Structural manipulation approaches towards enhanced sodium ionic conductivity in Na-rich antiperovskites

g rap hical a bstract � A series of Na-rich antiperovskites were developed as advanced solid electrolytes. � The materials are nonflammable, low-cost and suitable for thermo- plastic processing. � Enhanced sodium ionic conductivity was achieved by structural manipu- lation approaches. � The Na ionic conductivity of Na2.9S- r0.05OBr0.6I0.4 reaches 1.9 � 10 � 3 S/cm at 200 � C. abstract High-performance solid electrolytes are critical for realizing all-solid-state batteries with enhanced safety and cycling efficiency. However, currently available candidates (sulfides and the NASICON-type ceramics) still suffer from drawbacks such as inflammability, high-cost and unfavorable machinability. Here we present the structural manipulation approaches to improve the sodium ionic conductivity in a series of affordable Na-rich antiperovskites. Experimentally, the whole solid solutions of Na3OX (X ¼ Cl, Br, I) are synthesized via a facile and timesaving route from the cheapest raw materials (Na, NaOH and NaX). The materials are nonflammable, suitable for thermoplastic processing due to low melting tem- peratures (<300 � C) without decomposing. Notably, owing to the flexibility of perovskite-type structure, it's feasible to control the local structure features by means of size-mismatch substitution and unequivalent-doping for a favorable sodium ionic diffusion pathway. Enhancement of sodium ionic conductivity by 2 magnitudes is demonstrated by these chemical tuning methods. The optimized sodium ionic conductivity in Na2.9Sr0.05OBr0.6I0.4 bulk samples reaches 1.9 � 10 � 3 S/cm at 200 � C and even higher