Electrochemical splitting of LiF: A new approach to lithium-ion battery materials

Composites of LiF and lithium-free manganese compounds (MnF₂ and MnO_x) 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, MnO_x/LiF composites exhibited reversible reactivity with a sloping voltage profile, while MnF₂/LiF composites showed no reactivity. Reversible Li⁺ extraction from the MnO _x/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. Exsitu 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 MnO_x/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.