Mechanochemically prepared sodium-ion conducting fluorides in the system NaF–TaF₅

Abstract

We report a new sodium-ion conducting fluorides, NaTaF₆, Na₂TaF₇, and Na₃TaF₈ as the possible candidates for a solid electrolyte in composite positive electrode for all-solid-state sodium batteries with high operating voltage. The mechanochemically prepared Na₂TaF₇ sample shows the ionic conductivity of 1.1 × 10⁻⁶ S cm⁻¹ at 100 °C and the activation energy of 0.67 eV. The Na₂TaF₇ sample has the electrochemically stability between 1.6 and 4.2 V vs. Na₂Sn. This report pioneeringly develops the sodium-ion conducting fluorides with high electrochemical stability for all-solid-state batteries.