Preparation method of carbon-coated bismuth particles

Abstract

The invention discloses a preparation method of carbon-coated bismuth particles. The preparation method comprises the following steps: S1, preparing plate-shaped bismuth oxychloride P-BiOCl; s2, carrying out hydrothermal carbon shell coating on the platy bismuth oxychloride P-BiOCl, so as to obtain P-BiOCl (at) HC; and S3, the P-BiOCl (at) HC is subjected to carbonization treatment at the high temperature of 600-650 DEG C in the argon atmosphere, P-BiOCl in the P-BiOCl (at) HC is reduced, and carbon-coated Bi particles, namely Bi (at) PCS, are obtained. Different from common spherical carbon coating, due to the fact that the P-BiOCl precursor is adopted, a plate-shaped product is obtained, the unique plate-shaped structure is thin, Bi particles are distributed singly on the axis in the thickness direction, the stacking phenomenon does not occur, the mass transfer path is remarkably shortened, and the mass transfer process is accelerated.

Description

Technical Field

[0001] The invention relates to the technical field of batteries, and in particular to a method for preparing carbon-coated bismuth particles. Background Art

[0002] With the continuous growth of global energy demand and the gradual depletion of fossil fuels, the energy crisis has increasingly become the focus of global attention. In order to solve this problem, the development and utilization of new energy storage methods is imperative. As a new energy storage technology, sodium-ion batteries have received increasing attention in recent years. This is mainly due to the abundance of sodium resources and its low-cost advantages. Compared with traditional lithium-ion batteries, sodium-ion batteries are expected to play an important role in large-scale energy storage. However, due to the large radius of sodium ions, the performance and cycle life of existing electrode materials are still facing challenges. Therefore, the development of efficient electrode materials and the optimization of battery performance have become the key research directions in this field. These studies are not only expected to promote the commercialization of sodium-ion batteries, but also provide key technical support for the realization of sustainable energy development. Existing sodium-ion battery negative electrode materials mainly include carbon-based materials, metal oxides, sulfides and alloy materials. Among them, bismuth (Bi) has become a promising sodium-ion battery negative electrode material due to its high theoretical capacity (386mAh / g) and low operating voltage. However, Bi is prone to dramatic volume expansion (~352%) during the charge and discharge process, coupled with the accumulation and agglomeration between particles, resulting in poor battery performance and short life. Therefore, researchers usually alleviate the volume expansion problem of Bi negative electrode materials and enhance their cycle stability by compounding with other materials (such as coating Bi particles with carbon-based materials). However, the existing carbon-coated Bi particle materials still have the serious problem of Bi particle agglomeration inside the carbon shell. As the charge and discharge cycles increase, the carbon layer may be gradually destroyed, resulting in instability of the electrode structure. In addition, the Bi particles located at the center of the spherical carbon are far away from the carbon-electrolyte interface, which increases the mass transfer path. Summary of the invention

[0003] In order to solve the above problems, the present invention aims to provide a method for preparing carbon-coated bismuth particles, which uses glucose as a carbon source to coat the pre-prepared plate-like bismuth oxychloride (Plate-like BiOCl, hereinafter referred to as P-BiOCl) with a hydrothermal carbon shell (hydrochar, hereinafter referred to as HC), i.e., P-BiOCl@HC. Then, P-BiOCl@HC is subjected to high-temperature treatment in an argon atmosphere to further carbonize HC, and BiOCl is in situ reduced to Bi by utilizing the reducibility of carbon at high temperature, thereby obtaining a new morphology of Bi@PCS (Plate-like Carbonshell). Different from the common spherical carbon coating, there are no Bi particles located at the center of the carbon sphere in the spherical carbon. The inventor uses a plate-like bismuth oxychloride P-BiOCl precursor to obtain a plate-like product. The unique plate-like structure is thin, so that the Bi particles are uniformly distributed in the thickness direction axis, and no stacking phenomenon occurs, which significantly shortens the mass transfer path and accelerates the mass transfer process.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for preparing carbon-coated bismuth particles comprises the following steps: S1, preparing plate-like bismuth oxychloride P-BiOCl; S2, hydrothermally coating the plate-like bismuth oxychloride P-BiOCl with a carbon shell to obtain P-BiOCl@HC;

[0006] S3. Performing a high-temperature carbonization treatment of 600-650° C. on P-BiOCl@HC in an inert gas atmosphere to reduce P-BiOCl in P-BiOCl@HC to obtain carbon-coated Bi particles, namely Bi@PCS.

