Role of Li6CoO4Cathode Additive in Li-Ion Cells Containing Low Coulombic Efficiency Anode Material

Abstract

Li₆CoO₄ with an anti-fluorite structure was prepared and studied as a cathode additive for a Li-ion battery consisting of LiCoO₂ (namely LCO) cathode and Si-SiO_x (namely SiO_x) anodes. In situ XRD and TEM, combined with X-ray photoelectron spectroscopy (XPS) revealed that Li₆CoO₄ was decomposed to electrochemically inactive phases such as Li_6-xCoO₄ and Li₂O and CoO₂ during the first cycle. Due to this effect, Li₆CoO₄ showed the first charge and discharge capacities of 318 and 13 mAhg⁻¹, respectively between 4.4V and 1.0V, showing an irreversible capacity ratio of 96%. Because of such a high irreversible capacity, the additive could effectively compensate for the irreversible capacity of the Li-ion cell consisting of LCO cathode and SiO_x anode with a high irreversible capacity ratio of 57%. The first discharge capacity of a balanced full cell with LCO/SiO_x without an additive was 77 mAh/g. However, when the Li₆CoO₄ cathode additive was optimized to 15 wt% in the LCO composite in the same cell as above_, the first discharge capacity was 133 mAh/g.