synthesized, and their crystal structures were determined. The new compounds contained
three-dimensional (3D) sodium/lithium paths supported by P2O7 pillars in the crystal. First
principles calculations identified the complex 3D paths with their activation barriers and
revealed them as fast ionic conductors. The reversible electrode operation was found in both
Li and Na cells with capacities of one-electron reaction per Fe atom, 140 and 129 mAh g–1 …