A carbon-coated ion-doped vanadium oxide material, a preparation method and application thereof

Abstract

The application provides a carbon-coated ion-doped vanadium oxide material and a preparation method and application thereof. The preparation method comprises the following steps: performing a solvothermal reaction on a reaction solution containing doped metal ions, a vanadium oxide intermediate solution, an oxidizing agent, a solvent and glucose, and calcining a solid obtained in a protective atmosphere to obtain the carbon-coated ion-doped vanadium oxide material. The doped metal ions are selected from one or more of Fe 3+ , Ni 2+ and Cu 2+ . The application improves the conductivity of the vanadium oxide material and the electrochemical stability in the cycle process by embedding metal ions in the vanadium oxide.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a carbon-coated ion-doped vanadium oxide material, its preparation method, and its applications. Background Technology

[0002] With the depletion of non-renewable energy sources such as oil and fossil fuels, global warming and energy depletion are becoming increasingly serious problems, making the development of clean and renewable energy sources an urgent priority. The vigorous promotion of clean energy sources such as wind, solar, and tidal power has alleviated environmental problems to some extent, but these energy forms suffer from drawbacks such as unstable power generation and significant environmental impact. Therefore, rechargeable batteries have broad application scenarios. They can be used not only in transportation to reduce fossil fuel consumption but also in large-scale energy storage facilities to achieve efficient utilization of renewable resources. Over the past few decades, lithium-ion batteries (LIBs) have played a crucial role in human society due to their high energy density and long cycle life, but limited lithium resources have hindered their continued development. Since sodium and lithium belong to the same group and have similar properties, and sodium reserves are abundant, sodium-ion batteries have gained favor among researchers as an alternative to lithium-ion batteries.

[0003] Despite its many advantages over lithium-ion batteries, sodium-ion batteries also face a series of challenges. Sodium ions have a larger ionic radius than lithium ions, resulting in slower kinetics during charge and discharge, limiting ion transport and leading to lower capacity compared to lithium-ion batteries. Furthermore, the larger radius of sodium ions causes multiple phase transitions during charge and discharge, altering the material structure and reducing cycle stability. Therefore, it is necessary to explore an excellent cathode material to address these issues.

[0004] Vanadium oxide materials exhibit excellent performance in sodium-ion batteries due to their rich and variable valence states and high theoretical capacity, but their cycle stability is poor in practical applications. Considering these shortcomings, improving the performance of vanadium oxide cathode materials through ion doping and carbon coating is of significant research value. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a carbon-coated ion-doped vanadium oxide material, its preparation method, and its application, in order to solve the problems of low capacity and poor cycle stability of existing sodium-ion batteries.

[0006] To achieve the above and other related objectives, this invention provides a method for preparing carbon-coated ion-doped vanadium oxide materials. The method involves subjecting a reaction solution containing doped metal ions, a vanadium oxide intermediate solution, an oxidant, a solvent, and glucose to a solvothermal reaction, followed by calcination of the resulting solid under a protective atmosphere to obtain a carbon-coated ion-doped vanadium oxide material. The doped metal ions are selected from Fe... 3+ Ni 2+ and Cu 2+ One or more of them.

[0007] This invention achieves ion doping and carbon coating of vanadium oxide through a one-step hydrothermal post-annealing process. Compared with other multiple hydrothermal methods, this approach is simpler and less time-consuming, providing a useful reference for carbon-coated ion-doped vanadium oxides. This method utilizes the fact that incorporating metal ions into the vanadium oxide widens the interlayer spacing, effectively enhancing the material's stability. Simultaneously, carbon coating significantly improves the material's cycle stability.

[0008] Preferably, the chemical formula of the vanadium oxide intermediate in the vanadium oxide intermediate solution is VOC2O4.

[0009] Preferably, the vanadium oxide intermediate solution is prepared by dispersing V2O5 and oxalic acid in water and reacting at 60-80°C to obtain the vanadium oxide intermediate solution; more preferably, the temperature is 80°C and the reaction time is preferably 1 h.

