Magnesium-silicon coated silicon-carbon composite material, preparation method thereof and lithium ion battery

Abstract

The invention relates to a magnesium-silicon coated silicon-carbon composite material, a preparation method thereof and a lithium ion battery. The preparation method comprises the following steps: uniformly mixing a carbon source and a metal activator according to a mass ratio of the carbon source to the metal activator to a heteroatom compound of 100: (10-30): (1-5), drying to obtain a dried substance, and activating and carbonizing the dried substance in an inert atmosphere to obtain modified porous carbon; adding the modified porous carbon into a chlorosilane solution according to the mass ratio of the modified porous carbon to chlorosilane to magnesium of 100: (100-200): (1-10), heating and depositing nano silicon; magnesium steam and the modified porous carbon are introduced for deposition, and a magnesium-silicon alloy coated silicon-carbon precursor material is obtained; and transferring the precursor material into a tubular furnace, and introducing a carbon source / heteroatom mixed gas for deposition to obtain the heteroatom and magnesium-silicon alloy coated silicon-carbon composite material. The invention provides a magnesium-silicon coated silicon-carbon composite material with low expansion and high electronic conductivity.

Description

Technical Field

[0001] The present invention relates to the technical field of application materials for lithium-ion batteries, and particularly relates to a magnesium-silicon-coated silicon-carbon composite material, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] The novel silicon-carbon material consists of a core composed of porous carbon and nano-silicon deposited in the pores, and is coated with amorphous carbon on its surface. Due to the porous structure of the porous carbon itself, its electron conductivity is poor, and the contact between the nano-silicon and the porous carbon is poor, resulting in a large interfacial impedance and a reduction in power performance. At present, the main measures to reduce expansion are to increase the pores to reserve a larger expansion space for silicon expansion, and the main measures to improve power are to reduce the interfacial impedance between materials and to dope metal or compound materials with high electron conductivity to improve the electron or ion conductivity of the materials.

[0003] The existing patent (application number CN202211703916.4) discloses a composite material of silicon-carbon material doped with porous metal, a preparation method thereof and an application. The main preparation method is to prepare a porous metal compound; place it in an electrolyte containing a silane coupling agent and an organic lithium salt for electrochemical deposition, washing, and drying to obtain a silicon-doped porous metal compound; reduce it in a reducing atmosphere, and then carry out chemical vapor deposition in a carbon-nitrogen mixed gas atmosphere to obtain a composite material of silicon-carbon material doped with porous metal. Although the prepared material can improve the electron conductivity of the silicon-carbon material and reduce expansion, its expansion is large, the improvement range of electron conductivity is limited, and the preparation process is complex.

[0004] Therefore, the prior art needs to be improved. Summary of the Invention

[0005] In the prior art, although the electron conductivity of the silicon-carbon material can be improved and the expansion can be reduced, its expansion is large, the improvement range of electron conductivity is limited, and the preparation process is complex. Therefore, it is necessary to provide a magnesium-silicon-coated silicon-carbon composite material, a preparation method thereof, and a lithium-ion battery to solve the above problems.

[0006] To achieve the above object, in the first aspect, the present invention provides a preparation method of a magnesium-silicon-coated silicon-carbon composite material, which includes the following specific steps: S1. According to the mass ratio of carbon source: metal activator: heteroatom compound = 100: (10~30): (1~5), mix the carbon source and the metal activator evenly, dry to obtain a dried product, activate the dried product in an inert atmosphere, and carry out carbonization after activation to obtain a modified porous carbon; S2. According to the mass ratio of modified porous carbon: chlorosilane: magnesium = 100: (100 - 200): (1 - 10), add the modified porous carbon to the chlorosilane solution, heat and deposit nano-silicon; then introduce magnesium vapor to deposit with the modified porous carbon to obtain a magnesium-silicon alloy-coated silicon-carbon precursor material; S3. Transfer the magnesium-silicon alloy-coated silicon-carbon precursor material to a tubular furnace, introduce a carbon source / heteroatom mixed gas for deposition to obtain a heteroatom and magnesium-silicon alloy-coated silicon-carbon composite material.

