A Si / Mg2SiO4 composite material for lithium-ion battery shell structure based on magnesium thermal reduction, its preparation method and its application

Abstract

The application relates to a lithium ion battery shell structure Si / Mg2SiO4 composite material based on magnesium thermal reduction, a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. A certain proportion of Mg2SiO4 three-dimensional framework is produced in a reduction product through a magnesium thermal reduction reaction, and the obtained shell structure Si / Mg2SiO4 composite material has good morphology and high reversible capacity. In the process of reducing the shell structure silicon dioxide into silicon with a cavity, the generation of a certain proportion of Mg2SiO4 helps to form a stable three-dimensional network framework, prevents the fusion between adjacent Si nanoparticles in the reduction process, and plays a buffering role on the volume expansion of Si in the electrochemical cycle process.

Description

[0001] A Si / Mg2SiO4 composite material for lithium-ion battery shell structure based on magnesium thermal reduction, its preparation method and its application Technical Field

[0002] This invention relates to a Si / Mg2SiO4 composite material for lithium-ion battery shell structure based on magnesium thermal reduction, its preparation method and its application, belonging to the field of lithium-ion battery technology. Background Technology

[0003] In recent years, due to the depletion of fossil fuels and the aggravation of environmental pollution, exploring different types of clean and sustainable energy has become a major focus. Lithium-ion batteries, as a new energy storage technology, have advantages such as high specific energy, long cycle life, and environmental friendliness. The anode material of lithium-ion batteries has a significant impact on the battery's safety performance, energy density, and cycle life. Currently, graphite anode materials occupy 90% of the anode material market due to their mature technology, low cost, and good performance. However, although graphite materials have advantages in high conductivity and stability, even reaching their theoretical maximum energy density (372 mAh / g) is still insufficient to meet the high energy density requirements of next-generation mobile applications. Compared with graphite-based anode materials, silicon-based materials have a significant advantage in specific capacity, possessing a high theoretical capacity (4200 mAh / g), abundant reserves, and a favorable voltage platform (0.2-0.4 V vs Li / Li). + ), which is a more promising anode material.

[0004] However, silicon-based anode materials suffer from poor cycle stability (volume expansion of up to 300-400% during charge and discharge), poor conductivity (poor contact between the conductive agent and the anode binder), and low initial cycle coulombic efficiency (Li). + Problems such as the high degree of irreversibility during insertion / extraction processes exist. Current main directions for modification and optimization include: modifying the silicon source to prepare nano-silicon, porous silicon, or alloy silicon; preparing silicon-carbon composite materials; and preparing silicon suboxide (SiO₂). x Materials. Appropriate structural design of silicon-based materials is an effective way to mitigate the significant volume expansion of silicon during lithium intercalation. Examples include linear structures, tubular structures, shell structures, and porous structures. Among these, shell structures can provide internal space to accommodate the volume expansion during lithium intercalation, mitigating the stress caused by volume changes during cycling, improving the structural stability of the material, and enhancing the electrochemical performance of silicon anode materials.

[0005] Magnesium reduction is considered one of the practical preparation processes for silicon anode materials due to its low cost and simple procedure. However, since magnesium reduction is an exothermic reaction, localized heat accumulation can lead to side reactions and agglomeration of silicon particles in the product. Furthermore, the high temperature during the reaction process can easily damage the original shell structure.

