A multilayer nitrogen-doped carbon-coated bismuth material, its preparation method and application

Abstract

This invention discloses a multilayer nitrogen-doped carbon-coated bismuth material, its preparation method, and its applications. The method includes: preparing bismuth alginate gel spheres using sodium alginate, urea, and bismuth nitrate pentahydrate; freeze-drying the spheres; followed by two-step calcination and dopamine hydrochloride coating; and drying to obtain the multilayer nitrogen-doped carbon-coated bismuth material. This invention simultaneously employs bismuth-carbon composite and carbon coating methods, resulting in a multilayer nitrogen-doped carbon-coated bismuth material with uniform morphology and even bismuth metal dispersion, avoiding re-aggregation during preparation and improving structural stability. The multilayer nitrogen-doped carbon-coated bismuth material prepared by this method can be used as a negative electrode material for sodium-ion batteries, enabling assembled sodium-ion half-cells to exhibit high discharge specific capacity and good cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a multilayer nitrogen-doped carbon-coated bismuth material, its preparation method, and its application. Background Technology

[0002] In recent years, efficient and convenient large-scale energy storage technologies have received increasing attention from governments worldwide to achieve continuous and stable power output from renewable energy sources. Electrochemical energy storage technology, characterized by high conversion efficiency, convenient deployment, and simple maintenance, has become one of the most promising directions for large-scale energy storage. Among these technologies, lithium-ion batteries have developed rapidly and are widely used in 3C consumer products and electric vehicles, possessing high energy density and excellent stability. However, due to the scarcity and geographical limitations of lithium metal resources, the price of lithium metal resources has risen sharply in recent years, resulting in high costs and hindering their application in large-scale energy storage systems. Sodium, belonging to the same group as lithium, not only possesses similar physicochemical properties to lithium but also boasts widely distributed, readily available, and inexpensive sodium metal resources, giving sodium-ion batteries a unique advantage in the field of large-scale energy storage technology and attracting increasing attention.

[0003] Currently developed anode materials for sodium-ion batteries mainly include carbon-based materials, titanium-based materials, alloy materials, transition metal oxides, and organic compounds. Among them, alloy materials possess high theoretical specific capacity and suitable sodium-ionization voltage, making them one of the ideal choices for anode materials in sodium-ion batteries. Among alloy materials, bismuth metal exhibits a specific capacity of 385 mAh g / L. -1 The theoretical specific capacity and up to 3800mAh cm⁻¹ -3 Bismuth has a high theoretical volumetric capacity, and my country has abundant bismuth resources, making it very suitable as a negative electrode material for sodium-ion batteries. However, the significant volume expansion of the alloy material during charge-discharge cycles leads to poor electrical contact and severe capacity decay; the volume expansion rate of bismuth metal is 250%. To mitigate the adverse effects of volume expansion, carbon coating or composites of carbon and alloy materials are generally used. Carbon materials can prevent agglomeration, reduce the damage to the electrode structure caused by the volume changes of the alloy material, and act as an electron channel to improve conductivity.

[0004] Patent application one discloses a method for preparing and applying a double-carbon-layer protected bismuth nanoparticle composite material, which involves obtaining a BiMOF precursor using a bismuth source and organic ligands, then coating it with dopamine hydrochloride, followed by high-temperature calcination and carbonization to obtain a double-carbon-layer protected bismuth nanoparticle composite material. Patent application another discloses a bismuth-based nanomaterial and its preparation method and application, which involves preparing a precursor using a carbon source, a bismuth source, and a nitrogen-containing pore-forming agent, followed by electrospinning and high-temperature calcination to obtain the bismuth-based nanomaterial.

[0005] Although some progress has been made in the preparation of bismuth / carbon composites using carbon coating, problems remain, including high preparation temperatures, high energy consumption, low discharge specific capacity, and poor cycle stability. Therefore, developing an economical and effective method to mitigate the volume expansion of bismuth metal materials and improve cycle performance is of great significance for the application of sodium-ion batteries. Summary of the Invention

[0006] In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a multilayer nitrogen-doped carbon-coated bismuth material, its preparation method and application.

[0007] The objective of this invention is achieved by at least one of the following technical solutions.

[0008] This invention provides a method for preparing a multilayer nitrogen-doped carbon-coated bismuth material, comprising the following steps:

[0009] (1) Preparation of alginate solution: Sodium alginate and urea are added to water and stirred thoroughly to obtain alginate solution;

[0010] (2) Preparation of bismuth salt solution: Dissolve bismuth nitrate pentahydrate in nitric acid solution, add water to obtain bismuth salt solution;

[0011] (3) Add the alginate solution dropwise into the bismuth salt solution, let it stand, and then filter to obtain bismuth alginate gel balls. Freeze-dry the bismuth alginate gel balls.

