Preparation method of three-layer heterojunction for sodium ion battery negative electrode material

Abstract

The invention discloses a preparation method of a three-layer heterojunction for a sodium ion battery negative electrode material. The three-layer structure of the heterojunction is nickel diselenide / nitrogen-doped biomass charcoal / cobalt diselenide in sequence. The preparation method comprises the following steps: by taking biomass charcoal, urea, selenium powder, a nickel source and a cobalt source as raw materials, pre-carbonizing the biomass charcoal at high temperature, calcining the pre-carbonized biomass charcoal and urea at high temperature in inert gas to obtain nitrogen-doped biomass charcoal, growing cobalt diselenide / nitrogen-doped biomass charcoal by a solvothermal method, and preparing the cobalt diselenide / nitrogen-doped biomass charcoal. And finally, the nickel diselenide / nitrogen-doped biomass charcoal / cobalt diselenide three-layer heterojunction is prepared through interface assembly. The preparation method is characterized in that a solvothermal method, a high-temperature calcination method and an interface assembly method are simultaneously applied to the preparation process of the material, and when the material is used as a sodium-ion battery composite negative electrode material, the material has relatively high cycling stability and conductivity and shows excellent electrochemical performance. The method is safe in process and stable in yield.

Description

Technical Field

[0001] This invention relates to the preparation and application of composite anode materials for sodium-ion batteries. The invention, for the first time, demonstrates the preparation of a three-layer heterojunction of nickel diselenide / nitrogen-doped biochar / cobalt diselenide. Solvothermal, high-temperature calcination, and interfacial assembly methods are simultaneously applied to the preparation of this material. As a negative electrode material for sodium-ion batteries, this material exhibits excellent electrochemical performance. The process is safe and produces stable yields. Background Art

[0002] With the widespread use of lithium-ion batteries in our daily lives, the shortage and rapid depletion of lithium resources have led to a series of problems. The development of energy sources that can replace lithium-ion batteries is of great significance. Sodium resources are abundant in nature. Sodium-ion batteries have low energy density and power density, and they perform well as cathode materials. Therefore, research on high-sodium-ion battery anodes has become a hot topic.

[0003] The main challenges facing sodium-ion anode materials are: ① poor sodium-ion diffusion kinetics; ② structural damage during charge and discharge, leading to poor cycling stability. Currently, anode materials suitable for sodium-ion batteries include carbon-based materials, alloys, and metal-based composites. Carbon-based materials offer excellent conductivity, low cost, environmental friendliness, and non-toxicity, making them the preferred anode materials for sodium-ion batteries. Biomass carbon, a green, renewable material widely found in nature, has become a hot topic in heterojunction research.

[0004] Wang Jing et al. proposed (Preparation and Sodium Storage Performance of Hollow-Structured CoSe2 / C Anode Materials for Sodium-Ion Batteries, Journal of Inorganic Materials: 1-11 [2022-11-21]) using the metal-organic framework ZIF-67 as a precursor, etching it with tannic acid to create a hollow structure. The resulting hollow CoSe2 nanostructures were then prepared by carbonization and selenization, demonstrating excellent sodium storage performance and high cycling stability. Chinese patent CN114497564 A discloses a method for preparing a cobalt selenide / nickel selenide heterojunction as a lithium-sulfur battery catalytic material. Melamine, glucose, cobalt nitrate, and nickel nitrate are sequentially added to deionized water, heated and stirred, and the resulting mixture powder is treated at high temperature in an inert gas atmosphere to produce a cobalt / nickel-carbon nanotube composite. Chinese patent CN113314714A discloses a bimetallic selenide material, its preparation method, and application. The material comprises a core composed of cobalt diselenide and an outer shell composed of a composite of cobalt diselenide and nickel diselenide.

