or their derivatives. The NASICON structure has the general formula of A x MM'(XO 4 ) 3 , typical elements being A = Li, Na, K, Mg, Ca and A x = 0 -5, M/M' = Fe, V, Ti, Zr, Mn and X = S, P, Si. Due to their higher charge and therefore lower occupation of crystal sites, multivalent ions like magnesium or calcium only occupy the Na1-position within the NASICON framework.