A method for preparing carbon nanoflower-coated bismuth electrode material for fast-charging batteries

Abstract

This invention relates to a method for preparing carbon nanoflower-coated bismuth electrode materials for fast-charging batteries, belonging to the field of new energy electrode material preparation technology. The invention involves adding bismuth oxide and chitin-like substances to deionized water and ultrasonically dispersing them to obtain a mixed solution. The mixed solution is then sealed in a reaction vessel and subjected to a high-temperature, high-pressure reaction, followed by solid-liquid separation to obtain the reaction product. The reaction product is calcined under a protective or reducing atmosphere to obtain the carbon nanoflower-coated bismuth electrode material. This carbon nanoflower-coated bismuth electrode material is a core-shell material, with a bismuth core and an outer shell of N-doped carbon nanoflowers, on which bismuth nanoparticles are loaded. The nanoflower coating layer of this invention exhibits high electrolyte permeability and wettability, buffering the volumetric expansion of the internal bismuth electrode during charging and discharging. The bismuth nanoparticles loaded on the carbon nanoflowers effectively improve the electrode's diffusion kinetics. The carbon nanoflower-coated bismuth electrode material possesses a large volumetric capacity and excellent fast-charging performance.

Description

Technical Field

[0001] This invention relates to a method for preparing carbon nanoflower-coated bismuth electrode material for fast-charging batteries, belonging to the field of new energy electrode material preparation technology. Background Technology

[0002] Bismuth, as a potential anode material for fast-charging batteries, possesses high electronic conductivity and volumetric capacity. However, its significant volume expansion during rapid charging and discharging leads to drawbacks such as capacity decay and shortened cycle life. Researchers typically address this volume expansion issue by constructing a stable coating layer on the bismuth electrode surface.

[0003] Carbon coating technology is now widely used in the preparation of energy storage materials, medical nanomaterials, and photo / electrocatalytic materials. In the field of new energy electrode materials, carbon coating is one of the most common material modification methods. The structural stability of electrode materials is a key factor in maintaining battery capacity; however, electrode materials undergo significant volume expansion due to phase transitions during charging and discharging, and their structure can collapse during repeated expansion and contraction. Carbon coating can improve the material's conductivity and buffer volume expansion, maintaining electrode structural stability and providing a stable chemical and electrochemical reaction interface.

[0004] The most common carbon coating technologies include polydopamine coating, resorcinol-formaldehyde resin coating, glucose coating, sucrose coating, polyvinylpyrrolidone (PVP) coating, and tannic acid coating. These coating methods share a common strategy: obtaining the precursor in a solution environment, followed by high-temperature carbonization in an inert atmosphere. The advantages are the inexpensive and readily available raw materials, relatively simple coating processes, and adjustable coating thickness. However, these methods rely on the adhesive properties of carbon-containing organic materials. The precursor completely coats the particle surface in a solution environment, and then carbonization yields a carbon coating layer. This coating layer has small pores and poor electrolyte permeability, requiring ions in the electrolyte to diffuse into the interior of the carbon coating layer. Compared to many electrode materials, carbon has a relatively high diffusion barrier (0.28 eV), which slows down the ion insertion / extraction kinetics on the coated electrode surface, causing polarization and affecting the battery's fast charge / discharge efficiency.

[0005] Therefore, there is a need for a method to prepare carbon coatings for bismuth electrodes that allows the coating layer to pass through the electrolyte, uses inexpensive and readily available raw materials, effectively mitigates volume expansion, and has a relatively simple process. Summary of the Invention

[0006] To address the problem that existing carbon coatings completely seal the electrode material and prevent electrolyte penetration, this invention proposes a method for preparing carbon nanoflower-coated bismuth electrode materials for fast-charging batteries. Chitosan-based materials are used as the raw material for carbon coating, and nano / micro bismuth oxide powder is used as the coating body. A chitosan-based nanoflower coating layer is constructed on the surface of bismuth oxycarbonate through a high-temperature, high-pressure hydrolysis reaction in water. Subsequently, high-temperature carbonization and reduction are carried out under an inert atmosphere to obtain carbon nanoflower-coated bismuth powder. The coating layer thickness is controlled by adjusting the hydrothermal time, and the nitrogen content in the carbon nanoflowers is changed by controlling the calcination temperature. This method can effectively form a carbon nanoflower coating layer without changing the original carbon coating process, and the thickness and doping amount are controllable, making it convenient and cost-effective.

