Li-oxide garnets . Observed lattice parameters are a = 12.4118(2) Å and are of similar size to those of the material obtained by Takeda, et al. , also by precipitation from an aqueous solution with a = 12.407(2) Å. In the structure of Na 3 Fe 2 Li 3 F 12 , sodium occupies the 24c site with an eightfold fluor atom coordination, the octahedrally coordinated 16a site hosts iron, while Li resides on the 24d position and is in tetrahedral coordination. Based on the Rietveld refinements (Fig. ) on the powder diffraction data, the 24c and the 16a site appear to be fully occupied, however, a slight Li deficit might be present at the 24d site, due to the low scattering contrast of Li, but this cannot be fully validated (see SI for more details). Fe Mössbauer spectroscopy in Fig. proved the presence of solely ferric iron in octahedral coordination, no Fe 2+ is present, nor is there any hint for Fe 3+ on other sites. Rather broad lines and slightly asymmetric shape indicate some distributions of local distortion environments around the iron atoms maybe related to nano-scale nature of the particles (~40 nm; see Fig. showing NFLF particles embedded in the composite electrode), hence surface terminated Fe contributions will get significant (see SI for more details). Such structural merit may facilitate the lithium insertion/deinsertion that fundamentally contributes to pseudocapacitive energy storage of the anode.