[0006] Mg₂SiO₄ has an olivine structure, with chemical bonds in its crystals including ionic and covalent bonds. It exhibits high-temperature and chemical stability, and combining it with silicon materials can improve the structural stability of the material. (Reference: Xu B, Shen H, Ge J, et al. Improved cycling performance of SiO₂) x The paper describes the preparation of SiO2 / MgO / Mg2SiO4 / C composite anode materials for lithium-ion batteries using a magnesothermic reduction process (MgO / Mg2SiO4 / C composite anode materials for lithium-ion batteries [J]. Applied Surface Science, 2021, 546:148814). x Materials with a MgO / Mg2SiO4 / C composite structure are proposed, and the relationship between Mg2SiO4 and SiO2 is also discussed. x The SiO2 particles are interwoven within spherical particles, allowing for uniform control of SiO2 in different directions. x The volume change is significant. However, since the raw material used is solid granules with a compact internal structure, it is still difficult to provide enough space to control the volume expansion of Si. The structure is prone to breakage during cycling, and the presence of MgO will result in a relatively low capacity of the composite material. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a lithium-ion battery shell structure Si / Mg2SiO4 composite material based on magnesia-reduction, its preparation method, and its application. This invention uses shell structure SiO2 as raw material and regulates the production of a certain proportion of Mg2SiO4 three-dimensional framework in the reduction products through a magnesia-reduction reaction. The resulting shell structure Si / Mg2SiO4 composite material exhibits good morphology and high reversible capacity. During the reduction of cavity-structured shell structure silicon dioxide to silicon, the formation of a certain proportion of Mg2SiO4 helps to form a stable three-dimensional network framework, preventing the fusion of adjacent Si nanoparticles during the reduction process, and simultaneously buffering the volume expansion of Si during electrochemical cycling.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows.

[0009] A method for preparing Si / Mg2SiO4 composite material for lithium-ion battery shell structure based on magnesium thermal reduction, the method steps include: (1) In a protective gas atmosphere, SiO2 with shell structure is mixed evenly with magnesium powder to obtain a mixed powder; (2) The mixed powder is loaded into a sealed reaction vessel, placed in a tube furnace, and reduced at high temperature in a protective gas atmosphere. After cooling, a solid product is obtained. (3) The solid product was treated with dilute acid, then washed with deionized water and ethanol, centrifuged and dried to obtain a shell structure Si / Mg2SiO4 composite material. In step (1), the shell structure SiO2 is a submicron-sized spherical shell structure material with an internal cavity, and the shell thickness is 150nm~250nm; the mass ratio of the shell structure SiO2 to the metallic magnesium powder is 1:0.4~1.5. In step (2), the high-temperature reaction temperature is 630℃~750℃, and the holding time is 1~15h; In step (3), the concentration of the dilute acid is 0.1 mol / L to 2 mol / L, the acid treatment time is 1 to 4 hours, and the amount of dilute acid used is 100 to 1200 times the mass of the solid product.

[0010] Preferably, in step (1), the mass ratio of the shell structure SiO2 to the magnesium powder is 1:0.8~1.2.

[0011] Preferably, in step (2), the high-temperature reaction temperature is 650℃~700℃ and the heat preservation time is 4~10h.

[0012] Preferably, in step (2), the heating rate is 2℃ / min to 15℃ / min and the cooling rate is 1℃ / min to 10℃ / min.

[0013] Preferably, in step (3), the dilute acid is one or more of hydrochloric acid, sulfuric acid, nitric acid and hydrofluoric acid.

[0014] Preferably, in step (3), the concentration of the dilute acid is 0.5 mol / L to 1 mol / L, the acid treatment time is 2 h to 3 h, and the amount of dilute acid used is 100 to 200 times the mass of the solid product.

[0015] Preferably, in step (3), the centrifugation speed is 8000 rpm to 10000 rpm.

[0016] Preferably, in step (3), the drying method is vacuum drying, the temperature is 75℃~95℃, and the time is 12h~24h.

[0017] Preferably, the protective gas is nitrogen or an inert gas (the gaseous element corresponding to all group 0 elements in the periodic table).

[0018] A lithium-ion battery shell structure based on magnesia reduction, comprising Si / Mg2SiO4 composite material, is prepared by the method described in this invention. The composite material has a particle size of 600-700 nm and an internal cavity. The shell consists of a reduced Si layer and a Mg2SiO4 layer that encapsulates the Si particles in a three-dimensional network framework. The total thickness of the shell is 10-15 nm, wherein Mg2SiO4 accounts for 20%-45% of the total mass of the composite material.

