Microelectrode Studies on Kinetics of Charge Transfer at an Interface of Li Metal and Li₂S-P₂S₅ Solid Electrolytes

Abstract

Charge transfer kinetics at the Li metal electrode/electrolyte interface for three inorganic solid electrolytes and an organic liquid electrolyte were elucidated with two parameters, exchange current density (i₀) for Li/Li⁺ couple reactions and ionic conductivity in electrolyte. The former was evaluated by potential step method with a microelectrode, while the latter was done by electrochemical impedance spectroscopy. Both i₀ and ionic conductivity showed Arrhenius type dependence, and activation energies (E_a) for the charge transfer reactions and ionic conduction were evaluated. In the case of the organic liquid electrolyte, E_a for the Li/Li⁺ couple reactions was higher than that for ionic conduction because of the solvation/desolvation of Li⁺ ion. However, for the Li₂S-P₂S₅ solid solid electrolytes, the E_a for the Li/Li⁺ couple reactions was quite close to that for ionic conduction due to the lack of the solvation/desolvation.