Method for preparing porous silicon material by high-energy ball milling method

Abstract

The invention relates to a method for preparing a porous silicon material, in particular to a method for preparing a porous silicon material by using a ball milling method, which comprises the following steps: (S1) preparing a raw material at least comprising magnesium silicide; (S2) mixing the raw material containing magnesium silicide obtained in the step (S1) with oxidizing gas, and performing ball milling in a high-energy ball mill; and (S3) enabling the product in the step (S2) to pass through a pickling solution to obtain the porous silicon. According to the method for preparing the porous silicon material disclosed by the invention, a magnesiothermic reaction can be promoted through collision of ball-milled particles, so that the energy consumption is reduced; and the particle size can be refined in the ball milling process to obtain porous silicon particles with smaller sizes, so that better electrochemical performance is realized.

Description

Technical Field

[0001] The present invention relates to a method for preparing porous silicon material, in particular to a method for preparing porous silicon material by utilizing ball milling method. Background Art

[0002] With the rapid development of the electric vehicle and energy storage industries, demand for high-energy-density batteries has increased. Optimizing and improving positive and negative electrode materials is an effective means of increasing the energy density of lithium-ion batteries. Currently, the primary anode material used in large-scale commercial lithium-ion batteries is graphite. However, graphite's theoretical capacity density is only 372 mAh / g, a significant constraint on lithium-ion battery development. Silicon anode materials have garnered widespread attention due to their high theoretical capacity (4200 mAh / g) and abundance in the Earth's crust (27.6%, second only to oxygen), making them the recognized next-generation anode material for lithium-ion batteries.

[0003] However, silicon materials experience a volume expansion effect of up to 300% during the charge-discharge cycle, causing silicon particles to break and differentiate during the cycle, losing electrical contact and leading to rapid capacity decay. At the same time, the broken silicon particles expose new surfaces, forming a new solid electrolyte interface (SEI) during the next cycle. This process results in the loss of active lithium and is a key factor in capacity decay. Porous silicon, with its numerous internal voids, can provide a buffer against this volume expansion effect, effectively addressing it.

[0004] At present, the preparation of porous silicon usually uses magnesium thermal reduction method, which is suitable for large-scale preparation of porous silicon. The Chinese invention patent application with patent publication number CN105347346A discloses a method for preparing porous nano-silicon with air assistance. The technical solution adopted is to put a mixture of magnesium silicide and magnesium oxide into a muffle furnace in an atmosphere containing oxygen, and heat it to 300-800℃ at a heating rate of 1-30℃ / min, and keep it warm for 2-18h to promote the occurrence of magnesium thermal reaction; the Chinese invention patent application with patent publication number CN110649243A discloses a preparation method and application of ultrafine phosphorus-doped porous silicon nanomaterials, and the technical solution adopted is After cooling the silicon / magnesium silicide alloy mixture to room temperature, an oxygen-argon mixture with a 5-15% oxygen volume fraction is introduced. The heat treatment temperature is then raised to 600-850°C to cause the magnesium silicide alloy to undergo a decomposition reaction for 2-8 hours. Chinese patent application publication number CN108269989B discloses carbon-coated micronized silicon, its preparation method, and application. The technical solution employed is to use magnesium silicide as a raw material and react it at 400-800°C in a carbon dioxide atmosphere for 2-24 hours to produce a crude product containing magnesium oxide and carbon-coated silicon.

[0005] As can be seen from the above technical solutions, in the preparation process of porous silicon, it is common practice to use high temperature to induce magnesium thermal reaction, which inevitably leads to a large amount of energy consumption. Summary of the Invention

[0006] In order to overcome the deficiencies in the prior art and reduce energy consumption, the present invention provides a method for preparing porous silicon materials by high-energy ball milling.

[0007] To achieve the above object, the present invention discloses a method for preparing porous silicon material by high-energy ball milling, comprising the following steps: (S1) preparing a raw material comprising at least magnesium silicide; (S2) mixing the raw material containing magnesium silicide obtained in step (S1) with an oxidizing gas and ball milling the mixture in a high-energy ball mill; (S3) The product of step (S2) is washed with an acid solution to obtain porous silicon.