[0019] An application of a Si / Mg2SiO4 composite material for lithium-ion battery shell structure based on magnesium thermal reduction, wherein the composite material is coated with a carbon layer to obtain a Si / Mg2SiO4@C composite anode material.

[0020] A lithium-ion battery, wherein the negative electrode material of the battery is a Si / Mg2SiO4@C composite negative electrode material as described in this invention.

[0021] Beneficial effects This invention provides a method for preparing a Si / Mg2SiO4 composite material for lithium-ion battery shell structure based on magnesiothermal reduction. Using SiO2 and magnesium powder as raw materials, the ratio of Si to Mg2SiO4 is controlled by adjusting the magnesiothermal reduction conditions (magnesium powder ratio, sintering temperature, and holding time). Furthermore, controlling the concentration and processing rate of dilute acid during the acid washing process leads to a more uniformly distributed Si / Mg2SiO4 composite material. In the shell-structured Si / Mg2SiO4 composite material, Mg2SiO4 maintains the stability of the shell structure, forming a protective network and mitigating the volume expansion of Si during electrochemical processes. The shell-structured Si / Mg2SiO4 composite material exhibits high specific capacity and good cycle stability after carbon coating. The preparation process is simple, effective, and inexpensive. Attached Figure Description

[0022] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the Si / Mg2SiO4 composite material prepared in Example 2.

[0023] Figure 2 The image shows a scanning electron microscope (SEM) image of the Si / Mg2SiO4 composite material prepared in Example 2.

[0024] Figure 3 The electrochemical charge-discharge curves are for the battery assembled in Example 2. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to specific embodiments.

[0026] In the following embodiments or comparative examples: (1) XRD test: Take out an appropriate amount of finished powder, place it on a glass slide and flatten it. Then, according to the conventional XRD test method, test it under the XRD test instrument to obtain the corresponding data.

[0027] (2) SEM test: Take out a small amount of finished powder and stick it onto the copper platform with conductive adhesive. Then, take pictures under the SEM test instrument according to the conventional SEM imaging method to obtain the corresponding images.

[0028] (3) Button cell assembly and electrochemical performance testing: At room temperature, the electrochemical performance test was conducted using CR2025 button cells. The working electrode preparation process is as follows: First, the active material and acetylene black prepared in the examples or comparative examples are mixed. Carboxymethyl cellulose aqueous solution (CMC) and styrene-butadiene rubber (SBR) are added dropwise to the mixed sample as binders. The concentration of CMC solution is 10 mg / ml, so that the mass ratio of the material prepared in the examples or comparative examples, acetylene black, CMC and SBR is 8:1:0.5:0.5, and a uniform slurry is obtained. Then, the obtained slurry is uniformly coated onto copper foil with a scraper and kept at 100°C for vacuum drying for 12 hours. Finally, the copper foil coated with the sample is pressed into small discs with a diameter of 1.1 cm using a punching machine as the negative electrode, and lithium sheet is used as the positive electrode material. The electrolyte is a mixed solvent of 1.0 M LiPF6 dissolved in ethylene carbonate (EC): diethyl carbonate (DEC): dimethyl carbonate (DMC) in a volume ratio of 1:1:1, with 10% fluoroethylene carbonate (FEC) additive. The charge and discharge tests were performed using the Blue Battery testing system. The test voltage range was 0.01-1.5 V, the test temperature was room temperature (30℃), and the test current density was 0.05C (1C=1500 mA / g).

[0029] Example 1 1.0 g of shell-structured SiO2 and 1.0 g of magnesium powder were weighed in a 1:1 mass ratio and uniformly ground and mixed in an argon-filled glove box. The mixed powder was then loaded into a sealed reactor. The sealed reactor was placed in a tube furnace and heated to 630 °C at a rate of 5 °C / min under an argon atmosphere, and held at that temperature for 10 h. The mixture was then cooled to room temperature at a rate of 5 °C / min to obtain a solid product.

