Achieving a Reversible Four-Electron Sn Metal Aqueous Battery

The renewable energy transition requires long-duration energy storage technologies with low cost and high safety. Aqueous batteries using inexpensive, non-toxic elements and non-flammable electrolytes offer an attractive sustainable solution, but their low realized energy density and poor cyclability hinder widespread implementation. Among the anode options, Sn has gained increasing attention due to its dendrite-free plating, large hydrogen evolution overpotential, and high theoretical capacity. However, the four-electron electrochemistry of Sn remains challenging to achieve, with only limited cell energy densities demonstrated thus far.<br/>In this talk, we will discuss our recent progress in understanding and developing four-electron Sn anodes for energy-dense aqueous batteries. Using correlative operando and ex situ characterization, we identified an asymmetric mechanism with direct four-electron plating and stepwise two-by-two electron stripping. This mechanistic understanding was employed engineer a pouch cell with maximized Coulombic efficiency (CE). At 2 mAh cm^-2, our Sn-Ni pouch cells demonstrate a high CE of ~99% and high round-trip efficiency of ~80% for over 200 stable cycles (800 h). Deep cycling tests achieve a high volumetric capacity of 170.5 Ah L^-1 and a high overall energy density of 143.1 Wh L^-1. Our findings offer compelling evidence for the detailed mechanism behind the four-electron Sn metal anode, paving the way for reversible and robust multi-electron reactions in metal anodes. The remarkable performance under mild temperature makes the Sn-Ni battery a good candidate for diverse applications including grid-scale energy storage, facilitating the transition to a sustainable energy landscape.