Solid-state Li batteries are promising energy-storage devices owing to their high-energy densities with improved safety. However, the large interface resistance at the interfaces of solid-electrolytes and electrodes hinders the development of solid-state Li batteries.
We fabricated thin-film Li batteries with Li3PO4 and LiNi0.5Mn1.5O4 interface resistance below ~ 5 Ωcm2; the value is smaller than that observed in liquid-electrolyte-based Li-ion batteries. Furthermore, the activation energy of the interface resistance was found to be ~ 0.3 eV, which is comparable to that of ionic migration in Li-superionic conductors. The fabricated interface showed no degradation even after 100 cycles of charging and discharging at a rate of 3600C (current density of 14 mA/cm2), indicating the formation of a very stable interface. These studies strongly encourage solid-state Li battery research, by demonstrating the low interface resistance leading to the fast charging and discharging.