Gradient-structure micron silicon negative electrode material and preparation method thereof

Abstract

The invention provides a gradient-structure micron silicon negative electrode material and a preparation method thereof, and belongs to the field of lithium ion battery negative electrode materials. The negative electrode is prepared by a low-temperature molten salt aluminothermic method, the prepared micron silicon has a gradient structure and comprises an oxygen atom-doped silicon elementary substance sphere core and a silicon dioxide shell containing oxygen vacancies from the center to the outer layer, and the outermost layer is coated with a carbon layer. The gradient structure and the component change of the micron silicon can inhibit the phase change from the amorphous lithium silicon alloy to the crystalline lithium silicon alloy, accelerate the transmission of ions and electrons, and relieve the structural damage caused by lithium ion embedding, thereby effectively improving the cycling stability of the silicon negative electrode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a gradient structure micron-scale silicon negative electrode material and a preparation method thereof. Background Art

[0002] At present, lithium-ion batteries are widely used in portable electronic devices such as smart phones and laptop computers. However, with the development of emerging electric transportation systems, such as plug-in hybrid electric vehicles and all-electric vehicles, batteries are required to have higher energy densities. Graphite has been widely recognized in the market due to its high electrical conductivity, high stability, and low cost. However, the theoretical capacity of graphite negative electrodes is only 372 mAh g -1 , which greatly limits the improvement space of the energy density of lithium-ion batteries. Therefore, developing new lithium-ion battery negative electrode materials with higher specific capacities than commercial graphite negative electrodes will have important value and significance.

[0003] Silicon negative electrode materials are recognized as the most commercially promising next-generation high-energy density lithium-ion battery negative electrode materials due to their ultra-high theoretical specific capacity of 4200 mAh g -1 , rich reserves, and working voltage similar to commercial graphite negative electrodes. However, there are still many challenges in using silicon materials as lithium-ion battery negative electrode materials. As an alloy-type lithium storage material, the alloying reaction between lithium ions and silicon involves breaking the bonding between host atoms. Therefore, the insertion of lithium ions will cause a huge volume change in the silicon material, resulting in rapid capacity decay. Moreover, due to the mechanical fracture of particles and irreversible side effects with organic electrolytes, the surface SEI film structure is unstable and continuously grows, showing extremely poor cycle stability and rate performance. Chinese Patent No. CN115036511B discloses a low-expansion silicon-based negative electrode material, its preparation method and application. In this invention, the three-dimensional dendritic fumed silica dispersed in the silicon monoxide matrix has a low tap density, resulting in a decrease in the energy density of the electrode material. Summary of the Invention

[0004] The object of the present invention is to provide a gradient structure micron-scale silicon negative electrode material and a preparation method thereof to solve the problems of poor cycle stability and poor electrical conductivity during the charge and discharge process of micron-scale silicon-based negative electrode materials. The outer layer of the silicon sphere is a silicon dioxide layer with oxygen vacancies, which can accelerate the transmission of lithium ions and electrons, avoid mechanical damage caused by excessive surface stress due to the aggregation of ions on the surface of micron-scale silicon particles, and improve the cycle stability and rate performance of the silicon negative electrode material. Moreover, the pinning effect of trace oxygen atoms in the internal silicon single substance inhibits the phase transformation from amorphous lithium-silicon alloy to crystalline lithium-silicon alloy, improving the cycle stability of the silicon negative electrode material.

[0005] In the present invention, the diffusion process of oxygen atoms from the interior of silicon dioxide is finely controlled by low-temperature molten salt reduction technology. In this structure, oxygen atoms are preferentially pumped out from the inner core of the micron silicon sphere. As the oxygen concentration decreases, silicon is preferentially formed inside. By controlling the reduction time, a continuous multi-level structure with silicon inside and oxygen vacancies on the outer layer is obtained.

[0006] The present invention also provides a method for preparing the above-mentioned gradient structure micron silicon negative electrode material, comprising the following steps:

[0007] (1) SiO2@C was mixed with aluminum powder and AlCl3 in a ratio of 1:3:10 and then placed in a stainless steel liner. -1 The heating rate was 250 ° C for 9 hours. After cooling to room temperature naturally, the mixture was stirred and dispersed in 1M HCl solution for 24 hours, and then vacuum filtered and washed several times to obtain micron silicon particles (Si (o) @SiO2 (v) @C).

