Preparation method of carbon-coated manganese oxide hollow microspheres and application thereof

Abstract

The application provides a preparation method of carbon-coated manganese oxide hollow microspheres, relates to the field of electrochemistry, and comprises the following steps: A solution preparation, B solution preparation, precursor preparation and calcination, wherein the A solution preparation is that manganese acetate tetrahydrate and polyvinylpyrrolidone are added into a mixed solvent of anhydrous ethanol and deionized water, the B solution preparation is that 1,3,5-benzene tricarboxylic acid is added into a mixed solvent of anhydrous ethanol and deionized water, and the precursor preparation is that the B solution is added into the A solution. The method can prepare carbon-coated manganese oxide hollow microspheres with uniform morphology and large diameter, and the carbon-coated manganese oxide hollow microspheres have excellent rate performance and long cycle life, so that the electrochemical performance of a battery taking the material as a positive electrode material is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, specifically to a method for preparing carbon-coated manganese oxide hollow microspheres and their applications. Background Technology

[0002] Due to the overexploitation and large-scale use of non-renewable energy sources, humanity is facing a severe energy crisis, urgently requiring the development of green and renewable new energy sources. Aqueous zinc-ion batteries (AZIBs) are advantageous due to their low toxicity, abundant zinc resources, low cost, high safety, suitable redox potential (-0.76V vs. standard hydrogen electrode (SHE)), and high theoretical capacity (820mAh g / g). -1 With its advantages such as [missing information], zinc-ion batteries have broad application prospects in large-scale energy storage and portable electronic devices, making them one of the current research hotspots in the energy storage field. Among them, the cathode material is a key component for improving the capacity and stability of zinc-ion batteries, playing a crucial role in charge storage (Zn [missing information]). 2+ The insertion / extraction of cathode materials is a crucial task. However, cathode materials face problems such as active material dissolution, poor conductivity, slow diffusion kinetics, and rapid capacity decay during cycling, which seriously hinder the large-scale commercial application of zinc-ion batteries.

[0003] Compared to PBAs (Prussian Blue Analogues) with low specific capacity and vanadium oxides with high toxicity and low discharge voltage, manganese oxides offer advantages such as high power density, high operating voltage, and abundant resources, making them widely studied as cathode materials for aqueous zinc-ion batteries. Among the various manganese oxides, MnO electrode materials have advantages such as low cost and reversible reaction mechanisms, but they often face problems such as low initial capacity, weak structural stability, and poor conductivity. To address these issues, researchers have improved the performance of manganese oxide electrode materials through methods such as constructing porous materials, combining with conductive materials, and introducing oxygen vacancies. Constructing porous structures can increase the specific surface area and porosity of the material, thereby enhancing electrolyte permeability and ion transport rate; combining with conductive materials improves the electronic conductivity and charge transport efficiency of the electrode material and stabilizes the material structure, thereby improving the rate performance and cycle stability of the electrode material; introducing oxygen vacancies into the material can regulate the electronic structure, increase electrochemical reaction active sites, enhance electrochemical activity, and thus increase the conductivity of the material.

[0004] In recent years, existing technologies have developed methods that use manganese-based metal-organic frameworks (Mn-MOFs) as precursors and calcine manganese oxide materials in situ to generate carbon coatings, thereby achieving hollow structure construction, carbon layer coating, and oxygen vacancy introduction. However, in the existing precursor preparation process, the products obtained by direct pyrolysis have poor morphological uniformity, and the hollow structures are prone to collapse at high temperatures, making it difficult to form effective hollow microsphere structures. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a method for preparing carbon-coated manganese oxide hollow microspheres. This method can prepare carbon-coated manganese oxide hollow microspheres with uniform morphology and large diameter, which have both excellent rate performance and long cycle life, thereby effectively improving the electrochemical performance of batteries using this material as the positive electrode material.

[0006] Another objective of this invention is to provide an application of carbon-coated manganese oxide hollow microspheres, which are used in aqueous zinc-ion battery composite cathode materials.

