained in step (1), add 2g of amino acid material (glutamic acid) and mix and grind at a speed of 400 rpm for 1 hour to obtain a uniform mixed material.

[0058] (3) The mixed material obtained in step (2) is transferred to a tube furnace and heated to 600°C at a heating rate of 5°C / min under an argon protective atmosphere. The mixture is then held for calcination for 3 hours to obtain the high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material of this embodiment.

[0059] Example 2

[0060] A method for preparing a high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material includes the following steps:

[0061] (1) Place 5g of biomass porous silica material (round diatoms) in a ball mill jar, add 10mL of grinding aid (ethanol) and 50g of ball milling media (zirconia balls with a particle size of 1-10mm), put them in a ball mill and ball mill at a speed of 400 rpm for 6 hours. After filtering the ball milling solution, place it in a forced-air drying oven and dry at 80℃ for 24 hours to obtain small-particle-size biomass porous silica material.

[0062] (2) Weigh 1g of the biomass porous silica material obtained in step (1), add 2g of amino acid material (glutamic acid) and mix and grind at a speed of 400 rpm for 1 hour to obtain a uniform mixed material.

[0063] (3) The mixed material obtained in step (2) is transferred to a tube furnace and heated to 600°C at a heating rate of 5°C / min under an argon protective atmosphere. The mixture is then held for calcination for 3 hours to obtain the high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material of this embodiment.

[0064] Example 3

[0065] A method for preparing a high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material includes the following steps:

[0066] (1) Place 5g of biomass porous silica material (round diatoms) in a ball mill jar, add 10mL of grinding aid (ethanol) and 50g of ball milling media (zirconia balls with a particle size of 1-10mm), and put them into a ball mill and mill at a speed of 400 rpm for 3 hours. After filtering the ball milling suspension, place it in a forced-air drying oven and dry at 80℃ for 24 hours to obtain small-particle-size biomass porous silica material.

[0067] (2) Weigh 1g of the biomass porous silica material obtained in step (1), add 2g of amino acid material (glutamic acid) and mix and grind at a speed of 400 rpm for 1 hour to obtain a uniform mixed material.

[0068] (3) The mixed material obtained in step (2) is transferred to a tube furnace and heated to 600°C at a heating rate of 5°C / min under an argon protective atmosphere. The mixture is then held for calcination for 3 hours to obtain the high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material of this embodiment.

[0069] Example 4

[0070] A method for preparing a high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material includes the following steps:

[0071] (1) Place 5g of biomass porous silica material (round diatoms) in a ball mill jar, add 10mL of grinding aid (ethanol) and 50g of ball milling media (zirconia balls with a particle size of 1-10mm), and put it into a ball mill and mill at a speed of 400 rpm for 6 hours. After filtering the ball milling suspension, place it in a forced-air drying oven and dry at 80℃ for 24 hours to obtain small-particle-size biomass porous silica material.

[0072] (2) Weigh 1g of the biomass porous silica material obtained in step (1), add 1g of amino acid material (glutamic acid) and mix and grind at a speed of 400 rpm for 1 hour to obtain a uniform mixed material.

[0073] (3) The mixed material obtained in step (2) is transferred to a tube furnace and heated to 600°C at a heating rate of 5°C / min under an argon protective atmosphere. The mixture is then held for calcination for 3 hours to obtain the high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material of this embodiment.

[0074] Example 5

[0075] A method for preparing a high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material includes the following steps:

[0076] (1) Place 5g of biomass porous silica material (round diatoms) in a ball mill jar, add 10mL of grinding aid (ethanol) and 50g of ball milling media (zirconia balls with a particle size of 1-10mm), and put it into a ball mill and mill at a speed of 400 rpm for 6 hours. After filtering the ball milling suspension, place it in a forced-air drying oven and dry at 80℃ for 24 hours to obtain small-particle-size biomass porous silica material.

[0077] (2) Weigh 1g of the biomass porous silica material obtained in step (1), add 5g of amino acid material (glutamic acid) and mix and grind at a speed of 400 rpm for 1 hour to obtain a uniform mixed material.

