Sr2+-doped rhombohedral LiHf2(PO4)3 solid electrolyte for all-solid-state Li-metal battery

Solid-state electrolytes in rechargeable all-solid-state Li-metal batteries, which have better safety and higher specific capacity than conventional rechargeable Li-ion batteries with liquid electrolytes, are limited by the low Li-ion conductivity of the solid electrolyte and the large electrolyte/electrode interfacial resistance. Here, we report a new rhombohedral NASICON structure Li1.4Sr0.2Hf1.8(PO4)3 with a high Li-ion conductivity of 1.62 × 10−5 S·cm−1 at 25 °C, and its conductivity can be improved to 3.4 × 10−5 S·cm−1 after the densification of the pellet by hot pressing. Li1.4Sr0.2Hf1.8(PO4)3 coated by a thin layer of polymer electrolyte showed a stable low-impedance dendrite-free plating/stripping process in a symmetric Li/Li cell for 100 h; moreover, the Li1.4Sr0.2Hf1.8(PO4)3 electrolyte had a small interfacial resistance in all-solid-state Li/LiFePO4 cell, which allows a high Coulombic efficiency and good cycling of the cell.