VO2 positive electrode material for aqueous zinc ion battery and preparation method of VO2 positive electrode material

Abstract

The invention discloses a VO2 positive electrode material for an aqueous zinc ion battery and a preparation method, and the preparation method specifically comprises the following steps: step 1, weighing 5g of urea, dissolving in 6ml of deionized water, adding ammonium metavanadate after the urea is dissolved, and stirring to obtain a mixed solution; step 2, pouring the mixed solution into a crucible, drying to obtain a faint yellow solid, and grinding and sieving the solid to obtain precursor powder; 3, sequentially carrying out annealing reaction and water bath reduction treatment on the precursor powder to obtain pure-phase VO2; and step 4, grinding and mixing conductive carbon black, polyvinylidene fluoride and the pure-phase VO2 obtained in the step 3, and adding N-methyl pyrrolidone while grinding to obtain the VO2 positive electrode material. According to the invention, the capacity of the water-based zinc ion battery is improved, and meanwhile, the cycling stability of the water-based zinc ion battery is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of positive electrode materials for aqueous zinc ion batteries, and in particular relates to VO2 positive electrode materials for aqueous zinc ion batteries and a preparation method thereof. Background Art

[0002] With the increasing demand for sustainable energy, zinc-ion batteries have become a research hotspot for replacing lithium-ion batteries due to their high safety and low cost. The positive electrode material is one of the key factors that determine the performance of zinc-ion batteries. However, the positive electrode materials of existing aqueous zinc-ion batteries generally face the problems of low capacity and poor cycle stability. Common manganese-based, cobalt-based and other materials, due to the volume expansion and structural changes of the materials during long-term cycles, lead to battery capacity decay and short cycle life.

[0003] As a transition metal oxide, VO2 exhibits good conductivity and capacity stability in lithium-ion batteries. VO2 has reversible phase change characteristics and can maintain good structural stability under different charge and discharge conditions, so it is widely studied in the battery field. Although VO2 has certain advantages in other types of batteries, in aqueous zinc-ion batteries, VO2 still faces problems such as low ion diffusion rate, poor compatibility with zinc ions, and insufficient battery cycle performance. Therefore, how to effectively improve the capacity and cycle stability of VO2 materials in aqueous zinc-ion batteries has become a hot topic in current research.

[0004] At present, the main methods for synthesizing vanadium oxide are hydrothermal / solvent method, sol-gel method and solid phase method. The solid phase method is to obtain VO2 material by mixing a vanadium source with an oxidant or a reductant and then reacting it at high temperature in a solid phase reaction; this method is suitable for mass production and can provide a higher yield. In response to the problem of low capacity and poor cycle stability of VO2 material in aqueous zinc ion batteries, CN110627122A discloses a method for preparing VO2 phase change material by a solid phase method, in which V2O5, V2O3 and sulfuric acid are evenly mixed, and under the protection of argon, VOSO4 is first reacted to generate VOSO4, and then VOSO4 is decomposed to obtain VO2. CN109536748A synthesizes high-purity VO2 by a solid phase method and applies it to aqueous zinc ion batteries to improve the capacity and cycle stability of the battery. The method selects vanadium source (V2O5) and zinc source (ZnSO4) as raw materials, and performs a solid phase reaction between 450°C and 750°C to obtain VO2 material with an ideal crystal structure.

[0005] Although the solid phase method has the advantages of simple operation and low equipment requirements, the uniformity of the prepared materials is poor and needs further optimization. Therefore, how to prepare aqueous zinc ion battery positive electrode materials with good uniformity, high capacity and excellent cycle stability has become a key issue that needs to be solved urgently. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a VO2 positive electrode material for an aqueous zinc ion battery, thereby increasing the capacity of the aqueous zinc ion battery and improving the cycle stability of the aqueous zinc ion battery.

[0007] Another object of the present invention is to provide a VO2 positive electrode material for aqueous zinc ion batteries.

