Germanium Thin Film Protected Lithium Aluminum Germanium Phosphate for Solid-State Li Batteries

Solid-state Li batteries using Na + superionic conductor type solid electrolyte attracts wide interest because of its safety and high theoretical energy density. The NASCION type solid electrolyte LAGP (Li 1. 5 Al 0.5 Ge 0.5 P 3 O 12 ) shows favorable conductivity as well as good mechanical strength to prevent Li dendrite penetration. However, the instability of LAGP with Li metal remains a great challenge. In this work, an amorphous Ge thin film is sputtered on an LAGP surface, which can not only suppress the reduction reaction of Ge 4+ and Li, but also produces intimate contact between the Li metal and the LAGP solid electrolyte. The symmetric cell with the Ge-coated LAGP solid electrolyte shows superior stability and cycle performance for 100 cycles at 0.1 mA cm −2 . A quasi-solid-state Li–air battery has also been assembled to further demonstrate this advantage. A stable cycling performance of 30 cycles in ambient air can be obtained. This work helps to achieve a stable and ionic conducting interface in solid-state Li batteries.