Sodium-selenium battery cathode material and application thereof

Abstract

The application discloses a sodium-selenium battery positive electrode material and application thereof, and belongs to the field of methods or devices for directly converting chemical energy into electric energy. In the preparation process of the positive electrode material, the bituminous coal powder is soaked in a nitric acid solution to remove metal elements, and is soaked in a hydrofluoric acid to remove SiO2. Then, the prepared bituminous coal powder is subjected to structure reforming through chemical activation to prepare hierarchical porous bituminous coal-based hard carbon. Finally, the hierarchical porous bituminous coal-based hard carbon is used as a carbon source to synthesize a V2O3@Se / C sodium-selenium battery positive electrode material through a one-step hydrothermal method and a thermal annealing method. The material presents a layered'seed-hypocotyl' composite structure similar to a pomegranate. The prepared sodium-selenium battery positive electrode material has the advantages of high reversible specific capacity, low electrode reaction resistance, good rate performance, excellent cycle stability and high initial coulombic efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of methods or devices for directly converting chemical energy into electrical energy, in particular to a sodium-selenium battery cathode material and its application. BACKGROUND

[0002] With the rapid development of renewable energy systems and electric vehicles, there is an urgent need to develop high-energy density, low-cost energy storage devices. Lithium-ion batteries are currently the mainstream, but their large-scale application is limited by the scarcity and uneven distribution of lithium resources. Sodium-ion batteries, with their abundant sodium resources and low cost, have become an ideal alternative to lithium-ion batteries. Therefore, developing sodium-ion batteries with high capacity, long life and safety is a key strategy to promote sustainable energy storage.

[0003] Among the many sodium-ion battery systems, sodium-selenium batteries stand out with moderate theoretical specific capacity (678 mAh / g) and high volumetric capacity (3253 Ah / L). In addition, the high electronic conductivity of Se (1 x 10 -3 S / m) further facilitates the high utilization of active materials in the battery. These advantages of Se make it a promising anode material for high-energy rechargeable batteries. However, Se undergoes severe volume expansion during charging and discharging, and the formed polyselenides dissolve in the electrolyte, resulting in "shuttle effect", which leads to low coulombic efficiency, rapid capacity decay and other problems, which have plagued the development of sodium-selenium batteries. SUMMARY

[0004] The purpose of the present application is to provide a sodium-selenium battery cathode material and its application, which combines V2O3 with hierarchical porous anthracite-based hard carbon to suppress the shuttle effect of sodium polyselenide.

[0005] The technical solutions adopted by the present application are as follows:

[0006] In a first aspect, the present application provides a sodium-selenium battery cathode material, and the preparation method of the cathode material comprises the following steps:

[0007] Step 1: soak anthracite powder raw material with nitric acid solution to remove metal elements; then filter out the solid, soak the solid with hydrofluoric acid solution to remove SiO2; then filter out the solid, wash with water, and dry to obtain anthracite powder without metal impurities and SiO2.

[0008] Further, in step 1, the preparation method of the anthracite powder raw material is as follows: crush the anthracite raw material by ball mill, and select the fractionated part after 80 mesh screening as the raw material.

[0009] Preferably, in step 1, the concentration of the used nitric acid solution is 2 mol / L; the anthracite powder raw material is prepared according to the mass and volume ratio of 1g:6mL with the nitric acid solution; the anthracite powder raw material is fully soaked for 24h to remove part of metal impurities.

[0010] Preferably, in step 1, the concentration of the used hydrofluoric acid solution is 2 mol / L; the anthracite powder raw material is prepared according to the mass and volume ratio of 1g:6mL with the hydrofluoric acid; when the hydrofluoric acid is soaked, a 60℃ water bath condition is preferably used for soaking, and stirring is performed during soaking; fully soaked for 4h to remove SiO2.

[0011] Preferably, in step 1, the solid filtered out after hydrofluoric acid soaking treatment is repeatedly centrifuged and washed with deionized water to collect black powder; then dried in a 60℃ air oven for 12h to obtain anthracite powder from which metal impurities and SiO2 are removed.

[0012] Step 2, mix the pore-forming agent with the anthracite powder prepared in step 1, then add deionized water to cover the mixture and soak; then heat and dry to remove water; then calcine and activate in a N2 atmosphere; finally, the calcined and activated product is naturally cooled and washed with deionized water until the pH is neutral to obtain a hierarchical porous anthracite-based hard carbon.

[0013] Further, in step 2, the pore-forming agent uses any one of KOH, K2CO3, ZnCl2 or phosphoric acid; the amount of anthracite powder and pore-forming agent is prepared according to the mass ratio of 1:0.5~4.

[0014] Preferably, in step 2, after soaking treatment with deionized water for 24h, directly put into an air drying oven to heat and dry at a temperature of 70℃, and the heating time is 24h.

[0015] Preferably, in step 2, heat to 600-800℃ at a heating rate of 10℃ / min for calcination, and the calcination time is 1.0~3.0h.

[0016] Step 3, dissolve the vanadium organometallic complex and SeO2 in deionized water to prepare a solution, then add methanol to the solution and stir uniformly; then add the hierarchical porous anthracite-based hard carbon prepared in step 2 to the solution and stir uniformly to prepare a mixture solution.

[0017] Further, in step 3, the vanadium organometallic complex uses any one of vanadyl acetylacetonate, triisopropyl vanadyl alcohol, ethyl maltol vanadyl, methyl maltol vanadyl, and oxalic acid vanadyl.

[0018] Further, in step 3, the amount of vanadium organometallic complex and SeO2 is prepared according to the molar ratio of 1:0.5~2.

[0019] Further, in step 3, deionized water is added in a molar-to-volume ratio of 1 mmol: 10-20 mL of vanadium organometallic complex to deionized water.

[0020] Further, in step 3, methanol is added in a volume ratio of 1:2-8 of methanol to deionized water.

[0021] Further, in step 3, SeO2 is added to the hierarchical porous anthracite-based hard carbon prepared in step 2 in a mass ratio of 1:1-0.1 of SeO2 to the hierarchical porous anthracite-based hard carbon.

[0022] Step 4, the mixture solution prepared in step 3 is treated by a hydrothermal method: the mixture solution is heated to 180-220℃ in a high-pressure device and kept for 12-36 h, and then naturally cooled to room temperature; then, the product after heating treatment is separated by centrifugation to obtain a solid product, the solid product is washed with deionized water and alcohol to remove excess impurity ions in the reaction process; then, the solid product is heated and dried.

[0023] Preferably, in step 4, the mixture solution is placed in a 200 mL Teflon-lined stainless steel autoclave, and then the stainless steel autoclave is heated in a forced air drying oven; heated to 200℃ at a heating rate of 5℃ / min and kept for 24 h.

[0024] Preferably, in step 4, the solid product is dried in a 60℃ air oven for 12 h.

[0025] Step 5, the solid product prepared in step 4 is treated by a thermal annealing method: the solid product prepared in step 4 is placed in a tube furnace and calcined at a heating rate of 5℃ / min to 400-600℃ under N2 atmosphere, the calcination time is 1-5 h, and then naturally cooled to obtain a V2O3@Se / C composite material.

[0026] Preferably, in step 5, the calcination is performed at a heating rate of 5℃ / min to 500℃, and the calcination time is 3 h.

[0027] In a second aspect, the application provides an application of a sodium-selenium battery cathode material, which uses the above-mentioned sodium-selenium battery cathode material as a sodium ion battery cathode material.

[0028] The beneficial effects of this invention are as follows: This invention provides a sodium selenide battery cathode material and its application. In the preparation process of this cathode material, anthracite powder is soaked in nitric acid solution to remove metal elements and infused with hydrofluoric acid to remove SiO2. Then, the obtained anthracite powder is chemically activated to restructure it and prepare hierarchical porous anthracite-based hard carbon. Finally, using the hierarchical porous anthracite-based hard carbon as a carbon source, V2O3@Se / C sodium selenide battery cathode material is synthesized by a one-step hydrothermal method and a thermal annealing method. This material exhibits a pomegranate-like layered "seed-aril" composite structure.

