Preparation method and application of anode catalyst of metal-air secondary battery

Abstract

The invention belongs to the technical field of secondary battery processing, and particularly relates to a preparation method of a positive electrode catalyst of a metal-air secondary battery, and the preparation method comprises the following steps: heating a metal salt solution to 80-100 DEG C at a constant temperature, and dropwise adding ammonia water to adjust the pH value to be greater than 8.5; adding an amine compound into the mixed solution, stirring for 1 hour, and adding acetic acid to adjust the pH value to 7.5-8.0; evaporating the solvent at constant temperature to obtain a precursor, crushing and grinding for later use; and sintering the precursor in argon or hydrogen-argon mixed gas at a high temperature of 700-900 DEG C for 6-12 hours to obtain the carbon nanotube coated metal oxide catalyst. The positive electrode catalyst of the metal-air battery with the carbon nano tube coated with the metal oxide is obtained through a pyrolysis method, and the catalyst can fully expose active sites, promote adsorption and desorption of intermediates, accelerate electron transport and reduce reaction energy barriers, so that the charge-discharge overpotential is greatly reduced, and the service life of the battery is prolonged. And the metal-air secondary battery with more excellent cycling stability can be realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of secondary batteries, and particularly relates to a positive electrode catalyst of a metal-air secondary battery and a metal-air secondary battery based on the positive electrode catalyst. BACKGROUND

[0002] Currently, with the continuous development of technology, the demand for energy in society is increasing, and traditional energy supply has been difficult to meet this urgent demand. At the same time, the progress of society also urgently needs cleaner energy that is safer, more stable, and renewable, as well as more economical and affordable energy storage devices. Lithium-ion batteries have provided excellent endurance performance for various portable electronic devices in the past years, and have also become the preferred energy storage solution for most electric vehicles. Although lithium-ion batteries have achieved remarkable success in commercial applications, there are still a series of problems from a technical point of view, including high manufacturing cost and relatively low energy density. These problems obviously cannot meet the future demand for high energy density and high power density power and energy storage batteries, and lithium-ion batteries also have safety hazards. Metal-air batteries have become the focus of attention as a storage solution due to their extremely high energy density, environmentally friendly characteristics, and great development potential.

[0003] Currently, research on metal-air batteries mainly focuses on the development of high-performance catalysts. Such catalysts can optimize the reaction pathway through a catalytic mechanism to overcome the challenges faced by metal-air secondary batteries, thereby improving battery performance. Common catalyst materials currently include noble metals, metal oxides, and carbon-based catalysts, but the high cost of noble metals and the instability of carbon-based catalysts limit their large-scale application.

[0004] In recent years, transition metal catalysts have attracted attention due to their good stability and low price. However, the electrical conductivity of transition metals is relatively poor, so surface engineering strategies are usually needed to improve their catalytic performance. By doping heteroatoms (such as nitrogen, phosphorus, sulfur, etc.) on carbon materials with high specific surface area and high electrical conductivity, and anchoring metal-based materials on their surface in situ, the electrical conductivity of the catalyst is greatly improved. This method not only promotes the uniform dispersion of metals, but also significantly enhances the ability of electronic conduction and mass transfer of molecules / ions. In addition, heteroatom-doped carbon materials also help to improve the activity of the oxygen reduction reaction (ORR). Therefore, this is considered to be a very effective method that can significantly improve the performance of ORR and oxygen evolution reaction (OER) catalysts, providing great potential for the application of metal-air batteries.

[0005] The application adopts an industrial route with low raw material price and wide source, and obtains a MO@CNTs (M=Fe, Co, Ni, Cu) catalyst of carbon nanotube coated metal oxide through pyrolysis reaction, and the carbon coated metal oxide can have higher catalytic activity, and effectively improves the cycle performance of metal-air batteries. SUMMARY

[0006] Therefore, the application aims to solve the technical problem of providing a metal-air battery positive electrode catalyst of carbon nanotube coated metal oxide and a metal-air secondary battery based on the positive electrode catalyst, which can fully expose active sites, promote the adsorption and desorption of intermediates, accelerate electron transport, and reduce the reaction energy barrier, thereby greatly reducing the charge and discharge overpotential, and the good conductivity and high specific surface area of the carbon nanotube help to realize a metal-air secondary battery with more excellent cycle stability.