[0007] In one implementation, the carbon source is any one of urea-formaldehyde resin, polyimide resin, benzoxazine resin, and polyarylacetylene resin; the metal activator is any one of LiOH, LiCO3, Mg(OH)2, MgCO3, and MgCl2; the heteroatom compound is any one of melamine, urea, and dopamine.

[0008] In one implementation, in S1, the activation specifically includes: introducing carbon dioxide and activating at a temperature of 300 - 500 °C for 1 - 6 h; the carbonization specifically includes: heating to a temperature of 700 - 1100 °C for carbonization for 1 - 6 h to obtain modified porous carbon.

[0009] In one implementation, in S2, heating and depositing nano-silicon specifically includes: evacuating to a vacuum degree of 0.1 - 0.5 Mpa, heating to 300 - 500 °C to deposit nano-silicon in the pores of the modified porous carbon.

[0010] In one implementation, in S2, introducing magnesium vapor to deposit with the modified porous carbon specifically includes: heating magnesium to 1200 - 1500 °C in a vacuum furnace to generate magnesium vapor, introducing it into the reaction kettle, with a flow rate of 10 - 100 ml / min, and depositing at a temperature of 700 - 900 °C for 30 - 300 min.

[0011] In one implementation, in S2, the chlorosilane includes any one of dichlorosilane, trichlorosilane, tetrachlorosilane, trimethylchlorosilane, vinyltrichlorosilane, and triisopropylchlorosilane.

[0012] In one implementation, in S3, it specifically includes: transferring the magnesium-silicon alloy-coated silicon-carbon precursor material to a tubular furnace, introducing an inert gas to discharge the air in the tube, heating to 700 - 1000 °C, and introducing the carbon source / heteroatom mixed gas for 0.5 - 2 h to obtain a heteroatom and magnesium-silicon alloy-coated silicon-carbon composite material; where the volume ratio of the carbon source: heteroatom gas in the mixed gas is 10: (1 - 5), and the flow rate is 100 - 500 ml / min.

[0013] In one implementation, in S3, the heteroatom gas includes any one of ammonia, nitrogen trifluoride, phosphine, and sulfur dioxide.

[0014] In a second aspect, the present invention also provides a magnesium-silicon-coated silicon-carbon composite material, which is prepared by the preparation method of the magnesium-silicon-coated silicon-carbon composite material described in any one of the above.

[0015] In a third aspect, the present invention also provides a lithium-ion battery, which uses the above magnesium-silicon-coated silicon-carbon composite material as the negative electrode.

[0016] Beneficial effects: In the preparation method of the magnesium-silicon-coated silicon-carbon composite material provided by the present invention, the electronic conductivity of the material is improved by metal-doped porous carbon, and then the structural stability of the material is improved by forming a deposited magnesium-silicon alloy transition layer with magnesium vapor and silicon, and amorphous carbon is deposited on its outer layer to improve the coating integrity and high-temperature storage performance of the material. Combining the use of modified porous carbon and magnesium-silicon alloy, multiple performance improvements of the magnesium-silicon-coated silicon-carbon composite material in the application of lithium-ion batteries are achieved, including specific capacity, conductivity, cycle stability, rate performance, and safety, providing a magnesium-silicon-coated silicon-carbon composite material with low expansion and high power. Description of the Drawings

[0017] Figure 1 is a flowchart of the steps of the preparation method of the magnesium-silicon-coated silicon-carbon composite material provided by the present invention; Figure 2 is an SEM image of the magnesium-silicon-coated silicon-carbon composite material prepared in Example 1.

[0018] The realization, functional characteristics, and advantages of the objectives of the present invention will be further described in conjunction with the embodiments and with reference to the drawings. Detailed Embodiments

[0019] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the descriptions of the above terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms are not necessarily directed to the same embodiment or example. Moreover, the technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0020] Refer to Figure 1 , Figure 1It is the process flow diagram of the preparation method of the magnesium-silicon-coated silicon-carbon composite material provided by the present invention. The present invention provides a preparation method of a magnesium-silicon-coated silicon-carbon composite material, which includes the following specific steps: S1. According to the mass ratio of carbon source: metal activator: heteroatom compound = 100: (10-30): (1-5), mix the carbon source and the metal activator evenly, dry to obtain a dried product, activate the dried product under an inert atmosphere, and perform carbonization after activation to obtain modified porous carbon; S2. According to the mass ratio of modified porous carbon: chlorosilane: magnesium = 100: (100-200): (1-10), add the modified porous carbon to the chlorosilane solution, heat and deposit nano-silicon; then introduce magnesium vapor to deposit with the modified porous carbon to obtain a magnesium-silicon alloy-coated silicon-carbon precursor material; S3. Transfer the magnesium-silicon alloy-coated silicon-carbon precursor material to a tube furnace, introduce a carbon source / heteroatom mixed gas for deposition to obtain a silicon-carbon composite material coated with heteroatoms and a magnesium-silicon alloy.

