NASICON-type medium entropy Li1.5Sn1.0Al0.5Zr0.5(PO4)3 electrolyte for solid state Li metal batteries

Abstract

Developing solid electrolytes for all-solid-state lithium batteries with superior performance is crucial for portable energy storage. This study uses a traditional solid-state reaction technique to fabricate a NASICON-type medium entropy Li1.5Sn1.0Al0.5Zr0.5(PO4)3 (LSAZP) ceramic electrolyte. The Rietveld refinement of room temperature X-ray diffraction (XRD) data confirms a pure rhombohedral phase (R3‾c) for LSAZP ceramic sintered at 1050 °C. Temperature-dependent synchrotron XRD data demonstrates an increase in lattice parameter c with a positive coefficient of thermal expansion (+2.40 × 10−5 K−1) and a negative coefficient of thermal expansion (−1.26 × 10−6 K−1) for the lattice parameter a with increasing temperature. Interestingly, despite the anisotropic thermal expansion, no intergranular cracks, typically observed in rhombohedral NASICON-type phases, are noticeable in the scanning electron micrographs of the LSAZP samples. The sample sintered at 1050 °C (relative density ∼90 %) exhibits an excellent room temperature conductivity of ∼2.95 × 10−4 S cm−1 and activation energy ∼0.39 ± 0.02 eV. The Li-ion transference number is ∼0.99, suggesting that Li-ion is the dominant charge carrier in the sample. During galvanostatic lithium plating-stripping tests, the symmetric Li|LSAZP|Li cell demonstrates excellent lithium plating-stripping stability over 50 h at a current density of 4 μA cm−2.