[0007] The objective of this invention is achieved through the following technical solution: A method for preparing carbon-coated manganese oxide hollow microspheres includes: Step S1, Preparation of Solution A: Add manganese acetate tetrahydrate and polyvinylpyrrolidone (PVP K30) to a mixed solvent of anhydrous ethanol and deionized water, and stir until clear to obtain the solution; Step S2, Solution B preparation: Add 1,3,5-pyromellitic acid (H3BTC) to a mixed solvent of anhydrous ethanol and deionized water, and stir until clear to obtain the solution; Step S3, Precursor Preparation: Add solution B to solution A, stir and mix, then let stand; then, wash, centrifuge and dry in a forced-air dryer to obtain the Mn-MOFs precursor. Step S4, Calcination: The Mn-MOFs precursor is placed in a tube furnace and calcined in situ under an argon atmosphere to obtain carbon-coated manganese oxide hollow microspheres rich in oxygen vacancies.

[0008] Based on further optimization of the above scheme, in the preparation of solution A, the mass-volume ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone and the mixed solution is 0.5g:2g:100mL; in the preparation of solution A, the mixture is stirred at 380-420rpm for 28-32min at 15-20℃.

[0009] Based on further optimization of the above scheme, in the preparation of solution B, the mass-volume ratio of 1,3,5-pyromellitic acid to the mixed solvent is 1g:80mL; in the preparation of solution B, the mixture is stirred at 180-220rpm for 13-17min at 5-10℃.

[0010] Based on further optimization of the above scheme, in the preparation process of solutions A and B, the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 3:1.

[0011] Based on further optimization of the above scheme, in the precursor preparation process, solution B is added dropwise to solution A at a rate of 0.7-0.9 mL / min at 15-20℃, wherein the mass ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone, and 1,3,5-pyromellitic acid is 1:4:2. The mixture is stirred at a speed of 280-320 rpm while being added dropwise. After the addition is completed, stirring is continued for 28-32 min; then the mixture is allowed to stand for 14.5-15.5 h.

[0012] Based on further optimization of the above scheme, the washing and centrifugation process in the precursor preparation process is as follows: first, the reaction solution after standing is centrifuged at a speed of 7500-8500 rpm for 7-9 min, and the precipitate is collected; then, the precipitate after centrifugation is washed three times each with deionized water and anhydrous ethanol (i.e., first washed three times with deionized water, then washed three times with anhydrous ethanol), and the amount of washing solvent is the same as the amount of reaction solution after standing. The supernatant is discarded and the precipitate is retained. The specific process of forced-air drying is as follows: the precipitate after washing and centrifugation is placed in a forced-air drying oven and dried at 58-62℃ for 23.5-24.5h to obtain Mn-MOFs precursor powder.

[0013] Based on further optimization of the above scheme, step S4 specifically involves: heating to 695–705°C at a heating rate of 9.5–10.5°C / min under an argon atmosphere, calcining in situ for 1.9–2.1 hours, and then cooling to room temperature with the furnace to obtain the final product.

[0014] An application of carbon-coated manganese oxide hollow microspheres is as follows: the above-mentioned carbon-coated manganese oxide hollow microspheres are used to prepare the positive electrode material of aqueous zinc-ion batteries.

[0015] The following are the technical effects of this invention: This invention, through specific raw material ratios and reaction temperatures, enables carbon-coated manganese oxide hollow microspheres rich in oxygen vacancies to possess excellent hollow microsphere morphology, exhibiting uniformity and a relatively large diameter. The hollow microspheres prepared by this invention have larger hollow cavities, effectively improving the stability of the material structure during cycling and increasing the contact sites with the electrolyte. Simultaneously, the excellent conductivity of the coating carbon layer increases the material's conductivity, resulting in better rate performance during charge and discharge. Furthermore, the carbon layer also acts as a buffer layer, effectively mitigating volume changes during charge and discharge, thus contributing to the material's superior stability.

[0016] The preparation method of this invention is simple, low-cost, low-energy, and environmentally friendly, thus effectively adapting to the practical application of aqueous zinc-ion battery materials. Attached Figure Description

[0017] Figure 1 The image shows the XRD pattern of the carbon-coated manganese oxide hollow microspheres prepared in Example 2 of this invention.

[0018] Figure 2 This is a SEM image of the carbon-coated manganese oxide hollow microspheres prepared in Example 2 of the present invention.

[0019] Figure 3 This is a TEM image of the carbon-coated manganese oxide hollow microspheres prepared in Example 2 of the present invention.