[0029] The material properties prepared in this invention are described below: Using a hydrothermal method, V₂O₃ nanosheets are first coated onto the surface of selenium spheres, and then combined with hierarchical porous anthracite-based hard carbon to form a unique garnet-like structure. In this structure, the selenium nanospheres are initially encapsulated by V₂O₃ and subsequently embedded in the hierarchical porous anthracite-based hard carbon matrix. During electrochemical cycling, V₂O₃ reacts with Na₂Se₂. x The intermediate exhibits strong chemisorption and catalytic activity, promoting its reduction to Na₂Se and facilitating nucleation. The subsequently formed Na₂Se... x It is further captured and catalyzed by V₂O₃, maintaining its redox activity. Meanwhile, the hierarchical porous anthracite-based hard carbon framework physically adsorbs and spatially confines the uncatalyzed Na₂Se. x Simultaneously, it synergistically enhances the catalytic efficiency of V2O3 and provides an electronic pathway, thereby promoting the catalytic activity of long-chain Na2Se. x To short chain Na2Se x The conversion process was observed. Testing revealed that the V₂O₃@Se / C cathode offered a high specific capacity of 670.3 mAh / g at 0.1 A / g and maintained 362 mAh / g at 10 A / g. Notably, at an ultra-high current density of 30 A / g, it maintained a reversible capacity of 310.01 mAh / g after 2500 cycles, equivalent to an ultra-low capacity decay rate of 0.00063% per cycle.

[0030] In summary, the sodium selenide battery cathode material prepared by this invention has high reversible specific capacity, low electrode reaction resistance, good rate performance, excellent cycle stability and high initial coulombic efficiency. Attached Figure Description

[0031] Figure 1 The image shown is a SEM image of the graded porous anthracite-based hard carbon obtained in step 2 of Example 1 of this application. Figure 1 Adsorption / desorption isotherms of a and N2 Figure 1 b.

[0032] Figure 2 The image shown is a TEM image of the Se@V2O3-27% / C composite material prepared in Example 1 of this application.Figure 2 a, 2b, HRTEM Figure 2 c, Energy dispersive x-ray spectroscopy (EDS) elemental mapping image 2d, Figure 2 e is Figure 2 d, the distribution map of V element, Figure 2 f is Figure 2 d, the distribution map of O element, Figure 2 g is Figure 2 d, the distribution map of Se element, Figure 2 h is Figure 2 d, the distribution map of C element.

[0033] Figure 3 a is the SEM image of Se@V2O3 prepared in Comparative Example 1 of the present application; Figure 3 b is the SEM image of Se@V2O3-38%C prepared in Example 2 of the present application; Figure 3 c is the SEM image of Se@V2O3-17%C prepared in Example 3 of the present application; Figure 3 d is the TEM image of Se@V2O3 prepared in Comparative Example 1 of the present application; Figure 3 e is the HRTEM image of Se@V2O3 prepared in Comparative Example 1 of the present application; Figure 3 f is the selected area diffraction (SAED) image of Se@V2O3 prepared in Comparative Example 1 of the present application; Figure 3 g is the EDS elemental mapping image of Se@V2O3 prepared in Comparative Example 1 of the present application; Figure 3 h is Figure 3 g, the distribution map of V element, Figure 3 i is Figure 3 g, the distribution map of Se element, Figure 3 j is Figure 3 g, the distribution map of O element.

[0034] Figure 4 a is the SEM image of Se / C prepared in Comparative Example 2 of the present application; Figure 4 b is the TEM image of Se / C prepared in Comparative Example 2 of the present application; Figure 4 c is the C element distribution map of EDS spectrogram of Se / C prepared in Comparative Example 2 of the present application; Figure 4 d is the Se element distribution map of EDS spectrogram of Se / C prepared in Comparative Example 2 of the present application.

[0035] Figure 5 The N2 adsorption-desorption curves and pore size distribution curves of the samples of Examples 1-3 and Comparative Examples 1-2 of the present application are shown; wherein 5a, 5c are N2 adsorption-desorption curves, and 5b, 5d are pore size distribution curves.

[0036] Figure 6The XRD patterns of the samples of the application examples 1-3 and comparative examples 1-2 are shown; wherein 6a is the XRD pattern of Se powder, hierarchical porous anthracite-based hard carbon and comparative example 2 sample; 6b is the XRD pattern of the samples of examples 1-3 and comparative example 1.

[0037] Figure 7 The Raman spectra of the samples of the application examples 1-3 and comparative examples 1-2 are shown; wherein, 7a is the Raman spectrum of Se powder, hierarchical porous anthracite-based hard carbon, example 1 and comparative example 2 sample; 7b is the Raman spectrum of the samples of examples 1-3 and comparative example 1.

[0038] Figure 8 a is the cyclic voltammetry (CV) curve of the V2O3@Se / C positive electrode prepared in the application example 1, Figure 8 b is the cyclic voltammetry (CV) curve of the Se / C positive electrode prepared in the comparative example 2 of the application; Figure 8 c is the cyclic voltammetry (CV) curve of the V2O3@Se positive electrode of the application.

[0039] Figure 9 a shows the charge-discharge curve of V2O3@Se-27% / C prepared in example 1 at 0.1A / g, Figure 9 b is the cycle performance graph of the V2O3@Se / C prepared in example 1, Se / C prepared in comparative example 2 and V2O3@Se positive electrode at 0.1A / g, Figure 9 c is the cycle performance graph of the V2O3@Se / C prepared in examples 1-3, Se / C prepared in comparative example 2 and V2O3@Se positive electrode at 3.0A / g, Figure 9 d shows the charge-discharge curve of V2O3@Se-27% / C prepared in example 1 at 3.0A / g, Figure 9 e is the cycle performance graph of the V2O3@Se / C prepared in example 1, Se / C prepared in comparative example 2 and V2O3@Se positive electrode at 1.0A / g.

[0040] Figure 10 The statistical curve graph of the electrode rate performance detection of the samples of the application examples 1 and comparative examples 1-2 is shown; wherein, Figure 10 a is the charge-discharge curve of V2O3@Se-27% / C prepared in example 1 at different current densities; Figure 10 b is the rate performance comparison graph of the V2O3@Se / C prepared in example 1, Se / C prepared in comparative example and V2O3@Se positive electrode; Figure 10 c is the rate performance comparison graph of various sodium selenium battery positive electrodes.

[0041] Figure 11 The CV curve of V2O3@Se / C prepared in the application example 1 at different scanning rates is shownFigure 11 a, log(i) vs. log(v) at different oxidation and reduction states Figure 11 b, capacitance ratio at different scan rates Figure 11 c, capacitance contribution at 1.6 mV / s Figure 11 d.

[0042] Figure 12 CV curves of Se / C prepared in Comparative Example 2 of the present application at different scan rates are shown Figure 12 a, log(i) vs. log(v) at different oxidation and reduction states Figure 12 b, capacitance ratio at different scan rates Figure 12 c, capacitance contribution at 1.6 mV / s Figure 12 d.

[0043] Figure 13 CV curves of V2O3@Se prepared in Comparative Example 1 of the present application at different scan rates are shown Figure 13 a, log(i) vs. log(v) at different oxidation and reduction states Figure 13 b, capacitance ratio at different scan rates Figure 13 c, capacitance contribution at 1.6 mV / s Figure 13 d.

[0044] Figure 14 are the long-term cycling performance detection graphs of Se / C, V2O3@Se and V2O3@Se / C electrodes under the condition of 30 A / g.

[0045] Figure 15 are the comparison graphs of the color change of the separator after 120 cycles of pure Se, Comparative Examples 1-2 and the electrode material of Example 1; wherein, Figure 15 a is the display graph of the color of the separator after 120 cycles of pure Se as the positive electrode of sodium selenium battery; Figure 15 b is the display graph of the color of the separator after 120 cycles of the sample of Comparative Example 2 as the positive electrode of sodium selenium battery; Figure 15 c is the display graph of the color of the separator after 120 cycles of the sample of Comparative Example 1 as the positive electrode of sodium selenium battery; Figure 15 d is the display graph of the color of the separator after 120 cycles of the sample of Example 1 as the positive electrode of sodium selenium battery.

[0046] Figure 16 are the Na2Se adsorbed on C, V2O3 and C-V2O3 x side view and top view of the adsorption configuration; wherein, Figure 16 a is Na2Se adsorbed on C x side view and top view of the adsorption configuration; Figure 16 b is Na2Se adsorbed on V2O3 x side view and top view of the adsorption configuration;Figure 16 c is Na2Se on C-V2O3 x Side view and top view of the adsorption configuration.

[0047] Figure 17 Na2Se is shown x Density of states (DOS) of C (a), V2O3 (b) and C-V2O3 (c) before adsorption, and Na2Se x Density of states (DOS) of C (d), V2O3 (e) and C-V2O3 (f) after adsorption; wherein, Figure 17 a is Na2Se x Density of states of C before adsorption; Figure 17 b is Na2Se x Density of states of V2O3 before adsorption; Figure 17 c is Na2Se x Density of states of C-V2O3 (c) before adsorption; Figure 17 d is Na2Se x Density of states of C after adsorption; Figure 17 e is Na2Se x Density of states of V2O3 (e) after adsorption; Figure 17 f is Na2Se x Density of states of C-V2O3 (f) after adsorption.

