Preparation method of high-rate molecular sieve composite silicon-carbon negative electrode material

Abstract

The invention relates to the technical field of preparation of composite silicon-carbon negative electrode materials, in particular to a preparation method of a high-rate molecular sieve composite silicon-carbon negative electrode material. The method comprises the following steps: step 1, putting porous alumina into a vertical fluidized bed, adding nitrogen, emptying until the oxygen content of tail gas is less than 100ppm, then reducing the flow rate of the nitrogen, heating, then introducing monosilane into a cavity of the vertical fluidized bed, and using nitrogen as carrier gas; 2, reducing the flow of monosilane and the flow of nitrogen in the later stage of siliconizing; and step 3, heating the equipment to 700-1000 DEG C, carrying out carbon coating, opening methane, and carrying out vapor deposition to obtain the silicon-carbon composite material. According to the molecular sieve composite silicon-carbon negative electrode material, non-carbon-based porous carriers such as porous aluminum oxide and the like are utilized, so that the side reaction of nano silicon and a porous matrix during high-temperature carbon coating can be effectively avoided, the high-capacity first effect of the material is kept, and the molecular sieve composite silicon-carbon negative electrode material has high rate performance and has the capacity retention ratio of 90% or above after 100 cycles of fast charging.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of composite silicon-carbon anode materials, and specifically, to a preparation method of a high-rate molecular sieve composite silicon-carbon anode material. Background Art

[0002] With the rapid development of electric vehicles, mobile power sources, and renewable energy storage systems, the demand for lithium-ion batteries with high energy density, long life, and high safety is increasing day by day. Silicon-carbon anode materials are considered ideal anode materials for the next generation of lithium-ion batteries due to their high theoretical specific capacity (about 4200 mAh / g) and low de-lithiation potential. However, problems such as volume expansion and poor conductivity during charge and discharge of silicon limit its application.

[0003] Molecular sieve composite silicon-carbon anode materials are a new type of lithium-ion battery anode material, aiming to solve the limitations of traditional graphite anode materials in terms of energy density, cycle stability, and fast charge and discharge performance. However, the existing molecular sieve composite silicon-carbon anode materials still have the following deficiencies:

[0004] 1. Insufficient rate performance of CVD silicon-carbon: Patent Publication No.: CN117577819A developed a preparation process of a porous carbon, silicon, and silicon-lithium alloy composite. This highly compact composite structure greatly improves the cycle and expansion of silicon anode materials. However, power batteries have higher requirements for the rate performance of anode materials, and the CVD silicon-carbon anode materials on the market cannot yet reach the capacity of 6C. In high-rate cycling, lithium deposition occurs on the surface of the anode, even leading to a "diving" situation.

[0005] 2. Insufficient high-power charge and discharge performance of CVD silicon-carbon: Due to the large internal specific surface area in CVD porous carbon, a large number of silicon-carbon interfaces are generated, which is prone to transformation into silicon carbide phase at high temperatures, resulting in poor electronic and ionic conductivities of the material. During high-power charge and discharge, due to the high DCR of the telecommunications, a large amount of heat is generated, leading to potential safety hazards. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method of a highly stable, high-rate, and high-cycle retention silicon-carbon anode material to solve the problems raised in the above background art.

[0007] To achieve the above purpose, the present invention provides a preparation method of a high-rate molecular sieve composite silicon-carbon anode material, including the following steps:

[0008] Step 1: Place porous alumina with an average pore diameter of 2 - 5 nm into a vertical fluidized bed, add nitrogen, and evacuate with a nitrogen flow rate of 5 L / min until the oxygen content in the tail gas is less than 100 ppm. Then, reduce the nitrogen flow rate to 1 L / min, heat up to 450 °C at a rate of 5 °C / min, hold for 30 min, and then introduce 2 L / min of silane (SiH 4 ), using nitrogen as the carrier gas with a set flow rate of 10 L / min throughout the process;

[0009] Step 2: After 2 h of introducing silane, i.e., in the later stage of silicon infiltration, reduce the silane flow rate to 1 L / min and the nitrogen flow rate to 8 L / min, and hold for 300 min to ensure that no silicon floats on the surface;

[0010] Step 3: Heat the equipment to 700 - 1000 °C for carbon coating, turn on methane with a flow rate of 1 L / min, and perform chemical vapor deposition for 2 h to obtain the final silicon-carbon composite material.

