Although Li-oxide garnets are well known as solid electrolytes, they can also be used as electrode material if a redox active center is present as Goodenough and coworkers demonstrated . They were able to reversibly insert 4 Li + per formula unit (Li 3 Nd 3 W 6+ 2 O 12 + 4Li + + 2e -↔ Li 7 Nd 3 W 4+ 2 O 12 ) into the oxide-garnet lattice with an initial capacity of 105 mAh/g. In the case for Li-fluoride garnets (Na 3 M 2 Li 3 F 12 , with M = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) theoretical gravimetric and volumetric capacities of up to 260 mAh/g and 745 mAh/cm 3 could be potentially achieved, respectively. A further advantage of cryolithionites is the possibility to synthesize the material at room temperature -this makes its preparation low cost, which is particularly important to drop the price per kWh. Cryolithionite is a fluoride that tends to form strong Li-F bonds, which is a disadvantage in terms of Li mobility, hence, Li insertion. However, this could become an attractive material for energy storage by inducing pseudocapacitive characteristics due to the Fe 2+ /Fe 3+ redox activity present in the crystal lattice.