Compositional flexibility in irreducible antifluorite electrolytes for next-generation battery anodes

Solid state batteries currently receive ample attention due to their potential to outperform lithium ion batteries in terms of energy density when featuring next generation anodes such as lithium metal or silicon. One key remaining challenge is identifying solid electrolytes that combine high ionic conductivity with stability in contact with the highly reducing potentials of next-generation anodes. Fully reduced electrolytes, based on irreducible anions, offer a promising solution by avoiding electrolyte decomposition altogether. In this study, we demonstrate the compositional flexibility of the disordered antifluorite framework accessible by mechanochemical synthesis and leverage it to discover irreducible electrolytes with high ionic conductivities. We show that the recently investigated Li9N2Cl3 and Li5NCl2 phases are part of the same solid solution of Li-deficient antifluorite phases existing on the LiCl-Li3N tie line with a general chemical formula of Li1+2xCl1-xNx (0.33