Hybrid Polymer/Garnet Electrolyte with a Small Interfacial Resistance for Lithium-Ion Batteries

Li7La3Zr2O12-based Li-rich garnets react with water and carbon dioxide in air to form a Li-ion insulating Li2CO3 layer on the surface of the garnet particles, which results in a large interfacial resistance for Li-ion transfer. Here, we introduce LiF to garnet Li6.5La3Zr1.5Ta0.5O12 (LLZT) to increase the stability of the garnet electrolyte against moist air; the garnet LLZT-2 wt% LiF (LLZT-2LiF) has less Li2CO3 on the surface and shows a small interfacial resistance with Li metal, a solid polymer electrolyte, and organic-liquid electrolytes. An all-solid-state Li/polymer/LLZT-2LiF/ LiFePO4 battery has a high Coulombic efficiency and long cycle life; a Li-S cell with the LLZT-2LiF electrolyte as a separator, which blocks the polysulfide transport towards the Li-metal, also has high Coulombic efficiency and kept 93% of its capacity after 100 cycles.