[0030] The obtained solid product was treated with 1 mol / L hydrochloric acid. The hydrochloric acid was slowly added dropwise while stirring on a magnetic stirrer. The amount of dilute acid was 100 times the mass of the solid product. The treatment time was 2 h until no bubbles were generated. Then, the product was repeatedly washed with deionized water and centrifuged at 8000 rpm until the supernatant was neutral as measured by pH paper. The product was then washed with ethanol and centrifuged twice. The product was then placed in a vacuum oven and dried at 85°C for 20 h to obtain the final product, a shell-structured Si / Mg2SiO4 composite material.

[0031] Weigh 0.4 g of Si / Mg2SiO4 powder and 0.27 g of maltodextrin into a glass weighing bottle, add about 2 ml of deionized water, and sonicate at high speed (1200 rpm, 70% ultrasonic power) for half an hour. Once the solution is uniformly dispersed, a suspension is obtained. Dispense the suspension into centrifuge tubes, rapidly freeze them with liquid nitrogen, transfer them to a vacuum freeze dryer, and dry for 24 h to obtain a shell-structured Si / Mg2SiO4@C composite anode precursor. Spread the prepared precursor material evenly in a ceramic boat, push it to the center of a tube furnace, introduce argon gas, and heat to 800℃ at a heating rate of 5℃ / min, hold for 2 h, then cool to room temperature at the same rate. Remove the product from the ceramic boat using heat-resistant gloves; this is the shell-structured Si / Mg2SiO4@C composite anode material.

[0032] The Mg2SiO4 content in the shell-structured Si / Mg2SiO4 composite material was calculated to be 23.4% based on the XRD diffraction pattern.

[0033] The battery performance results assembled from the shell structure Si / Mg2SiO4@C composite anode material are shown in Table 1.

[0034] Example 2 1.0 g of shell-structured SiO2 and 1.0 g of magnesium powder were weighed out in a 1:1 mass ratio and uniformly ground and mixed in an argon-filled glove box. The mixed powder was then loaded into a sealed reactor. The sealed reactor was placed in a tube furnace and heated to 650 °C at a rate of 5 °C / min under an argon atmosphere, and held at that temperature for 10 h. The mixture was then cooled to room temperature at a rate of 5 °C / min to obtain a solid product.

[0035] The obtained solid product was treated with 1 mol / L hydrochloric acid. The hydrochloric acid was slowly added dropwise while stirring on a magnetic stirrer. The amount of dilute acid was 100 times the mass of the solid product. The treatment time was 2 h until no bubbles were generated. Then, the product was repeatedly washed with deionized water and centrifuged at 8000 rpm until the supernatant was neutral as measured by pH paper. The product was then washed with ethanol and centrifuged twice. The product was then placed in a vacuum oven and dried at 85°C for 20 h to obtain a shell-structured Si / Mg2SiO4 composite material.

[0036] Weigh 0.4 g of Si / Mg2SiO4 powder and 0.27 g of maltodextrin into a glass weighing bottle, add about 2 ml of deionized water, and sonicate at high speed (1200 rpm, 70% ultrasonic power) for half an hour. Once the solution is uniformly dispersed, a suspension is obtained. Dispense the suspension into centrifuge tubes, rapidly freeze them with liquid nitrogen, transfer them to a vacuum freeze dryer, and dry for 24 h to obtain a shell-structured Si / Mg2SiO4@C composite anode precursor. Spread the prepared precursor material evenly in a ceramic boat, push it to the center of a tube furnace, introduce argon gas, and heat to 800℃ at a heating rate of 5℃ / min, hold for 2 h, then cool to room temperature at the same rate. Remove the product from the ceramic boat using heat-resistant gloves; this is a shell-structured Si / Mg2SiO4@C composite anode material.

[0037] Figure 1 The XRD test results of the shell structure Si / Mg2SiO4 composite material show that the content of Mg2SiO4 in the mixture is 33.8%.

[0038] Figure 2 The SEM results of the shell structure Si / Mg2SiO4 composite material show that the particle size of the material after magnesothermic reduction is 600~700 nm, the shell structure is intact, and the shell thickness is 10~15 nm.

