Preparation Method and Application of Cobalt-Doped and MXene-Coated Sodium Vanadate Composite Powder

Abstract

The present invention discloses a preparation method of cobalt-doped and synergistically MXene-coated sodium vanadate composite powder. Using water as a solvent, sodium iodide anhydrous and vanadyl phosphate monohydrate as the sodium source and vanadium source, and introducing cobalt acetate tetrahydrate, by synergistically controlling parameters such as concentration and ratio, reaction temperature, reaction time, filling ratio, etc., the synthesis of HNaV6O embedded with cobalt ions assembled by nanosheets through a one-step hydrothermal method is achieved. 16 Using CTAB, the etched Ti3C2Tx and HNaV6O 16 ·4H2O are compositely assembled through electrostatic coupling, and finally cobalt-doped and synergistically Ti3C2Tx-coated HNaV6O 16 ·4H2O is prepared; the present invention improves the crystal structure and electronic conductivity of HNaV6O 16 ·4H2O, enhances its capacity and cycle stability, and the present invention also discloses the application of this material in the cathode material of sodium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for ion batteries, and relates to a preparation method of cobalt-doped and MXene-coated sodium vanadate composite powder.

[0002] The present invention also relates to the application of cobalt-doped and MXene-coated sodium vanadate composite powder in the field of sodium ion batteries. Background Art

[0003] With concerns about global warming and environmental pollution caused by the rapid consumption of fossil fuels by people, the energy crisis is escalating; Electrochemical energy storage devices, such as rechargeable lithium-ion batteries, can effectively store and release electricity through chemical reactions, providing great market potential for electric vehicles and smart grids. As an alternative to lithium-ion batteries, due to the rich sodium resources and their uniform distribution around the world, people have been looking for sodium ion batteries with a similar chemical storage mechanism; When many layered transition metal oxide materials are used as the cathode of sodium ion batteries, the phase change during the charge and discharge process will cause serious capacity attenuation, resulting in poor cycle life; In recent years, layered vanadium-based oxide materials have become a research hotspot for cathode materials of sodium ion batteries due to their high working voltage, structural stability and high specific capacity. Due to the multi-electron transfer of vanadium, vanadium-based oxides have a high theoretical specific capacity; Therefore, a series of vanadium-based oxide materials have been prepared and used as active cathode materials in sodium ion batteries;

[0004] As one of the vanadium-based oxides, HNaV6O 16 ·4H2O is composed of [V3O8] layers, and sodium ions are located in the octahedral vacancies, playing a supporting role between the layers and stabilizing the crystal structure. It is a promising cathode material; However, its low electronic conductivity and slow sodium ion diffusion rate result in rapid capacity attenuation during cycling and poor rate performance; In view of the above disadvantages of HNaV6O 16 ·4H2O, whether the chemical embedding of transition metal ions can significantly improve its structural instability, conductivity and ion diffusion kinetics during the reversible Na + storage and release process has become a problem worthy of exploration; However, the embedding of a large number of metal ions may reduce the specific capacity of HNaV6O 16 ·4H2O; In this study, we used a general hydrothermal method to achieve the chemical embedding of a small amount of cobalt ions between the layers of HNaV6O 16 ·4H2O, which can effectively improve the ion diffusion kinetics, electronic conductivity and structural stability of HNaV6O 16 ·4H2O, thereby improving the electrochemical performance. Due to the embedding of cobalt ions, not only can the fast charging ability be enhanced, but also the reversibility during the electrochemical process can be promoted;

[0005] In addition, during the charge-discharge process, the volume expansion caused by the insertion and extraction of ions leads to the collapse of the material structure; the capacity decay during the charge-discharge process is caused by the dissolution of vanadium, the decomposition of the electrolyte at high voltage (or high temperature), and the pulverization of HNaV 16 ·4H2O particles; a major factor inducing vanadium dissolution is the erosion of trace acidic substances (HF) in the liquid electrolyte; the dissolution of vanadium will damage the crystal structure of HNaV 16 ·4H2O, resulting in irreversible capacity decay or low Coulomb efficiency; subsequently, vanadium ions in the liquid electrolyte may deposit on the anode surface, thereby increasing the battery impedance or damaging the solid electrolyte interface (SEI) layer. Surface modification is an effective method to inhibit vanadium dissolution. It is usually achieved by coating (or wrapping) a protective layer (such as graphene, metal oxide, active electrode material, and polymer) on the surface of HNaV 16 ·4H2O particles; the protective layer can prevent the direct contact between HNaV 16 ·4H2O particles and the electrolyte, reducing the corrosion of HF;

