Silicon-based porous negative electrode material and preparation method thereof

Abstract

The application discloses a silicon-based porous negative electrode material and a preparation method thereof, and the preparation method comprises the following steps: adding silicon-iron powder into dilute hydrochloric acid for soaking and stirring to obtain partially de-alloyed silicon-iron powder; placing the partially de-alloyed silicon-iron powder into a mixed solution of hydrofluoric acid and hydrogen peroxide, stirring and reacting, filtering and drying to obtain the silicon-based porous negative electrode material. The silicon-based porous negative electrode material takes silicon-iron as raw material, after de-alloying, through a chemical etching process intervened by Fenton reaction, under a double-hole injection process of hydroxyl radicals and hydrogen peroxide, a hierarchical porous electrode material containing mesopores and micropores is formed. The electrode made of the silicon-based porous negative electrode material has not only a cost far lower than that of a traditional porous silicon electrode prepared from high-purity silicon powder, but also a more abundant pore size distribution and excellent electrochemical performance, and is suitable for lithium batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a silicon-based porous anode material and its preparation method. Background Technology

[0002] Silicon-based porous materials, represented by porous silicon, are widely used in various electrochemical fields, including lithium-ion batteries and photoelectrocatalytic devices. Since the 1950s, dozens of technologies for producing porous silicon have been developed. In terms of raw materials, these technologies can be divided into two main categories: bottom-up and top-down processes. The former typically prepares porous silicon using chemical reactions of silicon-containing compounds (e.g., magnesothermic reduction). These methods are scalable and compatible with established industrial facilities; however, they usually involve energy-intensive processes. The latter typically starts with silicon wafers or particles and forms porous structures primarily through etching processes, including electrochemical etching, staining etching, and metal-assisted chemical etching (MACE). Compared to bottom-up methods, top-down methods can be performed under relatively mild conditions. However, most etching processes were originally designed for wafers used in the microelectronics field. For example, electrochemical etching is considered capable of producing highly oriented anisotropic porous structures, making it more suitable for the mass production of wafers with their inherent electrochemical properties. MACE (Metal Etching Process) is a highly controllable and adaptable top-down chemical process capable of producing nanopores or nanowire arrays for virtually any silicon material, including wafers, powders, and particles. However, to obtain these well-controlled porous structures, MACE involves noble metal salts such as silver nitrite, which inevitably increases the overall cost for large-scale production. Considering the massive scale of the electrochemical field, especially the lithium-ion battery industry, which is still growing rapidly, it seems necessary to develop a chemical etching process using low-cost materials to supply porous silicon powder products. Given the chemical etching mechanism of silicon in acidic fluoride solutions, the formation of porous silicon depends on hole injection by a strong oxidant and the subsequent reaction of fluoride ions with electron-deficient silicon to form soluble compounds. The oxidant undoubtedly plays a crucial role in this process. Hydroxyl radicals are extremely powerful oxidants, with a redox potential as high as 2.8V, second only to fluorine. The Fenton process, based on a mixed acid solution of hydrogen peroxide and ferrous ions in a pH range of 2–4, is one of the most widely used techniques for generating hydroxide radicals in aqueous solutions. Hydroxyl radicals in Fenton's reagent can serve as effective hole injectors for silicon chemical etching; however, few publications explicitly report the preparation of porous silicon in the presence of hydroxyl radicals generated by the Fenton process. In this invention, we use ferrosilicon (an inexpensive silicon-iron alloy) as the starting material and a mixed solution of hydrogen fluoride and hydrogen peroxide as the etchant to prepare porous silicon microparticles. During this process, hydroxyl radicals are continuously generated by the reaction of hydrogen peroxide and ferrous ions, which can be supplied by the iron in the ferrosilicon under acidic conditions. Experimental results show that silicon microparticles with abundant porous structures (including micropores and mesopores) can be successfully prepared using this novel top-down process.Compared to industrial-grade silicon powder (~$3000 / ton) traditionally used for lithium-ion battery anode preparation, ferrosilicon ($1200-$1500 / ton) has a lower cost, making this method promising and feasible for large-scale production of silicon-based anode materials.