[0008] Preferably, in step (S1), silicon powder and magnesium powder are first mixed in a molar ratio of magnesium powder to silicon powder of ≥2:1; after mixing, they are calcined at a high temperature under an inert gas, the calcination temperature being 500-600°C; the calcination temperature is kept for 1-3 hours; and after cooling to room temperature with the furnace, magnesium silicide or a mixture of magnesium silicide and magnesium is obtained; the above-mentioned inert gas refers to helium or argon.

[0009] Preferably, in step (S2), the mixture of magnesium silicide and magnesium powder is placed in a ball mill, and an oxidizing gas is introduced into the ball mill under vacuum to promote magnesium thermal reaction through ball milling; the rotation speed of the ball mill is 400-1000 rpm, and the ball-to-material ratio is 40-100:1.

[0010] Preferably, in step (S3), magnesium oxide in the product obtained in step (S2) is removed by pickling, and then excess pickling solution is washed away with deionized water, and the porous silicon material is obtained after drying.

[0011] Preferably, the oxidizing gas contains at least oxygen and / or carbon dioxide, and the concentration of oxygen and / or carbon dioxide in the oxidizing gas is not less than 20%.

[0012] Preferably, the pickling solution is one or both of a hydrochloric acid aqueous solution and a hydrofluoric acid aqueous solution.

[0013] Preferably, the mixing method in step (S1) is one of stirring mixing, grinding mixing, and low-energy ball milling mixing.

[0014] The present invention has the following technical effects: (1) During high-energy ball milling, the high-speed collisions between the milling beads and between the milling beads and the milling tank wall can create an instantaneous high-temperature and high-pressure environment in the micro-region. This environment can promote the occurrence of magnesium thermal reaction. After a long period of continuous ball milling, all magnesium silicide substances can effectively react with the oxidizing gas until the reaction is complete to form magnesium oxide and silicon. The generated magnesium oxide and silicon continue to collide with each other in the ball mill. After physical crushing, the particle size will be further reduced. Finally, the magnesium oxide is removed by acid washing to obtain silicon with a porous structure. In the magnesium thermal reaction process, it does not need to be promoted by high temperature, which saves energy.

[0015] (2) Refining the particle size during ball milling to obtain smaller porous silicon particles, thereby achieving better electrochemical performance BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a SEM image of the porous silicon product in Example 1; Figure 2 is the BET diagram of the porous silicon product in Example 1; Figure 3 is a cycle life diagram of porous silicon in Example 1; Figure 4 is a SEM image of the porous silicon product in Example 2; Figure 5 is the BET diagram of the porous silicon product in Example 2; Figure 6 This is a cycle life diagram of porous silicon in Example 2. DETAILED DESCRIPTION

[0017] The principles and features of the present invention are described below in conjunction with embodiments; the examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0018] Example 1 (S1) Magnesium powder and silicon powder are mixed in a molar ratio of 2:1. The mixing method can be stirring, grinding, or low-energy ball milling. Each of the three mixing methods has advantages and disadvantages. Low-energy ball milling can reduce material structural damage by reducing the rotational speed and impact strength, making it suitable for brittle materials or composites that require morphology preservation. Long-term low-speed grinding can achieve nano-scale dispersion and enhance the interfacial bonding strength of the composite material. Therefore, low-energy ball milling is preferred in this embodiment. During ball milling, the ball milling speed is 300 rpm and the mixing time is 2 hours.

[0019] The ball-milled product was sintered at 550°C, protected by argon gas during the sintering process, and cooled in the furnace.

[0020] (S2) placing the product obtained in step (S1) into a ball mill, evacuating the ball mill, and then filling the ball mill with 3 bar of pure oxygen to induce a magnesium thermal reaction through ball milling. The high-energy ball milling speed is 400 rpm, the ball milling time is 3 hours, and the ball-to-material ratio is 40:1.

[0021] (S3) removing magnesium oxide from the product obtained in step (S2) by pickling, washing away excess pickling solution with deionized water, and drying to obtain a porous silicon material.

