Preparation process of manganese-based positive electrode based on oxygen reduction catalyst modification

Abstract

The invention belongs to the technical field of electrode materials, and particularly relates to a manganese-based positive electrode preparation process based on oxygen reduction catalyst modification, which comprises the following steps: preparing a zinc-containing framework material and a manganese-containing framework material; the preparation method comprises the following steps: mixing a zinc-containing and manganese-containing framework material with polyethylene glycol, carrying out a hydrothermal reaction, and calcining a product to obtain ZnMn2O4; and preparing a pole piece by using ZnMn2O4, and carrying out Pt modification on the surface of the pole piece to obtain the ZnMn2O4 / Pt composite material. The manganese-based positive electrode based on oxygen reduction catalyst modification is simple in preparation process, relatively low in cost, safe and simple in operation steps, free of hazardous chemicals in the preparation process and free of strong oxidizing or highly toxic chemicals, has the advantages of environmental friendliness, safety and controllability, and is easy for industrial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode materials, and in particular relates to a method for preparing a manganese-based positive electrode based on modification of an oxygen reduction catalyst. Background Art

[0002] With increasing fossil fuel consumption and increasingly severe environmental issues, renewable energy sources such as wind and solar power are becoming mainstream. However, their intermittent nature requires the development of efficient and safe energy storage technologies. Electrochemical energy storage is gaining increasing attention due to its high conversion efficiency, lack of geographical restrictions, and high safety. Aqueous secondary batteries, however, are considered an ideal energy storage system due to their lack of electrolyte flammability and explosion risks, as well as their high power density and ionic conductivity.

[0003] Traditional manganese-based cathode materials are widely used in aqueous batteries due to their low cost and environmental friendliness. However, in the actual charge and discharge process, manganese-based cathodes often face the problem of oxygen evolution (OER). The generated oxygen and H + Not only will it lead to the decomposition of the electrolyte, but it will also promote the + These problems not only lead to electrolyte decomposition and shortened cycle life, but also seriously affect the overall performance of the battery. Summary of the Invention

[0004] The present invention mainly provides a manganese-based cathode material modified with an oxygen reduction reaction (ORR) catalyst and a preparation process of the material to solve the problems of electrolyte decomposition and H + To solve the embedding problem and improve the performance of aqueous zinc batteries, the specific technical solutions are as follows: A process for preparing a manganese-based positive electrode based on oxygen reduction catalyst modification includes the following steps: preparing a zinc-containing skeleton material and a manganese-containing skeleton material; mixing the zinc-containing and manganese-containing skeleton materials with polyethylene glycol, subjecting the mixture to a hydrothermal reaction, and calcining the product to obtain ZnMn2O4; using ZnMn2O4 to prepare an electrode piece, and performing Pt modification on the surface of the electrode piece to obtain the cathode.

[0005] Furthermore, the preparation of the zinc-containing framework material or the manganese-containing framework material includes the following steps: mixing N,N-dimethylformamide with water, adding terephthalic acid and sodium hydroxide, mixing thoroughly, continuing to add zinc salt or manganese salt, and reacting at 50-60°C for 6-8 hours; fully washing and drying the product to obtain the zinc-containing framework material or the manganese-containing framework material.

[0006] Furthermore, the volume ratio of the N,N-dimethylformamide to water is 1-3:1; the molar ratio of the terephthalic acid to sodium hydroxide is 1:1.5-1.8; and the molar ratio of the zinc in the zinc salt or the manganese in the manganese salt to terephthalic acid is 1.5-2:1.

[0007] Furthermore, the zinc salt includes one or more of zinc nitrate, zinc chloride, zinc sulfate or zinc acetate; the manganese salt includes one or more of manganese chloride, manganese nitrate or manganese sulfate.

[0008] Furthermore, the preparation of ZnMn2O4 includes the following steps: heating a low molecular weight polyethylene glycol in a water bath, adding a zinc-containing framework material and a manganese-containing framework material to fully disperse them, adding ethanol, and continuing to stir for 1 to 2 hours to obtain a precursor liquid; vacuum-treating the precursor liquid for 12 to 24 hours, and then drying it; after drying, calcining it at 300 to 400°C for 1 to 2 hours, and then heating it to 550 to 650°C and calcining it for 2 to 4 hours to obtain the product.

[0009] Furthermore, the molar ratio of zinc to manganese in the zinc-containing framework material and the manganese-containing framework material is 1-1.5:2; and the volume ratio of the low molecular weight polyethylene glycol to ethanol is 4-6:1.

[0010] Furthermore, the water bath heating temperature is 50-70° C.; and the vacuum treatment is performed at -50-150 Pa.

[0011] Furthermore, before mixing the zinc-containing and manganese-containing framework materials with polyethylene glycol, the zinc-containing and manganese-containing framework materials are ground with ethanol for 0.3-0.8 hours, and then heat-treated at 200-300° C. for 3-5 hours.