[0006] Two-dimensional material MXene has been proven to have outstanding potential in energy conversion and storage. Ti3C2Tx is the most studied MXene, which is synthesized by selectively etching Al from the Ti3AlC2 MAX phase using HF; Ti3C2Tx has excellent electronic conductivity, good mechanical properties, and a relatively easy preparation process; importantly, Ti3C2Tx is prepared in an HF environment and is stable to HF. Therefore, Ti3C2Tx can basically meet the above criteria and is a suitable choice for the protective layer to inhibit vanadium dissolution of HNaV 16 ·4H2O particles; here, wrinkled Ti3C2Tx nanosheets are proposed as a protective layer to inhibit vanadium dissolution; HNaV 16 ·4H2O particles are encapsulated in wrinkled Ti3C2Tx nanosheets, and it is found that this greatly improves the rate and cycling ability;

[0007] In summary, the present invention utilizes the technical idea of metal ion doping in cooperation with Ti3C2Tx coating. Cobalt ions are embedded to improve the crystal structure and electronic conductivity of HNaV 16 ·4H2O, thereby enhancing the cycling stability of HNaV 16 ·4H2O; then, Ti3C2Tx coating is used to inhibit vanadium dissolution, suppress volume expansion and particle pulverization during the charge-discharge process, and improve the capacity and cycling stability of the material. Summary of the Invention

[0008] The object of the present invention is to provide a preparation method of cobalt-doped and MXene-coated sodium vanadate composite powder, which solves the problems of the existing HNaV6O 16· Problems of cyclic instability and small capacity existing in the 4H2O material.

[0009] The technical solution adopted in the present invention is a preparation method of cobalt-doped and MXene-coated sodium vanadate composite powder, which is specifically implemented according to the following steps:

[0010] Step 1: Weigh vanadyl phosphate monohydrate and disperse it in deionized water, and perform ultrasonic dispersion to obtain solution A;

[0011] Step 2: Weigh 15 - 16 mg of cobalt acetate tetrahydrate and 90 - 95 mg of anhydrous sodium iodide, and add them to solution A to obtain solution B;

[0012] Step 3: Ultrasonically treat solution B;

[0013] Step 4: Pour the ultrasonically treated solution B into the inner lining of the reaction kettle, then install the inner lining in the outer kettle and fix it, put it into a forced-air drying oven, and then perform cleaning;

[0014] Step 5: After vacuum drying, collect the product, and after grinding, obtain cobalt-doped HNaV6O 16 · 4H2O powder sample;

[0015] Step 6: Add HNaV6O 16 · 4H2O particles to the CTAB aqueous solution, and obtain solution C through magnetic stirring;

[0016] Step 7: Drop solution C into the beaker of the Ti3C2Tx suspension, and obtain solution D through magnetic stirring;

[0017] Step 8: Perform vacuum filtration and cleaning on solution D, then vacuum dry and collect the product to obtain a cobalt-doped and Ti3C2Tx-coated HNaV6O 16 · 4H2O powder sample.

[0018] The features of the present invention also lie in:

[0019] Specifically, step 1 is as follows: Weigh 250 - 350 mg of vanadyl phosphate monohydrate, disperse it in 30 - 40 ml of deionized water, the ultrasonic power is 80 - 120 W, and perform ultrasonic treatment at room temperature for 0.5 h - 1.5 h to obtain solution A;

[0020] Specifically, step 2 is as follows: Weigh 15 - 16 mg of cobalt acetate tetrahydrate and 90 - 95 mg of anhydrous sodium iodide, add them to solution A to obtain solution B, and cobalt acetate tetrahydrate is for micro adjustment, and the weighing instrument is an analytical balance;

[0021] Specifically, step 3 is as follows: Ultrasonically treat solution B for 1 h - 3 h until the solution gradually changes from wine red to black, the ultrasonic power is 80 - 120 W, and perform it at room temperature;