[0007] A method for preparing carbon nanoflower-coated bismuth electrode material for fast-charging batteries, the specific steps of which are as follows:

[0008] (1) Bismuth oxide and chitin-like substances were added to deionized water and ultrasonically dispersed to obtain a mixed solution;

[0009] (2) The mixed solution is sealed in a reaction vessel and subjected to high temperature and high pressure reaction, and the reaction products are obtained by solid-liquid separation;

[0010] (3) The reaction product is calcined under a protective atmosphere or a reducing atmosphere to obtain a carbon nanoflower-coated bismuth electrode material. The carbon nanoflower-coated bismuth electrode material is a core-shell material, with a core of bismuth and an outer shell of carbon nanoflowers formed by N-doped carbon. Nano bismuth particles are loaded on the carbon nanoflowers.

[0011] The chitinous substance in step (1) is α-chitosan, β-chitosan, γ-chitosan, cellulose or chitin.

[0012] In step (1), the mass ratio of bismuth oxide to chitin is 1:1-5, and the solid-liquid ratio of bismuth oxide to deionized water is 3:80-160 (g:mL).

[0013] The temperature of the high-temperature and high-pressure reaction in step (2) is 150-250℃, the pressure is 0.1-5.0MPa, and the time is 1-5h.

[0014] In step (3), the calcination temperature is 600-1000℃ and the time is 2-8h.

[0015] In step (3), the protective gas is high-purity argon or high-purity nitrogen; the reducing gas is a hydrogen-argon mixture.

[0016] Fast charging performance test: Carbon nanoflower-coated bismuth electrode material was prepared into an electrode slurry with PVDF and acetylene black in a mass ratio of 8:1:1. The slurry was coated onto the surface of copper foil using a coating machine, vacuum dried, cut into pieces, assembled into 2025 button cells, and the fast charging performance of the cells was tested.

[0017] The principle of bismuth coating on carbon nanoflowers (taking chitin as an example): The coating mechanism of chitin hydrolysis under high temperature and high pressure is as follows:

[0018] Chitosan hydrolysis low sugar (CTS) + CO2 + Bi2O3 → Bi2O2CO3·0.5H2O@CTS (1)

[0019] Because Bi₂O₂CO₃·0.5H₂O decomposes upon exposure to light or heat, at 600℃ it decomposes into Bi₂O₃, CO₂, and H₂O. With the high-temperature carbonization of the CTS (carbonized precipitate), the carbonized outer shell of Bi₂O₃ is reduced to elemental Bi. The reaction formula is:

[0020] Bi2O2CO3·0.5H2O@CTS→Bi@C+CO2+H2O (2)

[0021] The thickness of the CTS coating layer in reaction (1) can be controlled by the reaction time. In reaction (2), the decomposition products CO2 and H2O of Bi2O2CO3·0.5H2O will be carried away by the continuously introduced inert gas, thus promoting the continuous progress of reaction (2) and completely reducing Bi2O2CO3·0.5H2O to a large amount of nano-sized elemental bismuth.

[0022] The beneficial effects of this invention are:

[0023] (1) The present invention constructs a carbon nanoflower coating layer on the surface of the electrode bismuth that can be permeated by the electrolyte, which can enhance the specific surface area of ​​the electrode and help provide more reactive sites; it can buffer the volume expansion during charging and discharging; it can help ions in the electrolyte to pass freely and improve the diffusion coefficient; at the same time, the nanoscale bismuth particles loaded on the carbon nanoflowers increase the active sites and improve the reaction kinetics of charging and discharging.

