A multi-level composite anode material and its preparation method

Abstract

This invention relates to the field of lithium-ion battery materials technology, and particularly to a multi-level composite anode material and its preparation method. The multi-level composite anode material comprises, from the inside out: a core, a first coating layer, and a second coating layer. The core comprises silicon nanoparticles, the first coating layer comprises silicon suboxide, and the second coating layer is a carbon layer. The carbon layer is derived from the pyrolysis of heavy oil. This invention uses silicon suboxide as a transition layer, combining the advantages of silicon, silicon suboxide, and carbon layers. It retains the high lithium storage capacity of silicon anodes while utilizing the high capacity and relatively small volume expansion rate of silicon suboxide. Furthermore, it employs pitch-derived carbon formed from heavy oil as the outermost mechanical buffer layer. Through this transition buffering mechanism, the internal volume expansion is buffered and released step by step to maintain structural stability, thereby improving the cycle stability of the silicon-silicon suboxide-carbon composite anode.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, and in particular to a multi-level composite anode material and its preparation method. Background Technology

[0002] With the continuous increase in energy demand and the ongoing adjustment of the energy structure, lithium-ion batteries are playing an increasingly important role in the development of new energy sources. At the same time, the demands and requirements for lithium-ion batteries are becoming increasingly diverse; only lithium-ion batteries with higher energy density, longer cycle life, and better rate performance can meet future development needs. Currently, the most widely used graphite anode has a limited theoretical capacity (372 mAh / g), which cannot meet future development requirements, while silicon anodes have extremely high theoretical lithium storage capacity (4200 mAh / g). Therefore, developing silicon anodes is a major development direction for new high-performance lithium-ion batteries.

[0003] However, the main problem with silicon as a negative electrode is its large volume effect (300%), which may cause silicon particles to break or even pulverize during lithium storage and delithiation, leading to battery failure and making its commercial application challenging.

[0004] In existing technologies, patent CN114068869A uses γ-aminopropyltriethoxysilane, dialdehyde molecules, and nano-silicon powder as raw materials to obtain a core-shell structured silicon@silicon suboxide / carbon anode material through aldehyde-amine condensation reaction and high-temperature pyrolysis under an inert atmosphere. This method is simple, but controlling the degree of reaction is relatively difficult. Patents CN113363433A and CN116314714A use magnesium powder and aluminum powder as reducing agents to partially reduce silicon dioxide to obtain silicon suboxide, which is then mixed with a carbon source to obtain a composite anode material. Patent CN112133896A simultaneously mixes and calcines silicon, silicon suboxide, graphite, and a carbon source to obtain a graphite-silicon-silicon suboxide composite material. This method introduces a metal reducing agent during preparation, making the process relatively complex and potentially leading to residual metal impurities later. Patent CN110993907A uses high-temperature, high-energy ball milling to mix nano-sized silicon powder and silica powder with a carbon source, passivating their surfaces to form a composite powder of nanocrystalline silicon-silicon suboxide-carbon. This preparation technology is simple, but it requires a lot of energy input during the preparation process, which is not conducive to large-scale application.

[0005] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a multi-level composite anode material and its preparation method, which aims to solve the problems of high energy input and poor reaction controllability in the preparation of anode materials by existing methods.

[0007] The technical solution of the present invention is as follows:

[0008] A multi-layered composite anode material comprises, from the inside out: a core, a first coating layer, and a second coating layer; the core comprises silicon nanoparticles, the first coating layer comprises silicon suboxide, and the second coating layer is a carbon layer; the carbon layer is derived from the pyrolysis of heavy oil.

[0009] The multi-level composite anode material, wherein the silicon nanoparticles have a particle size of 50-100 nm.

[0010] The multi-level composite anode material is characterized in that the particle size of the core is 30-80 nm; and / or the thickness of the first coating layer is 20-50 nm; and / or the thickness of the second coating layer is 20-50 nm.

[0011] A method for preparing a multi-level composite anode material includes the following steps:

[0012] The silicon source is oxidized to obtain a silicon source with an oxidized surface.

[0013] The silicon source after surface oxidation is mixed with a carbon source and an organic solvent to obtain a mixed dispersion.

