Preparation method of composite silicon-carbon negative electrode material

Abstract

The invention relates to the technical field of material preparation, in particular to a preparation method of a composite silicon-carbon negative electrode material, which comprises the following steps: putting porous carbon into a rotary furnace for emptying operation; heating the rotary furnace, and opening acetylene to obtain silicon carbon; pouring aluminum nitrate nonahydrate into a beaker, and adding deionized water for dissolving for later use; putting magnetons, stirring, and adding a silicon-carbon material; putting the beaker into a water bath kettle, adding a diammonium hydrogen phosphate solution, dissolving, adding the solution into the beaker, and stirring until the solution is evaporated; and drying to obtain powder, grinding the powder into powder, and carrying out heat treatment in a tubular furnace to obtain the A < l > PO4 coated silicon carbon material. According to the invention, CVD silicon carbon is coated with A-based compounds such as A < l > PO4 and the like, the coating material has excellent uniformity and integrity, and the rate capability of the material is effectively improved and the cycle capability of the material is improved based on the relatively strong desolvation capability and high bonding strength of the material.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, specifically to a method for preparing a composite silicon-carbon anode material. Background Technology

[0002] Patent application number (CN202411377080.2) developed a preparation process for porous carbon and silicon-carbon composite materials containing surface functional groups. It is intended to improve the wettability and rate performance of the material by showing functional groups. However, most functional groups will significantly degrade the first coulombic efficiency of the anode material, and this rate increase will cause the rapid consumption of surface active lithium, thereby deteriorating the room temperature cycling.

[0003] This highly compact composite structure significantly improves the cycling and expansion of silicon anode materials. However, research has revealed that the kinetics of this material exhibit a significant decline compared to traditional nano-silicon materials. Although the mechanism of this kinetic deterioration is not yet clear to the scientific and industrial communities, it is evident that this silicon-carbon material has a high lithium-ion transport resistance, which is particularly pronounced at low SOC levels, failing to meet the fast-charging requirements of current new energy power batteries. To address this, patent application number (CN202311376166.9) proposes a scheme for constructing an alumina surface coating layer, which improves the kinetics of silicon-carbon materials to some extent. However, this coating method is too simple and cannot guarantee the bonding force between alumina and silicon-carbon, nor the integrity of the alumina layer.

[0004] Currently, most patents that improve the rate performance of silicon-carbon materials essentially involve increasing active sites or introducing fast ion conductor coatings. However, these methods cannot effectively guarantee the original cycling capability of silicon-carbon materials. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the present invention provides a method for preparing composite silicon-carbon anode materials, which can effectively solve the problems mentioned in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a composite silicon-carbon anode material, comprising the following steps:

[0008] Step 1: Place porous carbon with Dv 50-7 microns and Dn 10-2 microns into a rotary kiln. Purge the gas with nitrogen at a flow rate of 5 L / min until the oxygen content in the tail gas is less than 100 ppm. Reduce the nitrogen flow rate to 1 L / min and heat the gas to 450℃ at a rate of 5℃ / min. Hold the temperature for 30 min. Introduce silane into the rotary kiln cavity at a flow rate of 2 L / min. Use N2 as the carrier gas and set the flow rate to 10 L / min throughout the process.

[0009] Step 2: Heat the rotary kiln to 600-800℃, turn on the acetylene, the acetylene flow rate is 1L / min, and perform vapor deposition at atmospheric pressure for 2 hours to obtain silicon-carbon.

[0010] Step 3: Take 2.456g of aluminum nitrate nonahydrate, pour it into a beaker, and add 100mL of deionized water to dissolve it for later use.

[0011] Step 4: Place a magnetic stir bar in aluminum nitrate nonahydrate and stir until transparent, then add 80g of silicon carbide material;

[0012] Step 5: Place the beaker in a water bath and set it to 80°C. Add 0.864g of diammonium hydrogen phosphate solution to 100ml of deionized water. After dissolving, add the solution to the beaker from Step 4 and stir continuously until the solution has completely evaporated.

