Silicon monoxide-based negative electrode composite material with core-shell structure and preparation method thereof

Abstract

A method for preparing a core-shell structured silicon suboxide-based anode composite material includes the following steps: a) mixing Mg₂Si, lithium oxide, and silicon suboxide, followed by ball milling, sieving, and a first solid-state reaction, then cooling and undergoing a first pulverization and classification process to obtain a reaction product; b) treating the reaction product obtained in step a) with a weak acid solution, filtering, and washing with water to obtain a carbon-free material; c) mixing the carbon-free material obtained in step b) with an aqueous solution of an organic carbon source, drying, undergoing a second solid-state reaction, cooling, and then undergoing a second pulverization and classification process to obtain a single-layer carbon-coated material; d) performing chemical vapor deposition on the single-layer carbon-coated material obtained in step c) using a carbon source gas, cooling, and then undergoing a third pulverization and classification process to obtain the silicon suboxide-based anode composite material. The silicon suboxide-based anode composite material prepared by the method provided by this invention exhibits both high charge-discharge capacity and high first coulombic efficiency.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a core-shell structured silicon suboxide-based anode composite material and its preparation method. Background Technology

[0002] With the rapid development of modern technology, people have higher requirements for energy storage and utilization, especially for high-capacity lithium-ion batteries. Currently, most commercially available lithium battery anode materials are graphite (theoretical specific capacity: 372 mAh / g), but this relatively low capacity is insufficient for daily use, especially in electric vehicles. Silicon anodes, due to their higher theoretical specific capacity (approximately 4200 mAh / g) and lower operating potential (0.2–0.3 V vs Li / Li), offer a more competitive alternative. + Furthermore, silicon is abundant and environmentally friendly, making it a promising alternative to graphite. However, the massive volume expansion (300%) that occurs during the lithiation / delithiation process of silicon anodes can easily cause material pulverization and irreversible damage to the battery due to the detachment of active material from the current collector, thus hindering the practical application of Si.

[0003] The high theoretical specific capacity of silicon suboxide (approximately 2400 mAh / g) and its superior cycle stability compared to silicon make it one of the most promising alternative anode materials for lithium-ion batteries. However, silicon suboxide exhibits a low initial coulombic efficiency (approximately 70%), primarily due to the irreversible reaction between lithium and silicon suboxide during the first lithiation process, which generates irreversible phases (Li₂O and Li₂). x SiO y This leads to excessive consumption of lithium ions, resulting in a low initial coulombic efficiency.

[0004] Patent CN201610863902.7 describes a method that uses a metal reducing agent and SiO under high temperature heating in a negative pressure environment to vaporize and react in the gaseous phase, then obtains a composite through condensation. This method requires a high vacuum environment and must reach the material's vaporization temperature, which places high demands on equipment safety. Furthermore, the high energy consumption due to the high temperature increases costs, making this method costly to produce and difficult to scale up for industrial production.

[0005] Patent CN201711318537.2 describes a method for processing SiO under an inert atmosphere. x The material and the metal undergo a redox reaction, the metal is oxidized to obtain its compound, and then the metal compound is etched away by acid to achieve SiO2. xThe O / Si ratio x of the (0.5 < x < 1.5) material is adjusted to y (0.2 < y < 0.9), reducing the oxygen content of the negative electrode and thus reducing the amount of irreversible phase formed during the first lithium insertion, i.e., reducing the loss of irreversible lithium, thereby improving the initial coulombic efficiency of the material. However, this method uses acid etching of the metal oxide, resulting in significant acid waste and generating large amounts of waste liquid, which is environmentally unfriendly. These subsequent treatments require substantial costs, increasing production costs and hindering large-scale applications.

[0006] Patent CN201710193442.6 describes a method for producing silicon oxide (SiO2) by subjecting a Si / SiO2 raw material powder mixture to a gas-phase reaction with metallic magnesium. x The material (0 < x < 2) contains silicon particles, MgSiO3 (enstatite), and Mg2SiO4 (magnesium silicate) crystals. This method also utilizes a gas-phase reaction, which places extremely high demands on the equipment. Furthermore, the direct use of magnesium powder during the magnesothermic reduction reaction releases a large amount of heat locally, posing a safety risk. In addition, the charge / discharge capacity of this material is low (approximately 700 mAh / g), making large-scale application difficult.

