A pre-magnesium silicon suboxide anode material and its preparation method

Abstract

This invention discloses a pre-magnesium silicon suboxide anode material and its preparation method. The method involves mixing silicon suboxide powder, halide molten salt, and a magnesium source in a specific ratio, followed by heat treatment under a slightly positive pressure inert atmosphere. The acid washing process is precisely controlled to obtain a pre-magnesium silicon suboxide anode material with Mg₂SiO₄ as the absolute main phase. This method uses a molten salt with a lower melting point and addresses the issues of excessively high pre-magnesium temperatures and molten salt volatilization under vacuum conditions, resulting in a novel anode material that exhibits superior electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of silicon suboxide anode materials, and more particularly to a pre-magnesium silicon suboxide anode material and its preparation method. Background Technology

[0002] Since their commercial application in the 1990s, lithium-ion batteries have gradually become the mainstream of chemical energy storage due to their advantages such as high energy density and long cycle life. In recent years, with the development of electric vehicles, the demand for lithium battery products has been growing at a rate of over 30%, while also placing higher demands on their performance in terms of capacity, safety, fast charging, and cycle life.

[0003] Currently, the main anode materials for lithium-ion batteries on the market are carbon-based materials, represented by graphite, and the capacity of mainstream products is approaching their theoretical capacity. Developing new lithium-ion battery anode materials has become crucial. Silicon anode materials have a theoretical specific capacity of 4200 mAh / g, but they experience significant volume changes (>300%) during charge and discharge, leading to material breakage, rapid capacity decay, and potential safety hazards. Anode materials made by carbon-coating silicon suboxide offer high capacity, small expansion volume, high initial charge-discharge coulombic efficiency, and longer cycle life, making them an important development direction for high-energy silicon-based anode materials. However, during the initial charge-discharge process, silicon suboxide forms electrochemically inert substances such as lithium silicate and lithium oxide, which result in a lower initial coulombic efficiency. Therefore, a pre-magnesification reaction is employed, where a magnesium source reacts with silicon suboxide to generate magnesium silicate. Magnesium silicate is an irreversible compound with high mechanical strength. It is difficult to amorphize during charging and discharging and will not undergo a reversible reaction to generate active SiO2. Furthermore, due to its irreversibility, it can also act as a buffer layer to suppress SiO2 formation. x The volume expansion of the negative electrode material is beneficial to improving the battery's initial coulombic efficiency, reversible capacity, and cycle performance.

[0004] Chinese patent application CN117855434A (application date 2024.01.08) discloses a pre-magnesiumized silicon-oxygen anode material for lithium-ion batteries and its preparation method. This method does not involve the addition of molten salt and employs high-temperature calcination (900-1200℃). However, this method cannot guarantee uniform diffusion and intercalation of magnesium ions. Furthermore, the solid-state mixed magnesium source (such as magnesium powder or magnesium oxide) has point-to-point mechanical contact with the silicon-oxygen particles, rather than the encapsulating "liquid-phase contact" provided by the molten salt method. This results in highly uneven reaction initiation points. Silicon-oxygen materials (SiO₂) xThe ideal structure of silicon-oxygen materials is amorphous. Above 700℃, significant phase separation and crystallization begin to occur, generating crystalline Si and SiO2 with poor conductivity and large volume effect. High temperatures of 900-1200℃ will severely exacerbate this process, destroying the inherent ability of silicon-oxygen materials to buffer volume expansion, thereby impairing their cycle stability.

[0005] Chinese patent CN116544381B (application date 2023.05.30) discloses a pre-magnesium silicon-oxygen anode material, its preparation method, and a secondary battery. This method, like others, does not involve molten salts but instead incorporates latent heat agents made from cadmium, selenium, etc. The latent heat agents used in this technology are too expensive and contain too many impurities, which is detrimental to improving electrochemical performance. The core of the "latent heat agent" (such as a Cd-Se alloy) is to utilize its low melting point (e.g., the Cd-Se eutectic point may be below 400℃) to melt and absorb heat during heating, forming a brief liquid phase to promote magnesium diffusion. However, this liquid phase window is very short and uncontrollable. Once the material temperature exceeds the boiling point of the latent heat agent (e.g., cadmium's boiling point is 765℃), the latent heat agent will rapidly volatilize, the liquid phase environment will disappear, and the subsequent reaction will revert to solid-state diffusion. This results in a severely insufficient effective reaction time, and the uniform embedding of magnesium is far from complete.

