Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2020 / Paper 1 / Section B / 12 / i / b

A primary battery is intended for a single discharge; a secondary battery is designed for repeated electrical recharge through sufficiently reversible reactions. A microbattery is defined by its small dimensions or microfabricated construction, not by rechargeability. Therefore microbatteries can belong to either class. A thin-film Li-ion microbattery with reversible insertion electrodes is secondary because lithium can shuttle back and forth during discharge and charging; a miniature cell using irreversible primary chemistry remains primary. Small size alone does not justify assigning every microbattery to the secondary class.