A Critical Evaluation of the Limiting Current Density in Polymer Electrolytes: Interplay of Ion Transport, Mechanical Stability, and Conformal Li-Electrolyte Interfaces

Solid-state batteries with lithium metal anodes are among the promising candidates to fulfill the actual requirements of growing energy demands in comparison to commercially available lithium-ion batteries, despite the current challenges of inhomogeneous lithium metal deposition upon cycling. In the present literature, the limiting current density is referred to as a key performance indicator for faster charging of solid-state batteries, though from a practical point of view, it is defined as the maximum endurable current density that might be applied without possible cell failure. In this study, we evaluate the obtained values of limiting current densities for lithium metal batteries operating with polymer electrolytes. Notably, we critically compare various experimental procedures to determine the actual limiting current density and discuss the impact of external factors such as scan rate, temperature, and applied cell pressure, thereby invoking model-type PEO-based electrolytes to examine available mechanical properties that may afford suppression of lithium dendrite formation. In fact, we demonstrate that experimentally derived limiting current densities are not intrinsic electrolyte characteristics but rather entities strongly dependent on the applied conditions and hence should ideally be determined based on different techniques to deliver meaningful data.