阅读说明：本技术 一种无定形硅材料的制备方法 (Preparation method of amorphous silicon material ) 是由 包志豪 黄曦 于 2020-07-10 设计创作，主要内容包括：本发明涉及一种无定形硅材料的制备方法,属于锂离子电池电极材料技术领域。该工艺是将二氧化硅材料包覆钛酸四丁酯经水解形成二氧化硅/二氧化钛复合材料后,将其与金属铝在氯化盐中反应,再经过酸洗去除杂质并干燥后,获得无定形硅电极材料。本发明的优点在于其二氧化硅原材料来源丰富、工艺过程简单并能够规模化生产。该制备方法相较于传统铝热反应,能获得更好无定形态的硅纳米材料,并更好地保持其二氧化硅原始的形貌。作为锂离子电池负极材料表现出了优异的电化学性能,具有广泛的应用价值。(The invention relates to a preparation method of an amorphous silicon material, belonging to the technical field of lithium ion battery electrode materials. The process comprises the steps of hydrolyzing tetrabutyl titanate coated by a silicon dioxide material to form a silicon dioxide/titanium dioxide composite material, reacting the silicon dioxide/titanium dioxide composite material with metal aluminum in chloride, removing impurities by acid washing, and drying to obtain the amorphous silicon electrode material. The invention has the advantages of rich sources of silicon dioxide raw materials, simple technical process and large-scale production. Compared with the traditional aluminothermic reaction, the preparation method can obtain better amorphous silicon nano-materials and better keep the original shape of silicon dioxide. The lithium ion battery cathode material has excellent electrochemical performance and wide application value.)

1. A method for preparing an amorphous silicon material, which is characterized by comprising the following steps: the method comprises the steps of hydrolyzing tetrabutyl titanate coated with a silicon dioxide raw material to form a silicon dioxide/titanium dioxide composite material, reacting the composite material with aluminum powder in chloride to generate a silicon-containing mixture, removing impurities from the mixture through acid washing, and drying to generate the amorphous silicon material.

2. A method of producing an amorphous silicon material as claimed in claim 1, characterised in that: the method specifically comprises the following steps:

(1) uniformly soaking a silicon dioxide raw material into an ethanol solution of tetrabutyl titanate, separating, performing hydrolysis reaction at normal temperature, and drying to obtain a silicon dioxide/titanium dioxide composite material;

(2) adding aluminum powder and chloride salt into the composite material prepared in the step (1), uniformly mixing, heating and reacting in an inert atmosphere, after the reaction is finished, sequentially immersing reaction products into sufficient hydrochloric acid aqueous solution and hydrofluoric acid solution, removing impurities, and then separating and drying to obtain the amorphous silicon material.

3. A method of producing an amorphous silicon material as claimed in claim 2, characterised in that: the silicon dioxide raw material in the step (1) is one or more of nano silicon dioxide ball powder, diatomite, white carbon black, rice hull ash, glass fiber waste, sand, sandy soil and powder of ball-milled glass.

4. A method of producing an amorphous silicon material as claimed in claim 2, characterised in that: the molar concentration of the ethanol solution of tetrabutyl titanate in the step (1) is 100-800 mmol/L.

5. A method of producing an amorphous silicon material as claimed in claim 2, characterised in that: the hydrolysis reaction condition in the step (1) is reaction for 1-5 minutes at normal temperature.

6. A method of producing an amorphous silicon material as claimed in claim 2, characterised in that: the inert atmosphere in the step (2) is pure argon gas or a mixed gas of hydrogen (5 v%) and argon (95 v%).

7. A method of producing an amorphous silicon material as claimed in claim 2, characterised in that: the chloride salt in the step (2) is aluminum chloride or a mixture of the aluminum chloride and other chloride salts.

8. A method of producing an amorphous silicon material as claimed in claim 2, characterised in that: the molar ratio of the aluminum powder and the chloride salt in the step (2) to the silicon dioxide in the silicon dioxide raw material in the step (1) is 1.28: 2: 3: 0.5 to 1.

9. A method of producing an amorphous silicon material as claimed in claim 2, characterised in that: the heating reaction condition in the step (2) is that the reaction temperature is 250-500 ℃, and the reaction is carried out for 3-12 hours at constant temperature.

10. Amorphous silicon material obtainable by a process according to any one of claims 1 to 9.

Technical Field

The invention relates to a preparation method of an amorphous silicon material, belonging to the technical field of lithium ion battery electrode materials.

