Sodium-selenium battery positive electrode material and application thereof

Abstract

The invention 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 anthracite duff is soaked in a nitric acid solution to remove metal elements, and SiO2 is soaked in hydrofluoric acid to remove; then, carrying out structure reforming on the prepared anthracite duff through chemical activation to prepare graded porous anthracite-based hard carbon; and finally, synthesizing the V2O3 (at) Se / C sodium-selenium battery positive electrode material by taking the graded porous anthracite-based hard carbon as a carbon source through a one-step hydrothermal method and a thermal annealing method. The material presents a layered'seed-aril 'composite structure similar to pomegranate; the sodium-selenium battery positive electrode material prepared by the preparation method disclosed by the invention has relatively high reversible specific capacity, relatively low electrode reaction resistance, good rate capability, excellent cycling stability and relatively high first coulombic efficiency.

Description

Technical Field

[0001] The present invention relates to the field of methods or devices for directly converting chemical energy into electrical energy, and in particular to a sodium-selenium battery positive electrode material and application thereof. Background Art

[0002] With the rapid development of renewable energy systems and electric vehicles, the development of high-energy-density, low-cost energy storage devices is urgently needed. 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 advantages such as 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 for promoting sustainable energy storage.

[0003] Among many sodium-ion battery systems, sodium-selenide batteries stand out with their moderate theoretical specific capacity (678 mAh / g) and high volumetric capacity (3253 Ah / L). -3 The high electronic conductivity of Se (S / m) further facilitates high utilization of active materials in batteries. These advantages make Se a promising anode material for high-energy rechargeable batteries. However, Se undergoes dramatic volume expansion during charge and discharge, and the resulting polyselenides dissolve in the electrolyte, resulting in a "shuttle effect." This leads to low Coulombic efficiency and rapid capacity decay, problems that have plagued the development of sodium-selenide batteries. Summary of the Invention

[0004] The object of the present invention is to provide a sodium-selenium battery positive electrode material and its application, wherein the sodium-selenium battery positive electrode material combines V2O3 with graded porous anthracite-based hard carbon to inhibit the shuttle effect of sodium polyselenide.

[0005] The technical solution adopted in the present invention is as follows: In a first aspect, the present invention provides a sodium-selenium battery positive electrode material, and a method for preparing the positive electrode material comprises the following steps: Step 1: Soak the anthracite powder raw material in nitric acid solution to remove the metal elements therein; then filter out the solid, soak the solid in hydrofluoric acid solution to remove SiO2; then filter out the solid, wash it with water, and dry it to obtain anthracite powder with metal impurities and SiO2 removed.

[0006] Furthermore, in step 1, the anthracite powder raw material is prepared by the following method: the anthracite raw material is crushed by a ball mill, and the fraction after sieving with 80 mesh is selected as the raw material.

[0007] Preferably, 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 in a mass-to-volume ratio of 1 g:6 mL; and the anthracite powder raw material is fully soaked for 24 hours to remove metal impurities.

[0008] Preferably, in step 1, the concentration of the hydrofluoric acid solution used is 2 mol / L; the anthracite powder raw material and hydrofluoric acid are prepared in a mass-to-volume ratio of 1 g:6 mL; when soaking in hydrofluoric acid, it is preferably soaked in a 60°C water bath and stirred during soaking; and the SiO2 is fully soaked for 4 hours.

[0009] Preferably, in step 1, the solid filtered out after the hydrofluoric acid soaking treatment is repeatedly centrifuged and washed with deionized water to collect the black powder; and then dried in an air oven at 60° C. for 12 hours to obtain anthracite powder from which metal impurities and SiO 2 are removed.

[0010] 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 it in a N2 atmosphere; finally, cool the calcined and activated product naturally and wash it with deionized water until the pH is neutral to obtain graded porous anthracite-based hard carbon.

[0011] Furthermore, 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 in a mass ratio of 1:0.5~4.

[0012] Preferably, in step 2, after soaking in deionized water for 24 hours, the mixture is directly placed in an air drying oven and heated and dried at 70° C. for 24 hours.

[0013] Preferably, in step 2, the temperature is heated to 600-800° C. at a heating rate of 10° C. / min for calcination, and the calcination time is 1.0-3.0 h.

[0014] Step 3: dissolving the vanadium organometallic complex and SeO2 in deionized water to prepare a solution, then adding methanol to the solution and stirring evenly; then adding the graded porous anthracite-based hard carbon prepared in step 2 to the solution and stirring evenly to prepare a mixture solution.

[0015] Furthermore, in step 3, the vanadium organometallic complex is any one of vanadyl acetylacetonate, vanadyl triisopropoxide, vanadyl ethyl maltol, vanadyl methyl maltol, and vanadyl oxalate.

[0016] Furthermore, in step 3, the vanadium organometallic complex and SeO2 are prepared in a molar ratio of 1:0.5-2.

[0017] Furthermore, in step 3, deionized water is added at a molar to volume ratio of vanadium organometallic complex to deionized water of 1 mmol:10-20 mL.

[0018] Furthermore, in step 3, methanol is added at a volume ratio of methanol to deionized water of 1:2 to 8.

[0019] Furthermore, in step 3, the graded porous anthracite-based hard carbon prepared in step 2 is added at a mass ratio of SeO2 to graded porous anthracite-based hard carbon of 1:1 to 0.1.

[0020] Step 4: Treating the mixture solution prepared in step 3 by a hydrothermal method: heating the mixture solution to 180-220° C. in a high-pressure device and keeping the temperature for 12-36 hours; then naturally cooling it to room temperature; then, separating the solid product from the heated product by centrifugation, washing the solid product with deionized water and alcohol to remove excess impurity ions during the reaction; and then, heating and drying the solid product.

[0021] 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 placed in a forced air drying oven for heating; the mixture is heated to 200° C. at a heating rate of 5° C. / min and kept warm for 24 h.

[0022] Preferably, in step 4, the solid product is dried in an air oven at 60° C. for 12 h.

[0023] Step 5: Treat the solid product prepared in step 4 by thermal annealing: Place the solid product prepared in step 4 in a tubular furnace, heat it to 400-600°C at a heating rate of 5°C / min under N2 atmosphere, and calcine it for 1-5 hours. Then cool it naturally to obtain a V2O3@Se / C composite material.

[0024] Preferably, in step 5, the calcination is carried out by heating to 500° C. at a heating rate of 5° C. / min, and the calcination time is 3 h.

[0025] In a second aspect, the present invention provides an application of a sodium-selenium battery positive electrode material, wherein the above-mentioned sodium-selenium battery positive electrode material is used as a sodium ion battery positive electrode material.

[0026] The beneficial effects of the present invention are as follows: the present invention provides a sodium-selenium battery positive electrode material and its application. During the preparation process of the positive electrode material, anthracite powder is soaked in nitric acid solution to remove metal elements, and hydrofluoric acid is soaked to remove SiO2; then, the prepared anthracite powder is structurally reformed by chemical activation to prepare graded porous anthracite-based hard carbon; finally, the graded porous anthracite-based hard carbon is used as a carbon source to synthesize a V2O3@Se / C sodium-selenium battery positive electrode material by a one-step hydrothermal method and a thermal annealing method; the material exhibits a pomegranate-like layered "seed-aril" composite structure.

