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

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-SiOx (namely SiOx) anodes. In situ XRD and TEM, combined with X-ray photoelectron spectroscopy (XPS) revealed that Li6CoO4 was decomposed to electrochemically inactive phases such as Li6-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 SiOx anode with a high irreversible capacity ratio of 57%. The first discharge capacity of a balanced full cell with LCO/SiOx 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.