[0007] Patent CN201980006246.0 discloses a silicon-based composite material with a porous structure, wherein a polymer with volume shrinkage occupies the porous structure, and a metal compound is distributed in SiO. x The surface and interior of (0≤x≤2). The required pore structure in this process is obtained after treatment with strong alkali. The use of a large amount of alkali solution generates a large amount of waste liquid. Improper treatment causes certain harm to the environment, and subsequent treatment is also troublesome, which greatly increases the production cost.

[0008] In patent CN201910621840.2, a method was invented to use magnesium silicide as a reducing agent to improve the first coulombic efficiency of silicon suboxide. However, due to the low content used, the improvement in the first coulombic efficiency of the prepared material was not very obvious; and the heat treatment temperature was high, resulting in energy waste.

[0009] Patent CN202110973237.8 discloses a method containing one or more of elemental silicon or silicon compounds, with magnesium contained in the silicon oxide. The main principle is to utilize magnesium silicide to improve the electrochemical performance of silicon suboxide. This invention employs a high magnesium silicide content and utilizes atomization under a high-temperature argon atmosphere followed by cooling in a wall-cooled vacuum chamber. This demanding method results in significant energy waste and increases production costs.

[0010] Patent CN112331854A discloses a method for pre-lithiating lithium magnesium silicate into silicon suboxide anode material. This method primarily utilizes the reaction of magnesium oxide and lithium oxide with silicon suboxide to form lithium magnesium silicate, thereby improving the coulombic efficiency of silicon suboxide. However, the capacity of the material synthesized by this method is relatively low, and the relatively high heat treatment temperature leads to energy waste. Therefore, further in-depth exploration is needed for this type of method.

[0011] In summary, the main drawbacks of the methods disclosed in the prior art are: the extensive use of gas-phase reactions, which places extremely stringent requirements on production equipment; the use of strong acids and bases (such as hydrochloric acid (HCl) and sodium hydroxide (NaOH) during the manufacturing process, posing safety hazards and increasing subsequent processing costs; and, while these methods improve the initial coulombic efficiency to some extent, they result in lower charge-discharge capacity of the material. Therefore, developing a new technology with a simple process flow, conducive to large-scale production, lower production costs, and environmental friendliness to improve the charge-discharge capacity and initial coulombic efficiency of silicon suboxide has become a pressing technical challenge for those skilled in the art. Summary of the Invention

[0012] In view of this, the purpose of the present invention is to provide a core-shell structured silicon suboxide-based anode composite material and its preparation method. The preparation method provided by the present invention has a simple process flow, low cost, environmental friendliness, and is conducive to large-scale production. Furthermore, the core-shell structured silicon suboxide-based anode composite material prepared by the present invention has both high charge-discharge capacity and high first coulombic efficiency.

[0013] This invention provides a method for preparing a core-shell structured silicon suboxide-based anode composite material, comprising the following steps:

[0014] a) After mixing Mg2Si, lithium oxide and silicon suboxide, the mixture is successively ball-milled, sieved and subjected to a first solid-phase reaction. After cooling, it is subjected to a first pulverization and classification process to obtain the reaction product.

[0015] b) The reaction product obtained in step a) is treated with a weak acid solution, filtered, and washed with water to obtain a material without carbon coating.

[0016] c) The uncoated material obtained in step b) is mixed with an aqueous solution of organic carbon source and dried. A second solid-phase reaction is carried out, and after cooling, a second pulverization and classification process is performed to obtain a single-layer carbon-coated material.

[0017] d) The single-layer carbon-coated material obtained in step c) is subjected to chemical vapor deposition using a carbon source gas, and after cooling, it is subjected to a third crushing and classification process to obtain a core-shell structured silicon suboxide-based anode composite material.