[0020] Figure 4 This is a characterization diagram of oxygen vacancies in the carbon-coated manganese oxide hollow microspheres prepared in Example 2 of the present invention.

[0021] Figure 5 The graph shows the rate charge-discharge performance of the carbon-coated manganese oxide hollow microspheres prepared in Example 2 of this invention as a positive electrode material for an aqueous zinc-ion battery.

[0022] Figure 6 This is a rate performance diagram of the carbon-coated manganese oxide hollow microspheres prepared in Example 2 of the present invention as a positive electrode material for an aqueous zinc-ion battery.

[0023] Figure 7 The graph shows the rate charge-discharge performance of the carbon-coated manganese oxide hollow microspheres prepared in Example 2 of this invention as a positive electrode material for an aqueous zinc-ion battery after 4000 cycles. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0025] Example 1: A method for preparing carbon-coated manganese oxide hollow microspheres includes: Step S1, Preparation of Solution A: Add manganese acetate tetrahydrate and polyvinylpyrrolidone (PVP K30) to a mixed solvent of anhydrous ethanol and deionized water. The mass-to-volume ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone and the mixed solution is 0.5g:2g:100mL. The volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 3:1. Stir at 380rpm for 32min at 15℃ to obtain the solution.

[0026] Step S2, Solution B preparation: 1,3,5-pyromellitic acid (H3BTC) is added to a mixed solvent of anhydrous ethanol and deionized water. The mass-to-volume ratio of 1,3,5-pyromellitic acid to the mixed solvent is 1 g: 80 mL, and the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 3:1. Stir at 180 rpm for 17 min at 5 °C to obtain the solution.

[0027] Step S3, Precursor Preparation: At 15℃, solution B is added dropwise to solution A at a rate of 0.7 mL / min. The mass ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone, and 1,3,5-pyromellitic acid is 1:4:2. The mixture is stirred at 280 rpm while being added dropwise. After the addition is complete, stirring is continued for 32 min. The mixture is then allowed to stand for 15.5 h.

[0028] Afterwards, the mixture was washed, centrifuged, and dried in a forced-air environment to obtain the Mn-MOFs precursor. The washing and centrifugation process was as follows: the reaction solution after standing was first centrifuged at 7500 rpm for 9 min, and the precipitate was collected. Then, the precipitate after centrifugation was washed three times each with deionized water and anhydrous ethanol (i.e., first washed three times with deionized water, then washed three times with anhydrous ethanol). The amount of washing solvent was the same as the amount of reaction solution after standing. The supernatant was discarded and the precipitate was retained. The specific process of forced-air drying is as follows: the precipitate after washing and centrifugation is placed in a forced-air drying oven and dried at 58°C for 24.5 hours to obtain Mn-MOFs precursor powder.

[0029] Step S4, Calcination: The Mn-MOFs precursor is placed in a tube furnace and heated to 695°C at a heating rate of 9.5°C / min under an argon atmosphere. It is then calcined in situ for 2.1 h and cooled to room temperature with the furnace to obtain carbon-coated manganese oxide hollow microspheres rich in oxygen vacancies.

[0030] Example 2: A method for preparing carbon-coated manganese oxide hollow microspheres includes: Step S1, Preparation of Solution A: Add manganese acetate tetrahydrate and polyvinylpyrrolidone (PVP K30) to a mixed solvent of anhydrous ethanol and deionized water. The mass-to-volume ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone and the mixed solution is 0.5g:2g:100mL. The volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 3:1. Stir at 17.5℃ and 400rpm for 30min to obtain the solution.

[0031] Step S2, Solution B preparation: 1,3,5-Pyromellitic acid (H3BTC) is added to a mixed solvent of anhydrous ethanol and deionized water. The mass-to-volume ratio of 1,3,5-pyromellitic acid to the mixed solvent is 1 g: 80 mL, and the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 3:1. Stir at 200 rpm for 15 min at 7.5 °C to obtain the solution.

[0032] Step S3, Precursor Preparation: At 17.5℃, solution B is added dropwise to solution A at a rate of 0.8 mL / min. The mass ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone, and 1,3,5-pyromellitic acid is 1:4:2. The mixture is stirred at 300 rpm while being added dropwise. After the addition is complete, stirring is continued for 30 min. The mixture is then allowed to stand for 15 h.