[0024] (2) In this invention, chitin is used as the coating material and bismuth oxide is used as the coating body. The chitin nanoflower coating layer is formed on the intermediate bismuth oxycarbonate through a high temperature and high pressure reaction in an aqueous solution system. Then, carbon nanoflower-coated bismuth spheres are obtained by calcination under an inert atmosphere. The preparation process is simple. The carbon nanoflower coating layer is constructed in situ by dissolving, regrowing and carbonizing chitin under high temperature and high pressure. This coating layer has a large specific surface area, can directly permeate the electrolyte, and has good wettability to the electrolyte. Therefore, it can greatly improve the reaction kinetics of the battery. Attached Figure Description

[0025] Figure 1 The images show scanning electron microscope (SEM) images of the original Bi2O3, the intermediate Bi2O2CO3·0.5H2O@CTS, and the carbon nanoflower-coated product Bi@C from Example 1. a is the original Bi2O3, b is the intermediate Bi2O2CO3·0.5H2O@CTS, and c is Bi@C.

[0026] Figure 2 The images show scanning electron microscope (SEM) and transmission electron microscope (TEM) images of Bi@C, the carbon nanoflower-coated product in Example 1. a is a cross-sectional view of Bi@C, b is a TEM image of Bi@C, and c is a high-resolution TEM image of Bi nanoparticles.

[0027] Figure 3 The XRD patterns of the original Bi2O3, the intermediate Bi2O2CO3·0.5H2O@CTS, and the carbon nanoflower-coated product Bi@C in Example 2 are shown below.

[0028] Figure 4 These are photographs of the electrode contact angle test on the copper foil in Example 1. a is a photograph before contact, b is a photograph during contact, and c is a photograph after wetting.

[0029] Figure 5 The lithium-ion battery charge-discharge curves under different fast charging currents in Example 1 are shown.

[0030] Figure 6 The cycle performance of the lithium-ion battery assembled in Example 1;

[0031] Figure 7 The charge-discharge curves of the sodium-ion battery assembled in Example 1 for 10C fast charging are shown.

[0032] Figure 8 The charge-discharge curves of the lithium-ion battery assembled in Example 2 for 10C fast charging are shown.

[0033] Figure 9 The charge and discharge curves of the lithium-ion battery assembled in Example 3 for 10C fast charging are shown.

[0034] Figure 10 The charge and discharge curves of the lithium-ion battery assembled in Example 4 for 10C fast charging are shown.

[0035] Figure 11 The charge and discharge curves of the lithium-ion battery assembled in Example 5 for 10C fast charging are shown. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0037] Example 1: A method for preparing carbon nanoflower-coated bismuth electrode material for fast-charging batteries, the specific steps of which are as follows:

[0038] (1) Bismuth oxide and chitin were added to deionized water and ultrasonically dispersed for 0.5 h to obtain a mixed solution; the mass ratio of bismuth oxide and chitin was 1:1, and the solid-liquid ratio of bismuth oxide to deionized water was 3:80 g:mL.

[0039] (2) The mixed solution was sealed in the reaction vessel and subjected to high temperature and high pressure reaction for 1 hour at a temperature of 180℃ and a pressure of 0.1MPa. The solid-liquid separation was then performed to obtain the reaction product.

[0040] (3) The reaction product was calcined at 600℃ for 2 hours under a nitrogen atmosphere (nitrogen flow rate of 10 mL / min) to obtain carbon nanoflower-coated bismuth electrode material. The carbon nanoflower-coated bismuth electrode material is a core-shell material with a core of bismuth and a shell of carbon nanoflowers formed by N-doped carbon. Nano bismuth particles are loaded on the carbon nanoflowers.