[0008] The technical solution adopted by the present invention is a method for preparing a VO2 positive electrode material for an aqueous zinc ion battery, which specifically comprises the following steps: Step 1, weigh 5g of urea and dissolve it in 6ml of deionized water, and after the urea is dissolved, add ammonium metavanadate and stir to obtain a mixed solution; Step 2, pouring the mixed solution into a crucible for drying to obtain a light yellow solid, and grinding and sieving the solid to obtain a precursor powder; Step 3, annealing the precursor powder and performing water bath reduction treatment in sequence to obtain pure phase VO2; Step 4, grinding and mixing the conductive carbon black, polyvinylidene fluoride and the pure phase VO2 of step 3, adding N-methylpyrrolidone while grinding to obtain VO2 positive electrode material.

[0009] The present invention is also characterized in that In step 1, the mass ratio of urea to ammonium metavanadate is 1:1-1.15, and the stirring to obtain the mixed solution is specifically stirring at a temperature of 60°C-80°C for 1h-2h.

[0010] The drying process in step 2 is specifically drying in air at 60°C to 80°C for 8h to 10h.

[0011] In step 2, an agate mortar is used for grinding, and the sieve opening is 200 mesh.

[0012] The annealing reaction in step 3 specifically includes the following steps: Step 3.1, evenly spread the precursor powder in the Al2O3 crucible, then tightly wrap the entire crucible with tin foil, cover the crucible with a lid, and further wrap and seal it with tin foil; Step 3.2, placing the crucible in a muffle furnace, and performing high temperature annealing from room temperature to 500°C~600°C at a heating rate of 2°C / min~5°C / min for 4h~6h; Step 3.3, after annealing is completed, cool naturally to room temperature.

[0013] The water bath reduction treatment in step 3 specifically includes the following steps: Step 3.4, weighing a hydrazine hydrate ethanol solution prepared from hydrazine hydrate and anhydrous ethanol; Step 3.5, immersing the VO2 powder after annealing in step 3.3 in a hydrazine hydrate ethanol solution for reduction for 12h~48h to obtain a VO2 precipitate; Step 3.6, wash the VO2 precipitate by centrifugation with anhydrous ethanol for 3 to 5 times, and then dry it in an oven at 60°C to 80°C for 10h to 12h to obtain pure VO2.

[0014] The volume ratio of hydrazine hydrate to anhydrous ethanol is 1:10-20; the mass ratio of VO2 to hydrazine hydrate ethanol solution is 1:50-100.

[0015] The mass ratio of conductive carbon black, polyvinylidene fluoride and pure phase VO2 is 1:2~1:7~8.

[0016] The technical solution adopted by the present invention is that the VO2 positive electrode material for aqueous zinc ion batteries is prepared by the above-mentioned preparation method of the VO2 positive electrode material for aqueous zinc ion batteries. The beneficial effects of the present invention are: (1) The preparation method of VO2 positive electrode material for aqueous zinc ion battery of the present invention adopts ammonium metavanadate (vanadium source) and urea (reducing agent) to act together during high temperature annealing. Urea decomposes during heating to release ammonia and carbon dioxide, and has a reducing effect. Urea reacts with the vanadium source to convert vanadium from a high valence state (such as V 5 ⁺) is reduced to a low valence state (such as V 4 ⁺), thereby promoting the production of VO2.

[0017] (2) The VO2 nanoparticles prepared by the present invention have a smaller particle size and a larger specific surface area, which provides more electrochemical active sites for the positive electrode material of aqueous zinc ion batteries. With the optimization of the annealing process, the VO2 particles can maintain good conductivity, enhance the kinetics of zinc ion insertion / extraction, and significantly improve the capacity and power density of the battery.

[0018] At the same time, the structural stability of the prepared VO2 positive electrode material is effectively improved. The VO2 material can maintain structural stability during repeated charge and discharge, avoiding performance degradation caused by particle agglomeration or volume expansion. In addition, the redox properties of VO2 can optimize the insertion / deinsertion reaction of zinc ions, further improving the cycle life of the battery.

