Positive electrode active material and preparation method and application thereof

Abstract

The present application provides a positive electrode active material, which includes at least one sheet structure, the sheet structure includes a plurality of particles, the particles include a composite and a carbon layer encapsulating the composite, the composite including vanadium trioxide and vanadium carbide. The heterogeneous structure formed by vanadium trioxide and vanadium carbide accelerates the electron and ion transport within the particles, the construction of vanadium carbide and carbon layer can also significantly improve the conductivity, and the sheet structure also shortens the ion transport path, thereby obtaining a positive electrode active material with excellent rate performance, high reversible capacity and long cycle life. The present application also provides a preparation method and application of the positive electrode active material.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to positive electrode active materials, preparation methods, and applications thereof. Background Art

[0002] Zinc-ion batteries (Zn-ion batteries) have attracted widespread attention due to their low redox potential, high specific capacity, and low cost. Vanadium-based oxides, with their multi-electron redox chemistry, offer potential for the fabrication of high-energy-density Zn-ion batteries. However, the difficulty in rapidly storing zinc ions within vanadium-based oxides has limited their use in Zn-ion batteries. Summary of the Invention

[0003] In view of this, the present application provides a positive electrode active material and a preparation method thereof, a positive electrode and a zinc ion battery. The positive electrode active material has excellent rate performance, reversible capacity and cycle life, which is conducive to its application in batteries.

[0004] In a first aspect, the present application provides a positive electrode active material, comprising at least one sheet structure, wherein the sheet structure comprises a plurality of particles, wherein the particles comprise a composite and a carbon layer wrapping the composite, wherein the composite comprises vanadium trioxide and vanadium carbide.

[0005] Optionally, a plurality of the sheet-like structures form a flower cluster.

[0006] Furthermore, the lateral size of the flower cluster is 3 μm-5 μm.

[0007] Optionally, the sheet-like structure has through holes, and further, the through holes have a diameter of 0.8 nm to 8 nm.

[0008] Optionally, the thickness of the sheet structure is 20nm-40nm.

[0009] Optionally, the width of the sheet structure is 0.8 μm-1.2 μm.

[0010] In second aspect, the present application provides a method for preparing a positive electrode active material, comprising: adding a vanadium salt and a carbon source to an ethanol solution to form a mixed solution, wherein the carbon source includes at least one of trimesic acid and terephthalic acid, and the volume ratio of ethanol to water in the ethanol solution is 1.8-2.1; the mixed solution is heated to obtain a precursor; under an inert atmosphere, the precursor is calcined to obtain a positive electrode active material, the calcination temperature is 720°C-850°C, and the calcination time is greater than or equal to 8h, the positive electrode active material includes at least one flaky structure, the flaky structure includes a plurality of particles, the particles include a composite and a carbon layer wrapping the composite, and the composite includes vanadium trioxide and vanadium carbide.

[0011] Optionally, the heating temperature is 150° C.-180° C., and the heating time is 18 h-30 h.

[0012] Optionally, the mass concentration of the vanadium salt in the mixed solution is 8.6 g / L-9.8 g / L.

[0013] Optionally, the mass concentration of the carbon source in the mixed solution is 5.2 g / L-5.8 g / L.

[0014] Optionally, the vanadium salt includes at least one of vanadium acetylacetonate, vanadyl acetylacetonate and vanadium chloride.

[0015] In a third aspect, the present application provides a positive electrode, comprising the positive electrode active material described in the first aspect or the positive electrode active material prepared by the preparation method described in the second aspect.

[0016] In a fourth aspect, the present application provides a zinc ion battery comprising the positive electrode described in the third aspect.

[0017] The positive electrode active material provided by the present application has particles of carbon-coated vanadium trioxide and vanadium carbide. The heterogeneous structure formed by vanadium trioxide and vanadium carbide accelerates the electron and ion transport of zinc ions inside the particles. The arrangement of vanadium carbide and carbon layer can significantly improve the conductivity, and the sheet structure shortens the ion transport path, thereby obtaining a positive electrode active material with excellent rate performance, high reversible capacity and long cycle life. The preparation method of the positive electrode active material is simple, easy to operate, low in preparation cost and high in preparation efficiency, which is conducive to the use of the positive electrode active material. The positive electrode and zinc ion electrons with the positive electrode active material have excellent electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] Figure 1 A method for preparing a positive electrode active material is provided in one embodiment of the present application.