[0010] Preferably, the mass ratio of V2O5 to oxalic acid is (0.5~2):(1~5), more preferably 1.2:2.49.

[0011] Preferably, the oxidant is selected from one or more of hydrogen peroxide, ammonium persulfate, and potassium dichromate.

[0012] Preferably, the solvent is one or a combination of methanol and ethanol.

[0013] Preferably, the volume ratio of the vanadium oxide intermediate solution, oxidant and solvent is (10~50):(3~5):(10~30), more preferably 30:3:20.

[0014] More preferably, the order of adding the above reaction solution is as follows: first, the vanadium oxide intermediate solution is mixed with the oxidant and solvent to obtain solution A, and then glucose and doped metal ions are added to solution A.

[0015] Preferably, the doped metal ions are added in the form of soluble metal salts, and the mass ratio of the soluble metal salts to glucose is (0.05~0.2):(0.5~1).

[0016] More preferably, the feeding ratio of solution A, soluble metal salt and glucose is (30~50) ml:(0.05-0.2) g:(0.5~1) g, and the most preferred ratio is 50 ml:0.16 g:0.9 g.

[0017] More preferably, the soluble metal salt is one or more selected from Fe(NO3)3·9H2O, Ni(NO3)2·6H2O, and Cu(NO3)2·3H2O. Preferably, the solvothermal reaction temperature is 160~200℃, and the reaction time is 24~48 h.

[0018] More preferably, the solvothermal reaction temperature is 170°C and the reaction time is 48 h.

[0019] Preferably, the calcination temperature is 300~600℃ and the time is 1~3h, more preferably 550℃ and more preferably 2h.

[0020] Preferably, the solid-liquid separation, washing, and vacuum drying processes are included before calcination.

[0021] More preferably, the obtained solid is repeatedly washed with deionized water and ethanol.

[0022] More preferably, the vacuum drying temperature is 60~80℃ and the time is 10~12.

[0023] The present invention also provides a carbon-coated ion-doped vanadium oxide material prepared by the above preparation method.

[0024] The present invention also provides an application of the above-mentioned carbon-coated ion-doped vanadium oxide material as a positive electrode active material in the preparation of sodium-ion batteries.

[0025] As described above, the present invention has the following beneficial effects:

[0026] (1) By embedding metal ions into vanadium oxides, the conductivity of vanadium oxide materials and their electrochemical stability during cycling are improved;

[0027] (2) By carbon coating the metal ion-doped vanadium oxide material, the collapse problem caused by the change in crystal spacing during cycling is alleviated, and the cycling stability of the vanadium oxide material is greatly improved.

[0028] (3) The raw materials of the present invention are readily available, have good stability, and the preparation method is simple to operate and low in cost. Attached Figure Description

[0029] Figure 1The images shown are SEM images of carbon-coated ion-doped vanadium oxide (a) prepared in Example 1, VO2 (b) prepared in Comparative Example 1, and FeVO2 (c) prepared in Comparative Example 2.

[0030] Figure 2 The images shown are a TEM image (a) and a corresponding EDS image (b) of the carbon-coated ion-doped vanadium oxide prepared in Example 1.

[0031] Figure 3 The XRD patterns shown are those of carbon-coated ion-doped vanadium oxide (a) prepared in Example 1, VO2 prepared in Comparative Example 1, and FeVO2 prepared in Comparative Example 2 (b).

[0032] Figure 4 The sodium-ion battery shown is 1 mV s prepared in Example 1. -1 Cyclic voltammetry curves for the first three cycles at scan rate.

[0033] Figure 5 The sodium-ion battery shown in Example 1 operates at 0.2 mV s. -1 0.4 mV s -1 0.6 mV s -1 0.8mV s -1 1 mV s -1 Percentage of capacitance contribution at five scan speeds.

[0034] Figure 6 Sodium-ion batteries prepared using the products obtained in Example 1, Comparative Example 1, and Comparative Example 2 as positive electrode active materials were tested at 0.1 A g. -1 The long-cycle performance diagram at current density.

