Dendrite formation in solid-state batteries arising from lithium plating and electrolyte reduction.

All-solid-state batteries offer high-energy-density and eco-friendly energy storage but face commercial hurdles due to dendrite formation, especially with lithium metal anodes. Here we report that dendrite formation in Li/LiLaZrO/Li batteries occurs via two distinct mechanisms, using non-invasive solid-state nuclear magnetic resonance and magnetic resonance imaging. Tracer-exchange nuclear magnetic resonance shows non-uniform Li plating at electrode-electrolyte interfaces and local Li reduction at LiLaZrO grain boundaries. In situ magnetic resonance imaging reveals rapid dendrite formation via non-uniform Li plating, followed by sluggish bulk dendrite nucleation from Li reduction, with an intervening period of stalled growth. Formation of amorphous dendrites and subsequent crystallization, the defect chemistry of solid electrolytes and battery operating conditions play a critical role in shaping the complex interplay between the two mechanisms. Overall, this work deepens our understanding of dendrite formation in solid-state Li batteries and provides comprehensive insight that might be valuable for mitigating dendrite-related challenges.