A method for preparing carbon-coated bismuth particles

Abstract

The application discloses a preparation method of carbon-coated bismuth particles, which comprises the following steps: S1, preparing plate-like bismuth oxychloride P-BiOCl; S2, performing hydrothermal carbon shell coating on the plate-like bismuth oxychloride P-BiOCl to obtain P-BiOCl@HC; and S3, performing high-temperature carbonization treatment on the P-BiOCl@HC under an argon atmosphere at 600-650 DEG C, so that the P-BiOCl in the P-BiOCl@HC is reduced to obtain carbon-coated Bi particles, namely Bi@PCS. The application is different from common spherical carbon coating, because the plate-like product is obtained by using the P-BiOCl precursor, the unique plate-like structure is thin, the Bi particles are uniformly distributed on the thickness direction axis, the stacking phenomenon does not occur, and the mass transfer path is significantly shortened, and the mass transfer process is accelerated.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of batteries, in particular to a preparation method of carbon-coated bismuth particles. BACKGROUND

[0002] With the continuous growth of global energy demand and the gradual depletion of fossil fuels, energy crisis has become a global focus. In order to solve this problem, the development and utilization of new energy storage methods are imperative. Sodium-ion batteries as a new energy storage technology have received more and more attention in recent years. This is mainly due to the abundance of sodium resources and its low-cost advantage. 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 larger radius of sodium ions, the performance and cycle life of existing electrode materials still face challenges, so the development of efficient electrode materials and the optimization of battery performance have become the focus of research in this field. These studies not only hope to promote the commercialization process of sodium-ion batteries, but also will 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, etc. Among them, bismuth (Bi) has become a promising negative electrode material for sodium-ion batteries due to its high theoretical capacity (386 mAh / g) and low operating voltage. However, Bi is prone to severe volume expansion (-352%) during charging and discharging, and the accumulation and agglomeration between particles also lead to poor battery performance and short service life. Therefore, researchers usually composite with other materials (such as using carbon-based materials to coat Bi particles) to alleviate the volume expansion problem of Bi negative electrode materials and enhance its cycle stability. However, the existing carbon-coated Bi particle materials still have the problem of serious agglomeration of Bi particles inside the carbon shell. With the increase of charging and discharging cycles, the carbon layer may be gradually destroyed, leading to the 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

[0003] To solve the above problems, the present application aims to provide a preparation method of carbon-coated bismuth particles, which uses glucose as a carbon source to coat the plate-like bismuth oxychloride (P-BiOCl) prepared in advance with a hydrochar (HC) shell, i.e., P-BiOCl@HC. Then, the P-BiOCl@HC is subjected to high-temperature treatment in an argon atmosphere to further carbonize the HC, and the bismuth is reduced in situ from BiOCl by using the reducing property of carbon at high temperature to obtain a brand-new morphology of Bi@PCS (Plate-like Carbon shell), which is different from the common spherical carbon coating and does not have Bi particles at the center of the spherical carbon. The plate-like bismuth oxychloride P-BiOCl precursor is used to obtain a plate-like product, and the unique plate-like structure has a relatively thin thickness, so that the Bi particles are uniformly distributed on the thickness direction axis and do not appear to be stacked, which significantly shortens the mass transfer path and accelerates the mass transfer process.

[0004] The present application is implemented by the following technical solutions:

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

[0006] S3, subjecting the P-BiOCl@HC to carbonization treatment at a high temperature of 600-650 DEG C in an inert gas atmosphere to reduce the P-BiOCl in the P-BiOCl@HC to obtain carbon-coated Bi particles, i.e., Bi@PCS.

[0007] In S1, the plate-like P-BiOCl precursor is prepared by adding bismuth nitrate pentahydrate and potassium chloride into water to prepare a mixed solution, adjusting the pH of the mixed solution to 6-6.5, and then heating the solution to 160-180 DEG C for reaction. After the reaction, the product is collected, washed, and dried. In the implementation, the hydroxide, such as sodium hydroxide or potassium hydroxide, is added to the mixed solution to adjust the pH. The reaction temperature is increased to 180 DEG 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, which is prepared by adding the plate-like P-BiOCl precursor into a glucose solution and heating to 160-180 DEG C for reaction.

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

[0010] After being added into the glucose solution and subjected to ultrasonic treatment, the solution is subjected to magnetic stirring for 15-20 min. The magnetic stirring makes the solution uniformly mixed, and the bismuth ions and chlorine ions are uniformly dispersed.

[0011] S3, high temperature treatment P-BiOCl@HC, preparation of carbon-coated Bi particles, namely Bi@PCS: P-BiOCl@HC is heated to 600-650℃ under inert gas environment to obtain, and the inert gas is argon. In the present application, argon does not participate in the reaction, but the carbon generated by further carbonization at high temperature is used to reduce the bismuth compound (bismuth oxychloride) in situ, which involves a thought of using one of the final product components to prepare the whole composite material in situ. The product obtained has the following advantages: for example, the carbon shell on the surface of the generated bismuth particles may have small cracks, which is more conducive to the infiltration of the electrolyte into the bismuth particles, and the bismuth particles are relatively dispersed and basically do not contact each other, leaving space for volume change.

[0012] In S3, the temperature is raised at a rate of 5℃ / min.

