Revisiting the anodic stability of nickel-cobalt hydroxide/carbon composite electrodes for rechargeable Ni-Zn battery

Aqueous rechargeable Ni-Zn batteries are considered as a new generation of safe and reliable electrochemical energy storage system. However, low electronic conductivity of Ni-based cathodes hinders the practical application of Ni-Zn batteries. This problem can be overcome by compositing the Ni-based cathode with highly conductive carbon substrates. A chemical oxidation pre-treatment is popularly applied to the carbon substrates to increase their hydrophilicity and thus facilitate the growth of active materials in aqueous systems. However, the anodic stability of the oxidized carbon substrates is greatly challenged,which has never been addressed in previous reports. In this work, we first compared the anodic stability of carbon fiber paper with and without oxidation treatment and find that carbon substrate with the chemical treatment caused remarkable oxidization current in the required voltage range. To take both anodic stability and fine growth of active materials into account, here we demonstrated a facile physical surface-treatment method of ethanol wetting to replace the chemical treatment. The ethanol infiltration removes gas adsorption on carbon substrates and thus promotes their hydrophilicity. This cost-effective strategy simultaneously achieves a high anodic stability and a fine growth and uniform distribution of nickel-cobalt hydroxide on the carbon microfibers. The resulting Ni-Zn battery provides a high discharge capacity of 219 m Ah/g with an operation cell voltage of 1.75 V.