[0041] Scanning electron microscope (SEM) images of the original Bi₂O₃, the intermediate Bi₂O₂CO₃·0.5H₂O@CTS, and the carbon nanoflower-coated product Bi@C in this embodiment are shown below. Figure 1 Where a is the original Bi₂O₃, b is the intermediate Bi₂O₂CO₃·0.5H₂O@CTS, and c is Bi@C; from Figure 1 It can be seen that the original Bi2O3 is spherical with a size of 3μm, the intermediate has a nanoflower coating layer, and after calcination, nanoparticles are loaded on the nanoflower.

[0042] The scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the carbon nanoflower-coated product Bi@C in this embodiment are shown below. Figure 2 a) is a cross-sectional view of the nanoflower coating layer under scanning electron microscopy; b) is a bismuth nanoflower coating layer under transmission electron microscopy; c) is a nanoflower coating layer under high-resolution transmission electron microscopy. Figure 2 As can be seen from this, the thickness of the carbon nanoflower coating is 500 nm, and the size of the bismuth nanoparticles loaded on it is 5-50 nm.

[0043] Fast charging performance test: Carbon nanoflower-coated bismuth electrode material was prepared into an electrode slurry with PVDF and acetylene black in a mass ratio of 8:1:1. The slurry was coated onto the surface of copper foil using a coating machine, vacuum dried, cut into pieces, assembled into 2025 button cells, and the fast charging performance of the cells was tested.

[0044] In this embodiment, the electrode contact angle test photograph coated on the copper foil is shown in [the image]. Figure 4 a is a test photo before contact, b is a test photo during contact, and c is a test photo after immersion; from Figure 4 As can be seen from the data, the contact angle is close to 0.5°, indicating that using Bi@C, a carbon nanoflower-coated product, as an electrode slurry has good electrolyte wettability.

[0045] The lithium-ion battery charge-discharge curves under different fast-charging currents in this embodiment are shown below. Figure 5 ,from Figure 5 As can be seen from the data, when the fast charge / discharge rate decreases from 10C to 0.5C, the electrode achieves 1540.7, 1591.3, 1786.6, 1952.7, and 2259.5 mAh / cm³. 3 The volumetric specific capacity of the electrode in this embodiment is significantly higher than that of commercially available graphite electrodes (837 mAh / cm³). 3 );

[0046] The cycle performance of the lithium-ion battery assembled in this embodiment is shown in [reference]. Figure 6 ,from Figure 6 As can be seen from this, at a discharge rate of 5C, the battery can be charged and discharged 600 times and still retain 92% of its capacity.

[0047] The charge-discharge curve of the sodium-ion battery assembled in this embodiment for 10C fast charging is shown in [reference needed]. Figure 7 ,from Figure 7 As can be seen, at a charge / discharge rate of 10C, a sodium-ion battery can be charged to over 45mAh in 6 minutes.

[0048] Example 2: A method for preparing carbon nanoflower-coated bismuth electrode material for fast-charging batteries, the specific steps of which are as follows:

[0049] (1) Bismuth oxide and γ-chitosan were added to deionized water and ultrasonically dispersed for 0.8 h to obtain a mixed solution; the mass ratio of bismuth oxide to γ-chitosan was 1:2; the solid-liquid ratio of bismuth oxide to deionized water was 3:100 g:mL.

[0050] (2) The mixed solution was sealed in the reactor and subjected to high temperature and high pressure reaction for 2 hours at a temperature of 180℃ and a pressure of 0.5MPa. The solid-liquid separation was then performed to obtain the reaction product.

[0051] (3) The reaction product was calcined at 800℃ for 2 hours in an argon atmosphere (argon flow rate of 15 mL / min) to obtain carbon nanoflower-coated bismuth electrode material. The carbon nanoflower-coated bismuth electrode material is a core-shell material with bismuth as the core and carbon nanoflowers formed by N-doped carbon as the outer shell. Nano bismuth particles are loaded on the carbon nanoflowers.