[0012] Furthermore, the preparation of the electrode includes the following steps: mixing ZnMn2O4 with a conductive agent and a binder and coating the mixture on a current collector to obtain an electrode; immersing the electrode in a chloroplatinic acid solution and irradiating the electrode with light; taking out the electrode and allowing it to stand; and repeating the immersion and standing operations 2 to 5 times.

[0013] Furthermore, the concentration of the chloroplatinic acid solution is 0.01-0.05 M; and the illumination is performed for 5-20 min.

[0014] By adopting the above scheme, the method of the present invention has the following advantages: The present invention modifies the surface and interior of the manganese-based positive electrode with highly active Pt particles and clusters, and promptly reduces the oxygen generated during the charging process to water, thereby effectively inhibiting the oxygen and H generated by oxygen precipitation during the charging process of the ZnMn2O4 positive electrode. + embedding of oxygen and H + Reduction to water improves the structural stability of the positive electrode during charging and discharging, and significantly improves the cycle life and overall battery performance.

[0015] The manganese-based cathode material produced by this invention has an extremely high specific surface area, which facilitates the photocatalytic reaction of chloroplatinic acid and forms a uniform Pt modification. The multi-level pore structure generated in the electrode material precisely controls the Pt active sites, forming a stable catalytic layer, regulating oxygen circulation, balancing oxygen evolution and oxygen reduction reactions, and simultaneously shortening ion diffusion paths, accelerating transport rates, and promoting electrolyte penetration.

[0016] When polyethylene glycol is impregnated into a zinc and manganese skeleton material, ethanol is added. The small molecular volume of ethanol is utilized to first penetrate into the fine pores of the skeleton material, and then the high compatibility with polyethylene glycol is utilized to improve the affinity of the polyethylene glycol and the skeleton material. In addition, the violent molecular movement during ethanol volatilization is also conducive to reducing surface tension, thereby attracting the deep impregnation of polyethylene glycol.

[0017] The present invention utilizes a zinc and manganese framework material and a polyethylene glycol template to form an electrode material with a combination of small and large pores. The small pores formed by the decomposition of the polyethylene glycol in the organic framework increase the surface area while providing better spatial sites for Pt embedding and helping to reduce Pt desorption. The electrode material has strong structural stability, solving the problem of easy shedding and structural collapse of the impregnated and deposited catalytic material. The large pores formed by the polyethylene glycol template facilitate the miniaturization and dispersion of ZnMn2O4 crystals, fully improving the electrochemical performance of the electrode material.

[0018] The present invention uses a staged calcination method to first decompose polyethylene glycol at a lower temperature, reducing energy consumption and preventing the impact of carbon dioxide produced by polyethylene glycol decomposition on the product. This method also forms a zinc-manganese precursor with relatively easy internal atomic diffusion and rearrangement, resulting in a relatively disordered and low-crystallinity structure. This facilitates the subsequent formation of ZnMn2O4 crystals and pore control, resulting in a manganese-based cathode material with excellent structural stability and cycling performance.

[0019] The present invention uses a photodeposition method to modify the surface of a ZnMn2O4 positive electrode with Pt, forming a uniform Pt-modified layer on the surface of the ZnMn2O4 positive electrode. Excessive illumination time may cause dissolution of the positive electrode, such as the dissolution of manganese. Furthermore, prolonged illumination may result in the deposition of more Pt, forming a continuous film or large particles on the surface, which inhibits ion deintercalation. Excessive Pt also promotes oxygen evolution, leading to additional gas generation and electrolyte consumption. The method of the present invention is used to adjust the deposition time and illumination intensity, controllably adjusting the Pt loading and distribution to form a stable catalytic layer. This method can precisely control the morphology and size of the catalyst, thereby further optimizing the oxygen reduction activity of the positive electrode and significantly improving the battery's cycle stability and performance.

[0020] The preparation process of the present invention is simple, the cost is low, the operation steps are safe and simple, the preparation process does not require hazardous chemicals, and does not require strong oxidizing or highly toxic chemicals. It has the advantages of being environmentally friendly, safe and controllable, and is easy to industrially apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is an electron microscope photograph of ZnMn2O4 in Example 1.

[0022] Figure 2 This is a spherical aberration electron microscope photograph of the manganese-based positive electrode material of Example 1.

[0023] Figure 3 The long cycle test (a) and charge-discharge curve (b) of Example 1 and Comparative Example 1 at a current density of 0.1 A / g.

[0024] Figure 4 The long cycle test (a) and rate cycle test (b) of Example 1 and Comparative Example 1 were performed at a current density of 0.5 A / g.