[0019] (3) The method for preparing the VO2 positive electrode material for aqueous zinc ion batteries of the present invention uses ammonium metavanadate and urea as raw materials, and synthesizes VO2 by annealing reaction in air and reduction in a water bath. The process is simple and easy to industrialize. In addition, the raw materials of ammonium metavanadate and urea are widely available and of low cost, which helps to reduce the cost of battery manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic flow chart of a method for preparing a VO2 positive electrode material for an aqueous zinc ion battery of the present invention; Figure 2 This is a SEM image of VO2 prepared by using ammonium metavanadate and urea in a mass ratio of 1:1 according to the present invention; Figure 3 This is a SEM image of VO2 prepared by using ammonium metavanadate and urea in a mass ratio of 1:2 according to the present invention; Figure 4 This is a SEM image of VO2 prepared by using ammonium metavanadate and urea in a mass ratio of 1:4 according to the present invention; Figure 5 This is a SEM image of VO2 prepared by using ammonium metavanadate and urea in a mass ratio of 1:6; Figure 6 This is an XRD diagram of VO2 prepared by the method for preparing VO2 positive electrode material for aqueous zinc ion battery of the present invention; Figure 7 It is a schematic diagram of the charge and discharge characteristics of the VO2 positive electrode material prepared by the present invention with a loading amount of 0.5 mg at 0.1 A / g; Figure 8 It is a schematic diagram of the charge and discharge characteristics of the VO2 positive electrode material prepared by the present invention with a loading of 1.3 mg at 0.1 A / g; Fig. 9 It is a schematic diagram of the charge and discharge characteristics of the VO2 positive electrode material prepared by the present invention with a loading amount of 0.5 mg at 2A / g; Fig.10 It is a schematic diagram of the charge and discharge characteristics of the VO2 positive electrode material prepared by the present invention with a loading of 1.3 mg at 2A / g. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0022] Example 1 The present invention provides a method for preparing a VO2 positive electrode material for an aqueous zinc ion battery, such as Figure 1 As shown, the specific steps include: Step 1, weigh 5g of urea and dissolve it in 6ml of deionized water, and after the urea is dissolved, add ammonium metavanadate and stir to obtain a mixed solution; Step 2, pouring the mixed solution into a crucible covered with plastic wrap for drying to obtain a light yellow solid, and grinding and sieving the solid to obtain a precursor powder; Step 3, annealing the precursor powder and performing water bath reduction treatment in sequence to obtain pure phase VO2; Step 4, grinding and mixing the conductive carbon black, polyvinylidene fluoride and the pure phase VO2 of step 3, adding N-methylpyrrolidone while grinding to obtain VO2 positive electrode material.

[0023] The prepared positive electrode material is coated on conductive carbon paper and dried at 60°C~100°C for 10h~12h to obtain a positive electrode of an aqueous zinc ion battery.

[0024] The present invention uses ammonium metavanadate (vanadium source) and urea (reducing agent) to work together during high temperature annealing. Urea decomposes during heating to release ammonia and carbon dioxide, and has a reducing effect. Urea reacts with the vanadium source to convert vanadium from a high valence state (such as V 5 ⁺) is reduced to a low valence state (such as V 4 ⁺), thereby promoting the production of VO2.

[0025] Example 2 The method for preparing a VO2 positive electrode material for an aqueous zinc ion battery of the present invention specifically comprises the following steps: Step 1, weigh 5g of urea and dissolve it in 6ml of deionized water, add ammonium metavanadate after the urea is dissolved, and stir at a temperature of 60°C to 80°C for 1h to 2h to obtain a mixed solution; Further, the mass ratio of urea to ammonium metavanadate is 1:(1-1.15); Step 2, pouring the mixed solution into a crucible covered with plastic wrap for drying to obtain a light yellow solid, then removing the plastic wrap, grinding the solid with an agate mortar and sieving to obtain a precursor powder, the sieve opening being 200 mesh; Furthermore, the drying process is specifically drying in air at 60°C to 80°C for 8h to 10h.

[0026] Step 3, annealing the precursor powder and performing water bath reduction treatment in sequence to obtain pure phase VO2; Step 4, grinding and mixing the conductive carbon black, polyvinylidene fluoride and the pure phase VO2 of step 3, adding N-methylpyrrolidone while grinding to obtain VO2 positive electrode material.

