Mechanochemically Prepared Li(2)S–P(2)S(5)–LiBH(4) Solid Electrolytes with an Argyrodite Structure

[Image: see text] Solid electrolytes with compositions of (100 – x)(0.75Li(2)S·0.25P(2)S(5))·xLiBH(4) (mol %, 0 ≤ x ≤ 100) were mechanochemically prepared from the 75Li(2)S·25P(2)S(5) (mol %) glass and LiBH(4) crystal. The samples with x ≥ 43 have crystalline phases and those with x ≤ 33 formed a glassy phase. The crystalline phase was identified as argyrodite Li(6)PS(5)(BH(4)). The x = 50 sample formed a crystalline phase and demonstrated a high lithium-ion conductivity of 1.8 × 10(–3) S cm(–1) at 25 °C with an activation energy of 16 kJ·mol(–1). The argyrodite-type crystal with a BH(4)(–) anion that occupies the halide site is a novel and promising solid electrolyte.