CN104009211B - Preparation method for porous silicon nanofiber/carbon composite material - Google Patents

Abstract

The invention relates to a method for preparing a porous silicon nanofiber/carbon composite material, belonging to the technical field of lithium ion batteries. Firstly, the chrysotile asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers from which impurities of alkali metal oxides have been removed; adding reducing metals to the silica nanofibers and mixing them uniformly, and performing a reduction reaction to obtain a reduced product , the reduction product was acid-washed, washed with water, and dried to prepare porous silicon nanofibers; the obtained porous silicon nanofibers were mixed with carbon precursors to obtain a mixed material, and then the mixed material was dissolved in a solvent, and under ultrasonic conditions The mixed solution is obtained by dispersing, and the dispersed mixed solution is pyrolytically carbonized or hydrothermally carbonized under the protection of an inert gas to prepare a porous silicon nanofiber/carbon composite material. The method uses natural minerals as raw materials, and is low in cost and simple; the porous silicon nanofiber/carbon composite material has the characteristics of high capacity density, high initial Coulombic efficiency, stable cycle performance and the like.

Description

A kind of preparation method of porous silicon nanofiber/carbon composite material

technical field

The invention relates to a method for preparing a porous silicon nanofiber/carbon composite material, belonging to the technical field of lithium ion batteries.

Background technique

With the rapid development of the electronics and information industries, mobile communications, digital cameras and portable computers are widely used, and the research and development of electric vehicles is also being carried out extensively and deeply, thus driving the rapid development of lithium-ion batteries, which provide energy for the above-mentioned equipment. develop. Compared with traditional nickel-metal hydride batteries and nickel-cadmium batteries, lithium-ion batteries have the advantages of high energy density, high working voltage, small self-discharge, fast charging and discharging, and good safety performance. They are the fastest growing and brightest market prospects. A secondary battery.

At present, the focus of lithium-ion battery research and development is to develop high-capacity and high-power power lithium-ion batteries and battery packs. The anodes of commercial lithium-ion batteries mainly use carbonaceous materials such as mesophase carbon microspheres, modified natural graphite, and artificial graphite. However, the theoretical capacity of these graphitized carbonaceous materials is only 372mAh/g, which greatly limits the further improvement of the overall capacity of the battery. In order to meet the needs of high-capacity lithium-ion batteries, research and development of high-capacity non-carbon lithium-ion battery anode materials has become very urgent and necessary.

Among the non-carbon negative electrode materials, the theoretical specific capacity of silicon is as high as 4200mAh/g, which is 11 times that of graphite negative electrode materials. Its lithium intercalation potential is below 0.5V, and silicon has abundant reserves on the earth and low cost. Promising anode materials for lithium-ion batteries. However, during the charge and discharge process of silicon, due to the large volume expansion caused by the alloying reaction of intercalation and deintercalation of lithium, and during the charge and discharge process, the SEI film is continuously eroded by the hydrofluoric acid formed by the contact reaction with the electrolyte, resulting in The first irreversible capacity of silicon is larger and the capacity fades faster. In recent years, researchers have modified silicon-based negative electrode materials, including nano-silicon, porous structure, carbon coating and alloying, etc., which have improved the capacity and cycle performance of silicon-based negative electrode materials to a certain extent.

The one-dimensional nano-silicon material has a nanometer-scale diameter. As a silicon anode material, it can significantly suppress the volume change of the material and reduce the intercalation distance of lithium ions, thereby improving the electrochemical cycle performance of the material. Cui Y, et al. used silane as the silicon source and gold as the catalyst to grow silicon nanowires on stainless steel through a gas-liquid-solid process. Silicon nanowires have the theoretical charge capacity of silicon, and the discharge capacity reaches 75%, with little capacity fading during cycling [Chan CK, Peng HL, Liu G, McIlwrath K, Zhang XF, Huggins RA, Cui Y. High-performance lithium battery anodes using silicon nanowires. Nature nanotechnology, 2008, 3: 31-35.]. Yoo JK et al.[ Yoo JK, Kim J, Lee H, Choi J. Porous silicon nanowires for lithium rechargeable batteries. Nanotechnology, 2013, 24: (2013) 424008(7pp)] used orthoethyl silicate (TEOS) as the The raw materials are prepared by electrospinning and then burning off organic matter to prepare nano-silica wires, then magnesia thermal reduction to prepare one-dimensional nano-silicon, and carbon-encapsulated one-dimensional nano-silicon/carbon composite negative electrode material.

From the above preparation methods, it can be seen that the preparation of one-dimensional nano-silicon is prepared by a "bottom-up" method. Although the synthesized samples are of high purity, there are disadvantages of complicated process procedures and high costs. Moreover, toxic and expensive silicon precursors are used as the silicon source. All of these are not conducive to the practical application of one-dimensional nano-silicon.