[0027] The mass ratio between conductive carbon black, polyvinylidene fluoride and pure phase VO2 is 1:(2~1):(7~8).

[0028] Example 3 On the basis of Example 2, the annealing reaction in step 3 of the method for preparing VO2 positive electrode material for aqueous zinc ion battery of the present invention specifically comprises the following steps: Step 3.1, evenly spread the precursor powder in the Al2O3 crucible, then tightly wrap the entire crucible with tin foil, cover the crucible with a lid, and further wrap and seal it with tin foil; Step 3.2, placing the crucible in a muffle furnace, and performing high temperature annealing from room temperature to 500°C~600°C at a heating rate of 2°C / min~5°C / min for 4h~6h; Step 3.3, after annealing is completed, cool naturally to room temperature.

[0029] Example 4 On the basis of Example 3, the water bath reduction treatment in step 3 of the method for preparing VO2 positive electrode material for aqueous zinc ion battery of the present invention specifically comprises the following steps: Step 3.4, weighing a hydrazine hydrate ethanol solution prepared from hydrazine hydrate and anhydrous ethanol; Step 3.5, immersing the VO2 powder after annealing in step 3.3 in a hydrazine hydrate ethanol solution for reduction for 12h~48h to obtain a VO2 precipitate; Step 3.6, wash the VO2 precipitate by centrifugation with anhydrous ethanol for 3 to 5 times, and then dry it in an oven at 60°C to 80°C for 10h to 12h to obtain pure VO2.

[0030] Furthermore, the volume ratio of hydrazine hydrate to anhydrous ethanol is 1:(10-20); the mass ratio of VO2 to hydrazine hydrate ethanol solution is 1:(50-100).

[0031] The VO2 positive electrode material for an aqueous zinc ion battery of the present invention is prepared by adopting the above-mentioned method for preparing the VO2 positive electrode material for an aqueous zinc ion battery.

[0032] Example 5 On the basis of Example 4, in this example, ammonium metavanadate and urea are prepared in a ratio of 1:1 to obtain a mixed solution, and then a positive electrode material is prepared based on the mixed solution, such as Figure 2 As shown in the SEM image of VO2 nanoparticles generated by annealing at high temperature using ammonium metavanadate and urea in a ratio of 1:1, it can be observed that the generated VO2 particles are evenly distributed and the particles are relatively dispersed, indicating that at this ratio, the VO2 nanoparticles are small in size, regular in morphology, and the agglomeration phenomenon between particles is relatively light. This result shows that the ratio of ammonium metavanadate and urea of ​​1:1 helps to obtain evenly distributed VO2 nanoparticles.

[0033] Comparative Example 1 On the basis of Example 5, the other preparation conditions were kept unchanged, and only the ratio of ammonium metavanadate to urea was changed. O2 nanoparticles were prepared using ammonium metavanadate to urea ratios of 1:2, 1:4 and 1:6, respectively. The SEM images of the prepared VO2 nanoparticles were as follows: Figure 3 , Figure 4 and Figure 5 shown.

[0034] like Figure 3 As shown in the figure, the SEM image of VO2 nanoparticles generated by high temperature annealing of ammonium metavanadate and urea at a ratio of 1:2 is shown. It can be seen that the particle size becomes larger, and the agglomeration between particles increases, and the particle distribution is not as uniform as when the ratio is 1:1. The degree of agglomeration is significantly aggravated, and the particle morphology and dispersion are poor.

[0035] like Figure 4 The figure shows the SEM image of VO2 nanoparticles generated by high temperature annealing of ammonium metavanadate and urea at a ratio of 1:4. At this ratio, the particle agglomeration phenomenon is more serious, the particle sizes are different, and the distribution is more uneven. The connectivity between the particles increases, resulting in a further decrease in the dispersion of the particles.

[0036] like Figure 5 As shown in the figure, the SEM image of VO2 nanoparticles generated by high temperature annealing of ammonium metavanadate and urea at a ratio of 1:6 is shown. The figure shows that the agglomeration phenomenon of VO2 particles at this ratio is more obvious, the particles are irregular, and the aggregates between particles are large, resulting in extremely uneven distribution of particles and large differences in particle size, which seriously affects the dispersion of the particles.