[0007] In order to achieve the above-mentioned purpose, the application adopts the following technical solutions: In a first aspect, the application provides a preparation method of a positive electrode catalyst of a metal-air secondary battery, which comprises the following steps: S1, heating the metal salt solution to 80-100℃, and then adding ammonia water to adjust the pH to greater than 8.5; S2, adding an amine compound to the mixed solution obtained in step S1, stirring for 1h, and then adding acetic acid to adjust the pH to 7.5-8.0; S3, evaporating the solvent in the mixed solution at constant temperature to obtain a precursor, which is uniformly crushed and ground for standby; S4, high-temperature sintering the precursor powder, the sintering temperature is 700-900℃, the treatment time is 6-12h, and the sintering atmosphere is argon or hydrogen-argon mixed gas (H2 10%Vol), and the carbon nanotube coated metal oxide catalyst is obtained after being cooled to room temperature. Preferably, the metal salt in step S1 is nitrate, chloride, sulfate or acetate of iron, cobalt, nickel or manganese, and is preferably acetate.

[0008] Preferably, the constant temperature treatment temperature in step S1 is 80℃.

[0009] Preferably, the amine compound in step S2 is melamine, dicyandiamide or ethylenediamine, and the mass is 2-4 times the mass of the metal salt weighed in step S1, preferably dicyandiamide, and the mass is 3 times the mass of the metal salt.

[0010] Preferably, the high-temperature treatment temperature in step S4 is 700-900℃, and the treatment time is 6-12h, preferably 800℃ high-temperature treatment for 8h.

[0011] Secondly, the present invention provides a metal-air secondary battery based on the aforementioned positive electrode catalyst, comprising a negative electrode, a positive electrode, an electrolyte, and a separator located between the positive and negative electrodes, wherein the positive electrode is obtained by coating a composite of the aforementioned positive electrode catalyst and a binder onto a current collector.

[0012] Preferably, the negative electrode is any one of lithium foil, lithium sheet, lithium alloy, sodium foil, sodium sheet, sodium alloy, potassium foil, potassium sheet, potassium alloy, magnesium foil, magnesium sheet, and magnesium alloy.

[0013] Preferably, the diaphragm is a glass fiber membrane, a polyethylene microporous membrane, a polypropylene microporous membrane, or an ethylene-propylene copolymer microporous membrane.

[0014] Preferably, the binder for the positive electrode is polyvinylidene fluoride (PVDF).

[0015] Preferably, the mass ratio of the positive electrode catalyst to the binder in the positive electrode is 8~10:1, more preferably 9:1.

[0016] In this invention, the current collector of the positive electrode is a common current collector in the art, such as carbon paper.

[0017] In this invention, the metal-air secondary battery can be assembled as a button cell, a pouch cell, or a cylindrical cell.

[0018] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention obtains a positive electrode catalyst for a metal-air battery with carbon nanotubes coated with metal oxides by pyrolysis. This catalyst can fully expose active sites, promote the adsorption and desorption of intermediates, accelerate electron transport, and reduce the reaction energy barrier, thereby greatly reducing the charge and discharge overpotential. The good conductivity and high specific surface area of ​​carbon nanotubes help to achieve a metal-air secondary battery with better cycle stability.

[0019] (2) The metal-air secondary battery provided by the present invention has the characteristics of simple composition, low price and environmental friendliness, and shows great application prospects. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0021] Figure 1 This is a comparison chart of the capacity-voltage curves of Embodiments 1 and 2 of the present invention; Figure 2 This is a SEM image of Embodiment 1 of the present invention; Figure 3 This is a SEM image of Embodiment 5 of the present invention; Figure 4 This is a long-cycle performance diagram of Embodiment 1 of the present invention; Figure 5 This is a long-cycle performance diagram of Embodiment 3 of the present invention; Figure 6 This is a long-cycle performance diagram of Embodiment 4 of the present invention. Detailed Implementation

[0022] The present invention will be further described below through embodiments, but is not limited to these embodiments. Experimental methods not specifically described in the embodiments generally use conventional conditions and conditions described in manuals, or conditions recommended by the manufacturer. The general equipment, materials, reagents, etc., used are all commercially available unless otherwise specified. All raw materials required for the following embodiments are commercially available.