Natural raw materials with nanocomposition have the characteristics of wide sources and low cost, and the use of nanomaterials to prepare new nanostructures has the characteristics of simple process and low cost. For example, in recent years, rice husks are used as raw materials, and porous silicon is prepared by using nano-silica in it through magnesia thermal reduction, which is used as the negative electrode of lithium-ion batteries. Serpentine asbestos (Mg ₆ [Si ₄ O ₁₀ ](OH) ₈ ) is a natural nanofiber with a large aspect ratio, high flexibility, fire resistance, alkali resistance, wear resistance, and low thermal conductivity. It is an ideal raw material for making thermal insulation materials, and it can also be used as a reinforcing filler. Serpentine asbestos belongs to silicate minerals, and its crystal structure unit layer is composed of a layer of silicon-oxygen tetrahedron and magnesia octahedron. Due to the asymmetry of the unit layer, the structural layer bends to form a tubular structure with octahedron outside and tetrahedron inside. The outer diameter of the chrysotile fiber is between 16-56nm and the inner diameter is 3.5-24nm. A large amount of ^OH- on the surface of serpentine asbestos fibers is easy to react with H ⁺ , which leads to the exposure of ^Mg2+ . When H ⁺ is sufficient, MgO is also completely dissolved. The reaction equation is:

Mg ₆ [Si ₄ O ₁₀ ](OH) ₈ +12H ⁺ → 6Mg ²⁺ +4SiO ₂ +10H2O.

Contents of the invention

Aiming at the problems and deficiencies in the above-mentioned prior art, the present invention provides a preparation method of porous silicon nanofiber/carbon composite material. The present invention adopts a "top-down" method, using chrysoporite prepared from natural chrysotile as a raw material, pickling the nano-scale chrysoporite fiber in the mesoscopic field, and dissolving MgO therein to obtain the fiber shape nano-silicon dioxide; then obtain the fibrous nano-silicon dioxide by metal thermal reduction and acid leaching to obtain porous silicon nanofibers. Using the carbon precursor hydrothermal carbonization, pyrolytic carbonization or chemical vapor deposition method, the carbon coating is coated on the obtained porous silicon nanofiber to obtain a porous silicon nanofiber/carbon composite material, which is used as the negative electrode material of the lithium ion battery. The method has simple process and low cost, and will provide conditions for recycling asbestos tailings in asbestos mines and realizing sustainable development of enterprises and mineral resources. The present invention is realized through the following technical solutions.

A kind of preparation method of porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) Firstly, acid leaching, washing, filtering and drying the serpentine asbestos to obtain silica nanofibers from which alkali metal oxide impurities have been removed;

(2) Add reducing metals to the silica nanofibers obtained in step (1) and mix them evenly, then carry out a reduction reaction at a temperature of 500°C to 900°C in the absence of oxygen for 1h to 7h to obtain a reduced product, which is treated with acid Porous silicon nanofibers are prepared after washing, washing with water and drying;

(3) Preparation of porous silicon nanofiber/carbon composite material: Mix the porous silicon nanofiber obtained in step (2) with the carbon precursor at a mass ratio of 1:0.05-5 to obtain a mixed material, and then mix the mixed material according to the liquid-solid The ratio is 1:30-80g/ml dissolved in the solvent, and dispersed under ultrasonic conditions for 2-8 hours to obtain a mixed solution, and the dispersed mixed solution is pyrolytically carbonized or hydrothermally carbonized under the protection of an inert gas to prepare a porous silicon nanometer Fiber/Carbon Composite.

The chrysotile asbestos includes the following components in mass percentage: 19-35% Si, 19-25% Mg, 0.13-2.4% Fe, 0.03-0.32% Al, 42-53% O.

The solid-to-liquid ratio of the acid leaching process in the step (1) is 1:30-80g/ml, the leaching temperature is 80-100°C, the leaching time is 1.5-4h, the stirring speed is 400-700r/min, the acid leaching solution It is hydrochloric acid, sulfuric acid or nitric acid with H ⁺ concentration of 0.5-2mol/L.

The reducing metal in the step (2) is magnesium powder, aluminum powder, potassium, lithium, sodium or calcium particles, and the amount added is the theoretical amount for completely reducing the silicon dioxide in the silicon dioxide nanofiber.

The acid washing process of the reduction product in the step (2) is to first wash with HCl, HNO ₃ or H ₂ SO ₄ with a concentration of 5wt% to 40wt%, and then wash with 0.5wt% to 40wt% hydrofluoric acid. The temperature is 20°C-100°C, and the washing time is 0.2h-7h.

The carbon precursor in the step (3) is glucose, sucrose, starch, asphalt or phenolic resin.

The solvent in the step (3) is water, acetone, tetrahydrofuran, polyvinyl alcohol or polyethylene glycol.

The technical conditions of the pyrolytic carbonization in the step (3) are a temperature of 600-1300° C. and a holding time of 2-20 hours.

The hydrothermal carbonization process in the step (3) is to add the mixed solution into the reactor so that the mixed solution accounts for 50% to 90% of the volume of the reactor, and then keep the water temperature at 180 to 220°C for 12 ～48h, the solid is obtained after solid-liquid separation, and finally, under the protection of inert gas, the solid is carbonized at 400～1000°C for 2～24h.

