A new lithium–copper–iron-oxide as a negative electrode material for lithium-ion batteries

Synthesis, crystal structure and electrochemical reactivity of Li3CuFe3O7 in a lithium (Li) cell are reported as a new material for the first time. The crystal structure is γ-LiFeO2 type, and the chemical formula can be re-written as (Li0.714Cu0.286) (Li0.143Fe0.857)O2. The average charge–discharge voltages versus Li are 1.75/0.9 V, which indicates the material may be used as a negative electrode in Li-ion batteries. The material demonstrates a discharge capacity of up to 970 mAh/g, but shows also a significant irreversible capacity of >250 mAh/g. It decomposes to very small particles of lithium oxide and unidentified species during the first discharge. The reversibility is strongly dependent on C-rate, electrode composition, initial particle sizes and/or crystallinity, implying that a better electrochemical performance may be achieved by adjusting these parameters. The observation of higher than theoretical capacity (694 mAh/g) for the reversible reaction of Li3CuFe3O7+11Li↔7Li2O+Cu+3Fe, however, suggests the possibility that the Li–M (Cu, Fe) alloy formation–decomposition process is involved.