CN-121974356-A - Nano silicon material, surface oxide removal method thereof, lithium ion battery and application

CN121974356ACN 121974356 ACN121974356 ACN 121974356ACN-121974356-A

Abstract

The invention discloses a nano silicon material, a surface oxide removal method thereof, a lithium ion battery and application thereof, belonging to the technical field of lithium ion battery materials, wherein the method comprises the following steps: after pretreating the nano silicon material containing the surface oxide layer, carrying out dispersion treatment on the nano silicon material and cellulose ether in a solvent, so that the cellulose ether is adsorbed on the particle surfaces of the nano silicon material, and the particle agglomeration is destroyed by a steric hindrance and electrostatic repulsion dual mechanism; and then removing the surface oxide layer and byproducts of the nano silicon material by acid washing, and washing and drying to obtain the nano silicon material. The method has simple process and safe operation, can obviously reduce the oxygen content of the nano silicon material to below 5%, improves the conductivity and activity of the silicon electrode, releases the high specific capacity of the silicon electrode, improves the cycle stability of the battery from 400 mAh g ‑1 to 3500 mAh g ‑1 , and is suitable for large-scale preparation of high-purity silicon anode materials.

Inventors

WEI JIAN
ZHAO SIYU
HOU JIAYI
LI XUETING
ZHANG HAO

Assignees

西安建筑科技大学

Dates

Publication Date: 20260505
Application Date: 20260126

Claims (10)

1. A method for removing surface oxides of nano-silicon materials in a solvent, comprising: The preparation method comprises the steps of carrying out gradient acid washing pretreatment on a nano silicon material containing a surface oxide layer by hydrochloric acid to obtain a preactivated nano silicon material, dispersing the preactivated nano silicon material in a solvent to obtain nano silicon slurry, adding cellulose ether solution into the nano silicon slurry in three gradient stages, carrying out programmed dispersion treatment to enable the cellulose ether to be adsorbed on the particle surfaces of the nano silicon material, damaging particle agglomeration by a dual mechanism of steric hindrance and electrostatic repulsion, carrying out gradient acid washing etching by hydrofluoric acid to remove the surface oxide layer and byproducts of the nano silicon material, and washing and freeze-drying to obtain the nano silicon material.
2. The method for removing oxide on the surface of the nano silicon material in the solvent according to claim 1, wherein the preparation method of the nano silicon material containing the surface oxide layer comprises the steps of taking white carbon black as a silicon source, taking metal magnesium as a reducing agent, and triggering a magnesia thermal reduction reaction through high-energy ball milling in an inert atmosphere; The hydrochloric acid gradient pickling pretreatment conditions comprise that nano silicon materials containing surface oxide layers are sequentially pickled for 3-4 hours by 1M, 3M and 5M hydrochloric acid solutions, and each time of pickling is replaced and washed by an organic solvent under the protection of inert gas, so that preactivated nano silicon materials are obtained.
3. The method for removing oxide on the surface of a nano silicon material in a solvent according to claim 1, wherein the cellulose ether solution is added into the nano silicon slurry in three gradient stages, specifically comprising a first stage of dripping speed of 5-10 mL/min for 2-5 min, a second stage of dripping speed of 2-5 mL/min for 2-5 min and a third stage of dripping speed of 0.5-2 mL/min until the addition is completed; the addition amount of the cellulose ether solution is 0.05-0.3wt% of the mass of the nano silicon material; The cellulose ether solution is selected from any one of hydroxypropyl methyl cellulose, sodium carboxymethyl cellulose and cationic polyquaternium-10.
4. The method for removing oxide on the surface of a nano silicon material in a solvent according to claim 1, wherein the solvent is one or more of water, ethanol and isopropanol, and the programmed dispersion treatment specifically comprises stirring for 10min at 500-1000 rpm in a water bath at 40-60 ℃, then co-processing for 10min under microwave power of 150-200W and ultrasonic frequency of 120-200 kHz, and repeating the above steps for 20-60 min.
5. The method for removing oxide on the surface of a nano silicon material in a solvent according to claim 1, wherein the method is characterized by comprising the steps of firstly adding hydrofluoric acid with volume concentration of 1%, stirring and reacting for 10-20 min at 30-40 ℃ at 200-400 rpm, then adding hydrofluoric acid solution with volume concentration of 5%, reacting for 10-20 min at 40-50 ℃, finally adding mixed solution of hydrofluoric acid with volume concentration of 2% and nitric acid with volume concentration of 1%, standing and passivating for 10-20 min at room temperature, then dispersing for 10-20 min by ultrasonic at a frequency of 120-200 kHz, and repeating the steps for 40-80 min.
6. The method for removing oxide on the surface of a nano silicon material in a solvent according to claim 1, wherein the washing condition comprises washing twice with ethanol, centrifuging and decanting in a glove box operation station filled with high-purity argon gas, and the freeze drying condition comprises reducing the temperature to-40 to-50 ℃ at a rate of-2 ℃ per minute and preserving the temperature for 10-20 hours, then heating to 0 ℃ at a rate of 0.5 ℃ per minute and preserving the temperature for 10-20 hours under vacuum of 1-2 Pa, and finally heating to 25 ℃ and preserving the temperature for 5-10 hours.
7. The nano silicon material is characterized by being prepared by adopting the method for removing oxide on the surface of the nano silicon material in a solvent according to any one of claims 1-6, wherein the oxygen atom content of the nano silicon material is reduced to 5%.
8. A lithium ion battery anode material, which is characterized by comprising the nano silicon material prepared by the method for removing the oxide on the surface of the nano silicon material in a solvent according to any one of claims 1-6.
9. A lithium ion battery comprising the lithium ion battery anode material of claim 8.
10. The use of the lithium ion battery of claim 9 in electric vehicles, energy storage systems, and electronic products.