[0048] Figure 18 Energy state calculation curves of polyselenides on V2O3 and C-V2O3 during discharging and charging processes are shown; wherein, Figure 18 a is the energy state calculation curve of polyselenides on V2O3 and C-V2O3 during discharging; and b is the energy state calculation curve of polyselenides on V2O3 and C-V2O3 during charging. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0050] The raw materials used in the present application are described as follows:

[0051] The anthracite raw material used in the present application is provided by Baoyinemengke Coal Co., Ltd. in Ordos City. The component analysis table (absolute dry basis) of the anthracite raw material used in the embodiments of the present application is shown in Table 1 below.

[0052]

[0053] Example 1, a method for preparing Se@V2O3-27% / C composite material, comprising the following steps:

[0054] Step 1, using a ball mill to crush the anthracite raw material into anthracite powder, and selecting the fractionated part after 80 mesh screening as the raw material. The anthracite powder is mixed with 2 mol / L HNO3 solution in a mass to volume ratio of 1 g:6 mL, and soaked for 24 h to remove the metal impurities. In this embodiment, 100 g of anthracite powder and 600 mL of HNO3 solution are used; then the treated powder is filtered out and mixed with 2 mol / L hydrofluoric acid solution in a mass to volume ratio of 1 g:6 mL. In this embodiment, 80 g of anthracite powder treated with nitric acid and 480 mL of hydrofluoric acid solution are used; stirring at 60°C water bath for 4 h to remove SiO2. Then the solid is filtered out and treated with deionized water by repeated centrifugation, and the black powder is collected; finally, drying in a 60°C air oven for 12 h to obtain anthracite powder with metal impurities and SiO2 removed.

[0055] The elemental and component content table of the anthracite powder with metal impurities and SiO2 removed after step 1 of Example 1 of the application is shown in Table 2 below

[0056]

[0057] Step 2, using KOH as a pore former, mixing with the anthracite powder in a mass ratio of 1:2, then adding deionized water to cover the mixture, soaking in deionized water for 24 h, and then placing it in an air drying oven at a temperature of 70°C for forced heating and drying for 24 h. In this embodiment, 10 g of acid-treated anthracite powder and 20 g of KOH are used; then calcination and activation are carried out in a N2 atmosphere, and during calcination, the temperature is raised to 700°C at a rate of 10°C / min, and calcination is carried out at 700°C for 2 h. Finally, the calcined and activated product is naturally cooled and washed with deionized water until the pH is neutral to obtain a hierarchical porous anthracite-based hard carbon.

[0058] The pore structure parameter table of the hierarchical porous anthracite-based hard carbon prepared in step 2 of Example 1 of the application is shown in Table 3 below

[0059]

[0060] The elemental and component content table of the hierarchical porous anthracite-based hard carbon prepared in step 2 of Example 1 of the application is shown in Table 4 below

[0061]

[0062] This application uses scanning electron microscopy (SEM) and N2 adsorption / desorption isotherms to characterize the morphology and pore structure of the hierarchical porous anthracite-based hard carbon obtained in step 2 of Example 1. Figure 1 The image shown is a SEM image of the graded porous anthracite-based hard carbon obtained in step 2 of Example 1 of this application. Figure 1 Adsorption / desorption isotherms of a and N2 Figure 1 b.

[0063] from Figure 1 As can be seen from a, the graded porous anthracite-based hard carbon obtained in step 2 of Example 1 of this application exhibits an irregular shape, with pores of varying sizes distributed on its surface. From Figure 1 As can be seen in b, the presence of a type IV isotherm and an H3 hysteresis loop confirms the existence of a hierarchical porous structure in this application. This hierarchical porous structure can promote the growth of Na+. + During transmission, it is important to prevent polyselenides from escaping from the pores and dissolving in the electrolyte.

[0064] Step 3: First, add 8 mmol of vanadium acetylacetonate and 16 mmol of SeO2 to 120 mL of deionized water, and stir for 30 min to obtain a uniform blue transparent solution. Add 24 mL of methanol to the above solution and continue stirring at room temperature for 30 min. Add 0.9 g of graded porous anthracite-based hard carbon to the above transparent solution and stir until homogeneous to prepare a mixture solution.

[0065] Step 4: Treat the mixture solution prepared in Step 3 using a hydrothermal method: Transfer the mixture solution to a 200 mL Teflon-lined stainless steel autoclave, then place the autoclave in a forced-air drying oven for heating; heat to 200 °C at a heating rate of 5 °C / min, and maintain at 200 °C for 24 hours in the forced-air drying oven. Then allow it to cool naturally to room temperature. Next, collect the black powder from the heat-treated product by centrifugation, wash the black powder with deionized water and alcohol to remove excess impurity ions from the reaction process. Then, dry the black powder in a 60 °C air oven for 12 hours.

[0066] Step 5: Treat the solid product prepared in Step 4 using a thermal annealing method: Place the solid product prepared in Step 4 into a tube furnace and calcine it to 500°C at a heating rate of 5°C / min under a N2 atmosphere. Maintain the temperature for 3 hours, then allow it to cool naturally to obtain the V2O3@Se / C composite material. The sample obtained in this example has a V2O3 content of 27.66% and is named Se@V2O3-27% / C.

[0067] Table 5 below shows the elemental composition of the Se@V2O3-27% / C composite material prepared in Example 1 of this application.

[0068]

[0069] Figure 2 Figure 2a, 2b, HRTEM Figure 2 a, 2b, HRTEM Figure 2 c, Energy dispersive x-ray spectroscopy (EDS) elemental mapping image 2d, Figure 2 e is Figure 2 d, distribution map of V element, Figure 2 f is Figure 2 d, distribution map of O element, Figure 2 g is Figure 2 d, distribution map of Se element, Figure 2 h is Figure 2 d, distribution map of C element.

[0070] As Figure 2 a and Figure 2 b show, in the Se@V2O3-27% / C composite material, the Se@V2O3 domains are completely embedded in the continuous hierarchical porous anthracite-based hard carbon matrix, forming a "seed-pseudoseed coat" hierarchical structure similar to pomegranate.

[0071] Figure 2 c shows the HR-TEM image showing a clear interface between the Se ball and the V2O3 layer: Figure 2 On the left side of c, the lattice fringes with a spacing of about 0.27 nm correspond to V2O3 (104); while the right side Se ball presents a uniform contrast without obvious lattice fringes, indicating its amorphous nature.

[0072] Figure 2 d shows the energy dispersive x-ray spectroscopy (EDS) further reveals the layered element distribution of the structure: Se is concentrated in the core, V forms a shell around the Se ball, and C mainly exists in the outermost matrix. This layered structure provides strong spatial constraints for the Se core, promoting the effective capture and retention of Na2Se x during the electrochemical cycling process.

[0073] Example 2, a method for preparing a Se@V2O3-38% / C composite material, comprising the following steps:

[0074] Steps 1 and 2 of Example 1 are performed, and steps 3, 4, and 5 are performed as follows.

[0075] Step 3, first, 12 mmol vanadyl acetylacetonate and 16 mmol SeO2 were added into 120 mL deionized water, then stirred for 30 min to obtain a uniform blue transparent solution. 24 mL of methanol was added to the above solution, and stirring was continued at room temperature for 30 min. 0.18 g of hierarchical porous anthracite-based hard carbon was added to the above transparent solution and stirred to prepare a mixture solution.

[0076] Step 4, the mixture solution was transferred to a 200 mL Teflon-lined stainless steel autoclave, heated at a rate of 5 ℃ / min to 220 ℃, and then kept at 220 ℃ for 36 h in a blast drying oven, and then naturally cooled to room temperature. Then, the product after heating treatment was collected by centrifugal separation of black powder, and then washed with deionized water and alcohol for several times to remove the excess ions during the reaction. Then the powder was dried in an air oven at 60 ℃ for 36 h.

[0077] Step 5, the solid product prepared in step 4 was treated by heat annealing: the solid product prepared in step 4 was placed in a tube furnace and calcined at a rate of 5 ℃ / min to 600 ℃ under N2 atmosphere, kept for 3 h, and then naturally cooled to obtain V2O3@Se / C composite material. The V2O3 content of the sample prepared in this example is 38.40%, and is named Se@V2O3-38% / C.

