Electrochemical Impedance Spectroscopy Analysis of Dendrite Growth on the Lithium Metal Surface in Polysulfide-Insoluble Electrolytes

Lithium has been widely investigated owing to its high theoretical specific capacity and low electrochemical potential. This is required for high-energy-density lithium batteries such as lithium-sulfur (Li-S) batteries. Recently, Li-S batteries with polysulfide-insoluble electrolytes, such as sulfolane (SL) and triglyme (G3), have attracted research attention because they suppress the dissolution of lithium polysulfide intermediates. However, lithium dendrite growth on the Li metal anode during the charging-discharging process causes an internal short-circuit, which may lead to serious accidents. To realize a Li-S battery, a fail-safe system to prevent short-circuits is essential. In this study, we investigated the cycle degradation mechanism of a Li metal anode in SL and G3 electrolytes using electrochemical impedance spectroscopy. The changes in charge transfer resistance (R_ct) and solid electrolyte interphase resistance (R_SEI) of Li-Li symmetrical cells in SL and G3 electrolytes was measured under charge-discharge cycling in detail down to internal short-circuits. Consequently, in both the electrolyte systems, the R_SEI and R_ct behaviors were disparate during cycling, and a mechanism for the short-circuit process was proposed. In addition, before the short-circuit process occurred, the change in the trend of R_ct from stable to increasing was indicative of an imminent short-circuit.