[0021] Specifically, in S1, the carbon source is any one of urea-formaldehyde resin, polyimide resin, benzoxazine resin and polyarylacetylene resin. The metal activator is any one of LiOH, LiCO3, Mg(OH)2, MgCO3 and MgCl2. The heteroatom compound is any one of melamine, urea and dopamine.

[0022] In S1, the activation specifically includes: introducing carbon dioxide and activating at a temperature of 300-500 °C for 1-6 h; the carbonization specifically includes: heating to a temperature of 700-1100 °C for carbonization for 1-6 h to obtain modified porous carbon. By controlling the temperature and time, porous carbon with a stable structure can be obtained, which helps to alleviate the structural damage caused by the volume expansion of silicon during charge and discharge.

[0023] In S1, by using specific ratios of carbon source, metal activator and heteroatom compound, through mixing, drying, activation and carbonization, modified porous carbon is prepared. By optimizing the activation and carbonization conditions, the pore structure of the porous carbon can be effectively regulated, and its electronic conductivity can be significantly improved. The activation and carbonization processes under an inert atmosphere can reduce the generation of unwanted by-products and enhance the safety of the preparation process. Using the modified porous carbon as a substrate and combining the deposition of nano-silicon increases the specific surface area and porosity of the material, which helps to improve the intercalation and deintercalation efficiency of lithium ions in the anode material.

[0024] Specifically, in S2, heating and depositing nano-silicon specifically includes: evacuating to a vacuum degree of 0.1~0.5 Mpa, heating to 300~500 °C to deposit nano-silicon in the pores of the modified porous carbon. Passing magnesium vapor to deposit with the modified porous carbon specifically includes: heating magnesium to 1200~1500 °C in a vacuum furnace to generate magnesium vapor, passing it into a reaction kettle, with a flow rate of 10~100 ml / min, and depositing for 30~300 min at a temperature of 700~900 °C. Through the deposition process of the tubular furnace, the material preparation process is easier to control, forming a uniform magnesium-silicon alloy coating layer, which can improve the conductivity of the material and the overall conductivity of the battery. In this step, through the doping of magnesium, the conductivity and structural stability of the material are further improved. Further, the chlorosilane includes any one of dichlorosilane, trichlorosilane, tetrachlorosilane, trimethylchlorosilane, vinyltrichlorosilane, and triisopropylchlorosilane.

[0025] In S3, it specifically includes: transferring the magnesium-silicon alloy-coated silicon-carbon precursor material to a tubular furnace, passing an inert gas to discharge the air in the tube, heating to 700~1000 °C, and passing a carbon source / heteroatom mixed gas for 0.5~2 h to obtain a heteroatom and magnesium-silicon alloy-coated silicon-carbon composite material; where the volume ratio of the mixed gas is carbon source: heteroatom gas = 10: (1~5), and the passing flow rate is 100~500 ml / min.

[0026] Further, in S3, the heteroatom gas includes any one of ammonia, nitrogen trifluoride, phosphine, and sulfur dioxide. The introduction of heteroatoms forms a doping effect in the carbon material, optimizes the interfacial properties of the material, significantly reduces the interfacial impedance, and further enhances the mechanical strength and chemical stability of the material. At this time, due to the formation of the magnesium-silicon alloy and its uniform distribution in the silicon-carbon composite material, it helps to improve the fast charge and discharge ability of the material, and the synergistic effect of heteroatoms and the magnesium-silicon alloy can improve the electron mobility of the material, thereby enhancing the rate performance of the battery.