[0014] The mixed dispersion was subjected to stirring and heat treatment to obtain a composite anode material with a silicon-silicon suboxide-carbon multilayer structure.

[0015] The method for preparing the multi-level composite anode material, wherein the silicon source is nano-silicon particles; the carbon source is heavy oil; the organic solvent is aromatic hydrocarbon; and the asphaltenes content of the heavy oil is 30wt%-40wt%.

[0016] The method for preparing the multi-level composite anode material includes the following steps: oxidation treatment of the silicon source.

[0017] A mixture of silicon source, ammonia, hydrogen peroxide, and water is obtained.

[0018] The mixture is subjected to ultrasonic bubbling and heating stirring to obtain a silicon source with surface oxidation.

[0019] The method for preparing the multi-level composite negative electrode material, wherein the volume ratio of the ammonia, the hydrogen peroxide and the water is (0.2-0.3):(1-2):5; and / or, the mass of the silicon source accounts for 1-5 wt% of the mass of the water.

[0020] The method for preparing the multi-level composite negative electrode material includes the following: the ultrasonic bubbling treatment time is 30-60 min; and / or the heating and stirring treatment temperature is 70-100℃, the stirring speed is 500-700 rpm, and the heating and stirring treatment time is 10-60 min.

[0021] The method for preparing the multi-level composite anode material, wherein the mass ratio of the surface-oxidized silicon source to the carbon source is 1:(1-2); and / or, the stirring speed is 500-700 rpm, and the stirring time is 12-16 h.

[0022] The method for preparing the multi-level composite negative electrode material includes a heating rate of 5-10℃ / min, a holding temperature of 480-500℃, and a holding time of 1-3h; the heat treatment is carried out under an inert atmosphere.

[0023] Beneficial Effects: This invention provides a multi-level composite anode material and its preparation method. The multi-level composite anode material comprises, from the inside out: a core, a first coating layer, and a second coating layer. The core comprises silicon nanoparticles, the first coating layer comprises silicon suboxide, and the second coating layer is a carbon layer. The carbon layer is derived from the pyrolysis of heavy oil. This invention achieves silicon-silicon suboxide composite structure by effectively partially oxidizing the surface of silicon nanoparticles, and then coating the surface with a carbon layer to form a second coating layer, thus obtaining a silicon-silicon suboxide-carbon multi-level composite anode material. This structure uses silicon suboxide as a transition layer, combining the advantages of silicon, silicon suboxide, and carbon layers. It retains the high lithium storage capacity of silicon anodes while utilizing the high capacity and relatively small volume expansion rate of silicon suboxide. Furthermore, it uses pitch-derived carbon from heavy oil as the outermost mechanical buffer layer. Through transition buffering, the internal volume expansion is buffered and released step by step to maintain structural stability, thereby improving the cycle stability of the silicon-silicon suboxide-carbon composite anode. Furthermore, pitch-derived carbon possesses excellent conductivity, enabling the formation of a robust electron pathway network on the outermost layer of the anode material. The carbon layer, acting as a protective layer, separates the internal silicon suboxide and silicon nanoparticles from the formed SEI film, effectively preventing electrolyte consumption and anode failure caused by excessive SEI film growth. This enhances the overall electrochemical performance of the silicon-silicon suboxide-carbon multilevel composite anode material. Moreover, the preparation method allows for simple and effective adjustment of the degree of oxidation on the silicon source surface by controlling the addition ratio of hydrogen peroxide and ammonia, as well as the temperature and time of heating and stirring, thus obtaining silicon suboxide coating layers of varying thicknesses. Ultimately, by using the carbon layer as the outermost layer, a silicon-silicon suboxide-carbon multilevel composite anode material is obtained, forming a progressively buffering layer that effectively mitigates volume expansion. Combined with the high theoretical capacity of silicon suboxide and the excellent conductive network formed by the carbon layer, a lithium-ion battery anode material with high energy density, stable cycle performance, and good rate performance is achieved. Furthermore, this preparation method is simple to operate, easily controllable, energy-efficient, and does not introduce other impurities. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a multi-level composite negative electrode material according to the present invention;

[0025] Figure 2 This is a schematic flowchart of a method for preparing a multi-level composite negative electrode material according to the present invention.

