Synthesis, structure and electrochemical performance of the argyrodite Li₆PS₅Cl solid electrolyte for Li-ion solid state batteries

Abstract

The high lithium conductivity of argyrodite Li₆PS₅Cl makes it an attractive candidate as solid electrolyte in all solid-state Li batteries. Aiming at an optimal preparation strategy the structure and conductivity upon different mechanical milling times is investigated. Li₆PS₅Cl material with high ionic conductivity of 1.1·10⁻³ S/cm was obtained by milling for 8 hours at 550 rpm followed by a heat-treatment at 550 °C. All solid-state Li-S batteries were assembled, combining the Li₆PS₅Cl solid electrolyte, with a carbon-sulfur mixture as positive electrode and Li, Li-Al and Li-In as negative electrode. An optimum charge/discharge voltage window between 0.4 and 3.0 V vs. Li-In was obtained by CV experiments and galvanostatic cycling displays a very large capacity around 1400 mAh/g during the first cycles, decreasing below 400 mAh/g after 20 cycles. Impedance spectroscopy suggests that the origin of the capacity fading is related to an increasing electrode-electrolyte interface resistance.