[0022] Among them, step 4 is specifically as follows: the temperature of the drying oven is 140 - 160 °C, the drying time is 11 - 13 h, the product is washed alternately with water and alcohol for 2 - 4 times, and the alternate washing of water and alcohol is mainly carried out by suction filtration or centrifugation, and the collection is also mainly carried out by suction filtration or centrifugation;

[0023] Among them, the vacuum drying conditions in step 5 are: 50 - 70 °C, drying for 11 - 13 h. Before vacuum drying, the product of step 4 is sealed with plastic wrap, and then the plastic wrap is perforated to ensure sufficient drying under low-pressure conditions;

[0024] Among them, step 6 is specifically as follows: 0.4 - 0.6 g of HNaV6O 16 ·4H2O particles are added to 2.0 - 3.0 ml of an aqueous CTAB solution with a concentration of 1.0 - 1.5 mg / ml, and continuously stirred for 20 - 40 min. The rotational speed of magnetic stirring is 400 - 600 r / min, and it is carried out at room temperature to obtain solution C;

[0025] Among them, step 7 is specifically as follows: solution C is dropped into a beaker with 8 - 10 ml of a layered Ti3C2Tx suspension, and continuously stirred for 20 - 40 min to obtain solution D. The rotational speed of magnetic stirring is 400 - 600 r / min, and it is carried out at room temperature;

[0026] Among them, step 8 is specifically as follows: solution D is vacuum filtered, and washed with deionized water for 2 - 4 times to remove CTAB, and then the product is collected by vacuum drying. The vacuum drying temperature is 50 - 70 °C, and the drying time is 11 - 13 h. Before the product is placed in a petri dish for drying, it is sealed with plastic wrap, and the plastic wrap is perforated to ensure sufficient drying under low-pressure conditions.

[0027] The second technical solution of the present invention is the application of cobalt-doped and MXene-coated sodium vanadate composite powder in the field of sodium-ion batteries.

[0028] The beneficial effects of the present invention are:

[0029] (1) Since the present invention adopts a one-step hydrothermal reaction to directly synthesize the target powder, it has a low synthesis temperature, a simple synthesis route, does not require large equipment and harsh reaction conditions;

[0030] (2) The vanadium source and phosphorus source used in the present invention are vanadyl phosphate monohydrate, the sodium source is anhydrous sodium iodide, and the solvent is deionized water. These three substances are all common raw materials, which are cheap, easily available and low in cost. The whole reaction is easy to control and environmentally friendly, and the product does not require post-treatment, and is suitable for large-scale production;

[0031] (3) The selected Ti3C2Tx powder in the present invention is easy to etch and synthesize, with a mature process and simple and convenient operation;

[0032] (4) By strictly and coordinately controlling parameters such as the concentrations and ratios of the vanadium source, sodium source, and cobalt salt, reaction temperature, and reaction time in the present invention, and making full use of the reactions of the vanadium source, sodium source, and cobalt source, cobalt ions are successfully embedded into HNaV6O 16 ·4H2O nucleates and grows uniformly in deionized water, generating a petal structure with a size of about 5 μm assembled from nanosheets with a width of about 400 nm and a thickness of about 5 nm;

[0033] (5) The addition amount of the cobalt salt has a great influence on the structural order degree of cobalt-ion-embedded HNaV6O 16 ·4H2O and directly affects the performance of HNaV6O 16 ·4H2O as a cathode material for sodium-ion batteries;

[0034] (6) The reaction time plays a key role in the growth of cobalt-ion-embedded HNaV6O 16 ·4H2O. Too long or too short reaction time is not conducive to the assembly of a better micron-flower structure and directly affects the performance of HNaV6O 16 ·4H2O as a cathode material for sodium-ion batteries;

[0035] (7) The reaction temperature plays a key role in the growth of cobalt-ion-embedded HNaV6O 16 ·4H2O. Too high or too low reaction temperature is not conducive to the assembly of a better nano-flower structure and directly affects the performance of HNaV6O 16 ·4H2O as a cathode material for sodium-ion batteries;

[0036] (8) During the in-situ growth of cobalt ions embedded in HNaV6O 16 ·4H2O, the synergistic effect of the temperature field and pressure field generated by hydrothermal treatment enables cobalt ions to form strong chemical bonding in the interlayer of HNaV6O 16 ·4H2O and always stably exist in the interlayer during charge and discharge processes;

