Critical Current Density Measurements of Argyrodite Li6PS5Cl Solid Electrolyte at Ambient Pressure

Abstract

Sulfide electrolytes including the argyrodite family (Li6PS5X, X = Cl, Br, I) exhibit high ionic conductivities and transference numbers and are regarded as promising electrolytes for all-solid-state lithium batteries. Although high ionic conductivity is a necessary requirement for feasible battery operation, other parameters are equally important and have often been neglected in efforts to realize all-solid-state batteries. The so-called critical current density (CCD) is among the more relevant parameters for application and indicates the maximum current an electrolyte can sustain before breakdown. When Li metal electrodes are used, this breakdown is often initiated by heavy dendrite formation and subsequent growth through the electrolyte layer, resulting in internal shorting of the cell. Very promising CCD values are reported for the argyrodite family of >1 mA cm−2 at elevated temperatures and pressures. However, non-standardized cell setups and testing procedures are employed, which renders a proper comparison of values impossible. Thus, this work investigates the impact of these often-overlooked parameters and aims at establishing more standard measurement procedures for solid electrolytes under ambient or almost ambient pressure. Furthermore, an alternative method for evaluation of CCD values is presented adopted from Tafel analysis.