[0018] Preferably, the molar ratio of Mg2Si, lithium oxide and silicon suboxide in step a) is 1:(0.5-2):(3-9).

[0019] Preferably, the ball milling in step a) is a planetary ball mill with a ball-to-material ratio of (5-20):1 and a milling time of 1-4 hours; the sieve mesh size is 300-500 mesh.

[0020] Preferably, the process of the first solid-phase reaction in step a) is as follows:

[0021] The sieved product is placed into a tube furnace, sealed, and evacuated to below 0.01 Pa. Under an inert atmosphere, the temperature is increased to 500℃ to 900℃ at a heating rate of 5℃ / min to 10℃ / min, and then held for 1h to 6h.

[0022] Preferably, the weak acid solution in step b) is an acetic acid solution; the process of using the weak acid solution for treatment specifically includes:

[0023] Mix the reaction product obtained in step a) with a weak acid solution until homogeneous, seal and stir magnetically for 1 to 2 hours.

[0024] Preferably, the organic carbon source aqueous solution in step c) is a glucose aqueous solution, wherein the mass ratio of glucose to water in the glucose aqueous solution is 1:(5-7); and the drying temperature is 60℃-80℃.

[0025] Preferably, the second solid-phase reaction process in step c) specifically involves:

[0026] The dried product is placed in a tube furnace, sealed, and evacuated to below 0.01 Pa. Under an inert atmosphere, the temperature is increased to 700℃ to 900℃ at a heating rate of 5℃ / min to 10℃ / min, and then held for 1h to 4h.

[0027] Preferably, the carbon source gas in step d) is selected from one or more of ethylene gas, acetylene gas, and methane gas; the chemical vapor deposition process specifically includes:

[0028] The single-layer carbon-coated material obtained in step c) is placed in a chemical vapor deposition furnace, sealed, and evacuated to below 0.01 Pa. Under an inert atmosphere, the temperature is raised to 700℃ to 1000℃ at a heating rate of 5℃ / min to 10℃ / min, and then carbon source gas is introduced and kept at that temperature for 0.5h to 4h. The flow rate ratio of the inert gas to the carbon source gas in the inert atmosphere is (5 to 15): 1.

[0029] Preferably, the average particle size of the first crushing and grading treatment is 1 μm to 3 μm; the average particle size of the second crushing and grading treatment is 2 μm to 4 μm; and the average particle size of the third crushing and grading treatment is 4 μm to 6 μm.

[0030] The present invention also provides a core-shell structured silicon suboxide-based anode composite material, which is prepared by the preparation method described in the above technical solution.

[0031] This invention provides a method for preparing a core-shell structured silicon suboxide-based anode composite material, comprising the following steps: a) mixing Mg₂Si, lithium oxide, and silicon suboxide, followed by ball milling, sieving, and a first solid-state reaction, then cooling and undergoing a first pulverization and classification process to obtain a reaction product; b) treating the reaction product obtained in step a) with a weak acid solution, filtering, and washing with water to obtain a carbon-free material; c) mixing the carbon-free material obtained in step b) with an aqueous solution of an organic carbon source, drying, undergoing a second solid-state reaction, cooling, and then undergoing a second pulverization and classification process to obtain a single-layer carbon-coated material; d) performing chemical vapor deposition on the single-layer carbon-coated material obtained in step c) using a carbon source gas, cooling, and then undergoing a third pulverization and classification process to obtain a core-shell structured silicon suboxide-based anode composite material. Compared with the prior art, the preparation method provided by this invention employs specific process steps to achieve better overall interaction, preparing a double-layer carbon-coated core-shell structured silicon suboxide-based anode composite material containing metal elements; this silicon suboxide-based anode composite material exhibits both high charge / discharge capacity and high first coulombic efficiency.

[0032] Meanwhile, the preparation method provided by this invention has a simple process flow, low cost, and is environmentally friendly, which is conducive to large-scale production. Therefore, it has good application prospects and potential in the field of lithium-ion battery technology. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the core-shell structured silicon suboxide-based anode composite material prepared by the preparation method provided in Example 1 of the present invention.

