Air electrode preparation method and metal-air battery

Abstract

This invention provides a method for preparing an air electrode and a metal-air battery to improve battery performance. The air electrode preparation method includes the following steps: S1, mixing carbon material and catalyst material in a solvent to obtain a precursor mixture solution, wherein the mass percentage of carbon material is 50%–90%, and the mass percentage of catalyst material is 10%–50%; the catalyst material is a compound containing a transition metal element; S2, freezing the precursor mixture solution at a low temperature of -50 to -10°C; S3, subjecting the frozen precursor mixture solution to vacuum sublimation drying to obtain an air electrode with a porous structure. The air positive electrode of the metal-air battery of this invention is prepared using the above-described air electrode preparation method.

Description

Technical Field

[0001] This invention relates to the field of energy storage devices and materials, specifically to a method for preparing an air electrode and a metal-air battery. Background Technology

[0002] Metal-air batteries are safe and efficient energy conversion and storage devices with broad application prospects in portable mobile devices, backup power supplies, and new energy vehicles. Lithium and sodium metals, in particular, possess high electrochemical equivalents and theoretical voltages, with corresponding theoretical energy densities of 5200 Wh / kg and 2640 Wh / kg for metal-air batteries, respectively, making them a research hotspot for next-generation energy storage power sources.

[0003] Currently, metal-air batteries still face many unresolved issues. Non-aqueous lithium / sodium air batteries are a novel type of secondary battery involving gas-liquid-solid three-phase reactions. The air electrode generally needs good conductivity and redox properties, providing a high electrochemical specific surface area to enhance the overall chemical driving force of the reaction. Since discharge products such as peroxides / superoxides are insoluble in the electrolyte, they deposit in the pores of the air electrode, causing pore blockage and covering catalytic active sites, leading to premature battery failure. Therefore, a certain level of porosity is required to accommodate the discharge products. To ensure the flow of electrolyte and air, the air electrode also requires optimized pore distribution to improve air and ion transport rates while avoiding pore blockage caused by discharge product accumulation. Discharge capacity is closely related to pore size and pore volume density. Pores that are too small or too large are detrimental to oxygen reduction. Pores that are too small are easily blocked by discharge products, preventing further O2 diffusion; pores that are too large will completely wet the entire air electrode, with the two-phase interface replacing the three-phase interface, which is not conducive to accommodating more discharge products. Therefore, the air electrode must not only ensure sufficient flow paths for electrolyte and air, but also accommodate discharge products. The multi-level structural design of the electrode is crucial to battery performance.

[0004] A common electrode fabrication method involves coating porous current collectors such as carbon paper and nickel foam with carbon materials and catalysts with high specific surface area. This method is simple to operate, but because carbon particles tend to aggregate during the preparation process, the final specific surface area is often small, and the porosity inside the electrode is limited. Another common method is the template method, which has the advantages of regular morphology and high porosity, but the template needs to be removed by a secondary chemical process, making the operation complicated. The key to the development of metal-air batteries is the design of an air electrode structure with appropriate pore size distribution and specific surface area. It is necessary to comprehensively consider the influence of factors such as the storage of discharge products, gas diffusion, electrolyte wetting, ion diffusion, and electron conduction on the formation of the gas-liquid-solid three-phase interface and battery performance, and optimize the design and fabrication of the air electrode. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing an air electrode and a metal-air battery to improve battery performance.

[0006] To achieve the above objectives, the present invention provides a method for preparing an air electrode, comprising the following steps: S1, mixing carbon material and catalyst material in a solvent to obtain a precursor mixed solution, wherein the mass percentage of carbon material is 50% to 90% and the mass percentage of catalyst material is 10% to 50%; the catalyst material is a compound containing a transition metal element; S2, freezing the precursor mixed solution at a low temperature of -50 to -10°C; S3, subjecting the frozen precursor mixed solution to vacuum sublimation drying to obtain an air electrode with a porous structure.

[0007] In the above-mentioned method for preparing air electrodes, the carbon material is one or more of carbon nanotubes, carbon nanowires, carbon fibers, Ketjen Black, graphene, activated carbon, Super-P, Kuraray, and NORIT carbon.

[0008] In the above-mentioned method for preparing air electrodes, the transition metal element is selected from one or more of Mn, Fe, Co, Ni, Cu, Zn, Mo, and Cr.

[0009] In the above-mentioned method for preparing an air electrode, the solvent is one or more of water, ethanol, acetone, and N-methylpyrrolidone.

[0010] In the above method for preparing an air electrode, in step S3, the vacuum degree is 3 Pa to 30 Pa and the drying time is 2 h to 6 h.