[0003] Chinese Patent Publication No. CN108493417A discloses a gradient nanoporous silicon metal composite material and its preparation method. The method involves adding silicon alloy powder to an acid solution with a concentration of 0.1–2 mol / L for reaction. The silicon alloy is one or a mixture of two or more of ferrosilicon, magnesium silicon, lithium silicon, aluminum zinc silicon, and aluminum magnesium silicon. The acid is one or a mixture of two or more of hydrochloric acid, sulfuric acid, acetic acid, oxalic acid, citric acid, phosphoric acid, sulfurous acid, phosphoric acid, hydrofluoric acid, formic acid, benzoic acid, acetic acid, propionic acid, stearic acid, carbonic acid, hydrosulfuric acid, hypochlorous acid, boric acid, and silicic acid. This method can prepare porous silicon metal composite materials, increasing the electrochemical performance of the material. However, the principle of this method lies in removing non-silicon components from the silicon alloy; therefore, it can only obtain macroporous materials with pore sizes of several hundred nanometers, and cannot further form mesoporous and microporous structures. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a silicon-based porous anode material and its preparation method.

[0005] This invention is achieved through the following technical solution:

[0006] This invention provides a method for preparing a silicon-based porous anode material, comprising the following steps:

[0007] S1. Add dilute hydrochloric acid to ferrosilicon powder and stir to obtain partially dealloyed ferrosilicon powder.

[0008] S2. Partially dealloyed ferrosilicon powder is placed in a mixed solution of hydrofluoric acid and hydrogen peroxide, stirred and reacted, filtered and dried to obtain silicon-based porous anode material.

[0009] Preferably, the silicon content in the ferrosilicon powder in step S1 is 65-95 wt%.

[0010] Preferably, the particle size of the ferrosilicon powder is 100-300 mesh.

[0011] Preferably, the concentration of the dilute hydrochloric acid in step S1 is 1.0 to 4.0 mol / L.

[0012] Preferably, the soaking and stirring time in step S1 is 30 to 90 minutes.

[0013] Preferably, the iron content in the partially dealloyed ferrosilicon powder is 1-10%.

[0014] Preferably, the concentration of hydrofluoric acid in the mixed solution in step S2 is 3.0–5.0 mol / L.

[0015] Preferably, the concentration of hydrogen peroxide in the mixed solution in step S2 is 0.1–3.5 mol / L.

[0016] Preferably, the reaction temperature in step S2 is 5–15°C.

[0017] Preferably, the stirring rate in step S2 is 200-600 rpm, and the time is 12-24 hours.

[0018] Preferably, the drying method in step S2 includes drying in a nitrogen atmosphere at a temperature of 60–80°C and a pressure of 0.1–1 Pa.

[0019] Preferably, the pH value of the mixed solution in step S2 is 2.0 to 4.0.

[0020] The present invention also provides a silicon-based porous anode material prepared according to the above preparation method.

[0021] The present invention also provides a lithium-ion battery comprising the above-mentioned silicon-based porous anode material.

[0022] In the preparation method of this invention, the Fenton reaction between the residual small amount of iron and hydrogen peroxide in ferrosilicon is triggered in a solution containing HF, generating hydroxyl radicals, which serve as hole injectors for silicon etching. This is unique to this invention. The formation of the porous structure of silicon depends on the chemical etching of HF and the hole injector. The addition of hydroxyl radicals leads to the formation of a large number of micropores around 2 nm; without hydroxyl radicals, only mesopores can be formed, and there are no micropores smaller than 2 nm. If only acid washing is used (such as patent CN108493417A), only macropores of several hundred nanometers can be formed.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The silicon-based porous anode material of the present invention uses silicon iron as raw material. After dealloying, it is formed into a hierarchical porous electrode material containing mesopores and micropores through a chemical etching process intervened by Fenton reaction under the dual hole injection process of hydroxide free radicals and hydrogen peroxide.

[0025] (2) The hydroxyl radicals generated by the Fenton reaction between zero-valent iron and hydrogen peroxide serve as hole injectors, giving silicon-based porous anode materials a richer pore size distribution and excellent electrochemical performance, making them suitable for lithium batteries.

[0026] (3) The preparation method of the present invention uses ferrosilicon as raw material. Ferrosilicon itself contains iron and its price is only 1 / 3 of that of high-purity silicon powder. Therefore, it has more practical value and makes the cost of the electrode made of the silicon-based porous negative electrode material of the present invention much lower than that of the traditional porous silicon electrode made of high-purity silicon powder.

[0027] (4) A porous silicon structure was formed by chemical etching of silicon using semiconductor etching process through HF and hole injector. Attached Figure Description

[0028] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0029] Figure 1 This is a schematic diagram of the preparation process of the silicon-based porous anode material of the present invention;

[0030] Figure 2 The pore size distribution characterization results of the silicon-based porous anode material of the present invention are shown below.