[0078] (3) The mixed material obtained in step (2) is transferred to a tube furnace and heated to 600°C at a heating rate of 5°C / min under an argon protective atmosphere. The mixture is then held for calcination for 3 hours to obtain the high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material of this embodiment.

[0079] Example 6

[0080] A method for preparing a high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material includes the following steps:

[0081] (1) Place 5g of biomass porous silica material (round diatoms) in a ball mill jar, add 10mL of grinding aid (ethanol) and 50g of ball milling media (zirconia balls with a particle size of 1-10mm), and put it into a ball mill and mill at a speed of 400 rpm for 6 hours. After filtering the ball milling suspension, place it in a forced-air drying oven and dry at 80℃ for 24 hours to obtain small-particle-size biomass porous silica material.

[0082] (2) Weigh 1g of the biomass porous silica material obtained in step (1), add 2g of amino acid material (glutamic acid) and mix and grind at a speed of 400 rpm for 1 hour to obtain a uniform mixed material.

[0083] (3) The mixed material obtained in step (2) is transferred to a tube furnace and heated to 500°C at a heating rate of 5°C / min under an argon protective atmosphere. The material is then held at the temperature for 3 hours to obtain the high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material of this embodiment.

[0084] Example 7

[0085] A method for preparing a high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material includes the following steps:

[0086] (1) Place 5g of biomass porous silica material (round diatoms) in a ball mill jar, add 10mL of grinding aid (ethanol) and 50g of ball milling media (zirconia balls with a particle size of 1-10mm), and put it into a ball mill and mill at a speed of 400 rpm for 6 hours. After filtering the ball milling suspension, place it in a forced-air drying oven and dry at 80℃ for 24 hours to obtain small-particle-size biomass porous silica material.

[0087] (2) Weigh 1g of the biomass porous silica material obtained in step (1), add 2g of amino acid material (glutamic acid) and mix and grind at a speed of 400 rpm for 1 hour to obtain a uniform mixed material.

[0088] (3) The mixed material obtained in step (2) is transferred to a tube furnace and heated to 700°C at a heating rate of 5°C / min under an argon protective atmosphere. The mixture is then held for calcination for 3 hours to obtain the high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material of this embodiment.

[0089] Comparative Example 1

[0090] The only difference between Comparative Example 1 and Example 2 is that no amino acid materials were added during the preparation of the negative electrode material.

[0091] Comparative Example 2

[0092] The only difference between Comparative Example 2 and Example 2 is that, in the preparation of the negative electrode material, an equal amount of melamine material was used to replace the amino acid material in Example 2.

[0093] Comparative Example 3

[0094] The difference between Comparative Example 3 and Example 2 is that, in the preparation of the negative electrode material, an equal amount of dicyandiamide material was used to replace the amino acid material in Example 2.

[0095] Application examples

[0096] Using the negative electrode materials prepared in Examples 1-7 and Comparative Examples 1-3 as the active materials for the negative electrode sheets, 2032 button-type lithium-ion batteries were fabricated. The specific steps are as follows:

[0097] 1) Preparation of negative electrode sheet: The negative electrode material is mixed evenly with PAA and conductive carbon black in a mass ratio of 7:2:1, water is added to make a negative electrode slurry; then the negative electrode slurry is evenly coated on both sides of the negative electrode current collector copper foil, dried in a vacuum drying oven at 80°C for 24 hours, and then rolled and punched to obtain the negative electrode sheet.

[0098] 2) Preparation of electrolyte: EC, DMC and DEC are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a concentration of 1 mol / L. After complete dissolution, the electrolyte is obtained.

[0099] 3) Preparation of lithium-ion batteries: The above-mentioned negative electrode, separator (polyolefin film), positive electrode (lithium sheet), and electrolyte are assembled into 2032 button lithium-ion batteries in a glove box with an argon protective atmosphere where the water and oxygen contents are both less than 0.1 ppm.

