阅读说明：本技术 一种硼掺杂纳米硅的制备方法 (Preparation method of boron-doped nano silicon ) 是由 陈顺鹏 郑捷 李星国 于 2021-07-27 设计创作，主要内容包括：本发明公开了一种硼掺杂纳米硅的制备方法,包括以下步骤：(1)取氧化硅、镁粉和氧化硼混合,在室温下进行球磨,得到混合均匀的混合物；(2)向步骤(1)得到的混合物中加入戊醇,再加入重量百分比浓度为5％wt-20％wt的稀盐酸,浸没20-40分钟,固液分离,得到纳米硅固体；(3)向步骤(2)得到的纳米硅固体中依次加入乙醇和水进行洗涤,固液分离得到固体,在60-80℃的温度下真空加热干燥固体,得到硼掺杂纳米硅；(4)步骤(3)得到的硼掺杂纳米硅使用HF溶液刻蚀,除去所述硼掺杂纳米硅的表面氧化层,乙醇洗涤,固液分离得到固体,在60-80℃的温度下真空加热干燥固体,得到无氧化层的硼掺杂纳米硅。(The invention discloses a preparation method of boron-doped nano silicon, which comprises the following steps: (1) mixing silicon oxide, magnesium powder and boron oxide, and performing ball milling at room temperature to obtain a uniformly mixed mixture; (2) adding pentanol into the mixture obtained in the step (1), then adding dilute hydrochloric acid with the weight percentage concentration of 5-20% wt, immersing for 20-40 minutes, and performing solid-liquid separation to obtain nano silicon solid; (3) adding ethanol and water into the nano-silicon solid obtained in the step (2) in sequence for washing, carrying out solid-liquid separation to obtain a solid, and heating and drying the solid in vacuum at the temperature of 60-80 ℃ to obtain boron-doped nano-silicon; (4) and (4) etching the boron-doped nano silicon obtained in the step (3) by using an HF solution, removing a surface oxidation layer of the boron-doped nano silicon, washing by using ethanol, carrying out solid-liquid separation to obtain a solid, and heating and drying the solid in vacuum at the temperature of 60-80 ℃ to obtain the boron-doped nano silicon without the oxidation layer.)

1. A preparation method of boron-doped nano silicon is characterized by comprising the following steps:

(1) mixing silicon oxide, magnesium powder and boron oxide, and performing ball milling at room temperature to obtain a uniformly mixed mixture;

(2) adding pentanol into the mixture obtained in the step (1), then adding dilute hydrochloric acid with the weight percentage concentration of 5-20% wt, immersing for 20-40 minutes, and performing solid-liquid separation to obtain nano silicon solid;

(3) and (3) sequentially adding ethanol and water into the nano-silicon solid obtained in the step (2) for washing, carrying out solid-liquid separation to obtain a solid, and heating and drying the solid in vacuum at the temperature of 60-80 ℃ to obtain the boron-doped nano-silicon.

2. The method for preparing boron-doped nano-silicon according to claim 1, further comprising the steps of:

(4) and (4) etching the boron-doped nano silicon obtained in the step (3) by using an HF solution, removing a surface oxidation layer of the boron-doped nano silicon, washing by using ethanol, carrying out solid-liquid separation to obtain a solid, and heating and drying the solid in vacuum at the temperature of 60-80 ℃ to obtain the boron-doped nano silicon without the oxidation layer.

3. The method for preparing boron-doped nano silicon according to claim 1, wherein in the step (1), the mass fraction of the boron oxide in the mixture is 1-10%, and the mass ratio of the silicon oxide to the magnesium powder is 1-1.5.

4. The method as claimed in claim 1, wherein in the step (1), the ball-to-material ratio is 10:1-50:1, and the ball milling time is 200-600 min.

5. The method as claimed in claim 1, wherein the solid-liquid separation in step (3) is performed by centrifugation or filtration, wherein the rotation speed of centrifugation is 10000-15000 rpm.

6. The method for preparing boron-doped nano silicon according to claim 1, wherein in the step (3), the drying of the solid is carried out under vacuum condition, and the drying is carried out under vacuum heating at a temperature of 60-80 ℃ for 3-5 h.