[0026] Figure 3 A schematic diagram illustrating the structural formation of a silicon-silicon suboxide-carbon multilevel composite anode material;

[0027] Figure 4The image shows the microstructure of the silicon-silica-suboxide coated composite particles obtained in Example 1.

[0028] Figure 5 The above is an energy dispersive spectroscopy (EDS) image of the silicon-silica-suboxide coated composite particles prepared in Example 1.

[0029] Figure 6 The image shows the microstructure of the silicon-silica-pitch-derived carbon multilayer composite anode material prepared in Example 1.

[0030] Figure 7 The graph shows the cycle performance and rate performance data of the silicon-silica-pitch-derived carbon multilayer composite anode material prepared in Example 1 under 0.2C conditions. Detailed Implementation

[0031] This invention provides a multi-level composite anode material and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0033] Compared to silicon anodes, silicon suboxide (SiO2) x Silicon exhibits a relatively low volume expansion rate during lithium insertion / extraction and a high theoretical capacity (2680 mAh / g). Furthermore, during the initial lithiation, silicon suboxide forms lithium silicate and lithium oxide, acting as a buffer and improving cycle performance. Carbon materials, when used as a coating layer, also provide buffer protection, reducing volume changes. Simultaneously, the high conductivity of carbon materials compensates for the conductivity deficiencies of silicon and silicon suboxide. Combining silicon, silicon suboxide, and carbon to form the negative electrode integrates the advantages of all three, maintaining high specific capacity and conductivity while mitigating volume expansion, resulting in a lithium-ion battery with superior overall performance.

[0034] Based on this, such as Figure 1As shown, the present invention provides a multi-layered composite anode material, comprising, from the inside out: a core 10, a first coating layer 20, and a second coating layer 30; the core 10 comprises silicon nanoparticles, the first coating layer 20 comprises silicon suboxide, and the second coating layer 30 is a carbon layer; the carbon layer is derived from the pyrolysis of heavy oil.

[0035] In this embodiment, the composite anode material uses nano-silicon particles as the core, silicon suboxide as the first coating layer, and a carbon layer derived from heavy oil pyrolysis as the outermost layer. This allows silicon suboxide to act as a transition layer, combining the advantages of silicon, silicon suboxide, and carbon layers. It retains the high lithium storage capacity of silicon anodes while utilizing the high capacity and relatively small volume expansion rate of silicon suboxide. Pitch-derived carbon is used as the outermost mechanical buffer layer. Through this transition buffering method, the internal volume expansion can be buffered and released step by step to maintain structural stability, thereby improving the cycle stability of the silicon-silicon suboxide-carbon composite anode. Furthermore, pitch-derived carbon has good conductivity, enabling the anode material to form a good electron pathway network on the outermost layer. Simultaneously, the carbon layer acts as a protective layer, separating the internal silicon suboxide and silicon particles from the SEI film formed during charge and discharge, effectively preventing electrolyte consumption and anode failure caused by excessive SEI film growth. This enhances the overall electrochemical performance of the silicon-silicon suboxide-carbon multi-level composite anode material.

[0036] In some embodiments, the silicon nanoparticles have a particle size of 50-100 nm. Silicon nanoparticles of this size have extremely high lithium storage capacity. Using them as the core of the composite anode material can enable the composite anode material to have excellent comprehensive electrochemical performance.

[0037] In some embodiments, the core has a particle size of 30-80 nm; and / or, the thickness of the first coating layer is 20-50 nm; and / or, the thickness of the second coating layer is 20-50 nm.

[0038] In addition, such as Figure 2 As shown, the present invention also provides a method for preparing a multi-level composite anode material, comprising the following steps:

[0039] Step S10: Oxidize the silicon source to obtain a silicon source with an oxidized surface;

[0040] Step S20: Mix the surface-oxidized silicon source with a carbon source and an organic solvent to obtain a mixed dispersion;

[0041] Step S30: The mixed dispersion is stirred and heat-treated to obtain a composite anode material with a silicon-silicon suboxide-carbon multilayer structure.