[0012] (4) First step of calcination and coating: After freeze-drying, bismuth alginate gel balls are calcined under an inert atmosphere. After calcination, the balls are milled into powder. The milled powder is added to Tris-HCl buffer solution, ultrasonically dispersed, and then coated with dopamine hydrochloride. The mixture is stirred, filtered, and dried.

[0013] (5) Second step calcination and coating: The material coated in the first step is calcined under an inert atmosphere, and then ground into powder. The ground powder is added to Tris-HCl buffer solution, ultrasonically dispersed, and then coated with dopamine hydrochloride. Stirring is maintained, and the mixture is filtered and dried.

[0014] (6) Grind the material coated in the second step to obtain the multilayer nitrogen-doped carbon-coated bismuth material.

[0015] Furthermore, the raw materials for preparing the bismuth alginate gel spheres, by weight, include:

[0016] 35-50 parts sodium alginate;

[0017] 15-40 parts urea;

[0018] 25-35 parts of bismuth nitrate pentahydrate;

[0019] Preferably, the raw materials for preparing the bismuth alginate gel spheres include, by weight parts:

[0020] 40 parts sodium alginate;

[0021] 30 parts urea;

[0022] 30 parts of bismuth nitrate pentahydrate;

[0023] Furthermore, in step (4), in the first step of calcination and coating, the calcination temperature is 100-300℃ and the calcination time is 30-120min.

[0024] Preferably, in step (4), in the first step of calcination and coating, the calcination temperature is 200°C and the calcination time is 30 min.

[0025] Further, in step (4), in the first step of calcination and coating, the ball milling is performed using a planetary ball mill with a rotation speed of 200-400 r / min and a time of 2-4 h.

[0026] Preferably, in step (4), in the first step of calcination and coating, the ball milling is performed using a planetary ball mill at a speed of 400 r / min for 4 h.

[0027] Further, in step (4), in the first step of calcination and coating, the mass ratio of the ball-milled powder to dopamine hydrochloride is (2-6):1, and the stirring time is 1-6h.

[0028] Preferably, in step (4), in the first step of calcination and coating, the mass ratio of the ball-milled powder to dopamine hydrochloride is 3:1, and the stirring time is 3 hours.

[0029] Further, in step (4), in the first calcination and coating step, the concentration of the Tris-HCl buffer is 0.05-0.15M, the pH value is 8.0-9.0, and the ultrasonic dispersion time is 20-60min.

[0030] Preferably, in step (4), during the first calcination and coating step, the concentration of the Tris-HCl buffer is 0.1M, the pH value is 8.5, and the ultrasonic dispersion time is 30min.

[0031] Further, in step (5), in the second calcination and coating step, the calcination temperature is 400-600℃ and the calcination time is 30-120min.

[0032] Preferably, in step (5), in the second calcination and coating step, the calcination temperature is 500°C and the calcination time is 30 min.

[0033] Further, in step (5), in the second calcination and coating step, the mass ratio of the ground powder to dopamine hydrochloride is (2-6:1), and the stirring time is 1-6h.

[0034] Preferably, in step (5), in the second calcination and coating step, the mass ratio of the ground powder to dopamine hydrochloride is 3:1, and the stirring time is 3h.

[0035] Further, in step (5), in the second calcination and coating step, the concentration of the Tris-HCl buffer is 0.05-0.15M, the pH value is 8.0-9.0, and the ultrasonic dispersion time is 20-60min.

[0036] Preferably, in step (5), during the second calcination and coating step, the concentration of the Tris-HCl buffer is 0.1M, the pH value is 8.5, and the ultrasonic dispersion time is 30min.

[0037] The present invention provides a multilayer nitrogen-doped carbon-coated bismuth material prepared by the aforementioned preparation method.

[0038] The present invention also provides the application of the aforementioned multilayer nitrogen-doped carbon-coated bismuth material in sodium-ion batteries.

[0039] The preparation method provided by this invention uses an economical carbon source, sodium alginate, and a bismuth salt solution to disperse bismuth metal. This is followed by freeze-drying, low-temperature calcination, and dopamine hydrochloride coating. Simultaneously, the method employs bismuth-carbon composite and carbon coating techniques to uniformly disperse the bismuth metal while preventing its re-aggregation. The multilayer nitrogen-doped carbon-coated bismuth material prepared by this method can be used as a negative electrode material for sodium-ion batteries, enabling assembled sodium-ion half-cells to exhibit high discharge specific capacity and good cycle stability.

