Cr / Fe co-doped K0. 5Mn4O8 material and preparation method thereof

Abstract

The invention discloses a Cr / Fe co-doped K0. 5Mn4O8 material and a preparation method thereof, and belongs to the field of inorganic materials. The method comprises the following steps: dissolving potassium dichromate, ferric nitrate nonahydrate, urea, a manganous nitrate aqueous solution and potassium permanganate in purified water, and putting the solution into a hydrothermal reaction kettle for constant-temperature reaction. And filtering and drying the reaction product, calcining in a muffle furnace, and cooling to obtain the Cr / Fe co-doped K0. 5Mn4O8 material. According to the method, the electrochemical performance of the K0. 5Mn4O8 material is effectively improved through co-doping of Cr and Fe elements. The obtained material presents a unique morphology in which a micron-sized laminated blocky matrix and nanoparticles are closely symbiotic on a microstructure, and the micron and nano composite structure is beneficial to increasing the contact area between an electrode and an electrolyte, providing more ion migration channels, buffering the volume change in the cyclic charging and discharging process, and improving the electrochemical performance of the electrode. Therefore, the performance of the material in the positive electrode of the zinc ion battery is improved.

Description

Technical Field

[0001] This invention discloses Cr / Fe co-doped K 0.5 Mn4O8 materials and their preparation methods belong to the field of aqueous zinc-ion battery technology in inorganic materials. Background Technology

[0002] With the continuous increase in the proportion of renewable energy power generation and the rapid development of the electric vehicle industry, developing new energy storage technologies that combine high safety, low cost, and environmental friendliness has become a global consensus. Among various energy storage systems, aqueous zinc-ion batteries have attracted much attention due to their unique advantages. The aqueous electrolytes they use possess characteristics such as high ionic conductivity, low cost, and good safety, making this system show significant application potential in large-scale energy storage. However, the commercialization of aqueous zinc-ion batteries still faces key challenges, one of which is the lack of matching high-performance cathode materials. An ideal cathode material should possess a stable crystal structure to support the reversible insertion and extraction of Zn ions, high conductivity to achieve rapid charge transfer, and resistance to structural degradation during long-term charge-discharge cycles.

[0003] Among numerous candidate materials, manganese-based oxides possess advantages such as diverse ionic valence states, abundant raw material reserves, low production costs, and simple preparation methods, making them widely used in cathode materials for batteries. 0.5 Mn4O8 material is considered one of the most promising cathode materials due to its open ion diffusion channels, which enable it to offer high theoretical capacity. Regarding K... 0.5 The challenges of Mn4O8 materials in terms of cycle stability and structural evolution have prompted researchers to continuously improve its electrochemical performance by optimizing synthesis conditions and introducing multiple transition metals, thereby promoting its application in energy storage materials.

[0004] Current research largely focuses on the manipulation of bulk crystal structure by single-ion doping, while systematic studies on multi-ion synergistic doping are still lacking. Multi-ion synergistic doping holds promise for achieving more comprehensive performance improvements through complementary advantages. Fe 3+ Because of Mn 3+ Due to their similar ionic radii and low cost, Cr has been widely studied. Doping with Cr can improve structural stability to some extent, but its effect on capacity improvement is often limited. 3+ Doping, due to its strong metal-oxygen covalent bond, exhibits unique advantages in enhancing structural rigidity. Cr 3+ with Fe 3+ Co-doping is expected to exert a synergistic stabilizing effect, thereby improving K 0.5 Comprehensive performance of Mn4O8 materials. Summary of the Invention

[0005] To improve K0.5 The electrochemical properties of Mn4O8 materials, and this invention provides Cr / Fe co-doped K 0.5 Mn4O8 material and its preparation method. In the preparation of this material, potassium dichromate, ferric nitrate nonahydrate, urea, manganese nitrate aqueous solution, and potassium permanganate were added sequentially to pure water. After thorough stirring, the mixture was placed in a hydrothermal reactor for constant-temperature reaction. The reaction product was filtered, dried, calcined in a muffle furnace, and cooled to obtain Cr / Fe co-doped K. 0.5 Mn4O8 material. The synthesis method is simple, low-cost, and suitable for large-scale industrial production.

[0006] The Cr / Fe co-doped K of the present invention 0.5 The Mn4O8 material exhibits XRD diffraction peaks at 12.61°, 18.13°, 28.75°, 37.52°, and 41.83°; XPS peaks at 291.15 eV, 293.97 eV, 529.12 eV, 575.69 eV, 585.27 eV, 641.78 eV, 653.36 eV, 709.75 eV, and 724.28 eV. Cr and Fe are both +3 valence, while Mn exhibits both +3 and +4 valence.