[0007] The preparation of the plate-like P-BiOCl precursor in S1 is specifically as follows: bismuth nitrate pentahydrate and potassium chloride are added to water to prepare a mixed solution, the pH of the mixed solution is adjusted to 6-6.5, and then the solution is heated to 160-180°C for reaction, and the solution is collected, washed and dried after the reaction is completed; during implementation, a hydroxide is added to the mixed solution to adjust the pH, and the hydroxide is sodium hydroxide or potassium hydroxide. The reaction is heated to 180°C, and the reaction time can be reduced by about one third.

[0008] In S2, glucose is used as a carbon source to prepare P-BiOCl@HC, specifically, a plate-like P-BiOCl precursor is added to a glucose solution and heated to 160-180°C for reaction to obtain the obtained product.

[0009] The heating rate is 3-5℃ / min.

[0010] After being added to the glucose solution and subjected to ultrasonic treatment, magnetic stirring is performed for 15-20 minutes. The magnetic stirring makes the solution evenly mixed and the bismuth ions and chloride ions evenly dispersed.

[0011] S3. High temperature treatment of P-BiOCl@HC to prepare carbon-coated Bi particles, namely Bi@PCS: P-BiOCl@HC is heated to 600-650°C in an inert gas environment for reaction, and the inert gas is argon. In the present invention, argon does not participate in the reaction, but the carbon generated by further carbonization at high temperature is used to in-situ reduce the bismuth compound (bismuth oxychloride), which involves the idea of ​​in-situ preparation of an overall composite material by one of the components of the final product. The product obtained in this way has the following advantages: For example, the carbon shell on the surface of the generated bismuth particles may have smaller cracks, which is more conducive to the electrolyte infiltration of the bismuth particles, and the bismuth particles are relatively dispersed and basically do not contact each other, leaving space for volume changes.

[0012] In S3, the temperature is increased at a heating rate of 5°C / min.

[0013] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0014] 1. The present invention is different from the common spherical carbon coating. Due to the use of P-BiOCl precursor, a plate-like product is obtained, so that the Bi particles are at a minimum distance from the carbon-electrolyte interface in the thickness axis direction. There is no Bi particle located at the center of the carbon sphere in the spherical carbon, which is far away from the carbon-electrolyte interface.

[0015] 2. When P-BiOCl@HC is treated at high temperature, HC is further carbonized, and the in-situ generated carbon reduces BiOCl to Bi. The reaction consumes carbon atoms, causing a large number of cracks to appear on the surface of the carbon shell, which is conducive to the infiltration of the electrolyte.

[0016] 3. Compared with the common spherical carbon coating, Bi particles have good dispersion and almost no contact between particles, which reserves space for volume expansion during charging and discharging. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0018] Figure 1 This is the SEM image of Bi@PCS.

[0019] Figure 2 This is the Raman spectrum of Bi@PCS.

[0020] Figure 3 This is the rate performance diagram of Bi@PCS as the negative electrode of sodium ion battery. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary implementation modes of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0022] Example 1

[0023] 1. Preparation of P-BiOCl: ① Add 2mmol (0.97g) of Bi(NO3)3·5H2O (bismuth nitrate pentahydrate) and 2mmol (0.149g) of KCl (potassium chloride) to 30ml of deionized water and stir magnetically for 10min. ② Add 1M NaOH (sodium hydroxide) solution to the mixed solution, adjust the pH to 6, and continue to stir magnetically for 30min. ③ Transfer the solution to a 50ml stainless steel reactor with a polytetrafluoroethylene liner, heat it to 160℃ in a muffle furnace at a heating rate of 5℃ / min, and react for 24h. After the reaction is completed, cool it naturally to room temperature. ④ Collect the obtained white powder product, wash it three times with deionized water, and dry it at 60℃ for 12h. During implementation, adjust the pH to 6-6.5 to obtain plate-like BiOCl.

