A bismuth-carbon composite electrode material, a preparation method therefor and applications thereof

Abstract

The application discloses a kind of bismuth carbon composite electrode materials and preparation method and application thereof.The bismuth carbon composite electrode material has three-dimensional openwork structure carbon skeleton, which contains bismuth nanosphere coated by carbon layer inside;In the bismuth carbon composite electrode material, bismuth accounts for 85-90% by mass percentage.The bismuth carbon composite electrode material obtained by carrying out joule heat treatment on bismuth subsalicylate under inert gas protection is prepared.The bismuth carbon composite electrode material obtained by the application is applied to sodium ion battery, and has high first circle coulomb efficiency, high reversible capacity, excellent cycle stability and high rate performance, and the comprehensive electrochemical performance is very excellent;The preparation process is simple, the time consumption is greatly shortened, the production efficiency is significantly improved, the energy consumption is small, the yield is high and the obtained product bismuth content is high, and has industrial application prospect.

Description

Technical Field

[0001] This invention relates to the fields of nanomaterials and electrochemical technology, and more specifically, to a bismuth-carbon composite electrode material, its preparation method, and its application. Background Technology

[0002] With the continuous development of society and the economy, human demand for energy is increasing daily. However, due to over-reliance on fossil fuels, a serious environmental crisis and excessive resource consumption have occurred. Currently, the widely used energy system relies heavily on traditional non-renewable energy sources. Therefore, to reduce the environmental problems caused by fossil fuels, the global energy structure is rapidly shifting towards a more environmentally friendly and clean energy system. Among various energy storage technologies, electrochemical energy storage technology is the most promising.

[0003] Although lithium-ion batteries are a relatively mature energy storage system, the uneven distribution and insufficient reserves of lithium resources keep their cost high and cannot meet the growing demand for large-scale energy storage. Therefore, the need to develop alternative energy systems with high energy density, high power density, and low cost is becoming increasingly urgent. Sodium is inexpensive and abundant, and sodium ions have a smaller solvation energy, resulting in a smaller Stokes radius in the electrolyte and superior diffusion kinetics compared to lithium ions. Therefore, sodium-ion batteries hold promise for high-rate performance and have a brighter future. However, sodium-ion battery electrode materials are prone to volume effects during cycling, leading to electrode pulverization and capacity loss. Therefore, the main challenge in the current development of sodium-ion batteries is the lack of electrode materials that combine high capacity, high rate capability, excellent cycle life, and a suitable voltage platform.

[0004] Bismuth (Bi) has attracted extensive research in the field of sodium-ion batteries due to its high electron / ion migration rate, suitable voltage plateau, and good theoretical capacity. However, bismuth exhibits a severe volume effect during cycling, leading to pulverization of the active material and continuous formation of the solid electrolyte interface, reducing its cycling stability and resulting in poor rate performance and cycle performance. Studies have shown that bismuth-carbon composites, prepared by combining bismuth with carbon, can effectively mitigate the volume strain generated during cycling and improve its electrochemical performance. However, current methods for preparing bismuth-carbon composites mainly include spray drying, electrospinning, or the use of strong reducing agents, and most methods require subsequent high-temperature treatment. These methods are cumbersome, requiring tens of hours or days for synthesis, consuming significant energy, and cannot be rapidly prepared. Furthermore, the preparation process may generate hydrogen gas, posing a safety hazard, and the obtained electrochemical performance is not stable enough. Therefore, how to rapidly prepare bismuth-carbon composites with excellent performance and apply them to sodium-ion batteries to obtain good electrochemical performance is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a bismuth-carbon composite electrode material, its preparation method, and its application. The obtained bismuth-carbon composite electrode material, when applied to sodium-ion batteries, exhibits high first-cycle coulombic efficiency, high reversible capacity, excellent cycle stability, and high rate performance, demonstrating excellent overall electrochemical performance. Furthermore, the preparation process is simple, time-consuming, and energy-efficient, showing promising prospects for industrial application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A bismuth-carbon composite electrode material is provided, the main structure of which is a three-dimensional hollow carbon skeleton, with bismuth nanospheres coated with carbon layers inside; in the bismuth-carbon composite electrode material, the bismuth content is 85-90% by mass percentage.