[0039] Figure 3 The discharge curves of the assembled battery using the Si / Mg2SiO4@C composite anode material with the shell structure are shown in Table 1.

[0040] Example 3 1.0 g of shell-structured SiO2 and 1.0 g of magnesium powder were weighed in a 1:1 mass ratio and uniformly ground and mixed in an argon-filled glove box. The mixed powder was then loaded into a sealed reactor. The sealed reactor was placed in a tube furnace and heated to 700°C at a rate of 5°C / min under an argon atmosphere, and held at that temperature for 10 h. The mixture was then cooled to room temperature at a rate of 5°C / min to obtain a solid product.

[0041] The obtained solid product was treated with 1 mol / L hydrochloric acid. The hydrochloric acid was slowly added dropwise while stirring on a magnetic stirrer. The amount of dilute acid was 100 times the mass of the solid product. The treatment time was 2 h until no bubbles were generated. Then, the product was repeatedly washed with deionized water and centrifuged at 8000 rpm until the supernatant was neutral as measured by pH paper. The product was then washed with ethanol and centrifuged twice. The product was then placed in a vacuum oven and dried at 85°C for 20 h to obtain the final product, a shell-structured Si / Mg2SiO4 composite material.

[0042] Weigh 0.3 g of Si / Mg2SiO4 powder and 0.2 g of maltodextrin into a glass weighing bottle, add about 1.5 ml of deionized water, and sonicate at high speed (1200 rpm, 70% ultrasonic power) for half an hour. Once the solution is uniformly dispersed, a suspension is obtained. Dispense the suspension into centrifuge tubes, rapidly freeze them with liquid nitrogen, transfer them to a vacuum freeze dryer, and dry for 24 h to obtain a shell-structured Si / Mg2SiO4@C composite anode precursor. Spread the prepared precursor material evenly in a ceramic boat, push it to the center of a tube furnace, introduce argon gas, and heat to 800℃ at a heating rate of 5℃ / min, hold for 2 h, then cool to room temperature at the same rate. Remove the product from the ceramic boat using heat-resistant gloves; this is the shell-structured Si / Mg2SiO4@C composite anode material.

[0043] The XRD diffraction pattern of the sample showed many impurity peaks, and the calculated content of Mg2SiO4 in the shell structure Si / Mg2SiO4 composite material was 35%.

[0044] The battery performance results assembled from the shell structure Si / Mg2SiO4@C composite anode material are shown in Table 1.

[0045] Example 4 1.0 g of shell-structured SiO2 and 1.0 g of magnesium powder were weighed in a 1:1 mass ratio and uniformly ground and mixed in an argon-filled glove box. The mixed powder was then loaded into a sealed reactor. The sealed reactor was placed in a tube furnace and heated to 650°C at a rate of 5°C / min under an argon atmosphere, held at that temperature for 2 h, and then cooled to room temperature at a rate of 5°C / min to obtain a solid product.

[0046] The obtained solid product was treated with 1 mol / L hydrochloric acid. The hydrochloric acid was slowly added dropwise while stirring on a magnetic stirrer. The amount of dilute acid was 100 times the mass of the solid product. The treatment time was 2 h until no bubbles were generated. Then, the product was repeatedly washed with deionized water and centrifuged at 8000 rpm until the supernatant was neutral as measured by pH paper. The product was then washed with ethanol and centrifuged twice. The product was then placed in a vacuum oven and dried at 85°C for 20 h to obtain the final product, a shell-structured Si / Mg2SiO4 composite material.

