Electrochemical properties and Mِssbauer effect of anti-fluorite type compound, Li5FeO4

The anti-fluorite type materials, low and high temperature forms of Li5FeO4, were prepared and studied as a cathode for lithium secondary battery. The maximum amount of 1.2 equivalent lithium was de-intercalated from and reversibly intercalated to Li5FeO4, which corresponds to the capacity of 200 mA h/g in Li/Li5FeO4 cell (4 V–2 V). In the first charge, anti-fluorite type Li5FeO4 changed to amorphous-like phase which concerned the following discharge and charge processes. In an initial few cycles, the discharge capacity was lower than the charged capacity and the efficiency became 100% after the fifth cycle. The Mössbauer effect measurement showed that the amounts of oxidized iron such as the Fe4+ state formed by the charging process did not coincide with that of the charge transferred in the Li/Li5FeO4 cell. The oxidation in oxide ion side was suggested.