[0020] Figure 2 This is a microscopic morphology of the positive electrode active material prepared in Example 1.

[0021] Figure 3 The X-ray diffraction results of the positive electrode active materials prepared in Example 1 and Comparative Example 1 are shown.

[0022] Figure 4 The Raman spectra of the positive electrode active materials prepared in Example 1 and Comparative Example 1 are shown.

[0023] Figure 5 This is the rate performance test result diagram.

[0024] Figure 6 This is the cycle performance test result diagram. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0026] The present application provides a positive electrode active material, the positive electrode active material includes at least one sheet structure, the sheet structure includes a plurality of particles, the particles include a composite and a carbon layer wrapped around the composite, the composite including vanadium trioxide and vanadium carbide. In the present application, the positive electrode active material contains vanadium trioxide, vanadium trioxide has a high specific capacity (theoretical specific capacity is 715mAh / g), and the heterogeneous structure formed by vanadium trioxide and vanadium carbide accelerates the electron and ion transport of zinc ions inside the particles, solving the problem that existing zinc ions cannot be quickly stored inside vanadium-based oxides, and the carbon layer and metal-like vanadium carbide can improve its conductivity, and multiple particles form a sheet structure, and the setting of the two-dimensional sheet structure can shorten the transmission path of ions, so that the rate performance, high reversible capacity and long cycle life of the positive electrode active material can be significantly improved, which is beneficial to the use of the positive electrode active material in the positive electrode and zinc ion battery.

[0027] In the present application, a plurality of particles are stacked or assembled to form a sheet structure, and the positive electrode active material may have one or more sheet structures. In an embodiment of the present application, the thickness of the sheet structure is 20nm-40nm, and the width is 0.8μm-1.2μm. The sheet structure of the above size is more conducive to shortening the ion transmission path, while ensuring the stability of the overall structure, preventing collapse, and improving service life. Specifically, the thickness of the sheet structure may be, but is not limited to, 20nm, 23nm, 25nm, 27nm, 30nm, 24nm, 35nm, 36nm or 40nm, and the width may be, but is not limited to, 0.8μm, 0.85μm, 0.9μm, 0.95μm, 1μm, 1.1μm, 1.15μm or 1.2μm. In one embodiment, the thickness of the sheet structure is 20nm-30nm, and the width is 0.8μm-1μm. In another embodiment, the thickness of the sheet-like structure is 30 nm to 40 nm, and the width is 1 μm to 1.2 μm. In yet another embodiment, the thickness of the sheet-like structure is 25 nm to 35 nm, and the width is 0.9 μm to 1.1 μm.

[0028] In an embodiment of the present application, the sheet structure has a through hole. In this way, it is beneficial to the contact between the positive electrode active material and the electrolyte, and can also relieve the stress generated in the electrochemical process. In one embodiment, the pore size of the through hole is 0.8nm-8nm. It is beneficial to relieve the stress generated in the electrochemical process and ensure the structural stability of the positive electrode active material. Specifically, the pore size of the through hole can be, but is not limited to, 0.8nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 4nm, 5nm, 6nm, 7nm or 8nm. In one embodiment, the pore size of the through hole is 1nm-3nm. In another embodiment, the pore size of the through hole is 3nm-5nm. In yet another embodiment, the pore size of the through hole is 5nm-8nm.

