Relaxation of the Interface Resistance between Solid Electrolyte and 5 V‑Class Positive Electrode

Solid-state Li batteries using 5 V-class positive electrode materials display a higher energy density. However, the high resistance at the interface of the electrolyte and positive electrode (interface resistance, R i) hinders their practical applications. Here, we report the relaxation of R i between a solid electrolyte (Li3PO4) and a 5 V-class electrode (LiCo0.5Mn1.5O4). Although R i is small at the Mn3+/4+ redox voltage of 4.0 V vs Li/Li+ (11 Ω cm2), it rapidly increases by more than 2 orders of magnitude as the voltage increases above the Co3+/4+ redox voltage of 5.2 V vs Li/Li+. After the applied voltage is reduced to 4.0 V vs Li/Li+, R i decays to the original value after 3 h. The relaxation of R i after exposure to high voltages suggests that the increase in R i above 5 V vs Li/Li+ is attributable to the formation of an interfacial layer at the LPO/LCMO interface.