[0006] Chinese patent CN115663151B (application date 2022.11.10) discloses a pre-magnesium silicate composite material, a silicon-based anode material, a preparation method, and a secondary battery. This method incorporates a mixed molten salt containing sodium chloride and magnesium chloride, defining the melting point of this mixed molten salt as lower than that of the magnesium source. The material is heat-treated at 900℃ to obtain a calcined material, followed by acid washing and carbon coating. The anode material obtained by this method has MgSiO3 as the main phase, accounting for no less than 80% of the mass of the magnesium silicate compound. Although the NaCl-MgCl2 mixed molten salt provides a liquid phase environment, when the heat treatment temperature reaches 900℃, the corrosion and etching effects of the molten salt on the silicate particles are very strong, potentially excessively damaging the particle morphology, increasing the specific surface area, and thus increasing side reactions.

[0007] Chinese patent application CN117613223A (filed on November 22, 2023) discloses a pre-magnesium silicate material, its preparation method, applications, and lithium-ion batteries. It proposes a two-layer carbon coating process and utilizes Grignard reagents to replace the traditional magnesium source. However, this method does not explore the impact of heat treatment on the composition and particle size distribution of magnesium silicate materials. Furthermore, Grignard reagents are extremely sensitive to water and oxygen, requiring synthesis, storage, and reaction under harsh conditions of inert atmosphere protection and ultra-dryness. This necessitates extremely high levels of sealing and purification in the entire production equipment, leading to soaring equipment investment and maintenance costs, and a slow production pace.

[0008] The development of pre-magnesium silicon suboxide anode materials is still under continuous exploration. How to control the composition of magnesium silicate and how to control the heat treatment, acid washing, and carbon coating processes to obtain materials with better electrochemical performance are still issues that need further exploration in this field. Summary of the Invention

[0009] Purpose of the invention: The purpose of this invention is to provide a method for preparing a finely controlled silicon suboxide anode material, which obtains a material with Mg2SiO4 as the main phase by controlling the volatilization of molten salt; another purpose of this invention is to provide a pre-magnesium silicon suboxide anode material prepared by the aforementioned method, and a lithium-ion battery prepared using this material.

[0010] Technical solution: To achieve the above-mentioned objective, the present invention provides a method for preparing a pre-magnesium silicon suboxide anode material, comprising:

[0011] The silica powder, halide molten salt, and magnesium source are mixed in a mass ratio of 100:(30-50):(5-20), heated to 500-800℃, and calcined in an inert atmosphere with slight positive pressure for 3-6 hours to obtain the calcined material.

[0012] The calcined material is acid-washed, vacuum filtered, and then dried to obtain the acid-washed material.

[0013] The pickled material is heated to 700-900℃ and a carbon source is introduced for carbon coating. The sintered material is then pulverized to obtain the pre-magnesium silicon suboxide anode material.

[0014] While existing technologies have explored various aspects of pre-magnesium processes, they often focus excessively on improving the dispersibility of molten salt pre-magnesium while neglecting the volatilization issues caused by excessively high pre-magnesium temperatures and vacuum environments in actual production. This problem leads to unstable composition and performance, thus failing to achieve the desired effect of lowering the magnesium melting point for solid-liquid pre-magnesium reactions under normal pressure. Therefore, this invention proposes pre-magnesium calcination at 500-800℃ under a slightly positive pressure inert atmosphere. As a preferred embodiment of this invention, the pre-magnesium heat treatment temperature is preferably 550-650℃. The slightly positive pressure refers to the airflow within a sealed space, resulting in an internal pressure slightly higher than conventional atmospheric pressure; the preferred slightly positive pressure is 105-110 kPa. Conventional pre-magnesium heat treatment typically involves calcination at a vacuum-sealed environment (e.g., 0.1 kPa).

[0015] In addition, this application improves the molten salt. The inventors discovered that by adjusting the heat treatment temperature and pressure through the above steps, and by adding silver chloride with a lower melting point to the molten salt in a certain proportion, a new pre-magnesium silicon suboxide anode material with almost no MgSiO3 can be obtained. This material further improves the electrochemical performance and achieves unexpected results.

[0016] In a preferred embodiment of the present invention, the halide molten salt comprises at least 50 wt% silver chloride. More specifically, the halide molten salt further comprises any one or more combinations of sodium chloride, potassium chloride, calcium chloride, and magnesium chloride.

