Electrochemical Characteristics of Graphite–LiF Composite Electrodes for Lithium-Based Energy Storage Systems

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This work presents the fabrication of a large-capacity dual-graphite battery positive electrode based on the fluorination and de-fluorination of graphite. The graphite–LiF (GL) composite electrode was prepared by mixing graphite and LiF and exhibited a significantly large capacity during charge and discharge measurements in 4.6 mol kg –1 LiBF 4 /sulfolane (SL) electrolyte. Solid-state nuclear magnetic resonance and X-ray photoelectron spectroscopy analyses revealed that during the charge and discharge process, BF 4 – ion insertion and de-insertion occurred along with fluorination and de-fluorination of graphite. In addition, the X-ray diffraction results suggested that the fluorination of graphite during the first charge cycle was accompanied by its amorphization. Because the GL electrode exhibited little capacity in LiPF 6 /SL, its large reversible capacity results from the fluorination of graphite, during which F – ions intercalated into the bulk of graphite via BF 4 – present between graphite interlayers and formed bonds with carbon. This large-capacity GL electrode also released Li + ions into the electrolyte during charging, making it a promising positive electrode material for dual-graphite batteries.