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

Abstract

The application belongs to the technical field of electrode materials, and particularly relates to a preparation process of a manganese-based positive electrode based on oxygen reduction catalyst modification, preparation of a zinc-containing framework material and a manganese-containing framework material; the zinc-containing framework material and the manganese-containing framework material are mixed with polyethylene glycol, and after hydrothermal reaction, the product is calcined to obtain ZnMn2O4; the ZnMn2O4 is used to prepare an electrode sheet, and Pt modification is performed on the surface of the electrode sheet, and the manganese-based positive electrode based on oxygen reduction catalyst modification is obtained. The preparation process of the manganese-based positive electrode based on oxygen reduction catalyst modification is simple, the cost is low, the operation steps are safe and simple, the preparation process does not need dangerous chemicals, and also does not need strong oxidizing or toxic chemicals, and has the advantages of environmental friendliness, safety controllability, and easy industrial application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrode materials, and particularly relates to a method for preparing a manganese-based positive electrode based on an oxygen reduction catalyst. BACKGROUND

[0002] With the increasing consumption of fossil fuels and the increasingly serious environmental problems, new energy such as wind energy and solar energy gradually becomes mainstream energy, but its intermittent nature requires the development of efficient and safe energy storage technology. Electrochemical energy storage is increasingly concerned due to its high conversion efficiency, no geographical restrictions and high safety. Among them, aqueous secondary batteries are considered as ideal energy storage systems because they do not have the risk of flammable and explosive electrolyte, and have high power density and ionic conductivity.

[0003] Traditional manganese-based positive electrode materials are widely used in aqueous batteries due to their low cost and environmental protection. However, in the actual charging and discharging process, the manganese-based positive electrode often faces the problem of oxygen evolution (OER), and the generated oxygen and H + not only causes the decomposition of electrolyte, but also promotes the insertion of H + , affecting the cycle stability of the battery. These problems not only lead to electrolyte decomposition and short cycle life, but also seriously affect the overall performance of the battery. SUMMARY

[0004] The application mainly provides a manganese-based positive electrode material modified by an oxygen reduction reaction (ORR) catalyst, and a preparation process of the material, to solve the problems of electrolyte decomposition and H + insertion caused by oxygen evolution reaction in the prior art, improve the performance of aqueous zinc batteries, and the specific technical solutions are as follows:

[0005] A preparation process of a manganese-based positive electrode based on an oxygen reduction catalyst, comprising 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, and after hydrothermal reaction, calcining the product to obtain ZnMn2O4; using ZnMn2O4 to prepare an electrode sheet, and performing Pt modification on the surface of the electrode sheet, to obtain the same.

[0006] Further, the preparation of the zinc-containing skeleton material or the manganese-containing skeleton material comprises the following steps: mixing N, N-dimethylformamide with water, adding terephthalic acid and sodium hydroxide, and fully mixing; continuing to add zinc salt or manganese salt, and reacting at 50-60℃ for 6-8h; fully washing and drying the product to obtain the zinc-containing skeleton material or the manganese-containing skeleton material.

[0007] Further, the volume ratio of the N,N-dimethylformamide and water is 1-3:1; the molar ratio of the terephthalic acid and sodium hydroxide is 1:1.5-1.8; the molar ratio of the zinc or manganese in the zinc or manganese salt and the terephthalic acid is 1.5-2:1.

[0008] Further, the zinc salt includes one or more of zinc nitrate, zinc chloride, zinc sulfate or zinc acetate; and the manganese salt includes one or more of manganese chloride, manganese nitrate or manganese sulfate.

[0009] Further, the preparation of the ZnMn2O4 includes the following steps: heating a low-molecular-weight polyethylene glycol water bath, adding a zinc-containing skeleton material and a manganese-containing skeleton material to be fully dispersed, adding ethanol, continuing to stir for 1-2 hours to obtain a precursor liquid; vacuum treating the precursor liquid for 12-24 hours, and then drying; after drying, calcining at 300-400 DEG C for 1-2 hours, and then increasing the temperature to 550-650 DEG C to calcine for 2-4 hours.

[0010] Further, the molar ratio of the zinc and 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 and the ethanol is 4-6:1.