[0017] Furthermore, the magnesium source includes, but is not limited to, any one of metallic magnesium, magnesium oxide, and magnesium oxide-coated metallic magnesium. Preferably, the magnesium source is selected from metallic magnesium. More preferably, the magnesium source is a metal powder that can pass through a 200-250 mesh sieve.

[0018] In a preferred embodiment of the present invention, silver chloride and magnesium chloride each account for 50% of the mass of the halide molten salt. The mixing temperature is controlled at no more than 40°C.

[0019] Furthermore, the acid solution used in the pickling process includes any one or more combinations of hydrochloric acid, nitric acid, and sulfuric acid, with a concentration of 8-12 v / v% and a pickling time of 5-15 min. The pickling process has a significant impact on the composition, specific surface area, and electrochemical properties of magnesium silicate materials. Too high a pickling concentration will consume the Mg2SiO4 formed in the reaction, while too low a concentration will prevent the removal of magnesium oxide generated on the particle surface due to the pre-magnesium reaction. However, the inventors discovered that adding a mixed molten salt to the base of silicon suboxide and magnesium powder, followed by pre-magnesium calcination, forms a more stable Mg2SiO4 phase. Under pickling conditions of 8-12 v / v%, the Mg2SiO4 phase was not removed and showed significantly stronger characteristic peaks than MgSiO3 in XRD.

[0020] Furthermore, the size D50 of the silicon suboxide powder is 5-6 μm.

[0021] Furthermore, the carbon source is selected from any one of methane, acetylene, ethylene, carbon monoxide, and carbon tetrachloride.

[0022] Furthermore, the filter membrane used in the vacuum filtration is an aqueous filter membrane with a pore size of 0.2-0.45 μm, the drying temperature is 100-120℃, and the drying time is 24-48h.

[0023] Furthermore, the pulverization is performed using an airflow with a pressure of 0.2-0.3 MPa.

[0024] The pre-magnesium silicon suboxide anode material prepared by the above method has the following characteristics in XRD testing: the peak intensity of single-crystal silicon at the strongest peak diffraction angle of 28.4°±0.5° is I1; the peak intensity of Mg2SiO4 at the strongest peak diffraction angle of 32.4°±0.5° is I2; and the peak intensity of MgSiO3 at the strongest peak diffraction angle of 30.0°±0.5° is I3; wherein, 0.20≤I2 / I1≤0.35, and 0≤I3 / I1≤0.15.

[0025] The present invention also provides a negative electrode sheet, comprising a conductive agent, a binder, and a pre-magnesium silicon suboxide negative electrode material prepared by the aforementioned method, which are mixed in a volume ratio of 1:1:8, a solvent is added, and the mixture is coated on a copper foil, dried, and sliced ​​to obtain the electrode sheet.

[0026] The present invention also provides a lithium-ion battery, which is prepared using a negative electrode material or a negative electrode sheet. Attached Figure Description

[0027] Figure 1 These are the XRD diffraction patterns of comparative examples and some embodiments of the present invention;

[0028] Figure 2 The voltage-specific capacity charge-discharge curve of the lithium-ion battery assembled with the negative electrode material described in Example 1 was measured at 30°C.

[0029] Figure 3 The voltage-specific capacity charge-discharge curves of the lithium-ion battery assembled with the negative electrode material described in Comparative Example 2 were measured at 30°C.

[0030] Figure 4 The voltage-specific capacity charge-discharge curves of the lithium-ion battery assembled with the negative electrode material described in Comparative Example 3 were measured at 30°C. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and all materials publicly cited herein and cited by them are incorporated herein by reference.

[0033] Equivalent technologies of the specific embodiments described herein that are readily apparent to those skilled in the art through routine experimentation are included in this application.

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the instruments and equipment used in the following examples are all standard laboratory instruments and equipment; unless otherwise specified, the experimental materials used in the following examples were all purchased from regular biochemical reagent stores.

[0035] Example 1

[0036] 1) Preparation of the mixture: Weigh 100g of silica powder, 10g of magnesium powder, 25g of silver chloride, and 25g of magnesium chloride and mix them at 25℃ to obtain the mixture;

[0037] 2) Preparation of calcined material: The mixture was placed in a rotary calcining furnace and heated from room temperature to 600℃ at a heating rate of 5℃ / min under a slight positive pressure. The calcination time was 4h and the calcination atmosphere was high-purity argon.