[0033] Afterwards, the mixture was washed, centrifuged, and dried in a forced-air environment to obtain the Mn-MOFs precursor. The washing and centrifugation process was as follows: the reaction solution after standing was first centrifuged at 8000 rpm for 8 min, and the precipitate was collected. Then, the precipitate after centrifugation was washed three times each with deionized water and anhydrous ethanol (i.e., first washed three times with deionized water, then washed three times with anhydrous ethanol). The amount of washing solvent was the same as the amount of reaction solution after standing. The supernatant was discarded and the precipitate was retained. The specific process of drying by forced air is as follows: the precipitate after washing and centrifugation is placed in a forced air drying oven and dried at 60°C for 24 hours to obtain Mn-MOFs precursor powder.

[0034] Step S4, Calcination: The Mn-MOFs precursor is placed in a tube furnace and heated to 700°C at a heating rate of 10°C / min under an argon atmosphere. It is then calcined in situ for 2 hours and cooled to room temperature with the furnace to obtain carbon-coated manganese oxide hollow microspheres rich in oxygen vacancies.

[0035] X-ray diffractometer with Cu Kα radiation source was used, with a scanning range of 10°–80° and a scanning step of 0.02°. The test sample was dried microsphere powder, used to analyze the crystal phase composition and crystallinity. The phase was confirmed by comparison with standard PDF cards. The test results are as follows: Figure 1 As shown, the test results indicate that there are no obvious impurity peaks, which means that the calcination process produces products with high purity, no impurity phases such as Mn2O3 and Mn3O4, and the carbon layer is amorphous carbon with no sharp carbon diffraction peaks.

[0036] Field emission scanning electron microscopy (FESEM) was used with an accelerating voltage of 3 kV, a magnification of MAG=10000, and a scale bar of 1 μm. Before testing, the sample was dispersed in ethanol, dropped onto a dried silicon wafer, and then sputter-coated with gold. This was used to observe the microsphere morphology, particle size distribution, surface condition, and dispersibility. The test results are as follows: Figure 2 As shown: the final product contains a large number of intact hollow microspheres, with no obvious breakage or agglomeration.

[0037] Transmission electron microscopy was used with an accelerating voltage of 200 kV and a scale bar of 500 nm. Before testing, the sample was ultrasonically dispersed in anhydrous ethanol, and the supernatant was dropped onto a dried microgrid carbon film to observe the internal hollow structure, carbon coating thickness, grain size, and elemental distribution. The test results are as follows: Figure 3 As shown: There are obvious cavities inside the microspheres, and the outer shell is assembled from MnO nanoparticles; the outer layer of the microspheres is coated with a thin amorphous carbon film to achieve uniform C coating of MnO.

[0038] Example 3: A method for preparing carbon-coated manganese oxide hollow microspheres includes: Step S1, Preparation of Solution A: Add manganese acetate tetrahydrate and polyvinylpyrrolidone (PVP K30) to a mixed solvent of anhydrous ethanol and deionized water. The mass-to-volume ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone and the mixed solution is 0.5g:2g:100mL. The volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 3:1. Stir at 420rpm for 28min at 20℃ to obtain the solution.

[0039] Step S2, Solution B preparation: 1,3,5-pyromellitic acid (H3BTC) is added to a mixed solvent of anhydrous ethanol and deionized water. The mass-to-volume ratio of 1,3,5-pyromellitic acid to the mixed solvent is 1 g: 80 mL, and the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 3:1. Stir at 220 rpm for 13 min at 10 °C to obtain the solution.

[0040] Step S3, Precursor Preparation: At 15–20°C, solution B is added dropwise to solution A at a rate of 0.9 mL / min. The mass ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone, and 1,3,5-pyromellitic acid is 1:4:2. The mixture is stirred at 320 rpm while being added dropwise. After the addition is complete, stirring is continued for 28 min. The mixture is then allowed to stand for 14.5 h.