[0040] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0041] (1) The multilayer nitrogen-doped carbon-coated bismuth material prepared by the present invention has a uniform morphology and uniform bismuth metal dispersion, which avoids re-aggregation during high-temperature calcination and improves the stability of the structure. In addition, the sodium-ion half-cell assembled from the multilayer nitrogen-doped carbon-coated bismuth material prepared by the present invention exhibits high discharge specific capacity and good cycle stability.

[0042] (2) The carbon source used in this invention has a low cost and a low calcination temperature, which saves energy and is more environmentally friendly and economical in large-scale production. Attached Figure Description

[0043] Figure 1 The image shows a SEM image of the multilayer nitrogen-doped carbon-coated bismuth material prepared in Example 2.

[0044] Figure 2 The images show the XRD patterns of the multilayer nitrogen-doped carbon-coated bismuth materials prepared in Examples 1, 2, and 3.

[0045] Figure 3 The diagram shows the rate performance of sodium-ion half-cells assembled from the multilayer nitrogen-doped carbon-coated bismuth materials prepared in Examples 1, 2, and 3.

[0046] Figure 4 The diagram shows the long-cycle performance of sodium-ion half-cells assembled from multilayer nitrogen-doped carbon-coated bismuth materials prepared in Examples 1, 2, and 3. Detailed Implementation

[0047] The following examples further illustrate specific implementations of the present invention, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described below are those that can be implemented or understood by those skilled in the art by referring to existing technology. Reagents or instruments whose manufacturers are not specified are considered to be conventional products that can be purchased commercially.

[0048] Example 1

[0049] A method for preparing a multilayer nitrogen-doped carbon-coated bismuth material includes the following steps:

[0050] (1) Preparation of alginate solution: Add 2g (40 parts) sodium alginate and 1.5g (30 parts) urea to 70mL of distilled water and stir thoroughly to obtain alginate solution;

[0051] (2) Preparation of bismuth salt solution: Dissolve 1.5g (30 parts) of bismuth nitrate pentahydrate in 3mL of concentrated nitric acid with a mass percentage concentration of 66%, and dilute with 50mL of distilled water to obtain bismuth salt solution;

[0052] (3) Transfer the alginate solution into a constant pressure funnel, let it drip naturally into the bismuth salt solution, let it stand for 2 hours and then filter to obtain bismuth alginate gel balls, and freeze-dry the bismuth alginate gel balls.

[0053] (4) First step of calcination and coating: After freeze-drying, bismuth alginate gel balls were calcined at 200℃ for 30 min under Ar atmosphere. After calcination, they were ball-milled at 400 r / min for 4 h to obtain powder. 300 mg of the ball-milled powder was added to 50 mL of 0.1 M Tris-HCl buffer (pH 8.5), ultrasonically dispersed for 30 min, and 100 mg of dopamine hydrochloride was added for coating. The mixture was stirred for 3 h, filtered, and dried in an oven at 60℃ for 12 h.

[0054] (5) Second step calcination and coating: The material coated in the first step was calcined at 400℃ for 30 min under Ar atmosphere. After calcination, it was ground to obtain powder. 120 mg of the ground powder was added to 50 mL of 0.1 M Tris-HCl buffer (pH 8.5), ultrasonically dispersed for 30 min, and 40 mg of dopamine hydrochloride was added for coating. The mixture was stirred for 3 h, filtered, and dried in a vacuum oven at 80℃ for 12 h.

[0055] (6) Grind the material coated in the second step to obtain the multilayer nitrogen-doped carbon-coated bismuth material.

[0056] Example 2

[0057] A method for preparing a multilayer nitrogen-doped carbon-coated bismuth material includes the following steps:

[0058] (1) Preparation of alginate solution: Add 2g (40 parts) sodium alginate and 1.5g (30 parts) urea to 70mL of distilled water and stir thoroughly to obtain alginate solution;

[0059] (2) Preparation of bismuth salt solution: Dissolve 1.5g (30 parts) of bismuth nitrate pentahydrate in 3mL of concentrated nitric acid with a mass percentage concentration of 66%, and dilute with 50mL of distilled water to obtain bismuth salt solution;

[0060] (3) Transfer the alginate solution into a constant pressure funnel, let it drip naturally into the bismuth salt solution, let it stand for 2 hours and then filter to obtain bismuth alginate gel balls, and freeze-dry the bismuth alginate gel balls.