[0038] 3) Preparation of pickling material: The calcined material obtained in step 2) is mixed with acid solution for pickling. The acid solution concentration is 10 v / v%, and the pickling time is 10 min. Then, it is filtered by vacuum-assisted filtration. After filtration, it is dried in a forced-air drying oven at 100℃ for 24 h to obtain the pickling material.

[0039] 4) The pickling material obtained in step 3) is heated from room temperature to 800℃ at a heating rate of 5℃ / min to deposit acetylene for coating. The deposition flow rate is 0.5 L / min and the deposition time is 3h. The sintered material is then subjected to air jet pulverization at a pressure of 0.2 MPa to obtain the premagnesium silicon oxide anode material.

[0040] Example 2

[0041] 1) Preparation of the mixture: Weigh 100g of silica powder, 10g of magnesium powder, 25g of silver chloride and 25g of sodium chloride and mix them at 25℃ to obtain the mixture;

[0042] 2) Preparation of calcined material: The mixture was placed in a rotary calcining furnace and heated from room temperature to 600℃ at a heating rate of 5℃ / min under a slight positive pressure. The calcination time was 4h and the calcination atmosphere was high-purity argon.

[0043] 3) Preparation of pickling material: The calcined material obtained in step 2) is mixed with acid solution for pickling. The acid solution concentration is 10 v / v%, and the pickling time is 10 min. Then, it is filtered by vacuum-assisted filtration. After filtration, it is dried in a forced-air drying oven at 100℃ for 24 h to obtain the pickling material.

[0044] 4) The pickling material obtained in step 3) is heated from room temperature to 800℃ at a heating rate of 5℃ / min to deposit acetylene for coating. The deposition flow rate is 0.5 L / min and the deposition time is 3h. The sintered material is then subjected to air jet pulverization at a pressure of 0.2 MPa to obtain the premagnesium silicon oxide anode material.

[0045] Example 3

[0046] 1) Preparation of the mixture: Weigh 100g of silica powder, 10g of magnesium powder, 25g of silver chloride, and 25g of potassium chloride and mix them at 25℃ to obtain the mixture;

[0047] 2) Preparation of calcined material: The mixture was placed in a rotary calcining furnace and heated from room temperature to 600℃ at a heating rate of 5℃ / min under a slight positive pressure. The calcination time was 4h and the calcination atmosphere was high-purity argon.

[0048] 3) Preparation of pickling material: The calcined material obtained in step 2) is mixed with acid solution for pickling. The acid solution concentration is 10 v / v%, and the pickling time is 10 min. Then, it is filtered by vacuum-assisted filtration. After filtration, it is dried in a forced-air drying oven at 100℃ for 24 h to obtain the pickling material.

[0049] 4) The pickling material obtained in step 3) is heated from room temperature to 800℃ at a heating rate of 5℃ / min to deposit acetylene for coating. The deposition flow rate is 0.5 L / min and the deposition time is 3h. The sintered material is then subjected to air jet pulverization at a pressure of 0.2 MPa to obtain the premagnesium silicon oxide anode material.

[0050] Example 4

[0051] 1) Preparation of the mixture: Weigh 100g of silica powder, 10g of magnesium powder, 25g of silver chloride, and 25g of calcium chloride and mix them at 25℃ to obtain the mixture;

[0052] 2) Preparation of calcined material: The mixture was placed in a rotary calcining furnace and heated from room temperature to 600℃ at a heating rate of 5℃ / min under a slight positive pressure. The calcination time was 4h and the calcination atmosphere was high-purity argon.

[0053] 3) Preparation of pickling material: The calcined material obtained in step 2) is mixed with acid solution for pickling. The acid solution concentration is 10 v / v%, and the pickling time is 10 min. Then, it is filtered by vacuum-assisted filtration. After filtration, it is dried in a forced-air drying oven at 100℃ for 24 h to obtain the pickling material.

[0054] 4) The pickling material obtained in step 3) is heated from room temperature to 800℃ at a heating rate of 5℃ / min to deposit acetylene for coating. The deposition flow rate is 0.5 L / min and the deposition time is 3h. The sintered material is then subjected to air jet pulverization at a pressure of 0.2 MPa to obtain the premagnesium silicon oxide anode material.

