An in-situ symbiotic silicon-carbon anode material and its preparation method

Abstract

This invention provides an in-situ co-existing silicon-carbon anode material and its preparation method, comprising a carbon coating layer, a matrix carbon coated by the carbon coating layer, and silicon microregions and pores distributed within the matrix carbon; the molar ratio of carbon to silicon in the anode material is between 4:1 and 1:1, the thickness of the carbon coating layer is less than 200 nm, and the particle size of the silicon microregions ranges from 1 to 200 nm; the average particle size of the anode material is 2-30 μm, and the specific surface area is 1-50 m². 2 / g. The silicon-carbon anode material prepared by this invention has the advantages of uniform internal distribution, excellent cycle performance, and simple preparation process.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, and in particular to an in-situ symbiotic silicon-carbon anode material and its preparation method. Background Technology

[0002] Compared to graphite anodes, numerous alloy and conversion-type novel anodes exhibit higher capacities. Among them, silicon, with its highest specific capacity (4200 mAh / g), low lithium insertion / extraction potential, and abundant reserves, is increasingly approaching practical application thanks to the efforts of numerous research institutions and commercial companies. However, silicon itself undergoes a significant volume change (280%) during lithium insertion / extraction, leading to stress during use and ultimately pulverization and loss of electrical contact. This process also involves the formation of new interfaces and the reaction with the electrolyte to generate more SEI film. These factors ultimately cause the capacity of silicon anodes to continuously decay during cycling, hindering their practical application. Furthermore, silicon's poor conductivity necessitates its combination with conductive materials for effective use.

[0003] Synthesizing nano-silicon-carbon materials is one of the main methods to improve the cycle stability of silicon anodes. Nanoparticles can not only effectively shorten the lithium-ion transport path and improve capacity utilization, but also effectively eliminate the internal stress of nano-silicon particles during charge and discharge, thus improving cycle stability. Carbon materials can effectively improve the conductivity of the material and enhance the rate performance of the composite material. The microstructures of nano-silicon-carbon composite materials include supported, coated, and dispersed types. In supported nano-silicon-carbon materials, nano-silicon particles are dispersed on the surface of a carbon matrix. During cycling, silicon particles are prone to peeling off, causing performance degradation. In coated structures, the surface of nano-silicon particles is coated with a carbon layer. The preparation of this structure often involves chemical vapor deposition or atomic layer deposition, which has low yield, complex processes, and high costs. In dispersed structures, nano-silicon and carbon materials are uniformly dispersed. The carbon materials effectively limit the volume expansion of nano-silicon and improve conductivity, thus improving the cycle stability of nano-silicon. This type is considered the most promising nano-silicon-carbon material structure for industrialization. Currently, the preparation of dispersed structured nano-silicon carbon materials mainly involves physical mixing methods such as mechanical ball milling. Although the process is relatively simple, the nano-silicon particles are prone to severe agglomeration, making it difficult to achieve highly uniform dispersion of nano-silicon particles in the carbon material matrix, and the electrochemical performance of the material is still not ideal. Summary of the Invention

[0004] This invention provides an in-situ symbiotic silicon-carbon anode material and its preparation method, in order to solve the technical problems of uneven internal and external distribution, complex process and high cost in the preparation of materials in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] An in-situ co-existing silicon-carbon anode material includes a carbon coating layer, a matrix carbon coated by the carbon coating layer, and silicon microregions and pores distributed within the matrix carbon. The molar ratio of carbon to silicon in the anode material is between 4:1 and 1:1, the thickness of the carbon coating layer is less than 200 nm, and the particle size of the silicon microregions ranges from 1 to 200 nm. The average particle size of the anode material is 2-30 μm, and the specific surface area is 1-50 m². 2 / g; where the pores are mainly caused by byproducts from cleaning the interior of the carbon matrix, and the silicon microregions and pores are distributed uniformly within the carbon matrix.

[0007] Optionally, the particle size of the silicon microregions in the anode material ranges from 1 to 50 nm; the average particle size of the anode material is 5 to 15 μm, and the specific surface area is 5 to 30 m². 2 / g.

[0008] Furthermore, the present invention also provides a method for preparing the in-situ symbiotic silicon-carbon anode material, comprising:

[0009] Step S1: Add the crushed metal carbide and silicon tetrachloride into a mixing and crushing device, and add anhydrous metal chloride at the same time to obtain a first mixture. Then mix the first mixture at a certain speed for a certain time to obtain a second mixture.

[0010] Step S2: Transfer the second mixture to a sealed container and heat-treat it at high temperature for a period of time under a protective atmosphere to obtain the calcined product;

[0011] Step S3: The calcined product is acid-washed and deionized water-washed, and then dried at a certain temperature to obtain the dried product;

[0012] Step S4: The dried product is carbon-coated under a protective atmosphere to obtain in-situ symbiotic silicon-carbon anode material.