[0041] Afterwards, the mixture was washed, centrifuged, and dried in a forced-air environment to obtain the Mn-MOFs precursor. The washing and centrifugation process was as follows: the reaction solution after standing was first centrifuged at 8500 rpm for 7 minutes, and the precipitate was collected. Then, the precipitate after centrifugation was washed three times each with deionized water and anhydrous ethanol (i.e., first washed three times with deionized water, then washed three times with anhydrous ethanol). The amount of washing solvent was the same as the amount of reaction solution after standing. The supernatant was discarded and the precipitate was retained. The specific process of forced-air drying is as follows: the precipitate after washing and centrifugation is placed in a forced-air drying oven and dried at 62°C for 23.5 hours to obtain Mn-MOFs precursor powder.

[0042] Step S4, Calcination: The Mn-MOFs precursor is placed in a tube furnace and heated to 705°C at a heating rate of 10.5°C / min under an argon atmosphere. It is then calcined in situ for 1.9 h and cooled to room temperature with the furnace to obtain carbon-coated manganese oxide hollow microspheres rich in oxygen vacancies.

[0043] Example 4: An application of carbon-coated manganese oxide hollow microspheres is specifically as follows: the above-mentioned carbon-coated manganese oxide hollow microspheres are used to prepare a positive electrode material for an aqueous zinc-ion battery; comprising: carbon-coated manganese oxide hollow microspheres (prepared using any one of Examples 1 to 3), acetylene black, and a binder, wherein their mass ratio is 7:2:1, the binder is polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) is used as the solvent, and the specific preparation method is as follows: First, polyvinylidene fluoride (PVDF) was dissolved in N-methylpyrrolidone to prepare a 5% (w / w) clear slurry, which was then stirred at 300 rpm for 4 h. Next, carbon-coated manganese oxide hollow microspheres and acetylene black were weighed according to the formula and manually ground in an agate mortar for 10 min to initially and uniformly mix the conductive agent and active powder. Then, the mixed powder was transferred to a centrifuge tube, and the corresponding amount of clear slurry was added. N-methylpyrrolidone solvent was added to adjust the slurry solid content to 15%. The mixture was first magnetically stirred at 300 rpm for 30 min, then ultrasonically stirred in a water bath (40 kHz, 300 W) for 20 min, and finally magnetically stirred at 300 rpm for 6 h to obtain a uniform, sediment-free positive electrode slurry. Then, using a doctor blade coater or automatic coater, the slurry was uniformly coated onto a 20 μm stainless steel foil current collector, with a wet film thickness controlled at 100 μm. After coating, the mixture was allowed to stand at room temperature for 30 minutes. The surface is allowed to level naturally to avoid pinholes. Then, it is first placed in a forced-air drying oven and dried at 60°C for 6 hours (to remove most of the solvent). Then, it is transferred to a vacuum drying oven and dried under vacuum at 60°C and -0.085 MPa for 12 hours (to completely remove residual NMP). Finally, it is punched into a circular positive electrode sheet with a diameter of 12 mm using a punching machine, and then lightly pressed into a tablet using a powder tablet press at a pressure of 5 MPa for 30 seconds to obtain the positive electrode sheet.

[0044] The negative electrode uses 0.1mm thick high-purity zinc foil (99.99%); a glass fiber membrane is used as the separator. The electrolyte is an aqueous solution consisting of 2 mol / L zinc sulfate heptahydrate (ZnSO4·7H2O) and 0.2 mol / L manganese sulfate monohydrate (MnSO4·H2O); The assembly method is the existing conventional battery assembly method (assembling CR2032 button cells).

[0045] Comparative Example 1: A method for preparing manganese oxide microspheres, comprising: Step S1, Preparation of Solution A: Add manganese acetate tetrahydrate and polyvinylpyrrolidone (PVP K30) to a mixed solvent of anhydrous ethanol and deionized water. The mass-to-volume ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone and the mixed solution is 0.5g:2g:100mL. The volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 2:1. Stir at 17.5℃ and 400rpm for 30min to obtain the solution.

[0046] Step S2, Solution B preparation: 1,3,5-Pyromellitic acid (H3BTC) was added to a mixed solvent of anhydrous ethanol and deionized water. The mass-to-volume ratio of 1,3,5-pyromellitic acid to the mixed solvent was 0.9 g: 80 mL, and the volume ratio of anhydrous ethanol to deionized water in the mixed solvent was 2:1. The mixture was stirred at 200 rpm for 15 min at 7.5 °C to obtain the solution.