[0055] Example 5

[0056] 1) Preparation of the mixture: Weigh 100g of silica powder, 5g of magnesium powder, 25g of silver chloride, and 25g of magnesium chloride and mix them at 25℃ to obtain the mixture;

[0057] 2) Preparation of calcined material: The mixture was placed in a rotary calcining furnace and heated from room temperature to 600℃ at a heating rate of 5℃ / min under a slight positive pressure. The calcination time was 4h and the calcination atmosphere was high-purity argon.

[0058] 3) Preparation of pickling material: The calcined material obtained in step 2) is mixed with acid solution for pickling. The acid solution concentration is 10 v / v%, and the pickling time is 10 min. Then, it is filtered by vacuum-assisted filtration. After filtration, it is dried in a forced-air drying oven at 100℃ for 24 h to obtain the pickling material.

[0059] 4) The pickling material obtained in step 3) is heated from room temperature to 800℃ at a heating rate of 5℃ / min to deposit acetylene for coating. The deposition flow rate is 0.5 L / min and the deposition time is 3h. The sintered material is then subjected to air jet pulverization at a pressure of 0.2 MPa to obtain the premagnesium silicon oxide anode material.

[0060] Example 6

[0061] 1) Preparation of the mixture: Weigh 100g of silica powder, 15g of magnesium powder, 25g of silver chloride, and 25g of magnesium chloride and mix them at 25℃ to obtain the mixture;

[0062] 2) Preparation of calcined material: The mixture was placed in a rotary calcining furnace and heated from room temperature to 600℃ at a heating rate of 5℃ / min under a slight positive pressure. The calcination time was 4h and the calcination atmosphere was high-purity argon.

[0063] 3) Preparation of pickling material: The calcined material obtained in step 2) is mixed with acid solution for pickling. The acid solution concentration is 10 v / v%, and the pickling time is 10 min. Then, it is filtered by vacuum-assisted filtration. After filtration, it is dried in a forced-air drying oven at 100℃ for 24 h to obtain the pickling material.

[0064] 4) The pickling material obtained in step 3) is heated from room temperature to 800℃ at a heating rate of 5℃ / min to deposit acetylene for coating. The deposition flow rate is 0.5 L / min and the deposition time is 3h. The sintered material is then subjected to air jet pulverization at a pressure of 0.2 MPa to obtain the premagnesium silicon oxide anode material.

[0065] Example 7

[0066] 1) Preparation of the mixture: Weigh 100g of silica powder, 20g of magnesium powder, 25g of silver chloride, and 25g of magnesium chloride and mix them at 25℃ to obtain the mixture;

[0067] 2) Preparation of calcined material: The mixture was placed in a rotary calcining furnace and heated from room temperature to 600℃ at a heating rate of 5℃ / min under a slight positive pressure. The calcination time was 4h and the calcination atmosphere was high-purity argon.

[0068] 3) Preparation of pickling material: The calcined material obtained in step 2) is mixed with acid solution for pickling. The acid solution concentration is 10 v / v%, and the pickling time is 10 min. Then, it is filtered by vacuum-assisted filtration. After filtration, it is dried in a forced-air drying oven at 100℃ for 24 h to obtain the pickling material.

[0069] 4) The pickling material obtained in step 3) is heated from room temperature to 800℃ at a heating rate of 5℃ / min to deposit acetylene for coating. The deposition flow rate is 0.5 L / min and the deposition time is 3h. The sintered material is then subjected to air jet pulverization at a pressure of 0.2 MPa to obtain the premagnesium silicon oxide anode material.

[0070] Comparative Example 1

[0071] 1) Preparation of the mixture: Weigh 100g of silica powder, 10g of magnesium powder and 50g of magnesium chloride and mix them at 25℃ to obtain the mixture;

[0072] 2) Preparation of calcined material: The mixture was placed in a rotary calcining furnace and heated from room temperature to 600℃ at a heating rate of 5℃ / min under a slight positive pressure. The calcination time was 4h and the calcination atmosphere was high-purity argon.

[0073] 3) Preparation of pickling material: The calcined material obtained in step 2) is mixed with acid solution for pickling. The acid solution concentration is 10% and the pickling time is 10 min. Then, it is filtered by vacuum-assisted filtration. After filtration, it is dried in a forced-air drying oven at 100℃ for 24 h to obtain the pickling material.

[0074] 4) The pickling material obtained in step 3) is heated from room temperature to 800℃ at a heating rate of 5℃ / min to deposit acetylene for coating. The deposition flow rate is 0.5 L / min and the deposition time is 3h. The sintered material is then subjected to air jet pulverization at a pressure of 0.2 MPa to obtain the premagnesium silicon oxide anode material.