7. The method for preparing boron-doped nano silicon according to claim 2, wherein in the step (4), the HF solution has a concentration of 0.1 wt% to 40 wt% by weight.

8. The method as claimed in claim 2, wherein the solid-liquid separation in step (4) is performed by centrifugation or filtration, wherein the rotation speed of centrifugation is 10000-15000 rpm.

9. The method for preparing boron-doped nano silicon according to claim 2, wherein in the step (4), the drying of the solid is carried out under vacuum condition, and the drying is carried out under vacuum heating at a temperature of 60-80 ℃ for 3-5 h.

Technical Field

The invention belongs to the field of lithium battery materials, and particularly relates to a preparation method of boron-doped nano silicon.

Background

Currently, silicon has an excellent theoretical specific capacity (3579mAh g) ^-1) And becomes a new generation of lithium battery negative electrode material which attracts attention. However, silicon undergoes a large volume change during charge and discharge cycles, so that a silicon-based material with poor conductivity is cracked and loses electrical contact with a conductive agent, a current collector and the like, and the cycle performance is extremely poor. Meanwhile, the material fragmentation can cause the breakage and regeneration of a solid electrolyte interface film on the surface, so that lithium ions in the anode material are continuously consumed, and the first-cycle coulomb efficiency of the silicon-based material is low.

The preparation of nano-silicon usually requires a more rigorous method and precise instrument, such as chemical vapor deposition, and expensive raw materials (such as SiH)₄) And the high reaction temperature makes the preparation cost of the nano silicon too high. The silicon material is doped with heteroatoms such as boron, phosphorus, germanium and the like, so that the conductivity of the silicon-based material can be remarkably improved, and the energy band structure of the silicon-based material can be adjusted. For example, trace boron atoms are doped into silicon, so that the silicon is converted from an intrinsic semiconductor into a p-shaped semiconductor, and the conductivity of the silicon is greatly improved; meanwhile, the Fermi level of the silicon-based material can be adjusted by introducing boron, so that the Fermi level of the silicon-based material is shifted to a valence band, and the oxidation resistance of the silicon-based material is improved. However, the cost of the nano silicon is very high at present, and the difficulty in obtaining boron-doped nano silicon is greater. The conditions for doping boron into Silicon are also very harsh, for example, boron doping by means of Ion implantation combined with High temperature annealing is required in the semiconductor industry, for example, Li et al report that magnesium silicide and boric acid are used as raw materials, and boron is doped into Nano Silicon by High temperature calcination at 900 ℃ for 3 hours in a tube furnace under the atmosphere of High purity argon (99.999%) (ping Li, Jang-Yeon Hwang, Yang-Kook sun, Nano/microstrured Silicon-Graphite Composite Anode for High-Energy-Density Li-Ion battery.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

Aiming at the problems, the invention aims to provide a preparation method of boron-doped nano silicon, which solves the problems of harsh production conditions, high difficulty and high cost of the boron-doped nano silicon.

In order to achieve the purpose, the preparation method of the boron-doped nano silicon provided by the invention comprises the following steps:

(1) mixing silicon oxide, magnesium powder and boron oxide, and performing ball milling at room temperature to obtain a uniformly mixed mixture;

(2) adding pentanol into the mixture obtained in the step (1), then adding dilute hydrochloric acid with the weight percentage concentration of 5-20% wt, immersing for 20-40 minutes, and performing solid-liquid separation to obtain nano silicon solid;

(3) and (3) sequentially adding ethanol and water into the nano-silicon solid obtained in the step (2) for washing, carrying out solid-liquid separation to obtain a solid, and heating and drying the solid in vacuum at the temperature of 60-80 ℃ to obtain the boron-doped nano-silicon.

Further, the method also comprises the following steps:

(4) and (4) etching the boron-doped nano silicon obtained in the step (3) by using an HF solution, removing a surface oxidation layer of the boron-doped nano silicon, washing by using ethanol, carrying out solid-liquid separation to obtain a solid, and heating and drying the solid in vacuum at the temperature of 60-80 ℃ to obtain the boron-doped nano silicon without the oxidation layer.