The pyrolytic carbonization or hydrothermal carbonization of the step (3) to prepare the porous silicon nanofiber/carbon composite material can be replaced by the following steps: first, the porous silicon nanofiber is placed in a furnace with an inert gas and a carbon source gas, Pyrolysis at 600-1000°C for 0.5-10 hours to obtain a porous silicon nanofiber/carbon composite material in which carbon is deposited on the porous silicon nanofiber, wherein the carbon source gas includes acetylene, ethylene, benzene vapor, toluene, methane, ethane, propane , butane or cyclohexane; the inert gas includes nitrogen, argon and/or helium.

Any combination of the conditional values of any of the above-mentioned parameters can realize the present invention, and the porous silicon nanofiber/carbon composite material can be prepared.

The beneficial effects of the present invention are: (1) In the method for preparing the porous silicon nanofiber/carbon composite material of the present invention, the raw material resources used are abundant and the preparation process cost is low; (2) as the negative electrode material of lithium ion battery, the prepared porous Silicon nanofiber/carbon composite material has the characteristics of high capacity density, good rate performance, high initial Coulombic efficiency, and stable cycle performance; (3) The invention extracts nano-silica fibers from chrysotile, and is the first to use this fiber to pass through Porous silicon nanofibers were prepared by metallothermal reduction and applied to lithium-ion battery anode materials, which broadened the application of chrysotile.

detailed description

The present invention will be further described below in combination with specific embodiments.

Example 1

The preparation method of the porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) First, 1g of chrysotile asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers free of alkali metal oxide impurities, wherein the chrysotile asbestos includes the following mass percentage components: Si35 %, Mg19%, Fe2.4%, Al0.29%, O42.7%, the solid-liquid ratio of the acid leaching process is 1:30g/ml, the leaching temperature is 96°C, the leaching time is 127min, and the stirring speed is 400r/ min, the pickling solution is hydrochloric acid with H ⁺ concentration 2mol/L;

(2) Add reducing metals to the silica nanofibers obtained in step (1) and mix them evenly, then perform a reduction reaction for 7 hours at a temperature of 550°C in the absence of oxygen to obtain a reduced product, which is washed with acid, washed with water, and dried Porous silicon nanofibers are prepared in the end, wherein the reducing metal is magnesium powder, and the addition amount is the theoretical amount that the silicon dioxide in the silicon dioxide nanofibers is completely reduced; Washing, and then washing with 0.5wt% hydrofluoric acid, the washing temperature is 20°C, and the washing time is 0.2h;

(3) Preparation of porous silicon nanofiber/carbon composite material: Mix 0.1 g of porous silicon nanofiber and carbon precursor obtained in step (2) at a mass ratio of 1:2 to obtain a mixed material, and then mix the mixed material according to liquid-solid Dissolve in the solvent at a ratio of 1:80g/ml, and disperse under ultrasonic conditions for 2 hours to obtain a mixed solution. The dispersed mixed solution is hydrothermally carbonized under the protection of an inert gas to prepare a porous silicon nanofiber/carbon composite material, wherein the carbon The precursor is sucrose, and the solvent is water; the process of hydrothermal carbonization is to add the mixed solution into the reactor so that the mixed solution accounts for 50% of the volume of the reactor, and then keep it at a controlled hydrothermal temperature of 180°C for 24 hours, and pass through the solid-liquid carbonization process. After separation, a solid was obtained, and finally, under the protection of an inert gas, the solid was carbonized at 400° C. for 24 hours.

The prepared porous silicon nanofiber/carbon composite material is used as the negative pole of lithium-ion battery, and it is tested for charge-discharge specific capacity and cycle performance: one-dimensional nanoporous silicon and conductive agent, binder by mass ratio 8: 1:1 mixed to make the working electrode pole piece, metal lithium as the counter electrode, the electrolyte is a mixture of EC, DEC and DMC (volume ratio 1:1:1), 1M LiFP6 as the electrolyte salt, the diaphragm is Celgard2400, in A button cell was assembled in an argon atmosphere glove box. The charging and discharging voltage of the button cell is 0.01V-1.4V (vs. Li+/Li), and the current density is 100mA/g.

Test results: The first charge capacity of one-dimensional nanoporous silicon is 1900mAh/g, the first Coulombic efficiency is 80%, and the charge capacity after 30 cycles is 1460mAh/g.

Example 2

The preparation method of the porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) Firstly, 10g of chrysotile asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers from which alkali metal oxide impurities are removed, wherein the chrysotile asbestos includes the following mass percentage components: Si19 %, Mg25%, Fe1.6%, Al0.32%, O53%; the solid-liquid ratio of the acid leaching process is 1:60g/ml, the leaching temperature is 80°C, the leaching time is 3h, and the stirring speed is 700r/min. The pickling solution is hydrochloric acid with H ⁺ concentration of 2mol/L;

(2) Add a reducing metal to the silica nanofibers obtained in step (1) and mix them evenly, then perform a reduction reaction for 5 hours at a temperature of 600°C in the absence of oxygen to obtain a reduced product, which is washed with acid, washed with water, and dried Afterwards, the porous silicon nanofiber is prepared, wherein the reducing metal is aluminum powder, and the addition amount is the theoretical amount that the fiber silicon dioxide in the silicon dioxide nanometer is completely reduced; ₃ washing, and then washing with 0.5wt% hydrofluoric acid, the washing temperature is 100°C, and the washing time is 7h;