[0011] Preferably, the concentration of silane is 5 - 95%, and the introduction time is 200 min.

[0012] Preferably, the molecular sieve matrix is at least one of alumina, titanium oxide, and aluminosilicate porous materials.

[0013] Preferably, the equipment includes a vertical fluidized bed and a horizontal rotary furnace.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] 1. In the preparation method of this high-rate molecular sieve composite silicon-carbon anode material, by using non-carbon-based porous carriers such as porous alumina, side reactions between nano-silicon and the porous matrix during high-temperature carbon coating can be effectively avoided, maintaining the advantage of high initial efficiency of the material's high capacity.

[0016] 2. In the preparation method of this high-rate molecular sieve composite silicon-carbon anode material, compared with the CVD porous carbon-silicon anode material in the industry, the high-rate molecular sieve composite silicon-carbon anode material of the present invention can avoid the contact between silicon and carbon in the inner interface to form silicon carbide. The electron and ion conductivity of silicon carbide is extremely poor. Therefore, the molecular sieve composite silicon-carbon anode material of the present invention has high-rate performance, with a capacity retention rate of more than 90% after 100 fast charge cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a column chart comparing the 1.5 V initial efficiency and the 5C cycle capacity retention rate of the molecular sieve composite silicon-carbon anode material provided in the examples and comparative examples of the present invention. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0019] To solve the problem of lithium deposition on the surface of the negative electrode and even triggering a dive during high-rate cycling, and at the same time to solve the problem that the large internal specific surface area in CVD porous carbon leads to the generation of a large number of silicon-carbon interfaces, which is prone to transformation into silicon carbide phase at high temperatures, resulting in poor electronic and ionic conductivities of the material. During high-power charge and discharge, due to the high DCR of the telecommunications, a large amount of heat is generated, leading to potential safety hazards. This will be specifically described through the following embodiments.

[0020] Example 1

[0021] The embodiment of the present invention provides a preparation method of a high-rate molecular sieve composite silicon-carbon negative electrode material, including the following method steps:

[0022] S1. Put porous alumina with an average pore diameter of 2 - 5 nm into a vertical fluidized bed, evacuate with a nitrogen flow rate of 5 L / min until the oxygen content in the tail gas is less than 100 ppm, then reduce the nitrogen flow rate to 1 L / min, heat up to 450 °C at a rate of 5 °C / min, keep warm for 30 min, and then introduce 2 L / min of silane (SiH 4 ) into the cavity of the vertical fluidized bed. Use nitrogen as the carrier gas, and set the whole process flow rate to 10 L / min; introduce for 200 min.

[0023] S2. After introducing silane for 2 h, that is, in the later stage of silicon infiltration, reduce the silane flow rate to 1 L / min and cool down, and the nitrogen flow rate is 8 L / min, and keep for 300 min;

[0024] S3. Heat up the equipment to 700 °C for carbon coating, open acetylene, the acetylene flow rate is 1 L / min, and carry out chemical vapor deposition for 2 h to obtain the final silicon-carbon composite material.

[0025] Example 2

[0026] Compared with Example 1, the difference in this embodiment is that in step S3, the equipment is heated up to 850 °C for carbon coating, and the other steps are the same as those in Example 1, so this embodiment will not be elaborated again.

[0027] Example 3

[0028] Compared with Example 1, the difference in this embodiment is that in step S3, the equipment is heated up to 1000 °C for carbon coating, and the other steps are the same as those in Example 1, so this embodiment will not be elaborated again.