[0007] This invention also provides Cr / Fe co-doped K 0.5 The preparation method of Mn4O8 material includes the following steps:

[0008] First, disperse potassium dichromate and ferric nitrate nonahydrate in deionized water, then add urea, manganese nitrate aqueous solution and potassium permanganate in sequence, and stir until well mixed.

[0009] The second step is to place the well-stirred solution into a hydrothermal reactor, react it at a constant temperature in an oven, and then allow it to cool naturally.

[0010] The third step is to remove the product from the hydrothermal reactor, wash and filter it, and then put it into an oven to dry.

[0011] The fourth step involves calcination in a muffle furnace followed by cooling to obtain Cr / Fe co-doped K. 0.5 Mn4O8 material.

[0012] Furthermore, in the above technical solution, in the first step, the molar ratio of potassium dichromate to ferric nitrate nonahydrate is 5:1.

[0013] Furthermore, in the above technical solution, the molar ratio of potassium dichromate to manganese nitrate is 2:3.

[0014] Furthermore, in the above technical solution, in the first step, the molar ratio of potassium dichromate to potassium permanganate is 10:9.

[0015] Furthermore, in the above technical solution, the molar ratio of potassium permanganate to urea is 1:8.

[0016] Furthermore, in the above technical solution, in the second step, the constant temperature reaction temperature is 160℃ and the reaction time is 6 hours.

[0017] Furthermore, in the above technical solution, in the third step, the reaction product is cleaned with pure water. The reaction product is placed in pure water to form a suspension, and then ultrasonicated in an ultrasonic cleaner for 5 minutes. The suspension is then filtered, and the process is repeated a total of 5 times.

[0018] Furthermore, in the above technical solution, in the third step, the drying temperature is 85℃ and the drying time is 1 hour.

[0019] Furthermore, in the above technical solution, in the fourth step, the calcination temperature is 450℃, and the constant temperature calcination time is 5 hours, of which the heating program is set for 2 hours and the cooling to below 200℃ for 2 hours.

[0020] The present invention also provides the above-mentioned Cr / Fe co-doped K 0.5 Application of Mn4O8 material in aqueous zinc-ion batteries.

[0021] Beneficial effects of the invention

[0022] 1. This invention prepares Cr / Fe co-doped K 0.5 Mn4O8 materials use low-cost and readily available raw materials, have a simple and controllable synthesis route, mild reaction conditions, and good potential for large-scale production.

[0023] 2. Through Cr / Fe co-doping, a unique morphology was constructed in the material, in which a micron-scale stacked bulk matrix and nanoparticles coexist closely. This micron-nano composite structure can effectively increase the contact area between the electrode and the electrolyte, provide more ion migration channels, and buffer volume changes during cycling, thereby improving electrode reaction kinetics and structural stability.

[0024] 3. Co-doping of Cr and Fe synergistically modulates K 0.5 The valence state and electronic structure of manganese in Mn4O8 enhance the material's conductivity and structural stability. When used as a cathode in zinc-ion batteries, it exhibits high specific capacity and cycle stability. Attached Figure Description

[0025] Figure 1 The K-type co-doped Cr / Fe material in Example 4 of this invention 0.5 XRD pattern of Mn4O8 material;

[0026] Figure 2 The K-type co-doped Cr / Fe material in Example 4 of this invention0.5 SEM images of Mn4O8 material;

[0027] Figure 3 The K-type co-doped Cr / Fe material in Example 4 of this invention 0.5 XPS spectra of Mn4O8 material; where: (a) is the full XPS spectrum; (b) is the XPS spectrum of Cr2p; (c) is the XPS spectrum of Fe2p; (d) is the XPS spectrum of K2p; (e) is the XPS spectrum of Mn2p; (f) is the XPS spectrum of O1s.

