Lithium-ion Mobility in Li 6 B 18 (Li 3 N) and Li Vacancy Tuning in the Solid Solution Li 6 B 18 (Li 3 N) 1-x (Li 2 O) x .

All-solid-state batteries are promising candidates for safe energy-storage systems due to non-flammable solid electrolytes and the possibility to use metallic lithium as an anode. Thus, there is a challenge to design new solid electrolytes and to understand the principles of ion conduction on an atomic scale. We report on a new concept for compounds with high lithium ion mobility based on a rigid open-framework boron structure. The host-guest structure Li 6 B 18 (Li 3 N) comprises large hexagonal pores filled with ∞ 1 [ ${{}_{{\rm { \infty }}}{}^{{\rm { 1}}}{\rm { [}}}$ Li 7 N] strands that represent a perfect cutout from the structure of α-Li 3 N. Variable-temperature 7 Li NMR spectroscopy reveals a very high Li mobility in the template phase with a remarkably low activation energy below 19 kJ mol -1 and thus much lower than pristine Li 3 N. The formation of the solid solution of Li 6 B 18 (Li 3 N) and Li 6 B 18 (Li 2 O) over the complete compositional range allows the tuning of lithium defects in the template structure that is not possible for pristine Li 3 N and Li 2 O.