[0013] Step 6: Transfer the beaker to a forced-air drying oven and dry at 120℃ for 4 hours to obtain powder. Grind the powder into powder using a mortar and pestle, and heat-treat it in a tube furnace at 300℃ for 2 hours to obtain Al PO4-coated silicon-carbon material.

[0014] Preferably, the porous carbon in step 1 has a microporosity of 80%–99%, a maximum pore size of less than or equal to 10 nm, and a pore volume of 0.5–1.2 cm³. 3 / g, BET is 1400-2800m 2 / g, has been passivated to remove surface functional groups, and the precursor is biomass, resin or petroleum coke.

[0015] Preferably, the concentration of silane in step 1 is 5% to 95%, and the introduction time is 300 min.

[0016] Preferably, the acetylene purity in step 2 is greater than 97%.

[0017] The technical solution provided by this invention has the following advantages compared with the known prior art:

[0018] This invention coats CVD silicon-carbon with Al-based compounds such as AlPO4. The coating material has excellent uniformity and integrity. Based on the material's strong desolvation ability and high bonding strength, it effectively improves the material's rate performance and cycle life, making it more suitable for use in battery cells with different requirements. For example, for cylindrical or prismatic cells that require fast charging, it can improve the lithium plating phenomenon during fast charging cycles, thereby solving the problem of low efficiency under high rate cycling. The combination of cycle improvement features allows it to meet the application scenarios that simultaneously require high power and long cycle life of the battery cell. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0020] Figure 1 The Raman spectrum of the material in Example 1 of this invention;

[0021] Figure 2 This is an EDS mapping analysis diagram of the material in Example 1 of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] The present invention will be further described below with reference to embodiments.

[0024] Example 1:

[0025] Step 1: Place 700g of porous carbon into a rotary kiln, purge with nitrogen at a flow rate of 5L / min until the oxygen content in the tail gas is less than 100ppm, reduce the nitrogen flow rate to 1L / min, raise the temperature to 450℃ at a rate of 5℃ / min, hold for 30min, introduce silane into the rotary kiln cavity at a rate of 2L / min, maintain atmospheric pressure throughout the process, kiln pressure 100-500Pa, rotation speed 0.1rpm, use N2 as carrier gas, set the flow rate to 3L / min throughout the process, and introduce silane for 300min.

[0026] Step 2: Heat the rotary kiln to 600℃, turn on the acetylene, the acetylene flow rate is 1L / min, and perform vapor deposition for 2 hours to obtain silicon-carbon.

[0027] Step 3: Take 2.456g of aluminum nitrate nonahydrate, pour it into a beaker, and add 100mL of deionized water to dissolve it for later use.

[0028] Step 4: Place a clean magnetic ball into aluminum nitrate nonahydrate and stir at 70 rpm until transparent, then add 80g of silicon carbide material;

[0029] Step 5: Place the beaker in a water bath and set it to 80°C. Add 0.864g of diammonium hydrogen phosphate to 100ml of deionized water to dissolve it. Then add the solution to the beaker from Step 4 and stir continuously until the solution has completely evaporated.

[0030] Step 6: Transfer to a forced-air drying oven and dry at 120℃ for 4 hours. Gently grind the powder into powder using a mortar and pestle, and heat-treat in a tube furnace at 300℃ for 2 hours, with 1 s lm N2 introduced throughout the process, to obtain AlPO4-coated silicon-carbon material.

[0031] Example 2:

[0032] Step 1: Place 700g of porous carbon into a rotary kiln, purge with nitrogen at a flow rate of 5L / min until the oxygen content in the tail gas is less than 100ppm, reduce the nitrogen flow rate to 1L / min, raise the temperature to 450℃ at a rate of 5℃ / min, hold for 30min, introduce silane into the rotary kiln cavity at a rate of 2L / min, maintain atmospheric pressure throughout the process, kiln pressure 100-500Pa, rotation speed 0.1rpm, use N2 as carrier gas, set the flow rate to 3L / min throughout the process, and introduce silane for 300min.