[0035] Figure 7 The sodium-ion battery shown is 0.5 A g prepared in Example 1. -1 The long-cycle performance diagram at current density. Detailed Implementation

[0036] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0037] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.

[0038] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0039] Example 1

[0040] This application provides a method for preparing a carbon-coated ion-doped vanadium oxide material, comprising the following steps:

[0041] (1) Preparation of vanadium oxide intermediate solution: In a beaker, 1.2 g V2O5 and 2.49 g H2C2O4·2H2O were added to 40 ml of deionized water and stirred in a water bath at 80℃ for 1 h to obtain a dark blue vanadium oxide intermediate VOC2O4 solution.

[0042] (2) Take 30 ml of vanadium oxide intermediate VOC2O4 solution and add it to a 100 ml reaction vessel. Then add 3 ml of H2O2 and 20 ml of methanol to it in sequence and stir at room temperature for 30 min. Add 0.9 g of glucose and 0.16 g of Fe(NO3)3·9H2O to it, mix and stir for 10 min, and then put it into a forced-air drying oven for a solvothermal reaction at 170℃ for 48 h.

[0043] (3) The obtained solid was repeatedly washed with deionized water and ethanol. The product was dried under vacuum at 60°C for 12 h. The dried powder was then calcined at a heating rate of 2°C / min until it reached 550°C. The temperature was then maintained at a constant temperature for 2 h to obtain carbon-coated ion-doped vanadium oxide.

[0044] This embodiment also provides a method for preparing a positive electrode sheet, including the following steps:

[0045] Weigh the carbon-coated ion-doped vanadium oxide prepared above, and mix it with conductive agent conductive carbon black and binder polyvinylidene fluoride in a mass ratio of 8:1:1. Grind it thoroughly, then add N-methyl-2-pyrrolidone dropwise with a pipette and stir until uniform. Then coat the mixed electrode material onto aluminum foil, vacuum dry for 12 h, and cut it into circular electrode sheets to obtain the positive electrode sheet.

[0046] This embodiment also provides a method for preparing a sodium-ion battery, including the following steps:

[0047] In the glove phase, a sodium metal sheet is used as the negative electrode, and the positive electrode sheet prepared above is used. A glass fiber membrane (GF / D) is used as the separator. NaPF6 is selected as the solute and DEC:EC = 1:1 Vol% with 5% FEC as the solvent. The cells are assembled into 2032 button cells using a battery packaging machine.

[0048] Example 2

[0049] The difference between Example 2 and Example 1 is that the types of doped metal ions are different. The 0.16 g Fe(NO3)3·9H2O added in step (2) is replaced with 0.116 g Ni(NO3)2·6H2O, and the rest of the process is exactly the same.

[0050] The sodium-ion battery prepared in this embodiment operates at a current density of 0.1 A g. -1 The initial capacity at the current density is 110 mA hg -1 The capacity retention rate is 98% after 200 cycles.

[0051] Example 3

[0052] The difference between Example 3 and Example 1 is that the solvothermal reaction time in step (2) is different, specifically 24 h, while the rest of the process is exactly the same.

[0053] The sodium-ion battery prepared in this embodiment operates at a current density of 0.1 A g. -1 The initial capacity at the current density is 105 mA hg -1 The capacity retention rate is 95% after 200 cycles.

[0054] Example 4

[0055] The difference between Example 4 and Example 1 is that the preparation temperature of the vanadium oxide intermediate solution in step (1) is different, specifically room temperature, while the rest of the process is exactly the same.

[0056] Specifically, 1.2 g of V2O5 and 2.49 g of H2C2O4·2H2O were added to 40 ml of deionized water in a beaker and stirred at room temperature for 24 h to obtain a dark blue vanadium oxide intermediate VOC2O4 solution.

[0057] The sodium-ion battery prepared in this embodiment operates at a current density of 0.1 A g. -1 The initial capacity at the current density is 90 mA hg -1The capacity retention rate is 100% after 200 cycles.