[0029] In an embodiment of the present application, a plurality of sheet structures form a flower cluster. It is understandable that a plurality of particles in the positive electrode active material are assembled to form a two-dimensional sheet structure, wherein some sheet structures self-assemble to form a flower cluster, and the number of flower clusters is not limited. The flower cluster formed increases the distribution density of particles in the positive electrode active material, which is beneficial to improving the electrochemical properties of the positive electrode active material. In an embodiment of the present application, the lateral dimension of the flower cluster is 3μm-5μm. Among them, the lateral dimension is the maximum distance between any two points in the flower cluster. Specifically, the lateral dimension of the flower cluster can be, but is not limited to, 3μm, 3.3μm, 3.5μm, 3.7μm, 4μm, 4.2μm, 4.5μm or 5μm, etc.

[0030] This application also provides a method for preparing a positive electrode active material, which can be used to prepare the positive electrode active material in any of the above embodiments. Figure 1, a method for preparing a positive electrode active material provided in one embodiment of the present application, comprising:

[0031] S101: adding a vanadium salt and a carbon source to an ethanol solution to form a mixed solution, wherein the carbon source comprises at least one of trimesic acid and terephthalic acid, and the volume ratio of ethanol to water in the ethanol solution is 1.8-2.1.

[0032] S102: The mixed solution is heated to obtain a precursor.

[0033] S103: Under an inert atmosphere, calcining the precursor to obtain a positive electrode active material, the calcination temperature is 720°C-850°C, and the calcination time is greater than or equal to 8 hours. The positive electrode active material includes at least one flaky structure, the flaky structure includes a plurality of particles, the particles include a composite and a carbon layer wrapping the composite, and the composite includes vanadium trioxide and vanadium carbide.

[0034] In S101, a vanadium salt and a carbon source are mixed to form a mixed solution, wherein the carbon source includes at least one of trimesic acid and terephthalic acid. At least one of the trimesic acid and terephthalic acid can be complexed with the vanadium salt during heating to form a precursor. In the present application, an ethanol solution is used for mixing, and the volume ratio of ethanol to water in the ethanol solution is 1.8-2.1. The inventors have found that the ethanol solution formed by mixing in the above ratio is conducive to the uniform dispersion of the vanadium salt and the carbon source, while also ensuring the formation of particles and flaky structures in the positive electrode active material. Specifically, the volume ratio of ethanol to water in the ethanol solution can be, but is not limited to, 1.8, 1.85, 1.9, 1.96, 2, 2.05, or 2.1, etc.

[0035] In an embodiment of the present application, the mixing temperature may be 60° C. to 85° C., and the mixing time may be 0.5 h to 3 h, which is more conducive to uniform dispersion of the components in the mixed solution. Specifically, the mixing temperature may be, but is not limited to, 60° C., 62° C., 65° C., 70° C., 75° C., 79° C., 80° C., 83° C., or 85° C., and the mixing time may be, but is not limited to, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, or 3 h.

[0036] In the present application, the vanadium salt can be uniformly dispersed in the mixed solution. In an embodiment of the present application, the vanadium salt includes at least one of vanadium acetylacetonate, vanadium oxyacetylacetonate and vanadium chloride. The above-mentioned vanadium salt can be dispersed in the mixed solution more quickly. In an embodiment of the present application, the mass concentration of the vanadium salt in the mixed solution can be 8.6g / L-9.8g / L, which is conducive to the formation of the precursor. Specifically, the mass concentration of the vanadium salt in the mixed solution can be, but is not limited to, 8.6g / L, 8.8g / L, 9g / L, 9.1g / L, 9.3g / L, 9.5g / L, 9.6g / L or 9.8g / L, etc. In one embodiment, the mass concentration of the vanadium salt in the mixed solution can be 8.6g / L-9.2g / L. In another embodiment, the mass concentration of the vanadium salt in the mixed solution can be 9.2g / L-9.8g / L.

[0037] In an embodiment of the present application, the mass concentration of the carbon source in the mixed solution may be 5.2 g / L-5.8 g / L, which is conducive to the formation of the precursor. Specifically, the mass concentration of the carbon source in the mixed solution may be, but is not limited to, 5.2 g / L, 5.3 g / L, 5.4 g / L, 5.5 g / L, 5.6 g / L, 5.7 g / L or 5.8 g / L. In one embodiment, the mass concentration of the carbon source in the mixed solution may be 5.2 g / L-5.5 g / L. In another embodiment, the mass concentration of the carbon source in the mixed solution may be 5.5 g / L-5.8 g / L.

