Electrochemical Splitting of LiF: A New Approach to Lithium-Ion Battery Materials

Composites of LiF and lithium-free manganese compounds (MnF2 and MnOx) were prepared by high-energy ball milling and their electrochemical activities as cathode were investigated. Within the voltage range of 1.5 - 4.8 V, MnOx/LiF composites exhibited reversible reactivity with a sloping voltage profile, while MnF2/LiF composites showed no reactivity. Reversible Li+ extraction from the MnOx/LiF composites was observed in a full cell configuration with graphite anode, where total Li+ balance was monitored by chemical analysis of the anode and the cathode. Ex-situ X-ray diffraction and X-ray absorption fine structure (XAFS) experiments further confirmed that during the first charge LiF is split electrochemically and the Mn oxidation state changes accordingly, but the MnOx/LiF remained amorphous. Composites containing the redox oxide and the lithium compound as two separate solid phases could be used as a source of Li+ and it offers a new type of cathode materials for lithium-ion batteries.