| Energy crisis and environment problem are becoming more serious, so it’s important to find safe, efficient and clean energy. Metal-air batteries offer many advantages, including simple system structure, high energy density, low cost and so on. It has great application in outdoor, miniature electronic devices, transportation and military. However, these batteries have some serious problems, such as poor gas diffusivity and channel blocking. This paper aimed to investigate the permeability of gas diffusion layer and electrochemical properties of magnesium-air battery, so we choose hydrophobic and oleophobic films with large pores to replace the gas diffusion layer of air cathode, and use them to assemble air battery. It provides a good idea for new design of air cathode and air battery, especially secondary air batteries.First, we prepared hydrophobic and oleophobic films through sol-gel and corrosion method respectively, and then modified them by different organics. The results of SEM show that there are many coarse structures formed on hydrophobic and olelphobic films after disposed, these coarse structures are good for improving films’ hydrophobic and olelphobic performance. From contact angle test, we can find that: Water contact angle of hydrophobic cotton cloth is about 140°, and oil contact angle of copper nets is about 129°. The treated cotton cloth and copper nets couldn’t be infiltrated by electrolyte for a long time(>4 d). In other words, the film can prevent electrolyte leakage efficiently. The results of gas permeability show that: At the same rate of air inflow, the volume of displacement using hydrophobic film, oleophobic film and current gas diffusion layer are 54 ml, 53 ml, 19 ml respectively, it means that the treated cotton cloth and copper nets have better gas permeability.Then hydrophobic film was used to assemble magnesium-air battery and then characterized it. The results of electrochemical show that: The discharge performance of the magnesium-air battery with hydrophobic film show an open circuit potential of 1.4 V, with a peak power density of 40 m W cm-2 at room temperature. The battery, with a small area of Mg sheet as anode(1×1.5×0.07 cm), can discharge at about 1.4 V over 4 h at the constant current of 1 m Acm-2 stably. The electrochemical results of battery with hydrophobic film demonstrate that oxygen can easily pass through the film and diffusion into battery to attend the electrochemical reaction.We used oleophobic film to assemble magnesium-air secondary battery, and investigated its electrochemical properties. A small gas diffusion area in button cell can provide enough oxygen to guarantee a big discharge current in discharge process. But the oleophobic film has poor gas selectivity, the moisture, which has a great influence of battery performance in the air, can easily enter into the battery, and attend the electrochemical reaction. So the electrochemical measurement must be carried out in a dry system. Compared with traditionalstructure battery, the magnesium-air secondary battery with oleophobic film has a higher discharge specific capacity and voltage. With the increase of discharge current, the performance of traditional structure battery declines seriously, but new designed battery don’t.Because of corrosion of Mg sheet and bad reversibility of discharge products, all battery show serious cyclicity. |
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