[0005] The present invention combines the solvent thermal method, high-temperature calcination method and interface assembly method for the first time to prepare a three-layer heterojunction of nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide, and applies it to the composite negative electrode material of sodium ion batteries. Summary of the Invention

[0006] On the one hand, the present invention provides a method for preparing a nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide triple-layer heterojunction sodium ion battery negative electrode material, the method comprising the following steps:

[0007] Step 1: calcining biochar and nitrogen-containing organic matter at high temperature to obtain nitrogen-doped biochar;

[0008] Step 2: dissolving the nitrogen-doped biochar obtained in step 1 together with selenium powder, a cobalt source, and a reducing agent in an organic solvent; the resulting mixture is kept at 50-200° C. for 6-24 hours, cooled to room temperature, washed, and protonated with a protonic acid to obtain cobalt diselenide / nitrogen-doped biochar;

[0009] Step 3: Place nickel diselenide in water and disperse it by microwave to obtain a uniformly dispersed nickel diselenide mixed solution, centrifuge it, and take the upper suspension for standby use; take the upper suspension of nickel diselenide and add it dropwise to the cobalt diselenide / nitrogen-doped biochar obtained in step 2, and calcine it at high temperature under the protection of protective gas to obtain a three-layer heterojunction sodium ion battery negative electrode material of nickel diselenide / nitrogen-doped biochar / cobalt diselenide.

[0010] Furthermore, the step 1 is: after cutting and cleaning the biochar, calcining it at 200-300°C for 2-8 hours for pre-carbonization, grinding the product, adding an appropriate amount of urea, and calcining it at 900-1100°C for 2-8 hours to obtain nitrogen-doped biochar.

[0011] Furthermore, the nickel diselenide is prepared by the following steps: selenium powder, nickel source, reducing agent, and surfactant are placed in an organic solvent and stirred, the mixture is then kept at 50-200° C. for 6-24 h, cooled, washed, and filtered to obtain nickel diselenide.

[0012] Furthermore, the reducing agent is selected from one or more of ascorbic acid, sodium thiosulfate or sodium borohydride.

[0013] Furthermore, the surfactant is preferably sodium dodecylbenzenesulfonate.

[0014] Furthermore, the organic solvent is preferably ethanol.

[0015] Furthermore, the protective gas is selected from one or more of nitrogen, helium, neon, argon, krypton, xenon or carbon dioxide.

[0016] Furthermore, the high temperature calcination temperature in step 3 is 300-500° C., and the calcination time is 4-12 h.

[0017] Furthermore, the protonic acid is selected from one or more of nitric acid, sulfuric acid, hydrochloric acid or permanganic acid.

[0018] Another aspect of the present invention is to provide a three-layer heterojunction sodium ion battery negative electrode material of nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide, wherein the upper layer of the three-layer heterojunction is nickel diselenide, the middle layer is nitrogen-doped biomass carbon, and the lower layer is cobalt diselenide. The general chemical formula of the heterojunction is C x N y CoSe2NiSe2, where x+y=1 (0.4≤x≤0.8, 0.4≤y≤0.8).

[0019] Furthermore, the particle size of the sodium ion battery negative electrode material is 0.1-8 μm, and the tap density is 0.60-2.10 g / cm 3 .

[0020] Furthermore, the sodium ion battery negative electrode material is prepared by the following steps:

[0021] Step 1: calcining biochar and nitrogen-containing organic matter at high temperature to obtain nitrogen-doped biochar;

[0022] Step 2: dissolving the nitrogen-doped biochar obtained in step 1 together with selenium powder, a cobalt source, and a reducing agent in an organic solvent; the resulting mixture is kept at 50-200° C. for 6-24 hours, cooled to room temperature, washed, and protonated with a protonic acid to obtain cobalt diselenide / nitrogen-doped biochar;

[0023] Step 3: Place nickel diselenide in water and disperse it by microwave to obtain a uniformly dispersed nickel diselenide mixed solution, centrifuge it, and take the upper suspension for standby use; take the upper suspension of nickel diselenide and add it dropwise to the cobalt diselenide / nitrogen-doped biochar obtained in step 2, and calcine it at high temperature under the protection of protective gas to obtain a three-layer heterojunction sodium ion battery negative electrode material of nickel diselenide / nitrogen-doped biochar / cobalt diselenide.

[0024] Furthermore, the step 1 is: after cutting and cleaning the biochar, calcining it at 200-300°C for 2-8 hours for pre-carbonization, grinding the product, adding an appropriate amount of urea, and calcining it at 900-1100°C for 2-8 hours to obtain nitrogen-doped biochar.