[0042] In this embodiment, a carbon source is dissolved in an organic solvent and a silicon source with surface oxidation (silicon-silicon suboxide composite structure) is added, causing the carbon source to adsorb onto the surface of the silicon-silicon suboxide composite structure to form a second coating layer. Stirring is used to improve the uniformity of adsorption and shorten the adsorption time. Finally, a heat treatment method is used to pyrolyze the carbon source at high temperature, forming a carbon layer coating, thereby obtaining a silicon-silicon suboxide-carbon multilevel composite anode material. Silicon anodes have extremely high theoretical specific capacity, but their large volume expansion rate hinders their practical application. The multilevel structure formed by silicon-silicon suboxide-carbon creates a transitional buffer layer, effectively mitigating volume expansion. Combined with the high theoretical capacity of silicon suboxide and the good conductive network pathway formed by pitch-derived carbon, a lithium-ion battery anode material with high energy density, stable cycle performance, and good rate performance is obtained.

[0043] In some embodiments, step S10 involves oxidizing the silicon source, including the following steps:

[0044] Step S11: Mix the silicon source, ammonia, hydrogen peroxide and water to obtain a mixture;

[0045] Step S12: The mixture is subjected to ultrasonic bubbling and heating stirring to obtain a silicon source with surface oxidation.

[0046] In this embodiment, hydrogen peroxide is used as an oxidant under alkaline conditions, and energy is input through heating and stirring to oxidize the surface of the silicon source. By utilizing the oxidizing properties of hydrogen peroxide, the surface of the silicon source is effectively partially oxidized to form a silicon-silicon suboxide composite structure. Specifically, the outer layer is silicon suboxide and the core is nano-silicon particles.

[0047] Specifically, by adjusting the ratio of hydrogen peroxide and ammonia, as well as the temperature and time of heating and stirring, the degree of oxidation on the silicon source surface can be easily and effectively controlled to obtain silicon suboxide coating layers of different thicknesses. Finally, by using a carbon layer as the outermost layer, a composite anode material with a silicon-silicon suboxide-carbon multi-level structure is obtained, forming a progressively buffering layer that effectively alleviates volume expansion. Combined with the high theoretical capacity of silicon suboxide and the excellent conductive network pathways formed by the carbon layer, a lithium-ion battery anode material with high energy density, stable cycle performance, and good rate performance is obtained. Furthermore, this preparation method is simple to operate, easy to control, consumes little energy, and does not introduce other impurities.

[0048] In some embodiments, the silicon source is nano-silicon particles; the carbon source is heavy oil; and the organic solvent is an aromatic hydrocarbon.

[0049] Specifically, the carbon source is heavy oil, a byproduct of petroleum refining; the organic solvent is a high-boiling-point aromatic hydrocarbon, also a byproduct of refining. The organic solvent provides an environment for the mixing of the surface-oxidized silicon source and the carbon source, allowing the carbon source to be uniformly adsorbed on the surface of the surface-oxidized silicon source. Combined with stirring, this improves the uniformity of adsorption and shortens the adsorption time.

[0050] In some embodiments, the asphaltene content of the heavy oil is 30wt%-40wt%. Controlling the asphaltene content of the heavy oil between 30wt% and 40wt% can ensure the effective construction of the carbon protective layer.

[0051] In some embodiments, the initial concentration of the ammonia solution is 25wt%-28wt%; and / or, the initial concentration of the hydrogen peroxide is 30wt%-31wt%. By controlling the initial concentrations of the ammonia solution and the hydrogen peroxide, the surface partial oxidation of silicon nanoparticles can be effectively regulated, resulting in silicon suboxide coating layers of different thicknesses.

[0052] In some embodiments, the volume ratio of the ammonia, the hydrogen peroxide, and the water is (0.2-0.3):(1-2):5; and / or, the mass of the silicon source accounts for 1-5 wt% of the mass of the water.

[0053] In some embodiments, the ultrasonic bubbling treatment time is 30-60 min; and / or, the heating and stirring treatment temperature is 70-100°C, the stirring speed is 500-700 rpm, and the heating and stirring treatment time is 10-60 min. By controlling the volume ratio of ammonia, hydrogen peroxide, and water, the amount of silicon source added, and the parameters of the ultrasonic bubbling treatment and the heating and stirring treatment, the surface oxidation of silicon particles can be effectively controlled.

[0054] In some embodiments, step S20, after ultrasonic bubbling and heating stirring of the mixture, further includes solvent evaporation; the solvent evaporation temperature is 60-80℃ and the solvent evaporation time is 12-14 hours. After solvent evaporation, a silicon source with surface oxidation is obtained, i.e., a silicon-silicon suboxide composite structure.