[0034] Figure 2 A cross-sectional SEM image of the core-shell structured silicon suboxide-based anode composite material prepared by the preparation method provided in Example 1 of this invention;

[0035] Figure 3 Thermogravimetric curve of the core-shell structured silicon suboxide-based anode composite material prepared by the preparation method provided in Example 1 of the present invention;

[0036] Figure 4 The XRD phase diagram of the core-shell structured silicon suboxide-based anode composite material prepared by the preparation method provided in Example 1 of this invention. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] This invention provides a method for preparing a core-shell structured silicon suboxide-based anode composite material, comprising the following steps:

[0039] a) After mixing Mg2Si, lithium oxide and silicon suboxide, the mixture is successively ball-milled, sieved and subjected to a first solid-phase reaction. After cooling, it is subjected to a first pulverization and classification process to obtain the reaction product.

[0040] b) The reaction product obtained in step a) is treated with a weak acid solution, filtered, and washed with water to obtain a material without carbon coating.

[0041] c) The uncoated material obtained in step b) is mixed with an aqueous solution of organic carbon source and dried. A second solid-phase reaction is carried out, and after cooling, a second pulverization and classification process is performed to obtain a single-layer carbon-coated material.

[0042] d) The single-layer carbon-coated material obtained in step c) is subjected to chemical vapor deposition using a carbon source gas, and after cooling, it is subjected to a third crushing and classification process to obtain a core-shell structured silicon suboxide-based anode composite material.

[0043] The present invention first mixes Mg2Si, lithium oxide and silicon suboxide, and then sequentially ball-mills, sieves and undergoes a first solid-phase reaction. After cooling, it undergoes a first pulverization and classification process to obtain the reaction product.

[0044] The present invention does not impose any particular restrictions on the source of the Mg2Si, lithium oxide (Li2O), and silicon suboxide (SiO), and any commercially available products or self-made products well known to those skilled in the art can be used. In the present invention, the molar ratio of the Mg2Si, lithium oxide, and silicon suboxide is preferably 1:(0.5-2):(3-9), more preferably 1:(0.5-2):(3-7).

[0045] In this invention, the ball milling is preferably a planetary ball mill, wherein the balls used are preferably agate balls, the ball-to-material ratio is preferably (5-20):1, more preferably 10:1, and the ball milling time is preferably 1h-4h, more preferably 2h.

[0046] In this invention, the mesh size of the sieve is preferably 300 to 500 mesh, and more preferably 400 mesh.

[0047] In this invention, the process of the first solid-phase reaction is preferably as follows:

[0048] The sieved product is placed into a tube furnace, sealed, and evacuated to below 0.01 Pa. Under an inert atmosphere, the temperature is increased to 500℃ to 900℃ at a heating rate of 5℃ / min to 10℃ / min and then held for 1h to 6h.

[0049] More preferably:

[0050] The sieved product was placed into a tube furnace, sealed, and evacuated to below 0.01 Pa. Under an argon atmosphere, the temperature was increased to 550℃~850℃ at a heating rate of 5℃ / min and held for 2 hours.

[0051] In this invention, the cooling temperature is room temperature; the average particle size of the first crushing and grading treatment is preferably 1μm to 3μm, more preferably 2μm (D50).

[0052] After obtaining the reaction product, the present invention treats the obtained reaction product with a weak acid solution, filters it, and washes it with water to obtain a material without carbon coating.

[0053] In this invention, the weak acid solution is preferably an acetic acid solution; the source of the acetic acid solution is not particularly limited and commercially available products well known to those skilled in the art can be used.

[0054] In this invention, the process of using a weak acid solution for treatment is preferably as follows:

[0055] Mix the reaction product obtained in step a) with a weak acid solution until homogeneous, seal and stir magnetically for 1 to 2 hours;

[0056] More preferably:

[0057] Mix the reaction product obtained in step a) with a weak acid solution until homogeneous, seal and stir magnetically for 1 hour.

[0058] In this invention, the number of water washings is preferably 1 to 3 times, more preferably 2 times; the filtered solid product is washed with water to obtain a carbon-free material, which can be used directly as a negative electrode material.