[0011] Further, the temperature of the water bath heating is 50-70 DEG C; and the vacuum treatment is performed at -50--150 pa.

[0012] Further, before mixing the zinc-containing and manganese-containing skeleton materials with the polyethylene glycol, the zinc-containing and manganese-containing skeleton materials are ground with ethanol for 0.3-0.8 hours, and then heat treated at 200-300 DEG C for 3-5 hours.

[0013] Further, the preparation of the pole piece includes the following steps: mixing the ZnMn2O4 and a conductive agent and a binder, and then coating onto a current collector to obtain a pole piece; immersing the pole piece in a chloroplatinic acid solution and irradiating; taking out the pole piece and standing; repeating the immersing and standing operations for 2-5 times.

[0014] Further, the concentration of the chloroplatinic acid solution is 0.01-0.05 M; and the irradiation is performed for 5-20 minutes.

[0015] By using the above scheme, the method has the following advantages:

[0016] The present application modifies high-activity Pt particles and clusters on the surface and inside of the manganese-based positive electrode, and reduces the oxygen generated in the charging process in time to water, thereby effectively inhibiting the embedding of oxygen and H + generated by oxygen precipitation in the charging process of the ZnMn2O4 positive electrode. +Reduction to water, improve the structure stability of the positive electrode in the process of charge and discharge, and significantly improve the cycle life and overall battery performance.

[0017] The manganese-based positive electrode material prepared by the application has an extremely high specific surface area, is conducive to photocatalytic chloroplatinic acid, and forms uniform Pt modification. The generated hierarchical pore structure in the electrode material can accurately control the active sites of Pt, form a stable catalytic layer, regulate oxygen circulation, balance oxygen evolution and oxygen reduction reaction, and also take into account the effects of shortening the ion diffusion path, accelerating the transmission rate, and promoting the penetration of the electrolyte.

[0018] When the polyethylene glycol is impregnated into the zinc and manganese framework material, ethanol is added, and the small molecular volume of ethanol is used to first penetrate into the small pores of the framework material, and then the high compatibility with polyethylene glycol is used to improve the affinity of polyethylene glycol and the framework material, and the intense molecular movement during the volatilization of ethanol also helps to reduce the surface tension and attract the deep impregnation of polyethylene glycol.

[0019] The zinc and manganese framework material and the polyethylene glycol template are used to form an electrode material combining small pores and large pores. The small pores formed under the influence of the decomposition of the polyethylene glycol template provide better spatial sites for the embedding of Pt while increasing the surface area, and are also conducive to reducing the detachment of Pt. The structure of the electrode material is stable, and the problem of easy detachment and collapse of the structure of the impregnated and deposited catalytic material is solved. The large pores formed by the polyethylene glycol template are conducive to the miniaturization and dispersion of ZnMn2O4 crystals, and fully improve the electrochemical performance of the electrode material.

[0020] The method of staged calcination is adopted, the polyethylene glycol is first decomposed at a lower temperature to reduce energy consumption, and the influence of carbon dioxide generated by the decomposition of polyethylene glycol on the product is avoided. At the same time, a zinc-manganese precursor with relatively easy diffusion and rearrangement of internal atoms, relatively disorder and low crystallinity can be formed, which is conducive to the formation and pore control of the subsequent ZnMn2O4 crystal. The manganese-based positive electrode material prepared by the application has good structure stability and cycle performance.

[0021] The method of photo-deposition is used to modify the surface of the ZnMn2O4 positive electrode to form a uniform Pt modification layer. Long light exposure time may cause the dissolution of the positive electrode, such as the dissolution of manganese. In addition, long-term light exposure may cause more Pt deposition, forming a continuous film or large-size particles on the surface, which inhibits ion deintercalation. More Pt will also promote oxygen evolution, causing additional gas generation and electrolyte consumption. By adjusting the deposition time and light intensity, the load and distribution of Pt can be controlled to form a stable catalytic layer. This method can accurately control the morphology and size of the catalyst, thereby further optimizing the oxygen reduction activity of the positive electrode and significantly improving the cycle stability and performance of the battery.

[0022] The preparation process of the present application is simple, low in cost, safe and simple in operation steps, does not need dangerous chemicals, strong oxidizing or toxic chemicals in the preparation process, has the advantages of environmental friendliness, safety and controllability, and is easy to be applied in industrialization. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is an electron microscope photo of ZnMn2O4 of Example 1.

