Lightweight Al–Mg–In alloy based seawater batteries for long endurance applications: pack mass and cost optimization†

Abstract

Low-mass and pressure tolerant (PT) energy sources are essential to power underwater vehicles and devices to collect oceanic data at depth. At present, Li-based batteries are the main energy sources used, but at large depths, they must be enclosed in high-pressure chambers, effectively increasing the battery mass. Herein, we successfully prepared an Al-alloy based long endurance seawater battery (SWB) that can operate at depth, and has a superior energy density. An SWB with an open architecture was prepared using the alloy anode and a Pt/C cathode. The cell potential and self-corrosion rate were measured at several current densities and temperatures (5–25 °C). Electrochemical and surface characterizations show that the introduction of In into the Al anode can weaken the surface oxide, resulting in a remarkable increase in the cell potential (∼300 mV). Moreover, co-doping Al with In and Mg inhibits self-corrosion, yielding an especially large anode utilization efficiency (∼93%). Using the measured potential and self-corrosion rate as the input, the pack mass and cost of the SWB required to provide a target power and endurance was calculated at any given operating current density. This work illustrates that, by judiciously choosing the operating current density, the SWB mass can be greatly reduced. We show that an SWB constructed with Al anodes containing 3 wt% Mg and 0.1 wt% In, along with Pt–C cathodes, can exhibit a remarkable performance in underwater applications. Extrapolations based on small area cells and short duration experiments indicate that for a low-power (5 W), long-endurance (12 months) application, the SWB can weigh as little as 43 kg, while for a moderate-power (33 W), medium-duration (120 days) scenario, the SWB weight can be just 103 kg. These SWB configurations have the potential to offer an energy density that significantly surpasses that of benchmark PT lithium-based batteries.