[0059] In this invention, the specific reaction formulas for the above steps are as follows:

[0060] Mg₂Si + Li₂O + SiO → MgO + Li₂SiO₃ + Si;

[0061] After weak acid treatment, all MgO and some residual Mg2Si and Li2O are removed. It is clear that the material is composed of Li2SiO3 and Si, and Si mainly participates in the charge and discharge process. Therefore, the initial coulombic efficiency of the material can theoretically be very high.

[0062] After obtaining the uncoated carbon material, the present invention mixes the uncoated carbon material with an aqueous solution of an organic carbon source, dries it, performs a second solid-phase reaction, cools it, and performs a second pulverization and classification process to obtain a single-layer carbon-coated material.

[0063] In this invention, the organic carbon source aqueous solution is preferably a glucose aqueous solution, and the mass ratio of glucose to water in the glucose aqueous solution is preferably 1:(5-7), more preferably 1:6. This invention does not impose any special restrictions on the source of the organic carbon source; commercially available products well known to those skilled in the art can be used.

[0064] In this invention, the drying temperature is preferably 60°C to 80°C, more preferably 80°C; drying can be carried out using an oven well known to those skilled in the art.

[0065] In this invention, the second solid-phase reaction process is preferably as follows:

[0066] The dried product was placed in a tube furnace, sealed, and evacuated to below 0.01 Pa. Under an inert atmosphere, the temperature was increased to 700℃ to 900℃ at a heating rate of 5℃ / min to 10℃ / min and then held for 1h to 4h.

[0067] More preferably:

[0068] The dried product was placed in a tube furnace, sealed, and evacuated to below 0.01 Pa. Under an argon atmosphere, the temperature was increased to 800°C at a heating rate of 10°C / min and held for 1 hour.

[0069] In this invention, the cooling temperature is room temperature; the average particle size of the second crushing and grading process is preferably 2μm to 4μm, more preferably 3μm (D50).

[0070] After obtaining the single-layer carbon-coated material, the present invention uses a carbon source gas to perform chemical vapor deposition on the obtained single-layer carbon-coated material, and after cooling, performs a third crushing and classification treatment to obtain a core-shell structured silicon suboxide-based anode composite material.

[0071] In this invention, the carbon source gas is preferably selected from one or more of ethylene gas, acetylene gas and methane gas, and more preferably ethylene gas; this invention does not have any special restrictions on the source of the carbon source gas, and commercially available products well known to those skilled in the art can be used.

[0072] In this invention, the chemical vapor deposition (CVD) process is preferably as follows:

[0073] The single-layer carbon-coated material obtained in step c) is placed in a chemical vapor deposition furnace, sealed, and evacuated to below 0.01 Pa. Under an inert atmosphere, the temperature is raised to 700℃ to 1000℃ at a heating rate of 5℃ / min to 10℃ / min, and then carbon source gas is introduced and kept at that temperature for 0.5h to 4h.

[0074] More preferably:

[0075] The single-layer carbon-coated material obtained in step c) is placed in a chemical vapor deposition furnace, sealed, and evacuated to below 0.01 Pa. Under an inert atmosphere, the temperature is raised to 850°C at a heating rate of 10°C / min, and then carbon source gas is introduced and kept at that temperature for 2 hours.

[0076] In this invention, the flow rate ratio of the inert gas to the carbon source gas in the inert atmosphere is preferably (5-15):1, more preferably 10:1. In a preferred embodiment of this invention, the inert gas is argon with a flow rate of 200 scc, and the carbon source gas is ethylene with a flow rate of 20 scc.

[0077] In this invention, the cooling temperature is room temperature; the average particle size of the third pulverizing and classifying process is preferably 4μm to 6μm, more preferably 5μm (D50).