[0078] Example 3, a preparation method of Se@V2O3-17% / C composite material, comprising the following steps:

[0079] Steps 1 and 2 of Example 1 were performed, and steps 3, 4 and 5 were performed as follows.

[0080] Step 3, first, 4 mmol vanadyl acetylacetonate and 16 mmol SeO2 were added into 120 mL deionized water, then stirred for 30 min to obtain a uniform blue transparent solution. 24 mL of methanol was added to the above solution, and stirring was continued at room temperature for 30 min. 1.8 g of hierarchical porous anthracite-based hard carbon was added to the above transparent solution and stirred to prepare a mixture solution.

[0081] Step 4, the mixture solution was transferred to a 200 mL Teflon-lined stainless steel autoclave, heated at a rate of 5 ℃ / min to 180 ℃, and then kept at 180 ℃ for 12 h in a blast drying oven, and then naturally cooled to room temperature. Then, the product after heating treatment was collected by centrifugal separation of black powder, and then washed with deionized water and alcohol for several times to remove the excess ions during the reaction. Then the powder was dried in an air oven at 60 ℃ for 12 h.

[0082] Step 5, treating the solid product prepared in step 4 by using a thermal annealing method: the solid product prepared in step 4 was placed in a tube furnace and calcined at 400℃ at a heating rate of 5℃ / min under N2atmosphere for 1h, and then naturally cooled to obtain the V2O3@Se / C composite material. The V2O3content of the sample prepared in this example was 17.17%, and was named Se@V2O3-17% / C.

[0083] Comparative Example 1, a method for preparing Se@V2O3, comprising the following steps:

[0084] The steps of Example 1 were performed, except that no hierarchical porous anthracite-based hard carbon was added when step 3 was performed, to prepare Se@V2O3.

[0085] Comparative Example 2, a method for preparing Se / C material, comprising the following steps:

[0086] The Se@V2O3-27% / C composite material prepared in Example 1 was soaked in 5mol / L dilute hydrochloric acid, heated to 60℃ with stirring for 2h; then filtered once with 0.5mol / L and 0.1mol / L hydrochloric acid respectively; finally washed with deionized water until neutral to ensure that V2O3was removed while no other impurity ions remained. Then placed in an oven at 60℃ for 12h to obtain the Se / C material.

[0087] The products prepared in Examples 1-3 and Comparative Example 1 were compared and analyzed as follows:

[0088] First, as shown in Table 6 below, is the element and component content statistical table of the samples of Examples 1-3 and Comparative Examples 1-2 of the present application

[0089]

[0090] Table 7 below is the pore structure parameter statistical table of the samples of Examples 1-3 and Comparative Examples 1-2 of the present application

[0091]

[0092] Figure 3 a is the SEM image of Se@V2O3prepared in Comparative Example 1 of the present application; Figure 3 b is the SEM image of Se@V2O3-38%C prepared in Example 2 of the present application; Figure 3 c is the SEM image of Se@V2O3-17%C prepared in Example 3 of the present application; Figure 3 d is the TEM image of Se@V2O3prepared in Comparative Example 1 of the present application; Figure 3 e is the HRTEM image of Se@V2O3prepared in Comparative Example 1 of the present application; Figure 3f is a selected area diffraction (SAED) pattern of Se@V2O3 prepared in Comparative Example 1 of the present application; Figure 3 g is an EDS element mapping of Se@V2O3 prepared in Comparative Example 1 of the present application; Figure 3 h is Figure 3 a distribution map of V element in g, Figure 3 i is Figure 3 a distribution map of Se element in g, Figure 3 j is Figure 3 a distribution map of O element in g.

[0093] Figure 4 a is a SEM image of Se / C prepared in Comparative Example 2 of the present application; Figure 4 b is a TEM image of Se / C prepared in Comparative Example 2 of the present application; Figure 4 c is a C element distribution map of EDS spectrum of Se / C prepared in Comparative Example 2 of the present application; Figure 4 d is a Se element distribution map of EDS spectrum of Se / C prepared in Comparative Example 2 of the present application.

[0094] From Figure 3 It can be seen from a that the V2O3 in the Se@V2O3 composite material prepared in Comparative Example 1 maintains a complete nanosheet self-assembled flower-like structure on the surface of Se. Since the total amount of Se generated in the reaction is basically the same, the more the content of hierarchical porous anthracite-based hard carbon increases, the more the carbon loaded on the surface of Se@V2O3, and the less obvious the morphology of the small ball is ( Figure 2 a and Figure 3 b-c). The corresponding TEM shows that Se exists in the form of an internal hollow structure ( Figure 2 a and Figure 3 d). High-resolution transmission electron microscopy (HRTEM) shows that its interplanar spacing is 0.3 nm and 0.27 nm, which matches the (101) plane of Se and the (104) plane of V2O3 ( Figure 3 e). This can be further confirmed by selected area electron diffraction (SAED) ( Figure 3 f). Finally, it is confirmed from energy dispersive spectroscopy (EDS) that Se, O and V elements are uniformly distributed in the Se@V2O3 composite material ( Figure 3 g). In addition, in order to make a comparison, the Se / C composite material prepared by completely removing V2O3 from the Se@V2O3-27% C composite material prepared in Example 1, the Se in the Se / C composite material retains a hollow spherical morphology ( Figure 4 b), and C and Se are uniformly distributed ( Figure 4 c).

[0095] As Figure 5The N2 adsorption-desorption curves and pore size distribution curves of the samples of the application examples 1-3 and the comparative examples 1-2 are shown; wherein, 5a and 5c are the N2 adsorption-desorption curves, and 5b and 5d are the pore size distribution curves.

[0096] From Figure 5 It can be seen from a that C has an IV-type isotherm and an H3 hysteresis loop, which confirms the existence of mesopores. In contrast, Se / C, Se@V2O3 and Se@V2O3 / C show a V-type isotherm and an H3 hysteresis loop, which confirms the existence of a hierarchical structure with micropores and mesopores. This hierarchical structure can promote the Na + transport while avoiding the escape of polyselenides from the pores to dissolve in the electrolyte. Se / C is synthesized by a hydrothermal method, unlike the previous impregnation method, and the specific surface area decreases from 762.31 m 2 / g to 35.17 m 2 / g after the addition of Se, which confirms the successful coating of the hierarchical porous anthracite-based hard carbon (Se content of 81.81%). For the Se@V2O3-27% / C composite, the specific surface area is 12.61 m 2 / g, which indicates the successful loading of V2O3 (V2O3 content of 27.66%).

[0097] Next, the application analyzes the phase structure and purity of the composite materials of the application examples 1-3 and the comparative examples 1-2 by X-ray diffraction (XRD). As Figure 6 shown in the XRD patterns of the samples of the application examples 1-3 and the comparative examples 1-2; wherein, 6a is the XRD pattern of the Se powder, the hierarchical porous anthracite-based hard carbon and the sample of the comparative example 2; and 6b is the XRD pattern of the samples of the application examples 1-3 and the comparative example 1.

[0098] From Figure 6 it can be seen that the original Se and Se@V2O3 materials are highly crystalline. With the increase of carbon content, the characteristic peaks of Se gradually weaken, and when the coating structure is completely formed, the diffraction peaks of Se disappear, which is consistent with the above-mentioned morphology change trend.

[0099] The application analyzes the chemical bonding of the composite materials of the application examples 1-3 and the comparative examples 1-2 by Raman spectroscopy. As Figure 7 shown in the Raman spectrograms of the samples of the application examples 1-3 and the comparative examples 1-2; wherein, 7a is the Raman spectrogram of the Se powder, the hierarchical porous anthracite-based hard carbon, the sample of the application example 1 and the comparative example 2; and 7b is the Raman spectrogram of the samples of the application examples 1-3 and the comparative example 1.

[0100] From Figure 7 it can be seen that the original Se, Se@V2O3 composite materials have a peak at 236 cm -1with a shoulder, attributed to the triangular Se of the chain structure. It is worth noting that with the increase of carbon content, the Se peak intensity decreases and moves to 260 cm -1 around, corresponding to the transition from crystalline Se (hexagonal) to molecular Se8 (amorphous ring) (same as XRD pattern). It is further confirmed that in Se@V2O3-27% / C composite, Se has been successfully confined inside the hierarchical porous anthracite-based hard carbon, only in amorphous form. All samples show similar peaks at 1345 cm -1 and 1593 cm -1 , which are the D band of disordered sp3 and the G band of graphite sp2 stretching, respectively, and the ratio reflects the defect properties of the material.

