Theoretical design of double anti-perovskite Na6SOI2 as a super-fast ion conductor for solid Na+ ion batteries

Abstract

Development of non-flammable solid electrolytes is necessary for sodium ion batteries, so that a sustainable battery technology can be extensively exploited for large scale energy storage when safety is of utmost importance. Here in this work, we have carried out extensive fundamental modelling, in search of solid electrolytes with superb ionic conductivity for Na⁺. A new class of materials is identified, based on a cubic double anti-perovskite phase of Na₆SOI₂. Through moderate off-stoichiometric composition setting to tune the alloy chemistry, e.g. Na₂₅S₅O₄I₇, superfast ionic conductivity is predicted with an activation energy as low as 0.16 eV for Na⁺, and remarkable ionic conductivity of 10.36 mS cm⁻¹ at room temperature and even 1.79 mS cm⁻¹ at −50 °C. Besides, the new solid electrolyte is electrochemically compatible with Na anodes and has a wide energy gap to prevent conduction of electrons.