Influence of fluorine substitution on the electrochemical performance of 3 V spinel Li4Mn5O12 − ηFη cathodes

Spinel Li4Mn5O12 − ηFη (0 ≤ η ≤ 0.2) oxyfluoride cathodes have been synthesized at 500 and 600 °C employing LiF as a fluorine source and characterized by X-ray diffraction, chemical analysis, and electrochemical cycling. Fluorine substitution is found to suppress the disproportionation of Li4Mn5O12 into lithium-rich spinel Li1 + xMn2 − xO4 and Li2MnO3 during synthesis. The oxyfluoride cathodes exhibit higher initial capacity and improved capacity retention at both 25 and 60 °C compared to the corresponding oxide analogs in both the LiClO4- and LiPF6-based electrolytes. The improved electrochemical performance is due to a suppression of the Li2MnO3 phase and Mn dissolution.