(3) Preparation of porous silicon nanofiber/carbon composite material: Mix 0.2 g of porous silicon nanofiber and carbon precursor obtained in step (2) at a mass ratio of 1:2.5 to obtain a mixed material, and then mix the mixed material according to liquid-solid Dissolve in the solvent at a ratio of 1:30g/ml, and disperse under ultrasonic conditions for 8 hours to obtain a mixed solution. The dispersed mixed solution is pyrolyzed and carbonized under the protection of an inert gas to prepare a porous silicon nanofiber/carbon composite material, wherein the carbon The precursor is phenolic resin, and the solvent is acetone; the process conditions of pyrolytic carbonization are temperature 800°C and holding time 5h.

Carry out battery assembly and test according to the same method in Example 1, test result: the initial charging capacity of porous silicon nanofiber/carbon composite material is 1500mAh/g, and first Coulombic efficiency is 83%, after 30 cycles, charging capacity is 1230mAh/g.

Example 3

The preparation method of the porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) First, 10g of chrysotile asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers free of alkali metal oxide impurities, wherein chophilolite asbestos includes the following mass percentage components: Si27 %, Mg22%, Fe1.3%, Al0.18%, O48%; the solid-liquid ratio of the acid leaching process is 1:60g/ml, the leaching temperature is 90°C, the leaching time is 4h, and the stirring speed is 600r/min. The pickling solution is sulfuric acid with H ⁺ concentration of 0.5mol/L;

(2) Add reducing metals to the silica nanofibers obtained in step (1) and mix them evenly, then perform a reduction reaction for 3 hours at a temperature of 700°C in the absence of oxygen to obtain a reduced product, which is washed with acid, washed with water, and dried Porous silicon nanofibers are prepared in the end, wherein the reducing metal is magnesium powder, and the addition amount is the theoretical amount that the silicon dioxide in the silicon dioxide nanofibers is completely reduced; ₂ SO ₄ washing, then washing with 25wt% hydrofluoric acid, the washing temperature is 80°C, and the washing time is 5h;

(3) Preparation of porous silicon nanofiber/carbon composite material: Mix 0.3 g of porous silicon nanofiber and carbon precursor obtained in step (2) at a mass ratio of 1:5 to obtain a mixed material, and then mix the mixed material according to the liquid-solid The ratio of 1:55g/ml was dissolved in the solvent, and dispersed under ultrasonic conditions for 5h to obtain a mixed solution, and the dispersed mixed solution was pyrolyzed and carbonized under the protection of an inert gas to prepare a porous silicon nanofiber/carbon composite material, wherein the carbon The precursor is asphalt, and the solvent is tetrahydrofuran; the process conditions of pyrolytic carbonization are temperature 800 ℃, holding time 5h.

Carry out battery assembly and test according to the same method in Example 1, test result: the initial charging capacity of porous silicon nanofiber/carbon composite material is 1370mAh/g, and first Coulombic efficiency is 84%, after 30 cycles, charging capacity is 1130mAh/g.

Example 4

The preparation method of the porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) Firstly, 10g of chrysotile asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers from which alkali metal oxide impurities are removed, wherein the chrysotile asbestos includes the following mass percentage components: Si19 .5%, Mg25.0%, Fe1.6%, Al0.32%, O52.7%; the solid-to-liquid ratio of the acid leaching process is 1:40g/ml, the leaching temperature is 80°C, the leaching time is 3h, stirring The speed is 600r/min, and the pickling solution is sulfuric acid with H ⁺ concentration of 1mol/L;

(2) Add reducing metals to the silica nanofibers obtained in step (1) and mix them evenly, then carry out a reduction reaction for 6 hours at a temperature of 800°C in the absence of oxygen to obtain a reduced product, which is washed with acid, washed with water, and dried Porous silicon nanofibers are prepared in the end, wherein the reducing metal is lithium particles, and the addition amount is the theoretical amount that the silicon dioxide in the silicon dioxide nanofibers is completely reduced; Washing, then washing with 10wt% hydrofluoric acid, the washing temperature is 60°C, and the washing time is 4h;

(3) Preparation of porous silicon nanofiber/carbon composite material: Mix 1 g of porous silicon nanofiber and carbon precursor obtained in step (2) at a mass ratio of 1:0.05 to obtain a mixed material, and then mix the mixed material according to the liquid-solid ratio Dissolve in the solvent at 1:55g/ml, and disperse under ultrasonic conditions for 3 hours to obtain a mixed solution. The dispersed mixed solution is hydrothermally carbonized under the protection of an inert gas to prepare a porous silicon nanofiber/carbon composite material, wherein the carbon precursor The body is glucose, and the solvent is polyethylene glycol; the process of hydrothermal carbonization is to add the mixed solution into the reactor so that the mixed solution accounts for 90% of the volume of the reactor, and then keep the temperature at 220°C for 48 hours under the control of the hydrothermal carbonization process. A solid was obtained after solid-liquid separation, and finally, under the protection of an inert gas, the solid was carbonized at 500° C. for 4 h.

