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

Abstract

Solid electrolytes with compositions of (100 – x)(0.75Li ₂S·0.25P ₂S ₅)· xLiBH ₄ (mol %, 0 ≤ x ≤ 100) were mechanochemically prepared from the 75Li ₂S·25P ₂S 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 ₆PS 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.