[0047] Step S3, Precursor Preparation: Same as step S3 in Example 2.

[0048] Step S4, calcination: Same as step S4 in Example 2.

[0049] Comparative Example 2: A method for preparing manganese oxide microspheres, comprising: Step S1, Precursor Preparation: Manganese acetate tetrahydrate and polyvinylpyrrolidone (PVP K30) were added to a mixed solvent of anhydrous ethanol and deionized water. The mass-to-volume ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone, and the mixed solution was 4 g: 1 g: 100 mL. The volume ratio of anhydrous ethanol to deionized water in the mixed solvent was 1:1. Simultaneously, 1,3,5-pyromellitic acid (H3BTC) was added. The mass ratio of 1,3,5-pyromellitic acid to manganese acetate tetrahydrate was 2:1. The mixture was stirred continuously at 17.5 °C and 400 rpm for 2 h, and then allowed to stand for 24 h.

[0050] Then, the product was washed, centrifuged, and dried in sequence to obtain the Mn-MOFs precursor; the washing, centrifugation, and drying were the same as step S3 in Example 2.

[0051] Step S2, calcination: Same as step S4 in Example 2.

[0052] Comparative Example 3: A method for preparing manganese oxide microspheres, comprising: Step S1, Preparation of Solution A: Add manganese acetate tetrahydrate and polyvinylpyrrolidone (PVP K30) to a mixed solvent of anhydrous ethanol and deionized water. The mass-to-volume ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone and the mixed solution is 4g:1g:100mL. The volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 1:1. Stir at 17.5℃ and 400rpm for 30min to obtain the solution.

[0053] Step S2, Solution B preparation: 1,3,5-Pyromellitic acid (H3BTC) is added to a mixed solvent of anhydrous ethanol and deionized water. The mass-to-volume ratio of 1,3,5-pyromellitic acid to the mixed solvent is 1 g: 80 mL, and the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 1:1. Stir at 200 rpm for 15 min at 7.5 °C to obtain the solution.

[0054] Step S3, Precursor Preparation: At 17.5℃, solution B is added dropwise to solution A at a rate of 0.8 mL / min. The mass ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone, and 1,3,5-pyromellitic acid is 4:1:8. The mixture is stirred at 300 rpm while being added dropwise. After the addition is complete, stirring is continued for 30 min. The mixture is then allowed to stand for 15 h.

[0055] Then, the product was washed, centrifuged, and dried in sequence to obtain the Mn-MOFs precursor; the washing, centrifugation, and drying were the same as step S3 in Example 2.

[0056] Step S4, calcination: Same as step S4 in Example 2.

[0057] Comparative Example 4: A method for preparing manganese oxide microspheres, comprising: Replace manganese acetate tetrahydrate in solution A with an equal mass of manganese nitrate, while keeping the other steps and amounts of substances unchanged.

[0058] Comparative Example 5: A method for preparing manganese oxide microspheres, comprising: Replace manganese acetate tetrahydrate in solution A with an equal mass of manganese chloride, while keeping the other steps and amounts of substances unchanged.

[0059] Following the preparation method of Example 4, carbon-coated manganese oxide hollow microspheres from Examples 1 to 3 and manganese oxide microspheres from Comparative Examples 1 to 5 were prepared into coin cells, which were then tested after standing at room temperature for 12 hours. The battery charge-discharge test system was used for testing. The voltage ranged from 1 to 1.8V, and constant current charge-discharge was performed sequentially at current densities of 0.1A / g, 0.2A / g, 0.5A / g, 1A / g, and 2A / g, with 5 cycles at each current density. The charge-discharge voltage-capacity curves were recorded, the discharge specific capacity at each current density was calculated, and the rate performance curve was plotted.

[0060] Meanwhile, constant current charge and discharge was performed at a current density of 2A / g for 4000 cycles, and the discharge specific capacity was recorded each week to calculate the capacity retention rate. After the 4000 cycles, the rate test procedure was repeated to plot the rate charge and discharge curves after the cycles and evaluate the performance retention rate after the cycles.