[0011] Another technical solution provided by the present invention is a metal-air battery, wherein the positive electrode is an air electrode prepared by the above-described air electrode preparation method.

[0012] The aforementioned metal-air battery further includes a negative electrode, an electrolyte, and a separator; the negative electrode is lithium metal or sodium metal, and the electrolyte is an organic electrolyte.

[0013] In the aforementioned metal-air battery, the electrolyte is a 1 mol / L LiTFSI / TEGMDE organic solution.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are:

[0015] (1) The porous structure of the air electrode of the present invention is mainly composed of macropores, which are sufficient to accommodate discharge products of micron size, thereby improving the battery discharge capacity.

[0016] (2) The method for preparing the air electrode of the present invention is simple;

[0017] (3) The air electrode of the present invention has good elasticity, which can effectively alleviate the volume change of the metal-air battery during charging and discharging.

[0018] (4) In the transition metal compound / carbon composite material of the present invention, the transition metal compound material, as an air electrode catalyst material, promotes the reversible progress of oxygen reduction reaction and oxygen evolution reaction;

[0019] (5) The metal-air battery of the present invention has good electrochemical performance and low material cost, and can be widely used in electronic devices, emergency power supplies, power supplies and other fields. Attached Figure Description

[0020] The method for preparing the air electrode and the metal-air battery of the present invention are given by the following embodiments and figures.

[0021] Figure 1 This is a SEM image of the air electrode for a metal-air battery according to Embodiment 1 of the present invention.

[0022] Figure 2 This is a charge-discharge curve of the metal-air battery in Embodiment 1 of the present invention. Detailed Implementation

[0023] The following will combine Figures 1-2 The method for preparing the air electrode and the metal-air battery of the present invention will be described in further detail.

[0024] The method for preparing the air electrode of the present invention includes the following steps:

[0025] S1, carbon materials and catalyst materials are mixed in a solvent to obtain a precursor mixed solution, wherein the mass percentage of carbon materials is 50% to 90% and the mass percentage of catalyst materials is 10% to 50%;

[0026] The carbon material is one or more of the following: carbon nanotubes, carbon nanowires, carbon fibers, Ketjenblack, graphene, activated carbon, Super-P, Kuraray, and NORIT carbon.

[0027] The catalyst material is a compound containing a transition metal element, which is selected from one or more of Mn, Fe, Co, Ni, Cu, Zn, Mo, and Cr.

[0028] The solvent is one or more of water, ethanol, acetone, and N-methylpyrrolidone;

[0029] S2, cryogenically freeze the precursor mixture solution at a temperature of -50 to -10°C;

[0030] S3, the frozen precursor mixture solution is subjected to vacuum sublimation drying to obtain an air electrode with a porous structure. The vacuum degree is 3 Pa to 30 Pa and the drying time is 2 h to 6 h.

[0031] The metal-air battery of the present invention comprises a positive electrode, a negative electrode, an electrolyte, and a separator; the air electrode prepared by the air electrode preparation method is the positive electrode, the negative electrode is a metal sheet, and the electrolyte is an organic electrolyte, preferably a 1 mol / L LiTFSI / TEGMDE electrolyte. The metal-air battery of the present invention can be used as a primary battery or as a secondary battery.

[0032] The air electrode preparation method of this invention is mainly based on freeze-drying molding technology: a solution containing carbon materials and catalyst materials is mixed and then freeze-dried. Utilizing the extrusion action during ice crystal formation in the freezing process, the carbon materials and catalyst materials are extruded into the cavity walls of a porous electrode. After the ice crystals sublimate, a porous electrode with a three-dimensional structure is formed, with the morphology as shown in the figure. Figure 1 As shown, this porous electrode consists of micron-sized, irregularly shaped cavities. The cavity walls, woven from carbon and catalyst materials, also exhibit a porous structure, facilitating the transport of electrolyte and air within the air electrode. The cross-sectional SEM image reveals that most cavities are larger than micrometers, sufficient to store large-sized discharge products. Furthermore, the cavities are interconnected, promoting the flow of electrolyte and air.

[0033] Porous carbon materials possess high electrical conductivity, a large specific surface area, and a relatively high degree of defect, thus exhibiting ideal catalytic performance. Transition metals, on the other hand, possess excellent oxygen evolution catalytic properties. Introducing transition metals into porous carbon materials and combining them with porous carbon materials can yield air electrode materials with bifunctional catalytic performance, thereby improving battery performance. Simultaneously, the use of transition metals replaces traditional expensive precious metals, significantly reducing the material cost of the battery and enabling the widespread application of metal-air batteries.