[0025] Furthermore, the nickel diselenide is prepared by the following steps: selenium powder, nickel source, reducing agent, and surfactant are placed in an organic solvent and stirred, the mixture is then kept at 50-200° C. for 6-24 h, cooled, washed, and filtered to obtain nickel diselenide.

[0026] Furthermore, the reducing agent is selected from one or more of ascorbic acid, sodium thiosulfate or sodium borohydride.

[0027] Furthermore, the surfactant is preferably sodium dodecylbenzenesulfonate.

[0028] Furthermore, the organic solvent is preferably ethanol.

[0029] Furthermore, the protective gas is selected from one or more of nitrogen, helium, neon, argon, krypton, xenon or carbon dioxide.

[0030] Furthermore, the high temperature calcination temperature in step 3 is 300-500° C., and the calcination time is 4-12 h.

[0031] Furthermore, the protonic acid is selected from one or more of nitric acid, sulfuric acid, hydrochloric acid or permanganic acid.

[0032] This invention, for the first time, produces a triple-layer heterojunction sodium-ion battery anode material consisting of nickel diselenide, nitrogen-doped biochar, and cobalt diselenide by calcining nitrogen-doped biochar at high temperature, then synthesizing the selenide / nitrogen-doped biochar via a solvothermal method. Finally, the material is assembled through an interfacial assembly process. This sodium-ion battery anode material exhibits excellent electrical properties, with an initial discharge capacity between 650 and 700 mAh / g and a capacity retention rate exceeding 95% after 80 charge-discharge cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the XRD spectrum of the nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide three-layer heterojunction sodium ion battery negative electrode material provided in Example 1.

[0034] Figure 2-Figure 6 This is the XPS spectrum of the nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide three-layer heterojunction sodium ion battery negative electrode material provided in Example 1.

[0035] Figure 7-Figure 9 These are TEM and HRTEM images of the nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide triple-layer heterojunction sodium ion battery negative electrode material provided in Example 1. DETAILED DESCRIPTION

[0036] The specific embodiments of the present technology are further described below so that those skilled in the art can further understand the present invention, but they do not constitute a limitation of the present invention.

[0037] Example 1

[0038] The method for synthesizing and preparing a nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide triple-layer heterojunction sodium ion battery negative electrode material, the specific steps of which are as follows:

[0039] 6 g of biochar was chopped, cleaned, and calcined at 250°C for 4 h to obtain 5 g of pre-carbonized biochar. The pre-carbonized biochar was ground, added with an appropriate amount of urea, and calcined at 950°C for 6 h to obtain 4.5 g of nitrogen-doped biochar.

[0040] 23 mL of ethanol was used as a solvent, and 0.4 g of selenium powder, 0.5 g of cobalt acetate, 2 g of sodium borohydride, and 1.5 g of nitrogen-doped biochar were put into the solvent and stirred. The mixture was then placed in a hydrothermal autoclave and kept warm at 140 ° C for 12 h. After the solvent heat was completed, it was cooled to room temperature and washed, protonated with 1 mol / L hydrochloric acid, washed with water, and dried in a vacuum drying oven to obtain 2 g of cobalt diselenide / nitrogen-doped biochar.

[0041] 0.4 g of selenium powder, 0.4 g of nickel acetate, 2 g of ascorbic acid, and 1 g of sodium dodecylbenzenesulfonate were placed in 23 mL of ethanol and stirred. The mixture was then placed in a hydrothermal autoclave and heated at 140°C for 12 h. The mixture was then cooled, washed, and filtered to obtain 0.6 g of nickel diselenide. 0.6 g of nickel diselenide was dispersed in deionized water using a microwave oven to obtain a uniformly dispersed nickel diselenide mixed solution. The nickel diselenide mixed solution was centrifuged, the upper suspension was collected for later use, and the solid matter at the bottom was removed.

[0042] 10 mL of nickel diselenide upper layer suspension was added dropwise to 1 g of cobalt diselenide / nitrogen-doped biochar. Under the protection of nitrogen as the filling gas, the mixture was calcined at 450 °C for 3 h to obtain 0.84 g of nickel diselenide / nitrogen-doped biochar / cobalt diselenide three-layer heterojunction sodium ion battery composite anode material. The particle size of the material was 1 μm and the tap density was 0.36 g / cm 3 .