[0052] The XRD patterns of the original Bi2O3, the intermediate Bi2O2CO3·0.5H2O@CTS, and the carbon nanoflower-coated product Bi@C in this embodiment are shown below. Figure 3 ,from Figure 3As can be seen, four amorphous peaks of approximately 27.4°, 32.5°, 46.7°, and 54.7° can be observed on the (120), (121), (041), and (-241) planes of Bi2O3. After a further high-temperature reaction, new and obvious peaks of 23.9°, 30.3°, 32.7°, 42.1°, 46.9°, and 56.7° appear on the (011), (013), (110), (114), (020), and (123) planes of Bi2O2CO3 (PDF#00-041-148), indicating that the high-temperature hydrolysis of carbonate by chitosan transforms amorphous Bi2O3 into Bi2O2CO3.

[0053] Fast charging performance test: Carbon nanoflower-coated bismuth electrode material was prepared into an electrode slurry with PVDF and acetylene black in a mass ratio of 8:1:1. The slurry was coated onto the surface of copper foil using a coating machine, vacuum dried, cut into pieces, assembled into 2025 button cells, and the fast charging performance of the cells was tested.

[0054] As a test of the fast charging performance of lithium-ion batteries, such as Figure 8 The battery can be fast charged to 450mAh / g within 12 minutes, and there is no significant capacity fluctuation or decay after 5 cycles.

[0055] Example 3: A method for preparing carbon nanoflower-coated bismuth electrode material for fast-charging batteries, the specific steps of which are as follows:

[0056] (1) Bismuth oxide and β-chitosan were added to deionized water and ultrasonically dispersed for 0.6 h to obtain a mixed solution; the mass ratio of bismuth oxide to β-chitosan was 1:3; the solid-liquid ratio of bismuth oxide to deionized water was 3:120 g:mL.

[0057] (2) The mixed solution was sealed in the reactor and subjected to high temperature and high pressure reaction for 3 hours at a temperature of 150℃ and a pressure of 2.0MPa. The reaction products were obtained by solid-liquid separation.

[0058] (3) The reaction product was calcined at 1000℃ for 3h in an argon atmosphere (argon flow rate of 10mL / min) to obtain carbon nanoflower-coated bismuth electrode material. The carbon nanoflower-coated bismuth electrode material is a core-shell material with bismuth as the core and carbon nanoflowers formed by N-doped carbon as the outer shell. Nano bismuth particles are loaded on the carbon nanoflowers.

[0059] Fast charging performance test: Carbon nanoflower-coated bismuth electrode material was prepared into an electrode slurry with PVDF and acetylene black in a mass ratio of 8:1:1. The slurry was coated onto the surface of copper foil using a coating machine, vacuum dried, cut into pieces, assembled into 2025 button cells, and the fast charging performance of the cells was tested.

[0060] As a test of the fast charging performance of lithium-ion batteries, such as Figure 9The battery can be fast charged to 450mAh / g within 12 minutes, and there is no significant capacity fluctuation or decay after 5 cycles.

[0061] Example 4: A method for preparing carbon nanoflower-coated bismuth electrode material for fast-charging batteries, the specific steps of which are as follows:

[0062] (1) Bismuth oxide and cellulose were added to deionized water and ultrasonically dispersed for 1.0 h to obtain a mixed solution; the mass ratio of bismuth oxide and cellulose was 1:5, and the solid-liquid ratio of bismuth oxide to deionized water was 3:160 g:mL.

[0063] (2) The mixed solution was sealed in the reactor and subjected to high temperature and high pressure reaction for 5 hours at a temperature of 150℃ and a pressure of 1.0MPa. The solid-liquid separation was then performed to obtain the reaction product.

[0064] (3) The reaction product was calcined at 1000℃ for 4 hours in an argon atmosphere (argon flow rate of 20 mL / min) to obtain carbon nanoflower-coated bismuth electrode material. The carbon nanoflower-coated bismuth electrode material is a core-shell material with a core of bismuth and a shell of N-doped carbon forming carbon nanoflowers. Nano bismuth particles are loaded on the carbon nanoflowers.

