Electrochemical performance of bulk-type all-solid-state batteries using small-sized Li7P3S11 solid electrolyte prepared by liquid phase as the ionic conductor in the composite cathode

A high lithium-ion conductive solid electrolyte with Li7P3S11 phase and small particle size was prepared by a liquid phase process, and the solid electrolyte was used as the ionic conductor in the composite cathode for bulk-type all-solid-state batteries. The electrochemical performance of the all-solid-state cell using Li7P3S11 solid electrolyte prepared by liquid phase was studied and compared to that using Li7P3S11 solid electrolyte prepared by ball milling. Solid electrolytes prepared by the liquid phase and ball milling processes consisted mainly of the Li7P3S11 crystal phase and the local structure was composed by PS43−, P2S74− and P2S64− units. Both solid electrolytes exhibited a comparable high ionic conductivity over 10−3 Scm−1. A particle size around 500 nm was obtained by the liquid phase process, while a particle size larger than 10 μm was obtained by the ball milling process. The composite cathode using the solid electrolyte obtained by the liquid phase process displayed a better distribution of the solid electrolyte and the active material, verified by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The all-solid-state cell using LiNi1/3Co1/3Mn1/3O2 and the solid electrolyte prepared by the liquid phase exhibited a better electrochemical performance than that using the solid electrolyte prepared by ball milling. The all-solid-state cells exhibited a first discharge capacity of 154 mAh g−1 and 46 mAh g−1, respectively. Furthermore, the structure of the solid electrolyte prepared by the liquid phase process, after charge-discharge measurements with charge-end voltages of 4.6 V vs Li, was investigated by using ex-situ Raman spectroscopy. Significant structural changes were not observed, indicating that Li7P3S11 is stable against charge-discharge processes.