[0025] Figure 5 This is a comparison chart of long cycle tests performed on Examples 2 to 5 at a current density of 0.1 A / g. DETAILED DESCRIPTION

[0026] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0027] Example 1: (1) 20 mL of N,N-dimethylformamide was mixed with 10 mL of water, 1.66 g of terephthalic acid and 0.65 g of sodium hydroxide were added, and the mixture was thoroughly mixed to obtain a mixed solution; 5.95 g of zinc nitrate hexahydrate was then added, and the mixture was reacted at 50°C for 7 h; the product was thoroughly washed and dried to obtain a zinc-containing skeleton material; according to the above method, 2.51 g of manganese chloride was used instead of zinc nitrate to prepare a manganese-containing skeleton material; (2) Before mixing the zinc-containing and manganese-containing framework materials with the polymer, take 12g of the zinc-containing framework material and 2g of the manganese-containing framework material, moisten them with ethanol, grind them in a mortar for 0.5h, and then heat-treat them at 250℃ for 4h; heat PEG-400 in a water bath at 70℃, add the zinc-containing framework material and the manganese-containing framework material to fully disperse them, add ethanol 0.2 times the volume of PEG-400, and continue stirring for 1~2h to obtain a precursor liquid; treat the precursor liquid at -100Pa vacuum for 18h, and then dry it; after drying, calcine it at 350℃ for 1.5h, and then heat it to 600℃ for calcination for 3h to obtain ZnMn2O4; Figure 1 It can be seen from the electron microscope photos that the obtained ZnMn2O4 powder is particles with uniform particle size.

[0028] (3) ZnMn2O4, conductive carbon black and polyvinylidene fluoride were mixed and ground in a mass ratio of 7:2:1, and then dispersed in N-methylpyrrolidone. After mixing evenly, the mixture was coated on a titanium foil and dried at 70°C for 12 hours to obtain an electrode. The electrode was immersed in a 0.025M chloroplatinic acid solution, slowly stirred at a speed of 280 rpm and irradiated with a xenon lamp with a total light power of 50 W for 10 minutes. The electrode was taken out and allowed to stand in the air for 1 hour. The immersion and standing operations were repeated 3 times. After drying at 60°C for 2 hours, a manganese-based positive electrode modified with an oxygen reduction catalyst (labeled as Pt-ZnMn2O4) was obtained.

[0029] The spherical aberration electron microscope photo of the manganese-based positive electrode obtained in Example 1 is as follows Figure 2 As shown in the figure, it can be seen that the morphology of ZnMn2O4 does not change significantly after photodeposition, and the main 211 crystal plane of ZnMn2O4 is present at a resolution of 2nm, indicating that the ZnMn2O4 prepared by the method of the present invention has a high purity. It also shows that the modification of Pt can ensure the integrity of the ZnMn2O4 structure without affecting the main body. In addition, the figure shows obvious light spots inside and on the surface of ZnMn2O4, which means that Pt is deposited inside and on the surface of ZnMn2O4 and is evenly distributed, that is, Pt is successfully modified on ZnMn2O4.

[0030] Example 2: The difference from Example 1 is that the electrode is immersed in a 0.01M chloroplatinic acid solution, slowly stirred at a speed of 280 rpm and irradiated with light for 5 minutes.

[0031] Example 3: The difference from Example 1 is that the electrode is immersed in a 0.01M chloroplatinic acid solution, slowly stirred at a speed of 280 rpm and irradiated with light for 10 minutes.

[0032] Example 4: The difference from Example 1 is that the electrode is immersed in a 0.01M chloroplatinic acid solution, slowly stirred at a speed of 280 rpm and irradiated with light for 15 minutes.

[0033] Example 5: The difference from Example 1 is that the electrode is immersed in a 0.01M chloroplatinic acid solution, slowly stirred at a speed of 280 rpm and irradiated with light for 20 minutes.

[0034] Comparative Example: The difference from Example 1 is that no Pt photodeposition was performed (marked as ZnMn2O4).

[0035] Test of samples of the embodiments and comparative examples: The manganese-based positive electrode prepared in each embodiment and comparative example was used, ZnF was used as the negative electrode, and 2M ZnSO4+0.15M MnSO4 was used as the electrolyte to make a full battery, and the electrochemical performance test was carried out. The results are as follows Figures 3-5 shown.

[0036] Figure 3 (a) and Figure 3 (b) shows the long cycle test and charge-discharge curves of Example 1 and Comparative Example 1 at a current density of 0.1 A / g, respectively. As can be seen from the figure, compared with the unmodified ZnMn2O4 positive electrode, the Pt-modified ZnMn2O4 positive electrode shows better electrochemical performance and higher stability, indicating that Pt modification can effectively maintain the stability of the positive electrode. Figure 3 From (a), it can be seen that Example 1 still shows no sign of decline after 100 cycles, indicating that the structure of ZnMn2O4 prepared by the method of the present invention is conducive to improving the loading stability of Pt, and can still have good catalytic activity after multiple cycles.