[0008] According to the above scheme, bismuth subsalicylate is prepared by Joule heat treatment under inert gas protection.

[0009] Preferably, the current for the Joule heat treatment is 110-130A.

[0010] Preferably, the Joule heat treatment time is 10-60 seconds.

[0011] According to the above scheme, the particle size of the bismuth nanospheres is 20-50 nm.

[0012] A method for preparing the above-mentioned bismuth-carbon composite electrode material is provided, comprising the following steps:

[0013] Bismuth subsalicylate is placed in a Joule heating device under inert gas protection. The Joule heating device current is controlled within the range of 110-130A, and the processing time is controlled within the range of 10-60s. After Joule heat treatment, bismuth-carbon composite electrode material is obtained.

[0014] This invention provides an application of the aforementioned bismuth-carbon composite electrode material as a negative electrode active material in sodium-ion batteries.

[0015] A sodium-ion battery negative electrode is provided, wherein the above-mentioned bismuth-carbon composite electrode material is used as the negative electrode active material.

[0016] According to the above scheme, the negative electrode also includes a conductive agent, a binder, and a current collector.

[0017] Preferably, the negative electrode active material, conductive agent (acetylene black), and binder (polytetrafluoroethylene) are thoroughly mixed in a ratio of 8:1:1, and a solvent is added to prepare a slurry. This slurry is then coated onto the current collector copper foil and dried to obtain the sodium-ion battery negative electrode. More preferably, the solvent is N-methylpyrrolidone (NMP).

[0018] A sodium-ion battery is provided, comprising the aforementioned sodium-ion battery negative electrode.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. This invention provides a bismuth-carbon composite electrode material, the main structure of which is a three-dimensional hollow carbon skeleton, with bismuth nanospheres coated by a carbon layer. The three-dimensional hollow carbon skeleton can increase the contact area with the electrolyte, shorten the ion diffusion path, and also serve as an electron transport network to promote electron transport, thereby improving its electrochemical kinetics and rate performance. At the same time, the three-dimensional hollow structure and the carbon layer coating the surface of the bismuth nanospheres can buffer the volume expansion of bismuth during charging and discharging, prevent the electrode material from pulverizing, and improve its cycle stability.

[0021] 2. The high-performance bismuth-carbon composite electrode material obtained in this invention, when used as a negative electrode active material in sodium-ion batteries, exhibits high first-cycle coulombic efficiency, exceeding 70%; it also possesses high reversible capacity and excellent cycle stability, wherein 1Ag -1 After 3000 cycles at a current density, the specific capacity retention rate was 96.90%; 5Ag -1 After 8000 cycles at high current density, the specific capacity retention rate is 96.65%; it also exhibits high rate performance at 55Ag. -1 It still has 306mAh g at current density -1 It has a high specific capacity and excellent overall electrochemical performance.

[0022] 3. This invention provides a method for preparing bismuth-carbon composite electrode materials. Using inexpensive bismuth subsalicylate as raw material, a high-performance bismuth-carbon composite electrode material can be prepared in tens of seconds through a one-step Joule heating calcination method. The preparation process is simple, the time consumption is greatly reduced, the production efficiency is significantly improved, the energy consumption is low, the yield is high, and the obtained product has a high bismuth content, which has promising prospects for industrial application. Attached Figure Description

[0023] Figure 1 This is the XRD pattern of the bismuth-carbon composite electrode material prepared rapidly by Joule heating according to Embodiment 1 of the present invention.

[0024] Figure 2 This is the Raman diagram of the rapid preparation of bismuth-carbon composite electrode material based on Joule heating as described in Embodiment 1 of the present invention.

[0025] Figure 3 This is the TG diagram of the bismuth-carbon composite electrode material prepared rapidly by Joule heating according to Embodiment 1 of the present invention.

[0026] Figure 4 These are SEM images of the bismuth-carbon composite electrode material prepared rapidly by Joule heating according to Embodiment 1 of the present invention; wherein Figure ac is a SEM image at a lower magnification; and Figure d is a SEM image at a higher magnification.