[0101] Further, the samples of Examples 1-3 and Comparative Examples 1-2 are made into working electrodes, and the electrode electrochemical performance is detected. The specific method is as follows:

[0102] The working electrode is made by mixing 80wt.% Se@V2O3 / C (Se@V2O3 and Se / C), 10wt.% Super-P carbon black and 10wt.% sodium alginate in aqueous solution; the mass loading of the electrode is 1.8~2.6mg / cm 2 ; Whatman glass fiber (GF / D) is used as a separator, and 1M NaPF6 dissolved in ethylene glycol dimethyl ether (DME)=100Vol% is used as an electrolyte.

[0103] Sodium sheet (counter electrode), separator, electrolyte (dimethyl ether solution containing NaPF6). All components (battery shell, electrode sheet, separator, etc.) need to be vacuum dried for 12 hours to remove moisture. The gas needs to be replaced more than three times before operation in the glove box to ensure an inert atmosphere. Glove box (water and oxygen content <1ppm), vacuum drying oven (60-80℃), tablet press (pressure 50MPa), pipette (accurately control the amount of electrolyte).

[0104] ‌Assembly sequence (starting with the positive shell) Positive shell → positive sheet → electrolyte (0.1-0.2mL) → separator (soaked in electrolyte) → sodium sheet (negative electrode) → gasket → spring → negative shell, the error of electrolyte injection needs to be controlled ±0.02mL, and the separator needs to be completely soaked. Use a digital tablet press to seal at a pressure of 50MPa to ensure that the contact resistance is <0.5mΩ. After standing for 4 hours, the open circuit voltage is detected, and abnormal values (such as <2.5V) need to be checked for short circuit risk.

[0105] The 2025 type button cell is used for electrochemical experiment, and the detection method is as follows:

[0106] In the voltage range of 0.01~3.0V (relative to Na / Na +Cyclic voltammetry tests were performed on the V2O3@Se / C, V2O3@Se, and V2O3 / C cathodes using a CHI760E electrochemical workstation.

[0107] The test results are as follows:

[0108] To evaluate the Na content of the V2O3@Se / C cathode + Storage performance was assessed by recording cyclic voltammetry (CV) curves of the V₂O₃@Se / C cathode within a voltage window of 0.01–3.0 V (vs. Na / Na⁺) at a scan rate of 0.1 mV / s. For example... Figure 8 a represents the cyclic voltammetry (CV) curve of the V2O3@Se / C cathode prepared in Example 1 of this application. Figure 8 b is the cyclic voltammetry (CV) curve of the Se / C cathode prepared in Comparative Example 2 of this application; Figure 8 c represents the cyclic voltammetry (CV) curve of the V2O3@Se cathode in this application.

[0109] like Figure 8 As shown in Figure a, in the first cycle, the two cathode peaks at ~1.92 and 1.10 V correspond to the stepwise mediation of Se: Se → Na₂Se. n (n≥4)→Na2Se. After the first scan, the ~0.50V characteristic disappeared, attributed to the formation of a solid electrolyte film. With electrode activation, the main anodic peak shifted to a slightly higher potential in subsequent cycles. Anodic scans showed two peaks at 1.62V and 1.82V, belonging to Na2Se oxidation and reversible reversion back to elemental Se, respectively. After the first cycle, the overall CV curve became more complex and was not fully stable even at the sixth cycle, a common behavior in diethyl ether electrolytes. Notably, in the first three cycles, the Se / C electrode exhibited almost identical CV curves to the V2O3@Se / C electrode. Figure 8 (b) indicates that the introduction of V₂O₃ does not alter the inherent Se redox pathway. For V₂O₃@Se ( Figure 8 c) Sodiumization still proceeds in two steps, but the redox peaks are sharper and more overlapping than those of the other two electrodes, indicating a more direct reaction pathway that can accelerate the reaction of Na₂Se. x Rapid formation promotes structural degradation or interfacial side reactions.

[0110] Furthermore, the electrodes prepared from the samples of Examples 1-3 and Comparative Examples 1-2 were subjected to cycle stability tests at 0.1 A / g, 3.0 A / g, and 10.0 A / g. The cycle stability of the electrodes was tested using a LAND-3100A Blue Electric Testing System, with the test environment temperature controlled at 25°C, and continuous charge-discharge tests were conducted at a current density of 0.1 A / g.

[0111] likeFigure 9 a shows the charge-discharge curves of V2O3@Se-27% / C prepared in Example 1 at 0.1 A / g, Figure 9 b is a cycle performance graph of V2O3@Se / C prepared in Example 1, Se / C prepared in Comparative Example 2 and V2O3@Se cathodes at 0.1 A / g, Figure 9 c is a cycle performance graph of V2O3@Se / C prepared in Examples 1-3, Se / C prepared in Comparative Example 2 and V2O3@Se cathodes at 3.0 A / g, Figure 9 d shows the charge-discharge curves of V2O3@Se-27% / C prepared in Example 1 at 3.0 A / g, Figure 9 e is a cycle performance graph of V2O3@Se / C prepared in Example 1, Se / C prepared in Comparative Example 2 and V2O3@Se cathodes at 1.0 A / g.

[0112] Figure 9 a shows the galvanostatic charge-discharge curves of Se@V2O3-27% / C composite at a current density of 0.1 A / g. The evolution of the discharge and charge platforms is consistent with the CV measurement results. The initial discharge and charge capacities are 670 and 535.3 mAh / g, respectively, which are much higher than those of other electrodes; the irreversible capacity of the initial cycle is related to the formation of solid electrolyte film (SEI) and the irreversible capture of Na in the bulk carbon and carbon pores.

[0113] From Figure 9 It can be seen from b that the capacity of Se decays quickly, and after 120 cycles, Se@V2O3-27% / C shows higher sodium storage capacity, even at a high current density of 3.0 A / g. Figure 9 b, Se@V2O3-27% / C material has excellent cycle stability, which means that the fixation and conversion of V2O3 to selenide is very effective; when more V2O3 is added as a catalyst, the adsorption capacity is too strong, which can lead to the decomposition of polyselenide and the blockage of active sites on the surface; on the contrary, weak adsorption capacity is not conducive to the capture of polyselenide for catalytic conversion, and the electrochemical trends shown in the figure well prove that when 27% of V2O3 is added as a catalyst, the specific capacity and cycle stability of the electrode material are optimal. In addition, at a current density of 3.0 A / g, the reversible specific capacity of Se@V2O3 / C material shows a trend of first increasing and then decreasing ( Figure 9 c); the main reason is that the catalytic effect of V2O3 is stronger than the adsorption capacity of hierarchical porous anthracite-based hard carbon, and under the condition of equivalent Se content, with the increase of carbon content, the content of V2O3 gradually decreases, and the elapse of sodium polyselenide intensifies, and the specific capacity decreases. In addition, at a current density of 3.0 A / g, the Se@V2O3-27% / C cathode prepared in Example 1 has almost coincided charge-discharge curves except the first charge-discharge curve.Figure 9 d) Further surface treatment of the Se@V2O3-27% / C cathode demonstrates good cycle stability. At a current density of 10 A / g, the capacity retention rate still reaches 97.33% after 2000 cycles. Figure 9 e).

[0114] Furthermore, the present invention, under room temperature conditions and within a voltage range of 0.01~3.0V (relative to Na / Na), + The electrochemical performance at different current densities was evaluated using constant current charge-discharge curves on a battery tester.

[0115] like Figure 10 The figure shown is a statistical curve of the electrode rate capability test of the samples in Example 1 and Comparative Examples 1-2 of this application. Among them, Figure 10 a represents the charge-discharge curves of V2O3@Se-27% / C prepared in Example 1 at different current densities; Figure 10 b is a comparison graph of the rate performance of the positive electrodes of V2O3@Se / C prepared in Example 1, Se / C prepared in the comparative example, and V2O3@Se; Figure 10 c is a comparison chart of the rate performance of various sodium selenide battery cathodes.

[0116] In this invention, the constant current charge-discharge (GCD) curves of the V2O3@Se-27% / C electrode under different current densities are shown. Figure 10 a) Two discharge plateaus are shown at approximately 1.0V and 0.6V, and two charge plateaus are shown at approximately 1.5V and 1.8V, consistent with the two-step redox process of selenium. Rate performance shows ( Figure 10 (b) At current densities of 0.1, 0.2, 0.5, 1.0, 3.0, 5.0, 10.0, 20, and 30.0 A / g, the reversible capacities were 432.74, 430.56, 428.20, 425.90, 418.94, 414.17, 406.11, 393.91, and 385.00 mAh / g, respectively. Even with a 300-fold increase in current density (0.1 → 30.0 A / g), the capacity retention remained at 88.97%, demonstrating excellent rate capability. Figure 10 As shown in c, compared with the previously reported cathode materials F2O3-Se@NC (348.6 mAh / g at 0.1 A / g to 218.6 mAh / g at 20 A / g, with a retention rate of 62.7%) and VSeG (392 mAh / g at 0.2 A / g to 320 mAh / g at 5 A / g, with a retention rate of 62.7%), the V2O3@Se / C electrode exhibits higher capacity over a high current density range, highlighting its superior rate performance in sodium selenide battery systems.