[0027] The characteristics of the material prepared by this invention are as follows: Using a hydrothermal method, V2O3 nanosheets are first coated on the surface of selenium spheres, and then combined with hierarchical porous anthracite-based hard carbon to form a unique pomegranate-like structure. In this structure, the selenium nanospheres are initially encapsulated by V2O3 and then embedded in the hierarchical porous anthracite-based hard carbon matrix. During the electrochemical cycle, V2O3 reacts with Na2Se x The intermediate has strong chemical adsorption and catalytic activity, which promotes its reduction to Na2Se and promotes nucleation. x The ions are further captured and catalyzed by V2O3, maintaining redox activity. Meanwhile, the hierarchical porous anthracite-based hard carbon framework physically adsorbs and spatially confines the uncatalyzed Na2Se x , while synergistically enhancing the catalytic efficiency of V2O3 and providing an electron pathway to promote the long-chain Na2Se x To short chain Na2Se x The V2O3@Se / C cathode was tested to provide 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.

[0028] In summary, the sodium-selenium battery positive electrode material prepared by the present invention has high reversible specific capacity, low electrode reaction resistance, good rate performance, excellent cycle stability and high first coulombic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The figure shows the SEM image of the hierarchical porous anthracite-based hard carbon obtained in step 2 of Example 1 of the present application. Figure 1 a and N2 adsorption / desorption isotherms Figure 1 b.

[0030] Figure 2 The TEM image of Se@V2O3-27% / C composite material prepared in Example 1 of the present application is shown. Figure 2 a, 2b, HRTEM Figure 2 c, Energy dispersive X-ray spectroscopy (EDS) elemental mapping image 2d, Figure 2 e is Figure 2 The distribution of V elements in d, Figure 2 f is Figure 2 The distribution of O elements in d, Figure 2 g is Figure 2 d. Distribution of Se elements in Figure 2 h is Figure 2 d Distribution of C element in .

[0031] Figure 3 a is a SEM image of Se@V2O3 prepared in Comparative Example 1 of this application; Figure 3 b is a SEM image of Se@V2O3-38%C prepared in Example 2 of the present application; Figure 3 c is a SEM image of Se@V2O3-17%C prepared in Example 3 of the present application; Figure 3 d is a 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 this application; Figure 3 f is the selected area diffraction (SAED) pattern of Se@V2O3 prepared in Comparative Example 1 of the present application; Figure 3 g is the EDS element mapping diagram of Se@V2O3 prepared in Comparative Example 1 of the present application; Figure 3 h is Figure 3 The distribution of V elements in g, Figure 3 i is Figure 3 Distribution of Se elements in g, Figure 3 J is Figure 3 Distribution of O element in g.

[0032] Figure 4 a is a SEM image of Se / C prepared in Comparative Example 2 of this application; Figure 4 b is a TEM image of Se / C prepared in Comparative Example 2 of the present application; Figure 4 c is the C element distribution diagram of the EDS spectrum of Se / C prepared in Comparative Example 2 of the present application; Figure 4 d is the Se element distribution diagram of the EDS spectrum of Se / C prepared in Comparative Example 2 of the present application.

[0033] Figure 5 Shown are 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; among them, 5a and 5c are N2 adsorption-desorption curves, and 5b and 5d are pore size distribution curves.

[0034] Figure 6Shown are the XRD patterns of the samples of Examples 1-3 and Comparative Examples 1-2 of the present application; 6a is the XRD pattern of Se powder, graded porous anthracite-based hard carbon and Comparative Example 2; 6b is the XRD pattern of the samples of Examples 1-3 and Comparative Example 1.

[0035] Figure 7 Shown are the Raman spectra of the samples of Examples 1-3 and Comparative Examples 1-2 of the present application; among them, 7a is the Raman spectra of Se powder, graded porous anthracite-based hard carbon, Example 1 and Comparative Example 2 samples; 7b is the Raman spectra of the samples of Examples 1-3 and Comparative Example 1.

[0036] Figure 8 a is the cyclic voltammetry (CV) curve of the V2O3@Se / C positive electrode prepared in Example 1 of the present application, Figure 8 b is the cyclic voltammetry (CV) curve of the Se / C positive electrode prepared in Comparative Example 2 of the present application; Figure 8 c is the cyclic voltammetry (CV) curve of the V2O3@Se positive electrode of this application.

[0037] Figure 9 a shows the charge-discharge curve of V2O3@Se-27% / C prepared in Example 1 at 0.1 A / g. Figure 9 b is the cycle performance diagram of the V2O3@Se / C prepared in Example 1, Se / C and V2O3@Se prepared in Comparative Example 2 at 0.1 A / g, Figure 9 c is the cycling performance diagram of the V2O3@Se / C prepared in Examples 1-3, Se / C prepared in Comparative Example 2, and V2O3@Se positive electrodes at 3.0 A / g. Figure 9 d shows the charge-discharge curve of V2O3@Se-27% / C prepared in Example 1 at 3.0 A / g. Figure 9 e Cycling performance diagram of the V2O3@Se / C prepared in Example 1, Se / C prepared in Comparative Example 2, and V2O3@Se positive electrodes at 1.0 A / g.

[0038] Figure 10 The graph shows the statistical curves of the rate performance test of the samples of Example 1 and Comparative Examples 1-2 of the present application; 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 a comparison 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-selenium battery positive electrodes.

[0039] Figure 11 The CV curves of V2O3@Se / C prepared in Example 1 of the present application at different scan rates are shown. Figure 11 a, log(i) versus log(v) at different oxidation and reduction states Figure 11 b, Capacitance ratio at different scan rates Figure 11 c, Capacitive contribution at 1.6mV / s Figure 11 d.

[0040] Figure 12 The 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) versus log(v) at different oxidation and reduction states Figure 12 b, Capacitance ratio at different scan rates Figure 12 c, Capacitive contribution at 1.6mV / s Figure 12 d.

[0041] Figure 13 The CV curves of V2O3@Se prepared in Comparative Example 1 of this application at different scan rates are shown. Figure 13 a, log(i) versus log(v) at different oxidation and reduction states Figure 13 b, Capacitance ratio at different scan rates Figure 13 c, Capacitive contribution at 1.6mV / s Figure 13 d.

[0042] Figure 14 This is the long-term cycling performance test diagram of Se / C, V2O3@Se and V2O3@Se / C electrodes at 30 A / g.

[0043] Figure 15 This is a comparison of the color changes of the diaphragm after 120 cycles of the electrode materials of pure Se, comparative examples 1-2, and embodiment 1; Figure 15 a is a diagram showing the color of the diaphragm after pure Se is used as the positive electrode of the sodium-selenium battery for 120 cycles; Figure 15 b is a diagram showing the color of the diaphragm after the sample of Example 2 was used as the positive electrode of the sodium-selenium battery for 120 cycles; Figure 15 c is a diagram showing the color of the diaphragm after the sample of Example 1 was used as the positive electrode of the sodium-selenium battery for 120 cycles; Figure 15 d is a diagram showing the color of the diaphragm after the sample of Example 1 was used as the positive electrode of a sodium-selenium battery for 120 cycles.