[0055] In some embodiments, the mass ratio of the surface-oxidized silicon source to the carbon source is 1:(1-2); and / or, the stirring speed is 500-700 rpm, and the stirring time is 12-16 h.

[0056] In some embodiments, the heating rate of the heat treatment is 5-10℃ / min, the holding temperature of the heat treatment is 480-500℃, and the holding time of the heat treatment is 1-3h; the heat treatment is carried out under an inert atmosphere.

[0057] Specifically, the stirring process employs magnetic stirring; the heat treatment is carried out in a tube furnace. By controlling the mass ratio of the surface-oxidized silicon source and the carbon source, as well as the heat treatment process, a multi-level composite structure of silicon-silica-pitch-derived carbon is effectively constructed.

[0058] In some embodiments, the inert atmosphere includes, but is not limited to, nitrogen, argon, and helium; the flow rate of the inert atmosphere is controlled at 80-150 mL / min.

[0059] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0060] Example 1

[0061] This embodiment provides a silicon-silicon suboxide-pitch-derived carbon multilayer composite anode material. A schematic diagram of the structure formation of the silicon-silicon suboxide-carbon multilayer composite anode material is shown below. Figure 3 As shown, the specific preparation steps are as follows:

[0062] 1 mL of hydrogen peroxide and 0.25 mL of ammonia were added to 5 mL of deionized water and mixed thoroughly to form a solution. 0.2 g of nano-silicon powder was added to this solution to form a mixture. The mixture was ultrasonically bubbled for 30 min to ensure thorough dispersion of the nano-silicon powder. Subsequently, the mixture was magnetically stirred for 10 min at 70℃ and 500 rpm to induce surface oxidation. After evaporating the solvent at 60℃ for 12 h, silicon-silica suboxide coated composite particles were obtained, with the following microstructure: Figure 4 As shown, the results indicate that the silicon-silica-suboxide coated composite particles exhibit a spherical nanostructure; the energy dispersive spectroscopy (EDS) pattern is shown in the figure below. Figure 5 As shown, the results indicate that silicon and oxygen elements are uniformly distributed on the particle surface.

[0063] Subsequently, the silicon-silica-suboxide coated composite particles were mixed with 0.2 g of heavy oil and 20 mL of organic solvent to form a mixed dispersion, which was magnetically stirred for 12 h. The mixed dispersion was placed in an alumina crucible and heated to 480 °C in a tube furnace at a heating rate of 10 °C / min and held for 1 h, while an N2 atmosphere was introduced with a gas flow rate controlled at 100 mL / min. After cooling to room temperature in the furnace, the product was obtained, and its microstructure is as follows. Figure 6As shown, the results indicate that a carbon coating layer derived from pitch pyrolysis is further formed on the outer layer of the silicon-silica-pitch-derived carbon multi-level composite particles, thus obtaining a silicon-silica-pitch-derived carbon multi-level composite structure. Figure 7 (a) and (b) in the figure represent its cycling performance and rate performance under 0.2C conditions, respectively.

[0064] Example 2

[0065] This embodiment provides a silicon-silicon suboxide-pitch-derived carbon multilayer composite anode material, and the specific preparation steps are as follows:

[0066] 1.5 mL of hydrogen peroxide and 0.25 mL of ammonia were added to 5 mL of deionized water and mixed thoroughly to form a solution. 0.2 g of nano-silicon powder was added to this solution to form a mixture. The mixture was ultrasonically bubbled for 30 min to ensure thorough dispersion of the nano-silicon powder. Subsequently, the mixture was magnetically stirred for 10 min at 70 °C and 500 rpm to induce surface oxidation. After evaporating the solvent at 60 °C for 12 h, silicon-silica-suboxide coated composite particles were obtained.

[0067] Subsequently, the silicon-silica-suboxide coated composite particles were mixed with 0.2 g of heavy oil and 20 mL of organic solvent to form a mixed dispersion, which was magnetically stirred for 12 h. The mixed dispersion was placed in an alumina crucible and heated to 480 °C in a tube furnace at a heating rate of 10 °C / min and held for 1 h, while an N2 atmosphere was introduced with a gas flow rate controlled at 100 mL / min. After cooling to room temperature in the furnace, a silicon-silica-pitch-derived carbon multilayer composite structure was obtained.