[0043] The above nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide three-layer heterojunction sodium ion battery composite anode material C x N y CoSe2NiSe2 was assembled into a sodium ion half-cell. At a current density of 100 mA / g, the initial discharge capacity was 660.8 mAh / g. After 80 charge and discharge cycles, the discharge capacity was 635.3 mAh / g, and the capacity retention rate was 96.14%.

[0044] Example 2

[0045] The method for synthesizing and preparing a nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide triple-layer heterojunction sodium ion battery negative electrode material, the specific steps of which are as follows:

[0046] 5 g of biochar was chopped, cleaned, and calcined at 300°C for 5 h to obtain 3 g of pre-carbonized biochar. The pre-carbonized biochar was ground, added with an appropriate amount of urea, and calcined at 900°C for 6 h to obtain 1.5 g of nitrogen-doped biochar.

[0047] 23 mL of ethanol was used as the solvent, and 0.4 g of selenium powder, 0.5 g of cobalt acetate, 2.5 g of ascorbic acid, and 1.5 g of nitrogen-doped biochar were put into the solvent and stirred. The mixture was then placed in a hydrothermal autoclave and kept at 170 ° C for 10 h. After the solvent heat was completed, it was cooled to room temperature and washed, protonated with 1 mol / L nitric acid, washed with water, and dried in a vacuum drying oven to obtain 1.9 g of cobalt diselenide / nitrogen-doped biochar.

[0048] 0.3 g of selenium powder, 0.3 g of nickel acetate, 1.9 g of glucose, and 2 g of sodium dodecylbenzenesulfonate were placed in 23 mL of ethanol and stirred. The mixture was then placed in a hydrothermal autoclave and heated at 170°C for 10 h. The mixture was then cooled, washed, and filtered to obtain 0.4 g of nickel diselenide. 0.4 g of nickel diselenide was dispersed in deionized water using a microwave oven to obtain a uniformly dispersed nickel diselenide mixed solution. The nickel diselenide mixed solution was centrifuged, the upper suspension was collected for later use, and the solid matter at the bottom was removed.

[0049] 9 mL of nickel diselenide upper layer suspension was added dropwise to 1.1 g of cobalt diselenide / nitrogen-doped biochar. Under the protection of argon as the filling gas, the mixture was calcined at 550 °C for 4 h to obtain 0.51 g of nickel diselenide / nitrogen-doped biochar / cobalt diselenide three-layer heterojunction sodium ion battery composite anode material. The particle size of the material was 0.8 μm and the tap density was 0.68 g / cm 3 .

[0050] The above nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide three-layer heterojunction sodium ion battery composite anode material C x N y CoSe2NiSe2 was assembled into a sodium ion half-cell. At a current density of 100 mA / g, the initial discharge capacity was 671.4 mAh / g. After 80 charge and discharge cycles, the discharge capacity was 638.6 mAh / g, and the capacity retention rate was 95.11%.

[0051] Example 3

[0052] The method for synthesizing and preparing a nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide triple-layer heterojunction sodium ion battery negative electrode material, the specific steps of which are as follows:

[0053] 4 g of biochar was chopped, cleaned, and calcined at 280°C for 3 h to obtain 3 g of pre-carbonized biochar. The pre-carbonized biochar was ground, added with an appropriate amount of urea, and calcined at 920°C for 7 h to obtain 1.4 g of nitrogen-doped biochar.

[0054] 23 mL of ethanol was used as the solvent, and 0.3 g of selenium powder, 0.4 g of cobalt acetate, 2.5 g of hydrazine hydrate, and 1.4 g of nitrogen-doped biochar were put into the solvent and stirred. The mixture was then placed in a hydrothermal autoclave and kept at 150 ° C for 9 h. After the solvent heat was completed, it was cooled to room temperature and washed, protonated with 1 mol / L hydrochloric acid, washed with water, and dried in a vacuum drying oven to obtain 1.3 g of cobalt diselenide / nitrogen-doped biochar.

