Electrochemical oxidation of trivalent chromium in a phosphate matrix: Li3Cr2(PO4)3 as cathode material for lithium ion batteries

The monoclinic form of Li3Cr2(PO4)3 is galvanostatically cycled in a half cell versus lithium as anode. For the first time active redox behaviour of trivalent chromium in a phosphate matrix at around 4.8 V vs. Li+/Li is demonstrated. The coulombic efficiency ideally approaches 80%. Based on extensive XPS analyses, a possible oxidation scenario is suggested, which considers the formation of both diphosphorus(V) pentaoxide and chromyl(IV) compounds. Further possible parasitic reactions like the formation of a solid electrolyte interface at the cathode side are discussed.