Double-layer membrane cathode with improved oxygen diffusivity in zincair batteries

The commercialization of portable zinc-air batteries has been limited to the coin cell shape, mainly due to issues related to the cathode morphology. These types of batteries commonly use an aqueous electrolyte, which is susceptible to changes in air temperature and humidity that can cause leakage and block the air-cathode. This problem entails the use of bulky systems that require an empty gap between the porous cathode and the electrolyte to avoid flooding. This paper presents a novel fabrication method and morphology for a conductive and flexible double-membrane nanocomposite air-cathode. The pore morphology for each membrane was designed for two purposes using two different foaming techniques. The foaming technique includes supercritical CO2 in a high-pressure chamber to create a hydrophobic closed-cell structure. On the other hand, NaCl was used as a temporary space-holder to create a hydrophilic open-cell morphology. The closed-cell membrane presented an optimal performance as a hydrophobic oxygen diffusion layer whereas the hydrophilic open-cell membrane, apart from increasing the catalytic surface area, also increased the water absorption by 12 times with a swelling capacity of 68%. The electrochemical tests exhibited stable performance without presenting leaking even when bent under a relative humidity of 85-90%. The specific energy density achieved was as high as 198 W h kg-1, which is similar to that of some of the available commercial alkaline cells. Furthermore, the double-membrane air-cathode also has the advantages of low cost, high recyclability and the possibility of multiple configurations including flexibility for both primary and secondary configurations.