Factors Controlling the Fluorine Content and the Electrochemical Performance of Spinel Oxyfluoride Cathodes

An investigation of spinel ( , ) cathodes synthesized by firing the cation-substituted oxide analogs with the fluorinating agent at reveals that the amount of fluorine that could be incorporated into the spinel lattice is limited by the Mn valence in the spinel lattice; it is difficult to incorporate fluorine as the Mn valence lowers to around . Although fluorine substitution increases the capacity, spinel cathodes with a Mn valence of encounters a larger lattice mismatch between the two cubic phases formed during the charge-discharge process and higher Mn dissolution, resulting in a degradation of the electrochemical properties. For example, with an initial Mn valence of exhibits a combination of high capacity, excellent cyclability with graphite anode at , good storage characteristics, high rate capability, and low irreversible capacity compared to .