A comprehensive research coupling experiment and computation has been performed to understand the phase transition of Na₃SbS₄ and to synthesize cubic Na₃SbS₄ (c-Na₃SbS₄), a high temperature phase of Na₃SbS₄ that is difficult to be preserved when cooled down to ambient temperature. The formation of c-Na₃SbS₄ is verified by Rietveld refinement, nuclear magnetic resonance spectroscopy as well as electrochemical impedance spectroscopy. Unlike tetragonal Na₃SbS₄ (t-Na₃SbS₄) appearing phase transition at high temperature, c-Na₃SbS₄ is stable not just at room temperature but also sustaining thermal cycling up to at least 200 °C. Both experiment and theoretical calculation reveal that the ionic conductivity of c-Na₃SbS₄ is higher than that of t-Na₃SbS₄, though the values are in the same order of magnitude. Both structures allow fast ion transport. All-solid-state cells with c-Na₃SbS₄ solid electrolyte demonstrate superior Coulombic efficiency, high specific capacity, and relatively good cycling stability. Na₃SbS₄ solid electrolyte is promising for all-solid-state sodium-ion batteries.

Exploration of advanced solid electrolytes with good interfacial stability toward electrodes is a highly relevant research topic for all-solid-state batteries. Here, we report PCL/SN blends integrating with PAN-skeleton as solid polymer electrolyte prepared by a facile method. This polymer electrolyte with hierarchical architectures exhibits high ionic conductivity, large electrochemical windows, high degree flexibility, good flame-retardance ability, and thermal stability (workable at 80 °C). Additionally, it demonstrates superior compatibility and electrochemical stability toward metallic Li as well as LiFePO₄ cathode. The electrolyte/electrode interfaces are very stable even subjected to 4.5 V at charging state for long time. The LiFePO₄/Li all-solid-state cells based on this electrolyte deliver high capacity, outstanding cycling stability, and superior rate capability better than those based on liquid electrolyte. This solid polymer electrolyte is eligible for next generation high energy density all-solid-state batteries.