[0037] (9) The Ti3C2Tx coating layer is tightly coated on the lattice surface of cobalt-doped HNaV6O 16 ·4H2O through electrostatic coupling, effectively inhibiting the volume expansion of HNaV6O 16 ·4H2O during charge and discharge processes, thereby improving the structural stability of HNaV6O 16 ·4H2O. And it effectively inhibits the corrosion of HNaV6O 16 ·4H2O by the electrolyte and the dissolution of vanadium, reduces capacity loss, and significantly improves cycle stability;

[0038] (10) The cobalt-doped and Ti3C2Tx-coated HNaV6O 16 ·4H2O prepared by the present invention has a unique micro-flower structure, and its large specific surface area accelerates the reaction kinetics; the introduction of cobalt ions not only enhances the conductivity of HNaV6O 16 ·4H2O, but also enhances the structural stability of HNaV6O 16 ·4H2O during charge and discharge. The (100) crystal plane has the largest interplanar spacing, which serves as a channel for metal ions to enter and exit the interlayer, and is very conducive to the storage and transmission of sodium ions in the V3O8 layer. The embedding of cobalt ions between the layers is beneficial to the transmission and structural stability of sodium ions, and finally exhibits excellent cycling performance and rate performance; the initial discharge capacity is 133 mAh / g at a current density of 1C, and the capacity retention rate is 71.3% after 100 cycles at a current density of 1C (the original sample is 129 mAh / g, and the retention rate is 25.3%);

[0039] (11) When the product prepared by the present invention is used as a cathode material for sodium-ion batteries, it can exhibit excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is the X-ray diffraction pattern of the product prepared in Example 1 of the present invention;

[0041] Figure 2 It is the low-magnification scanning electron micrograph of the product prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0042] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0043] The present invention provides a method for preparing cobalt-doped and MXene-coated sodium vanadate composite powder. Using water as a solvent, anhydrous sodium iodide and vanadyl phosphate monohydrate as sodium source and vanadium source, and introducing cobalt acetate tetrahydrate, by synergistically controlling parameters such as their concentrations and ratios, reaction temperature, reaction time, filling ratio, etc., a hydrothermal method for one-step synthesis of HNaV6O 16 ·4H2O powder assembled by nanosheets with cobalt ions embedded; on this basis, using CTAB to compound and assemble the etched Ti3C2Tx and HNaV6O 16 ·4H2O through electrostatic coupling, and finally successfully preparing cobalt-doped and Ti3C2Tx-coated HNaV6O 16 ·4H2O composite powder; the composite powder prepared by the present invention is composed of wrinkled micro-flowers with a size of about 5 μm assembled with a width of about 400 nm and a thickness of about 5 nm. The outer wrinkled nanosheets are Ti3C2Tx, and the inside is wrapped with Co-doped HNaV6O 16·4H2O material, the combination between Ti3C2Tx and Co-doped HNaV6O 16 ·4H2O is a physical combination rather than a chemical bond combination.

[0044] The present invention also provides the application of the above product to the cathode material of a sodium-ion battery, which can exhibit excellent electrochemical performance; the results show that Co-doped and Ti3C2Tx-coated HNaV6O 16 ·4H2O shows a significant improvement in performance as the cathode material of a sodium-ion battery.

[0045] Example 1

[0046] Step 1: Weigh 300 mg of vanadyl phosphate monohydrate, disperse it in 35 ml of deionized water, and ultrasonicate for 1 h to obtain solution A;

[0047] Step 2: Weigh 15.6 mg of cobalt acetate tetrahydrate and 92.80 mg of anhydrous sodium iodide and add them to solution A to obtain solution B;

[0048] Step 3: Ultrasonicate solution B for 2 h, and the solution gradually changes from wine red to black;

[0049] Step 4: Pour the ultrasonified solution B into a 50-ml reaction kettle liner, then install the liner in the outer kettle and fix it, and place it in a forced-air drying oven to react at 150 °C for 12 h. Wash the product alternately with 3 waters and 3 alcohols;

[0050] Step 5: Collect the product after vacuum drying, grind it to obtain a cobalt-doped HNaV6O 16 ·4H2O powder sample;

[0051] Step 6: Add 0.5 g of HNaV6O 16 ·4H2O particles to 2.5 ml of an aqueous CTAB solution with a concentration of 1.2 g / ml and stir continuously for 30 min to obtain solution C;

[0052] Step 7: Drop solution C into a beaker with 9 ml of a layered Ti3C2Tx suspension and stir continuously for 30 min to obtain solution D;

[0053] Step 8: Vacuum filter solution D, wash it 3 times with deionized water to remove CTAB, and then collect the product after vacuum drying to obtain a cobalt-doped and Ti3C2Tx-coated HNaV6O 16 ·4H2O powder sample.