Preferably, in the step (1), the mass fraction of the boron oxide in the mixture is 1-10%, and the mass ratio of the silicon oxide to the magnesium powder is 1-1.5.

Preferably, in the step (1), the ball-material ratio is 10:1-50:1, and the ball milling time is 200-600 min.

Preferably, in the step (3), the solid-liquid separation is performed by centrifugal separation or filtration separation, wherein the rotation speed of the centrifugal separation is 10000-15000 rpm.

Preferably, in step (3), the drying of the solid is carried out under vacuum conditions and the drying is carried out under vacuum heating at a temperature of 60-80 ℃ for 3-5 h.

Preferably, in step (4), the HF solution has a concentration of 0.1 wt% to 40 wt% by weight.

Preferably, in the step (4), the solid-liquid separation is performed by centrifugal separation or filtration separation, wherein the rotation speed of the centrifugal separation is 10000-15000 rpm.

Preferably, in step (4), the drying of the solid is carried out under vacuum, and the drying is carried out under vacuum heating at a temperature of 60-80 ℃ for 3-5 h.

The preparation method of the boron-doped nano silicon provided by the invention has the following beneficial effects:

1. the addition of boron oxide accelerates Mg and SiO under the condition of ball milling₂The reaction rate greatly improves the preparation efficiency of the nano silicon, and simultaneously realizes the uniform doping of boron in the nano silicon;

2. The method for preparing the boron-doped nano silicon by ball milling reduction of the magnesium powder at room temperature with the assistance of a small amount of boron oxide has simple and convenient preparation process and low energy consumption;

3. the raw materials are low in price, low in cost and high in yield, and industrial large-scale production can be realized;

4. the prepared boron-doped nano silicon material has small particle size of about 50-100nm, good crystallinity, uniform distribution of boron in silicon particles, better conductivity, higher first-week coulombic efficiency and reversible lithium storage capacity compared with the traditional silicon-based material.

Drawings

FIG. 1 is a powder X-ray diffraction pattern of boron-doped and undoped nano-silicon of example 2.

Fig. 2 is a scanning electron microscope image of the boron-doped nano silicon of the embodiment 2.

Fig. 3 is a high-resolution transmission electron microscope image of the boron-doped nano-silicon of the present embodiment 2.

FIG. 4 is a HADDF-STEM and elemental analysis chart of boron-doped nano-silicon of example 2.

Fig. 5 is a graph comparing the first-cycle coulombic efficiencies of boron-doped nano-silicon and undoped nano-silicon after HF etching according to example 2.

Fig. 6 is a comparison graph of the cycle performance of the boron-doped nano-silicon and the undoped nano-silicon after HF etching in this embodiment 2.

Fig. 7 is a graph comparing the rate capability of the boron-doped nano-silicon and the undoped nano-silicon after the HF etching in the embodiment 2.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments in order to make the technical field better understand the scheme of the present invention.

According to the preparation method of the boron-doped nano silicon, a small amount of boron oxide is added under the condition of room-temperature ball milling, so that the reaction of magnesium powder and silicon oxide is greatly accelerated, and boron-doped nano silicon particles can be quickly obtained. The method can obtain boron (B) -doped nano silicon at room temperature, wherein the average grain diameter of the boron-doped nano silicon is 50-100nm, and the doping amount of B is 1-10%.

The preparation method of the boron-doped nano silicon comprises the following steps:

1. taking silicon oxide, commercial magnesium powder and boron oxide, and carrying out ball milling at room temperature to obtain a mixture.

Wherein a vibration ball mill or a planetary ball mill is adopted for ball milling, the ball-material ratio is 10:1-50:1, preferably 20:1-40:1, and the ball milling time is 200-.

2. And adding n-amyl alcohol into the ball-milled mixture, performing grafting reaction by utilizing hydroxyl of the n-amyl alcohol and dangling bonds on the silicon surface, passivating the fresh nano silicon surface, reducing surface oxidation, adding dilute hydrochloric acid, immersing for 20-40 minutes, and performing solid-liquid separation to obtain a nano silicon solid.