[0037] Figure 4 (a) is a long cycle test of Example 1 and Comparative Example 1 at a current density of 0.5 A / g. Figure 4 (b) is the rate cycle test. As can be seen from the figure, the Pt-modified ZnMn2O4 cathode shows better high current cycle performance and rate performance than the ZnMn2O4 cathode. Figure 4 (a) shows that the specific capacity of the Pt-modified ZnMn2O4 positive electrode after 150 cycles is comparable to that of the first cycle, indicating that even at high current density and longer cycles, the ZnMn2O4 prepared by the present invention can still ensure uniform Pt modification and high activity.

[0038] Figure 5 This is a comparison chart of long cycle tests of Examples 2 to 5 performed at a current density of 0.1 A / g. It can be seen from the figure that the battery performance is best between 5 and 20 minutes, and at illumination times of 5 minutes and 10 minutes.

[0039] Those skilled in the art can make various other corresponding changes and deformations based on the technical solutions and concepts described above, and all of these changes and deformations should fall within the scope of protection of the claims of the present invention.

Claims

1. A process for preparing a manganese-based positive electrode modified with an oxygen reduction catalyst, characterized in that: The following steps are involved: A zinc-containing skeleton material and a manganese-containing skeleton material are prepared; low molecular weight polyethylene glycol is heated in a water bath, the zinc-containing skeleton material and the manganese-containing skeleton material are added and fully dispersed, ethanol is added, and stirring is continued for 1-2 hours to obtain a precursor liquid; the precursor liquid is vacuum-treated for 12-24 hours, and then dried; after drying, the precursor liquid is calcined at 300-400°C for 1-2 hours, and then the temperature is raised to 550-650°C and calcined for 2-4 hours to obtain ZnMn2O4; an electrode is prepared using ZnMn2O4, and Pt is modified on the surface of the electrode to obtain ZnMn2O4.

2. The process for preparing a manganese-based positive electrode modified with an oxygen reduction catalyst according to claim 1, wherein: The preparation of the zinc-containing framework material or the manganese-containing framework material comprises the following steps: mixing N,N-dimethylformamide with water, adding terephthalic acid and sodium hydroxide, fully mixing, continuously adding zinc salt or manganese salt, and reacting at 50-60° C. for 6-8 hours; and fully washing and drying the product to obtain the zinc-containing framework material or the manganese-containing framework material.

3. The process for preparing a manganese-based positive electrode modified with an oxygen reduction catalyst according to claim 2, wherein: The volume ratio of the N,N-dimethylformamide to water is 1-3:1; the molar ratio of the terephthalic acid to sodium hydroxide is 1:1.5-1.8; and the molar ratio of the zinc in the zinc salt or the manganese in the manganese salt to terephthalic acid is 1.5-2:

1.

4. The process for preparing a manganese-based positive electrode modified with an oxygen reduction catalyst according to claim 2, wherein: The zinc salt includes one or more of zinc nitrate, zinc chloride, zinc sulfate or zinc acetate; the manganese salt includes one or more of manganese chloride, manganese nitrate or manganese sulfate.

5. The process for preparing a manganese-based positive electrode modified with an oxygen reduction catalyst according to claim 1, wherein: The molar ratio of zinc to manganese in the zinc-containing skeleton material and the manganese-containing skeleton material is 1-1.5:2; and the volume ratio of the low molecular weight polyethylene glycol to ethanol is 4-6:

1.

6. The process for preparing a manganese-based positive electrode modified with an oxygen reduction catalyst according to claim 1, wherein: The water bath heating temperature is 50-70° C.; the vacuum treatment is performed at -50-150 Pa.

7. The process for preparing a manganese-based positive electrode modified with an oxygen reduction catalyst according to claim 1, wherein: Before mixing the zinc-containing and manganese-containing framework materials with polyethylene glycol, the zinc-containing and manganese-containing framework materials are ground with ethanol for 0.3-0.8 hours, and then heat-treated at 200-300° C. for 3-5 hours.

8. The process for preparing a manganese-based positive electrode modified with an oxygen reduction catalyst according to claim 1, wherein: The preparation of the electrode includes the following steps: mixing ZnMn2O4 with a conductive agent and a binder and coating the mixture on a current collector to obtain the electrode; immersing the electrode in a chloroplatinic acid solution and irradiating the electrode with light; taking the electrode out and allowing it to stand; and repeating the immersion and standing operations 2 to 5 times.

9. The process for preparing a manganese-based positive electrode modified with an oxygen reduction catalyst according to claim 8, characterized in that: The concentration of the chloroplatinic acid solution is 0.01-0.05 M; and the illumination is performed for 5-20 minutes.

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