[0047] Weigh 0.3 g of Si / Mg2SiO4 powder and 0.2 g of maltodextrin into a glass weighing bottle, add about 1.5 ml of deionized water, and sonicate at high speed (1200 rpm, 70% ultrasonic power) for half an hour. Once the solution is evenly dispersed, a suspension is obtained. Dispense the suspension into centrifuge tubes, rapidly freeze them with liquid nitrogen, transfer them to a vacuum freeze dryer, and dry for 24 h to obtain a shell-structured Si / Mg2SiO4@C composite anode precursor. Spread the prepared precursor material evenly in a ceramic boat, push it to the center of a tube furnace, introduce argon gas, and heat to 800℃ at a heating rate of 5℃ / min, hold for 2 h, then cool to room temperature at the same rate. Remove the product from the ceramic boat using heat-resistant gloves; this is the shell-structured Si / Mg2SiO4@C composite anode material.

[0048] The Mg2SiO4 content in the shell-structured Si / Mg2SiO4 composite material was found to be 27% by calculation based on the XRD diffraction pattern.

[0049] The battery performance results assembled from the shell structure Si / Mg2SiO4@C composite anode material are shown in Table 1.

[0050] Example 5 1.0 g of shell-structured SiO2 and 1.0 g of magnesium powder were weighed out in a 1:1 mass ratio and uniformly ground and mixed in an argon-filled glove box. The mixed powder was then placed into a sealed reactor. The sealed reactor was placed in a tube furnace and heated to 650°C at a rate of 5°C / min under an argon atmosphere, and held at that temperature for 5 h. The mixture was then cooled to room temperature at a rate of 5°C / min to obtain a solid product.

[0051] The obtained solid product was treated with 1 mol / L hydrochloric acid. The hydrochloric acid was slowly added dropwise while stirring on a magnetic stirrer. The amount of dilute acid was 100 times the mass of the solid product. The treatment time was 2 h until no bubbles were generated. Then, the product was repeatedly washed with deionized water and centrifuged at 8000 rpm until the supernatant was neutral as measured by pH paper. The product was then washed with ethanol and centrifuged twice. The product was then placed in a vacuum oven and dried at 85°C for 20 h to obtain the final product, a shell-structured Si / Mg2SiO4 composite material.

[0052] Weigh 0.4 g of Si / Mg2SiO4 powder and 0.27 g of maltodextrin into a glass weighing bottle, add about 2 ml of deionized water, and sonicate at high speed (1200 rpm, 70% ultrasonic power) for half an hour. Once the solution is uniformly dispersed, a suspension is obtained. Dispense the suspension into centrifuge tubes, rapidly freeze them with liquid nitrogen, transfer them to a vacuum freeze dryer, and dry for 24 h to obtain a shell-structured Si / Mg2SiO4@C composite anode precursor. Spread the prepared precursor material evenly in a ceramic boat, push it to the center of a tube furnace, introduce argon gas, and heat to 800℃ at a heating rate of 5℃ / min, hold for 2 h, then cool to room temperature at the same rate. Remove the product from the ceramic boat using heat-resistant gloves; this is the shell-structured Si / Mg2SiO4@C composite anode material.

[0053] The Mg2SiO4 content in the shell-structured Si / Mg2SiO4 composite material was calculated to be 30.5% based on the XRD diffraction pattern.

[0054] The battery performance results assembled from the shell structure Si / Mg2SiO4@C composite anode material are shown in Table 1.

[0055] Example 6 1.0 g of shell-structured SiO2 and 0.4 g of magnesium powder were weighed out in a mass ratio of 1:0.4. They were then uniformly ground and mixed in an argon-filled glove box. The mixed powder was then placed in a sealed reactor. The sealed reactor was placed in a tube furnace, and the temperature was increased to 650°C at a rate of 5°C / min under an argon atmosphere and held for 5 h. The mixture was then cooled to room temperature at a rate of 5°C / min to obtain a solid product.

[0056] The obtained solid product was treated with 1 mol / L hydrochloric acid. The hydrochloric acid was slowly added dropwise while stirring on a magnetic stirrer. The amount of dilute acid was 100 times the mass of the solid product. The treatment time was 2 h until no bubbles were generated. Then, the product was repeatedly washed with deionized water and centrifuged at 8000 rpm until the supernatant was neutral as measured by pH paper. The product was then washed with ethanol and centrifuged twice. The product was then placed in a vacuum oven and dried at 85°C for 20 h to obtain the final product, a shell-structured Si / Mg2SiO4 composite material.