[0028] Figure 4 The K-type co-doped Cr / Fe material in Example 4 of this invention 0.5 EDS image of Mn4O8 material;

[0029] Figure 5 The K-type co-doped Cr / Fe material in Example 4 of this invention 0.5 Elemental distribution diagrams of Mn4O8 material; where: (a) is the Cr elemental distribution diagram; (b) is the Fe elemental distribution diagram; (c) is the K elemental distribution diagram; (d) is the Mn elemental distribution diagram; (e) is the O elemental distribution diagram;

[0030] Figure 6 The K-type co-doped Cr / Fe material in Example 4 of this invention 0.5 Infrared spectrum of Mn4O8 material;

[0031] Figure 7 The K-type co-doped Cr / Fe material in Example 4 of this invention 0.5 Raman spectrum of Mn4O8 material;

[0032] Figure 8 The K-type co-doped Cr / Fe in Example 5 of this invention 0.5 Cyclic charge-discharge diagram of Mn4O8 material;

[0033] Figure 9 The K-type co-doped Cr / Fe in Example 5 of this invention 0.5 Cyclic voltammetry of Mn4O8 material;

[0034] Figure 10 The K-type co-doped Cr / Fe in Example 5 of this invention 0.5 AC impedance diagram of Mn4O8 material. Detailed Implementation

[0035] The present invention will be further described below through specific examples. However, these examples are merely exemplary and are not limited to the scope of protection of the present invention; they are merely embodiments.

[0036] In the following embodiments, unless otherwise specified, the reagents, materials and instruments used are all conventional reagents, materials and instruments, and are commercially available. The reagents involved can also be synthesized by conventional synthesis methods.

[0037] Example 1

[0038] First, weigh 2.0593g of potassium dichromate, 0.808g of ferric nitrate nonahydrate and 4.3243g of urea, and dissolve them in 60mL of purified water, stirring as needed.

[0039] The second step involves adding 5.3685g of a 50% manganese nitrate aqueous solution and 1.4223g of potassium permanganate to the well-mixed solution and stirring for 1 hour.

[0040] The third step is to place the above-mentioned well-mixed solution into a hydrothermal reactor and react it at a constant temperature of 160°C in an oven for 6 hours, followed by natural cooling.

[0041] The fourth step is to remove the reaction product from the hydrothermal reactor and perform a cleaning operation. Use pure water to clean and filter the reaction product, place the reaction product in pure water to form a suspension, and sonicate it in an ultrasonic cleaner for 5 minutes. Then filter the suspension. A total of 5 cleaning operations are performed.

[0042] Fifth step: Place the cleaned and filtered product into an oven and dry at 85°C for 1 hour.

[0043] The sixth step involves calcining the dried product in a muffle furnace. After calcination, the furnace is cooled to obtain Cr / Fe co-doped K. 0.5 Mn4O8 material. The calcination temperature is 450℃, with the heating program set for 2 hours, cooling to below 200℃ for 2 hours, and the isothermal calcination time for 5 hours.

[0044] Example 2

[0045] First, weigh 2.3535g of potassium dichromate, 0.808g of ferric nitrate nonahydrate and 4.3243g of urea, and dissolve them in 60mL of purified water and stir.

[0046] The second step involves adding 5.3685g of a 50% manganese nitrate aqueous solution and 1.4223g of potassium permanganate to the well-mixed solution and stirring for 1 hour.

[0047] The third step is to place the above-mentioned well-mixed solution into a hydrothermal reactor and react it at a constant temperature of 160°C in an oven for 6 hours, followed by natural cooling.

[0048] The fourth step is to remove the reaction product from the hydrothermal reactor and perform a cleaning operation. Use pure water to clean and filter the reaction product, place the reaction product in pure water to form a suspension, and sonicate it in an ultrasonic cleaner for 5 minutes. Then filter the suspension. A total of 5 cleaning operations are performed.

[0049] Fifth step: Place the cleaned and filtered product into an oven and dry at 85°C for 1 hour.

[0050] The sixth step involves calcining the dried product in a muffle furnace. After calcination, the furnace is cooled to obtain Cr / Fe co-doped K. 0.5 Mn4O8 material. The calcination temperature is 450℃, with the heating program set for 2 hours, cooling to below 200℃ for 2 hours, and the isothermal calcination time for 5 hours.

[0051] Example 3

[0052] First, weigh 2.6476g of potassium dichromate, 0.808g of ferric nitrate nonahydrate and 4.3243g of urea, and dissolve them in 60mL of purified water, stirring as needed.

[0053] The second step involves adding 5.3685g of a 50% manganese nitrate aqueous solution and 1.4223g of potassium permanganate to the well-mixed solution and stirring for 1 hour.

[0054] The third step is to place the above-mentioned well-mixed solution into a hydrothermal reactor and react it at a constant temperature of 160°C in an oven for 6 hours, followed by natural cooling.

[0055] The fourth step is to remove the reaction product from the hydrothermal reactor and perform a cleaning operation. Use pure water to clean and filter the reaction product, place the reaction product in pure water to form a suspension, and sonicate it in an ultrasonic cleaner for 5 minutes. Then filter the suspension. A total of 5 cleaning operations are performed.