[0058] Comparative Example 1

[0059] This comparative example provides a method for preparing VO2, including the following steps:

[0060] (1) Preparation of vanadium oxide intermediate solution: In a beaker, 1.2 g V2O5 and 2.49 g H2C2O4·2H2O were added to 40 ml of deionized water and stirred in a water bath at 80℃ for 1 h to obtain a dark blue vanadium oxide intermediate VOC2O4 solution.

[0061] (2) Take 30 ml of the dark blue vanadium oxide intermediate VOC2O4 solution and add it to a 100 ml reaction vessel. Then add 3 ml of H2O2 and 20 ml of methanol to it in sequence. After stirring at room temperature for 30 min, place it in a forced-air drying oven and hydrothermally react at 170 °C for 48 h. The solid obtained after the hydrothermal reaction is washed by centrifugation with deionized water and ethanol several times. The product is dried under vacuum at 60 °C for 12 h to obtain VO2.

[0062] Comparative Example 2

[0063] This comparative example provides an Fe 3+ The method for preparing doped VO2 includes the following steps:

[0064] (1) Preparation of vanadium oxide intermediate solution: In a beaker, 1.2 g V2O5 and 2.49 g H2C2O4·2H2O were added to 40 ml of deionized water and stirred in a water bath at 80℃ for 1 h to obtain a dark blue vanadium oxide intermediate VOC2O4 solution.

[0065] (2) Take 30 ml of the dark blue vanadium oxide intermediate VOC2O4 solution and add it to a 100 ml reaction vessel. Then add 3 ml of H2O2 and 20 ml of methanol in sequence and stir at room temperature for 30 min. Add 0.9 g of glucose and 0.16 g of Fe(NO3)3·9H2O, mix and stir for 10 min, and then place it in a forced-air drying oven for hydrothermal reaction at 170℃ for 48 h. The solid obtained after hydrothermal reaction is washed by centrifugation with deionized water and ethanol multiple times. The product is dried under vacuum at 60℃ for 12 h to obtain Fe. 3+ The doped VO2 is denoted as FeVO2.

[0066] The samples prepared in Example 1 and the comparative example were characterized and analyzed, and the results are shown below:

[0067] Figure 1(a) is a SEM image of the carbon-coated ion-doped vanadium oxide prepared in Example 1, for comparison. Figure 1 (b) Comparative Example 1 Figure 1 (c) The SEM images of Comparative Example 2 show that the microstructure of VO2 and FeVO2 synthesized before carbon coating is a flower-like structure composed of aggregated nanosheets, while the microstructure after carbon coating is a flower-like structure with the surface coated, proving that the coating was successful.

[0068] Figure 2 The images show TEM and EDS spectra of the material prepared in Example 1. Figure 2 As shown in (a), the central part is an aggregated vanadium oxide material, and the edge part is an amorphous carbon material without lattice fringes. Furthermore, the edge material exhibits a halo under selected electron diffraction, proving its amorphous nature. Figure 1 and Figure 2 (b) The uniform distribution of C in the selected region in EDS, while V, O and Fe are only distributed in the central part, proves the success of carbon coating.

[0069] Figure 3 (a) is the XRD pattern of the material prepared in Example 1, for comparison. Figure 3 (b) The XRD patterns of Comparative Examples 1 and 2 show that the diffraction peaks of VO2 and FeVO2 at 15.6°, 25.3°, and 30.2° before carbon coating correspond to the characteristic peaks of the (001), (110), and (002) crystal planes of VO2 (PDF#97-019-6175), respectively. After carbon coating, the diffraction peaks at 24.2°, 33.0°, 36.4°, 41.3°, and 54.0° correspond to the characteristic peaks of the (012), (104), (110), (113), and (116) crystal planes of V2O3 (PDF#97-009-4768), and the diffraction peak at 27.9° corresponds to the characteristic peak of the (011) crystal plane of VO2 (PDF#97-064-7604). This demonstrates that a phase transformation occurs after carbon coating.