[0057] Weigh 0.4 g of Si / Mg2SiO4 powder and 0.27 g of maltodextrin into a glass weighing bottle, add about 2 ml of deionized water, and sonicate at high speed (1200 rpm, 70% ultrasonic power) for half an hour. Once the solution is uniformly dispersed, a suspension is obtained. Dispense the suspension into centrifuge tubes, rapidly freeze them with liquid nitrogen, transfer them to a vacuum freeze dryer, and dry for 24 h to obtain a shell-structured Si / Mg2SiO4@C composite anode precursor. Spread the prepared precursor material evenly in a ceramic boat, push it to the center of a tube furnace, introduce argon gas, and heat to 800℃ at a heating rate of 5℃ / min, hold for 2 h, then cool to room temperature at the same rate. Remove the product from the ceramic boat using heat-resistant gloves; this is the shell-structured Si / Mg2SiO4@C composite anode material.

[0058] The Mg2SiO4 content in the shell-structured Si / Mg2SiO4 composite material was calculated to be 45.6% based on the XRD diffraction pattern.

[0059] The battery performance results assembled from the shell structure Si / Mg2SiO4@C composite anode material are shown in Table 1.

[0060] Example 7 1.0 g of shell-structured SiO2 and 1.2 g of magnesium powder were weighed out in a mass ratio of 1:1.2 and uniformly ground and mixed in an argon-filled glove box. The mixed powder was then placed into a sealed reactor. The sealed reactor was placed in a tube furnace and heated to 650°C at a rate of 5°C / min under an argon atmosphere, and held at that temperature for 5 h. The mixture was then cooled to room temperature at a rate of 5°C / min to obtain a solid product.

[0061] The obtained solid product was treated with 1 mol / L hydrochloric acid. The hydrochloric acid was slowly added dropwise while stirring on a magnetic stirrer. The amount of dilute acid was 120 times the mass of the solid product. The treatment time was 2 h until no bubbles were generated. Then, the product was repeatedly washed with deionized water and centrifuged at 8000 rpm until the supernatant was neutral as measured by pH paper. The product was then washed with ethanol and centrifuged twice. The product was then placed in a vacuum oven and dried at 85°C for 20 h to obtain the final product, a shell-structured Si / Mg2SiO4 composite material.

[0062] Weigh 0.4 g of Si / Mg2SiO4 powder and 0.27 g of maltodextrin into a glass weighing bottle, add approximately 2 ml of deionized water, and sonicate at high speed (1200 rpm, 70% ultrasonic power) for half an hour. Once the solution is uniformly dispersed, a suspension is obtained. Dispense the suspension into centrifuge tubes, rapidly freeze them with liquid nitrogen, and transfer them to a vacuum freeze dryer. Dry for 24 h to obtain a shell-structured Si / Mg2SiO4@C composite anode precursor. Spread the prepared precursor material evenly in a ceramic boat, push it to the center of a tube furnace, introduce argon gas, and heat to 800℃ at a heating rate of 5℃ / min. Hold at this temperature for 2 h, then cool to room temperature at the same rate. Remove the product from the ceramic boat using heat-resistant gloves; this is the shell-structured Si / Mg2SiO4@C composite anode material.

[0063] The Mg2SiO4 content in the shell-structured Si / Mg2SiO4 composite material was found to be 20.7% by calculation based on the XRD diffraction pattern.

[0064] The battery performance results assembled from the shell structure Si / Mg2SiO4@C composite anode material are shown in Table 1.

[0065] Comparative Example 1 The difference between this comparative example and Example 5 is that the obtained solid product was treated with 5 mol / L hydrochloric acid. The hydrochloric acid was rapidly added dropwise while stirring on a magnetic stirrer. The amount of dilute acid used was 25 times the mass of the solid product, and the treatment time was 0.5 h until no more bubbles were generated. The rest was the same as in Example 5.