Carry out battery assembly and test according to the same method in Example 1, test result: the initial charge capacity of porous silicon nanofiber/carbon composite material is 1800mAh/g, and the first coulombic efficiency is 85%, after 30 cycles, charge capacity is 1520mAh/g.

Example 5

The preparation method of the porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) Firstly, the cherolite asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers from which alkali metal oxide impurities are removed, wherein the christolite asbestos includes the following mass percentage components: Si19% , Mg20%, Fe0.13%, Al0.03%, O53%; the solid-liquid ratio of the acid leaching process is 1:40g/ml, the leaching temperature is 80°C, the leaching time is 3h, the stirring speed is 600r/min, the acid The immersion solution is nitric acid with H ⁺ concentration of 0.5mol/L;

(2) After adding reducing metals to the silica nanofibers obtained in step (1) and mixing them uniformly, the reduction reaction was carried out for 2.5 hours in the absence of oxygen at a temperature of 700°C to obtain a reduction product, which was washed with acid, washed with water, Prepare porous silicon nanofibers after drying, wherein the reducing metal is potassium particles, and the addition amount is the theoretical amount that the silicon dioxide in the silicon dioxide nanofibers is completely reduced; Washing with H ₂ SO ₄ , and then washing with 40wt% hydrofluoric acid, the washing temperature is 80°C, and the washing time is 6h;

(3) Preparation of porous silicon nanofiber/carbon composite material: Mix 1 g of porous silicon nanofiber and carbon precursor obtained in step (2) at a mass ratio of 1:4 to obtain a mixed material, and then mix the mixed material according to the liquid-solid ratio Dissolve in a solvent at 1:55g/ml, and disperse under ultrasonic conditions for 2 hours to obtain a mixed solution. The dispersed mixed solution is hydrolyzed and carbonized under the protection of an inert gas to prepare a porous silicon nanofiber/carbon composite material, wherein the carbon precursor The body is sucrose, the solvent is water, and the process of hydrothermal carbonization is to add the mixed solution into the reactor so that the mixed solution accounts for 80% of the volume of the reactor, and then control the hydrothermal temperature at 190 ° C for 12 hours, and separate the solid and liquid Finally, a solid was obtained, and finally, under the protection of an inert gas, the solid was carbonized at 1000° C. for 24 hours.

Carry out battery assembly and test according to the same method in Example 1, test result: the first charge capacity of porous silicon nanofiber/carbon composite material is 2100mAh/g, and the first coulombic efficiency is 85%, after 30 cycles, charge capacity is 1770mAh/g.

Example 6

The preparation method of the porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) Firstly, 10g of chrysotile asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers from which alkali metal oxide impurities have been removed, wherein chophilolite asbestos includes the following mass percentage components: Si21 %, Mg25.3%, Fe0.13%, Al0.03%, O42%; the solid-to-liquid ratio of the acid leaching process is 1:40g/ml, the leaching temperature is 70°C, the leaching time is 3h, and the stirring speed is 500r/ min, the pickling solution is nitric acid with H ⁺ concentration of 1mol/L;

(2) Add reducing metals to the silica nanofibers obtained in step (1) and mix them evenly, then carry out a reduction reaction at 850°C in the absence of oxygen for 1.5 hours to obtain a reduced product, which is washed with acid, washed with water, Prepare porous silicon nanofibers after drying, wherein the reducing metal is sodium particles, and the amount is the theoretical amount that the silicon dioxide in the silicon dioxide nanofibers is completely reduced; Washing with HCl, then washing with 20wt% hydrofluoric acid, the washing temperature is 80°C, and the washing time is 5h;

(3) Preparation of porous silicon nanofiber/carbon composite material: Mix the porous silicon nanofiber obtained in step (2) with the carbon precursor at a mass ratio of 1:4 to obtain a mixed material, and then mix the mixed material according to the liquid-solid ratio of 1:55g/ml dissolved in the solvent, and dispersed under ultrasonic conditions for 6 hours to obtain a mixed solution, the dispersed mixed solution was pyrolyzed and carbonized under the protection of an inert gas to prepare a porous silicon nanofiber/carbon composite material, in which the carbon precursor The body is glucose, the solvent is water, and the technological conditions of pyrolytic carbonization are temperature 800°C and holding time 16h.

Carry out battery assembly and test according to the same method in Example 1, test result: the initial charging capacity of porous silicon nanofiber/carbon composite material is 1370mAh/g, and first Coulombic efficiency is 84%, after 30 cycles, charging capacity is 1130mAh/g.