[0013] Optionally, in step S1, the metal carbide is selected from at least one of calcium carbide and aluminum carbide, and the mass ratio of the metal carbide to silicon tetrachloride is 1:1 to 1:4; the mixing and crushing equipment is selected from a ball mill or a sand mill; the anhydrous metal chloride is selected from at least one of anhydrous ferric chloride, anhydrous cobalt chloride, and anhydrous nickel chloride, and the amount of anhydrous metal chloride added is 0-5% of the sum of the mass of the metal carbide and silicon tetrachloride.

[0014] Optionally, in step S1, the first mixture is mixed by ball milling or sand milling at a speed of 200-500 rpm for a mixing time of 1-8 h.

[0015] Optionally, in step S2, the protective atmosphere is selected from at least one of nitrogen and argon, the heat treatment temperature is 200-800℃, the heating rate is 1-10℃ / min, and the holding time is 1-12h.

[0016] Optionally, in step S3, the washing is performed with a dilute acid with a pH of 1-6 for 1-6 hours, followed by rinsing with deionized water until the pH is neutral. The preferred dilute acid is dilute hydrochloric acid. The drying method is vacuum drying at a temperature of 60-120°C for 6-12 hours.

[0017] Optionally, in step S4, the high-temperature heat treatment process for coating carbon includes: mixing the dried product with a carbon source, and then holding it at 600-1200℃ for 1-12 hours under at least one protective atmosphere selected from nitrogen and argon; the carbon source is selected from at least one of asphalt, sucrose, phenolic resin, epoxy resin, and polyvinylpyrrolidone; the carbon coating amount is 1-5% of the mass of the in-situ symbiotic silicon-carbon anode material.

[0018] Optionally, in step S4, the high-temperature heat treatment process for coating carbon is a CVD coating process, which is carried out at 600-1200℃ for 1-12 hours under at least one protective atmosphere selected from nitrogen and argon; the carbon source is selected from at least one of acetylene, methane, ethane and ethylene, and the carbon coating amount is 1-5% of the mass of the in-situ co-generated silicon-carbon anode material.

[0019] Furthermore, the present invention also provides the application of in-situ symbiotic silicon-carbon anode materials in batteries.

[0020] This invention achieves performance comparable to SiO through in-situ symbiosis of silicon and carbon. x The uniformity of carbon distribution is more conducive to buffering expansion and improving cycle stability. At the same time, the uniform distribution of carbon further improves conductivity and promotes the utilization of silicon capacity. While silicon and carbon coexist in situ, some by-products will also coexist in situ. These by-products will volatilize or turn into liquid phase at high temperature and be washed away during the washing process, automatically forming pores, further buffering expansion and improving cycle stability.

[0021] During the reaction, by controlling the silicon-carbon raw materials, product uniformity can be easily achieved; by controlling the ball milling speed and time during the reaction, impurity generation can be avoided and subsequent reactions can be promoted; adding anhydrous metal chlorides to the reaction products can promote graphitization while reducing the generation of reaction impurities; by controlling the calcination temperature during the reaction, it is possible to avoid excessively high temperatures leading to the generation of a large number of impurities, and to avoid excessively low temperatures leading to the inability to discharge reaction byproducts and resulting in a fragile structure.

[0022] The beneficial effects of the technical solution provided by this invention include at least the following:

[0023] This invention employs a simple solid-state method to produce SiO₂ with similar properties. xThis method utilizes a uniformly distributed silicon-carbon anode material both internally and externally, with a microporous structure that buffers expansion and provides excellent cycle performance. Furthermore, the method employs safe and inexpensive raw materials and a simple process, further promoting the practical commercial application of silicon-carbon anodes. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the in-situ symbiotic silicon-carbon anode material of the present invention;

[0026] Figure 2 SEM image of the product prepared in Example 1;

[0027] Wherein 1-silicon microregion, 2-carbon coating layer, 3-matrix carbon, 4-pores. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] Crushed calcium carbide and SiCl4 were added to a ball mill at a mass ratio of 1:1.33, along with 2% anhydrous FeCl3 of the total mass of calcium carbide and SiCl4. The mixture was then stirred in the ball mill at 300 rpm for 2 hours.

[0031] After mixing, the product was transferred to a sealed high-temperature furnace and heated to 500°C at a heating rate of 2°C / min under nitrogen protection, and held at that temperature for 2 hours.

[0032] The calcined product was washed with dilute hydrochloric acid at pH 3 for 1 hour, then rinsed with deionized water until the pH was neutral. The washed product was then vacuum dried at 100°C for 10 hours.

[0033] After drying, the product was mixed with carbon source sucrose at a mass ratio of 100:7.2, heated to 1000℃ and held for 4 hours under nitrogen protection, and then cooled to obtain an in-situ symbiotic silicon-carbon anode material with a carbon coating of 3%.