Background

With the rapid development of electronic devices and electric automobiles, the technical breakthrough of lithium ion batteries becomes a problem which needs to be solved urgently, so that the preparation of electrode materials becomes a hot research topic. Among these, silicon has been studied in recent years in large quantities for a new generation of lithium ion batteries because of its high energy density as a negative electrode material. Compared with the theoretical capacity (372mAh/g) of the traditional graphite, the silicon has the specific capacity (4200mAh/g) which is 10 times larger than that of the traditional graphite, and the characteristics of abundant resources and high safety of the silicon make the silicon more popular with researchers.

However, the silicon negative electrode material has very significant defects, and during the charging and discharging processes, silicon undergoes huge volume expansion (> 300%), so that the active material is cracked and easily falls off from the current collector during the lithiation process, and thus loses activity, and the electrochemical performance is deteriorated. In order to solve the above problems, researchers have been increasingly focusing on amorphous silicon in recent years. Amorphous silicon is only isotropically strained/stressed during lithiation/delithiation and is therefore more resistant to cracking due to volume expansion than crystalline silicon. In addition, amorphous silicon has a higher operating potential than crystalline silicon (amorphous: 0.22V; crystalline: 0.12V), and thus the problems of lithium dendrites and volume expansion can be effectively suppressed by increasing the cut-off potential.

Document 1, Sakabe, j.; ohta, n.; ohnishi, t.; mitsuishi, k.; takada, K.PorousAmorphous Silicon films for High-Capacity and Stable al-Solid-State Lithium batteries, Commun.Chem.2018,1,24-32, prepares porous amorphous Silicon thin Film electrodes by magnetron sputtering, but has the disadvantages of High cost and small yield, and is not easy to be applied in large scale. Document 2, Lin, n.; han, Y.; zhou, j.; zhang, k.; xu, t.; zhu, y.; qian, Y.A Low Temperature Mobile Salt Process for aluminum thermal Reduction of Silicon Oxides to Crystalline Si for Li-IonBatteries energy environ Sci 2015,8,3187 3191, aluminothermic Reduction of Silicon nanoparticles in aluminum chloride fused Salt, but the product can not keep original morphology to form smaller particles, and the prepared Silicon has better crystal form.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a preparation method of an amorphous silicon material, which has a simple and convenient process, and the preparation method comprises the steps of coating titanium dioxide on a silicon dioxide material by using a method for hydrolyzing tetrabutyl titanate to form a silicon dioxide/titanium dioxide composite material, reacting the silicon dioxide/titanium dioxide composite material with metal aluminum in chloride, removing impurities by acid washing, and drying to obtain the amorphous silicon electrode material. In the traditional aluminothermic reduction method, the generated silicon product is in a fine nano-particle shape, the original shape of the silicon dioxide raw material cannot be maintained, and the silicon nano-particle has a high crystallization degree. According to the invention, through the chemical adsorption and hydrolysis processes of tetrabutyl titanate, a titanium dioxide protective layer is pre-coated on the surface of silicon dioxide, and chloride is added in the reduction process, so that excessive heat generated in the reaction process is effectively absorbed, the contact area of reactants is greatly increased, the reaction is more efficient and uniform, the structural damage in the reaction process is greatly relieved, the product keeps the shape of the silicon dioxide raw material, and a large amount of amorphous state in the silicon product is formed. Provides a good preparation scheme for preparing amorphous silicon electrode materials. Meanwhile, various raw materials with different shapes, such as nano silicon dioxide ball powder, diatomite, white carbon black, rice hull ash, glass fiber waste, sand, sandy soil and powder after glass ball milling, are utilized, so that the utilization rate of some waste materials is greatly improved, and the shapes of final products are diversified.

In order to achieve the above object, the present invention adopts the following technical solutions:

and hydrolyzing tetrabutyl titanate coated by a silicon dioxide material to form a silicon dioxide/titanium dioxide composite material, reacting the silicon dioxide/titanium dioxide composite material with metal aluminum in chloride, removing impurities by acid washing, and drying to obtain the amorphous silicon electrode material.

The method specifically comprises the following steps:

(1) uniformly soaking a silicon dioxide raw material into an ethanol solution of tetrabutyl titanate, separating, performing hydrolysis reaction at normal temperature, and drying to obtain a silicon dioxide/titanium dioxide composite material;

(2) adding aluminum powder and chloride salt into the composite material prepared in the step (1), uniformly mixing, heating to react in an inert atmosphere, and cooling to obtain a reactant;

(3) and (3) sequentially immersing the reaction product into sufficient hydrochloric acid aqueous solution and hydrofluoric acid solution to remove impurities, and separating and drying to obtain the amorphous silicon material.

