Pseudo-ternary LiBH${}_4$–LiCl–P${}_2$S${}_5$ system as structurally disordered bulk electrolyte for all-solid-state lithium batteries

The properties of the mixed system LiBH${}_4$–LiCl–P${}_2$S${}_5$ 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 BH${}_4$ 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 TiS${}_2$, 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.