[0068] Example 3

[0069] This embodiment provides a silicon-silicon suboxide-pitch-derived carbon multilayer composite anode material, and the specific preparation steps are as follows:

[0070] 2 mL of hydrogen peroxide and 0.25 mL of ammonia were added to 5 mL of deionized water and mixed thoroughly to form a solution. 0.2 g of nano-silicon powder was added to this solution to form a mixture. The mixture was ultrasonically bubbled for 30 min to ensure thorough dispersion of the nano-silicon powder. Subsequently, the mixture was magnetically stirred for 30 min at 70 °C and 500 rpm to induce surface oxidation. After evaporating the solvent at 60 °C for 12 h, silicon-silica-suboxide coated composite particles were obtained.

[0071] Subsequently, the silicon-silica-suboxide coated composite particles were mixed with 0.4 g of heavy oil and 40 mL of organic solvent to form a mixed dispersion, which was magnetically stirred for 12 h. The mixed dispersion was placed in an alumina crucible and heated to 480 °C in a tube furnace at a heating rate of 10 °C / min and held for 1 h, while an N2 atmosphere was introduced with a gas flow rate controlled at 100 mL / min. After cooling to room temperature in the furnace, a silicon-silica-pitch-derived carbon multilayer composite structure was obtained.

[0072] Example 4

[0073] This embodiment provides a silicon-silicon suboxide-pitch-derived carbon multilayer composite anode material, and the specific preparation steps are as follows:

[0074] 2 mL of hydrogen peroxide and 0.25 mL of ammonia were added to 5 mL of deionized water and mixed thoroughly to form a solution. 0.2 g of nano-silicon powder was added to this solution to form a mixture. The mixture was ultrasonically bubbled for 30 min to ensure thorough dispersion of the nano-silicon powder. Subsequently, the mixture was magnetically stirred for 60 min at 70 °C and 500 rpm to induce surface oxidation. After evaporating the solvent at 60 °C for 12 h, silicon-silica-suboxide coated composite particles were obtained.

[0075] Subsequently, the silicon-silica-suboxide coated composite particles were mixed with 0.2 g of heavy oil and 20 mL of organic solvent to form a mixed dispersion, which was magnetically stirred for 12 h. The mixed dispersion was placed in an alumina crucible and heated to 500 °C in a tube furnace at a heating rate of 10 °C / min and held for 1 h, while an N2 atmosphere was introduced with a gas flow rate controlled at 100 mL / min. After cooling to room temperature in the furnace, a silicon-silica-pitch-derived carbon multilayer composite structure was obtained.

[0076] Example 5

[0077] This embodiment provides a silicon-silicon suboxide-pitch-derived carbon multilayer composite anode material, and the specific preparation steps are as follows:

[0078] 2 mL of hydrogen peroxide and 0.25 mL of ammonia were added to 5 mL of deionized water and mixed thoroughly to form a solution. 0.2 g of nano-silicon powder was added to this solution to form a mixture. The mixture was ultrasonically bubbled for 30 min to ensure thorough dispersion of the nano-silicon powder. Subsequently, the mixture was magnetically stirred for 60 min at 90 °C and 500 rpm to induce surface oxidation. After evaporating the solvent at 60 °C for 12 h, silicon-silica-suboxide coated composite particles were obtained.

[0079] Subsequently, the silicon-silica-suboxide coated composite particles were mixed with 0.4 g of heavy oil and 40 mL of organic solvent to form a mixed dispersion, which was magnetically stirred for 12 h. The mixed dispersion was placed in an alumina crucible and heated to 500 °C for 2 h in a tube furnace at a heating rate of 10 °C / min, while maintaining the temperature at 500 °C for 2 h, with an N2 atmosphere introduced and the gas flow rate controlled at 100 mL / min. After cooling to room temperature in the furnace, a silicon-silica-pitch-derived carbon multilayer composite structure was obtained.