[0031] Figure 3 This is a scanning electron microscope image of the silicon-based porous anode material of the present invention. Detailed Implementation

[0032] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0033] Example 1

[0034] This embodiment provides a silicon-based porous anode material, and the preparation method of the silicon-based porous anode material includes the following steps:

[0035] S1, 1 part ferrosilicon FeSi 90 Al 1.5 The mixture was stirred and soaked in 100 parts of dilute hydrochloric acid for a period of time, filtered, washed with deionized water, and dried to obtain partially dealloyed ferrosilicon powder.

[0036] Among them, FeSi 90 Al 1.5 The particle size was 300 mesh, the concentration of dilute hydrochloric acid was 3.0 mol / L, the reaction temperature was 25℃, the reaction time was 75 min, and the stirring speed was 200 rpm.

[0037] S2. One part of partially dealloyed ferrosilicon is placed in a mixed solution of 100 parts of hydrofluoric acid and hydrogen peroxide, and stirred at a certain temperature for 18 hours. After filtration and drying, silicon-based porous anode material is obtained.

[0038] The concentrations of hydrofluoric acid and hydrogen peroxide were 3.0 mol / L, the pH of the mixed solution was 2.1, the reaction temperature was 10℃, the stirring rate was 200 rpm, the drying temperature was 60℃, the atmosphere was nitrogen, and the pressure was 0.1 Pa.

[0039] Example 2

[0040] This embodiment provides a silicon-based porous anode material, and the preparation method of the silicon-based porous anode material includes the following steps:

[0041] S1, 1 part ferrosilicon FeSi 75 Al 1.0 -A was stirred and soaked in 100 parts of dilute hydrochloric acid for a period of time, filtered, washed with deionized water, and dried to obtain partially dealloyed ferrosilicon powder.

[0042] Among them, FeSi 75 Al 1.0 - The particle size of A is 200 mesh, the concentration of dilute hydrochloric acid is 4.0 mol / L, the reaction temperature is 25℃, the reaction time is 30 min, and the stirring speed is 200 rpm.

[0043] S2. One part of partially dealloyed ferrosilicon is placed in a mixed solution of 100 parts of hydrofluoric acid and hydrogen peroxide, and stirred at a certain temperature for 24 hours. After filtration and drying, silicon-based porous anode material is obtained.

[0044] The concentration of hydrofluoric acid was 5.0 mol / L, the concentration of hydrogen peroxide was 0.1 mol / L, the pH of the mixed solution was 2.3, the reaction temperature was 15℃, the stirring rate was 300 rpm, the drying temperature was 70℃, the atmosphere was nitrogen, and the pressure was 0.2 Pa.

[0045] Example 3

[0046] This embodiment provides a silicon-based porous anode material, the preparation method of which includes the following steps:

[0047] S1, 1 part ferrosilicon FeSi 65 The mixture was stirred and soaked in 100 parts of dilute hydrochloric acid for a period of time, filtered, washed with deionized water, and dried to obtain partially dealloyed ferrosilicon powder.

[0048] Among them, FeSi 65The particle size was 200 mesh, the concentration of dilute hydrochloric acid was 1.0 mol / L, the reaction temperature was 25℃, the reaction time was 90 min, and the stirring speed was 200 rpm.

[0049] S2. One part of partially dealloyed ferrosilicon is placed in a mixed solution of 100 parts of hydrofluoric acid and hydrogen peroxide, stirred at a certain temperature for 12 hours, filtered and dried to obtain silicon-based porous anode material.

[0050] The concentration of hydrofluoric acid was 4.0 mol / L, the concentration of hydrogen peroxide was 2.2 mol / L, the pH of the mixed solution was 2.4, the reaction temperature was 5℃, the stirring rate was 600 rpm, the drying temperature was 80℃, the atmosphere was nitrogen, and the pressure was 1 Pa.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 1 is as follows:

[0053] Ferrosilicon (FeSi) is not used. 90 Al 1.5 Industrial silicon powder 1101 (200 mesh) was used.

[0054] Comparative Example 2

[0055] The difference between this comparative example and Example 2 is as follows:

[0056] Ferrosilicon (FeSi) is not used. 75 Al 1.0 -A, while using industrial silicon powder 1101 (200 mesh).

[0057] Comparative Example 3

[0058] The difference between this comparative example and Example 3 is as follows:

[0059] Ferrosilicon (FeSi) is not used. 65 Industrial silicon powder 1101 (200 mesh) was used.

[0060] Comparative Example 4

[0061] The difference between this comparative example and Example 1 is as follows:

[0062] Replace the mixed solution of hydrofluoric acid and hydrogen peroxide with a hydrogen peroxide solution at a concentration of 3.5 mol / L. All other steps remain the same.