[0024] Figure 2 is a spherical aberration electron microscope photo of the manganese-based positive electrode material of Example 1.

[0025] Figure 3 is a 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.

[0026] Figure 4 is a long cycle test (a) and rate cycle test (b) of Example 1 and Comparative Example 1 at a current density of 0.5 A / g.

[0027] Figure 5 is a comparison chart of long cycle tests of Examples 2-5 at a current density of 0.1 A / g. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0029] 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 mixed thoroughly to obtain a mixed solution; 5.95 g of zinc nitrate hexahydrate was further added, and reacted at 50°C for 7 h; the product was washed thoroughly and dried to obtain a skeleton material containing zinc; according to the above method, 2.51 g of manganese chloride was used to replace zinc nitrate to prepare a skeleton material containing manganese;

[0030] (2) 12 g of the zinc-containing framework material and 2 g of the manganese-containing framework material were moistened with ethanol, ground in a mortar for 0.5 h, and then heat-treated at 250°C for 4 h; PEG-400 was heated in a water bath at 70°C, the zinc-containing framework material and the manganese-containing framework material were added and dispersed, 0.2 times the volume of ethanol was added to the PEG-400, and stirring was continued for 1-2 h to obtain a precursor solution; the precursor solution was treated under a vacuum of -100 Pa for 18 h, and then dried; after drying was completed, the mixture was calcined at 350°C for 1.5 h, and then the temperature was increased to 600°C for calcination for 3 h to obtain ZnMn2O4; the ZnMn2O4 was characterized by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) as shown in FIG. 1. Figure 1 As can be seen from the TEM image of FIG. 1, the obtained ZnMn2O4 powder is a particle with uniform particle size.

[0031] (3) ZnMn2O4, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 7:2:1, ground, and dispersed in N-methylpyrrolidone, and then uniformly mixed to obtain a slurry; the slurry was coated on a titanium foil, and then dried at 70°C for 12 h to obtain an electrode sheet; the electrode sheet was immersed in a 0.025 M 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 min; the electrode sheet was taken out and allowed to stand in air for 1 h, and the immersion and standing operations were repeated three times; the electrode sheet was dried at 60°C for 2 h to obtain a manganese-based positive electrode modified with an oxygen reduction catalyst (labeled as Pt-ZnMn2O4).

[0032] A STEM image of the manganese-based positive electrode obtained in Example 1 is shown in FIG. 2. Figure 2 As can be seen from FIG. 2, the morphology of ZnMn2O4 did not change significantly after photodeposition, and the main 211 crystal face of ZnMn2O4 was observed at a resolution of 2 nm, indicating that the ZnMn2O4 obtained by the method of the present application has high purity, and also indicating that the modification of Pt can ensure the integrity of the ZnMn2O4 structure and does not affect the main body. In addition, obvious light spots can be seen in the ZnMn2O4 interior and surface, meaning that Pt is deposited in the interior and on the surface of ZnMn2O4 and is uniformly distributed, i.e., Pt is successfully modified on ZnMn2O4.

[0033] Example 2: The difference from Example 1 is that the electrode sheet was immersed in a 0.01 M chloroplatinic acid solution, slowly stirred at a speed of 280 rpm, and irradiated with a xenon lamp for 5 min.

[0034] Example 3: The difference from Example 1 is that the electrode sheet was immersed in a 0.01 M chloroplatinic acid solution, slowly stirred at a speed of 280 rpm, and irradiated with a xenon lamp for 10 min.

[0035] Example 4: The difference from Example 1 is that the electrode sheet was immersed in a 0.01 M chloroplatinic acid solution, slowly stirred at a speed of 280 rpm, and irradiated with a xenon lamp for 15 min.

[0036] Example 5: The difference from Example 1 is that the electrode was immersed in a 0.01M chloroplatinic acid solution, stirred slowly at 280 rpm and irradiated with light for 20 min.

[0037] Comparative Example: The difference from Example 1 is that Pt photodeposition (labeled as ZnMn2O4) was not performed.

