Lithium conduction and the role of alkaline earth cations in Li2S–P2S5–MS (M = Ca, Sr, Ba) glasses

Abstract

There has been considerable interest in lithium-sulfide glasses with high lithium ion conductivities because of their potential applications in solid-state electrolytes. Here, new sulfide glasses containing alkaline earth cations, Li2S–P2S5–MS (M = Ca, Sr, Ba), were synthesized by melt quenching. Furthermore, the glass-forming regions in these glasses were identified.Three samples containing equimolar alkaline earth cations (60Li2S–30P2S5–10MS) were selected and their Li+ conductivities were measured. Lower Li+ conductivities were observed in 60Li2S–30P2S5–10MS than in Li2S–P2S5. The local structures of P and Li were characterized by 31P and 6Li solid-state magic angle spinning (MAS) NMR to determine the cause for the observed decrease in the Li+ conductivities and understand the role of alkaline earth cations in the Li2S–P2S5 glasses. A higher-field shift of the PS43− was observed in the 31P MAS NMR spectra of the glasses containing alkaline earth cations, which was attributed to the formation of bridging structures between PS43− units by alkaline earth cations. Moreover, more than half of the Li had low mobility, which is consistent with the conductivity. These results highlight the presence of an effective conduction path around the PS43− in contrast to P2S74− and P2S64−.