[0055] 0.3 g of selenium powder, 0.3 g of nickel acetate, 1.9 g of sodium thiosulfate, and 2 g of sodium dodecylbenzenesulfonate were placed in 23 mL of ethanol and stirred. The mixture was then placed in a hydrothermal autoclave and heated at 170°C for 10 h. The mixture was then cooled, washed, and filtered to obtain 0.3 g of nickel diselenide. 0.3 g of nickel diselenide was dispersed in deionized water using a microwave to obtain a uniformly dispersed nickel diselenide mixed solution. The nickel diselenide mixed solution was centrifuged, the upper suspension was collected for later use, and the solid matter at the bottom was removed.

[0056] 8 mL of nickel diselenide upper layer suspension was added dropwise onto 1.3 g of cobalt diselenide / nitrogen-doped biochar. Under the protection of nitrogen as the filling gas, the mixture was calcined at 450 °C for 5 h to obtain 0.71 g of nickel diselenide / nitrogen-doped biochar / cobalt diselenide three-layer heterojunction sodium ion battery composite anode material. The particle size of the material was 1.3 μm and the tap density was 0.54 g / cm 3 .

[0057] The above nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide three-layer heterojunction sodium ion battery composite anode material C x N y CoSe2NiSe2 was assembled into a sodium ion half-cell. At a current density of 100 mA / g, the initial discharge capacity was 669.1 mAh / g. After 80 charge and discharge cycles, the discharge capacity was 658.8 mAh / g, and the capacity retention rate was 98.46%.

[0058] Example 4

[0059] The method for synthesizing and preparing a nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide triple-layer heterojunction sodium ion battery negative electrode material, the specific steps of which are as follows:

[0060] 6 g of biochar was chopped, cleaned, and calcined at 270°C for 4 h to obtain 5 g of pre-carbonized biochar. The pre-carbonized biochar was ground, added with an appropriate amount of urea, and calcined at 930°C for 8 h to obtain 3.3 g of nitrogen-doped biochar.

[0061] 23 mL of ethanol was used as a solvent, and 0.5 g of selenium powder, 0.7 g of cobalt acetate, 3.5 g of formic acid, and 2.4 g of nitrogen-doped biochar were put into the solvent and stirred. The mixture was then placed in a hydrothermal autoclave and kept at 180°C for 16 h. After the solvent heat was completed, it was cooled to room temperature and washed, protonated with 1 mol / L hydrochloric acid, washed with water, and dried in a vacuum drying oven to obtain 2.3 g of cobalt diselenide / nitrogen-doped biochar.

[0062] 0.5 g of selenium powder, 0.7 g of nickel acetate, 3.9 g of formaldehyde, and 3 g of sodium dodecylbenzenesulfonate were placed in 23 mL of ethanol and stirred. The mixture was then placed in a hydrothermal autoclave and heated at 180°C for 16 h. The mixture was then cooled, washed, and filtered to obtain 0.5 g of nickel diselenide. 0.5 g of nickel diselenide was dispersed in deionized water using a microwave to obtain a uniformly dispersed nickel diselenide mixed solution. The nickel diselenide mixed solution was centrifuged, the upper suspension was collected for later use, and the solid matter at the bottom was removed.

[0063] 11 mL of the nickel diselenide upper layer suspension was added dropwise to 2.3 g of cobalt diselenide / nitrogen-doped biochar. Under the protection of nitrogen as the filling gas, the mixture was calcined at 500 °C for 9 h to obtain 1.11 g of a nickel diselenide / nitrogen-doped biochar / cobalt diselenide three-layer heterojunction sodium ion battery composite anode material. The particle size of the material was 1.4 μm and the tap density was 1.18 g / cm 3 .

[0064] The above nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide three-layer heterojunction sodium ion battery composite anode material C x N y CoSe2NiSe2 was assembled into a sodium ion half-cell. At a current density of 100 mA / g, the initial discharge capacity was 668.3 mAh / g. After 80 charge and discharge cycles, the discharge capacity was 646.1 mAh / g, and the capacity retention rate was 96.68%.

[0065] Example 5

[0066] The method for synthesizing and preparing a nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide triple-layer heterojunction sodium ion battery negative electrode material, the specific steps of which are as follows:

[0067] 6 g of biochar was chopped, cleaned, and calcined at 290°C for 3 h to obtain 5.1 g of pre-carbonized biochar. The pre-carbonized biochar was ground, added with an appropriate amount of urea, and calcined at 950°C for 8 h to obtain 4.3 g of nitrogen-doped biochar.