[0038] Example and Comparative Sample Testing: Using the manganese-based positive electrode prepared in each example and comparative example, with ZnF as the negative electrode and 2M ZnSO4 + 0.15M MnSO4 as the electrolyte, full cells were constructed and their electrochemical performance was tested. The results are as follows: Figures 3~5 As shown.

[0039] Figure 3 (a) and Figure 3 Figure (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 cathode, the Pt-modified ZnMn2O4 cathode exhibits superior electrochemical performance and higher stability, indicating that Pt modification can effectively maintain cathode stability. Figure 3 As can be seen from (a) in Example 1, there is still no sign of decline after 100 cycles, indicating that the structure of ZnMn2O4 prepared by the method of the present invention is beneficial to improving the stability of Pt loading and can still have good catalytic activity after multiple cycles.

[0040] Figure 4 (a) shows the long-cycle test conducted on Example 1 and Comparative Example 1 at a current density of 0.5 A / g. Figure 4 Figure (b) shows the rate cycling test results. As can be seen from the figure, the Pt-modified ZnMn2O4 cathode exhibits better high-current cycling performance and rate performance compared to the standard ZnMn2O4 cathode. Figure 4 (a) shows that the specific capacity of the Pt-modified ZnMn2O4 cathode after 150 cycles is comparable to that after the first cycle, indicating that even under high current density and longer cycles, the ZnMn2O4 prepared in this invention can still ensure the uniformity and high activity of Pt modification.

[0041] Figure 5 The graph shows a comparison of long-cycle tests conducted in Examples 2-5 at a current density of 0.1 A / g. As can be seen from the graph, the battery performance is best at 5 min and 10 min of illumination time, which are between 5 and 20 min.

[0042] For those skilled in the art, other various corresponding changes and modifications can be made to the above described technical solutions and concepts, and all these changes and modifications should belong to the protection scope of the claims of the present application.

Claims

1. A process for the preparation of a manganese-based positive electrode based on a modification of an oxygen reduction catalyst, characterized in that, The method comprises the following steps: The preparation of the zinc-containing framework material and the manganese-containing framework material comprises the following steps: mixing N, N-dimethylformamide with water, adding terephthalic acid and sodium hydroxide, mixing thoroughly, continuously adding zinc salt or manganese salt, and reacting at 50-60 DEG C for 6-8 hours; washing and drying the product to obtain the zinc-containing framework material or the manganese-containing framework material; The preparation of the zinc-containing framework material and the manganese-containing framework material comprises the following steps: mixing N, N-dimethylformamide with water, adding terephthalic acid and sodium hydroxide, mixing thoroughly, continuously adding zinc salt or manganese salt, and reacting at 50-60 DEG C for 6-8 hours; washing and drying the product to obtain the zinc-containing framework material or the manganese-containing framework material; The preparation of the zinc-containing framework material and the manganese-containing framework material comprises the following steps: mixing N, N-dimethylformamide with water, adding terephthalic acid and sodium hydroxide, mixing thoroughly, continuously adding zinc salt or manganese salt, and reacting at 50-60 DEG C for 6-8 hours; washing and drying the product to obtain the zinc-containing framework material or the manganese-containing framework material; 2. The process for the preparation of a manganese-based positive electrode modified with an oxygen reduction catalyst according to claim 1, characterized in that, 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 zinc in the zinc salt or manganese in the manganese salt to the terephthalic acid is 1.5-2:

1.

3. The process for the preparation of a manganese-based positive electrode modified with an oxygen reduction catalyst according to claim 1, characterized in that, The zinc salt comprises one or more of zinc nitrate, zinc chloride, zinc sulfate or zinc acetate; and the manganese salt comprises one or more of manganese chloride, manganese nitrate or manganese sulfate.

4. The process for the preparation of a manganese-based positive electrode modified with an oxygen reduction catalyst according to claim 1, characterized in that, 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.

5. The process for the preparation of a manganese-based positive electrode modified with an oxygen reduction catalyst according to claim 1, characterized in that, The water bath is heated at a temperature of 50-70 DEG C; and the vacuum treatment is performed at a pressure of -50--150 pa.

6. The process for the preparation of a manganese-based positive electrode modified with an oxygen reduction catalyst according to claim 1, characterized in that, Before mixing the zinc-containing and manganese-containing framework materials with the 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 DEG C for 3-5 hours.

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