Effect of Pressure on Lithium Metal Deposition and Stripping against Sulfide-Based Solid Electrolytes.

Fundamental challenges for lithium metal anode cycling against solid electrolytes (SEs) at high current densities and high areal capacities include lithium dendrite penetration during Li deposition and void formation during Li stripping. These two dynamic processes have a distinct dependency on the external pressure. The majority of research to date on Li cycling behaviors adopt symmetric cell (Li/SE/Li) configurations, where the stack pressure and the failure associated with the deposition and the stripping processes cannot be delineated. In this work, we investigate the effect of external pressure on the deposition and the stripping of Li metal anodes separately against a sulfide-based SE by employing asymmetric cell configurations. We show that (1) for Li striping, the pressure required is positively correlated with stripping current densities; (2) for Li deposition, higher pressure leads to lower maximum allowed current densities, defined as the current densities beyond which dendrite penetration occurs. The apparent opposing requirement for external pressure of Li deposition and Li stripping elucidates why the methodology of Li metal cycling in symmetric cell configurations is fundamentally flawed and highlights the importance of refined pressure regulation in all-solid-state Li metal batteries.