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

[0014] 1. The present application is different from the common spherical carbon coating. Due to the use of P-BiOCl precursor, a plate-shaped product is obtained, so that the Bi particles away from the carbon-electrolyte interface have a minimum distance in the thickness axis direction, and 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, consumes carbon atoms, and causes a large number of cracks 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, the Bi particles have good dispersibility, and there is almost no mutual contact between the particles, leaving space for volume expansion during the charging and discharging process. BRIEF DESCRIPTION OF DRAWINGS

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

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

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

[0020] Figure 3 Rate performance diagram of Bi@PCS as a sodium ion battery negative electrode. DETAILED DESCRIPTION

[0021] In order to make the objects, technical solutions and advantages of the present application clearer, further, the present application is described in detail below with examples and drawings. The schematic embodiments of the present application and the descriptions thereof are only used to explain the present application, and do not limit the present application.

[0022] Example 1

[0023] I. Preparation of P-BiOCl: ① 2 mmol (0.97 g) of Bi (NO3) 3·5H2O (bismuth nitrate pentahydrate) and 2 mmol (0.149 g) of KCl (potassium chloride) were added to 30 ml of deionized water, and magnetically stirred for 10 min. ② 1M NaOH solution was added to the mixed solution, and the pH was adjusted to 6, and then magnetically stirred for 30 min. ③ The solution was transferred to a stainless steel reaction kettle with a polytetrafluoroethylene liner, and heated to 160℃ at a heating rate of 5℃ / min in a muffle furnace, and reacted for 24 h. After the reaction was completed, it was naturally cooled to room temperature. ④ The white powder product obtained was washed with deionized water three times, and then dried at 60℃ for 12 h. In the implementation, the pH was adjusted to 6-6.5 to obtain plate-like BiOCl.

[0024] II. Preparation of P-BiOCl@HC with glucose as carbon source: ① 0.5405 g of anhydrous glucose was added to 30 ml of deionized water, and magnetically stirred for 30 min. ② Then 1.0809 g of P-BiOCl prepared was added, and ultrasonically treated for 10 min, and then magnetically stirred for 20 min. The suspension was transferred to a stainless steel reaction kettle with a polytetrafluoroethylene liner, and heated to 180℃ at a heating rate of 5℃ / min in a muffle furnace, and reacted for 6 h. The brown powder obtained was washed with a washing solution of anhydrous ethanol: deionized water = 1:1 by centrifugation three times, and then freeze-dried to obtain P-BiOCl@HC.

[0025] III. High-temperature treatment of P-BiOCl@HC to prepare carbon-coated Bi particles, i.e. Bi@PCS: ① P-BiOCl@HC was transferred to a porcelain boat and evenly spread, and the lid was covered and a gap was reserved. ② The porcelain boat was placed in a tube furnace, and argon was quickly introduced for 30 min to exhaust the air in the pipeline. ③ Slowly introduce argon, and heat to 650℃ at a heating rate of 5℃ / min, and react for 2 h. ④ After the reaction was completed, it was naturally cooled to room temperature, and the black and gray powder was collected, washed with anhydrous ethanol by centrifugation three times, and then dried at 90℃ for 12 h to obtain the final product.

[0026] Figure 1The image shows a SEM image of Bi@PCS. A clear coating structure is visible, indicating good dispersion of Bi particles within the PCS with almost no interparticle contact, thus allowing space for volume changes during charge and discharge. Cracks appear on the PCS surface at some Bi particle locations. This is likely due to the partial consumption of carbon atoms to reduce P-BiOCl to Bi. Thanks to the in-situ reaction, the cracks coincide with the positions of the Bi particles, facilitating rapid electrolyte wetting and mass transfer.

[0027] Figure 2 This is the Raman spectrum of Bi@PCS. From this spectrum, it can be seen that Bi particles at a depth of 69 cm⁻¹... -1 and 94cm -1 The peaks at these locations correspond to the E values ​​of metallic Bi. g and A 1 g Vibration mode. Additionally, 1356cm -1 and 1591cm -1 The peaks at the positions point to the D and G peaks of carbon, respectively, and the Raman results further confirm the successful preparation of Bi@PCS.

[0028] Figure 3 The graph shows the rate performance of Bi@PCS as a negative electrode in sodium-ion batteries. It can be seen from the graph that Bi@PCS has a nearly consistent high reversible capacity at different current densities, which is due to the unique composite structure of Bi@PCS.

[0029] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment 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 within the scope of protection of the present invention.

Claims

1. A method for preparing carbon-coated bismuth particles, characterized in that, Includes the following steps: S1. Prepare plate-shaped bismuth oxychloride P-BiOCl; S2. Coat the plate-shaped bismuth oxychloride P-BiOCl with a hydrothermal carbon shell to obtain P-BiOCl@HC; S3. Perform high-temperature carbonization treatment on P-BiOCl@HC at 600-650℃ under an inert gas atmosphere to reduce P-BiOCl in P-BiOCl@HC and obtain carbon-coated Bi particles, namely Bi@PCS.

2. The preparation method according to claim 1, characterized in that, The preparation of the plate-shaped P-BiOCl precursor in S1 is 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. Then, the solution is heated to 160-180℃ to react. After the reaction is completed, the product is collected, washed and dried.

3. The preparation method according to claim 2, characterized in that, Add a hydroxide to the mixed solution to adjust the pH; the hydroxide is sodium hydroxide or potassium hydroxide.

4. The preparation method according to claim 2, characterized in that, The temperature is raised to 180℃ to carry out the reaction.

5. The preparation method according to claim 1, characterized in that, In S2, P-BiOCl@HC is prepared using glucose as the carbon source. Specifically, the plate-like P-BiOCl precursor is added to a glucose solution and heated to 160-180℃ to react.

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 glucose solution and sonicating, stir magnetically 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 rate of 5℃ / min.

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