Theoretical formulation of Na3AO4X (A = S/Se, X = F/Cl) as high-performance solid electrolytes for all-solid-state sodium batteries

Abstract

It is very important and yet extremely challenging to develop solid state electrolytes to make sodium ion batteries (SIBs) safer, since the much larger size of Na⁺ than that of Li⁺ makes transport of Na⁺ rather difficult. Here in this work, we have carried out high throughput first principles calculations to tune the materials chemistry of Na₃AO₄X (A = chalcogen, X = halogen) to convert them into superb ionic conductors. In addition to confirming the excellent stability of Na₃SO₄F_0.5Cl_0.5, a known mineral existing in nature, we have identified a Na₃SeO₄F_0.5Cl_0.5 compound with the same structure as a desirable Na⁺ conductor. Such a newly formulated compound has extremely low activation energy for Na⁺ transport (0.137 eV) and a remarkably high Na⁺ conductivity of 8.167 mS cm⁻¹ at room temperature (300 K). Furthermore, this superb solid electrolyte is insensitive to air/moisture, together with a very wide electrochemical window of up to 4.215 V against Na⁺/Na.