Mesoscale Anatomy of Dead Lithium Formation

Lithium metal anodes are an attractive option for next-generation batteries because of high gravimetric and volumetric energy densities. The formation of dendritic morphology of electrodeposition during charging, however, poses safety concerns, which, in particular, have been a focus of intense research. The formation of "dead lithium" with successive cycling, on the other hand, has been relatively unexplored as the deterioration in performance is gradual. Dead lithium is the fragment of lithium that is detached from the lithium electrode during electrodissolution or stripping. In this study, the mesoscale underpinnings of dead lithium formation via a synergistic computational and experimental approach are presented. The mechanistic focus centers on the morphological evolution of the lithium electrode–electrolyte interface and the relative quantification of dead lithium formation under a range of operating temperatures and currents. This study reveals that the amount of dead lithium formed during stripping increases with decreasing current and increasing temperatures. This finding is in direct contrast to the operating conditions that lead to dendritic deposition during charging, i.e., at higher currents and lower temperatures. During stripping, more dead lithium is formed when the interface has thin narrow structures. The ionic diffusion and self-diffusion of lithium at the interface play a key role in the evolution of narrow structures at the interface. Therefore, more dead lithium is formed when diffusive processes are facilitated compared to the oxidative reaction at the interface.