[0044] Figure 16 Shown are Na2Se on C, V2O3 and C-V2O3 x Side view and top view of the adsorption configuration; wherein, Figure 16 a is Na2Se on C x Side and top views of the adsorption configuration; Figure 16 b is Na2Se on V2O3 x Side and top views of the adsorption configuration; Figure 16 c is Na2Se on C-V2O3 x Side and top views of the adsorption configuration.

[0045] Figure 17 The figure shows Na2Se 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; where, 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.

[0046] Figure 18 The figure shows the energy state calculation curve of polyselenide on V2O3 and C-V2O3 during the discharge and charge processes; Figure 18 a is the energy state calculation curve of polyselenides on V2O3 and C-V2O3 during the discharge process; 18b is the energy state calculation curve of polyselenides on V2O3 and C-V2O3 during the charging process. DETAILED DESCRIPTION

[0047] The following is a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0048] The raw materials used in the present invention are described as follows: The anthracite raw material used in the present invention is provided by Ordos Bayin Mengke Coal Co., Ltd. As shown in Table 1, the composition analysis table of the anthracite raw material used in the examples of this application (absolute dry basis)

[0049] Example 1: A method for preparing a Se@V2O3-27% / C composite material, comprising the following steps: Step 1: Use a ball mill to pulverize anthracite raw material into anthracite powder. The fraction after 80-mesh screening is selected as the raw material. The anthracite powder is mixed with a 2 mol / L HNO3 solution at a mass-to-volume ratio of 1 g:6 mL and allowed to soak for 24 hours to remove metallic impurities. In this example, 100 g of anthracite powder and 600 mL of HNO3 solution are used. The treated powder is then filtered and mixed with a 2 mol / L hydrofluoric acid solution at a mass-to-volume ratio of 1 g:6 mL. In this example, 80 g of anthracite powder treated with nitric acid and 480 mL of hydrofluoric acid are used. The mixture is stirred in a 60°C water bath for 4 hours to remove SiO2. The solid is then filtered and repeatedly centrifuged with deionized water to collect the black powder. Finally, the mixture is dried in an air oven at 60°C for 12 hours to obtain anthracite powder free of metallic impurities and SiO2.

[0050] Table 2 below shows the elements and composition of the anthracite powder after the metal impurities and SiO2 are removed after treatment in step 1 of Example 1 of the present application.

[0051] Step 2: Use KOH as a pore-forming agent and mix it with anthracite powder in a mass ratio of 1:2. Then add deionized water to cover the mixture. After soaking in deionized water for 24 hours, place it in an air drying oven and force heat and dry it at 70°C for 24 hours. In this example, 10g of acid-treated anthracite powder and 20g of KOH were used; then calcination and activation were carried out in a N2 atmosphere. During the calcination process, the product was heated to 700°C at a heating rate of 10°C / min and calcined at 700°C for 2 hours. Finally, the calcined and activated product was naturally cooled and washed with deionized water until the pH was neutral to obtain a graded porous anthracite-based hard carbon.

[0052] Table 3 below shows the pore structure parameters of the hierarchical porous anthracite-based hard carbon obtained in step 2 of Example 1 of the present application.

[0053] Table 4 below shows the elements and composition of the graded porous anthracite-based hard carbon obtained in step 2 of Example 1 of the present application.

[0054] The present application uses scanning electron microscopy (SEM) and N2 adsorption / desorption isotherm curves to characterize the morphology and pore structure of the hierarchical porous anthracite-based hard carbon prepared in step 2 of Example 1. Figure 1SEM of the hierarchically porous anthracite-based hard carbon prepared in Step 2 of Example 1 of the present application Figure 1 a and N2adsorption / desorption isotherm Figure 1 b.

[0055] From Figure 1 As can be seen from a, the hierarchically porous anthracite-based hard carbon prepared in Step 2 of Example 1 of the present application presents irregular shape, with pore structures of different sizes distributed on the surface. From Figure 1 As can be seen from b, with type IV isotherm and H3 hysteresis loop, confirming the presence of the hierarchically porous structure of the present application. Such hierarchically porous structure can promote the Na + transport, while avoiding the escape of polyselenides from the pores to dissolve in the electrolyte.

[0056] Step 3, first, 8 mmol vanadyl acetylacetonate and 16 mmol SeO2 were added to 120 mL of 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. 0.9 g of hierarchically porous anthracite-based hard carbon was added to the above transparent solution and stirred to prepare a mixture solution.

[0057] Step 4, the mixture solution prepared in Step 3 was treated by hydrothermal method: the mixture solution was transferred to a 200 mL Teflon-lined stainless steel autoclave, and then the stainless steel autoclave was placed in a blast drying oven for heating; heated at a rate of 5°C / min to 200°C, and kept at 200°C in the blast drying oven for 24 h. Then naturally cooled to room temperature. Then, the product after heating treatment was collected by centrifugal separation of black powder, and the black powder was washed with deionized water and alcohol to remove excess impurity ions in the reaction process. Then, the black powder was dried in a 60°C air oven for 12 h.

[0058] Step 5, the solid product prepared in Step 4 was treated by thermal annealing method: the solid product prepared in Step 4 was placed in a tube furnace and calcined at a rate of 5°C / min to 500°C under N2atmosphere, kept for 3 h, and then naturally cooled to obtain V2O3@Se / C composite material. The V2O3content of the sample prepared in this example is 27.66%, named Se@V2O3-27% / C.

[0059] As shown in Table 5 below is the element and composition content table of the Se@V2O3-27% / C composite material prepared in Example 1 of the present application

[0060] Figure 2 TEM of the Se@V2O3-27% / C composite material prepared in Example 1 of the present 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 The distribution of V elements in d, Figure 2 f is Figure 2 The distribution of O elements in d, Figure 2 g is Figure 2 d. Distribution of Se elements in Figure 2 h is Figure 2 d Distribution of C element in .

[0061] like Figure 2 a and Figure 2 As shown in b, in the Se@V2O3-27% / C composite material, the Se@V2O3 domains are fully embedded in the continuous hierarchical porous anthracite-based hard carbon matrix, forming a pomegranate-like "seed-aril" hierarchical structure.

[0062] Figure 2 c shows the HR-TEM image showing a clear interface between the Se spheres 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 Se spheres on the right show uniform contrast and no obvious lattice fringes, indicating their amorphous nature.

[0063] Figure 2 Energy dispersive X-ray spectroscopy (EDS) (d) further reveals the layered element distribution of the structure: Se is concentrated in the core, V forms a shell around the Se sphere, and C is mainly present in the outermost matrix. This layered structure provides strong spatial confinement for the Se core, promoting the electrochemical cycling of Na2Se x effective capture and retention.

[0064] Example 2: A method for preparing a Se@V2O3-38% / C composite material, comprising the following steps: Execute steps 1 and 2 of Example 1, and steps 3, 4, and 5 as follows.

