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 (Li 3 PO 4 ) and a 5 V-class electrode (LiCo 0.5 Mn 1.5 O 4 ). Although R i is small at the Mn 3+/4+ redox voltage of 4.0 V vs Li/Li + (11 Ω cm 2 ), it rapidly increases by more than 2 orders of magnitude as the voltage increases above the Co 3+/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.