Lithium ionic conduction in composites of Li(BH4)0.75I0.25 and amorphous 0.75Li2S·0.25P2S5 for battery applications

Abstract Solid state electrolytic properties of mixtures of Li(BH 4 ) 0.75 I 0.25 and amorphous 0.75Li 2 S·0.25P 2 S 5 are reported in this study. The enhanced Li-ion conductivities for the Li(BH 4 ) 0.75 I 0.25 phase after addition of 0.75Li 2 S·0.25P 2 S 5 were found to be within the range for practical solid-state electrochemical storage near room temperature. The highest ionic conductivities are found for the borohydride/sulfide system at 1:2 wt ratio with ∼10 −3  S cm -1  at room temperature and an activation energy of 0.30(2) eV. Combined experimental analyses with powder X-ray diffraction and infrared spectroscopy suggest that the synthesized material still include both [PS 4 3− ] and [BH 4 − ] entities. Density functional theory (DFT) calculations provide more insights about the origin of the observed ionic behavior according to the induced structural modifications in the BH 4 –BH 4 interactions. Finally, the electrolyte functionality and its compatibility toward an active material are successfully demonstrated by means of cyclic voltammetry (Au vs . Li + /Li) in a large voltage window (up to 5 V) and battery cycling tests with TiS 2 electrode, respectively.