[0037] By comparing Example 5 with Comparative Example 1, i.e. different ratios of ammonium metavanadate and urea (1:1, 1:2, 1:4, 1:6), the dispersibility and agglomeration of VO2 nanoparticles can be intuitively observed through SEM images. As the urea ratio increases, the agglomeration of VO2 particles gradually intensifies, the distribution is uneven, and the particle size is irregular, indicating that the appropriate ratio of ammonium metavanadate and urea can effectively control the dispersibility and morphology of VO2 nanoparticles.

[0038] Example 6 The method for preparing a VO2 positive electrode material for an aqueous zinc ion battery of the present invention specifically comprises the following steps: Step 1, weigh 5g of urea and dissolve it in 6ml of deionized water, add ammonium metavanadate after the urea is dissolved, and stir at 70°C for 2h to obtain a mixed solution, wherein the mass ratio of urea to ammonium metavanadate is 1:1; Step 2, pouring the mixed solution into a crucible covered with plastic wrap, drying in air at 80°C for 8 hours to obtain a light yellow solid, and grinding and sieving the solid to obtain a precursor powder; Step 3, annealing the precursor powder and performing water bath reduction treatment in sequence to obtain pure phase VO2; Step 4, grind and mix the conductive carbon black, polyvinylidene fluoride and the pure phase VO2 of step 3, the mass ratio of the conductive carbon black, polyvinylidene fluoride and the pure phase VO2 is 1:2:7, and add N-methylpyrrolidone while grinding to obtain VO2 positive electrode material.

[0039] like Figure 6 As shown, the VO2 cathode material prepared in this embodiment is subjected to an X-ray diffraction (XRD) spectrum test, and the XRD spectrum shows typical diffraction peaks of VO2, indicating that the material has a good crystalline structure. This figure can be used to confirm the crystal phase of the VO2 cathode material and verify that it is pure phase VO2.

[0040] The prepared positive electrode material is then coated on a conductive carbon paper and dried at 100° C. for 10 h to obtain a positive electrode of an aqueous zinc ion battery.

[0041] Finally, button-type aqueous zinc-ion batteries were assembled using VO2 positive electrode, 12mm zinc foil negative electrode, ZnSO4 solution and glass fiber separator, and the specific capacity of the assembled batteries at different VO2 positive electrode material loadings was tested.

[0042] like Figure 7 As shown in the figure, when the VO2 positive electrode material loading is 0.5 mg, the specific capacity of the battery at a current density of 0.1 A / g is 850 mAh / g. This result shows that the VO2 material with a lower loading has a higher specific capacity, indicating that it has good electrochemical properties and efficient energy storage capacity. In addition, since the charge and discharge curves are almost the same, it further shows that the coulomb efficiency is close to 100%.

[0043] like Figure 8 As shown in the figure, when the VO2 positive electrode material loading is 1.3 mg, the specific capacity of the battery at a current density of 0.1 A / g is 493 mAh / g. Compared with the result when the loading is 0.5 mg, the specific capacity at a higher loading is reduced, which indicates that at a higher loading, the energy storage capacity of the battery is reduced, but it still has good electrochemical performance.

[0044] In addition, the charge and discharge performance of aqueous zinc-ion batteries with a VO2 positive electrode material loading of 0.5 mg at a current density of 2 A / g was tested. Fig. 9 As shown in the figure, after 200 cycles of activation, the specific capacity of the battery reached 760mAh / g; after 1000 cycles of activation, the specific capacity dropped to 575mAh / g. The data show that the battery with a VO2 loading of 0.5mg still maintains a high specific capacity after 200 charge and discharge cycles, indicating that it has good cycle stability and a long service life.

[0045] The charge and discharge performance of aqueous zinc-ion batteries with a VO2 cathode material loading of 1.3 mg at a current density of 2 A / g was tested. Fig.10 As shown in the figure, after 400 cycles of activation, the specific capacity is 243mAh / g; after 1000 cycles, the specific capacity is still maintained at 237mAh / g, and the capacity retention rate is 97.5%. This result shows that the battery with a VO2 loading of 1.3mg still exhibits excellent cycle stability and capacity retention at high current density, especially the capacity retention rate is close to 97.5%, showing its reliability in long-term use.