[0027] Example 1 A preparation method of a magnesium-silicon-coated silicon-carbon composite material includes the following steps: S1. Mix 100 g of urea-formaldehyde resin, 20 g of LiOH, and 3 g of melamine evenly, dry to obtain a dried product, under an argon inert atmosphere, pass carbon dioxide gas (flow rate 100 ml / min), and activate at a temperature of 400 °C for 3 h, then heat to a temperature of 950 °C and carbonize for 3 h to obtain modified porous carbon; S2. Add 100 g of modified porous carbon to 150 g of silicon tetrachloride solution, add it to a reaction kettle, evacuate to a vacuum degree of 0.3 Mpa, heat to 400 °C, and deposit nanosilicon in the pores of the modified porous carbon; then heat 1 g of magnesium to 1300 °C in a vacuum furnace to generate magnesium vapor, introduce it into the reaction kettle at a flow rate of 50 ml / min, and deposit for 120 min in an environment with a temperature of 800 °C to form a magnesium-silicon alloy-coated silicon-carbon precursor material on its surface; S3. Transfer the magnesium-silicon alloy-coated silicon-carbon precursor material to a tubular furnace. First, introduce argon inert gas to discharge the air in the tube, then heat to 950 °C, and introduce a methane / ammonia mixed gas (volume ratio, methane: ammonia = 10:3, flow rate 300 ml / min) for 1 h to obtain a heteroatom- and magnesium-silicon alloy-coated silicon-carbon composite material.

[0028] Example 2 A preparation method of a magnesium-silicon-coated silicon-carbon composite material, comprising the following steps: S1. Mix 100 g of polyimide resin, 10 g of LiCO3, and 1 g of urea evenly, dry to obtain a dried product, introduce carbon dioxide gas (flow rate 100 ml / min) under an inert atmosphere, activate at a temperature of 300 °C for 6 h, and then carbonize at a temperature of 700 °C for 6 h to obtain modified porous carbon; S2. Add 100 g of modified porous carbon to 100 g of trichlorosilane solution, add it to a reaction kettle, evacuate to a vacuum degree of 0.1 Mpa, heat to 300 °C, and deposit nanosilicon in the pores of the modified porous carbon; then heat 1 g of magnesium to 1200 °C in a vacuum furnace to generate magnesium vapor, introduce it into the reaction kettle at a flow rate of 10 ml / min, and deposit for 300 min in an environment with a temperature of 700 °C to form a magnesium-silicon alloy-coated silicon-carbon precursor material on its surface; S3. Transfer the magnesium-silicon alloy-coated silicon-carbon precursor material to a tubular furnace. First, introduce argon inert gas to discharge the air in the tube, then heat to 700 °C, and introduce an acetylene / nitrogen trifluoride mixed gas (volume ratio, acetylene: nitrogen trifluoride = 10:1, flow rate 100 ml / min) for 2 h to obtain a heteroatom- and magnesium-silicon alloy-coated silicon-carbon composite material.

[0029] Example 3 A preparation method of a magnesium-silicon-coated silicon-carbon composite material, comprising the following steps: S1. Mix 100 g of polyarylacetylene resin, 30 g of MgCO3, and 5 g of dopamine evenly, dry to obtain a dried product, introduce carbon dioxide (flow rate 100 ml / min) under an argon inert atmosphere, activate at a temperature of 500 °C for 1 h, and then carbonize at a temperature of 1100 °C for 1 h to obtain modified porous carbon; S2. Add 100 g of modified porous carbon to 200 g of trimethylchlorosilane solution, add it to the reaction kettle, evacuate to a vacuum degree of 0.5 Mpa, heat to 500 °C, and deposit nano-silicon in the pores of the modified porous carbon; then heat 10 g of magnesium to 1500 °C in a vacuum furnace to generate magnesium vapor, and introduce it into the reaction kettle at a flow rate of 100 ml / min, and deposit for 30 min at a temperature of 900 °C to form a magnesium-silicon alloy-coated silicon-carbon precursor material on its surface; S3. Transfer the magnesium-silicon alloy-coated silicon-carbon precursor material to a tubular furnace. First, introduce argon inert gas to discharge the air in the tube, then heat to 1000 °C, and introduce a mixture of ethylene / sulfur dioxide (volume ratio, ethylene: sulfur dioxide = 10:5, flow rate 500 ml / min) for 0.5 h to obtain a heteroatom and magnesium-silicon alloy-coated silicon-carbon composite material.