[0027] Figure 5 These are HRTEM images of the bismuth-carbon composite electrode material prepared rapidly by Joule heating according to Embodiment 1 of the present invention; wherein Figure ac is an HRTEM image at a lower magnification; and Figure d is an HRTEM image at a higher magnification (the inset image is the lattice fringes of the selected area).

[0028] Figure 6 This is a size distribution diagram of the bismuth-carbon composite electrode material prepared rapidly by Joule heating according to Embodiment 1 of the present invention.

[0029] Figure 7 This is the bismuth-carbon composite electrode material prepared rapidly by Joule heating as described in Example 1 of the present invention, in 1Ag -1 Cyclic performance diagram at current density.

[0030] Figure 8 This is the bismuth-carbon composite electrode material prepared rapidly by Joule heating as described in Example 1 of the present invention, in 5Ag... -1 Cyclic performance diagram at current density.

[0031] Figure 9 This is the bismuth-carbon composite electrode material prepared rapidly by Joule heating as described in Example 1 of the present invention, in 5Ag... -1 The charge-discharge curves at current density.

[0032] Figure 10This is a magnification diagram of the bismuth-carbon composite electrode material prepared rapidly by Joule heating according to Embodiment 1 of the present invention.

[0033] Figure 11 This is a charge-discharge curve of the bismuth-carbon composite electrode material prepared rapidly by Joule heating according to Embodiment 1 of the present invention at different current densities. Detailed Implementation

[0034] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0035] The Joule heating device used in this embodiment is model JH3.1.1-VCRVVP-30, manufactured by Hefei High-Tech Co., Ltd.

[0036] Example 1:

[0037] This embodiment provides a method for rapidly preparing bismuth-carbon composite electrode materials based on Joule heating, including the following steps:

[0038] Under an argon atmosphere, 200 mg of bismuth subsalicylate was placed on a tungsten boat and placed in a Joule heating device. The treatment current was 120 A and the treatment time was 30 s to obtain the product bismuth-carbon composite material.

[0039] The bismuth-carbon composite electrode material prepared in Example 1 based on Joule heating for rapid fabrication was characterized to obtain the following results: Figure 1-6 The result is shown in the figure.

[0040] Figure 1 The X-ray diffraction (XRD) pattern of the bismuth-carbon composite electrode material prepared rapidly by Joule heating as described in Example 1 is shown below. Figure 1 It can be seen that the material has obvious diffraction peaks, and the peak positions can be compared with those of the JCPDS card to find that the main component of the product is elemental bismuth.

[0041] Figure 2 This is the Raman spectroscopy analysis of the bismuth-carbon composite electrode material prepared rapidly by Joule heating as described in Example 1. Figure 2 It can be seen that the material exhibits distinct D and G peaks characteristic of carbon materials. The degree of graphitization of the carbon material can be determined by the relative intensity ratio R of the D and G peaks (R = I). D / I G According to calculations, the R value of this bismuth-carbon composite material is 1, indicating a suitable degree of graphitization. The material contains disordered carbon, which can provide a certain capacity and improve its conductivity, thus promoting electron transport during the charging and discharging process.

[0042] Figure 3The thermogravimetric analysis (TG) chart of the bismuth-carbon composite electrode material prepared rapidly by Joule heating as described in Example 1 shows a significant increase in mass between 170-250°C, primarily due to the oxidation of elemental bismuth to form bismuth oxide. Subsequently, the mass decreases significantly between 300-400°C, corresponding to the conversion of carbon to carbon dioxide upon heating. Based on the TG results, the bismuth content of this material is calculated to be 87.53%.

[0043] Figure 4 These are scanning electron microscope (SEM) images of the bismuth-carbon composite electrode material rapidly prepared by Joule heating as described in Example 1. Figure 4 It can be seen that the material is a bismuth nanosphere structure coated with a carbon layer, and its main carbon skeleton exhibits a three-dimensional hollow structure. Its unique three-dimensional hollow structure can increase the contact area with the electrolyte, promote electron transport during charging and discharging, shorten the ion diffusion path, and help improve its rate performance and electrochemical kinetics.