[0023] Example 1: Weigh out 4g of cobalt acetate tetrahydrate, dissolve the cobalt salt in 50mL of deionized water, heat to 80℃ and maintain constant temperature; add ammonia water to adjust the pH to be greater than 8.5, then add dicyandiamide (12g); stir at constant temperature for 1h, then add acetic acid solution to adjust the pH to 7.5~8.0, and then evaporate the solvent at constant temperature until the solvent is completely evaporated; crush, grind and sieve the collected precursor, and treat the obtained precursor powder at 800℃ for 8h under argon atmosphere, and obtain the catalyst Co-1 after cooling to room temperature.

[0024] Example 2: Weigh out 4g of cobalt acetate tetrahydrate, dissolve the cobalt salt in 50mL of deionized water, heat to 80℃ and maintain constant temperature; add ammonia water to adjust the pH to be greater than 8.5, then add melamine (12g); stir at constant temperature for 1h, then add acetic acid solution to adjust the pH to 7.5~8.0, and then evaporate the solvent at constant temperature until the solvent is completely evaporated; crush, grind and sieve the collected precursor, and treat the obtained precursor powder at 800℃ for 8h under an argon atmosphere, and obtain the catalyst Co-2 after cooling to room temperature.

[0025] Example 3: Weigh out 4g of cobalt acetate tetrahydrate, dissolve the cobalt salt in 50mL of deionized water, heat to 80℃ and maintain constant temperature; add ammonia water to adjust the pH to be greater than 8.5, then add dicyandiamide (8g); stir at constant temperature for 1h, then add acetic acid solution to adjust the pH to 7.5~8.0, and then evaporate the solvent at constant temperature until the solvent is completely evaporated; crush, grind and sieve the collected precursor, and treat the obtained precursor powder at 700℃ for 8h under argon atmosphere, and obtain the catalyst Co-3 after cooling to room temperature.

[0026] Example 4: Weigh out 4g of cobalt acetate tetrahydrate, dissolve the cobalt salt in 50mL of deionized water, heat to 80℃ and maintain constant temperature; add ammonia water to adjust the pH to be greater than 8.5, then add dicyandiamide (16g); stir at constant temperature for 1h, then add acetic acid solution to adjust the pH to 7.5~8.0, and then evaporate the solvent at constant temperature until the solvent is completely evaporated; crush, grind and sieve the collected precursor, and treat the obtained precursor powder at 900℃ for 8h under argon atmosphere, and obtain the catalyst Co-4 after cooling to room temperature.

[0027] Example 5: Weigh out 4g of cobalt acetate tetrahydrate, dissolve the cobalt salt in 50mL of deionized water, heat to 80℃ and maintain constant temperature; add ammonia water to adjust the pH to be greater than 8.5, then add dicyandiamide (12g); stir at constant temperature for 1h, then evaporate the solvent at constant temperature until the solvent is completely evaporated; crush, grind and sieve the collected precursor, and treat the obtained precursor powder at 800℃ for 8h under argon atmosphere, and obtain the catalyst Co-5 after cooling to room temperature.

[0028] Positive electrode sheet preparation examples Co-1 (Example 1), Co-2 (Example 2), Co-3 (Example 3), Co-4 (Example 4), and Co-5 (Example 5) were used as positive electrode catalysts. The positive electrode catalyst materials and polyvinylidene fluoride (PVDF) were dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 9:1. After stirring for 6-8 hours, a uniform paste slurry was obtained. 70 μL of the slurry was transferred by pipette and dropped onto carbon paper (12 mm in diameter). The solvent was evaporated under vacuum at 120 °C to obtain a positive electrode sheet, which was then placed in an argon-filled glove box for later use.