[0065] Step 3: First, add 12 mmol of vanadyl acetylacetonate and 16 mmol of SeO2 to 120 mL of deionized water and stir for 30 minutes to obtain a uniform blue transparent solution. Add 24 mL of methanol to this solution and continue stirring at room temperature for 30 minutes. Add 0.18 g of graded porous anthracite-based hard carbon to this transparent solution and stir to obtain a uniform mixture solution.

[0066] Step 4: Transfer the mixture to a 200 mL Teflon-lined stainless steel autoclave and heat to 220°C at a heating rate of 5°C / min. Maintain the temperature at 220°C in a forced air drying oven for 36 hours, then cool naturally to room temperature. The heated product is then centrifuged to collect a black powder, which is then washed multiple times with deionized water and alcohol to remove excess impurities from the reaction. The powder is then dried in an air oven at 60°C for 36 hours.

[0067] Step 5: Thermally anneal the solid product prepared in Step 4. The solid product prepared in Step 4 was placed in a tube furnace and calcined at a heating rate of 5°C / min to 600°C under a nitrogen atmosphere for 3 hours. The mixture was then naturally cooled to obtain a V2O3@Se / C composite material. The sample prepared in this example had a V2O3 content of 38.40% and was designated Se@V2O3-38% / C.

[0068] Example 3: A method for preparing a Se@V2O3-17% / C composite material, comprising the following steps: Execute steps 1 and 2 of Example 1, and steps 3, 4, and 5 as follows.

[0069] Step 3: First, add 4 mmol of vanadyl acetylacetonate and 16 mmol of SeO2 to 120 mL of deionized water and stir for 30 minutes to obtain a uniform blue transparent solution. Add 24 mL of methanol to this solution and continue stirring at room temperature for 30 minutes. Add 1.8 g of graded porous anthracite-based hard carbon to this transparent solution and stir to obtain a uniform mixture solution.

[0070] Step 4: Transfer the mixture to a 200 mL Teflon-lined stainless steel autoclave and heat to 180°C at a rate of 5°C / min. Maintain the temperature at 180°C in a forced air drying oven for 12 hours, then allow to cool naturally to room temperature. The heated product is then centrifuged to collect a black powder, which is then washed multiple times with deionized water and alcohol to remove excess impurities from the reaction. The powder is then dried in an air oven at 60°C for 12 hours.

[0071] Step 5: Thermally anneal the solid product prepared in Step 4. The solid product prepared in Step 4 was placed in a tube furnace and calcined at a heating rate of 5°C / min to 400°C under a nitrogen atmosphere. The temperature was maintained for 1 hour, followed by natural cooling to obtain a V2O3@Se / C composite material. The sample prepared in this example had a V2O3 content of 17.17% and was designated Se@V2O3-17% / C.

[0072] Comparative Example 1: A method for preparing Se@V2O3, comprising the following steps: The steps of Example 1 were performed, except that the graded porous anthracite-based hard carbon was not added during step 3, to produce Se@V2O3.

[0073] Comparative Example 2: A method for preparing a Se / C material, comprising the following steps: The Se@V2O3-27% / C composite prepared in Example 1 was immersed in 5 mol / L dilute hydrochloric acid, heated to 60°C with stirring, and maintained for 2 hours. The mixture was then filtered through 0.5 mol / L and 0.1 mol / L hydrochloric acid, respectively. Finally, the mixture was washed with deionized water until neutral, ensuring that no other impurities remained while removing the V2O3. The mixture was then dried in an oven at 60°C for 12 hours to obtain the Se / C material.

[0074] The present application conducts a comparative study and analysis of the products obtained in Examples 1-3 and Comparative Example 1 as follows: First, the following table 6 is a statistical table of the elements and component contents of the samples of Examples 1-3 and Comparative Examples 1-2 of the present application.

[0075] Table 7 below is a statistical table of pore structure parameters of samples of Examples 1-3 and Comparative Examples 1-2 of the present application.

[0076] Figure 3 a is a SEM image of Se@V2O3 prepared in Comparative Example 1 of this application; Figure 3 b is a SEM image of Se@V2O3-38%C prepared in Example 2 of the present application; Figure 3 c is a SEM image of Se@V2O3-17%C prepared in Example 3 of the present application; Figure 3 d is a 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 this application; Figure 3 f is the selected area diffraction (SAED) pattern of Se@V2O3 prepared in Comparative Example 1 of the present application; Figure 3 g is the EDS element mapping diagram of Se@V2O3 prepared in Comparative Example 1 of the present application; Figure 3 h is Figure 3 The distribution of V elements in g, Figure 3 i is Figure 3 Distribution of Se elements in g, Figure 3 J is Figure 3 Distribution of O element in g.

[0077] Figure 4 a is a SEM image of Se / C prepared in Comparative Example 2 of this application; Figure 4b is a TEM image of Se / C prepared in Comparative Example 2 of the present application; Figure 4 c is the C element distribution diagram of the EDS spectrum of Se / C prepared in Comparative Example 2 of the present application; Figure 4 d is the Se element distribution diagram of the EDS spectrum of Se / C prepared in Comparative Example 2 of the present application.

[0078] from Figure 3 As can be seen in Figure a, in the Se@V2O3 composite material prepared in Comparative Example 1, V2O3 maintains a complete flower-like structure of self-assembled nanosheets on the surface of Se. Since the total amount of Se produced in the reaction is basically the same, as the content of the graded porous anthracite-based hard carbon increases, more carbon is loaded on the surface of Se@V2O3, and the morphology of the small balls becomes less obvious ( Figure 2 a and Figure 3 bc). 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 the interplanar spacing is 0.3nm and 0.27nm, 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, energy dispersive spectroscopy (EDS) confirmed that Se, O, and V elements were uniformly distributed in the Se@V2O3 composite material ( Figure 3 g). In addition, for comparison, the Se / C composite material obtained by completely removing V2O3 from the Se@V2O3-27%C composite material obtained in Example 1 was used to prepare the Se / C composite material. In the Se / C composite material, the Se retained the hollow sphere morphology ( Figure 4 b), C and Se are evenly distributed ( Figure 4 c).

[0079] like Figure 5 Shown are 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; among them, 5a and 5c are N2 adsorption-desorption curves, and 5b and 5d are pore size distribution curves.

[0080] from Figure 5 As can be seen in a, C has a type IV isotherm and H3 hysteresis loop, confirming the existence of mesopores. In contrast, Se / C, Se@V2O3, and Se@V2O3 / C show V-type isotherms and H3 hysteresis loops, which confirms the existence of a hierarchical structure with micropores and mesopores. This hierarchical structure can promote the Na + While transporting, it prevents polyselenide from escaping from the pores and dissolving in the electrolyte. Se / C is synthesized by hydrothermal method, which is different from the previous impregnation method. After adding Se, the specific surface area increases from 762.31m 2 / g to 35.17 m 2 / g, which confirmed the successful coating of hierarchical porous anthracite-based hard carbon (Se content of 81.81%). For Se@V2O3-27% / C composite, the specific surface area was 12.61 m 2 / g, which indicated the successful loading of V2O3 (V2O3 content of 27.66%).