[0054] As Figure 1 shown, all diffraction peaks can be well matched with HNaV6O 16·4H2O standard card PDF #49 - 0996; Since the content of cobalt ions introduced is small, the crystal structure of HNaV6O 16 ·4H2O has not changed, and the crystallinity is good.

[0055] As Figure 2 shown, the cobalt - ion - embedded HNaV6O 16 ·4H2O is composed of multiple uniformly - grown wrinkled micro - flowers. The size of the obtained wrinkled micro - flowers is about 5 nm, and they are assembled by wrinkled nanosheets with a width of about 400 nm and a thickness of about 5 nm.

[0056] Example 2

[0057] Step 1: Weigh 250 mg of vanadium oxyphosphate monohydrate and disperse it in 30 ml of deionized water. Ultrasonic for 0.5 h to obtain solution A;

[0058] Step 2: Weigh 15 mg of cobalt acetate tetrahydrate and 90 mg of anhydrous sodium iodide and add them to solution A to obtain solution B;

[0059] Step 3: Ultrasonic solution B for 1 h, and the solution gradually changes from wine - red to black;

[0060] Step 4: Pour the ultrasonicated solution B into a 50 - ml reaction kettle liner, then install the liner in the outer kettle and fix it, and put it into a blast drying oven. React at 140 °C for 11 h, and wash the product alternately with water twice and alcohol twice;

[0061] Step 5: After vacuum drying, collect the product, grind it to obtain a cobalt - doped HNaV6O 16 ·4H2O powder sample;

[0062] Step 6: Add 0.4 g of HNaV6O 16 ·4H2O particles to 2.0 ml of a CTAB aqueous solution with a concentration of 1.0 g / ml, and continuously stir for 20 min to obtain solution C;

[0063] Step 7: Drop solution C into a beaker with an 8 - ml layered Ti3C2Tx suspension and continuously stir for 20 min to obtain solution D;

[0064] Step 8: Vacuum - filter solution D, wash it twice with deionized water to remove CTAB, and then collect the product after vacuum drying to obtain a cobalt - doped and Ti3C2Tx - coated HNaV6O 16 ·4H2O powder sample.

[0065] Example 3

[0066] Step 1: Weigh 350 mg of vanadyl phosphate monohydrate, disperse it in 40 ml of deionized water, and ultrasonicate for 1.5 h to obtain Solution A;

[0067] Step 2: Weigh 16 mg of cobalt acetate tetrahydrate and 95 mg of anhydrous sodium iodide and add them to Solution A to obtain Solution B;

[0068] Step 3: Ultrasonicate Solution B for 3 h, and the solution gradually changes from wine red to black;

[0069] Step 4: Pour the ultrasonified Solution B into a 50-ml reaction kettle liner, then install the liner in the outer kettle and fix it, and place it in a forced-air drying oven to react at 160 °C for 13 h. Wash the product alternately with water and alcohol 4 times;

[0070] Step 5: Collect the product after vacuum drying, grind it to obtain a cobalt-doped HNaV6O 16 ·4H2O powder sample;

[0071] Step 6: Add 0.6 g of HNaV6O 16 ·4H2O particles to 3.0 ml of an aqueous CTAB solution with a concentration of 1.5 g / ml, and stir continuously for 40 min to obtain Solution C;

[0072] Step 7: Drop Solution C into a beaker containing 10 ml of a layered Ti3C2Tx suspension, and stir continuously for 40 min to obtain Solution D;

[0073] Step 8: Vacuum filter Solution D, wash it 4 times with deionized water to remove CTAB, then collect the product after vacuum drying to obtain a cobalt-doped and synergistically Ti3C2Tx-coated HNaV6O 16 ·4H2O powder sample.

