Electroactive ZnO: Mechanisms, Conductivity, and Advances in Zn Alkaline Battery Cycling

Zinc oxide is of great interest for advanced energy devices because of its low cost, wide direct bandgap, non-toxicity, and facile electrochemistry. In zinc alkaline batteries, ZnO plays a critical role in electrode passivation, a process that hinders commercialization and remains poorly understood. Here, novel observations of an electroactive type of ZnO formed in Zn-metal alkaline electrodes are disclosed. The electrical conductivity of battery-formed ZnO is measured and found to vary by factors of up to 10(4), which provides a first-principles-based understanding of Zn passivation in industrial alkaline batteries. Simultaneous with this conductivity change, protons are inserted into the crystal structure and electrons are inserted into the conduction band in quantities up to approximate to 10(20) cm(-3) and approximate to 1 mAh g(ZnO)(-1). Electron insertion causes blue electrochromic coloration with efficiencies and rates competitive with leading electrochromic materials. The electroactivity of ZnO is evidently enabled by rapid crystal growth, which forms defects that complex with inserted cations, charge-balanced by the increase of conduction band electrons. This property distinguishes electroactive ZnO from inactive classical ZnO. Knowledge of this phenomenon is applied to improve cycling performance of industrial-design electrodes at 50% zinc utilization and the authors propose other uses for ZnO such as electrochromic devices.

Automated summary

This study reveals an electroactive type of zinc oxide formed in zinc-metal alkaline electrodes and measures its electrical conductivity change. The study finds that the conductivity change of the electroactive zinc oxide is closely related to the insertion of protons into the crystal structure and electrons into the conduction band. In addition, the rapid crystal growth of the electroactive zinc oxide allows it to have efficiencies and rates competitive with leading electrochromic materials. Understanding this phenomenon helps improve the cycling performance of industrial-design electrodes and suggests potential applications of zinc oxide in other fields.