Lithium Thiosilicophosphate Glassy Solid Electrolytes Synthesized by High-Energy Ball-Milling and Melt-Quenching:...

Due to the volatility of P₂S₅, the ambient pressure synthesis of Li₂S + P₂S₅ (LPS) has been limited to planetary ball-milling (PBM). To utilize PBM of LPS to generate a solid electrolyte (SE), the as-synthesized powder sample must be pressed into pellets, and as such the presence of as-pressed grain boundaries in the SE cannot be avoided. To eliminate the grain boundaries, LPS doped with SiS₂ has been studied because SiS₂ lowers the vapor pressure of the melt and promotes strong glass formation, which in combination allows for greater ease in synthesis. In this work, we have examined the structures and electrochemical properties of lithium thiosilicophosphate 0.6Li₂S + 0.4[xSiS₂ + 1.5(1 - x)PS_5/2], 0 ≤ x ≤ 1, glassy solid electrolytes (GSEs) prepared by both PBM and melt-quenching (MQ). It is shown that the critical current density improved after incorporating SiS₂, reaching 1.5 mA/cm² for the x = 0.8 composition. However, the interfacial reaction of MQ GSE with lithium metal introduced microcracks, which shows that further research is needed to explore and develop more stable GSE compositions. These fundamental results can help to understand the interface reaction and formation and as such can provide a guide to design improved homogeneous GSEs with SiS₂ as a glass former, which have no grain boundaries and thereby may help suppress lithium dendrite formation.