Claims

1. Preparation method of cobalt-doped and synergistically MXene-coated sodium vanadate composite powder, characterized in that, The implementation is specifically carried out according to the following steps: Step 1: Weigh vanadium oxyphosphate monohydrate and disperse it in deionized water, and perform ultrasonic dispersion to obtain solution A; Step 2: Weigh cobalt acetate tetrahydrate and sodium iodide anhydrous and add them to solution A to obtain solution B; Step 3: Ultrasonically treat solution B; Step 4: Pour the ultrasonically treated solution B into the inner lining of the reaction kettle, then install the inner lining in the outer kettle and fix it, put it into the blast drying oven, and then perform cleaning; Step 5, collect the product after vacuum drying, and grind it to obtain a cobalt-doped HNaV6O 16 ·4H2O powder sample; Step 6, adding HNaV6O 16 ·4H2O powder to the CTAB aqueous solution and obtaining solution C by magnetic stirring; Step 7: Drop solution C into the beaker with the Ti3C2Tx suspension, and obtain solution D through magnetic stirring; Step 8, subject the solution D to vacuum filtration and washing, then vacuum dry and collect the product to obtain a cobalt-doped and synergistically Ti3C2Tx-coated HNaV6O 16 ·4H2O powder sample; The specific steps of step 6 are as follows: Add 0.4 - 0.6 g of HNaV6O 16 ·4H2O powder to 2.0 - 3.0 ml of CTAB aqueous solution with a concentration of 1.0 - 1.5 mg / ml, continuously stir for 20 - 40 min, the rotation speed of magnetic stirring is 400 - 600 r / min, and it is carried out at room temperature to obtain solution C; The specific content of step 7 is as follows: Drop solution C into the beaker with 8 - 10 ml of the layered Ti3C2Tx suspension, continuously stir for 20 - 40 min to obtain solution D, the rotation speed of magnetic stirring is 400 - 600 r / min, and it is carried out at room temperature; The specific content of step 8 is as follows: Carry out vacuum filtration on solution D, and wash it 2 - 4 times with deionized water to remove CTAB, then perform vacuum drying to collect the product, the vacuum drying temperature is 50 - 70 °C, dry for 11 - 13 h, seal the product with plastic wrap before drying, and then make holes in the plastic wrap.

2. The preparation method of the cobalt-doped and synergistically MXene-coated sodium vanadate composite powder according to claim 1, characterized in that, The specific content of step 1 is as follows: Weigh 250 - 350 mg of vanadium oxyphosphate monohydrate, disperse it in 30 - 40 ml of deionized water, the ultrasonic power is 80 - 120 W, and perform ultrasonic treatment at room temperature for 0.5 h - 1.5 h to obtain solution A.

3. The preparation method of the cobalt-doped and synergistically MXene-coated sodium vanadate composite powder according to claim 1, characterized in that, The specific content of step 2 is as follows: Weigh 15 - 16 mg of cobalt acetate tetrahydrate and 90 - 95 mg of sodium iodide anhydrous and add them to solution A to obtain solution B.

4. The preparation method of the cobalt-doped and synergistically MXene-coated sodium vanadate composite powder according to claim 1, characterized in that, The specific content of step 3 is as follows: Ultrasonically treat solution B for 1 h - 3 h until the solution gradually changes from wine red to black, the ultrasonic power is 80 - 120 W, and it is carried out at room temperature.

5. The preparation method of the cobalt-doped and synergistically MXene-coated sodium vanadate composite powder according to claim 1, characterized in that, The specific content of step 4 is as follows: The temperature of the drying oven is 140 - 160 °C, the drying time is 11 - 13 h, and the product is alternately washed 2 - 4 times with water and 2 - 4 times with alcohol.

6. The preparation method of the cobalt-doped and synergistically MXene-coated sodium vanadate composite powder according to claim 1, wherein, The vacuum drying conditions in step 5 are as follows: 50 - 70 °C, dry for 11 - 13 h, seal the product of step 4 with plastic wrap before vacuum drying, and then make holes in the plastic wrap.

7. Application of the cobalt-doped and MXene-coated sodium vanadate composite powder according to any one of claims 1 - 6 in the field of sodium-ion batteries.

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