[0117] Further, the present application is in the room temperature condition, in the voltage range of 0.01~3.0V (relative to Na / Na + ), on the electrochemical workstation, the CV curve under different scanning rate is used to carry out V2O3@Se / C, V2O3@Se and V2O3 / C positive electrode electrochemical kinetics analysis.

[0118] In order to further study the electrode kinetics, the CV measurement is carried out in the scanning rate range of 0.1 to 2.0 mV / s.

[0119] As shown in Figure 11 , the CV curve of V2O3@Se / C prepared by the embodiment 1 of the present application under different scanning rates is shown in Figure 11 a, log (i) versus log (v) under different oxidation and reduction states Figure 11 b, the specific capacitance under different scanning rates Figure 11 c, the capacitance contribution under 1.6 mV / s Figure 11 d.

[0120] As shown in Figure 12 , the CV curve of Se / C prepared by the comparative example 2 of the present application under different scanning rates is shown in Figure 12 a, log (i) versus log (v) under different oxidation and reduction states Figure 12 b, the specific capacitance under different scanning rates Figure 12 c, the capacitance contribution under 1.6 mV / s Figure 12 d.

[0121] As shown in Figure 13 , the CV curve of V2O3@Se prepared by the comparative example 1 of the present application under different scanning rates is shown in a, log (i) versus log (v) under different oxidation and reduction states b, the specific capacitance under different scanning rates c, the capacitance contribution under 1.6 mV / s d.

[0122] As shown in Figure 11 a, the CV curve of V2O3@Se / C electrode keeps its characteristic shape under higher scanning rate, only a slight shift occurs, which indicates that it has good electrochemical stability. It is found by comparison that the three kinds of composite materials show similar characteristics (a and Figure 12 a and Figure 13 a), which indicates that the inherent redox pathway of Se remains unchanged after adding V2O3 and carbon.

[0123] The relationship between the scanning rate (v) and the peak current (i) is as follows: i= aν b , or log (i) = b log (ν) +log (a), where a and b are fitting constants. Typically, b = 0.5 represents a diffusion-controlled process, while b = 1.0 represents a capacitance-controlled process. For V₂O₃@Se / C, b = 1.06, 0.89, 0.97, and 0.83 ( Figure 11 b). The corresponding value for the Se / C electrode is slightly smaller ( Figure 12 b), while the b values ​​for V2O3@Se are significantly smaller (0.55, 0.69, 0.56, and 0.47); Figure 13 b) reflects more diffusion-limiting behavior. These results indicate that hierarchical porous anthracite-based hard carbon scaffolds significantly enhance the surface-induced pseudocapacitance contribution in V₂O₃@Se / C and Se / C.

[0124] Furthermore, using equations i ( v )= k 1 ν + k 2 ν 1 / 2 The storage mechanism of sodium was quantitatively analyzed, among which... k 1 ν Represents the contribution of capacitance (surface control). k 2 ν 1 / 2 Corresponding diffusion control contribution. For example... Figure 11 As shown in Figure c, for the V₂O₃@Se / C electrode, the capacitance contribution gradually increases from 86.98% at 0.1 mV / s to 96.90% at 2.0 mV / s. It is noteworthy that at 1.6 mV / s, the pseudo-capacitance contribution reaches 96.87% (…). Figure 11 d), indicating that the surface controls the dynamics primarily. Although at the same scan rate, the capacitance contribution of Se / C ( Figure 12 c) and pseudocapacitance ratio ( Figure 12 d) Slightly lower, but it still exhibits predominantly surface-controlled behavior, consistent with its strong fast-charging capability. In contrast, V2O3@Se exhibits weaker pseudo-capacitive behavior, with its capacitance contribution ranging from 40.55% to 72.29%. Figure 13 c), while at 1.6mV / s, its capacitance contribution is only 67.50% ( Figure 13 (d) This indicates that the synergistic effect between the conductive carbon matrix and V₂O₃ is crucial for the rapid reaction kinetics. These rapid kinetics directly translate into high-rate durability: even after 2500 cycles at 30 A / g, the V₂O₃@Se / C electrode still maintains a high reversible capacity of 310.01 mAh / g, with an average capacity decay of 0.00063% per cycle. Figure 14 ), exceeding most previously reported Na-Se cathodes. Figure 14Figure for long-term cycle performance test of Se / C, V2O3@Se and V2O3@Se / C electrodes at 30A / g.

[0125] Further, the present application uses a camera to take pictures of the separators of the batteries assembled with pure Se, V2O3@Se / C, V2O3@Se and V2O3 / C electrode materials after 120 cycles at a current density of 0.1A / g, and analyzes the elution of sodium polyselenide. Figure 15 Figure for comparison of color changes of separators after 120 cycles of pure Se, Comparative Example 1-2 and Example 1 electrode materials; wherein, Figure 15 a is a display of the color of the separator after 120 cycles of pure Se as the positive electrode of a sodium-selenium battery; Figure 15 b is a display of the color of the separator after 120 cycles of the sample of Comparative Example 2 as the positive electrode of a sodium-selenium battery; Figure 15 c is a display of the color of the separator after 120 cycles of the sample of Comparative Example 1 as the positive electrode of a sodium-selenium battery; Figure 15 d is a display of the color of the separator after 120 cycles of the sample of Example 1 as the positive electrode of a sodium-selenium battery.

[0126] As shown in Figure 15 , the inhibition of sodium polyselenide shuttle effect can be seen from the color change of the separator after 120 cycles: the color change of the separator of the V2O3@Se / C battery is the smallest, in sharp contrast to the obvious color change of the pure elemental selenium battery. This indicates that the presence of both hierarchical porous anthracite-based hard carbon and V2O3 is beneficial to the inhibition of the elution of sodium polyselenide. Figure 15 a, Figure 15 b and Figure 15 c). However, the chemical adsorption and catalytic effect of V2O3 on sodium polyselenide make the elution of sodium polyselenide less Figure 15 b and Figure 15 c). Of course, the coexistence of anthracite-based hard carbon and V2O3 is more beneficial to the inhibition of the elution of sodium polyselenide Figure 15 d).

[0127] The present application uses density functional theory (DFT) and Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) of exchange-related functional for theoretical calculation, and is realized in Vienna ab initio simulation package (VASP). The interaction between ion cores and valence electrons is described by the projection augmented wave (PAW) method. The plane wave basis is set to 520eV. For the plate model, a 15Å vacuum is established, the reciprocal space of the Brillouin zone is represented by the Gamma point, and all calculations are spin-polarized. The convergence criteria are total energy 1.36×10 -7 eV and force 0.02eV / Å. In order to better simulate the dispersion interaction inside the water adsorption system, the grime's DFT-D3 method with zero damping function is used to consider the van der Waals correction.

[0128] The Gibbs free energy of each reaction intermediate is defined as: G = E DFT + E ZEP – Figure 15 where E DFT , E ZEP and TS are the total energy, zero-point energy and entropy contribution (T set to 298.15 K) of DFT calculation, respectively. E ZEP and TS of the adsorbed species were calculated using the VASPKIT code.

[0129] To explore the synergistic effect of V2O3 and carbon at the atomic scale, density functional theory (DFT) calculations were performed. The stable adsorption configurations (side and top views) are shown in Figure 15 . TS, Figures 16a-16c show side and top views of Na2Se x adsorption configurations on C, V2O3 and C-V2O3, respectively. Figure 16a shows side and top views of the Na2Se x adsorption configuration on C; figure 16b shows side and top views of the Na2Se x adsorption configuration on V2O3; figure 16c shows side and top views of the Na2Se x adsorption configuration on C-V2O3. In the figures, carbon atoms, sodium atoms and selenium atoms are represented by brown, yellow and green spheres, respectively; vanadium and oxygen atoms in V2O3 are represented by a red large sphere and red small spheres, respectively.