[0081] Then, the present application analyzed the phase structure and purity of the composite materials of Examples 1-3 and Comparative Examples 1-2 by X-ray diffraction (XRD). As shown in Figure 6 , FIG. 6 is a graph of the XRD of the samples of Examples 1-3 and Comparative Examples 1-2 of the present application; wherein 6a is the XRD of Se powder, hierarchical porous anthracite-based hard carbon and Comparative Example 2 sample; 6b is the XRD of Examples 1-3 and Comparative Example 1 sample.

[0082] As can be seen from Figure 6 , 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 observed morphology change trend.

[0083] The present application analyzed the chemical bonding of the composite materials of Examples 1-3 and Comparative Examples 1-2 by Raman spectroscopy. As shown in Figure 7 , FIG. 7 is a graph of the Raman spectra of the samples of Examples 1-3 and Comparative Examples 1-2 of the present application; wherein 7a is the Raman spectra of Se powder, hierarchical porous anthracite-based hard carbon, Example 1 and Comparative Example 2 sample; 7b is the Raman spectra of Examples 1-3 and Comparative Example 1 sample.

[0084] As can be seen from Figure 7 , the original Se, Se@V2O3 composite material has a sharp peak at 236 cm -1 , which belongs to the triangular Se of chain structure. It is worth noting that with the increase of carbon content, the Se peak intensity decreases and moves to about 260 cm -1 , which corresponds to the transformation from crystalline Se (hexagonal system) to molecular Se8 (amorphous ring) (the same as the XRD graph). Further confirmed that in the Se@V2O3-27% / C composite material, Se has been successfully confined inside the hierarchical porous anthracite-based hard carbon, and only exists in amorphous form. Each sample shows 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.

[0085] Furthermore, the present invention prepared working electrodes from samples of Examples 1-3 and Comparative Examples 1-2, and tested the electrochemical performance of the electrodes. The specific method is as follows: The working electrode was made of 80 wt.% Se@V2O3 / C (Se@V2O3 and Se / C), 10 wt.% Super-P carbon black, and 10 wt.% sodium alginate in aqueous solution; the mass loading of the electrode was 1.8-2.6 mg / cm 2 ; Whatman's glass fiber (GF / D) was used as the separator, and 1MNaPF6 dissolved in ethylene glycol dimethyl ether (DME) = 100Vol% was used as the electrolyte.

[0086] Sodium plate (counter electrode), separator, and electrolyte (NaPF6 in dimethyl ether). All components (battery case, electrode, separator, etc.) must be vacuum dried for 12 hours to remove moisture. Before working in the glove box, the atmosphere must be replaced at least three times to ensure an inert atmosphere. Glove box (water and oxygen content <1ppm), vacuum drying oven (60-80°C), tablet press (pressure 50MPa), and pipette (for precise control of electrolyte volume).

[0087] Assembly sequence (starting with the positive electrode casing): Positive electrode casing → positive electrode sheet → electrolyte (0.1-0.2mL) → diaphragm (soaked in electrolyte) → sodium sheet (negative electrode) → gasket → spring → negative electrode casing. The electrolyte injection tolerance must be within ±0.02mL, and the diaphragm must be completely soaked. Use a digital tablet press at 50MPa to seal, ensuring contact resistance <0.5mΩ. After 4 hours of quiescence, check the open circuit voltage. Abnormal values ​​(e.g., <2.5V) require investigation for short circuit risks.

[0088] Electrochemical experiments were performed using 2025 button batteries. The detection method is as follows: At room temperature, within the voltage range of 0.01~3.0V (relative to Na / Na + ), cyclic voltammetry tests were carried out on the V2O3@Se / C, V2O3@Se and V2O3 / C positive electrodes on a CHI760E electrochemical workstation.

[0089] The test results are as follows: In order to evaluate the Na + Storage performance, the cyclic voltammetry (CV) curve of V2O3@Se / C cathode was recorded in the voltage window of 0.01-3.0V (vs.Na / Na⁺) with a scan rate of 0.1mV / s. Figure 8 a is the cyclic voltammetry (CV) curve of the V2O3@Se / C positive electrode prepared in Example 1 of the present application, Figure 8 b is the cyclic voltammetry (CV) curve of the Se / C positive electrode prepared in Comparative Example 2 of the present application; Figure 8c is the cyclic voltammetry (CV) curve of the V2O3@Se positive electrode of this application.

[0090] like Figure 8 As shown in a, in the first cycle, the two cathodic peaks at ~1.92 and 1.10 V correspond to the stepwise mediation of Se: Se→Na2Se n (n≥4)→Na2Se. The feature at ~0.50 V disappears after the first scan, which is attributed to the formation of the solid electrolyte film. As the electrode is activated, the main anodic peak shifts to a slightly higher potential in subsequent cycles. The anodic scan shows two peaks at 1.62 V and 1.82 V, which belong to the oxidation of Na2Se and the reversible conversion back to elemental Se, respectively. After the first cycle, the entire CV curve becomes more complicated and is still not fully stable at the sixth cycle, which is a common behavior in ether electrolytes. It is worth noting that in the first three cycles, the Se / C electrode shows a CV curve that is almost identical to that of the V2O3@Se / C electrode ( Figure 8 b), indicating that the introduction of V2O3 does not change the intrinsic Se redox pathway. For V2O3@Se ( Figure 8 c) Sodiumization still occurs 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 Na2Se x The rapid formation of ions promotes structural degradation or interfacial side reactions.

[0091] Furthermore, the present invention subjected the electrodes prepared from the samples of Examples 1-3 and Comparative Examples 1-2 to cycling stability tests at 0.1 A / g, 3.0 A / g, and 10.0 A / g. The cycling stability of the electrodes was tested using a LAND-3100A blue-electricity testing system. The test environment temperature was controlled at 25°C, and continuous charge and discharge tests were performed at a current density of 0.1 A / g.

[0092] like Figure 9 a shows the charge-discharge curve of V2O3@Se-27% / C prepared in Example 1 at 0.1 A / g. Figure 9 b is the cycle performance diagram of the V2O3@Se / C prepared in Example 1, Se / C and V2O3@Se prepared in Comparative Example 2 at 0.1 A / g, Figure 9 c is the cycling performance diagram of the V2O3@Se / C prepared in Examples 1-3, Se / C prepared in Comparative Example 2, and V2O3@Se positive electrodes at 3.0 A / g. Figure 9 d shows the charge-discharge curve of V2O3@Se-27% / C prepared in Example 1 at 3.0 A / g. Figure 9 e Cycling performance diagram of the V2O3@Se / C prepared in Example 1, Se / C prepared in Comparative Example 2, and V2O3@Se positive electrodes at 1.0 A / g.

[0093] Figure 9 Figure a shows the galvanostatic charge-discharge curves of the Se@V2O3-27% / C composite at a current density of 0.1 A / g. The evolution of the discharge and charge plateaus is consistent with the CV measurements. The initial discharge and charge capacities are 670 and 535.3 mAh / g, respectively, significantly higher than those of other electrodes. The irreversible capacity of the initial cycle is related to the formation of the solid electrolyte interphase (SEI) and the irreversible capture of Na in the bulk carbon and carbon pores.