[0061] (4) First step of calcination and coating: After freeze-drying, bismuth alginate gel balls were calcined at 200℃ for 30 min under Ar atmosphere. After calcination, they were ball-milled at 400 r / min for 4 h to obtain powder. 300 mg of the ball-milled powder was added to 50 mL of 0.1 M Tris-HCl buffer (pH 8.5), ultrasonically dispersed for 30 min, and 100 mg of dopamine hydrochloride was added for coating. The mixture was stirred for 3 h, filtered, and dried in an oven at 60℃ for 12 h.

[0062] (5) Second step calcination and coating: The material coated in the first step was calcined at 500℃ for 30 min under Ar atmosphere. After calcination, it was ground to obtain powder. 120 mg of the ground powder was added to 50 mL of 0.1 M Tris-HCl buffer (pH 8.5), ultrasonically dispersed for 30 min, and 40 mg of dopamine hydrochloride was added for coating. The mixture was stirred for 3 h, filtered, and dried in a vacuum oven at 80℃ for 12 h.

[0063] (6) Grind the material coated in the second step to obtain the multilayer nitrogen-doped carbon-coated bismuth material.

[0064] Example 3

[0065] A method for preparing a multilayer nitrogen-doped carbon-coated bismuth material includes the following steps:

[0066] (1) Preparation of alginate solution: Add 2g (40 parts) sodium alginate and 1.5g (30 parts) urea to 70mL of distilled water and stir thoroughly to obtain alginate solution;

[0067] (2) Preparation of bismuth salt solution: Dissolve 1.5g (30 parts) of bismuth nitrate pentahydrate in 3mL of concentrated nitric acid with a mass percentage concentration of 66%, and dilute with 50mL of distilled water to obtain bismuth salt solution;

[0068] (3) Transfer the alginate solution into a constant pressure funnel, let it drip naturally into the bismuth salt solution, let it stand for 2 hours and then filter to obtain bismuth alginate gel balls, and freeze-dry the bismuth alginate gel balls.

[0069] (4) First step of calcination and coating: After freeze-drying, bismuth alginate gel balls were calcined at 200℃ for 30 min under Ar atmosphere. After calcination, they were ball-milled at 400 r / min for 4 h to obtain powder. 300 mg of the ball-milled powder was added to 50 mL of 0.1 M Tris-HCl buffer (pH 8.5), ultrasonically dispersed for 30 min, and 100 mg of dopamine hydrochloride was added for coating. The mixture was stirred for 3 h, filtered, and dried in an oven at 60℃ for 12 h.

[0070] (5) Second step calcination and coating: The material coated in the first step was calcined at 600℃ for 30 min under Ar atmosphere. After calcination, it was ground to obtain powder. 120 mg of the ground powder was added to 50 mL of 0.1 M Tris-HCl buffer (pH 8.5), ultrasonically dispersed for 30 min, and 40 mg of dopamine hydrochloride was added for coating. The mixture was stirred for 3 h, filtered, and dried in a vacuum oven at 80℃ for 12 h.

[0071] (6) Grind the material coated in the second step to obtain the multilayer nitrogen-doped carbon-coated bismuth material.

[0072] Figure 1 This is a SEM image of the multilayer nitrogen-doped carbon-coated bismuth material prepared in Example 2. Figure 1 It can be seen that the multilayer nitrogen-doped carbon-coated bismuth material prepared in Example 2 has a uniform granular morphology. Based on the preparation method, it can be determined that some of the particles are coated together by dopamine hydrochloride, forming a whole.

[0073] Figure 2 The XRD patterns of the multilayer nitrogen-doped carbon-coated bismuth materials prepared in Examples 1, 2 and 3 are shown. The formation of metallic bismuth is confirmed by the characteristic diffraction peaks at the corresponding angles, and the intensity of the diffraction peaks gradually increases with the increase of calcination temperature.

[0074] Figure 3 The graph shows the rate performance of sodium-ion half-cells assembled from multilayer nitrogen-doped carbon-coated bismuth materials prepared in Examples 1, 2, and 3. Comparing the discharge specific capacity of the three examples, it was found that all three have a discharge specific capacity of around 0.1 Ag. -1 At current densities, they all exhibited values ​​close to 300 mAh g. -1 The three components exhibit high discharge specific capacity, and the differences between them gradually decrease as the current density increases. Among them, Example 2 demonstrates the highest discharge specific capacity and the best rate performance.