[0044] Figure 5 These are high-resolution transmission electron microscopy (HRTEM) images of the bismuth-carbon composite electrode material rapidly prepared by Joule heating as described in Example 1. Figure 5 As can be seen, the material exhibits a bismuth nanosphere structure encapsulated by a carbon layer. This carbon-coated bismuth nanosphere structure can buffer the volume expansion of bismuth during charging and discharging, reducing volume strain and thus improving its cycle stability. Furthermore, the interplanar spacing of the bismuth nanospheres can be observed to be... The (012) crystal plane corresponds to elemental bismuth.

[0045] Figure 6 This is a size distribution diagram based on HRTEM results, statistically analyzed, of the bismuth-carbon composite electrode material prepared rapidly by Joule heating as described in Example 1. Figure 6 It can be seen that the size of the bismuth nanoparticles in the prepared bismuth-carbon composite electrode material is 35.9±14.0 nm. The smaller particle size can shorten the diffusion path of sodium ions and improve its electrochemical performance.

[0046] The bismuth-carbon composite electrode material rapidly prepared based on Joule heating in Example 1 was used as the negative electrode active material. It was thoroughly mixed with an active material, conductive agent (acetylene black), and binder (polytetrafluoroethylene) in a ratio of 8:1:1. A small amount of NMP was added to prepare a slurry, which was then coated onto a current collector copper foil and dried to serve as the electrode sheet for a sodium-ion battery. Metallic sodium was used as the counter electrode, 1M NaPF6 in DME as the electrolyte, and GF / D glass fiber as the separator. A coin cell was assembled in a glove box using a CR2016 stainless steel battery casing. The coin cell was tested, and the results were as follows: Figure 7-11 The result is shown in the figure.

[0047] Figure 7 The bismuth-carbon composite electrode material prepared rapidly by Joule heating is in 1Ag -1 The cycling performance graph at current density shows that the material achieves a coulombic efficiency of 70.86% in the first cycle, which rapidly increases to 100% in subsequent cycles. After 3000 cycles, the specific capacity remains at 346.35 mAh g⁻¹. -1 Compared to the specific capacity of the third cycle, its capacity retention rate is 96.90%, demonstrating excellent cycle stability and capacity retention.

[0048] Figure 8 Based on Joule heating, rapid preparation of bismuth-carbon composite electrode materials in 5Ag -1 The cycling performance diagram at high current density shows that its coulombic efficiency reaches 71.7% in the first cycle, and the specific capacity remains at 350.46 mA hg after 8000 cycles. -1 Compared to the specific capacity of the third cycle, its capacity retention rate is 96.65%, indicating that the material maintains excellent cycle stability even at higher current densities.

[0049] Figure 9 Based on the rapid preparation of bismuth-carbon composite electrode materials using Joule heating at 5A g -1 The charge-discharge curves at different current densities and cycles show two distinct plateaus during discharge, located at 0.68V and 0.49V, respectively. Correspondingly, two plateaus exist during charging, located at 0.75V and 0.59V. These plateaus correspond to the two alloying reactions of bismuth: Bi reacts with Na to form NaBi, and further combines with Na to form Na3Bi. Furthermore, these plateaus remain stable after 8000 cycles, highlighting its excellent electrochemical performance.

[0050] Figure 10 This is a rate-of-magnification diagram of bismuth-carbon composite electrode materials prepared rapidly by Joule heating. The material is shown at 55 A g. -1 It still has 306 mA hg at current density -1 The specific capacity, and when the current density returns to 1A g -1 At that time, it can still have 350mA hg -1 The specific capacity demonstrates its superior high-rate performance.

[0051] Figure 11 The data shows the charge-discharge curves of bismuth-carbon composite electrode materials prepared by Joule heating at different current densities. It can be seen that the two voltage plateaus of the material remain stable at higher current densities, indicating that the material can still provide stable capacity at high current densities and has fast-charging characteristics.

[0052] In summary, the test results show that the bismuth-carbon composite electrode material prepared rapidly by Joule heating has excellent electrochemical performance and is a potential high-performance anode material for sodium-ion batteries.