Further, the silica raw material in the step (1) is one or more of nano silica ball powder, diatomite, white carbon black, rice hull ash, glass fiber waste, sand, sandy soil and powder of ball-milled glass.

Further, the molar concentration of the ethanol solution of tetrabutyl titanate in the step (1) is 100-800 mmol/L.

Further, the hydrolysis reaction condition in the step (1) is reaction for 1-5 minutes at normal temperature.

Further, the inert atmosphere in the step (2) is pure argon gas, or a mixed gas of hydrogen (5 v%) and argon (95 v%).

Further, the chloride salt in the step (2) is aluminum chloride or a mixture of the aluminum chloride and other chloride salts.

Further, the molar ratio of the aluminum powder and the chloride salt in the step (2) to the silicon dioxide in the silicon dioxide raw material in the step (1) is 1.28: 2: 3: 0.5 to 1.

Further, the heating reaction condition in the step (2) is that the reaction temperature is 250-350 ℃, and the reaction is carried out for 3-12 hours at constant temperature.

Furthermore, the silicon product in the amorphous silicon material finally prepared by the invention is nanospheres with uniform size and complete appearance. The amorphous silicon material prepared by the invention contains nano silicon spheres; the diameter of the nano silicon spheres in the whole amorphous silicon material is about 200 nm. Further applied, the finally prepared amorphous silicon material is used as a lithium ion battery negative electrode material, is uniformly mixed with a commercially available Super-P conductive agent and a sodium alginate binder according to a mass ratio of 60:20:20, is coated on a current collector copper foil, is dried at 60 ℃ in a vacuum box, is prepared into an electrode plate with the diameter of 1.2cm by a tablet press, and is dried for 12 hours in vacuum at 80 ℃. Using a metal lithium sheet as a counter electrode, adopting Celgard 2400 as a diaphragm and 1mol/L LiPF₆+ EC + DEC (EC: DEC volume ratio 1:1) containing 10 vol% FEC as electrolyte in a glove box (H)₂O<1ppm,O₂<1ppm) and electrochemical performance test is carried out by adopting a blue CT2001A type battery tester, and the charge-discharge cut-off voltage is 0.005-1V (vs. Li)⁺/Li) The test temperature is 25 ℃, and the test result shows that the first cycle specific capacity of the electrode material can reach 2763.3mAh g^-1The first coulombic efficiency is 78.6 percent, and the material has excellent rate capability of 0.5,1,1.5,2,2.5,3,4A g^-1The specific capacity respectively reaches 2800,2494,2274,2050,1865,1755,1604mAh g under the current density^-1At 4A g^-1The specific capacity can still reach 1339mAh g after the current density is cycled for 500 weeks^-1。

Compared with the prior art, the invention has the following characteristics:

1) compared with the traditional aluminothermic reduction method, the method can better ensure that the silicon product keeps the unique appearance of the raw material, and the prepared material has uniform size and complete structure.

2) The prepared silicon material has a better amorphous state, so that the silicon material can better relieve the volume expansion in the electrode circulation process compared with crystalline silicon, and provides excellent electrochemical performance in the application of lithium ion batteries.

Drawings

FIG. 1 is a schematic process flow diagram of an amorphous silicon material prepared by the method of the present invention.

FIG. 2 is a scanning electron microscope spectrum of an amorphous silicon material prepared in example 1 of the present invention;

FIG. 3 is a transmission electron microscope (FIG. 3a) and a selected area electron diffraction (FIG. 3b) of an amorphous silicon material prepared according to example 1 of the present invention;

fig. 4 is a graph of electrochemical rate performance and coulombic efficiency of the amorphous silicon material prepared in example 1 of the present invention. The horizontal coordinate is the cycle number of weeks, and the unit is week; the left ordinate is the specific discharge capacity, in units: milliampere hour gram^-1(mAh g^-1) The right ordinate is coulombic efficiency in units: percentage (%).

Fig. 5 is a graph of electrochemical cycling performance and coulombic efficiency of amorphous silicon material prepared in example 1 of the present invention. The horizontal coordinate is the cycle number of weeks, and the unit is week; the left ordinate is the specific discharge capacity, in units: milliampere hour gram^-1(mAh g^-1) Right side longitudinal seatDenoted coulombic efficiency in units of: percentage (%).

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.