[0130] On hierarchical porous anthracite-based hard carbon, the adsorption of Na2Se6, Na2Se4, Na2Se2 and Na2Se is relatively weak, with adsorption energies of -0.21, -0.27, -0.67 and -0.40 eV, respectively, indicating that it is mainly a physical adsorption dominated by van der Waals forces. In contrast, V2O3 exhibits stronger chemical adsorption, with exothermic adsorption energies of -5.38, -5.66, -5.47 and -4.20 eV for the same species. Notably, the C-V2O3 composite further enhances the adsorption capacity to -5.09, -5.74, -6.68 and -6.26 eV, respectively, indicating that V2O3 and hierarchical porous anthracite-based hard carbon synergize to fix and transform long-chain Na2Se x components.

[0131] To elucidate the mechanism of enhanced adsorption energy, the electronic structure was analyzed by calculating the density of states (DOS) before adsorption and the partial density of states (PDOS) after adsorption. As shown in Figure 16 figure 17 is a diagram showing the DOS and PDOS of Na2Se xDensity of states (DOS) of C (a), V2O3 (b), and C-V2O3 (c) before adsorption, and Na2Se x Density of states (DOS) of C (d), V2O3 (e), and C-V2O3 (f) after adsorption; wherein, Figure 16 a is Na2Se x Density of states of C before adsorption; Figure 17 b is Na2Se x Density of states of V2O3 before adsorption; Figure 17 c is Na2Se x Density of states of C-V2O3 (c) before adsorption; Figure 17 d is Na2Se x Density of states of C after adsorption; Figure 17 e is Na2Se x Density of states of V2O3 (e) after adsorption; Figure 17 f is Na2Se x Density of states of C-V2O3 (f) after adsorption.

[0132] As can be seen from Figure 17 Figures 17a-17c, before adsorption, the conduction and valence bands of C, V2O3, and C-V2O3 all cross the Fermi level (E Figure 17 a-17c), the density of states near the Fermi level becomes broadened when V2O3 coexists with hierarchical porous anthracite-based hard carbon, increasing the available electronic states and thus improving the overall electrical conductivity. The hierarchical porous anthracite-based hard carbon not only provides additional conduction pathways, but also enhances the coupling between V2O3 and the carbon network, further improving the charge transfer performance. Since Na2Se x is an insulator, the electrical conductivity of the substrate after adsorption is crucial for the effective conversion of selenium. Therefore, PDOS analysis of the Se / C / Na2Se2, V2O3@Se / Na2Se4, and V2O3@Se / C / Na2Se4 systems shows that Figure 17 d-17f), Se / C / Na2Se2 has very few states at the Fermi level, indicating weak electronic interaction and negligible orbital hybridization. In contrast, the V2O3@Se / Na2Se4 interface exhibits increased density of states near the Fermi level due to strong interface coupling between the unfilled V3d orbitals and the Na2Se4 orbitals, which reflects strong chemical adsorption and charge redistribution. V2O3@Se / C / Na2Se4 shows the most significant density of states near the Fermi level, and PDOS analysis indicates that V atoms contribute the most, highlighting the dominant role of V2O3 in regulating the interface electronic structure. Compared with V2O3@Se / Na2Se4, V2O3@Se / C / Na2Se4 composite exhibits higher density of states near the Fermi level, which is consistent with the reduced electrochemical impedance and the improved catalytic performance of the catalyst with Na2Se xThis is consistent with the promotion of electron transfer between them. This improved electronic interaction facilitates the reversible conversion of selenium and enhances the electrochemical performance of sodium-selenium batteries.

[0133] Finally, to evaluate the impact of the composite material on redox thermodynamics, this application calculated the Gibbs free energy curve of selenium conversion ( Figure 17 ).like Figure 17 The figure shows the calculated energy state curves of polyselenides on V₂O₃ and C-V₂O₃ during the discharge and charging processes; among them, Figure 18 Figure 18 Figure 18 18b is the calculated energy state curve of polyselenides on V2O3 and C-V2O3 during the discharge process; 18b is the calculated energy state curve of polyselenides on V2O3 and C-V2O3 during the charging process.

[0134] It is worth noting that the conversion of Na₂Se to Na₂Se₆ is an exothermic and spontaneous reaction, while the reverse conversion from Na₂Se₆ to Na₂Se is endothermic. The conversion step from Na₂Se₄ to Na₂Se₂ shows the largest positive ΔG, indicating that this is the rate-determining step in the discharge process.

[0135] Along the discharge path, the minimum free energy of C-V₂O₃ is more favorable (more negative) than that of V₂O₃ (ΔG). min =-10.49eV vs. -7.64eV), indicating that C-V₂O₃ is thermodynamically favorable for selenium reduction. Conversely, during charging, the oxidation of Na₂Se₄ on C-V₂O₃ requires a higher free energy barrier, while V₂O₃ alone exhibits a lower and smoother energy barrier, which favors the formation of soluble Na₂Se. x .

[0136] In summary, these results indicate that the synergistic effect of C and V₂O₃ plays a crucial role in lowering the discharge free energy barrier and promoting Na₂Se formation, while V₂O₃ alone is relatively more favorable for the charging process. Due to the weak adsorption capacity of carbon, Se / C allows Na₂Se to form. x Diffusion into the electrolyte leads to a severe shuttle effect and loss of active material. In contrast, V₂O₃ exhibits strong chemisorption and catalytic activity, accelerating the absorption of Na₂Se. x Nucleation occurs through the V2O3@Se / C structure. Benefiting from its unique garnet-like structure, V2O3@Se / C exhibits enhanced adsorption and catalytic performance: the internal V2O3 captures and converts Na2Se, while the external hierarchical porous anthracite-based hard carbon physically confines unconverted Na2Se through adsorption and steric confinement. x This promotes its conversion into short-chain substances, thereby reducing the Na2Se content. x The accumulation of.

[0137] Further, the application uses different vanadium organic metal complexes to prepare sodium selenium battery positive electrode materials, and studies the characteristics thereof. The specific method is as follows:

[0138] On the basis of implementation 1, only the type of vanadium organic metal complex is changed, and other process conditions remain unchanged to prepare sodium selenium battery positive electrode materials. The vanadium organic metal complexes used are vanadyl acetylacetonate, vanadyl triisopropyl alcohol, vanadyl ethyl maltol, vanadyl methyl maltol and vanadyl oxalate.

[0139] Table 8 below is an element and ingredient content statistical table of Se@V2O3 / C composite sodium selenium battery positive electrode materials prepared using vanadyl acetylacetonate, vanadyl triisopropyl alcohol, vanadyl ethyl maltol, vanadyl methyl maltol and vanadyl oxalate as vanadium organic metal complexes

[0140]

[0141] Table 9 below is an electrochemical performance analysis statistical table of Se@V2O3 / C composite sodium selenium battery positive electrode materials prepared using vanadyl acetylacetonate, vanadyl triisopropyl alcohol, vanadyl ethyl maltol, vanadyl methyl maltol and vanadyl oxalate as vanadium organic metal complexes

[0142]

[0143] The comparative analysis is as follows: in the Se@V2O3 / C composite sodium selenium battery positive electrode materials prepared using different vanadium organic metal complexes, the Se content is similar, and the initial discharge specific capacity is similar. In addition, the V2O3 content in the Se@V2O3 / C composite sodium selenium battery positive electrode material is obviously different. After 2500 cycles at a current density of 30 A / g, the capacity retention rate shows an increasing trend with the increase of the V2O3 content, because V2O3 in the Se@V2O3 / C composite sodium selenium battery positive electrode material exhibits enhanced chemical adsorption energy and catalytic performance, thus playing a strong inhibitory role on the flow of sodium polyselenide. Therefore, under the condition that the Se content is similar, the higher the V2O3 content, the better the cycle stability.

[0144] Further, on the basis of embodiment 1, only the amount of hierarchical porous anthracite-based hard carbon is changed, and other process conditions remain unchanged to prepare sodium selenium battery positive electrode materials. The amount of hierarchical porous anthracite-based hard carbon is 0.18, 0.5, 0.9, 1.3 and 1.8 g, respectively.