[0038] In an embodiment of the present application, the molar ratio of the vanadium salt to the carbon source in the mixed solution is 1-1.8, which is more conducive to the formation of the precursor. Specifically, the molar ratio of the vanadium salt to the carbon source in the mixed solution can be, but is not limited to, 1, 1.05, 1.2, 1.4, 1.5, 1.6, 1.7, or 1.8.

[0039] In S102 , the components in the mixed solution are heated to cause complexation and other reactions to form a precursor precipitate.

[0040] In an embodiment of the present application, the heating temperature may be 150°C-180°C, and the heating time may be 18h-30h. In this way, it is more conducive to the complexation between the components in the mixed solution to form a precursor precipitate. Specifically, the heating temperature may be, but is not limited to, 150°C, 157°C, 160°C, 163°C, 170°C, 175°C or 180°C, and the heating time may be, but is not limited to, 18h, 20h, 22h, 25h, 27h, or 30h. In one embodiment, the heating temperature may be 150°C-165°C, and the heating time may be 25h-30h. In another embodiment, the heating temperature may be 160°C-170°C, and the heating time may be 20h-25h. In yet another embodiment, the heating temperature may be 170°C-180°C, and the heating time may be 18h-25h. The mixed solution may be placed in an oven for heating. Specifically, the mixed solution may be placed in a kettle and then heated in an oven.

[0041] In an embodiment of the present application, the precursor may also be cleaned and dried to remove the mixed liquid on the surface of the precursor and avoid the generation of impurities during the calcination process. In one embodiment, drying may include drying at 50°C-80°C for 8h-15h. Specifically, the drying temperature may be, but is not limited to, 50°C, 57°C, 60°C, 63°C, 65°C, 70°C, 75°C, 77°C or 80°C, and the drying time may be, but is not limited to, 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h, etc. In a specific embodiment, ethanol or water may be used for one or more cleanings and then dried.

[0042] In S103, the positive electrode active material is obtained by calcining the precursor, and the calcination process is carried out under an inert atmosphere to avoid the generation of impurities. At the same time, the calcination temperature and time are controlled to obtain a complex formed by vanadium trioxide and vanadium carbide and a carbon layer coating the complex.

[0043] In an embodiment of the present application, the inert atmosphere may include at least one of argon, nitrogen, and helium.

[0044] In the present application, the calcination temperature is 720°C-850°C, and the calcination time is greater than or equal to 8 hours, so as to ensure the formation of a composite of vanadium trioxide and vanadium carbide and the formation of a carbon layer coating the composite. The inventors have found that if the calcination temperature is too low and the time is too short, the composite heterostructure of vanadium trioxide and vanadium carbide cannot be formed and the carbon layer coating cannot be formed. If the calcination temperature is too high, excessive carbonization will occur and a composite of vanadium trioxide and vanadium carbide cannot be obtained. Specifically, the calcination temperature can be, but is not limited to, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C or 850°C. In one embodiment, the calcination temperature can be 720°C-760°C. In another embodiment, the calcination temperature can be 760°C-810°C. In another embodiment, the calcination temperature can be 800°C-850°C. In one embodiment of the present application, the calcination time is 8 hours-10 hours, which is more conducive to obtaining the positive electrode active material and avoiding excessive carbonization. Specifically, the calcination time can be, but is not limited to, 8 hours, 8.5 hours, 9 hours, 9.5 hours, or 10 hours.

[0045] The preparation method of the positive electrode active material provided in the present application is simple and easy to operate, and can realize the industrialized production of the positive electrode active material, which is conducive to the use of the positive electrode active material in batteries.

[0046] The present application also provides a positive electrode comprising the positive electrode active material of any of the above embodiments. The positive electrode comprising the above positive electrode active material has excellent rate performance, reversible capacity and cycle life.