[0034] Example 2

[0035] Crushed aluminum carbide and SiCl4 were added to a sand mill at a mass ratio of 1:3.55, along with 2% anhydrous CoCl2 of the total mass of aluminum carbide and SiCl4. The materials were then mixed in the sand mill at 250 rpm for 2 hours.

[0036] After mixing, the product was transferred to a sealed high-temperature furnace and heated to 400°C at a heating rate of 2°C / min under argon protection, and held at that temperature for 6 hours.

[0037] The calcined product was washed with dilute hydrochloric acid at pH 2 for 1 hour, then rinsed with deionized water until the pH was neutral. The washed product was then vacuum dried at 120°C for 8 hours.

[0038] The dried product was carbon-coated by CVD using acetylene as the carbon source. A mixture of acetylene and argon was introduced at a flow rate of 0.1 L / min and an argon:acetylene volume ratio of 9:1. The mixture was kept at 800℃ for 1 h and then cooled to obtain an in-situ symbiotic silicon-carbon anode material with a carbon coating of 2%.

[0039] Table 1 shows the performance of the in-situ symbiotic silicon-carbon anode materials obtained in Examples 1-2.

[0040]

[0041] As can be seen from the above two examples, the silicon-carbon anode prepared by this method can achieve an initial efficiency of about 80% without pre-lithiation. The molar ratio of C to Si can be controlled between 4:1 and 1:1 depending on the type and ratio of reactants, and the specific capacity is also adjusted accordingly.

[0042] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing an in-situ symbiotic silicon-carbon anode material, characterized in that, include: Step S1: Add the crushed metal carbide and silicon tetrachloride to a mixing and crushing device, and add anhydrous metal chloride at the same time to obtain a first mixture. Then, mix the first mixture at a certain speed for a certain time to obtain a second mixture. The metal carbide is selected from at least one of calcium carbide and aluminum carbide. The anhydrous metal chloride is selected from at least one of anhydrous ferric chloride, anhydrous cobalt chloride, and anhydrous nickel chloride. Step S2: Transfer the second mixture to a sealed container and heat-treat it under a protective atmosphere to obtain the calcined product; wherein the heat treatment process is as follows: heat up to 400-500℃ at a rate of 1-10℃ / min and hold at 400-500℃ for 1-12h. Step S3: The calcined product is acid-washed and deionized water-washed, and then dried at a certain temperature to obtain the dried product; Step S4: The dried product is carbon coated under a protective atmosphere to obtain in-situ symbiotic silicon-carbon anode material; The amount of anhydrous metal chloride added is 2-5% of the sum of the mass of the metal carbide and silicon tetrachloride; The anode material comprises a carbon coating layer, a carbon matrix coated by the carbon coating layer, and silicon microregions and pores distributed within the carbon matrix. The molar ratio of carbon to silicon in the anode material is between 4:1 and 1:1, the thickness of the carbon coating layer is less than 200 nm, and the particle size of the silicon microregions ranges from 1 to 200 nm. The average particle size of the anode material is 2-30 μm, and the specific surface area is 1-50 m². 2 / g.

2. The method according to claim 1, characterized in that, In step S1, the mass ratio of metal carbide to silicon tetrachloride is 1:1 to 1:4; the mixing and crushing equipment is selected from ball mill or sand mill.

3. The method according to claim 1, characterized in that, In step S1, the first mixture is mixed by ball milling or sand milling at a speed of 200-500 rpm for 1-8 hours.

4. The method according to claim 1, characterized in that, In step S2, the protective atmosphere is selected from at least one of nitrogen and argon.

5. The method according to claim 1, characterized in that, In step S3, the product is washed with dilute hydrochloric acid with a pH of 1-6 for 1-6 hours, and then rinsed with deionized water until the pH is neutral. The product is dried under vacuum at a temperature of 60-120°C for 6-12 hours.

6. The method according to claim 1, characterized in that, In step S4, the carbon coating process includes: mixing the dried product with a carbon source, and then holding it at 600-1200℃ for 1-12 hours under at least one protective atmosphere selected from nitrogen and argon; the carbon source is selected from at least one of asphalt, sucrose, phenolic resin, epoxy resin, and polyvinylpyrrolidone; the carbon coating amount is 1-5% of the mass of the in-situ symbiotic silicon-carbon anode material.

7. The method according to claim 1, characterized in that, In step S4, the high-temperature heat treatment process for carbon coating is a CVD coating process. The carbon source is selected from at least one of acetylene, methane, ethane, and ethylene. The carbon coating amount is 1-5% of the mass of the in-situ co-generated silicon-carbon anode material.

8. The method according to claim 1, characterized in that, The particle size range of silicon microregions in the anode material is between 1 and 50 nm; the average particle size of the anode material is 5-15 μm, and the specific surface area is 5-30 m². 2 / g.

9. The application of the in-situ symbiotic silicon-carbon anode material prepared by the method of any one of claims 1-8 in a battery.

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