[0080] In summary, this invention provides a multi-level composite anode material and its preparation method. The multi-level composite anode material, from the inside out, comprises: a core, a first coating layer, and a second coating layer. The core comprises silicon nanoparticles, the first coating layer comprises silicon suboxide, and the second coating layer is a carbon layer. The carbon layer is derived from pitch pyrolysis. This invention achieves silicon-silicon suboxide-carbon multi-level composite anode material by effectively partially oxidizing the surface of silicon nanoparticles to form a silicon-silicon suboxide composite structure, and then coating its surface with a carbon layer to form a second coating layer. This structure uses silicon suboxide as a transition layer, combining the advantages of silicon, silicon suboxide, and carbon layers. It retains the high lithium storage capacity of silicon anodes while utilizing the high capacity and relatively small volume expansion rate of silicon suboxide. Pitch-derived carbon is used as the outermost mechanical buffer layer. Through transition buffering, the internal volume expansion is buffered and released step by step to maintain structural stability, thereby improving the cycle stability of the silicon-silicon suboxide-carbon composite anode. Furthermore, pitch-derived carbon has good conductivity, enabling the anode material to form a good electronic pathway network on the outermost layer. In addition, the carbon layer acts as a protective layer, separating the internal silicon suboxide and silicon nanoparticles from the formed SEI film, effectively preventing problems such as electrolyte consumption and anode failure caused by excessive growth of the SEI film, thereby improving the overall electrochemical performance of the silicon-silicon suboxide-carbon multilayer composite anode material.

[0081] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a multi-level composite negative electrode material, characterized in that, Including the following steps: The silicon source is oxidized to obtain a silicon source with an oxidized surface. The silicon source after surface oxidation is mixed with a carbon source and an organic solvent to obtain a mixed dispersion. The mixed dispersion was subjected to stirring and heat treatment to obtain a composite anode material with a silicon-silicon suboxide-carbon multilayer structure; The silicon source is nano-silicon particles; the carbon source is heavy oil; the organic solvent is aromatic hydrocarbon; the asphaltenes content in the heavy oil is 30wt%-40wt%; The oxidation process of the silicon source includes the following steps: A mixture of silicon source, ammonia, hydrogen peroxide, and water is obtained. The mixture is subjected to ultrasonic bubbling and heating stirring to obtain a silicon source with surface oxidation. The volume ratio of the ammonia, hydrogen peroxide, and water is (0.2-0.3):(1-2):5; and / or the mass of the silicon source accounts for 1-5 wt% of the mass of the water. The initial concentration of the ammonia solution is 25wt%-28wt%; and / or, the initial concentration of the hydrogen peroxide is 30wt%-31wt%. The multi-layered composite anode material comprises, from the inside out: a core, a first coating layer, and a second coating layer; the core comprises silicon nanoparticles, the first coating layer comprises silicon suboxide, and the second coating layer is a carbon layer; the carbon layer is derived from the pyrolysis of heavy oil.

2. The method for preparing the multi-level composite negative electrode material according to claim 1, characterized in that, The ultrasonic bubbling treatment time is 30-60 min; and / or, the heating and stirring treatment temperature is 70-100℃, the stirring speed is 500-700 rpm, and the heating and stirring treatment time is 10-60 min.

3. The method for preparing the multi-level composite negative electrode material according to claim 1, characterized in that, The mass ratio of the surface-oxidized silicon source to the carbon source is 1:(1-2); and / or, the stirring speed is 500-700 rpm, and the stirring time is 12-16 h.

4. The method for preparing the multi-level composite negative electrode material according to claim 1, characterized in that, The heating rate of the heat treatment is 5-10℃ / min, the holding temperature of the heat treatment is 480-500℃, and the holding time of the heat treatment is 1-3h; the heat treatment is carried out in an inert atmosphere.

5. A multi-level composite anode material, characterized in that, The composite negative electrode material with a multi-level structure as described in any one of claims 1-4 was prepared using the preparation method of the composite negative electrode material with a multi-level structure as described in any one of claims 1-4.

6. The multi-level composite negative electrode material according to claim 5, characterized in that, The particle size of silicon nanoparticles is 50-100 nm.

7. The multi-level composite negative electrode material according to claim 5, characterized in that, The core has a particle size of 30-80 nm; and / or, the thickness of the first coating layer is 20-50 nm; and / or, the thickness of the second coating layer is 20-50 nm.

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