Example 7

The preparation method of the porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) Firstly, 10g of chrysotile asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers from which alkali metal oxide impurities are removed, wherein the chrysotile asbestos includes the following mass percentage components: Si19 .5%, Mg25.0%, Fe1.6%, Al0.32%, O52.7%; the solid-to-liquid ratio of the acid leaching process is 1:80g/ml, the leaching temperature is 100°C, the leaching time is 1.5, stirring The speed is 500r/min, and the pickling solution is hydrochloric acid with a H ⁺ concentration of 1.5mol/L;

(2) Add reducing metals to the silica nanofibers obtained in step (1) and mix them evenly, then perform a reduction reaction for 1 hour at a temperature of 900°C in the absence of oxygen to obtain a reduced product, which is washed with acid, washed with water, and dried Porous silicon nanofibers are prepared in the end, wherein the reducing metal is calcium particles, and the addition amount is the theoretical amount that the silicon dioxide in the silicon dioxide nanofibers is completely reduced; ₃ washing, and then washing with 30wt% hydrofluoric acid, the washing temperature is 80°C, and the washing time is 5h;

(3) Preparation of porous silicon nanofiber/carbon composite material: Mix 0.1 g of porous silicon nanofiber and carbon precursor obtained in step (2) at a mass ratio of 1:4 to obtain a mixed material, and then mix the mixed material according to the liquid-solid The ratio is 1:55g/ml dissolved in the solvent, and dispersed under ultrasonic conditions for 6h to obtain a mixed solution, the dispersed mixed solution is pyrolyzed and carbonized under the protection of an inert gas to prepare a porous silicon nanofiber/carbon composite material, in which the carbon The precursor is starch, and the solvent is water; the process conditions of pyrolytic carbonization are temperature 1300°C and holding time 2h.

Carry out battery assembly and test according to the same method in Example 1, test result: the initial charge capacity of porous silicon nanofiber/carbon composite is 1500mAh/g, and the first Coulombic efficiency is 85%, after 30 cycles, the charge capacity is 1256mAh/g.

Example 8

The preparation method of the porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) Firstly, the cherolite asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers from which alkali metal oxide impurities are removed, wherein the cherolite asbestos includes the following mass percentage components: Si19. 5%, Mg25.0%, Fe1.6%, Al0.32%, O52.7%; the solid-liquid ratio of the acid leaching process is 1:40g/ml, the leaching temperature is 90℃, the leaching time is 3h, the stirring speed is 600r/min, and the pickling solution is sulfuric acid with H ⁺ concentration of 1mol/L;

(2) Add reducing metals to the silica nanofibers obtained in step (1) and mix them evenly, then carry out a reduction reaction for 6 hours at a temperature of 500°C in the absence of oxygen to obtain a reduced product, which is washed with acid, washed with water, and dried Afterwards, porous silicon nanofibers are prepared, wherein the reducing metal is magnesium powder, and the amount added is the theoretical amount for completely reducing silicon dioxide in the silicon dioxide nanofibers;

(3) Preparation of porous silicon nanofiber/carbon composite material: Mix the porous silicon nanofiber obtained in step (2) with the carbon precursor at a mass ratio of 1:0.05 to obtain a mixed material, and then mix the mixed material according to the liquid-solid ratio of 1:40g/ml was dissolved in a solvent, and dispersed under ultrasonic conditions for 4 hours to obtain a mixed solution, and the dispersed mixed solution was pyrolyzed and carbonized under the protection of an inert gas to prepare a porous silicon nanofiber/carbon composite material, wherein the solvent was poly Vinyl alcohol; the technical conditions of pyrolytic carbonization are temperature 600°C and holding time 20h.

Carry out battery assembly and test according to the same method in Example 1, test result: the initial charge capacity of porous silicon nanofiber/carbon composite material is 2200mAh/g, and the first coulombic efficiency is 80%, after 30 cycles, the charge capacity is 1700mAh/g.

Example 9

The preparation method of the porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) Firstly, the cherolite asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers from which alkali metal oxide impurities are removed, wherein the cherolite asbestos includes the following mass percentage components: Si19. 5%, Mg25.0%, Fe1.6%, Al0.32%, O52.7%; the solid-liquid ratio of the acid leaching process is 1:40g/ml, the leaching temperature is 90℃, the leaching time is 3h, the stirring speed is 600r/min, and the pickling solution is sulfuric acid with H ⁺ concentration of 1mol/L;

(2) Add reducing metals to the silica nanofibers obtained in step (1) and mix them evenly, then carry out a reduction reaction for 6 hours at a temperature of 500°C in the absence of oxygen to obtain a reduced product, which is washed with acid, washed with water, and dried Afterwards, porous silicon nanofibers are prepared, wherein the reducing metal is magnesium powder, and the amount added is the theoretical amount for completely reducing silicon dioxide in the silicon dioxide nanofibers;

(3) Preparation of porous silicon nanofibers/carbon composites: put porous silicon nanofibers into a tube furnace with nitrogen and acetylene gas, and pyrolyze them at 600 °C for 0.5 h to obtain carbon deposited on porous silicon nanofibers. Porous silicon nanofiber/carbon composites.

Carry out battery assembly and test according to the same method in Example 1, test result: the initial charge capacity of porous silicon nanofiber/carbon composite material is 2000mAh/g, and the first coulombic efficiency is 81%, after 30 cycles, the charge capacity is 1596mAh/g.

