Whisker-free lithium electrodeposition by tuning electrode microstructure

Growth of lithium whiskers or dendrites is the major obstacle towards safe and stable utilization of lithium metal anodes in rechargeable batteries. In this study, we look deeper into the mechanism of lithium electrodeposition. We find that before lithium whisker or dendrite nucleation occurs, lithium is deposited into the grain boundaries of the metal electrode, which we directly observed in the focused ion beam cross-sections of the lithium electrode. The structure of grain boundaries near the surface predetermines the capacity for smooth deposition, which is proportional to the surface area of such boundaries. We then demonstrate that by reducing the metal grain average size we can extend whisker- and dendrite-free deposition of lithium. With a eutectic Ga-Li alloy containing only 2.5 atomic percent of gallium we observed morphologically stable lithium deposition for 10 hours. The results demonstrate deep interconnections between the metal microstructure and the whisker growth.