[0075] Comparative Example 2

[0076] 1) Preparation of the mixture: Weigh 100g of silica powder, 10g of magnesium powder, 25g of silver chloride, and 25g of magnesium chloride and mix them at 25℃ to obtain the mixture;

[0077] 2) Preparation of calcined material: The mixture was placed in a rotary calcining furnace and heated from room temperature to 600℃ at a heating rate of 5℃ / min under a slight positive pressure. The calcination time was 4h and the calcination atmosphere was high-purity argon.

[0078] 3) Preparation of pickling material: The calcined material obtained in step 2) is mixed with acid solution for pickling. The acid solution concentration is 3% and the pickling time is 10 min. Then, it is filtered by vacuum-assisted filtration. After filtration, it is dried in a forced-air drying oven at 100℃ for 24 h to obtain the pickling material.

[0079] 4) The pickling material obtained in step 3) is heated from room temperature to 800℃ at a heating rate of 5℃ / min to deposit acetylene for coating. The deposition flow rate is 0.5 L / min and the deposition time is 3h. The sintered material is then subjected to air jet pulverization at a pressure of 0.2 MPa to obtain the premagnesium silicon oxide anode material.

[0080] Comparative Example 3

[0081] 1) Preparation of the mixture: Weigh 100g of silica powder, 10g of magnesium powder, 25g of silver chloride, and 25g of magnesium chloride and mix them at 25℃ to obtain the mixture;

[0082] 2) Preparation of calcined material: The mixture was placed in a rotary calcining furnace and heated from room temperature to 600℃ at a heating rate of 5℃ / min under a slight positive pressure. The calcination time was 4h and the calcination atmosphere was high-purity argon.

[0083] 3) Preparation of pickling material: The calcined material obtained in step 2) is mixed with acid solution and pickled. The acid solution concentration is 30% and the pickling time is 10 min. Then, it is filtered by vacuum-assisted filtration. After filtration, it is dried in a forced-air drying oven at 100℃ for 24 h to obtain the pickling material.

[0084] 4) The pickling material obtained in step 3) is heated from room temperature to 800℃ at a heating rate of 5℃ / min to deposit acetylene for coating. The deposition flow rate is 0.5 L / min and the deposition time is 3h. The sintered material is then subjected to air jet pulverization at a pressure of 0.2 MPa to obtain the premagnesium silicon oxide anode material.

[0085] Comparative Example 4

[0086] 1) Preparation of the mixture: Weigh 100g of silica powder, 10g of magnesium powder, 25g of silver chloride, and 25g of magnesium chloride and mix them at 25℃ to obtain the mixture;

[0087] 2) Preparation of calcined material: The mixture was placed in a rotary calcining furnace and heated from room temperature to 600℃ at a heating rate of 5℃ / min under vacuum (-0.1KPa) conditions for 4 hours. The calcining atmosphere was high-purity argon.

[0088] 3) Preparation of pickling material: The calcined material obtained in step 2) is mixed with acid solution for pickling. The acid solution concentration is 10% and the pickling time is 10 min. Then, it is filtered by vacuum-assisted filtration. After filtration, it is dried in a forced-air drying oven at 100℃ for 24 h to obtain the pickling material.

[0089] 4) The pickling material obtained in step 3) is heated from room temperature to 800℃ at a heating rate of 5℃ / min to deposit acetylene for coating. The deposition flow rate is 0.5 L / min and the deposition time is 3h. The sintered material is then subjected to air jet pulverization at a pressure of 0.2 MPa to obtain the premagnesium silicon oxide anode material.

[0090] Experimental Example 1

[0091] To accurately characterize the phase composition of the silicon-based anode material described in this invention, particularly the crystallization and relative content of silicon (Si), magnesium silicate (Mg2SiO4), and magnesium metasilicate (MgSiO3), X-ray diffraction (XRD) technology was used for testing.

[0092] The instrument used was a Bruker D8 ADVANCE X-ray diffractometer (Germany). To ensure the accuracy, comparability, and repeatability of the test results, the following standardized test parameters were set:

[0093] (1) X-ray source: Cu target Kα rays (wavelength λ=0.15406 nm);

[0094] (2) Tube voltage and tube current: 40 kV and 40 mA;

[0095] (3) Scanning range (2θ): 10° to 90°, which can completely cover all the main diffraction peaks of target phases such as silicon and magnesium silicate;

[0096] (4) Scanning speed: 6° / min.