[0094] from Figure 9 As can be seen in b, the capacity of Se decays quickly. After 120 cycles, Se@V2O3-27% / C shows a higher sodium storage capacity, even at high current density ( Figure 9 b) Se@V2O3-27% / C material also has excellent cycle stability, which means that V2O3 is very effective in fixing and converting selenides. When more V2O3 is added as a catalyst, excessive adsorption capacity will lead to the decomposition of polyselenides and the blockage of surface active sites. On the contrary, weak adsorption capacity is not conducive to the capture of polyselenides for catalytic conversion. The electrochemical trend shown in the figure proves that when 27% 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 3.0A / g, with the increase of carbon content, 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 graded porous anthracite-based hard carbon. Under the condition of equivalent Se content, as the carbon content increases, the V2O3 content gradually decreases, the loss of sodium polyselenide intensifies, and the specific capacity decreases. In addition, at a current density of 3.0A / g, the Se@V2O3-27% / C positive electrode prepared in Example 1 has almost the same charge and discharge curve except for the first charge and discharge curve ( Figure 9 d), further surface Se@V2O3-27% / C positive electrode has good cycle stability. At a current density of 10 A / g, the capacity retention rate can still reach 97.33% after 2000 cycles ( Figure 9 e).

[0095] Furthermore, the present invention is at room temperature and within a voltage range of 0.01 to 3.0 V (relative to Na / Na + ), and the electrochemical performance at different current densities was evaluated using constant current charge and discharge curves on a battery tester.

[0096] like Figure 10 The graph shows the statistical curves of the rate performance test of the samples of Example 1 and Comparative Examples 1-2 of the present application. Figure 10a is the charge-discharge curve of V2O3@Se-27% / C prepared in Example 1 at different current densities; Figure 10 b is a comparison 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-selenium battery positive electrodes.

[0097] In the present invention, the constant current charge and discharge (GCD) curves of the V2O3@Se-27% / C electrode at different current densities ( Figure 10 a) shows two discharge platforms at approximately 1.0 V and 0.6 V, and two charge platforms at approximately 1.5 V and 1.8 V, consistent with the two-step redox process of selenium. The rate performance shows ( Figure 10 b) At 0.1, 0.2, 0.5, 1.0, 3.0, 5.0, 10.0, 20, and 30.0 A / g, the reversible capacities are 432.74, 430.56, 428.20, 425.90, 418.94, 414.17, 406.11, 393.91, and 385.00 mAh / g, respectively. Even when the current density increases 300 times (0.1→30.0 A / g), the capacity retention rate remains at 88.97%, demonstrating excellent rate capability. Figure 10 As shown in Figure c, compared with the reported positive electrode 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 large current density range, highlighting its superior rate performance in the sodium-selenium battery system.

[0098] Furthermore, the present invention is at room temperature and within a voltage range of 0.01 to 3.0 V (relative to Na / Na + ), on the electrochemical workstation, CV curves at different scan rates were used to perform electrochemical kinetic analysis of V2O3@Se / C, V2O3@Se and V2O3 / C cathodes.

[0099] To further investigate the electrode kinetics, CV measurements were performed in the scan rate range of 0.1 to 2.0 mV / s.

[0100] like Figure 11 The CV curves of V2O3@Se / C prepared in Example 1 of the present application at different scan rates are shown. Figure 11 a, log(i) versus log(v) at different oxidation and reduction states Figure 11 b, Capacitance ratio at different scan rates Figure 11c, Capacitive contribution at 1.6mV / s Figure 11 d.

[0101] like Figure 12 The 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) versus log(v) at different oxidation and reduction states Figure 12 b, Capacitance ratio at different scan rates Figure 12 c, Capacitive contribution at 1.6mV / s Figure 12 d.

[0102] like Figure 13 Shown are the CV curves of V2O3@Se prepared in comparative example 1 of the present application at different scan rates (a), the log(i) versus log(v) graph (b) under different oxidation and reduction states, the capacitance ratio graph (c) at different scan rates, and the capacitance contribution graph (d) at 1.6 mV / s.

[0103] like Figure 11 As shown in a, the CV curve of the V2O3@Se / C electrode maintains its characteristic shape at a higher scan rate with only a slight shift, indicating that it has good electrochemical stability. By comparison, it was found that the three composite materials exhibited similar characteristics ( Figure 12 a and Figure 13 a), indicating that the intrinsic redox pathway of Se remains unchanged after the addition of V2O3 and carbon.

[0104] The relationship between scan rate (v) and 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 indicates a diffusion-controlled process, while b = 1.0 indicates a capacitance-controlled process. For V2O3@Se / C, b = 1.06, 0.89, 0.97, and 0.83 ( Figure 11 b). The corresponding value of Se / C electrode is slightly smaller ( Figure 12 b), while the b values ​​of V2O3@Se are significantly smaller (0.55, 0.69, 0.56, and 0.47; Figure 13 b), reflecting a more diffusion-limited behavior. These results indicate that the hierarchical porous anthracite-based hard carbon scaffold significantly enhances the surface-induced pseudocapacitive contribution in V2O3@Se / C and Se / C.

[0105] Further, using equation i ( v )= k 1 ν +k 2 ν 1 / 2 The storage mechanism of sodium was quantitatively analyzed, including k 1 ν represents the capacitive (surface controlled) contribution, k 2 ν 1 / 2 Corresponding to the diffusion control contribution. Figure 11 As shown in 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 worth noting that at 1.6 mV / s, the pseudocapacitance contribution reaches 96.87% ( Figure 11 d), indicating that the surface mainly controls the dynamics. Although the capacitance contribution of Se / C is higher at the same scan rate ( Figure 12 c) and pseudocapacitance ratio ( Figure 12 d) is slightly lower, but it still shows a dominant surface-controlled behavior, consistent with the strong fast charging capability. In contrast, V2O3@Se shows a weaker pseudocapacitive 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), indicating that the synergistic effect between the conductive carbon matrix and V2O3 is crucial for the fast reaction kinetics. These fast 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 14 This is the long-term cycling performance test diagram of Se / C, V2O3@Se and V2O3@Se / C electrodes at 30 A / g.

[0106] Furthermore, the present invention uses a camera to cycle 120 times at a current density of 0.1 A / g for batteries assembled with pure Se, V2O3@Se / C, V2O3@Se and V2O3 / C electrodes, and then disassembles and takes photos of the diaphragm membrane to analyze the loss of sodium polyselenide. Figure 15 This is a comparison of the color changes of the diaphragm after 120 cycles of the electrode materials of pure Se, comparative examples 1-2, and embodiment 1; Figure 15 a is a diagram showing the color of the diaphragm after pure Se is used as the positive electrode of the sodium-selenium battery for 120 cycles; Figure 15 b is a diagram showing the color of the diaphragm after the sample of Example 2 was used as the positive electrode of the sodium-selenium battery for 120 cycles; Figure 15 c is a diagram showing the color of the diaphragm after the sample of Example 1 was used as the positive electrode of a sodium-selenium battery for 120 cycles; Figure 15 d is a diagram showing the color of the diaphragm after the sample of Example 1 was used as the positive electrode of a sodium-selenium battery for 120 cycles.

