Zinc film anodes for air microbatteries: fabrication, approaches, and utilization optimization

Abstract

Portable and autonomous microdevices often require on-board power sources such as thin film microbatteries. Air microbatteries are an attractive power source for such devices due to their high specific energy density. One particularly appropriate air chemistry is based on Zn, due to the multiple microfabrication approaches compatible with Zn anode formation. We demonstrate fabrication approaches to realize Zn film anodes in different thickness regimes using microelectromechanical systems based fabrication techniques—evaporation, electrodeposition, and laser micromachining; and evaluate their relative performance as power sources in a primary battery configuration. These fabrication techniques enable films in thickness regimes ranging from the micron scale to hundreds of microns. The fabricated films have been characterized using scanning electron microscopy and energy dispersive x-ray spectroscopy, and were found to be dense and reasonably free from impurities. The electrochemical and discharge properties of the fabricated films were studied in an air battery configuration comprising a Zn anode-alkaline hydrogel electrolyte-metal catalyst stack, in which the anode had a surface area of 0.78 cm2. Evaporated Zn anodes (1–10 µms) yielded Zn utilizations of 96.5% and 82% at 10 and 1 mA discharge rates, respectively. The specific capacity of the evaporated Zn anodes was 791 mAh g−1 when discharged at 10 mA, close to the Zn theoretical specific capacity of 820 mAh g−1. Electrodeposited Zn anodes (10–100 µms) yielded utilizations of 90.2% and 75.6% at 10 and 1 mA discharge rates, respectively. Laser micromachined Zn anodes (250 µms) yielded Zn utilization of 90% when discharged at 10 mA. These fabrication techniques offer the potential to realize high energy density Zn anodes of different thickness ranges for thin film microbatteries, which can be tailored to microdevice-based applications of interest.