[0100] Performance testing

[0101] 1. Material Characterization

[0102] Figure 1 The XRD pattern of the negative electrode material prepared in Example 2 is shown in the figure. The horizontal axis 2θ represents the diffraction angle, and the vertical axis Intensity represents the intensity of the diffraction peak. Figure 1 It can be seen that the anode material only has a bulge around the 21.7° angle, and there are no obvious crystalline diffraction peaks, indicating that the structure of the anode material is highly disordered.

[0103] Further elemental analysis was performed on the negative electrode material prepared in Example 2, and the test results are shown in Table 1.

[0104] Table 1:

[0105] element Content (at%) C 44.67 N 13.12 O 31.37 Si 10.84

[0106] As shown in Table 1, the negative electrode material prepared in Example 2 has a high nitrogen content. This is mainly due to the strong interaction between the amino acid materials and the Si-OH on the surface of the biomass porous silica material, which retains more nitrogen.

[0107] Figure 2 The image shows a SEM image of the negative electrode material prepared in Example 2. Figure 2 It can be seen that the negative electrode material has a rich hierarchical porous structure, and its pore structure distribution is as follows: Figure 3 As shown, the anode material comprises micropores (0.35-2 nm), mesopores (2-50 nm), and macropores (50-200 nm), with the proportions of micropores, mesopores, and macropores being 83%, 15%, and 2%, respectively. The presence of numerous microporous structures not only exposes more active sites but also limits excessive electrolyte penetration, reduces electrolyte decomposition, and effectively improves the reversible capacity of the silicon-oxygen material. Nitrogen adsorption-desorption tests were performed on this anode material, revealing a specific surface area ranging from 160 to 360 nm. 2 / g, the high specific surface area and porous nanoscale channels significantly shorten the diffusion path of lithium ions, accelerate the migration rate of lithium ions, promote the uniform deposition of solid electrolyte membranes, and reduce material cracking caused by local polarization.

[0108] 2. Electrochemical performance

[0109] The first-cycle charge specific capacity and first-cycle coulombic efficiency of the lithium-ion batteries prepared in the above application examples were tested under the following conditions: 30°C and 50 mA / g current density. The cycle performance of lithium-ion batteries prepared using the negative electrode materials obtained in Example 2 and Comparative Example 1 was also tested under the following conditions: 100 cycles at a current density of 100 mA / g. The results are shown in Table 2 and... Figure 4-5 As shown. Wherein: Figure 4 The horizontal axis, Specific capacity, represents the specific capacity during the first charge cycle, and the vertical axis, Voltage, represents the voltage. Figure 5 The horizontal axis represents the number of cycles, the left vertical axis represents the specific capacity, and the right vertical axis represents the Coulombic efficiency.

[0110] Table 2:

[0111]

[0112]

[0113] From Table 2 and Figure 4-5 It can be seen that the high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material prepared in Example 2 exhibits the best electrochemical performance. At 30°C and a current density of 50 mA / g, the initial charge-to-discharge ratio is 1112.26 mAh / g, and the initial coulombic efficiency is 65.47%. At a current density of 100 mA / g, the reversible specific capacity after 100 cycles is 586.01 mAh / g, with a capacity retention of 92%. In contrast, the biomass porous silicon-oxygen material of Comparative Example 1 (without nitrogen-doped carbon coating) has an initial charge-to-discharge ratio of only 469.05 mAh / g and an initial coulombic efficiency of only 39.88% under the same test conditions; the reversible specific capacity after 100 cycles is 101.36 mAh / g, with a capacity retention of 69.65%. This demonstrates that the addition of amino acid-based materials can significantly improve the battery performance of biomass porous silicon-oxygen anodes.

[0114] Comparing Example 2 with Examples 1 and 3 reveals that the ball milling time of the biomass porous silica material affects the particle size, thus influencing its electrochemical performance. This is because a short ball milling time results in micron-sized particles, forming an unstable solid electrolyte interphase (SEI) membrane, which is detrimental to subsequent carbonization. Conversely, a longer ball milling time easily damages the pore structure, hindering lithium-ion transport and diffusion, leading to irreversible capacity buildup. Therefore, this invention controls the ball milling time of the biomass porous silica material to promote a good bond between the amino acid-based material and the biomass porous silica material matrix, forming a uniform and dense carbon layer network structure. This allows the carbonized mixture to adapt to lithium-ion reactions and diffusion, ensuring structural stability during cycling.