[0068] 23 mL of ethanol was used as the solvent, and 0.3 g of selenium powder, 0.4 g of cobalt acetate, 1.5 g of hydrazine hydrate, and 2.5 g of nitrogen-doped biochar were put into the solvent and stirred. The mixture was then placed in a hydrothermal autoclave and kept at 180°C for 15 h. After the solvent heat was completed, it was cooled to room temperature and washed, protonated with 1 mol / L sulfuric acid, washed with water, and dried in a vacuum drying oven to obtain 2.4 g of cobalt diselenide / nitrogen-doped biochar.

[0069] 0.3 g of selenium powder, 0.4 g of nickel acetate, 1.9 g of hydrazine hydrate, and 2 g of sodium dodecylbenzenesulfonate were placed in 23 mL of ethanol and stirred. The mixture was then placed in a hydrothermal autoclave and heated at 180°C for 14 h. The mixture was then cooled, washed, and filtered to obtain 0.3 g of nickel diselenide. 0.3 g of nickel diselenide was dispersed in deionized water using a microwave to obtain a uniformly dispersed nickel diselenide mixed solution. The nickel diselenide mixed solution was centrifuged, the upper suspension was collected for later use, and the solid matter at the bottom was removed.

[0070] 11 mL of the nickel diselenide upper layer suspension was added dropwise to 2.4 g of cobalt diselenide / nitrogen-doped biochar. Under the protection of nitrogen as the filling gas, the mixture was calcined at 450 ° C for 4 h to obtain 1.3 g of nickel diselenide / nitrogen-doped biochar / cobalt diselenide three-layer heterojunction sodium ion battery composite anode material. The particle size of the material was 1.3 μm and the tap density was 0.16 g / cm 3 .

[0071] The above nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide three-layer heterojunction sodium ion battery composite anode material C x N y CoSe2NiSe2 was assembled into a sodium ion half-cell. At a current density of 100 mA / g, the initial discharge capacity was 671.1 mAh / g. After 80 charge and discharge cycles, the discharge capacity was 660.9 mAh / g, and the capacity retention rate was 98.48%.

[0072] Example 6

[0073] The method for synthesizing and preparing a nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide triple-layer heterojunction sodium ion battery negative electrode material, the specific steps of which are as follows:

[0074] 6 g of biochar was chopped, cleaned, and calcined at 280°C for 3 h to obtain 5.2 g of pre-carbonized biochar. The pre-carbonized biochar was ground, added with an appropriate amount of urea, and calcined at 950°C for 11 h to obtain 4.1 g of nitrogen-doped biochar.

[0075] 23 mL of ethanol was used as a solvent, and 0.3 g of selenium powder, 0.4 g of cobalt acetate, 2 g of sodium borohydride, and 2.1 g of nitrogen-doped biochar were put into the solvent and stirred. The mixture was then placed in a hydrothermal autoclave and kept at 150 ° C for 24 h. After the solvent heat was completed, it was cooled to room temperature and washed, protonated with 1 mol / L hydrochloric acid, washed with water, and dried in a vacuum drying oven to obtain 2.3 g of cobalt diselenide / nitrogen-doped biochar.

[0076] 0.3 g of selenium powder, 0.5 g of nickel acetate, 1.9 g of hydrazine hydrate, and 2 g of sodium dodecylbenzenesulfonate were placed in 23 mL of ethanol and stirred. The mixture was then placed in a hydrothermal autoclave and heated at 150°C for 24 h. The mixture was then cooled, washed, and filtered to obtain 0.4 g of nickel diselenide. 0.4 g of nickel diselenide was dispersed in deionized water using a microwave to obtain a uniformly dispersed nickel diselenide mixed solution. The nickel diselenide mixed solution was centrifuged, the upper suspension was collected for later use, and the solid matter at the bottom was removed.