[0065] Fast charging performance test: Carbon nanoflower-coated bismuth electrode material was prepared into an electrode slurry with PVDF and acetylene black in a mass ratio of 8:1:1. The slurry was coated onto the surface of copper foil using a coating machine, vacuum dried, cut into pieces, assembled into 2025 button cells, and the fast charging performance of the cells was tested.

[0066] As a test of the fast charging performance of lithium-ion batteries, such as Figure 10 The battery can be fast charged to 450mAh / g within 12 minutes, and there is no significant capacity fluctuation or decay after 5 cycles.

[0067] Example 5: A method for preparing carbon nanoflower-coated bismuth electrode material for fast-charging batteries, the specific steps of which are as follows:

[0068] (1) Bismuth oxide and α-chitosan were added to deionized water and ultrasonically dispersed for 0.5 h to obtain a mixed solution; the mass ratio of bismuth oxide to α-chitosan was 1:4, and the solid-liquid ratio of bismuth oxide to deionized water was 3:80 g:mL.

[0069] (2) The mixed solution was sealed in the reactor and subjected to high temperature and high pressure reaction for 5 hours at a temperature of 150℃ and a pressure of 5.0MPa. The solid-liquid separation was then performed to obtain the reaction product.

[0070] (3) The reaction product was calcined at 700℃ for 5h in a hydrogen-argon mixed atmosphere (the volume ratio of hydrogen to argon was 1:5 and the flow rate of the hydrogen-argon mixed gas was 20mL / min) to obtain carbon nanoflower-coated bismuth electrode material. The carbon nanoflower-coated bismuth electrode material is a core-shell material, with bismuth as the core and carbon nanoflowers formed by N-doped carbon as the outer shell, and nano bismuth particles loaded on the carbon nanoflowers.

[0071] Fast charging performance test: Carbon nanoflower-coated bismuth electrode material was prepared into an electrode slurry with PVDF and acetylene black in a mass ratio of 8:1:1. The slurry was coated onto the surface of copper foil using a coating machine, vacuum dried, cut into pieces, assembled into 2025 button cells, and the fast charging performance of the cells was tested.

[0072] As a test of the fast charging performance of lithium-ion batteries, such as Figure 11 The battery can be fast charged to 450mAh / g within 12 minutes, and there is no significant capacity fluctuation or decay after 5 cycles.

[0073] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. The application of carbon nanoflower-coated bismuth electrode material in the preparation of electrodes for fast-charging batteries, characterized in that, The preparation method of the carbon nanoflower-coated bismuth electrode material specifically comprises the following steps: (1) adding bismuth oxide and chitin substances into deionized water for ultrasonic dispersion to obtain a mixed solution; the mass ratio of the bismuth oxide and the chitin substances is 1:1-5, and the solid-liquid ratio g:mL of the bismuth oxide to the deionized water is 3:80-160; (2) sealing the mixed solution in a reaction kettle for high-temperature and high-pressure reaction, and then performing solid-liquid separation to obtain a reaction product; the high-temperature and high-pressure reaction is performed at a temperature of 150-250 ℃, a pressure of 0.1-5.0 MPa, and for 1-5 h; (3) calcining the reaction product in a protective atmosphere or a reducing atmosphere to obtain the carbon nanoflower-coated bismuth electrode material; the carbon nanoflower-coated bismuth electrode material is a core-shell material, the inner core is bismuth, the outer shell is carbon nanoflowers formed by N-doped carbon, and the carbon nanoflowers are loaded with nano bismuth particles; the calcination temperature is 600-1000 ℃.

2. Use according to claim 1, characterized in that: In step (1), the chitin substances are α-chitosan, β-chitosan, γ-chitosan or chitin.

3. Use according to claim 1, characterized in that: In step (3), the calcination time is 2-8 h.

4. Use according to claim 1, characterized in that: In step (3), the protective gas is high-purity argon or high-purity nitrogen, and the reducing gas is hydrogen-argon mixed gas.

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