Li+ Conduction in a Polymer/Li1.5Al0.5Ge1.5(PO4)3 Solid Electrolyte and Li-Metal/Electrolyte Interface

The solid oxide electrolyte Li1.5Al0.5Ge1.5(PO4)3 (LAGP) with a NASICON structure has a high bulk ionic conductivity of 10-4 S cm-1 at room temperature and good stability in the air because of the strong P5+-O2- covalence bonding. However, the Ge4+ ions in LAGP are quickly reduced to Ge3+ on contact with the metallic lithium anode, and the LAGP ceramic has insufficient physical contact with the electrodes in all-solid-state batteries, which limits the large-scale application of the LAGP electrolyte in all-solid-state Li-metal batteries. Here, we prepared flexible PEO/LiTFSI/LAGP composite electrolytes, and the introduction of LAGP as a ceramic filler in polymer electrolytes increases the total ionic conductivity and the electrochemical stability of the composite electrolyte. Moreover, the flexible polymer shows good contact with the electrodes, resulting in a small interfacial resistance and stable cycling of all-solid-state Li-metal batteries. The influence of the external pressure and temperature on Li+ transfer across the Li/electrolyte interface is also investigated.