[0053] Comparative Example 1:

[0054] A method for rapidly preparing bismuth-carbon composite electrode materials based on Joule heating is provided, comprising the following steps:

[0055] Under an argon atmosphere, 200 mg of bismuth subsalicylate was placed on a tungsten boat and placed in a Joule heating device. The treatment current was 100 A and the treatment time was 30 s to obtain the product bismuth-carbon composite material.

[0056] The bismuth-carbon composite electrode material prepared rapidly by Joule heating as in Comparative Example 1 was used as the negative electrode active material, and coin half-cells were assembled according to the method in Example 1 for electrochemical performance testing. The results are as follows: at 1 Ag... -1 At a current density of 49.72%, its initial coulombic efficiency reached 49.72%, and its specific capacity remained at 257.15 mAh g after 2000 cycles. -1 ; in 5Ag -1 At a current density of 5000 cycles, its first-cycle coulombic efficiency reaches 57.87%, and its specific capacity remains at 284 mAh g⁻¹. -1 Analysis revealed that the low Joule heating current resulted in a low heating temperature and insufficient calcination. The reduced elemental Bi content was 86.2%, but due to the low calcination temperature, the precursor was not completely carbonized, resulting in fewer active sites in the electrochemical reaction and more irreversible reactions, which in turn weakened the electrochemical performance.

[0057] Comparative Example 2:

[0058] A method for rapidly preparing bismuth-carbon composite electrode materials based on Joule heating is provided, comprising the following steps:

[0059] Under an argon atmosphere, 200 mg of bismuth subsalicylate was placed on a tungsten boat and placed in a Joule heating device. The treatment current was 140 A and the treatment time was 30 s to obtain the product bismuth-carbon composite material.

[0060] The bismuth-carbon composite electrode material prepared rapidly by Joule heating as in Comparative Example 2 was used as the negative electrode active material, and coin half-cells were assembled according to the method in Example 1 for electrochemical performance testing. The results are as follows: at 1 Ag... -1 At a current density of 64.82%, its initial coulombic efficiency reached 64.82%, and its specific capacity remained at 305.95 mAh g after 2000 cycles. -1 ; in 5Ag -1At a current density of 62.83%, its first-cycle coulombic efficiency reaches 62.83%, and its specific capacity remains at 291 mA hg after 5000 cycles. -1 Analysis revealed that the excessive current applied during Joule heating led to an excessively high heating temperature, causing the generated elemental Bi to sublimate and vaporize. This resulted in a low elemental Bi content of 82% in the product, which in turn weakened the electrochemical performance.

Claims

1. A bismuth-carbon composite electrode material, characterized in that, Its main structure is a three-dimensional hollow carbon skeleton containing bismuth nanospheres coated with carbon layers; in the bismuth-carbon composite electrode material, bismuth accounts for 85-90% by mass percentage. The bismuth-carbon composite electrode material is prepared by Joule heat treatment of bismuth subsalicylate under inert gas protection; the Joule heat treatment current is 110-130 A and the time is 10-60 s.

2. The bismuth-carbon composite electrode material according to claim 1, characterized in that, The bismuth nanospheres have a particle size of 20-50 nm.

3. A method for preparing the bismuth-carbon composite electrode material according to claim 1, characterized in that, Includes the following steps: Bismuth subsalicylate is placed in a Joule heating device under inert gas protection. The Joule heating device current is controlled within the range of 110-130A, and the processing time is controlled within the range of 10-60 s. After Joule heat treatment, bismuth-carbon composite electrode material is obtained.

4. The application of the bismuth-carbon composite electrode material according to any one of claims 1-2 as a negative electrode active material in a sodium-ion battery.

5. A sodium-ion battery negative electrode, characterized in that, The bismuth-carbon composite electrode material according to any one of claims 1-2 is used as the negative electrode active material.

6. The sodium-ion battery negative electrode according to claim 5, characterized in that, The negative electrode also includes a conductive agent, a binder, and a current collector.

7. A sodium-ion battery, characterized in that, Includes the sodium-ion battery negative electrode as described in claim 5.

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