[0046] Figure 7~Figure 10 The charge and discharge performance of VO2 nanoparticles as positive electrode materials for aqueous zinc-ion batteries was demonstrated, and the specific capacity and cycle stability at different loadings and current densities were analyzed. Batteries with low loadings (such as 0.5 mg) can maintain a higher specific capacity at higher current densities, while batteries with higher loadings (such as 1.3 mg) show higher capacity retention and longer life in cycle tests.

[0047] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0048] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a VO2 positive electrode material for an aqueous zinc ion battery, characterized in that: The specific steps include: Step 1, weigh 5g of urea and dissolve it in 6ml of deionized water, and after the urea is dissolved, add ammonium metavanadate and stir to obtain a mixed solution; Step 2, pouring the mixed solution into a crucible for drying to obtain a light yellow solid, and grinding and sieving the solid to obtain a precursor powder; Step 3, annealing the precursor powder and performing water bath reduction treatment in sequence to obtain pure phase VO2; Step 4, grinding and mixing the conductive carbon black, polyvinylidene fluoride and the pure phase VO2 of step 3, adding N-methylpyrrolidone while grinding to obtain VO2 positive electrode material.

2. The method for preparing a VO2 cathode material for an aqueous zinc ion battery according to claim 1, wherein: In the step 1, the mass ratio of urea to ammonium metavanadate is 1:1-1.15, and the stirring to obtain the mixed solution is specifically stirring at a temperature of 60°C-80°C for 1h-2h.

3. The method for preparing a VO2 cathode material for an aqueous zinc ion battery according to claim 1, wherein: The drying process in step 2 is specifically drying in air at 60°C to 80°C for 8h to 10h.

4. The method for preparing a VO2 cathode material for an aqueous zinc ion battery according to claim 1, wherein: In step 2, an agate mortar is used for grinding, and the sieve opening is 200 meshes.

5. The method for preparing a VO2 cathode material for an aqueous zinc ion battery according to claim 1, wherein: The annealing reaction in step 3 specifically comprises the following steps: Step 3.1, evenly spread the precursor powder in the Al2O3 crucible, then tightly wrap the entire crucible with tin foil, cover the crucible with a lid, and further wrap and seal it with tin foil; Step 3.2, placing the crucible in a muffle furnace, and performing high temperature annealing from room temperature to 500°C~600°C at a heating rate of 2°C / min~5°C / min for 4h~6h; Step 3.3, after annealing is completed, cool naturally to room temperature.

6. The method for preparing a VO2 cathode material for an aqueous zinc ion battery according to claim 5, wherein: The water bath reduction treatment in step 3 specifically includes the following steps: Step 3.4, weighing a hydrazine hydrate ethanol solution prepared from hydrazine hydrate and anhydrous ethanol; Step 3.5, immersing the VO2 powder after annealing in step 3.3 in a hydrazine hydrate ethanol solution for reduction for 12h~48h to obtain a VO2 precipitate; Step 3.6, wash the VO2 precipitate by centrifugation with anhydrous ethanol for 3 to 5 times, and then dry it in an oven at 60°C to 80°C for 10h to 12h to obtain pure VO2.

7. The method for preparing a VO2 cathode material for an aqueous zinc ion battery according to claim 6, wherein: The volume ratio of the hydrazine hydrate to anhydrous ethanol is 1:10-20; the mass ratio of the VO2 to the hydrazine hydrate ethanol solution is 1:50-100.

8. The method for preparing a VO2 cathode material for an aqueous zinc ion battery according to claim 1, wherein: The mass ratio of the conductive carbon black, polyvinylidene fluoride and pure phase VO2 is 1:2-1:7-8.

9. A VO2 positive electrode material for an aqueous zinc ion battery, characterized in that: The VO2 positive electrode material for aqueous zinc ion batteries is prepared by the preparation method of any one of claims 1 to 8.

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