All-solid-state Li-ion batteries are attracting considerable attention as possible alternatives to conventional liquid electrolyte-based devices as they present a viable opportunity for increased energy density and safety. In recent years, a number of candidate materials have been explored as possible solid electrolytes, including garnets, Li-stuffed garnets, Li-rich anti-perovskites (LiRAPs), thio-LISICONs and complex spinels. LiRAPs, including Li3−xOHxCl, have generated considerable interest based on their reported ionic conductivities (on the order of 10−3 S cm−1).1,2 However, until very recently, their lithium and proton transport capabilities as a function of composition were not fully understood. Hence, current research efforts have focused on the synthesis and structural characterisation of Li3−xOHxCl using a combination of ab initio molecular dynamics and variable-temperature 1,2H, 7Li and 35Cl solid-state NMR spectroscopy. Using this unique combination of techniques, it is possible to study the mobility of both the Li ions and protons. We will demonstrate that Li-ion transport is highly correlated with the proton and Li-ion vacancy concentrations. In particular, we will show that the Li ions are free to move throughout the structure, whilst the protons are restricted to solely rotation of the OH− groups. Based on these findings, and the strong correlation between long-range Li-ion transport and OH− rotation, we have proposed a new Li-ion hopping mechanism, which suggests that the Li-rich anti-perovskite system is an excellent candidate electrolyte for all-solid-state batteries.3 However, to fully understand the mechanism for conduction, multiple, complementary characterisation techniques are needed.
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- J. A. Dawson, T. S. Attari, H. Chen, S. P. Emge, K. E. Johnston and M. S. Islam, Energy Environ. Sci., 2018, 10, 2993.