Wherein the diluted hydrochloric acid has a concentration of 5% wt to 20% wt, preferably 5% wt to 10% wt, in weight percent, and functions to convert MgO in the reactant into MgCl which is soluble in water₂And the subsequent washing removal is convenient.

3. And (3) sequentially adding ethanol and water to wash the nano-silicon solid, performing solid-liquid separation again to obtain a solid, and drying the solid to obtain the boron-doped nano-silicon.

The solid-liquid separation adopts a centrifugal separation or filtration separation method, wherein the centrifugal separation is performed at 10000-. In order to prevent the surface of the boron-doped nano silicon from being further oxidized, the step of drying the solid can be carried out under the vacuum condition and heated and dried for 3-5h under the vacuum at the temperature of 60-80 ℃.

4. Etching the boron-doped nano silicon by using HF solution with the weight percentage concentration of 0.1-40 wt%, removing a surface oxidation layer, washing by using ethanol, carrying out solid-liquid separation to obtain a solid, and drying the solid to obtain the boron-doped nano silicon without the oxidation layer.

Wherein the preferred weight percent concentration of the HF solution is from 2% wt to 40% wt. The solid-liquid separation adopts a centrifugal separation or filtration separation method, wherein the centrifugal separation is performed at 10000-. The solid drying step can be carried out under vacuum condition, and vacuum heating drying is carried out at 60-80 deg.C for 3-5 h.

The method adopts reagents such as ethanol or water and the like, and steps such as filtration and separation, and can be realized by adopting conventional reagents and steps in a laboratory if no special description is provided.

The trace boron doping of the nano silicon can improve the conductivity of the silicon-based negative electrode material and can also improve the first-week coulombic efficiency and reversible lithium storage capacity of the material. The application provides a preparation method of boron-doped nano silicon, which is characterized in that silicon oxide is used as a silicon source, and the boron-doped nano silicon is prepared by ball milling reduction of magnesium powder at room temperature under the assistance of a small amount of boron oxide. By adding boron oxide, Mg and SiO are accelerated under the condition of ball milling₂The reaction rate greatly improves the preparation efficiency of the nano silicon, and simultaneously realizes the uniform doping of boron in the nano silicon. The method has the advantages of low price of raw materials, simple and convenient preparation process, low cost, low energy consumption, high yield and industrial scale production prospect. Compared with the traditional silicon-based material, the prepared boron-doped nano silicon material has better conductivity, higher first-week coulombic efficiency and reversible lithium storage capacity.

Embodiment 1, the preparation of boron-doped nano-silicon by planetary ball milling of silicon oxide, magnesium powder and boron oxide comprises the following steps:

(1) 1.20g of silicon oxide, 0.964g of magnesium powder and 0.035g of boron oxide are put into a 100mL stainless steel ball milling tank, 20 tungsten steel balls with the mass of 4g are added, and the mixture is ball milled for 300min by a planetary ball mill at room temperature to obtain a mixture. Wherein the type of the planetary ball mill is FRITSCH, Pulveriszttz 5.

(2) And adding n-amyl alcohol into the ball-milled mixture, adding a proper amount of dilute hydrochloric acid, immersing for 30min, and performing centrifugal separation by using a high-speed centrifuge at 15000rpm to obtain a nano silicon solid.

(3) And (3) repeatedly washing the nano-silicon solid by deionized water and ethanol for 2-3 times, carrying out high-speed centrifugal operation at 15000rpm after each washing, and carrying out vacuum drying for 3h at the temperature of 60 ℃ to obtain the boron-doped nano-silicon.

(4) Etching the boron-doped nano silicon obtained in the step (3) by using 5 wt% of HF solution to remove a surface oxide layer,

washing with deionized water and ethanol, centrifuging at 15000rpm for 2-3 times, and vacuum drying the centrifuged solid at 60 deg.C for 3h to obtain boron-doped nano-silicon without oxide layer.

