Interfacial excess charge dynamics as a quantitative descriptor to understand lithium dendrite growth

Unraveling the origins of Li dendrite growth remains a critical challenge for lithium metal batteries. Existing studies often treat diffusion-reaction mismatches or electrode surface excess charge in isolation, overlooking the coupled interfacial processes at the nanoscale solid-liquid interface that govern Li dendrite growth. Herein, we introduce the interfacial excess charge distribution factor, a quantitative descriptor that captures the dynamic equilibrium by integrating the contributions of electrode surface excess charge, charge depletion rate and solvation chemistry. We further propose an electrochemical method to monitor Li dendrite growth rates, confirming that electrolytes with rapid excess charge redistribution ability favor planar Li plating. Our findings reveal that the depletion rate of interfacial excess charge governed by Li⁺-dipole-anion interactions, and the degree of electrode excess charge modulated by solvation structures and cation screening, competitively determine the interfacial excess charge dynamics. Guided by these insights, we designed an electrolyte with optimized excess charge redistribution capability, which suppresses dendrite formation and enables stable cycling in ~6.4 Ah lithium metal batteries. This work provides mechanistic insight into how competitive interfacial processes dictate Li dendrite growth.