[0097] Take an appropriate amount of the pre-magnesium silicon suboxide anode material powder sample prepared in the embodiments and comparative examples of this invention, place the powder sample into the groove of the glass sample holder, and gently press and smooth the powder surface with a clean glass slide until it is flush with the edge of the sample holder, forming a flat, dense and smooth test plane. Place the prepared sample holder securely on the sample stage of the diffractometer.

[0098] Before testing, the diffractometer was calibrated for angle and intensity using standard silicon powder (such as NIST SRM 640d) to ensure the instrument was in optimal working condition. After setting the parameters, the test program was started, and the instrument automatically completed the scanning and data acquisition.

[0099] XRD tests were performed on the negative electrode material samples corresponding to Examples 1-4 and Comparative Examples 1-4. Then, phase identification was performed using the "PDF" card library in Jade software. By matching the peak position (2θ) and further calculating the peak intensity (I1) and peak area (A1) of the strongest peak diffraction angle of single crystal silicon at 28.4°±0.5°, the peak intensity (I2) and peak area (A2) of the strongest peak diffraction angle of Mg2SiO4 at 32.4°±0.5°, and the peak intensity (I3) and peak area (A3) of the strongest peak diffraction angle of Mg2SiO4 at 32.4°±0.5°, the peak intensity ratios I2 / I1, I3 / I1 and the peak area ratios A2 / A1, A3 / A1 were calculated respectively. The results are shown in Table 1.

[0100] Table 1. Main Phase Analysis of Magnesia Silicates

[0101]

[0102] The above experiments show that Mg2SiO4 is the main phase in the solution provided by this invention, and its content is significantly higher than that of the comparative example. In Comparative Example 3, due to the use of a high-concentration acid washing process, the characteristic peaks of Mg2SiO4 and MgSiO3 could no longer be identified in the XRD test. In Comparative Example 4, calcination under vacuum conditions resulted in the easy volatilization of the molten salt, leading to unstable composition and properties. Therefore, it failed to achieve the effect of effectively lowering the melting point of magnesium under normal pressure for solid-liquid pre-magnesium reaction, only forming MgSiO3, which is less structurally stable than Mg2SiO4, and without the presence of Mg2SiO4 characteristic peaks.

[0103] Further integration Figure 1It can be seen that the strongest peak of MgSiO3 in the negative electrode materials obtained in Examples 1-4 of this invention is mainly at 30.0°±0.5°, and is almost invisible. Combined with the XRD pattern of Comparative Example 1, it can be seen that the addition of silver chloride molten salt significantly improves the content of Mg2SiO4 in magnesium silicate materials. Combined with Comparative Example 2, it can be seen that the lower concentration acid washing process produces obvious MgO reaction byproducts, while the acid washing concentration is too high, and Mg2SiO4 and other substances cannot be identified in the pattern of Comparative Example 3. Comparative Example 4 involves pre-magnesium heat treatment under vacuum. Due to the volatilization of the molten salt, the effect of effectively lowering the magnesium melting point and carrying out the solid-liquid pre-magnesium reaction by micro-positive pressure cannot be achieved. The resulting negative electrode material can only identify MgSiO3, but the crystal phase structure stability of MgSiO3 is not as good as that of Mg2SiO4. Subsequent experiments also show that the negative electrode material with Mg2SiO4 as the main phase exhibits better electrochemical performance.

[0104] Experimental Example 2

[0105] The negative electrode materials of Examples 1-7 and Comparative Examples 1-4 were respectively prepared into negative electrode sheets: Silicon-oxygen negative electrode material coated with carbon nanotubes was mixed with conductive graphite and sodium carboxymethyl cellulose in a volume ratio of 8:1:1. After thorough grinding with the addition of solvent, the mixture was coated onto copper foil and dried in an oven at 60-120℃. After drying, it was cut into 12 mm diameter discs and stored in a glove box for later use. The positive electrode shell, positive electrode, electrolyte, separator, electrolyte, negative electrode, gasket, and negative electrode shell were assembled sequentially and then pressed together; the electrolyte was EC / DEC = 1:1, 10% FEC, and 1% VC. Experimental lithium-ion coin cell samples were obtained.