[0033] Step 2: Heat the rotary kiln to 600℃, turn on the acetylene, the acetylene flow rate is 1L / min, and perform vapor deposition for 2 hours to obtain silicon-carbon.

[0034] Step 3: Take 3.684g of aluminum nitrate nonahydrate, pour it into a beaker, and add 100mL of deionized water to dissolve it for later use;

[0035] Step 4: Place a clean magnetic ball into aluminum nitrate nonahydrate and stir at 70 rpm until transparent, then add 80g of silicon carbide material;

[0036] Step 5: Place the beaker in a water bath and set it to 80°C. Add 0.864g of diammonium hydrogen phosphate to 100ml of deionized water to dissolve it. Then add the solution to the beaker from step 4 and stir continuously until the solution has completely evaporated.

[0037] Step 6: Transfer to a forced-air drying oven and dry at 120℃ for 4 hours. Gently grind the powder into powder using a mortar and pestle, and heat-treat in a tube furnace at 300℃ for 2 hours, with 1 s lm N2 introduced throughout the process, to obtain AlPO4-coated silicon-carbon material.

[0038] Example 3:

[0039] Step 1: Place 700g of porous carbon into a rotary kiln, purge with nitrogen at a flow rate of 5L / min until the oxygen content in the tail gas is less than 100ppm, reduce the nitrogen flow rate to 1L / min, raise the temperature to 450℃ at a rate of 5℃ / min, hold for 30min, introduce silane into the rotary kiln cavity at a rate of 2L / min, maintain atmospheric pressure throughout the process, kiln pressure 100-500Pa, rotation speed 0.1rpm, use N2 as carrier gas, set the flow rate to 3L / min throughout the process, and introduce silane for 300min.

[0040] Step 2: Heat the rotary kiln to 600℃, turn on the acetylene, the acetylene flow rate is 1L / min, and perform vapor deposition for 2 hours to obtain silicon-carbon.

[0041] Step 3: Take 1.228g of aluminum nitrate nonahydrate, pour it into a beaker, and add 100mL of deionized water to dissolve it for later use;

[0042] Step 4: Place a clean magnetic ball into aluminum nitrate nonahydrate and stir at 70 rpm until transparent, then add 80g of silicon carbide material;

[0043] Step 5: Place the beaker in a water bath and set it to 80°C. Add 0.864g of diammonium hydrogen phosphate to 100ml of deionized water to dissolve it. Then add the solution to the beaker from step 4 and stir continuously until the solution has completely evaporated.

[0044] Step 6: Transfer to a forced-air drying oven and dry at 120℃ for 4 hours. Gently grind the powder into powder using a mortar and pestle, and heat-treat in a tube furnace at 300℃ for 2 hours, with 1 s lm N2 introduced throughout the process, to obtain AlPO4-coated silicon-carbon material.

[0045] Comparative Example 1:

[0046] The steps for Comparative Example 1 are as follows:

[0047] Step 1: Place 700g of porous carbon into a rotary kiln, purge with nitrogen at a flow rate of 5L / min until the oxygen content in the tail gas is less than 100ppm, reduce the nitrogen flow rate to 1L / min, raise the temperature to 450℃ at a rate of 5℃ / min, hold for 30min, introduce silane into the rotary kiln cavity at a rate of 2L / min, maintain atmospheric pressure throughout the process, kiln pressure 100-500Pa, rotation speed 0.1rpm, use N2 as carrier gas, set the flow rate to 3L / min throughout the process, and introduce silane for 300min.

[0048] Step 2: Heat the rotary kiln to 600℃, turn on the acetylene, set the acetylene flow rate to 1L / min, and perform vapor deposition for 2 hours to obtain silicon-carbon.