Example 10

The preparation method of the porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) Firstly, the cherolite asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers from which alkali metal oxide impurities are removed, wherein the cherolite asbestos includes the following mass percentage components: Si19. 5%, Mg25.0%, Fe1.6%, Al0.32%, O52.7%; the solid-liquid ratio of the acid leaching process is 1:40g/ml, the leaching temperature is 90℃, the leaching time is 3h, the stirring speed is 600r/min, and the pickling solution is sulfuric acid with H ⁺ concentration of 1mol/L;

(2) Add reducing metals to the silica nanofibers obtained in step (1) and mix them evenly, then carry out a reduction reaction for 6 hours at a temperature of 500°C in the absence of oxygen to obtain a reduced product, which is washed with acid, washed with water, and dried Afterwards, porous silicon nanofibers are prepared, wherein the reducing metal is magnesium powder, and the amount added is the theoretical amount for completely reducing silicon dioxide in the silicon dioxide nanofibers;

(3) Preparation of porous silicon nanofibers/carbon composites: Put porous silicon nanofibers into a tube furnace with argon and methane gas, and pyrolyze them at 1000°C for 10 hours to obtain carbon deposited on porous silicon nanofibers. Porous silicon nanofiber/carbon composites.

Carry out battery assembly and test according to the same method in Example 1, test result: the initial charge capacity of porous silicon nanofiber/carbon composite material is 1800mAh/g, and the first coulombic efficiency is 80%, after 30 cycles, the charge capacity is 1410mAh/g.

Example 11

The preparation method of the porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) Firstly, the cherolite asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers from which alkali metal oxide impurities are removed, wherein the cherolite asbestos includes the following mass percentage components: Si19. 5%, Mg 25.0%, Fe1.6%, Al0.32%, O52.7%; the solid-liquid ratio of the acid leaching process is 1:40g/ml, the leaching temperature is 90℃, the leaching time is 3h, and the stirring speed is 600r/min, the pickling solution is sulfuric acid with a H ⁺ concentration of 1mol/L;

(2) Add reducing metals to the silica nanofibers obtained in step (1) and mix them evenly, then carry out a reduction reaction for 6 hours at a temperature of 500°C in the absence of oxygen to obtain a reduced product, which is washed with acid, washed with water, and dried Afterwards, porous silicon nanofibers are prepared, wherein the reducing metal is magnesium powder, and the amount added is the theoretical amount for completely reducing silicon dioxide in the silicon dioxide nanofibers;

(3) Preparation of porous silicon nanofibers/carbon composites: put porous silicon nanofibers into a tube furnace with helium and toluene vapor, and pyrolyze them at 800 °C for 5 hours to obtain carbon deposited on porous silicon nanofibers. Porous silicon nanofiber/carbon composites.

Carry out battery assembly and test according to the same method in Example 1, test result: the initial charge capacity of porous silicon nanofiber/carbon composite material is 1900mAh/g, and the first coulombic efficiency is 82%, after 30 cycles, the charge capacity is 1525mAh/g.

Example 12

The preparation method of the porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) Firstly, the cherolite asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers from which alkali metal oxide impurities are removed, wherein the cherolite asbestos includes the following mass percentage components: Si19. 5%, Mg25.0%, Fe1.6%, Al0.32%, O52.7%; the solid-liquid ratio of the acid leaching process is 1:40g/ml, the leaching temperature is 90℃, the leaching time is 3h, the stirring speed is 600r/min, and the pickling solution is sulfuric acid with H ⁺ concentration of 1mol/L;

(2) Add reducing metals to the silica nanofibers obtained in step (1) and mix them evenly, then carry out a reduction reaction for 6 hours at a temperature of 500°C in the absence of oxygen to obtain a reduced product, which is washed with acid, washed with water, and dried Afterwards, porous silicon nanofibers are prepared, wherein the reducing metal is magnesium powder, and the amount added is the theoretical amount for completely reducing silicon dioxide in the silicon dioxide nanofibers;

(3) Preparation of porous silicon nanofiber/carbon composite material: put the porous silicon nanofiber into a tube furnace with helium and propane gas, and pyrolyze it at 900°C for 0.5h to obtain carbon deposited on the porous silicon nanofiber porous silicon nanofiber/carbon composites.

Carry out battery assembly and test according to the same method in embodiment 1, test result: the initial charge capacity of porous silicon nanofiber/carbon composite material is 1700mAh/g, and the first coulombic efficiency is 87%, after 30 cycles, charge capacity is 1460mAh/g.

Example 13

The preparation method of the porous silicon nanofiber/carbon composite material, its specific steps are as follows:

(1) Firstly, the cherolite asbestos is acid-leached, washed with water, filtered and dried to obtain silica nanofibers from which alkali metal oxide impurities are removed, wherein the cherolite asbestos includes the following mass percentage components: Si19. 5%, Mg25.0%, Fe1.6%, Al0.32%, O52.7%; the solid-liquid ratio of the acid leaching process is 1:40g/ml, the leaching temperature is 90℃, the leaching time is 3h, the stirring speed is 600r/min, and the pickling solution is sulfuric acid with H ⁺ concentration of 1mol/L;

(2) Add reducing metals to the silica nanofibers obtained in step (1) and mix them evenly, then carry out a reduction reaction for 6 hours at a temperature of 500°C in the absence of oxygen to obtain a reduced product, which is washed with acid, washed with water, and dried Afterwards, porous silicon nanofibers are prepared, wherein the reducing metal is magnesium powder, and the amount added is the theoretical amount for completely reducing silicon dioxide in the silicon dioxide nanofibers;

(3) Preparation of porous silicon nanofibers/carbon composites: put porous silicon nanofibers into a tube furnace with argon and ethylene gas, and pyrolyze them at 600 °C for 10 h to obtain carbon deposited on porous silicon nanofibers. Porous silicon nanofiber/carbon composites.