[0078] The preparation method provided by this invention employs specific process steps, utilizing silicon elements introduced by silicides to compensate for the capacity loss of silicon suboxide caused by the formation of inactive lithium silicate. Simultaneously, under the action of silicides, lithium oxide is used to modify silicon suboxide, achieving better overall interaction. This results in a double-layer carbon-coated silicon suboxide-based anode composite material with a core-shell structure containing metal elements. It has a unique core-shell structure, with the outer shell being lithium silicate and the core being disproportionated silicon suboxide, with lithium silicate coating the disproportionated silicon suboxide. This silicon suboxide-based anode composite material exhibits both high charge-discharge capacity and initial coulombic efficiency.

[0079] This invention also provides a core-shell structured silicon suboxide-based anode composite material, prepared using the preparation method described above. This invention provides a double-layer carbon-coated core-shell structured silicon suboxide-based anode composite material containing metal elements. The core is disproportionated silicon suboxide, and the outer shell is lithium silicate crystals, forming a unique core-shell structure. Furthermore, the surface is coated with a double layer of carbon, thereby improving the initial coulombic efficiency, charge-discharge capacity, and cycle stability of silicon suboxide.

[0080] In this invention, if Li2O is used directly without adding silicide, the capacity of the material will be reduced. Adding nano-silicon can also increase the capacity of the material, but this increases the cost. For the material system, the nano-silicon is added as a mixture to the silicon suboxide system, and is not a primary particle of silicon-based anode material with a unique core-shell structure as shown in this system.

[0081] This invention provides a method for preparing a core-shell structured silicon suboxide-based anode composite material, comprising the following steps: a) mixing Mg₂Si, lithium oxide, and silicon suboxide, followed by ball milling, sieving, and a first solid-state reaction, then cooling and undergoing a first pulverization and classification process to obtain a reaction product; b) treating the reaction product obtained in step a) with a weak acid solution, filtering, and washing with water to obtain a carbon-free material; c) mixing the carbon-free material obtained in step b) with an aqueous solution of an organic carbon source, drying, undergoing a second solid-state reaction, cooling, and then undergoing a second pulverization and classification process to obtain a single-layer carbon-coated material; d) performing chemical vapor deposition on the single-layer carbon-coated material obtained in step c) using a carbon source gas, cooling, and then undergoing a third pulverization and classification process to obtain a core-shell structured silicon suboxide-based anode composite material. Compared with the prior art, the preparation method provided by this invention employs specific process steps to achieve better overall interaction, preparing a double-layer carbon-coated core-shell structured silicon suboxide-based anode composite material containing metal elements; this silicon suboxide-based anode composite material exhibits both high charge / discharge capacity and high first coulombic efficiency.

[0082] Meanwhile, the preparation method provided by this invention has a simple process flow, low cost, and is environmentally friendly, which is conducive to large-scale production. Therefore, it has good application prospects and potential in the field of lithium-ion battery technology.

[0083] To further illustrate the present invention, the following embodiments are provided for detailed description. All raw materials used in the following embodiments of the present invention are commercially available.

[0084] Example 1

[0085] (1) Preparation of negative electrode material:

[0086] 1) Weigh out Mg2Si, lithium oxide and silicon suboxide raw materials in a molar ratio of 1:1:3, mix them evenly, and then perform planetary ball milling with a ball-to-material ratio of 10:1. After ball milling for 2 hours, the mixture is then sieved through a 400-mesh sieve. The sieved product is collected and placed in a tube furnace, sealed, and evacuated to below 0.01 Pa. Under an argon atmosphere, the temperature is raised to 550°C at a heating rate of 5°C / min and held for 2 hours. After cooling to room temperature, the mixture is pulverized and classified to obtain an average particle size of 2 μm (D50).

[0087] 2) Take the product from step 1) and mix it evenly with acetic acid solution, seal it, stir it magnetically for 1 hour, filter it, and then wash it with water twice to obtain the material without carbon coating.

[0088] 3) Take the product from step 2) and mix it evenly with a glucose aqueous solution (mass ratio of glucose:water = 1:6). After drying in an oven at 80°C, place it in a tube furnace, seal it, and evacuate it to below 0.01Pa. Then, under an argon atmosphere, heat it to 800°C at a heating rate of 10°C / min and hold it at that temperature for 1 hour. After cooling to room temperature, perform pulverization and classification treatment. The average particle size is 3μm (D50), and a single-layer carbon-coated material (carbon content 4wt%) is obtained.