[0022] By the attached Figure 1 It can be seen that the particle size of silicon particles is about 350nm, and there are many tiny void structures inside. Figure 2 It can be seen that the specific surface area of the porous Si product is 103.2 m 2 / g, compared with the specific surface area of 6.0 m 2 / g has been significantly improved. In addition, the pore volume is about 5nm. The material is made into an electrode and assembled into a half-cell test. After 50 cycles of charge and discharge, Figure 3 As shown in the figure, the capacity remains at 1099 mAh / g, and the capacity retention rate is as high as 97.6%.

[0023] Example 2 (S1) Magnesium powder and silicon powder are mixed in a molar ratio of 2.5:1. The mixing method can be stirring, grinding, or low-energy ball milling. Each of the three mixing methods has advantages and disadvantages. Low-energy ball milling can reduce material structural damage by reducing the rotational speed and impact strength, making it suitable for brittle materials or composites that require morphology preservation. Long-term low-speed grinding can achieve nano-scale dispersion and enhance the interfacial bonding strength of the composite material. Therefore, low-energy ball milling is preferred in this embodiment. During ball milling, the ball milling speed is 300 rpm and the mixing time is 2 hours.

[0024] The ball-milled product was sintered at 550°C, protected by helium during the sintering process, and cooled in the furnace.

[0025] (S2) placing the product obtained in step (S1) into a ball mill, evacuating the ball mill, and then filling the ball mill with 3 bar of pure oxygen to induce a magnesium thermal reaction through ball milling. The high-energy ball milling speed is 400 rpm, the ball milling time is 3 hours, and the ball-to-material ratio is 100:1.

[0026] (S3) removing magnesium oxide from the product obtained in step (S2) by pickling, washing away excess pickling solution with deionized water, and drying to obtain a porous silicon material.

[0027] Depend on Figure 4It can be seen that the particle size of silicon particles is about 300nm, and there are many tiny void structures inside. The specific surface area of the porous Si product is 76.1 m 2 / g. The material was made into an electrode and assembled into a half-cell test. After 50 cycles of charge and discharge, Figure 6 As shown in the figure, the capacity remains at 926 mAh / g, and the capacity retention rate is as high as 95.1%.

[0028] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing porous silicon material by high-energy ball milling, characterized in that: The following steps are involved: (S1) preparing a raw material comprising at least magnesium silicide; (S2) mixing the raw material containing magnesium silicide obtained in step (S1) with an oxidizing gas and ball milling the mixture in a high-energy ball mill; (S3) The product of step (S2) is washed with an acid solution to obtain porous silicon.

2. The method for preparing porous silicon material by high-energy ball milling according to claim 1, characterized in that: In step (S1), silicon powder and magnesium powder are first mixed in a molar ratio of magnesium powder to silicon powder of ≥2:1; after mixing, they are calcined at a high temperature of 500-600°C under inert gas; the calcination temperature is kept for 1-3 hours; and after cooling to room temperature with the furnace, magnesium silicide or a mixture of magnesium silicide and magnesium is obtained.

3. The method for preparing porous silicon material by high energy ball milling according to claim 1, characterized in that: In step (S2), a mixture of magnesium silicide and magnesium powder is placed in a ball mill. Under vacuum conditions, 4 to 10 g / L of oxidizing gas is introduced into the ball mill to induce a magnesium thermal reaction through ball milling. The ball mill rotates at a speed of 400 to 1000 rpm, and the ball-to-material ratio is 40 to 100:

1.

4. The method for preparing porous silicon material by high energy ball milling according to claim 1, characterized in that: In step (S3), magnesium oxide in the product obtained in step (S2) is removed by pickling, and then excess pickling solution is washed away with deionized water, and the porous silicon material is obtained after drying.

5. The method for preparing porous silicon material by high energy ball milling according to claim 1 or 3, characterized in that: The oxidizing gas contains at least oxygen and / or carbon dioxide, and the concentration of oxygen and / or carbon dioxide in the oxidizing gas is not less than 20%.

6. The method for preparing porous silicon material by high energy ball milling according to claim 1 or 4, characterized in that: The pickling solution is one or both of a hydrochloric acid aqueous solution and a hydrofluoric acid aqueous solution.

7. The method for preparing porous silicon material by high energy ball milling according to claim 2, characterized in that: The mixing method in step (S1) is one of stirring mixing, grinding mixing, and low-energy ball milling mixing.

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