Spatial Heterogeneities and Onset of Passivation Breakdown at Lithium Anode Interfaces

Effective passivation of lithium metal surfaces, and prevention of battery-shorting lithium dendrite growth, are critical for implementing lithium metal anodes for batteries with increased power densities. Nanoscale surface heterogeneities can be "hot spots" where anode passivation breaks down. Motivated by the observation of lithium dendrites in pores and grain boundaries in all-solid batteries, we examine lithium metal surfaces covered with Li₂O and/or LiF thin films with grain boundaries in them. Electronic structure calculations show that at >0.25 V computed equilibrium overpotential Li₂O grain boundaries with sufficiently large pores can accommodate Li0 atoms which aid e– leakage and passivation breakdown. Strain often accompanies Li insertion; applying an ~1.7% strain already lowers the computed overpotential to 0.1 V. Lithium metal nanostructures as thin as 12 Å are thermodynamically favored inside cracks in Li₂O films, becoming "incipient lithium filaments". LiF films are more resistant to lithium metal growth. Finally, the models used herein should in turn inform passivating strategies in all-solid-state batteries.