[0049] The silicon-carbon anode materials prepared in Examples 1-3 and Comparative Example 1 were mixed in a mass ratio of silicon-carbon composite material (anode active material): polyacrylic acid resin (PAA): carbon nanotubes (CNT): conductive carbon black (SP) of 90:5:1:4. The mixture was prepared into a slurry with deionized water, uniformly coated onto copper foil, and vacuum dried at 80°C for 24 hours to obtain the experimental battery electrode. A lithium sheet was used as the counter electrode, and a 1.1 mol / L LiPF6 electrolyte was used. The solvent was a four-component mixed solvent: ethylene carbonate (EC): vinylene carbonate (VC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) = 1:1:1:1. A polypropylene microporous membrane was used as the separator. The cells were assembled into CR2025 coin cell half-cells in a vacuum glove box and tested using a battery testing system (Arb., USA). In a multi-channel battery testing system (Labstar 1200 / 780 glove box model from Braun GmbH, Germany), the capacity, initial charge-discharge efficiency, and cycle retention were tested. The test results are shown in Table 1.

[0050] Table 1. Electrochemical performance of samples from Examples 1-3 and Comparative Example 1

[0051]

[0052] Data analysis: Table 1 shows that Al PO4 coating can effectively improve the rate performance and cycle retention at 0.1C of the material. This is because Al PO4’s excellent desolvation ability and strong covalent bonds provide high mechanical support. However, the optimal amount of Al PO4 is controlled at 1%. In Example 2, the first efficiency of silicon-carbon was slightly reduced, and in Example 3, the expansion and rate performance of silicon-carbon were slightly insufficient.

[0053] Reference Figure 1 The Raman spectrum of the sample in Example 1 showed a peak near 600 cm⁻¹ corresponding to OPO, indicating that Al PO₄ was successfully coated.

[0054] Reference Figure 2 The EDS mapping analysis of the sample in Example 1 shows a clear distribution of Al, P, and O in the elemental surface scan, indicating that the coating was successful.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a composite silicon-carbon anode material, characterized in that, Includes the following steps: Step 1: Place porous carbon with Dv 50-7 microns and Dn 10-2 microns into a rotary kiln. Purge the gas with nitrogen at a flow rate of 5 L / min until the oxygen content in the tail gas is less than 100 ppm. Reduce the nitrogen flow rate to 1 L / min and heat the gas to 450℃ at a rate of 5℃ / min. Hold the temperature for 30 min. Introduce silane into the rotary kiln cavity at a flow rate of 2 L / min. Use N2 as the carrier gas and set the flow rate to 10 L / min throughout the process. Step 2: Heat the rotary kiln to 600-800℃, turn on the acetylene, the acetylene flow rate is 1L / min, and perform vapor deposition at atmospheric pressure for 2 hours to obtain silicon-carbon. Step 3: Take 2.456g of aluminum nitrate nonahydrate, pour it into a beaker, and add 100mL of deionized water to dissolve it for later use. Step 4: Place a magnetic stir bar in aluminum nitrate nonahydrate and stir until transparent, then add 80g of silicon carbide material; Step 5: Place the beaker in a water bath and set it to 80°C. Add 0.864g of diammonium hydrogen phosphate solution to 100ml of deionized water. After dissolving, add the solution to the beaker from Step 4 and stir continuously until the solution has completely evaporated. Step 6: Transfer the beaker to a forced-air drying oven and dry at 120℃ for 4 hours to obtain powder. Grind the powder into powder using a mortar and pestle, and heat-treat it in a tube furnace at 300℃ for 2 hours to obtain AlPO4-coated silicon-carbon material.

2. The method for preparing a composite silicon-carbon anode material according to claim 1, characterized in that, The porous carbon in step 1 has a microporosity of 80%–99%, a maximum pore size of less than or equal to 10 nm, and a pore volume of 0.5–1.2 cm³. 3 / g, BET is 1400-2800m 2 / g, has been passivated to remove surface functional groups, and the precursor is biomass, resin or petroleum coke.

3. The method for preparing a composite silicon-carbon anode material according to claim 1, characterized in that, The concentration of silane in step 1 is 5% to 95%, and the introduction time is 300 min.

4. The method for preparing a composite silicon-carbon anode material according to claim 1, characterized in that, The acetylene purity in step 2 is greater than 97%.

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