[0047] In an embodiment of the present application, the positive electrode includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material. In one embodiment of the present application, the positive electrode active material layer also includes at least one of a conductive agent and a binder. Specifically, the conductive agent may include, but is not limited to, at least one of carbon black, carbon nanotubes, carbon fibers, graphene, and graphite, and the binder may include, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose, and epoxy resin. In one embodiment, the content of the positive electrode active material in the positive electrode active material layer may be 65wt%-90wt%, the content of the conductive agent may be 5wt%-20wt%, and the content of the binder may be 5wt%-15wt%, which is beneficial to improving the electrochemical performance of the positive electrode.

[0048] In an embodiment of the present application, the positive electrode further comprises a positive electrode current collector, and the positive electrode active material is disposed on the surface of the positive electrode current collector. Furthermore, the positive electrode active material layer is disposed on the surface of the positive electrode current collector. Specifically, the material of the positive electrode current collector may include, but is not limited to, titanium or stainless steel.

[0049] The present application also provides a zinc ion battery comprising the positive electrode in any of the above embodiments. The zinc ion battery having the above positive electrode has excellent electrochemical performance, especially high energy density and high power density, which is beneficial to the use of the zinc ion battery.

[0050] In embodiments of the present application, the zinc ion battery may further include a negative electrode. In embodiments of the present application, the negative electrode may include a zinc electrode sheet or a zinc alloy electrode sheet. This negative electrode has low cost, a low redox potential, and a high specific capacity, which is beneficial for improving the electrochemical performance of the zinc ion battery. For example, the zinc negative electrode has a low redox potential (-0.76V vs. standard hydrogen electrode) and a high specific capacity (820mAh / g).

[0051] In an embodiment of the present application, the zinc ion battery may further include a separator. In an embodiment of the present application, the separator may be disposed between the positive electrode and the negative electrode. In an embodiment of the present application, the separator is made of at least one of glass fiber, cellulose, polyethylene, and polypropylene.

[0052] In one embodiment of the present application, the zinc ion battery may further include an electrolyte, wherein the electrolyte is an aqueous solution of an electrolyte, wherein the electrolyte includes a water-soluble zinc salt. In other words, the zinc ion battery is an aqueous zinc ion battery. Aqueous zinc ion batteries have high ionic conductivity and are environmentally friendly, making them more suitable for use. In one embodiment of the present application, the water-soluble zinc salt includes at least one of zinc sulfate, zinc chloride, zinc nitrate, bistrifluoromethylsulfonyl imide zinc, zinc trifluoromethanesulfonate, zinc phenolsulfonate, zinc gluconate, and zinc acetate. In another embodiment of the present application, the zinc ion battery may further include a solid electrolyte. In other words, the zinc ion battery is a solid-state zinc ion battery.

[0053] The effects of the positive electrode active material provided in this application are further illustrated below through specific examples.

[0054] Example 1

[0055] 289 mg of vanadium acetylacetonate and 168 mg of trimesic acid were added to 30 mL of ethanol solution (ethanol to deionized water, volume ratio 2:1) and stirred at 80°C for 1 hour to form a green solution. The solution was then transferred to a stainless steel autoclave containing 50 mL of polytetrafluoroethylene and heated in an oven at 180°C for 24 hours. The green precursor precipitate was collected, washed three times with 60 mL of ethanol, and dried at 60°C for 12 hours. The dried powder precursor was calcined at 750°C under an argon atmosphere for 8 hours to obtain a positive electrode active material. The positive electrode active material comprises a sheet structure formed by multiple particles. The particles comprise a composite and a carbon layer surrounding the composite. The composite comprises vanadium trioxide and vanadium carbide.

[0056] The micromorphology of the positive electrode active material was characterized by field emission scanning microscopy. Figure 2 As shown, it can be seen that the positive electrode active material includes a plurality of particles, and the plurality of particles form a two-dimensional sheet structure, the sheet structure has through holes, and part of the two-dimensional sheet structure is assembled to form a flower cluster.