Embodiment 2, the preparation of boron-doped nano-silicon by vibration ball milling of silicon oxide, magnesium powder and boron oxide comprises the following steps:

(1) putting 0.60g of silicon oxide, 0.482g of magnesium powder and 0.017g of boron oxide into an 80mL stainless steel ball milling tank, adding 50 tungsten steel balls with the mass of 1g, and carrying out ball milling for 30min at room temperature by using a vibration ball mill to obtain a mixture. Wherein the model of the vibration ball mill is Focus F-VC 200.

(2) And adding n-amyl alcohol into the ball-milled mixture, adding a proper amount of dilute hydrochloric acid, immersing for 30min, and performing centrifugal separation by using a high-speed centrifuge at 15000rpm to obtain a nano silicon solid.

(3) And repeatedly washing the nano silicon solid by deionized water and ethanol, centrifuging at a high speed of 15000rpm for 2-3 times, and drying in vacuum at the temperature of 60 ℃ for 3h to obtain the boron-doped nano silicon.

(4) And (4) etching the boron-doped nano silicon obtained in the step (3) by using a 5 wt% HF solution to remove a surface oxide layer, washing the boron-doped nano silicon once by using ethanol, centrifuging the boron-doped nano silicon at a high speed of 15000rpm, and drying the centrifuged solid for 3 hours at the temperature of 60 ℃ in vacuum to obtain the boron-doped nano silicon without the oxide layer.

The boron-doped nano-silicon without the oxide layer obtained in the example has the structural characteristics and the performance tests shown in fig. 1-7.

FIG. 1 is a powder X-ray diffraction pattern of boron-doped nano-silicon and undoped nano-silicon, wherein the XRD spectra (FIG. 2.4d) of the products before and after doping show peaks at 28.6 °, 47.4 °, 56.3 °, 69.3 ° and 76.5 ° corresponding to the diffraction peaks of the (111), (220), (311), (400) and (331) crystal planes of silicon, respectively. The spectral peak after boron doping obviously shifts towards the high-angle direction, and the higher the angle is, the larger the shift amount is. This is because after boron is doped into the crystal lattice of silicon, silicon atoms are randomly substituted by boron atoms with smaller atomic radius, resulting in a decrease in the crystal lattice constant of silicon, which also confirms that the ball milling method can conveniently realize the doping of boron element.

FIG. 2 is a scanning electron microscope image of the boron-doped nano-silicon, from which it can be seen that the particle size of the boron-doped nano-silicon is about 50-100 nm.

FIG. 3 is a transmission electron microscope image of boron-doped nano-silicon, in which lattice fringes, i.e. atomic clusters, of the nano-silicon can be clearly seen, and the nano-silicon synthesized by the method on the surface has good crystallinity.

FIG. 4 is a graph of HADDF-STEM and elemental analysis of boron-doped nano-silicon, and it can be seen from high-angle annular dark field image and EDS element characterization analysis that boron is uniformly distributed in silicon particles.

Fig. 5 is a comparison of first-cycle coulombic efficiencies of boron-doped nano-silicon and undoped nano-silicon after HF etching, and the first-cycle irreversible capacity of pure silicon nanoparticles before doping is 32.6%, that is, the first-cycle coulombic efficiency is only 67.4%. The first-cycle coulombic efficiency can be improved to 90.85% after boron doping.

Fig. 6 is a comparison of cycle performance of boron-doped nano silicon and undoped nano silicon after HF etching, and it can be seen that the specific capacity of pure nano silicon before doping is rapidly attenuated within 10 cycles, and the cycle performance of boron-doped nano silicon is significantly improved.

Fig. 7 is a comparison of rate performance of boron-doped nano silicon and undoped nano silicon after HF etching, where the performance of the nano silicon before and after doping is close to that of the nano silicon after low-rate charge and discharge, but the capacity retention rate of the boron-doped nano silicon is higher and the performance is significantly better than that of the undoped nano silicon during high-rate charge and discharge.

In conclusion, the boron-doped nano silicon without the oxide layer has good crystallinity and uniform particle size distribution, and shows excellent performance when used as a cathode material.

The inventive concept is explained in detail herein using specific examples, which are given only to aid in understanding the core concepts of the invention. It should be understood that any obvious modifications, equivalents and other improvements made by those skilled in the art without departing from the spirit of the present invention are included in the scope of the present invention.