Description

Nano silicon material, surface oxide removal method thereof, lithium ion battery and application Technical Field The invention belongs to the technical field of lithium ion battery materials, and particularly relates to a nano silicon material, a surface oxide removal method thereof, a lithium ion battery and application. Background With the rapid development of electric vehicles, large-scale energy storage systems and portable electronic devices, the market has put higher demands on the energy density, cycle life and safety performance of lithium ion batteries. The negative electrode material is used as a core component of the lithium ion battery, and the lithium storage performance of the negative electrode material directly influences the overall energy density of the battery. The theoretical specific capacity of the traditional graphite cathode is 372 mAh g -1, and the requirement of a high-energy-density battery is difficult to meet. Therefore, the development of a novel anode material having a higher specific capacity is becoming a current research hotspot. Silicon (Si) is regarded as one of the most potential negative electrode materials of next-generation high-energy-density lithium ion batteries because of its extremely high theoretical specific capacity (about 4200 mAh g -1, equivalent to more than 10 times of graphite), suitable lithium intercalation potential, abundant reserves, environmental friendliness, and the like. However, silicon undergoes severe volume expansion (> 300%) during charge and discharge, resulting in pulverization of materials, structural destruction of electrodes, and rapid capacity decay. In order to alleviate the problem, nanocrystallization becomes one of important strategies, and by reducing the size of the silicon material to the nanometer level, volume change can be effectively buffered, and the lithium ion diffusion path can be shortened, so that the cycle stability is improved. At present, the development of the silicon anode material mainly surrounds the aspects of nano structure design, compound modification, surface chemical treatment and the like. In the preparation process of nano silicon, a mechanical ball milling method is one of common large-scale preparation methods, and the method can realize the nanocrystallization and the compounding of the silicon material through high-energy mechanical action. However, in the ball milling process, a great number of dangling bonds are exposed on the surface of the new silicon, so that the new silicon has extremely high chemical activity, is extremely easy to react with oxygen or moisture in the environment, and forms an amorphous silicon dioxide (SiO 2) or silicon oxide (SiO x) passivation layer. The presence of the oxide layer significantly reduces the intrinsic electrochemical activity of the silicon material and impedes interfacial transport of lithium ions, resulting in a reduction in the initial coulombic efficiency, a reduction in the rate capability and a deterioration in the cycling stability of the battery. In order to remove the oxide layer on the silicon surface and improve the purity and electrochemical performance of the material, the prior art mainly adopts a wet chemical etching method. Among them, hydrofluoric acid (HF) solution treatment is the most common method. HF can chemically react with SiO 2 to produce soluble hexafluorosilicic acid and water, thereby dissolving the surface oxide layer. Although HF wet etching has a certain effect in removing silicon oxide, the method has a series of obvious limitations and problems when being practically applied to nano silicon materials prepared by high-energy ball milling. The nano silicon obtained by mechanical ball milling is usually presented as a hard agglomerated micron-sized secondary particle aggregate, and the nano silicon has compact internal structure and low porosity. The agglomeration structure can seriously obstruct the penetration of HF acid liquid into the interior of the particles, so that only the oxide layer on the outermost surface of the particles can be etched, the oxide layer on the surface of the silicon core in the interior can not be effectively removed, and incomplete etching and uneven material purity are caused. HF reacts with the silicon oxide and also reacts with the exposed fresh silicon surface to easily form stable Si-F covalent bonds, thereby introducing a hydrophobic fluorinated layer on the silicon surface. The hydrophobic layer not only can reduce the lyophilic property and the dispersity of the silicon material and influence the uniformity of the preparation of the subsequent electrode slurry, but also can further inhibit the migration of lithium ions at an interface and negatively influence the electrochemical performance. From the aspects of process safety and environmental protection, HF belongs to highly toxic and highly corrosive chemicals, and has high risk in the storage, use and treatment processes, and has extremel