[0075] Figure 4 Sodium-ion half-cells assembled from multilayer nitrogen-doped carbon-coated bismuth materials prepared in Examples 1, 2, and 3 were tested at 1 Ag. -1 The long-cycle performance graphs at current density show that after the initial cycling, the discharge specific capacity of all three materials stabilizes at a certain level. The cycling stability of Examples 2 and 3 is similar. After 1000 cycles, the multilayer nitrogen-doped carbon-coated bismuth material prepared in Example 2 maintains the highest discharge specific capacity and the best capacity retention.

[0076] Table 1 below shows the performance of the multilayer nitrogen-doped carbon-coated bismuth materials prepared in Examples 1, 2, and 3 of this invention when used in sodium-ion half-cells at 1 Ag. -1 The initial discharge specific capacity at the current density and the capacity retention rate after 1000 cycles.

[0077] Table 1

[0078]

[0079] Table 1 shows that increasing the calcination temperature can improve the initial discharge specific capacity of the multilayer nitrogen-doped carbon-coated bismuth material. Examples 1, 2, and 3 were tested after an initial 0.1 Ag... -1After low current density cycling, all exhibited high discharge specific capacity and good capacity retention. When using the optimal calcination temperature, the multilayer nitrogen-doped carbon-coated bismuth material prepared in Example 2 can ensure the reduction of bismuth compounds while avoiding severe aggregation of bismuth metal. It not only exhibits high initial discharge specific capacity but also has a higher capacity retention after 1000 cycles.

[0080] The above embodiments are merely preferred embodiments of the present invention and are only used to explain the present invention, not to limit the present invention. Any changes, substitutions, modifications, etc., made by those skilled in the art without departing from the spirit and essence of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a multilayer nitrogen-doped carbon-coated bismuth material, characterized in that, The method comprises the following steps: (1) preparing alginate solution: adding sodium alginate and urea into water, and stirring to obtain alginate solution; (2) preparing bismuth salt solution: dissolving bismuth nitrate pentahydrate in nitric acid solution, and adding water to obtain bismuth salt solution; (3) dropping alginate solution into bismuth salt solution, and then filtering to obtain bismuth alginate gel balls, and freeze-drying the bismuth alginate gel balls; (4) first step of calcination and coating: after freeze-drying, the bismuth alginate gel balls are calcined in an inert atmosphere, and then ball-milled into powder, and the ball-milled powder is added into Tris-HCl buffer solution, ultrasonic dispersed, and coated with dopamine hydrochloride, and then dried after filtration; (5) second step of calcination and coating: the material coated in the first step is calcined in an inert atmosphere, and then ground into powder, and the ground powder is added into Tris-HCl buffer solution, ultrasonic dispersed, and coated with dopamine hydrochloride, and then dried after filtration; (6) grinding the material coated in the second step to obtain the multilayer nitrogen-doped carbon-coated bismuth material; The raw materials include, by mass fraction: Sodium alginate 35-50 parts; Urea 15-40 parts; Bismuth nitrate pentahydrate 25-35 parts.

2. The method of claim 1, wherein the method is characterized by: In the first step of calcination and coating, the calcination temperature is 100-300℃, and the calcination time is 30-120min.

3. The method of claim 1, wherein the method is characterized by: In the first step of calcination and coating, the ball-milling is performed by using a planetary ball mill, the rotation speed is 200-400r / min, and the time is 2-4h.

4. The method of claim 1, wherein the method further comprises: In the first step of calcination and coating, the mass ratio of the ball-milled powder to dopamine hydrochloride is (2-6):1, and the stirring time is 1-6h.

5. The method of claim 1, wherein the method further comprises: In the second step of calcination and coating, the calcination temperature is 400-600℃, and the calcination time is 30-120min.

6. The method of claim 1, wherein the method further comprises: In the second step of calcination and coating, the mass ratio of the ground powder to dopamine hydrochloride is (2-6):1, and the stirring time is 1-6h.

7. The method of claim 1, wherein the method further comprises: In steps (4) and (5), the concentration of the Tris-HCl buffer solution is 0.05-0.15M, the pH value is 8.0-9.0, and the ultrasonic dispersion time is 20-60min.

8. The multilayer nitrogen-doped carbon-coated bismuth material prepared by the method of any one of claims 1-7.

9. The multilayer nitrogen-doped carbon-coated bismuth material of claim 8 for use in sodium ion batteries.

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