[0063] Comparative Example 5

[0064] The difference between this comparative example and Example 1 is as follows:

[0065] Replace the mixed solution of hydrofluoric acid and hydrogen peroxide with a hydrofluoric acid solution at a concentration of 3.0 mol / L. The other steps remain the same.

[0066] Performance testing

[0067] The pore size distribution and specific surface area of ​​each comparative example and embodiment were tested using the nitrogen adsorption method according to GB / T21650.2-2008 standard. ICE was measured by assembling CR2302 half-cells according to IEC-60086 standard.

[0068] The assembly method for a half-cell can be as follows:

[0069] 1. Place the positive electrode shell on a glass plate with the opening facing upwards inside the glove box; 2. Place the gasket and lithium metal positive electrode sheet into the positive electrode shell in sequence; 3. Use a syringe to draw electrolyte and wet the positive electrode sheet; 4. Place the separator on the positive electrode sheet and wet it again with electrolyte; 5. Place the negative electrode active material sheet on the separator; 6. Place the gasket on the negative electrode sheet; 7. Place the spring clip on the gasket; 8. Close the battery negative electrode shell and fasten it tightly. The lithium metal positive electrode sheet includes lithium foil (50μm thick); the separator is a Whatman GF / A1820-047 glass fiber membrane, and the electrolyte is LB-372 electrolyte; the negative electrode active material sheet includes negative electrode active material and a current collector. The current collector is a copper sheet, and the negative electrode active material is graphite and silicon-based porous negative electrode material. The mass ratio of graphite to silicon-based porous negative electrode material is 50, and the loading of the negative electrode active material is 10mg / cm³. 2 .

[0070] The test results are shown in Table 1:

[0071] Table 1 Performance Test Results

[0072] Aperture distribution range (nm) <![CDATA[Specific surface area (m 2 / g)]]> ICE (%) Example 1 1.5～25 3.7 71.1％ Example 2 1.7～30 3.5 70.5 Example 3 2.0～35 3.3 70.1 Comparative Example 1 4.2～50 1.8 62.4 Comparative Example 2 5.0～50 1.6 61.2 Comparative Example 3 7.0～50 1.5 60.9 Comparative Example 4 Non-porous structure 0.6 50.6 Comparative Example 5 75～350 0.8 52.1

[0073] The performance test results above show that the effects of Comparative Examples 1-3 are significantly worse than those of Examples 1-3. Comparative Examples 1-3 only contain mesoporous and macroporous structures, resulting in lower specific surface area and initial coulombic efficiency compared to Examples 1-3. In Comparative Example 4, the Fenton reaction was not triggered in a solution containing HF. Without HF, the oxidant alone cannot etch the silicon surface, thus failing to form a porous structure, resulting in lower specific surface area and initial coulombic efficiency compared to Examples 1-3. In Comparative Example 5, no hydrogen peroxide was added, preventing the Fenton reaction from being triggered. Porous structures were formed solely through acid washing, and macroporous structures could only be formed by removing some of the iron-containing phase from the alloy, resulting in lower specific surface area and initial coulombic efficiency compared to Examples 1-3.

[0074] It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in these embodiments can be arbitrarily combined with each other.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes a silicon-based porous anode material, and the preparation method of the silicon-based porous anode material includes the following steps: S1. Add dilute hydrochloric acid to ferrosilicon powder and stir to obtain partially dealloyed ferrosilicon powder. The concentration of the dilute hydrochloric acid in step S1 is 1.0~4.0 mol / L, and the soaking and stirring time is 30~90 min; the iron content in the partially dealloyed ferrosilicon powder is 1~10%. S2. Partially dealloyed ferrosilicon powder is placed in a mixed solution of hydrofluoric acid and hydrogen peroxide, stirred and reacted, filtered and dried to obtain silicon-based porous anode material. In step S2, the concentration of hydrofluoric acid in the mixed solution is 3.0~5.0 mol / L, and the concentration of hydrogen peroxide is 0.1~3.5 mol / L. The pH value of the mixed solution in step S2 is 2.0~4.

0.

2. The lithium-ion battery according to claim 1, characterized in that, The silicon content in the ferrosilicon powder in step S1 is 65~95wt%, and the particle size of the ferrosilicon powder is 100~300 mesh.

3. The lithium-ion battery according to claim 1, characterized in that, The reaction temperature in step S2 is 5~15℃.

4. The lithium-ion battery according to claim 1, characterized in that, The stirring rate in step S2 is 200-600 rpm, and the stirring time is 12-24 hours.

5. The lithium-ion battery according to claim 1, characterized in that, The drying method described in step S2 includes drying in a nitrogen atmosphere at a temperature of 60~80 °C and a pressure of 0.1~1 Pa.

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