Carry out battery assembly and test according to the same method in Example 1, test result: the initial charge capacity of porous silicon nanofiber/carbon composite material is 1850mAh/g, and the first coulombic efficiency is 86.5%, after 30 cycles, the charge capacity is 1576mAh/g.

Claims (10)

1. a kind of preparation method of porous silicon nanofiber/carbon composite, it is characterised in that comprise the following steps that：

（1）Obtain removing the dioxy of alkali metal oxide impurity first by choysotile asbestos acidleach, washing, filtration and after being dried SiClx nanofiber；

（2）To step（1）After the silica nano fibrous addition reducing metal for obtaining is well mixed, it is in anaerobic, temperature Reduction reaction 1h～7h is carried out under the conditions of 500 DEG C～900 DEG C and obtains reduzate, reduzate is made Jing pickling, washing, after being dried It is standby to obtain porous silicon nanofiber；

（3）Prepare porous silicon nanofiber/carbon composite：By step（2）The porous silicon nanofiber of gained and the forerunner of carbon Body in mass ratio 1：0.05～5 is well mixed and obtains mixed material, according to liquid-solid ratio is then 1 by mixed material：30～80g/ Ml is dissolved in solvent, and disperses 2～8h to obtain mixed liquor under ultrasound condition, by the mixed liquor after dispersion under controlled atmosphere Pyrolysis carbonization or hydrothermal carbonization prepare porous silicon nanofiber/carbon composite.

2. the preparation method of porous silicon nanofiber/carbon composite according to claim 1, it is characterised in that：It is described Choysotile asbestos includes following mass percent component：Si19～35%, Mg19～25%, Fe0.13～2.4%, Al0.03～ 0.32%th, O42～53%.

3. the preparation method of porous silicon nanofiber/carbon composite according to claim 1, it is characterised in that：It is described Step（1）The solid-to-liquid ratio of middle acidleach process is 1：30～80g/ml, extraction temperature be 80～100 DEG C, extraction time be 1.5～ 4h, mixing speed is 400～700r/min, and acid dip solution is H⁺The hydrochloric acid of 0.5～2mol/L of concentration, sulfuric acid or nitric acid.

4. the preparation method of porous silicon nanofiber/carbon composite according to claim 1, it is characterised in that：It is described Step（2）In reducing metal be magnesium powder, aluminium powder, potassium, lithium, sodium or calcium particle, addition is will be silica nano fibrous The theoretical amount that middle silica is restored completely.

5. the preparation method of porous silicon nanofiber/carbon composite according to claim 1, it is characterised in that：It is described Step（2）In reduzate acid cleaning process be first with HCl, HNO that concentration is 5wt%～40wt%₃Or H₂SO₄Washing, Ran Houyong The hydrofluoric acid wash of 0.5wt%～40wt%, wash temperature is 20 DEG C～100 DEG C, and wash time is 0.2h～7h.

6. the preparation method of porous silicon nanofiber/carbon composite according to claim 1, it is characterised in that：It is described Step（3）In carbon presoma be glucose, sucrose, starch, pitch or phenolic resin.

7. the preparation method of porous silicon nanofiber/carbon composite according to claim 1, it is characterised in that：It is described Step（3）In solvent be water, acetone, tetrahydrofuran, polyvinyl alcohol or polyethylene glycol.

8. the preparation method of porous silicon nanofiber/carbon composite according to claim 1, it is characterised in that：It is described Step（3）In pyrolysis carbonization process conditions be 600～1300 DEG C of temperature, 2～20h of temperature retention time.

9. the preparation method of porous silicon nanofiber/carbon composite according to claim 1, it is characterised in that：It is described Step（3）In the technique of hydrothermal carbonization be that mixed liquor is added in reactor make mixed liquor account for the reactor volume 50% ～90%, it is then 180～220 DEG C of 12～48h of insulation hydrothermal temperature is controlled, solid is obtained Jing after separation of solid and liquid, finally lazy Under property gas shielded, solid is carbonized under the conditions of 400～1000 DEG C 2～24h.

10. the preparation method of porous silicon nanofiber/carbon composite according to claim 1, it is characterised in that：It is described Step（3）Prepare porous silicon nanofiber/carbon composite to be replaced by following steps：First by porous silicon nanofiber It is put into and is connected with the stove of inert gas and carbon-source gas, at 600～1000 DEG C 0.5～10h is pyrolyzed, obtains Carbon deposition in porous silicon Porous silicon nanofiber/carbon composite on nanofiber.