[0106] The battery tests were primarily conducted using the Xinwei testing software at a temperature of 30℃. The electrochemical performance is shown in Table 2: Table 2 Electrochemical Test Data for Each Experimental Group

[0107]

[0108] Figures 2-4 The voltage-specific capacity charge-discharge curves of the coin cells prepared by Examples 1, 2, and 3 are shown at 30°C. The discharge curves of the materials exhibit a dominant long plateau in the range of 0.25V to 0.01V, contributing more than 75% of the discharge capacity, corresponding to the silicon alloying reaction. Further, referring to Table 2, it can be seen that the coin cells provided by the embodiments of the present invention show superior comprehensive advantages in discharge specific capacity, charge specific capacity, and first-efficiency performance. The voltage-specific capacity charge-discharge curve of Example 1 shows a lower plateau onset voltage, a longer length, and a flatter curve. Figure 2This indicates that pre-magnesification effectively reduces irreversible reactions and improves the reversibility and uniformity of the alloying reaction. Comparative Example 2, due to its low-concentration pickling process, exhibits significant magnesium oxide (MgO) reaction byproducts. Magnesium oxide is not an effective pre-magnesifying agent but rather a harmful impurity that consumes active lithium, increases interfacial impedance, and degrades structural stability. Its charge-discharge curves show abnormally high initial irreversible capacity, severely increased polarization, and accelerated capacity decay (…). Figure 3 The negative electrode material used in Comparative Example 3, due to its high-concentration acid washing process, resulted in almost no presence of Mg2SiO4 and MgSiO3, manifested as >0.5V (vs). In the high-potential region of ), a very long and large-capacity "slope" will appear. Figure 4 This corresponds to the irreversible reduction reaction of the SiO2 / lithium subsilicate component (such as the formation of...). The intense formation of lithium silicates and solid electrolyte interphase (SEI) membranes leads to severe consumption of active lithium, resulting in a decrease in initial coulombic efficiency.

[0109] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a pre-magnesium silicon suboxide anode material, characterized in that: The silica powder, halide molten salt, and magnesium source are mixed in a mass ratio of 100:(30-50):(5-20), heated to 500-800℃, and calcined in an inert atmosphere with slight positive pressure for 3-6 hours to obtain the calcined material. The calcined material is acid-washed, vacuum filtered, and then dried to obtain the acid-washed material. The pickled material is heated to 700-900℃ and a carbon source is introduced for carbon coating. The sintered material is then pulverized to obtain the pre-magnesium silicon suboxide anode material.

2. The method for preparing a pre-magnesia silicon monoxide negative material according to claim 1, characterized in that: The halide molten salt contains at least 50 wt% silver chloride.

3. The method according to claim 2, wherein the method is characterized by: The halide molten salt also includes any one or more combinations of sodium chloride, potassium chloride, calcium chloride, and magnesium chloride.

4. The method according to claim 1, wherein the method is characterized by: The magnesium source includes any one of metallic magnesium, magnesium oxide, or magnesium oxide coated with metallic magnesium.

5. The method according to claim 1, wherein the method is characterized by: The magnesium source is a powder that can pass through a 200-250 mesh sieve.

6. The method for preparing a pre-magnesium silicon suboxide anode material according to claim 1, characterized in that: The acid solution used in the pickling process includes any one or more combinations of hydrochloric acid, nitric acid, and sulfuric acid, and the concentration of the acid solution is 8-12 v / v %; the pickling time is 5-15 min.

7. The method according to claim 1, wherein the method is characterized by: The silicon suboxide powder has a size D50 of 5-6 μm.

8. The method for preparing a pre-magnesium silicon suboxide anode material according to claim 1, characterized in that: The carbon source is selected from any one of methane, acetylene, ethylene, carbon monoxide, and carbon tetrachloride.

9. The pre-magnesium silicon suboxide anode material prepared by the method described in claims 1-9, characterized in that: In XRD testing, the peak intensity of single-crystal silicon at the strongest diffraction angle of 28.4°±0.5° is I1; the peak intensity of Mg2SiO4 at the strongest diffraction angle of 32.4°±0.5° is I2; and the peak intensity of MgSiO3 at the strongest diffraction angle of 30.0°±0.5° is I3. Among these, 0.20≤I2 / I1≤0.35 and 0≤I3 / I1≤0.

15.

10. A lithium-ion battery, characterized by: It is made using the pre-magnesium silicon suboxide anode material as described in claim 9.

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