High Li-Ion Conductivity in Li{N(SO2F)2}(NCCH2CH2CN)2 Molecular Crystal

There is an urgent need to develop solid electrolytes based on organic molecular crystals for application in energy devices. However, the quest for molecular crystals with high Li-ion conductivity is still in its infancy. In this study, the high Li-ion conductivity of a Li{N(SO₂F)₂}(NCCH₂CH₂CN)₂ molecular crystal is reported. The crystal shows a Li-ion conductivity of 1 × 10^-4 S cm^-1 at 30 °C and 1 × 10^-5 S cm^-1 at -20 °C, with a low activation energy of 28 kJ mol^-1. The conductivity at 30 °C is one of the highest values attainable by molecular crystals, whereas that at -20 °C is approximately 2 orders of magnitude higher than previously reported values. Furthermore, the all-solid-state Li-battery fabricated using this solid electrolyte demonstrates stable cycling, thereby maintaining 90% of the initial capacity after 100 charge-discharge cycles. The finding of high Li-ion conductivity in molecular crystals paves the way for their application in all-solid-state Li-batteries.