[0077] 11 mL of the nickel diselenide upper suspension was added dropwise to 2.3 g of cobalt diselenide / nitrogen-doped biochar. Under the protection of nitrogen as the filling gas, the mixture was calcined at 450 ° C for 4 h to obtain 1.1 g of nickel diselenide / nitrogen-doped biochar / cobalt diselenide three-layer heterojunction sodium ion battery composite anode material. The particle size of the material was 0.9 μm and the tap density was 1.8 g / cm 3 .

[0078] The above nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide three-layer heterojunction sodium ion battery composite anode material C x N y CoSe2NiSe2 was assembled into a sodium ion half-cell. At a current density of 100 mA / g, the initial discharge capacity was 679.9 mAh / g. After 80 charge and discharge cycles, the discharge capacity was 675.4 mAh / g, and the capacity retention rate was 99.34%.

[0079] It can be seen from the above examples that the sodium ion half-cell assembled from the sodium ion battery composite negative electrode material prepared by the present invention has an initial discharge specific capacity between 650-700 mAh / g, and a capacity retention rate of more than 95% after 80 charge and discharge cycles.

Claims

1. A method for preparing a nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide triple-layer heterojunction sodium ion battery negative electrode material, characterized in that: The method comprises the following steps: Step 1: calcining biochar and nitrogen-containing organic matter at high temperature to obtain nitrogen-doped biochar; Step 2: dissolving the nitrogen-doped biochar obtained in step 1 together with selenium powder, a cobalt source, and a reducing agent in an organic solvent; the resulting mixture is kept at 50-200° C. for 6-24 hours, cooled to room temperature, washed, and protonated with a protonic acid to obtain cobalt diselenide / nitrogen-doped biochar; Step 3: Place the pre-prepared nickel diselenide in water and disperse it by microwave to obtain a uniformly dispersed nickel diselenide mixed solution, centrifuge it, and take the upper suspension for standby use; take the upper suspension of nickel diselenide and add it dropwise to the cobalt diselenide / nitrogen-doped biochar obtained in step 2, and calcine it at high temperature under the protection of protective gas to obtain a three-layer heterojunction sodium ion battery negative electrode material of nickel diselenide / nitrogen-doped biochar / cobalt diselenide.

2. The preparation method according to claim 1, characterized in that The first step is: after cutting and cleaning the biochar, calcining it at 200-300°C for 2-8 hours for pre-carbonization, grinding the product, adding an appropriate amount of urea, and calcining it at 900-1100°C for 2-8 hours to obtain nitrogen-doped biochar.

3. The preparation method according to claim 1, characterized in that The pre-prepared nickel diselenide is prepared by the following steps: selenium powder, a nickel source, a reducing agent, and a surfactant are placed in an organic solvent and stirred, the mixture is then kept at 50-200° C. for 6-24 hours, cooled to room temperature, washed, and filtered to obtain nickel diselenide.

4. The preparation method according to claim 1, characterized in that The protective gas is selected from one or more of nitrogen, helium, neon, argon, krypton, xenon or carbon dioxide.

5. The preparation method according to claim 1, characterized in that The high temperature calcination temperature in step 3 is 300-500° C., and the calcination time is 4-12 h.

6. The preparation method according to claim 1, characterized in that The protonic acid is selected from one or more of nitric acid, sulfuric acid, hydrochloric acid or permanganic acid.

7. The preparation method according to claims 1 and 3, characterized in that The reducing agent is selected from one or more of ascorbic acid, sodium thiosulfate or sodium borohydride.

8. A nickel diselenide / nitrogen-doped biomass carbon / cobalt diselenide triple-layer heterojunction sodium ion battery negative electrode material, characterized in that: The upper layer of the three-layer heterojunction is nickel diselenide, the middle layer is nitrogen-doped biomass carbon, and the lower layer is cobalt diselenide. The general chemical formula of the heterojunction is C x N y CoSe2NiSe2, where x+y=1 (0.4≤x≤0.8, 0.4≤y≤0.8).

9. The sodium ion battery negative electrode material according to claim 8, characterized in that The particle size of the sodium ion battery negative electrode material is 0.1-8 μm, and the tap density is 0.60-2.10 g / cm 3 .

10. The sodium ion battery negative electrode material according to claim 8 or 9, characterized in that It is prepared by the preparation method according to any one of claims 1 to 9.

Images