Improvement in self-discharge of Zn anode by applying surface modification for Zn-air batteries with high energy density

The self-discharge of Zn anode material is identified as a main factor that can limit the energy density of alkaline Zn-air batteries. Al2O3 has most positive effect on controlling the hydrogen evolution reaction accompanied by corroding Zn anode among various additives. The overpotential for hydrogen evolution is measured by potentio-dynamic polarization analysis. AI-oxide with high overpotential for hydrogen; evolution reaction is uniformly coated on the surface of Zn powders via chemical solution process. The morphology and composition of the surface-treated and pristine Zn powders are characterized by SEM, EDS, XRD and XPS analyses. Aluminum is distributed homogeneously over the surface of modified Zn powders, indicating uniform coating of Al-oxide, and O1s and Al2p spectra further identified surface coating layer to be the Al-oxide. The Al-oxide coating layer can prevent Zn from exposing to the KOH electrolyte, resulting in minimizing the side reactions within batteries. The 0.25 wt.% aluminum oxide coated Zn anode material provides discharging time of more than 10 h, while the pristine Zn anode delivers only 7 h at 25 mA cm(-2). Consequently, a surface-treated Zn electrode can reduce self-discharge which is induced by side reaction such as H-2 evolution, resulting in increasing discharge capacity. (C) 2012 Elsevier B.V. All rights reserved.