[0056] Fifth step: Place the cleaned and filtered product into an oven and dry at 85°C for 1 hour.

[0057] The sixth step involves calcining the dried product in a muffle furnace. After calcination, the furnace is cooled to obtain Cr / Fe co-doped K. 0.5 Mn4O8 material. The calcination temperature is 450℃, with the heating program set for 2 hours, cooling to below 200℃ for 2 hours, and the isothermal calcination time for 5 hours.

[0058] Example 4

[0059] First, weigh 2.9418g of potassium dichromate, 0.808g of ferric nitrate nonahydrate and 4.3243g of urea, and dissolve them in 60mL of purified water, stirring as needed.

[0060] The second step involves adding 5.3685g of a 50% manganese nitrate aqueous solution and 1.4223g of potassium permanganate to the well-mixed solution and stirring for 1 hour.

[0061] The third step is to place the above-mentioned well-mixed solution into a hydrothermal reactor and react it at a constant temperature of 160°C in an oven for 6 hours, followed by natural cooling.

[0062] The fourth step is to remove the reaction product from the hydrothermal reactor and perform a cleaning operation. Use pure water to clean and filter the reaction product, place the reaction product in pure water to form a suspension, and sonicate it in an ultrasonic cleaner for 5 minutes. Then filter the suspension. A total of 5 cleaning operations are performed.

[0063] Fifth step: Place the cleaned and filtered product into an oven and dry at 85°C for 1 hour.

[0064] The sixth step involves calcining the dried product in a muffle furnace. After calcination, the furnace is cooled to obtain Cr / Fe co-doped K. 0.5 Mn4O8 material. The calcination temperature is 450℃, with the heating program set for 2 hours, cooling to below 200℃ for 2 hours, and the isothermal calcination time for 5 hours.

[0065] Figure 1 K co-doped with Cr / Fe 0.5 The XRD pattern of Mn4O8 material shows a tetragonal crystal structure as the main phase. All diffraction peak positions closely match those of the standard card (PDF#04-021-8103), and no impurity characteristic peaks were detected, indicating that Cr and Fe elements have entered the main structure through lattice doping. The characteristic diffraction peaks at 12.61°, 18.13°, 28.75°, 37.52°, and 41.83° correspond to K2, respectively. 0.5 The (110), (200), (130), (211), and (301) crystal planes of Mn4O8. After Cr / Fe co-doping, the a and b axes of the material's unit cell shrink, while the c axis expands. This lattice distortion is mainly attributed to Fe. 3+ With Cr 3+ Mn preferentially replaces intralayer octahedral coordination 3+ / Mn 4+ Fe 3+ Ionic radius and Mn 3+ Similar but slightly smaller, the substitution causes local shrinkage of the octahedrons within the layer, resulting in a decrease in the a- and b-axis lattice parameters. This strengthens the intralayer structural connections, while the stress generated by the intralayer shrinkage is transmitted to the interlayer, relaxing the interlayer K-axis. + In the coordination environment, Cr ion substitution results in c-axis expansion.

[0066] Figure 2 K co-doped with Cr / Fe 0.5 SEM images of Mn4O8 material clearly show a structure where micron-sized stacked bulk particles and nanoparticles coexist. Spherical nanoparticles with sizes ranging from 50 to 200 nm are distributed on the surface of the micron-sized stacked bulk particles and in the intergranular spaces. These particles are well dispersed, without significant agglomeration, and form a tight contact with the matrix. This micron-nano composite structure effectively increases the contact area between the electrode and the electrolyte, provides more ion migration channels, and buffers volume changes during cycling, thereby improving electrode reaction kinetics and structural stability.

[0067] Figure 3 K co-doped with Cr / Fe 0.5 XPS images of Mn4O8 material. Figure 3 (a) is the full spectrum, from which characteristic peaks of Cr2p, Fe2p, K2p, Mn2p and O1s can be observed. Figure 3 In the Cr 2p spectrum of (b), the binding energy peaks at 575.69 eV and 585.27 eV are attributed to Cr 2p. 3 / 2 With Cr 2p 1 / 2 The orbitals indicate that Cr is stably doped in the crystal lattice in the +3 valence state. Figure 3 In the Fe 2p spectrum of (c), Fe 2p 3 / 2 Peaks were observed at 709.75 eV and 711.8 eV, Fe 2p 1 / 2 Located at 724.28 eV and 731.67 eV, it is confirmed that Fe is mainly incorporated into the material in the +3 valence form. Figure 3 In the K 2p spectrum of (d), typical K values ​​are observed at 291.15 eV and 293.97 eV. + The signal indicates that the doping process did not disrupt the structural stability of potassium ions. Figure 3 In the Mn 2p spectrum of (e), Mn 2p 3 / 2 Located at 641.78 eV, Mn 2p 1 / 2 The main peak is located at 653.36 eV, indicating that Mn has both +3 and +4 valences. Figure 3 In the O 1s spectrum of (f), the main peak at 529.12 eV belongs to lattice oxygen, indicating that the material has a complete manganese-oxygen framework.