[0145] Table 10 below is an element and ingredient content statistical table of Se@V2O3 / C composite sodium selenium battery positive electrode materials prepared using different amounts of hierarchical porous anthracite-based hard carbon

[0146]

[0147] The following table 11 is the statistical table of the electrochemical performance analysis of Se@V2O3 / C composite sodium selenium battery positive electrode materials prepared using different amounts of hierarchical porous anthracite-based hard carbon

[0148]

[0149] The comparative analysis is as follows: with the increase of the amount of hierarchical porous anthracite-based hard carbon, the V2O3 content in the Se@V2O3 / C composite sodium selenium battery positive electrode material decreases, and the Se content in the composite material is similar. After 2500 cycles at a current density of 30 A / g, with the increase of V2O3 content, the specific capacity retention rate of Se@V2O3 / C composite sodium selenium battery positive electrode shows a trend of first increasing and then decreasing, because V2O3 in the Se@V2O3 / C composite sodium selenium battery positive electrode material shows strong chemical adsorption energy and catalytic performance, thus playing a strong inhibitory effect on the flow of sodium polyselenide, and thus improving the cycle performance of the material. Then, V2O3 is a semiconductor, and has low electronic conductivity, and too much V2O3 content has a negative effect on the electrochemical performance of the Se@V2O3 / C composite sodium selenium battery positive electrode material. Therefore, with the increase of V2O3 content, the specific capacity retention rate of Se@V2O3 / C composite sodium selenium battery positive electrode shows a trend of first increasing and then decreasing.

[0150] Further, the present application studies the hierarchical porous anthracite-based hard carbon prepared under different pore-forming agents, different pore-forming agent amounts, different activation temperatures, and different activation times in step 2, and further studies the chemical composition of the prepared Se@V2O3 / C composite material and the electrochemical performance for sodium selenium battery positive electrode. The specific method is as follows:

[0151] On the basis of example 1 step 2, change the single variable according to the data in the following table; other process conditions remain unchanged, to prepare hierarchical porous anthracite-based hard carbon and Se@V2O3 / C composite material.

[0152] The following table 12 is the pore structure parameter of the hierarchical porous anthracite-based hard carbon prepared under different pore-forming conditions

[0153]

[0154] The following table 13 is the element and ingredient content statistical table of the Se@V2O3 / C composite material prepared according to example 1 step using the hierarchical porous anthracite-based hard carbon prepared under different pore-forming conditions

[0155]

[0156] The following table 14 is the statistical table of the electrochemical performance analysis of Se@V2O3 / C composite sodium selenium battery positive electrode material prepared according to example 1 step using the hierarchical porous anthracite-based hard carbon prepared under different pore-forming conditions

[0157]

[0158] By comparing and analyzing the above experimental data, the application researches and screens out the following preferred conditions: the best pore-forming agent is KOH. When KOH is used as the pore-forming agent, the mass ratio of the anthracite powder to the pore-forming agent is 1:2, the activation temperature is set to 700 DEG C, and the activation time is set to 2h, the specific surface area of the obtained graded porous anthracite-based hard carbon is the largest, the pore volume is the largest, and the adsorption capacity is the strongest.

[0159] In addition, it is found through comparison that, as the specific surface area of the graded porous anthracite-based hard carbon increases, the Se content in the Se@V2O3 / C composite sodium-selenium battery positive electrode material has an increasing trend, but the increasing amplitude is negligible. It is found through analysis of the electrochemical performance that, as the specific surface area of the graded porous anthracite-based hard carbon increases, the capacity retention rate of the Se@V2O3 / C composite sodium-selenium battery positive electrode at 30A / g gradually increases, and the cycle specific capacity gradually increases, but the increasing amplitude is also not too obvious. This is because the larger the specific surface area of the graded porous anthracite-based hard carbon, the larger the pore volume and the stronger the adsorption capacity, and in the sodium-selenium battery charging and discharging process, the more the polyselenium compound loss, and the stronger the cycle stability.

[0160] It can be understood that the present application is described through some embodiments, and those skilled in the art know that various changes or equivalent replacements can be made to these features and embodiments without departing from the spirit and scope of the present application. In addition, under the guidance of the present application, these features and embodiments can be modified to adapt to specific conditions and materials without departing from the spirit and scope of the present application. Therefore, the present application is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present application belong to the scope of protection of the present application.

Claims

1. A sodium selenide battery cathode material, characterized in that, The preparation method of this cathode material includes the following steps: Step 1: Soak the anthracite powder raw material in nitric acid solution to remove the metal elements; then filter out the solid and soak the solid in hydrofluoric acid solution to remove SiO2; then filter out the solid and wash and dry it to obtain anthracite powder with metal impurities and SiO2 removed. Step 2: Mix the pore-forming agent with the anthracite powder obtained in Step 1, then add deionized water to cover the mixture and soak it; then heat and dry to remove moisture; then calcine and activate in N2 atmosphere; finally, after the calcined and activated product is naturally cooled, wash it with deionized water until the pH is neutral to obtain graded porous anthracite-based hard carbon. Step 3: Dissolve the vanadium organometallic complex and SeO2 in deionized water to prepare a solution, then add methanol to the solution and stir until homogeneous; then add the graded porous anthracite-based hard carbon prepared in step 2 to the solution and stir until homogeneous to prepare a mixture solution. Step 4: Treat the mixture solution prepared in Step 3 using a hydrothermal method: Place the mixture solution in a high-pressure device and heat it to 180~220℃, and keep it at that temperature for 12~36h; then let it cool naturally to room temperature; next, separate the solid product from the heat-treated product by centrifugation, wash the solid product with deionized water and alcohol to remove excess impurity ions from the reaction process; then, heat and dry the solid product. Step 5: Treat the solid product prepared in step 4 with hot annealing: Place the solid product prepared in step 4 into a tube furnace and calcine it to 400~600℃ at a heating rate of 5℃ / min under N2 atmosphere for 1~5h. Then cool it naturally to obtain V2O3@Se / C composite material.

2. The sodium selenide battery cathode material according to claim 1, characterized in that, In step 1, the preparation method of the anthracite powder raw material is as follows: the anthracite raw material is crushed by ball mill, and the fractionated part after 80 mesh sieve is selected as the raw material.

3. The sodium selenide battery cathode material according to claim 1, characterized in that, In step 1, the concentration of the nitric acid solution used is 2 mol / L; the anthracite powder raw material and the nitric acid solution are prepared at a mass-to-volume ratio of 1 g: 6 mL; the anthracite powder raw material is soaked for 24 hours to remove some of the metallic impurities; the concentration of the hydrofluoric acid solution used is 2 mol / L; the anthracite powder raw material and the hydrofluoric acid are prepared at a mass-to-volume ratio of 1 g: 6 mL; during hydrofluoric acid soaking, a 60℃ water bath is used, and stirring is performed during soaking; the material is soaked for 4 hours to remove SiO2.

4. The sodium selenide battery cathode material according to claim 1, characterized in that, In step 1, the solid filtered after hydrofluoric acid soaking is repeatedly centrifuged and washed with deionized water to collect black powder; then it is dried in an air oven at 60°C for 12 hours to obtain anthracite powder with metal impurities and SiO2 removed.

5. The sodium selenide battery cathode material according to claim 1, characterized in that, In step 2, the pore-forming agent is any one of KOH, K2CO3, ZnCl2, or phosphoric acid; the amount of anthracite powder and the pore-forming agent is prepared at a mass ratio of 1:0.5~4; after soaking in deionized water for 24 hours, it is directly placed in an air drying oven and heated and dried at 70℃ for 24 hours; then it is heated to 600-800℃ at a heating rate of 10℃ / min for calcination for 1.0~3.0 hours.

6. The sodium selenide battery cathode material according to claim 1, characterized in that, In step 3, the vanadium organometallic complex is any one of acetylacetone vanadium oxyacetyl, triisopropanol vanadium oxyacetyl, ethyl maltol vanadium oxyacetyl, methyl maltol vanadium oxyacetyl, and vanadium oxalate.

7. The sodium selenide battery cathode material according to claim 1, characterized in that, In step 3, the relationship between the amount of vanadium organometallic complex and SeO2 is as follows: the mixture is prepared at a molar ratio of 1:0.5~2; deionized water is added at a molar to volume ratio of 1 mmol:10~20 mL; methanol is added at a volume ratio of 1:2~8; and the graded porous anthracite-based hard carbon prepared in step 2 is added at a mass ratio of 1:1~0.

1.

8. The sodium selenide battery cathode material according to claim 1, characterized in that, In step 4, the mixture solution is placed in a 200 mL Teflon-lined stainless steel autoclave, and then the stainless steel autoclave is placed in a forced-air drying oven for heating; the temperature is increased to 200°C at a heating rate of 5°C / min and held for 24 h; the solid product is dried in an air oven at 60°C for 12 h.

9. The sodium selenide battery cathode material according to claim 1, characterized in that, In step 5, the temperature is increased to 500℃ at a heating rate of 5℃ / min for calcination, and the calcination time is 3h.

10. An application of the sodium selenide battery cathode material according to any one of claims 1-9, characterized in that, Sodium selenide battery cathode material is used as a cathode material for sodium-ion batteries.

Images