[0107] like Figure 15 As shown in the figure, the inhibition of the sodium polyselenide shuttle effect is visible from the color change of the separator after 120 cycles: the separator color change of the V2O3@Se / C battery is minimal, which is in sharp contrast to the obvious color change of the pure elemental selenium battery. This shows that the presence of hierarchical porous anthracite-based hard carbon and V2O3 is beneficial to inhibit the evaporation 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 makes the loss of sodium polyselenide less ( Figure 15 b and Figure 15 c). Of course, the co-existence of anthracite-based hard carbon and V2O3 is more conducive to inhibiting the loss of sodium polyselenide ( Figure 15 d).

[0108] Theoretical calculations were performed using density functional theory (DFT) and the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) of the exchange-correlation functional, implemented in the Vienna Ab Initio Simulation Package (VASP). The interaction between the ion core and the valence electrons was described using the projected augmented wave (PAW) method. The plane wave basis was set to 520 eV. For the slab model, a vacuum of 15 Å was established, the Brillouin zone in reciprocal space was represented by the Gamma point, and all calculations were performed using spin polarization. The convergence criterion was a total energy of 1.36 × 10 -7 eV and force 0.02 eV / Å. In order to better simulate the dispersion interaction inside the water adsorption system, Grime's DFT-D3 method with zero damping function is used to consider the van der Waals correction.

[0109] The Gibbs free energy for each reaction intermediate is defined as: G = E DFT + E ZEP – TS, Among them E DFT 、E ZEP and TS are the total energy, zero-point energy, and entropy contribution of the DFT calculation (T is set to 298.15K). The E of the absorbing species is calculated using the VASPKIT code. ZEP and TS.

[0110] To investigate 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 2. Figure 16 shown. Figure 16Shown are Na2Se on C, V2O3 and C-V2O3 x Side view and top view of adsorption configuration. 16a shows Na2Se on C x Side view and top view of adsorption configuration; 16b shows Na2Se on V2O3 x Side view and top view of adsorption configuration; 16c shows Na2Se on C-V2O3 x Side view and top view of the adsorption configuration; in the figure, 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 large red spheres and small red spheres, respectively.

[0111] On the hierarchical porous anthracite-based hard carbon, the adsorption of Na2Se6, Na2Se4, Na2Se2 and Na2Se was relatively weak, with adsorption energies of -0.21, -0.27, -0.67 and -0.40 eV, respectively, indicating that physical adsorption was mainly dominated by van der Waals forces. In contrast, V2O3 exhibited stronger chemical adsorption, with exothermic adsorption energies of -5.38, -5.66, -5.47 and -4.20 eV for the same species, respectively. Notably, the C-V2O3 composite further enhanced 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 acted synergistically to fix and convert long-chain Na2Se x component.

[0112] To clarify the mechanism of enhanced adsorption energy, this application then analyzes the electronic structure by calculating the density of states (DOS) before adsorption and the partial density of states (PDOS) after adsorption. Figure 17 The figure shows Na2Se 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; where, 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 xDensity of states of C-V2O3 (f) after adsorption.

[0113] from Figure 17 It can be seen that before adsorption, the conduction band and valence band of C, V2O3 and C-V2O3 all cross the Fermi level ( Figure 17 a-17c), when V2O3 coexists with hierarchical porous anthracite-based hard carbon, the density of states near the Fermi level becomes wider, increasing the available electronic states and thus improving the overall conductivity. Hierarchical porous anthracite-based hard carbon not only provides additional conductive paths, but also enhances the coupling between V2O3 and the carbon network, further improving the charge transfer performance. x The component is an insulator, and the conductivity of the substrate after adsorption is crucial for the effective conversion of selenium. Therefore, the PDOS analysis of Se / C / Na2Se2, V2O3@Se / Na2Se4 and V2O3@Se / C / Na2Se4 systems showed that ( Figure 17 d-17f), Se / C / Na2Se2 has very few states at the Fermi level, indicating weak electronic interactions and negligible orbital hybridization. In contrast, the V2O3@Se / Na2Se4 interface exhibits an increased density of states near the Fermi level due to the strong interfacial coupling between the unfilled V3d orbitals and the Na2Se4 orbitals, reflecting strong chemical adsorption and charge redistribution. V2O3@Se / C / Na2Se4 shows the most significant density of states near the Fermi level, and PDOS analysis shows that the V atoms contribute the most, highlighting the dominant role of V2O3 in regulating the interfacial electronic structure. Compared with V2O3@Se / Na2Se4, the V2O3@Se / C / Na2Se4 composite material exhibits a higher density of states near the Fermi level, which is consistent with the reduced electrochemical impedance and the interaction between the catalyst and Na2Se x This improved electronic interaction is conducive to the reversible transformation of selenium and enhances the electrochemical performance of sodium-selenide batteries.

[0114] Finally, to evaluate the effect of the composite material on redox thermodynamics, the Gibbs free energy curve of selenium conversion was calculated ( Figure 18 ).like Figure 18 The figure shows the energy state calculation curve of polyselenide on V2O3 and C-V2O3 during the discharge and charge processes; Figure 18 a is the energy state calculation curve of polyselenides on V2O3 and C-V2O3 during the discharge process; 18b is the energy state calculation curve of polyselenides on V2O3 and C-V2O3 during the charging process.

[0115] It is noteworthy that the conversion of Na2Se to Na2Se6 is an exothermic and spontaneous reaction, while the reverse conversion from Na2Se6 to Na2Se is endothermic. The transition step from Na2Se4 to Na2Se2 shows the largest positive ΔG, indicating that this is the rate-determining step in the discharge process.

[0116] On the discharge path, the minimum free energy of C-V2O3 is more favorable (more negative) than that of V2O3 (△G min =-10.49eV vs. -7.64eV), indicating that C-V2O3 thermodynamically favors the reduction of selenium. In contrast, during the charge process, the oxidation of Na2Se4 on C-V2O3 requires a higher free energy barrier, while V2O3 alone presents a lower and smoother energy barrier, favoring the formation of soluble Na2Se x .

[0117] In summary, these results indicate that the synergistic effect of C and V2O3 plays a key role in reducing the discharge free energy barrier and promoting the formation of Na2Se, while V2O3 alone is relatively more beneficial to the charging process. Due to the weak adsorption capacity of carbon, Se / C allows Na2Se x Diffusion into the electrolyte leads to severe shuttle effect and loss of active materials. In contrast, V2O3 has strong chemical adsorption and catalytic activity, which can accelerate the Na2Se x Thanks to its unique pomegranate-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 the unconverted Na2Se through adsorption and spatial confinement. x , promoting its conversion into short-chain substances, thereby alleviating Na2Se x accumulation.

[0118] Furthermore, the present invention uses different vanadium organometallic complexes to prepare sodium selenium battery positive electrode materials and study their properties. The specific method is as follows: Based on Example 1, only the type of vanadium organometallic complex was changed, while other process conditions remained unchanged to prepare the positive electrode materials for sodium-selenium batteries. The vanadium organometallic complexes used were vanadyl acetylacetonate, vanadyl triisopropoxide, vanadyl ethyl maltol, vanadyl methyl maltol, and vanadyl oxalate.