[0061] The test results are shown in the table below:

[0062] As clearly shown in the table above, the carbon-coated manganese oxide hollow microspheres prepared using the technical solution of this invention (i.e., Examples 1 to 3) exhibit significantly better overall electrochemical performance as a cathode material for aqueous zinc-ion batteries than all comparative samples: the initial discharge specific capacity reaches a maximum of 391.7 mAh / g at a current density of 0.1 A / g, the rate capacity retention rate reaches a maximum of 75.9% at a current density of 1 A / g, and the capacity retention rate reaches a maximum of 137.4% after 4000 cycles at a high current density of 2 A / g. Therefore, this invention successfully prepared carbon-coated manganese oxide hollow microspheres with uniform morphology by controlling the solvent system, feeding method, raw material ratio, and manganese source type. This effectively solves the problems of poor conductivity and easy structural collapse during cycling of manganese oxide cathodes, significantly improving the rate performance and long cycle life of aqueous zinc-ion battery cathodes, and possesses good prospects for industrial application.

Claims

1. A method for preparing carbon-coated manganese oxide hollow microspheres, characterized in that: include: Step S1, Preparation of Solution A: Add manganese acetate tetrahydrate and polyvinylpyrrolidone to a mixed solvent of anhydrous ethanol and deionized water, and stir until clear to obtain the solution; Step S2, Solution B preparation: Add 1,3,5-pyromellitic acid to a mixed solvent of anhydrous ethanol and deionized water, and stir until clear to obtain the solution; Step S3, Precursor Preparation: Add solution B to solution A, stir and mix, then let stand; then, wash, centrifuge and dry in a forced-air dryer to obtain the Mn-MOFs precursor. Step S4, Calcination: The Mn-MOFs precursor is placed in a tube furnace and calcined in situ under an argon atmosphere to obtain carbon-coated manganese oxide hollow microspheres rich in oxygen vacancies.

2. The method for preparing carbon-coated manganese oxide hollow microspheres according to claim 1, characterized in that: In the preparation of solution A, the mass-to-volume ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone, and the mixed solution is 0.5g:2g:100mL; during the preparation of solution A, the mixture is stirred at 380-420rpm for 28-32min at 15-20℃.

3. The method for preparing carbon-coated manganese oxide hollow microspheres according to claim 1 or 2, characterized in that: In the preparation of solution B, the mass-to-volume ratio of 1,3,5-pyromellitic acid to the mixed solvent is 1 g: 80 mL; during the preparation of solution B, the mixture is stirred at 180-220 rpm for 13-17 min at 5-10 °C.

4. The method for preparing carbon-coated manganese oxide hollow microspheres according to claim 3, characterized in that: In the preparation of solutions A and B, the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 3:

1.

5. The method for preparing carbon-coated manganese oxide hollow microspheres according to claim 4, characterized in that: During the preparation of the precursor, solution B is added dropwise to solution A at a rate of 0.7-0.9 mL / min at 15-20°C. The mass ratio of manganese acetate tetrahydrate, polyvinylpyrrolidone, and 1,3,5-pyromellitic acid is 1:4:

2. The mixture is stirred at a speed of 280-320 rpm while being added dropwise. After the addition is complete, stirring is continued for 28-32 min. The mixture is then allowed to stand for 14.5-15.5 h.

6. The method for preparing carbon-coated manganese oxide hollow microspheres according to claim 5, characterized in that: In the process of preparing the precursor, the washing and centrifugation are as follows: First, the reaction solution after standing is centrifuged at a speed of 7500-8500 rpm for 7-9 min, and the precipitate is collected; then, the precipitate after centrifugation is washed three times each with deionized water and anhydrous ethanol, and the amount of washing solvent is the same as the amount of reaction solution after standing. The supernatant is discarded and the precipitate is retained. The specific process of forced-air drying is as follows: the precipitate after washing and centrifugation is placed in a forced-air drying oven and dried at 58-62℃ for 23.5-24.5h to obtain Mn-MOFs precursor powder.

7. The method for preparing carbon-coated manganese oxide hollow microspheres according to claim 6, characterized in that: Step S4 specifically involves: heating the furnace to 695–705°C at a heating rate of 9.5–10.5°C / min under an argon atmosphere, calcining it in situ for 1.9–2.1 hours, and then cooling it to room temperature in the furnace to obtain the final product.

Images