[0068] Figure 4 K co-doped with Cr / Fe 0.5 The EDS spectrum of Mn4O8 material shows the peaks of Cr, Fe, K, Mn and O elements.

[0069] Figure 5 K co-doped with Cr / Fe0.5 The elemental distribution diagram of Mn4O8 material shows that Mn and O are uniformly distributed in the bulk matrix, and their signal profiles are highly consistent with the particle morphology, reflecting the overall consistency of the bulk structure. The signals of K and Fe are relatively weak. Cr shows significant signal enhancement in the nanoparticle regions attached to the surface of the bulk particles, indicating that Cr is enriched to a certain extent at the surface and interface.

[0070] Figure 6 K co-doped with Cr / Fe 0.5 The infrared spectrum of Mn4O8 material is located at 675.08 cm⁻¹. -1 and 729.09 cm -1 The strong absorption peak is attributed to the stretching vibration of the Mn–O bond in the MnO6 octahedron, a characteristic vibrational mode of the manganese oxide framework. It is located at 528.5 cm⁻¹. -1 The nearby absorption is due to the stretching vibrations of the Fe–O and Cr–O bonds, providing Fe 3+ With Cr 3+ Spectral evidence of successful doping into the manganese oxide layer. Located at 470.63 cm⁻¹. -1 The peak at that point represents the bending vibration of Mn–O–Mn.

[0071] Figure 7 K co-doped with Cr / Fe 0.5 Raman spectrum of Mn4O8 material. Located at 147.49 cm⁻¹. -1 208.82cm -1 257.08cm -1 289.69cm -1 and 327.28 cm -1 The series of peaks in the low-frequency region are attributed to extralattice vibrations, mainly including interlayer shear modes and metallic bond vibrations. The peak position distribution directly reflects the Cr... 3+ with Fe 3+ The modulating effect of doping on lattice dynamics. At 374.6 cm⁻¹ -1 419.13cm -1 With 465.83 cm -1 The absorption peak appearing nearby corresponds to the bending vibration of the metal-oxygen pair. It is located at 644.86 cm⁻¹. -1 The high-intensity peaks are attributed to MnO6 octahedra. 4+ Symmetric stretching vibration of the –O bond, 575.37 cm⁻¹ -1 The peak at that location originates from Mn 3+ –O stretching vibration.

[0072] Example 5

[0073] The Cr / Fe co-doped K prepared in Examples 1-40.5 Mn4O8 material was used to prepare the positive electrode for aqueous zinc-ion batteries.

[0074] The first step is to weigh out the Cr / Fe co-doped K. 0.5 0.24g of Mn4O8 material and 0.03g of acetylene black were thoroughly ground using an agate mortar.

[0075] The second step involves adding a binder made from a mixture of 0.03g polyvinylidene fluoride and 0.6mL N-methylpyrrolidone to the ground product.

[0076] The third step is to coat the mixed slurry onto a 0.01mm thick stainless steel foil and dry it at a constant temperature of 80℃ for 1 hour.

[0077] The fourth step is to process the stainless steel foil into a positive electrode sheet with a diameter of 10mm after the active material is completely dried.

[0078] The fifth step involves assembling an aqueous zinc-ion battery using a zinc sheet as the negative electrode, glass fiber paper as the separator, and a mixture of 2 mol / L ZnSO4 solution and 0.2 mol / L MnSO4 solution as the electrolyte. The battery is then left to stand for 24 hours before testing.

[0079] Figure 8 K is co-doped with Cr / Fe 0.5 Cyclic charge-discharge diagram of an aqueous zinc-ion battery with Mn4O8 as the positive electrode. The charge-discharge test currents were set at 50 mA / g, 100 mA / g, 200 mA / g, 300 mA / g, and 500 mA / g. The Cr / Fe co-doped K2O3 battery prepared in Example 4... 0.5 The Mn4O8 material exhibits a high initial discharge specific capacity of 341.0 mAh / g at a low current density of 50 mA / g. After undergoing a high current discharge, the capacity reaches a maximum of 441.9 mAh / g when discharged again at a current density of 50 mA / g.

