Improvement of the ionic conductivity on new substituted borohydride argyrodites

Abstract The development of electrochemically stable Li-ion solid electrolytes with high conductivity is crucial for a successful performance of all-solid-state batteries. Li-containing argyrodite sulfides with the formula Li 6 PS 5 Z ( Z  = Cl, Br, I) are considered as promising solid electrolytes due to their high conductivity in the order of 10 −4 to 10 −3  S cm −1 and their wide stable electrochemical potential (up to 5 V vs Li/Li + ). In this work, argyrodites were mixed with LiBH 4 at different ratios to promote the partial substitution of halide Z − ions by [BH 4 ] - units. The powder characteristics and the ionic conductivity were systematically studied as function of mechanical and thermal steps applied during the synthesis of the prepared samples. The compositions Li 6 PS 5 Cl 0.83 (BH 4 ) 0.17 and Li 6 PS 5 I 0.83 (BH 4 ) 0.17 revealed a significant enhancement on the conductivity (4.0·10 −4 and 7.6·10 −4  S cm −1 , respectively) comparing to the pristine argyrodites. In addition, the wide electrochemical stability window from 0 to 5 V makes these compounds attractive for their future integration in high-power all-solid-state batteries.