[0057] Example 2

[0058] Vanadyl acetylacetonate and trimesic acid were added to an ethanol solution (the volume ratio of ethanol to deionized water was 1.8) and stirred at 75°C for 2 hours to form a mixed solution. The mass concentration of vanadyl acetylacetonate in the mixed solution was 8.7g / L and the mass concentration of trimesic acid was 5.3g / L. The mixed solution was placed in an autoclave and heated in an oven at 165°C for 20 hours. The precursor was collected and washed and dried. The dried precursor was calcined at 800°C for 10 hours under an argon atmosphere to obtain a positive electrode active material. The positive electrode active material includes multiple particles, the particles include a composite and a carbon layer wrapping the composite. The composite material includes vanadium trioxide and vanadium carbide. Multiple particles accumulate to form a sheet structure (thickness of about 25nm, width of about 1μm), and some sheet structures accumulate to form a flower cluster (lateral size of about 3.5μm).

[0059] Example 3

[0060] Vanadium chloride and terephthalic acid were added to an ethanol solution (the volume ratio of ethanol to deionized water was 2.1) and stirred at 65°C for 2 hours to form a mixed solution. The mass concentration of vanadium chloride in the mixed solution was 9.75g / L and the mass concentration of terephthalic acid was 5.75g / L. The mixed solution was placed in an autoclave and heated in an oven at 150°C for 26 hours. The precursor was collected, cleaned, and dried. The dried precursor was calcined at 820°C under an argon atmosphere for 9 hours to obtain a positive electrode active material. The positive electrode active material includes multiple particles, the particles including a composite and a carbon layer surrounding the composite. The composite material includes vanadium trioxide and vanadium carbide. The multiple particles are stacked to form a sheet structure (thickness approximately 32nm, width approximately 1.1μm), the sheet structure has through holes (pore diameter approximately 2nm), and the sheet structure is stacked to form multiple flower clusters (lateral size approximately 4.7μm).

[0061] Comparative Example 1

[0062] The method is substantially the same as Example 1, except that the powder precursor is calcined at 750° C. for 2 h under an argon atmosphere to obtain a positive electrode active material having vanadium trioxide (V 2 O 3 @C) particles coated with a carbon layer.

[0063] The positive electrode active materials prepared in Example 1 and Comparative Example 1 were subjected to X-ray diffractometer and Raman spectrometer tests. Figure 3As shown in FIG. 1 , the X-ray diffraction results of the positive electrode active materials prepared in Example 1 and Comparative Example 1 are shown. It can be seen that the positive electrode active material prepared in Example 1 contains V2O3 and VC, while the positive electrode active material prepared in Comparative Example 1 contains V2O3 but no VC. Figure 4 The following are Raman spectra of the positive electrode active materials prepared in Example 1 and Comparative Example 1. Characterizing the carbon material in the positive electrode active materials prepared in Example 1 and Comparative Example 1, the Raman spectra show D and G peaks, indicating that the positive electrode active materials prepared in Example 1 and Comparative Example 1 contain carbon material. Therefore, based on the X-ray diffractometer and Raman spectrometer test results, it can be determined that the positive electrode active material prepared in Example 1 contains V2O3, VC, and carbon.

