Sulfide solid electrolytes possess high ionic conductivity and moderate dendrite suppression capability, but rather poor compatibility against oxide cathodes and metallic Li. Here, we report O-doped Li₆PS₅Br as solid electrolyte synthesized by a facile solid-state sintering. Different from other O-incorporated sulfides, the O atoms in Li₆PS_5-xO_xBr prefer to substitute the S atoms at free S²⁻ sites rather than those at the PS₄ tetrahedra. Remarkably, without deteriorating the ionic conductivity, this inorganic solid electrolyte with O doping exhibits comprehensively enhanced properties including excellent dendrite suppression capability, superior electrochemical and chemical stability against Li metal as well as high voltage oxide cathodes, and good air stability. Li(Ni_0.8Co_0.1Mn_0.1)O₂ and LiCoO₂-based all-solid-state batteries with Li₆PS_4.7O_0.3Br electrolyte deliver high specific capacity, superior rate capability, and outstanding cycling stability accompanied with low interfacial resistivity. This type of inorganic solid electrolytes is promising for all-solid-state batteries with high energy density.

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.