[0089] 4) Take the product from step 3) and place it in a CVD chemical vapor deposition furnace. After sealing, evacuate to below 0.01 Pa and heat to 850°C at a rate of 10°C / min under an argon atmosphere (flow rate of 200 scc). Then, introduce ethylene gas and maintain the temperature for 2 hours (flow rate of 20 scc). After cooling to room temperature, perform pulverization and classification to obtain an average particle size of 5 μm (D50) to obtain a core-shell structured silicon suboxide-based anode composite material containing metal elements with a double-layer carbon coating (carbon content of 8 wt%). See the schematic diagram for its structure. Figure 1 As shown.

[0090] The cross-sectional characterization diagram of the obtained material is as follows: Figure 2 As shown, a unique core-shell structure is clearly displayed; and Figure 3 It was also shown that after carbon coating, the carbon content of the material was approximately 8%, and the material ultimately consisted of two phases: Si and Li₂SiO₃. (See [reference]). Figure 4 .

[0091] (2) Battery manufacturing:

[0092] The negative electrode material obtained in step (1), consisting of conductive carbon black (Super-P), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC), was uniformly mixed with a certain amount of deionized water at a mass ratio of 6:2:2 to prepare a negative electrode slurry. This slurry was then uniformly coated onto a copper foil current collector and dried at 80°C for 5 hours to obtain an electrode sheet. A coin cell was assembled using lithium foil as the counter electrode.

[0093] Example 2

[0094] Using the preparation method provided in Example 1, a core-shell structured silicon suboxide-based anode composite material was obtained, and a battery was further manufactured; the difference is that the molar ratio of Mg2Si, lithium oxide and silicon suboxide raw materials is 1:1:4.

[0095] Example 3

[0096] Using the preparation method provided in Example 1, a core-shell structured silicon suboxide-based anode composite material was obtained, and a battery was further manufactured; the difference is that the molar ratio of Mg2Si, lithium oxide and silicon suboxide raw materials is 1:1:5; and the heat treatment temperature in step 1) is increased to 650°C.

[0097] Example 4

[0098] Using the preparation method provided in Example 1, a core-shell structured silicon suboxide-based anode composite material was obtained, and a battery was further manufactured; the difference is that the molar ratio of Mg2Si, lithium oxide and silicon suboxide raw materials is 1:1:6; and the heat treatment temperature in step 1) is increased to 650°C.

[0099] Example 5

[0100] Using the preparation method provided in Example 1, a core-shell structured silicon suboxide-based anode composite material was obtained, and a battery was further manufactured; the difference is that the molar ratio of Mg2Si, lithium oxide and silicon suboxide raw materials is 2:1:6; and the heat treatment temperature in step 1) is increased to 750°C.

[0101] Example 6

[0102] Using the preparation method provided in Example 1, a core-shell structured silicon suboxide-based anode composite material was obtained, and a battery was further manufactured; the difference is that the molar ratio of Mg2Si, lithium oxide and silicon suboxide raw materials is 2:1:7; and the heat treatment temperature in step 1) is increased to 750°C.

[0103] Example 7

[0104] Using the preparation method provided in Example 1, a core-shell structured silicon suboxide-based anode composite material was obtained, and a battery was further manufactured; the difference is that the molar ratio of Mg2Si, lithium oxide and silicon suboxide raw materials is 1:2:6; and the heat treatment temperature in step 1) is increased to 850°C.

[0105] Example 8

[0106] Using the preparation method provided in Example 1, a core-shell structured silicon suboxide-based anode composite material was obtained, and a battery was further manufactured; the difference is that the molar ratio of Mg2Si, lithium oxide and silicon suboxide raw materials is 1:2:7; and the heat treatment temperature in step 1) is increased to 850°C.

[0107] Comparative Example 1

[0108] Using the carbon-free material prepared in step 2) of Example 1 as the negative electrode material, a coin cell was prepared according to the battery manufacturing in step (2) of Example 1.

