Low‐Temperature Synthesis, Characterization, and Stability of Spinel‐Type Li 2 NiF 4 and Solid‐Solutions Li 2 Ni 1– x Co x F 4

A new synthesis route to Li 2 NiF 4 based on a fluorolytic process using Ni(acac) 2 or Ni(OAc) 2 · 4H 2 O as precursor is presented. Variation of the synthesis conditions allows crystallite size control of the obtained powders. 6 Li and 7 Li MAS NMR experiments were carried out to study local environments of the lithium ions. Several attempts were made to synthesize Li 2 CoF 4 , which are, unfortunately, hitherto not successful. Nevertheless, our studies clearly reveal that solid solutions Li 2 NiF 4 –Li 2 CoF 4 are stable up to ca. 30 % cobalt. High‐temperature X‐ray diffraction measurements also show no evidence for the existence of pure Li 2 CoF 4 . These findings are supported by quantum chemical calculations.