[0030] Comparative Example 1: The difference from Example 1 is that LiOH and melamine are not added, and the others are the same as Example 1.

[0031] Comparative Example 2: The difference from Example 1 is that magnesium vapor deposition is not carried out in S2, and the others are the same as Example 1.

[0032] 1) SEM test Figure 2 Figure 18 is the SEM image of the magnesium-silicon-coated silicon-carbon composite material prepared in Example 1. It can be seen from the figure that the particle size of the material is between 5 - 10 μm, the material presents a granular structure, and there are pore structures and slight adhesion on the surface.

[0033] 2) Physical and chemical and coin cell tests: According to the method in the national standard GB / T 38823-2020 "Silicon Carbon", the tap density, specific surface area, silicon crystal grains, and specific capacity of each silicon-carbon composite material obtained in Examples 1 - 3 and Comparative Examples 1 - 2 were respectively tested; the powder resistivity was measured for the material before the four-probe test; the coating integrity of its powder material was tested by XPS. The test results are shown in Table 1 below.

[0034] Coin cell test: Each silicon-carbon composite material obtained in Examples 1 - 3 and Comparative Examples 1 - 2 was used as the active material of the battery negative electrode plate, and 9 coin cells were respectively prepared and assembled, and were sequentially marked as A1, A2, A3, B1, B2; Among them, the specific preparation process of each button cell is as follows: Prepare the battery negative electrode sheet: Add a binder, a conductive agent, and a solvent to each of the silicon-carbon composite materials (as the active material of the battery negative electrode sheet) corresponding to Examples 1 to 3 and Comparative Examples 1 to 2, stir to make a slurry, coat it on a copper foil, and obtain each battery negative electrode sheet through drying and rolling; among them, the binder uses LA132 binder, the conductive agent uses SP (conductive carbon black), the solvent is secondary distilled water, and the ratio is: silicon-carbon composite material: SP: LA132: secondary distilled water = 95g: 1g: 4g: 220mL; Prepare the button cell: The electrolyte uses a LiPF6 solution. Among them, the concentration of LiPF6 is 1.3 mol / L, and the solvent used is a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DMC) with a weight ratio of 1:1; Use a lithium metal sheet as the counter electrode, the separator uses polyethylene (PE), the simulated battery assembly is carried out in a glove box filled with argon, and the electrochemical performance is carried out on a Wuhan Blue Electric CT2001A battery tester. The test conditions are: the charge-discharge voltage range is 0.005V to 2.0V, and the charge-discharge rate is 0.1C; At the same time, test the charging DCR (0.1C, 50% SOC) and cycle performance of its button cell (the test conditions are: 0.2C / 0.2C, 100-week cycle), and test the expansion of the negative electrode sheet of its fully charged button cell; The test results are shown in Table 1 below.

[0035] Table 1. Test data table of silicon-carbon composite materials of each group and the button cells prepared therefrom It can be seen from Table 1 above that the magnesium-silicon-coated silicon-carbon composite materials provided in Examples 1 to 3 of this application have a high specific surface area, and the button cells prepared therefrom have excellent first discharge specific capacity, first efficiency, rate performance, and cycle performance, especially the result of its full charge expansion is significantly reduced; Through this experimental result, it shows that the reaction of magnesium vapor and nanosilicon at high temperature generates a magnesium-silicon alloy to improve the structural stability and specific capacity of the material, and can restrain the expansion of nanosilicon during the charge-discharge process.