[0064] The positive electrode active materials of Example 1 and Comparative Example 1 were mixed with conductive carbon black and a binder in a mass ratio of 7:2:1 to form a uniform slurry. The slurry was applied to a titanium foil current collector using a coating machine. Finally, the slurry was transferred to a vacuum drying oven at 70°C and dried for more than 12 hours to obtain the positive electrode. 3M zinc trifluoromethanesulfonate was selected as the electrolyte, metal zinc foil as the negative electrode (diameter 14mm), and porous fiber as the separator (diameter 17mm). Subsequently, button-type CR2032 zinc-ion batteries were assembled in an atmospheric environment in the order of negative electrode shell, spring, gasket, zinc foil, electrolyte, separator, electrolyte, positive electrode, and positive electrode shell (packaging pressure: ~7.5MPa). The assembled batteries were subjected to electrochemical performance testing on a blue electric test system. The main test parameters are as follows: voltage window: 0.2V-1.7V, current density of cycle performance test: 30A / g, current density of rate performance test is 1A / g, 3A / g, 5A / g, 10A / g, 30A / g, 60A / g and 100A / g. Figure 5 As shown in the figure, it is a graph of rate performance test results. It can be seen that the electrode containing the positive electrode active material of Example 1 shows a specific capacity of up to 244.3mAh / g at 100A / g; when returning from low current density to high current density (1A / g, 3A / g, 5A / g, 10A / g, 30A / g, 60A / g and 100A / g), it also shows excellent rate performance. However, the electrode containing the positive electrode active material prepared in Comparative Example 1 only shows a specific capacity of about 29mAh / g at 100A / g. Therefore, the rate performance of the positive electrode active material prepared in Example 1 is significantly better than the rate performance of the positive electrode active material prepared in Comparative Example 1. Figure 6 As shown in the figure, which is the cycle performance test result diagram, the electrode containing the positive electrode active material of Example 1 can still obtain a high specific capacity retention rate of 75% and a high reversible capacity of 284 mAh / g after 1600 cycles at a large current density of 60 A / g, indicating that it still has a stable cycle life at a large current density.

[0065] Therefore, the positive electrode active material provided in the present application can have excellent rate performance, reversible capacity and cycle life, can significantly improve the electrochemical performance of the positive electrode and the zinc ion battery, and is beneficial to the use of the zinc ion battery.

[0066] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A positive electrode active material, characterized in that The positive electrode active material includes at least one sheet structure, the sheet structure includes a plurality of particles, the particles include a composite and a carbon layer wrapping the composite, the composite includes a heterojunction formed of vanadium trioxide and vanadium carbide; The preparation of the positive electrode active material includes: adding a vanadium salt and a carbon source to an ethanol solution to form a mixed solution, heating the mixed solution to obtain a precursor, and calcining the precursor under an inert atmosphere to obtain the positive electrode active material, wherein the calcination temperature is 720°C-850°C and the calcination time is greater than or equal to 8 hours.

2. The positive electrode active material according to claim 1, wherein A plurality of the sheet-like structures form a flower cluster.

3. The positive electrode active material according to claim 2, wherein The lateral size of the flower cluster is 3 μm-5 μm.

4. The positive electrode active material according to claim 1, wherein The sheet structure has through holes, and the diameter of the through holes is 0.8 nm to 8 nm.

5. The positive electrode active material according to claim 1, wherein The sheet structure has a thickness of 20 nm to 40 nm and a width of 0.8 μm to 1.2 μm.

6. A method for preparing a positive electrode active material, characterized in that: include: The vanadium salt and the carbon source are added to an ethanol solution to form a mixed solution, wherein the carbon source comprises at least one of trimesic acid and terephthalic acid, and the volume ratio of ethanol to water in the ethanol solution is 1.8-2.1; The mixed solution is heated to obtain a precursor; The precursor is calcined under an inert atmosphere to obtain a positive electrode active material, the calcination temperature is 720°C-850°C, the calcination time is greater than or equal to 8 hours, the positive electrode active material includes at least one flaky structure, the flaky structure includes a plurality of particles, the particles include a composite and a carbon layer wrapping the composite, the composite includes vanadium trioxide and vanadium carbide.

7. The preparation method according to claim 6, wherein The heating temperature is 150° C.-180° C., and the heating time is 18 h-30 h.

8. The preparation method according to claim 6, wherein The mass concentration of the vanadium salt in the mixed solution is 8.6 g / L-9.8 g / L, and the mass concentration of the carbon source is 5.2 g / L-5.8 g / L; The vanadium salt includes at least one of vanadium acetylacetonate, vanadyl acetylacetonate and vanadium chloride.

9. A positive electrode, characterized in that The invention comprises the positive electrode active material according to any one of claims 1 to 5 or the positive electrode active material prepared by the preparation method according to any one of claims 6 to 8.

10. A zinc ion battery, characterized in that: Comprising the positive electrode according to claim 9.

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