Pseudo-ternary LiBH4·LiCl·P2S5 system as structurally disordered bulk electrolyte for all-solid-state lithium batteries

Abstract

The properties of the mixed system LiBH₄–LiCl–P₂S₅ are studied with respect to all-solid-state batteries. The studied material undergoes an amorphization upon heating above 60 °C, accompanied with increased Li⁺ conductivity beneficial for battery electrolyte applications. The measured ionic conductivity is ∼10⁻³ S cm⁻¹ at room temperature with an activation energy of 0.40(2) eV after amorphization. Structural analysis and characterization of the material suggest that BH₄ groups and PS₄ may belong to the same molecular structure, where Cl ions interplay to accommodate the structural unit. Thanks to its conductivity, ductility and electrochemical stability (up to 5 V, Au vs. Li⁺/Li), this new electrolyte is successfully tested in battery cells operated with a cathode material (layered TiS₂, theo. capacity 239 mA h g⁻¹) and Li anode resulting in 93% capacity retention (10 cycles) and notable cycling stability under the current density ∼12 mA g⁻¹ (0.05C-rate) at 50 °C. Further advanced characterisation by means of operando synchrotron X-ray diffraction in transmission mode contributes explicitly to a better understanding of the (de)lithiation processes of solid-state battery electrodes operated at moderate temperatures.