Fabrication and characterization of a coplanar nickel-metal hydride microbattery equipped with a gel electrolyte

Abstract

The growing utilization of portable and autonomous micro devices results in a need for novel integrated power supplies with low power densities and energy contents. We report on a rechargeable thin-film microbattery which is manufactured using typical microfabrication methods. In detail, the microbattery is based on the nickel-metal hydride chemistry and fabricated with a coplanar design on a glass wafer. Ionic conductivity is enabled with a gel electrolyte that is sealed with a polymer to prevent dessication. We compare the electrode characteristics in the gel electrolyte and in a corresponding liquid electrolyte. Charge-discharge measurements at different currents are performed to evaluate the performance of the microbattery. The capacity is found to be 2.8 μAh cm−2 μm−1 at a current density of 1 mA cm−2. We also investigate the microbattery degradation over the number of charge-discharge cycles using electrochemical impedance spectroscopy. The results reveal that the capacity after 100 cycles decreases to around half of the initial value which is mainly attributed to the gel electrolyte degradation.