[0036] 3) Soft-pack battery test: Dope 90% artificial graphite into each of the silicon-carbon composite materials obtained in Examples 1 to 3 and Comparative Examples 1 to 2 as the negative electrode material (i.e., the negative electrode sheet), and use the ternary material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2 was used as the cathode material, electrolyte, and separator to assemble a 5 Ah soft-pack battery; among them, the separator of the soft-pack battery was Celgard 2400, and the electrolyte was a LiPF6 solution. The solvent of the LiPF6 solution was a mixed solution of EC and DEC with a volume ratio of 1:1, and the concentration of LiPF6 was 1.3 mol / L; the soft-pack batteries prepared from the silicon-carbon composite materials corresponding to Examples 1 to 3 and Comparative Examples 1 to 2 were respectively marked as C1, C2, C3, D1, D2 and their corresponding negative electrode sheets of each battery, and the liquid absorption capacity and sheet resistivity of each negative electrode sheet were tested. The test results are shown in Table 2 below; Among them, the test process of the liquid absorption capacity was as follows: a 1 mL burette was used, and V mL of electrolyte was sucked. The electrolyte was dropped on the surface of the negative electrode sheet and timed until the electrolyte was completely absorbed, and the time t was recorded; and the sheet resistivity of the electrode was tested by a membrane resistance tester.

[0037] Table 2. Statistical table of the liquid absorption capacity and sheet resistivity of the negative electrode sheets of each group It can be seen from Table 2 above that the liquid absorption capacity and sheet resistivity of the negative electrode sheets prepared by using the magnesium-silicon-coated silicon-carbon composite materials provided in Examples 1 to 3 of the present application are significantly better than those of Comparative Examples 1 to 2. The main reason is that: the specific surface area of the silicon-carbon composite material provided in this example can significantly improve the liquid absorption and retention capacity of the electrode sheet and its low powder resistivity, and reduce the sheet resistivity of the electrode.

[0038] The present application also tested the rate performance, cycle performance, and high-temperature storage performance of each soft-pack battery. The test results are shown in Table 3 and Table 4 respectively. The conditions for the rate performance test were: The charge-discharge voltage range was 2.5 - 4.2 V, the temperature was 25 ± 3.0 °C, and each coin cell was charged at 1.0C, 3.0C, and 5.0C respectively, and discharged at 1.0C; The conditions for high-temperature storage were: First, the capacity of the battery was tested at room temperature as A1. Then, the battery was left standing at 60 °C for 30 days, and its capacity was tested as A2. Then, the battery was charged to a full charge state, and its capacity was tested as A3. Then, the state of charge of the battery was calculated = (A1 - A2) / A1 * 100%, and the capacity recovery of the battery was calculated = (A1 - A3) / A1 * 100%.

[0039] Table 3. Test table of the rate performance and cycle performance of the soft-pack batteries prepared by each group As can be seen from Table 3 above, the rate charge performance of the soft-pack batteries fabricated using the magnesium-silicon-coated silicon-carbon composite materials provided in Embodiments 1 to 3 of the present application is significantly better than that of Comparative Examples 1 to 3. That is, the soft-pack batteries fabricated in the embodiments of the present application have shorter and faster charging times. The reason is that the embodiments of the present application have low powder conductivity and high specific surface area, which improve the rate performance of the materials.

[0040] Table 4. High-temperature storage performance test table of soft-pack batteries prepared in each group As can be seen from Table 4 above, the high-temperature storage performance of the soft-pack batteries fabricated using the magnesium-silicon-coated silicon-carbon composite materials provided in Embodiments 1 to 3 of the present application is better than that of Comparative Examples 1 to 2. The reason is that the carbon-silicon composite material provided in the present application has good structural stability, low full-charge expansion, which improves the cycling performance of the material, and the surface is coated with a magnesium-silicon alloy to reduce the contact probability between the inner core silicon and the electrolyte, thereby improving the high-temperature storage performance.

[0041] In summary, in the preparation method of the magnesium-silicon-coated silicon-carbon composite material provided by the present invention, by doping a metal activator and a heteroatom compound in a porous carbon precursor (resin), the electronic conductivity of the material is improved, the defects of the material are reduced, the side reactions of the inner core are improved, and the first efficiency and storage performance are enhanced; reacting magnesium vapor with nanosilicon at high temperature to form a magnesium-silicon alloy can improve the structural stability and specific capacity of the material and restrain the expansion of nanosilicon during charge and discharge; depositing a heteroatom-doped amorphous carbon on the surface of the magnesium-silicon alloy-coated silicon-carbon precursor material by chemical vapor deposition can improve the electronic conductivity of the material and reduce the defects to enhance the first efficiency; by combining the double outer layer structures of the magnesium-silicon alloy and the heteroatom-doped amorphous carbon to coat the silicon-carbon material, the expansion of nanosilicon during charge and discharge is reduced, and multiple performance improvements of the silicon-carbon composite material in the application of lithium-ion batteries are achieved, including specific capacity, conductivity, cycle stability, rate performance, and safety.

