Enhanced ionic conductivity with Li7O2Br3 phase in Li3OBr anti-perovskite solid electrolyte

Cubic anti-perovskites with general formula Li3OX (X = Cl, Br, I) were recently reported as superionic conductors with the potential for use as solid electrolytes in all-solid-state lithium ion batteries. These electrolytes are nonflammable, low-cost, and suitable for thermoplastic processing. However, the primary obstacle of its practical implementation is the relatively low ionic conductivity at room temperature. In this work, we synthesized a composite material consisting of two antiperovskite phases, namely, cubic Li3OBr and layered Li7O2Br3, by solid state reaction routes. The results indicate that with the phase fraction of Li7O2Br3 increasing to 44 wt. %, the ionic conductivity increased by more than one order of magnitude compared with pure phase Li3OBr. Formation energy calculations revealed the meta-stable nature of Li7O2Br3, which supports the great difficulty in producing phase-pure Li7O2Br3 at ambient pressure. Methods of obtaining phase-pure Li7O2Br3 will continue to be explored, including both high pressure and metathesis techniques. Published by AIP Publishing.