[0070] Electrochemical tests and analyses were performed on the samples prepared in Example 1 and the comparative example, and the results are shown below:

[0071] Figure 4 Example 1 at 1 mV s -1 The cyclic voltammetry curves obtained at the specified scan rate show two broad peaks at 0.4 V and 0.75 V during the initial discharge process, corresponding to sodium ion insertion and SEI film formation, respectively. The broad peak around 0.5 V to 2.2 V can be interpreted as Na+ ion insertion. +Extraction occurs from sodium-intercalated vanadium oxides. Subsequent CV curves almost overlap, indicating good reversibility. The broad redox peaks observed in the CV curves reveal significant pseudocapacitive behavior. Therefore, the pseudocapacitance of Na+ can be measured by performing CV tests at different scan rates. + The contribution of storage, such as Figure 5 As shown, at 0.2 mV s -1 0.4mV s -1 0.6 mV s -1 0.8 mV s -1 1 mV s -1 The pseudocapacitive contributions were 50.2%, 56.1%, 59.7%, 65.3%, and 69.4%, respectively, indicating that the pseudocapacitive portion increases with increasing scan rate. Therefore, the sodium-ion battery obtained in Example 1 exhibits excellent capacity retention and cycle life.

[0072] Figure 6 Sodium-ion batteries prepared using the products obtained in Example 1, Comparative Example 1, and Comparative Example 2 as positive electrode active materials were tested at 0.1 A g. -1 The long-cycle performance diagram under current density is shown, where the charge / discharge voltage range is 0-3 V, and the initial capacity of VO2 corresponding to Comparative Example 1 is 230 mA hg. -1 After 350 cycles, the capacity retention was 26%, while the initial capacity of FeVO2 corresponding to Comparative Example 2 was 250 mA hg. -1 After 350 cycles, the capacity retention was 48%, and the initial capacity of Example 1 was 130 mA hg. -1 After 350 cycles, the capacity retention rate is 100%.

[0073] Figure 7 The example shown is from Example 1 at 0.5 A g. -1 The long-cycle performance graph at current density, with an initial capacity of 115 mAh g. -1 After 800 cycles, the capacity retention rate is 100%.

[0074] In summary, this invention improves the conductivity and electrochemical stability of vanadium oxide materials during cycling by embedding metal ions into them. Furthermore, carbon coating of the metal ion-doped vanadium oxide materials mitigates the collapse problem caused by changes in crystal spacing during cycling, significantly enhancing the cycling stability of the vanadium oxide materials. The raw materials used in this invention are readily available, exhibit good stability, and the preparation method is simple and low-cost. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial applicability.

[0075] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a carbon-coated ion-doped vanadium oxide cathode material suitable for sodium-ion batteries, characterized in that, A carbon-coated ion-doped vanadium oxide material is prepared by solvothermal reaction of a reaction solution containing doped metal ions, a vanadium oxide intermediate solution, an oxidant, a solvent, and glucose, followed by calcination of the resulting solid under a protective atmosphere; the doped metal ions are selected from Fe. 3+ Ni 2+ and Cu 2+ One or more of the following; The chemical formula of the vanadium oxide intermediate in the vanadium oxide intermediate solution is VOC2O4; The vanadium oxide intermediate solution is prepared by dispersing V2O5 and oxalic acid in water and reacting them at 60-80°C to obtain the vanadium oxide intermediate solution; the mass ratio of V2O5 to oxalic acid is (0.5-2):(1-5). The oxidant is selected from one or more of hydrogen peroxide, ammonium persulfate, and potassium dichromate; the solvent is one or a combination of methanol and ethanol. The volume ratio of the vanadium oxide intermediate solution, oxidant, and solvent is (10~50):(3~5):(10~30). The doped metal ions are added in the form of soluble metal salts, and the mass ratio of the soluble metal salts to glucose is (0.05~0.2):(0.5~1). The solvothermal reaction temperature is 160~200℃, and the reaction time is 24~48 h; The calcination temperature is 300~600℃, and the time is 1~3h.

2. A carbon-coated ion-doped vanadium oxide material prepared by the preparation method of claim 1.

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