[0109] Comparative Example 2

[0110] Using silicon suboxide as the negative electrode material, a coin cell was prepared according to step (2) of Example 1.

[0111] Electrochemical performance:

[0112] The prepared coin cells were discharged at a rate of 0.1C to a voltage of 0.005V and charged at a rate of 0.05C to a voltage of 2.0V to obtain the discharge specific capacity (mAh / g), charge specific capacity (mAh / g), and initial coulombic efficiency (charge specific capacity / discharge specific capacity). In addition, after the first charge and discharge of the cells, a cyclic test was performed at a rate of 0.2C starting from the second charge and discharge.

[0113] The results of the analysis of the charge / discharge specific capacity and initial coulombic efficiency are shown in Table 1.

[0114] Table 1. Charge / discharge specific capacity and initial coulombic efficiency data

[0115]

[0116]

[0117] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a core-shell structured silicon suboxide-based anode composite material, comprising the following steps: a) After mixing Mg2Si, lithium oxide and silicon suboxide in a molar ratio of 1:(0.5~2):(3~9), the mixture is ball-milled, sieved and subjected to a first solid-phase reaction. After cooling, it is subjected to a first pulverization and classification process to obtain the reaction product. The process of the first solid-phase reaction is as follows: The sieved product is placed into a tube furnace, sealed, and evacuated to below 0.01 Pa. Under an inert atmosphere, the temperature is increased to 500℃~900℃ at a heating rate of 5℃ / min~10℃ / min and then held for 1h~6h. b) The reaction product obtained in step a) is treated with a weak acid solution, filtered, and washed with water to obtain a material without carbon coating; The weak acid solution is an acetic acid solution; the process of using the weak acid solution for treatment is as follows: the reaction product obtained in step a) is mixed evenly with the weak acid solution, sealed and magnetically stirred for 1 to 2 hours. c) The uncoated material obtained in step b) is mixed with an aqueous solution of organic carbon source and dried. A second solid-phase reaction is carried out, and after cooling, a second pulverization and classification process is performed to obtain a single-layer carbon-coated material. The process of the second solid-phase reaction is as follows: The dried product was placed in a tube furnace, sealed, and evacuated to below 0.01 Pa. Under an inert atmosphere, the temperature was increased to 700℃~900℃ at a heating rate of 5℃ / min~10℃ / min and held for 1h~4h. d) The single-layer carbon-coated material obtained in step c) is subjected to chemical vapor deposition using a carbon source gas, and after cooling, it is subjected to a third pulverization and classification process to obtain a core-shell structured silicon suboxide-based anode composite material. The chemical vapor deposition process is specifically as follows: The single-layer carbon-coated material obtained in step c) is placed in a chemical vapor deposition furnace, sealed, and evacuated to below 0.01 Pa. Under an inert atmosphere, the temperature is raised to 700℃~1000℃ at a heating rate of 5℃ / min~10℃ / min, and then carbon source gas is introduced and kept at that temperature for 0.5h~4h. The flow rate ratio of the inert gas to the carbon source gas in the inert atmosphere is (5~15):

1.

2. The preparation method according to claim 1, characterized in that, The ball milling in step a) is a planetary ball mill with a ball-to-material ratio of (5~20):1 and a milling time of 1h~4h; the sieve mesh size is 300 mesh~500 mesh.

3. The preparation method according to claim 1, characterized in that, The organic carbon source aqueous solution mentioned in step c) is a glucose aqueous solution, and the mass ratio of glucose to water in the glucose aqueous solution is 1:(5~7); the drying temperature is 60℃~80℃.

4. The preparation method according to claim 1, characterized in that, The carbon source gas mentioned in step d) is selected from one or more of ethylene gas, acetylene gas and methane gas.

5. The preparation method according to claim 1, characterized in that, The average particle size of the first crushing and grading treatment is 1μm~3μm; the average particle size of the second crushing and grading treatment is 2μm~4μm; and the average particle size of the third crushing and grading treatment is 4μm~6μm.

6. A core-shell structured silicon suboxide-based anode composite material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.

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