[0080] Figure 9 K is co-doped with Cr / Fe 0.5 Cyclic voltammetry of an aqueous zinc-ion battery using Mn4O8 as the cathode. All samples exhibit a distinct oxidation peak at approximately 1.6 V, with two corresponding reduction peaks near 1.2 V and 1.4 V, corresponding to Mn4O8. 3+ / Mn 4+ The redox couple exhibits a multi-step reaction. The material prepared in Example 4 shows better peak symmetry and a smaller peak potential difference, indicating better electrochemical reversibility and lower polarization.

[0081] Figure 10 K is co-doped with Cr / Fe 0.5The AC impedance curves of an aqueous zinc-ion battery with Mn4O8 as the positive electrode show that the material prepared in Example 3 exhibits the lowest charge transfer resistance, while the sample prepared in Example 4 has a higher initial charge transfer resistance, but the material's performance is gradually activated during the charge and discharge process.

[0082] Based on the disclosure in the foregoing specification, those skilled in the art can make appropriate changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention.

Claims

1. Cr / Fe co-doped K 0.5 Mn4O8 material, characterized in that: The XRD diffraction peaks are at 12.61°, 18.13°, 28.75°, 37.52° and 41.83°; the XPS peaks are at 291.15 eV, 293.97 eV, 529.12 eV, 575.69 eV, 585.27 eV, 641.78 eV, 653.36 eV, 709.75 eV and 724.28 eV. Cr is in the +3 valence position, Fe is in the +3 valence position, and Mn is in both the +3 and +4 valence positions.

2. The Cr / Fe co-doped K as described in claim 1 0.5 The method for preparing Mn4O8 material is characterized by... Includes the following steps: First, disperse potassium dichromate and ferric nitrate nonahydrate in purified water, then add urea, manganese nitrate aqueous solution and potassium permanganate in sequence, and stir until well mixed. The second step is to place the well-stirred solution into a hydrothermal reactor, react it at a constant temperature in an oven, and then allow it to cool down naturally. The third step is to remove the product from the hydrothermal reactor, wash and filter it, and then put it into an oven to dry. The fourth step involves calcination in a muffle furnace followed by cooling to obtain Cr / Fe co-doped K. 0.5 Mn4O8 material.

3. The Cr / Fe co-doped K according to claim 2 0.5 The method for preparing Mn4O8 material is characterized by: In the first step, the molar ratio of potassium dichromate to ferric nitrate nonahydrate is 5:

1.

4. The Cr / Fe co-doped K according to claim 2 0.5 The method for preparing Mn4O8 material is characterized by: In the first step, the molar ratio of potassium dichromate to manganese nitrate is 2:

3.

5. The Cr / Fe co-doped K according to claim 2 0.5 The method for preparing Mn4O8 material is characterized by: In the first step, the molar ratio of potassium dichromate to potassium permanganate is 10:

9.

6. The Cr / Fe co-doped K according to claim 2 0.5 The method for preparing Mn4O8 material is characterized by: In the first step, the molar ratio of potassium permanganate to urea is 1:

8.

7. The Cr / Fe co-doped K according to claim 2 0.5 The method for preparing Mn4O8 material is characterized by: In the second step, the constant temperature reaction temperature is 160℃, and the reaction time is 6 hours.

8. The Cr / Fe co-doped K according to claim 2 0.5 The method for preparing Mn4O8 material is characterized by: In the third step, the reaction product is washed with pure water. The reaction product is placed in pure water to form a suspension, and then ultrasonicated in an ultrasonic cleaner for 5 minutes. The suspension is then filtered. The washing is repeated a total of 5 times.

9. The Cr / Fe co-doped K according to claim 2 0.5 The method for preparing Mn4O8 material is characterized by: In the third step, the drying temperature is 85℃ and the drying time is 1 hour.

10. The Cr / Fe co-doped K according to claim 2 0.5 The method for preparing Mn4O8 material is characterized by: In the fourth step, the calcination temperature is 450℃ and the constant temperature calcination time is 5 hours, of which: the heating program is set for 2 hours and the cooling to below 200℃ takes 2 hours.

11. The Cr / Fe co-doped K as described in claim 1 0.5 Application of Mn4O8 material in aqueous zinc-ion batteries.

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