[0119] Table 8 below is a statistical table of the elements and composition content of Se@V2O3 / C composite sodium selenium battery positive electrode materials prepared using vanadium oxyacetonate, vanadium oxytriisopropoxide, ethyl maltol oxyvanadium, methyl maltol oxyvanadium, and oxalate oxyvanadium as vanadium organometallic complexes.

[0120] Table 9 below is a statistical table of electrochemical performance analysis of Se@V2O3 / C composite sodium selenium battery cathode materials prepared using vanadium oxyacetonate, vanadium oxytriisopropoxide, ethyl maltol oxyvanadium, methyl maltol oxyvanadium, and oxalate oxyvanadium as vanadium organometallic complexes.

[0121] The comparative analysis is as follows: The Se@V2O3 / C composite sodium-selenium battery positive electrode materials prepared using different vanadium organometallic complexes have similar Se contents and similar first discharge specific capacities. In addition, the V2O3 content in the Se@V2O3 / C composite sodium-selenium battery positive electrode materials varies significantly. After 2500 cycles at a current density of 30A / g, the capacity retention rate shows an increasing trend with the increase of V2O3 content. This is because V2O3 exhibits enhanced chemical adsorption energy and catalytic performance in the Se@V2O3 / C composite sodium-selenium battery positive electrode material, and therefore has a strong inhibitory effect on the loss of sodium polyselenide. Therefore, when the Se content is similar, the higher the V2O3 content, the better the cycle stability.

[0122] Furthermore, based on Example 1, the present invention prepared a positive electrode material for a sodium-selenium battery by changing only the amount of graded porous anthracite-based hard carbon used, while keeping other process conditions unchanged. The amounts of graded porous anthracite-based hard carbon used were 0.18, 0.5, 0.9, 1.3, and 1.8 g, respectively.

[0123] Table 10 below is a statistical table of the elements and composition content of Se@V2O3 / C composite sodium selenium battery positive electrode materials prepared using different amounts of graded porous anthracite-based hard carbon.

[0124] Table 11 below is a statistical table of electrochemical performance analysis of Se@V2O3 / C composite sodium selenium battery positive electrode materials prepared using different amounts of graded porous anthracite-based hard carbon.

[0125] The comparative analysis is as follows: with the increase of the amount of hierarchical porous anthracite-based hard carbon, the content of V2O3 in the Se@V2O3 / C composite sodium-selenium battery positive electrode material decreases, and the content of Se in the composite material is similar. After 2500 cycles at a current density of 30 A / g, with the increase of the content of V2O3, the specific capacity retention rate of the 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 the content of V2O3, the specific capacity retention rate of the Se@V2O3 / C composite sodium-selenium battery positive electrode shows a trend of first increasing and then decreasing.

[0126] 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 of the material used for sodium-selenium battery positive electrode. The specific method is as follows: 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.

[0127] Table 12 below is the pore structure parameter of the hierarchical porous anthracite-based hard carbon prepared under different pore-forming conditions

[0128] Table 13 below 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

[0129] Table 14 below is the electrochemical performance analysis statistical table of the 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

[0130] By comparing and analyzing the experimental data, the application 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.

[0131] 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 less the polyselenium compound loss, and the stronger the cycle stability.

[0132] 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 the features and embodiments without departing from the spirit and scope of the present application. In addition, the features and embodiments can be modified to adapt to specific conditions and materials under the guidance of the present application 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 selenium battery positive electrode material, characterized in that The preparation method of the positive electrode material comprises the following steps: Step 1: soaking anthracite powder raw material in nitric acid solution to remove metal elements therein; then filtering out solids, soaking the solids in hydrofluoric acid solution to remove SiO2; then filtering out solids, washing with water, and drying to obtain anthracite powder from which metal impurities and SiO2 have been removed; Step 2: Mixing the pore-forming agent with the anthracite powder obtained in step 1, then adding deionized water to cover the mixture and soaking it; then heating and drying to remove moisture; then calcining and activating it in a nitrogen atmosphere; finally, cooling the calcined and activated product naturally and washing it with deionized water until the pH is neutral, thereby obtaining graded porous anthracite-based hard carbon; Step 3: dissolving the vanadium organometallic complex and SeO2 in deionized water to prepare a solution, then adding methanol to the solution and stirring evenly; then adding the graded porous anthracite-based hard carbon prepared in step 2 to the solution and stirring evenly to prepare a mixture solution; Step 4: hydrothermally treating the mixture solution prepared in step 3: heating the mixture solution to 180-220° C. in a high-pressure device and maintaining the temperature for 12-36 hours; then naturally cooling the mixture solution to room temperature; then, centrifuging the heated product to separate a solid product, washing the solid product with deionized water and alcohol to remove excess impurity ions during the reaction; and then, heating and drying the solid product. Step 5: Treat the solid product prepared in step 4 by thermal annealing: Place the solid product prepared in step 4 in a tubular furnace, heat it to 400-600°C at a heating rate of 5°C / min under N2 atmosphere, and calcine it for 1-5 hours. Then cool it naturally to obtain a V2O3@Se / C composite material.

2. The sodium-selenium battery positive electrode material according to claim 1, characterized in that In step 1, the anthracite powder raw material is prepared as follows: the anthracite raw material is crushed by a ball mill, and the fraction after sieving with 80 mesh is selected as the raw material.

3. The sodium-selenium battery positive electrode 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 in a mass-to-volume ratio of 1 g:6 mL; the anthracite powder raw material is fully soaked for 24 hours to remove the metal impurities; the concentration of the hydrofluoric acid solution used is 2 mol / L; the anthracite powder raw material and the hydrofluoric acid are prepared in a mass-to-volume ratio of 1 g:6 mL; when soaking in hydrofluoric acid, the anthracite powder raw material is soaked in a 60°C water bath and stirred during soaking; and the SiO2 is fully soaked for 4 hours.

4. The sodium-selenium battery positive electrode material according to claim 1, characterized in that In step 1, the solid filtered out after the hydrofluoric acid soaking treatment is repeatedly centrifuged and washed with deionized water to collect the black powder; then, the black powder is dried in an air oven at 60° C. for 12 hours to obtain anthracite powder from which metal impurities and SiO 2 are removed.

5. The sodium-selenium battery positive electrode 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 in 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 a temperature of 70°C for 24 hours; and heated to 600-800°C at a heating rate of 10°C / min for calcination, and the calcination time is 1.0~3.0 hours.

6. The sodium-selenium battery positive electrode material according to claim 1, characterized in that In step 3, the vanadium organometallic complex is any one of vanadyl acetylacetonate, vanadyl triisopropoxide, vanadyl ethyl maltol, vanadyl methyl maltol, and vanadyl oxalate.

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

1.

8. The sodium-selenium battery positive electrode 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 kept at this temperature for 24 h; the solid product is dried in an air oven at 60° C. for 12 h.

9. The sodium-selenium battery positive electrode material according to claim 1, characterized in that In step 5, the mixture is heated to 500° C. at a heating rate of 5° C. / min for calcination, and the calcination time is 3 h.

10. Use of the sodium-selenium battery positive electrode material according to any one of claims 1 to 9, characterized in that: The sodium-selenium battery positive electrode material is used as the sodium-ion battery positive electrode material.

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