Borohydride Substitution Effects of Li₆PS₅Cl Solid Electrolyte

Abstract

We report an electrochemically stable borohydride (BH 4 − )-substituted Liargyrodite solid electrolyte prepared by a mechanical ball-milling method. The crystal structure of BH 4 − -substituted argyrodite remains unchanged with x < 0.3 (Li 6 PS 5 Cl 1−x (BH 4 ) x ), whereas a complex phase (Li 2 S-P 2 S 5 -LiCl-LiBH 4 ) was obtained with x > 0.3. The highest ionic conductivity of 0.12 mS cm −1 at 25 °C was observed with x = 0.1 in Li 6 PS 5 Cl 1−x (BH 4 ) x , whereas there was virtually no change in the complex phase. The electrochemical window of Li 6 PS 5 Cl 0.9 (BH 4 ) 0.1 is between 1 and 4 V against lithium metal.

Rapid Synthesis of Highly Conductive Li6PS5Cl Argyrodite-Type Solid Electrolytes Using Pyridine Solvent

“…The observed peak positions coincided with the cubic crystal structure with the F 4̅3 m space group. This confirmed the successful formation of Li-argyrodite type solid electrolyte. − In addition, Li 3 PO 4 impurity peaks were observed at 2θ = 22.0°, 22.9°, 24.5°; Li 2 S and LiCl impurity peaks were observed at 26.8° and 49.9°, respectively . Usually, impurity peaks of Li 3 PO 4 , Li 2 S, and LiCl are observed during the preparation of argyrodite solid electrolyte by solution synthesis.…”

“…Thus, the solid electrolyte prepared by normal drying showed high conductivity (4.6 mS cm −1 ) at room temperature and was comparable to the ball-mill method. 11,19 In the case of vacuum drying, we observed impurity peaks in the XRD pattern, and no semicircles were observed in the Nyquist plot, indicating a complete drying process (Figures S1 and S2). Thus, vacuum drying successfully removed pyridine solvent and enhanced ionic conductivity.…”

Lithium Superionic Conduction in BH4‐Substituted Thiophosphate Solid Electrolytes

“…[ 4 ] Furthermore, this conductivity value is much higher than those reported in previous studies on borohydride argyrodite materials. [ 7 , 8 , 9 , 17 ] This result can be attributed to the thiophosphate local structure of the prepared materials, which is favorable for Li‐ion conduction. The local structure was closely examined as described later.…”

“…In other studies, Cl or I in the argyrodite crystal was partially or fully replaced with borohydride ions. [ 9 ] The borohydride‐substituted materials exhibited a higher stability with Li metal and enhanced ionic conductivities than did Li 6 PS 5 X (X = Cl and I). However, the ionic conductivity was still low, and the effect of the local structure of the thiophosphate on the ionic conductivity remains hitherto underexplored.…”

Borohydride and halide dual-substituted lithium argyrodites

“…13,16 Wang et al reported on BH 4 − -substituted Li 6 PS 5 Cl electrolytes with a low conductivity of 0.12 mS cm −1 at room temperature. 12 They heated the sample to 550 °C, and it is likely that BH 4 − did not substitute for X − but decomposed. Furthermore, they ball milled all the precursors together.…”