[0024] 2. Preparation of P-BiOCl@HC using glucose as carbon source: ① Add 0.5405g of anhydrous glucose to 30ml of deionized water and stir magnetically for 30min. ② Then add 1.0809g of the prepared P-BiOCl, ultrasonicate for 10min, and preferably stir magnetically for 20min. Transfer the suspension to a stainless steel reactor with a 50ml polytetrafluoroethylene liner, heat to 180℃ in a muffle furnace at a heating rate of 5℃ / min, and react for 6h. Wash the obtained brown powder three times by centrifugation with a washing solution of anhydrous ethanol: deionized water = 1:1, and then freeze-dry to obtain P-BiOCl@HC.

[0025] 3. High temperature treatment of P-BiOCl@HC to prepare carbon-coated Bi particles, namely Bi@PCS: ① Transfer P-BiOCl@HC to a porcelain boat and spread it evenly, making sure to cover the lid and leave a gap. ② Place the porcelain boat in a tube furnace, quickly pass argon for 30 minutes, and drain the air in the pipe. ③ Slowly pass argon, heat to 650℃ at a heating rate of 5℃ / min, and react for 2h. ④ After the reaction is completed, cool naturally to room temperature, collect black and gray powders, wash them three times by centrifugation with anhydrous ethanol, and then dry them at 90℃ for 12h to obtain the final product.

[0026] Figure 1This is the SEM image of Bi@PCS. From the SEM image, we can see the obvious coating structure. The Bi particles are well dispersed inside the PCS, and there is almost no contact between the particles, which reserves space for volume changes during the charge and discharge process. Cracks appear on the PCS surface where some Bi particles are located. This is probably caused by the partial consumption of carbon atoms to reduce P-BiOCl to Bi. Thanks to the in-situ reaction, the cracks coincide with the position of the Bi particles, which is conducive to the rapid infiltration and mass transfer of the electrolyte.

[0027] Figure 2 This is the Raman spectrum of Bi@PCS. It can be seen from the figure that Bi particles have a peak at 69 cm -1 and 94cm -1 The peaks at g and A 1 g Vibration mode. In addition, 1356cm -1 and 1591cm -1 The peaks at 400 nm and 800 nm point to the D peak and G peak of carbon respectively. The Raman results further confirm the successful preparation of Bi@PCS.

[0028] Figure 3 This is the rate performance diagram of Bi@PCS as the negative electrode of sodium ion battery. It can be seen from the figure that Bi@PCS has almost consistent high reversible capacity at different current densities, which is due to the unique composite structure of Bi@PCS.

[0029] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing carbon-coated bismuth particles, characterized in that: The following steps are involved: S1. Prepare plate-like bismuth oxychloride P-BiOCl; S2. Hydrothermally coat the plate-like bismuth oxychloride P-BiOCl with a carbon shell to obtain P-BiOCl@HC; S3. Carbonize P-BiOCl@HC at a high temperature of 600-650°C under an inert gas atmosphere to reduce the P-BiOCl in P-BiOCl@HC to obtain carbon-coated Bi particles, namely Bi@PCS.

2. The preparation method according to claim 1, characterized in that: The preparation of the plate-like P-BiOCl precursor in S1 is specifically as follows: bismuth nitrate pentahydrate and potassium chloride are added into water to prepare a mixed solution, the pH of the mixed solution is adjusted to 6-6.5, and then the solution is heated to 160-180° C. for reaction, and the solution is collected, washed and dried after the reaction is completed.

3. The preparation method according to claim 2, characterized in that: A hydroxide is added to the mixed solution to adjust the pH, and the hydroxide is sodium hydroxide or potassium hydroxide.

4. The preparation method according to claim 2, characterized in that: The temperature was raised to 180°C to carry out the reaction.

5. The preparation method according to claim 1, characterized in that: In S2, glucose is used as a carbon source to prepare P-BiOCl@HC, specifically, a plate-like P-BiOCl precursor is added to a glucose solution and heated to 160-180°C for reaction to obtain the obtained product.

6. The preparation method according to claim 5, characterized in that: The heating rate is 3-5℃ / min.

7. The preparation method according to claim 5, characterized in that: After adding the glucose solution for ultrasonic treatment, magnetic stirring was performed for 15-20 minutes.

8. The preparation method according to claim 1, characterized in that: The inert gas in S3 is argon.

9. The preparation method according to claim 1, characterized in that: In S3, the temperature is increased at a heating rate of 5°C / min.

Images