[0034] Example 1

[0035] 900 mg of carbon nanotubes (CNTs) were dispersed in 100 mL of aqueous solution, and then 100 mg of MnO2 nanowires were added. The solution containing CNTs and MnO2 nanowires was mixed thoroughly and pre-frozen in a freeze dryer to obtain a precursor mixture solution. The frozen precursor mixture solution was placed in a sealed vacuum container and heated at a vacuum level controlled between 10 Pa and 30 Pa for sublimation drying. The temperature was raised to 25 °C during the vacuum sublimation drying process, followed by desorption and further drying. Utilizing the compression effect during ice crystal formation during freezing, CNTs and MnO2 nanowires were compressed into the cavity walls of a porous electrode. After the ice crystals sublimated and dried, a porous air electrode with a three-dimensional structure was formed. The SEM image of the porous air electrode is shown below. Figure 1 As shown.

[0036] Using the air electrode fabricated above as the positive electrode, a lithium sheet as the negative electrode, and a 1 mol / L LiTFSI / TEGMDE organic solution as the electrolyte, a lithium-air battery was assembled. This lithium-air battery exhibited an efficiency of 1 mA / cm² within a voltage range of 2.0V to 4.5V. 2 Charge-discharge tests and cycle performance tests were conducted at current densities, and the results are as follows: Figure 2 As shown, the battery's charging and discharging voltage remains stable, and the discharge capacity reaches over 5000mAh / g.

[0037] Example 2

[0038] 800 mg of carbon nanowires were dispersed in 200 mL of aqueous solution, and then 200 mg of Co3O4 nanowires were added. The solution containing carbon nanowires and Co3O4 nanowires was mixed thoroughly and then pre-frozen in a freeze dryer to obtain a precursor mixture solution. The frozen precursor mixture solution was placed in a sealed vacuum container and heated at a vacuum level controlled between 10-30 Pa for sublimation drying. The temperature was raised to 25 °C during the vacuum sublimation drying process, followed by desorption and further drying. Utilizing the compression effect during ice crystal formation in the freezing process, the carbon nanowires and Co3O4 nanowires were compressed into the cavity walls of a porous electrode. After the ice crystals sublimated and dried, a porous electrode with a three-dimensional structure was formed.

[0039] Using the air electrode fabricated above as the positive electrode, the sodium sheet as the negative electrode, and a 1 mol / L NaTFSI / TEGMDE solution as the electrolyte, a sodium-air battery was assembled. This lithium-air battery exhibited a voltage range of 2.0V to 4.5V and an efficiency of 1 mA / cm². 2 Under the specified current density, charge-discharge tests and cycle performance tests were conducted. The battery's charge-discharge voltage remained stable, and there was no significant potential decay after more than 50 cycles.

[0040] The air electrode of this invention is prepared by freeze-drying, which is simple and quick. During the rapid freeze-drying process, it can maintain a multidimensional conductive porous structure. The metal-air battery using this air electrode has a high discharge specific capacity, which greatly improves the battery specific energy. At the same time, the air electrode has good elasticity and its thickness can be adaptively adjusted, giving the metal-air battery a self-adjusting function, thereby alleviating or solving the battery failure problem caused by battery volume expansion.

[0041] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A metal-air battery, characterized by, The positive electrode is an air electrode, which is prepared using the following steps: S1, carbon materials and catalyst materials are mixed in a solvent to obtain a precursor mixed solution, wherein the mass percentage of carbon materials is 50% to 90% and the mass percentage of catalyst materials is 10% to 50%; The catalyst material is a compound containing transition metal elements; S2, cryogenically freeze the precursor mixture solution at a temperature of -50 to -10°C; S3, the frozen precursor mixture solution is vacuum sublimated and dried to obtain an air electrode with a porous structure. The metal-air battery further includes a negative electrode, an electrolyte, and a separator; the negative electrode is metallic lithium or metallic sodium, and the electrolyte is an organic electrolyte.

2. The metal-air battery of claim 1, wherein, The carbon material is one or more of carbon nanotubes, carbon nanowires, carbon fibers, Ketjen black, graphene, activated carbon, and Super-P.

3. The metal-air battery of claim 1, wherein the air cathode comprises a catalyst layer, a microporous layer, a gas diffusion layer, and a gas permeable current collector. The transition metal elements are selected from one or more of Mn, Fe, Co, Ni, Cu, Zn, Mo, and Cr.

4. The metal-air battery as described in claim 1, characterized in that, The solvent is one or more of water, ethanol, acetone, and N-methylpyrrolidone.

5. The metal-air battery as described in claim 1, characterized in that, In step S3, the vacuum degree of vacuum sublimation drying is 3 Pa to 30 Pa, and the drying time is 2 h to 6 h.

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