[0042] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the specification and drawings of the present invention, or directly or indirectly applied to other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for preparing a magnesium-silicon-coated silicon-carbon composite material, characterized in that: The specific steps include: S1. According to the mass ratio of carbon source: metal activator: heteroatom compound = 100: (10-30): (1-5), the carbon source and the metal activator are uniformly mixed, dried to obtain a dried product, the dried product is activated under an inert atmosphere, and after activation, carbonized to obtain modified porous carbon; S2, modifying porous carbon according to the mass ratio of chlorosilane: magnesium = 100: (100-200): (1-10), adding the modified porous carbon into the chlorosilane solution, heating and depositing nano-silicon; Then, magnesium vapor is introduced to deposit with the modified porous carbon to obtain a magnesium-silicon alloy-coated silicon-carbon precursor material; S3. The magnesium-silicon alloy-coated silicon-carbon precursor material is transferred to a tubular furnace, and a carbon source / heteroatom mixed gas is introduced for deposition to obtain a silicon-carbon composite material coated with heteroatoms and magnesium-silicon alloy.

2. The method for preparing the magnesium-silicon coated silicon-carbon composite material according to claim 1, characterized in that: In S1, the carbon source is any one of urea-formaldehyde resin, polyimide resin, benzoxazine resin and polyarylacetylene resin; The metal activator is any one of LiOH, LiCO3, Mg(OH)2, MgCO3 and MgCl2; The heteroatom compound is any one of melamine, urea and dopamine.

3. The method for preparing the magnesium-silicon coated silicon-carbon composite material according to claim 1, characterized in that: In S1, activation specifically includes: introducing carbon dioxide and activating at a temperature of 300-500°C for 1-6h; The carbonization specifically includes: heating to 700-1100° C. for carbonization for 1-6 hours to obtain modified porous carbon.

4. The method for preparing the magnesium-silicon coated silicon-carbon composite material according to claim 1, characterized in that: In S2, heating and depositing nano-silicon specifically includes: evacuating to a vacuum degree of 0.1-0.5 MPa, heating to 300-500°C to deposit nano-silicon in the pores of the modified porous carbon.

5. The method for preparing the magnesium-silicon coated silicon-carbon composite material according to claim 1, characterized in that: In S2, introducing magnesium vapor and the modified porous carbon for deposition specifically includes: heating magnesium to 1200-1500° C. in a vacuum furnace to generate magnesium vapor, and introducing the magnesium vapor into a reactor at a flow rate of 10-100 ml / min, and depositing at a temperature of 700-900° C. for 30-300 min.

6. The method for preparing the magnesium-silicon coated silicon-carbon composite material according to claim 1, characterized in that: In S2, the chlorosilane includes any one of dichlorosilane, trichlorosilane, tetrachlorosilane, trimethylchlorosilane, vinyltrichlorosilane and triisopropylchlorosilane.

7. The method for preparing the magnesium-silicon coated silicon-carbon composite material according to claim 1, characterized in that: In S3, it specifically includes: transferring the magnesium-silicon alloy coated silicon-carbon precursor material to a tubular furnace, introducing an inert gas to exhaust the air in the tube, heating to 700-1000°C, and introducing a carbon source / heteroatom mixed gas for 0.5-2h to obtain a heteroatom and magnesium-silicon alloy coated silicon-carbon composite material; wherein the volume ratio of the mixed gas is carbon source: heteroatom gas = 10: (1-5), and the introduction flow rate is 100-500ml / min.

8. The method for preparing the magnesium-silicon coated silicon-carbon composite material according to claim 1, characterized in that: In S3, the heteroatom gas includes any one of ammonia, nitrogen trifluoride, phosphine and sulfur dioxide.

9. A magnesium-silicon-coated silicon-carbon composite material, characterized in that: It is prepared by the preparation method of the magnesium-silicon-coated silicon-carbon composite material according to any one of claims 1 to 8.

10. A lithium ion battery, characterized in that: The magnesium-silicon-coated silicon-carbon composite material of claim 9 is used as the negative electrode.

Images