[0029] Comparative Example

[0030] The difference between this comparative example and Example 1 lies in that in step S1, porous alumina is changed to porous carbon, and the remaining steps are the same as those in Example 1, which will not be elaborated in this example.

[0031] Table 1

[0032]

[0033] According to Table 1 and Figure 1 It can be seen that in Examples 1 - 3 of the present invention, the carbon coating temperature is increased in sequence. As the carbon coating temperature increases, the 5C cycle retention rate of the product is improved in sequence. This is because alumina itself has high lithium ion transport ability but poor electron transport ability. High temperature leads to further improvement of the conductivity by enhancing the quality of the carbon layer, making up for the disadvantage of insufficient electron conductivity of alumina. When using porous carbon as the carbon matrix in the comparative example, a large amount of silicon carbide is generated at high temperature, resulting in a significant decrease in the initial efficiency and 5C cycle retention rate.

[0034] Therefore, by using non-carbon-based porous carriers such as porous alumina in the present invention, the side reaction between nano-silicon and the porous matrix during high-temperature carbon coating can be effectively avoided, maintaining the advantage of high initial efficiency of the material. Secondly, compared with the CVD porous carbon-silicon anode materials in the industry, the high-rate molecular sieve composite silicon-carbon anode material of the present invention can avoid the contact between silicon and carbon in the inner interface to generate silicon carbide. The electron and ion conductivity of silicon carbide is extremely poor. Therefore, the molecular sieve composite silicon-carbon anode material of the present invention has high-rate performance and has a capacity retention rate of more than 90% after 100 fast charge cycles.

[0035] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only preferred examples of the present invention and do not limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-rate molecular sieve composite silicon-carbon negative electrode material, characterized in that: The following steps are involved: Step 1: Place porous alumina in a vertical fluidized bed, add nitrogen to evacuate until the oxygen content of tail gas is less than 100 ppm, then reduce the nitrogen flow rate and increase the temperature, and then introduce monosilane into the vertical fluidized bed cavity, using nitrogen as the carrier gas; Step 2: Reduce the flow rate of monosilane and nitrogen in the later stage of siliconization; Step 3: The equipment is heated to 700-1000°C for carbon coating, and methane is turned on for vapor deposition to obtain a silicon-carbon composite material.

2. The method for preparing a high-rate molecular sieve composite silicon-carbon negative electrode material according to claim 1, characterized in that: In the step 1, the average pore size of the porous alumina is 2-5 nm.

3. The method for preparing a high-rate molecular sieve composite silicon-carbon negative electrode material according to claim 1, characterized in that: In the step 1, the nitrogen flow rate is 5 L / min to evacuate until the oxygen content of the tail gas is less than 100 ppm, the nitrogen flow rate is reduced to 1 L / min, the temperature is increased to 450° C. at 5° C. / min, and the temperature is kept for 30 minutes.

4. The method for preparing a high-rate molecular sieve composite silicon-carbon negative electrode material according to claim 3, characterized in that: In the step 1, the flow rate of monosilane into the vertical fluidized bed chamber is 2 L / min, nitrogen is used as the carrier gas, and the whole flow rate is set to 10 L / min.

5. The method for preparing a high-rate molecular sieve composite silicon-carbon negative electrode material according to claim 4, characterized in that: In the step 2, after monosilane is introduced for 2 hours, i.e., in the late stage of siliconization, the flow rate of monosilane is reduced to 1 L / min and the flow rate of nitrogen is reduced to 8 L / min and maintained for 300 minutes.

6. The method for preparing a high-rate molecular sieve composite silicon-carbon negative electrode material according to claim 5, characterized in that: In the step 3, the methane flow rate is 1 L / min, and the vapor deposition is performed for 2 hours.

7. The method for preparing a high-rate molecular sieve composite silicon-carbon negative electrode material according to claim 1, characterized in that: In the step 1, the concentration of monosilane is 5-95%, and the introduction time is 200 minutes.

Images