[0115] Comparing Examples 2 with Examples 4 and 5 reveals that the amount of amino acid-based materials added affects the formation of the nitrogen-doped carbon layer structure and the content of in-situ doped nitrogen in the biomass porous silica material. By controlling the amount of amino acid-based materials added, the carbon layer structure and nitrogen content can be regulated in one step, simplifying the process and making it more suitable for industrial production. During carbonization, if the amount of amino acid-based materials added is too small, the nitrogen-doped carbon layer structure cannot completely cover the porous silica material, easily forming an unstable SEI film, leading to pulverization of the material during the electrochemical reaction. When the amount of amino acid-based materials added is too large, the carbon layer is too thick, and the nitrogen content is too high, increasing the diffusion rate of lithium ions during the reaction and reducing the electrochemical performance of the material. Therefore, this invention controls the amount of amino acid-based materials to promote good bonding between amino and carbon-based groups and the biomass porous silica material, making the biomass porous silica material suitable for reacting with lithium ions while ensuring structural stability during the cycling process.

[0116] Comparing Examples 2 with Examples 6 and 7 reveals that the calcination temperature of carbonization affects the types and content of pyrolysis products of amino acid-based materials, as well as the bonding structure of the pyrolysis and carbonization products with the biomass porous silica-oxygen material matrix. Therefore, this invention, by controlling the pyrolysis temperature of amino acid-based materials, enables nitrogen-doped biomass porous silica-oxygen carbon materials to exhibit optimal electrochemical performance.

[0117] Compared to Example 2, Comparative Examples 2 and 3 showed a significant decrease in the first-cycle discharge specific capacity and first coulombic efficiency of lithium-ion batteries due to the replacement of the amino acid-based materials in Example 2 with similar amino acid materials such as melamine and dicyandiamide. This demonstrates that the biomass porous silica-oxygen materials modified with amino acid-based materials have superior electrochemical performance.

[0118] For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. A method for preparing a high-capacity nitrogen-doped porous silicon-oxycarbide anode material, characterized in that, Includes the following steps: (1) Grind the biomass porous silica material and then mix it with amino acid materials to obtain a mixed material; The grinding process conditions are as follows: using grinding balls with a particle size of 1-10mm, grinding at a speed of 200-600 rpm for 3-48 hours; (2) The mixed material is annealed under an inert atmosphere to obtain the high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material; The annealing temperature regime is as follows: heat to 400-800℃ at a rate of 3-10℃ / min, and then hold at that temperature for 2-4 hours; The high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material comprises nitrogen-doped carbon material and biomass porous silicon-oxygen material, wherein the nitrogen-doped carbon material coats the biomass porous silicon-oxygen material, and the biomass porous silicon-oxygen material includes diatoms; in the high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material, the nitrogen content is ≥13 at%; The high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material has a hierarchical pore structure, including micropores, mesopores and macropores, and the proportion of micropores is greater than 80%. The raw materials for preparing the high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material include biomass porous silicon-oxygen materials and amino acid-based materials, wherein the mass ratio of the biomass porous silicon-oxygen materials to the amino acid-based materials is 1:(2-4).

2. The preparation method according to claim 1, characterized in that, The diatoms are selected from at least one of round diatoms and boat-shaped diatoms; and / or the amino acid material is selected from at least one of glutamic acid, proline, cysteine, glycine, and alanine.

3. A high-capacity nitrogen-doped porous silicon-oxygen-carbon anode material, characterized in that, It is prepared by the preparation method described in claim 1 or 2.

4. A negative electrode sheet, characterized in that, The negative electrode sheet includes the high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material as described in claim 3, or the high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material prepared by the preparation method described in claim 1 or 2.

5. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in claim 4.

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