Intergranular to transgranular lithium filamentation in a garnet solid-state electrolyte

Abstract

Solid-state Li-metal batteries employing a metallic lithium anode afford higher energy densities when compared to conventional Li-ion batteries. However, the growth of lithium filaments mainly along the grain boundaries of solid electrolytes (intergranular lithium flow) was shown to lead to premature cell failure. In this work, we propose a chemical modification approach to selectively convert Li₂CO₃ along grain boundary regions to LiF. We show that lithium-based garnet solid electrolytes with modified grain boundaries showed a previously unseen transition from an intergranular to a transgranular filamentation mode. Based on experimental data and a coupled electro-chemo-mechanical model, we show that LiF modification reduces current focusing at grain boundaries, thereby minimizing preferential plating in grain boundary regions. Our results also show that transgranular lithium growth affords about a 3-fold improvement in critical current densities for lithium filamentation.