[0029] Figure 1 A comparison of capacity-voltage curves for Examples 1 and 2 is presented. This graph, by comparing the corresponding voltage curves, reveals that Example 1 exhibits a more significant characteristic compared to Example 2: a lower overpotential. This difference demonstrates that the composite material prepared using dicyandiamide exhibits superior electrocatalytic performance. Specifically, Example 1 demonstrates superior electrocatalytic performance, which is significant for improving the performance of the battery system. It is worth emphasizing that this catalyst plays a crucial role in the entire battery reaction process, primarily by reducing the polarization of the electrode reaction, thereby enhancing the overall battery efficiency.

[0030] Figure 2 and Figure 3Scanning electron microscope (SEM) images of Examples 1 and 5 are presented. Comparative analysis of these two images revealed that no carbon nanotubes were formed in the catalyst when acetic acid was not added to adjust the pH in subsequent processes. This observation indicates that pH control has a crucial impact on the morphology of the final product. These experimental results further emphasize the importance of precise pH control in the process for the formation of catalysts with specific structures, providing valuable insights for future similar studies.

[0031] Figure 4 , Figure 5 and Figure 6 Long-term cycling performance graphs for Examples 1, 3, and 4 are presented. Under the condition of a set capacity of 1000 mAh g⁻¹, Example 1 exhibits superior cycling performance retention, lasting for over 50 weeks. In contrast, Examples 3 and 4 only maintained their cycling performance for 35 and 25 weeks, respectively, exhibiting significant capacity decay. This comparison reveals that by adjusting the mass ratio of dicyandiamide to metal salt, we can obtain catalysts with excellent electrochemical performance. This finding not only theoretically confirms the criticality of material design but also provides important practical guidance for further optimization of battery technology.

[0032] The above description represents preferred embodiments in conjunction with preferred embodiments, but it should not be construed as limiting the specific embodiments of the present invention to those described. For those skilled in the art, various variations and substitutions can be made without departing from the research concept of the present invention, and all such variations and substitutions are included within the scope defined by the present invention.

Claims

1. A method for preparing a positive electrode catalyst for a metal-air secondary battery, characterized in that, Includes the following steps: S1. After heating the metal salt solution to 80~100℃ at a constant temperature, add ammonia water dropwise to adjust the pH to be greater than 8.5; S2. Add amine compounds to the mixture from step S1, stir for 1 hour, and then add acetic acid to adjust the pH to 7.5-8.

0. S3. Evaporate the solvent at a constant temperature to obtain the precursor, then pulverize and grind it for later use. S4. The precursor is sintered at high temperature in argon or a hydrogen-argon mixture at 700-900℃ for 6-12 hours to obtain a carbon nanotube-coated metal oxide catalyst.

2. The preparation method according to claim 1, characterized in that, The metal salt is a nitrate, chloride, sulfate, or acetate of iron, cobalt, nickel, or manganese.

3. The preparation method according to claim 1, characterized in that, The constant temperature heating temperature in step S1 is 80℃.

4. The preparation method according to claim 1, characterized in that, The amine compound is melamine, dicyandiamide, or ethylenediamine, and its mass is 2 to 4 times the mass of the metal salt in step S1.

5. The preparation method according to claim 1, characterized in that, The high-temperature sintering temperature in step S4 is 800℃, and the processing time is 8 hours.

6. A metal-air secondary battery, comprising a negative electrode, a positive electrode, an electrolyte, and a separator, characterized in that, The positive electrode is a composite of a positive electrode catalyst and a binder prepared by any one of claims 1-5, coated onto a current collector.

7. The metal-air secondary battery according to claim 6, characterized in that, The negative electrode is a lithium foil, sodium foil, potassium foil, magnesium foil, or an alloy thereof.

8. The metal-air secondary battery according to claim 6, characterized in that, The diaphragm is a glass fiber membrane, a polyethylene microporous membrane, a polypropylene microporous membrane, or an ethylene-propylene copolymer microporous membrane.

9. The metal-air secondary battery according to claim 6, characterized in that, In the positive electrode, the mass ratio of the positive electrode catalyst to the binder is 8~10:1, and the binder is polyvinylidene fluoride.

10. The metal-air secondary battery according to claim 6, characterized in that, The current collector is carbon paper, and the battery is assembled as a button cell, pouch cell, or cylindrical cell.

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