[0066] The Mg2SiO4 content in the shell structure Si / Mg2SiO4 composite material obtained in this embodiment was found to be 28.4% by calculation based on the XRD diffraction pattern.

[0067] The battery performance results assembled from the Si / Mg2SiO4@C composite anode material with the described shell structure are shown in Table 1. In this comparative example, due to inappropriate control of acid concentration and addition rate during dilute acid treatment, the final shell structure was incomplete, with some silicon not encapsulated by the three-dimensional framework and exposed to the outside. Furthermore, the particle uniformity was poor, and agglomeration was severe, leading to a decrease in the reversible capacity of the Si / Mg2SiO4@C composite anode material.

[0068] Table 1 In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A lithium ion battery shell layer structure Si / Mg2Si04 composite material based on magnesium thermal reduction, characterized by: The material is prepared by the following method, the steps of which include: (1) In a protective gas atmosphere, SiO2 with shell structure is mixed evenly with magnesium powder to obtain a mixed powder; (2) The mixed powder is loaded into a sealed reaction vessel, placed in a tube furnace, and reduced at high temperature in a protective gas atmosphere. After cooling, a solid product is obtained. (3) The solid product was treated with dilute acid, then washed with deionized water and ethanol, centrifuged and dried to obtain a shell structure Si / Mg2SiO4 composite material. In step (1), the shell structure SiO2 is a submicron-sized spherical shell structure material with an internal cavity, and the shell thickness is 150nm~250nm; the mass ratio of the shell structure SiO2 to the metallic magnesium powder is 1:0.4~1.

5. In step (2), the high-temperature reaction temperature is 630℃~750℃, and the holding time is 1~15h; In step (3), dilute acid is slowly added dropwise while stirring. The dilute acid is one or more of hydrochloric acid, sulfuric acid, and nitric acid. The concentration of the dilute acid is in the range of 0.5 mol / L to 1 mol / L, the acid treatment time is 2 h to 3 h, and the amount of dilute acid used is 100 to 200 times the mass of the solid product. The composite material has a particle size of 600-700 nm and an internal cavity. The shell consists of a reduced Si layer and a Mg2SiO4 layer that encapsulates the Si particles in a three-dimensional network framework. The total thickness of the shell is 10-15 nm, and Mg2SiO4 accounts for 20%-45% of the total mass of the composite material.

2. A Si / Mg2Si04 composite material based on a magnesium thermal reduction of the shell structure of lithium-ion batteries according to claim 1, characterized by: In step (1), the mass ratio of the shell structure SiO2 to the magnesium powder is 1:0.8~1.

2.

3. A Si / Mg2Si04 composite material for a lithium-ion battery shell structure based on magnesium thermal reduction according to claim 1, characterized in that: In step (2), the high-temperature reaction temperature is 650℃~700℃ and the heat preservation time is 4~10h.

4. A Si / Mg2Si04 composite material for a lithium-ion battery shell structure based on magnesium thermal reduction according to claim 1, characterized in that: In step (2), the heating rate is 2℃ / min to 15℃ / min and the cooling rate is 1℃ / min to 10℃ / min.

5. A Si / Mg2Si04 composite material for lithium-ion battery shell structure based on magnesium thermal reduction according to claim 1, characterized in that: In step (3), the centrifugation speed is 8000rpm~10000rpm; the drying method is vacuum drying, the temperature is 75℃~95℃, and the time is 12h~24h.

6. A Si / Mg2Si04 composite material for lithium-ion battery shell structure based on magnesium thermal reduction according to claim 1, characterized in that: The protective gas is nitrogen or an inert gas.

7. An application of the Si / Mg2SiO4 composite material for lithium-ion battery shell structure based on magnesium thermal reduction as described in any one of claims 1 to 6, characterized in that: The composite material is coated with a carbon layer to obtain a Si / Mg2SiO4@C composite anode material.

8. A lithium-ion battery, characterized in that: The negative electrode material of the battery is a Si / Mg2SiO4@C composite negative electrode material as described in claim 7.

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