Small-scale, long-duration, and biodegradable zinc–air batteries

Abstract

The Internet of Things (IoT) consists of multiple networked nodes, typically comprising transducers and communication capability, that collect and exchange data to achieve a system goal. As IoT node adoption increases, the impact of e-waste on the environment must be considered. Many IoT nodes are therefore incorporating biodegradable sensors. A recent example is that of precision agricultural systems, in which biodegradable IoT nodes are placed on or below the soil to monitor the plant environment over timescales from weeks to months. Such nodes require energy sources that also biodegrade without harm to the environment. Herein we report Zn–air batteries fabricated from biodegradable materials, and characterize battery performance under sensor-relevant power requirements. The battery comprises a biodegradable Zn anode, a hydrogel electrolyte, and an air cathode (normally consisting of a gas diffusion layer and a catalyst layer). Battery dimensions studied range from 2 × 2 × 0.7 cm³ (large cell) to 10 × 8 × 5 mm³ (corn cell, approximately the size of a corn kernel). A scalable biowax encapsulation process was developed for battery passivation. A variety of hydrogel compositions and corrosion inhibitors were investigated to extend battery lifetime. Under discharge, large cell peak power densities ranging from 10 to 50 mW cm⁻², and lifetimes ranging from 15 days to 340 days, were achieved. Similarly, corn cell peak power densities ranging from 6.5 to 7.5 mW cm⁻², and lifetimes ranging from 7 days to 82 days were achieved. Battery operation was measured both in air and soil environments, showing the potential of this approach for environmental IoT applications.