[0008] The present invention provides a gradient structure micron silicon negative electrode material and a preparation method thereof, which has the advantages of

[0009] 1. The micron silicon particles of the present invention generally have a higher tap density than nano silicon particles due to their larger size. This means that in the same volume, the micron silicon particles can accommodate more active materials, thereby increasing the energy density of the battery;

[0010] 2. The multi-level structure is prepared from the silicon dioxide precursor in one step. The continuous transition between silicon dioxide and silicon particles avoids the problems of large interface resistance and stress mismatch caused by the traditional separated structure.

[0011] 3. Low-temperature molten salt reduction technology is used in the preparation of this material to obtain silicon particles, with low preparation cost and energy consumption; BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a scanning electron microscope (SEM) image of the SiO2@C composite material in Example 1;

[0013] Figure 2 The Si obtained in Example 1 (o) @SiO2 (v) @C Scanning electron microscope (SEM) image of the composite material;

[0014] Figure 3 is Si in Example 1 of the present invention (o) @SiO2 (v) EPR test data of @C and SiO2@C;

[0015] Figure 4 is Si in Example 1 of the present invention (o) @SiO2 (v) @C XRD test data before and after cycling;

[0016] Figure 5 is Si in Example 1 of the present invention (o) @SiO2 (v) @C Lithium battery negative electrode material, at a current density of 2A -1 The cycle performance curve measured below. DETAILED DESCRIPTION

[0017] The present invention is now described with reference to the following specific embodiments, and the technical solutions of the present invention are not limited to the specific implementation modes listed below.

[0018] Example 1

[0019] This embodiment is a gradient structure micron silicon negative electrode material and a preparation method thereof, which is carried out in the following steps:

[0020] (1) SiO2@C was mixed with Al and AlCl3 in a ratio of 1:3:10 and then placed in a stainless steel liner. -1 The heating rate was 250 ° C for 9 hours. After cooling to room temperature naturally, the mixture was stirred and dispersed in 1M HCl solution for 24 hours, and then vacuum filtered and washed several times to obtain micron silicon particles (Si (o) @SiO2 (v) @C), the characterization results are as follows Figure 2 ;

[0021] (2) The sample obtained in Example 1 was subjected to EPR analysis, and the characterization results were as follows Figure 3 , the Si obtained after reduction (o) @SiO2 (v) @C has a high oxygen vacancy content;

[0022] Application Example 1

[0023] The silicon-based composite material, conductive acetylene black and binder PAA obtained in Example 1 were added to 1-methyl-2-pyrrolidone in a mass ratio of 7:2:1 and fully ground. They were evenly coated on the copper foil current collector with a scraper to form an electrode sheet, which was baked in a vacuum oven at 110°C for 10 hours. The dried electrode sheet was punched out with a slicer to obtain an electrode sheet with a diameter of 12 mm. The lithium-ion half-cell was assembled in an argon glove box with a water value and an oxygen value of less than 0.01 ppm. After standing for 10 hours, the performance was tested on the blue electric test system.

[0024] from Figure 4As can be seen from the XRD pattern, when lithium ions are inserted into the silicon negative electrode in the discharged state, a gradient-structured micron-scale silicon-based lithium battery negative electrode material provided by the present invention does not transform into a crystalline lithium-silicon alloy.

[0025] From Figure 5 the cycle diagram, it can be seen that at a current density of 2Ag -1 after 500 charge-discharge cycles, a reversible capacity of ~900 mAh g -1 is still maintained. A gradient-structured micron-scale silicon-based lithium battery negative electrode material provided by the present invention has excellent cycle stability.

Claims

1. A gradient structure micron silicon negative electrode material and preparation method, characterized in that The steps include: The carbon-coated silica sample was mixed with metallic aluminum and anhydrous AlCl3 in a mass ratio of 1-2 parts, 3-5 parts, and 10-20 parts, respectively, and placed in a tube furnace for heating and reduction. After naturally cooling to room temperature, it was stirred and washed in an acidic solution, collected and dried to obtain a micron silicon negative electrode material with a gradient structure.

2. The low-temperature molten salt reduction method according to claim 1, characterized in that: The size of the silica microspheres is between 1 and 10 microns; at a temperature of 200 to 300°C, metal magnesium, aluminum, zinc (including granular, strip, flake, block) and molten AlCl3 are kept warm in argon for 3 to 12 hours; the silica particles are reduced to silicon spherical particles.

3. The gradient structure micron silicon negative electrode material according to claim 1, characterized in that: The microspheres have a continuous multi-level structure from the inside to the outside, and the oxygen content continues to increase. The internal silicon spheres are silicon atoms containing a small amount of oxygen atoms, and the external ones are silicon dioxide containing oxygen vacancies, and the oxygen vacancy content increases gradually from the inside to the outside.

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