Influence of Cationic Substitutions on the Oxygen Loss and Reversible Capacity of Lithium-Rich Layered Oxide Cathodes

The influence of cationic substitutions on the ease with which oxygen loss occurs from lithium-rich layered oxide cathodes during first charge has been studied with three series of samples: Li[Li0.33Mn0.67-xTix]O-2 (0 <= x <= 0.67), Li[Li0.2Mn0.54-xTixNi0.13Co0.13]O-2 (0 <= x <= 0.27), and Li[Li0.2Mn0.60-xTixNi0.20]O-2 (0 <= x <= 0.40). The lattice parameters and cell volume increase monotonically with the substitution of a larger Ti4+ for Mn4+, indicating the formation of solid solutions. It is found that substitution of Ti4+ for Mn4+ decreases the degree of oxygen loss and consequently the charge and discharge capacity values, while substitution of Co3+ for (Mn0.54+Ni0.52+) increases the oxygen loss and consequently the charge and discharge capacity values. While the former is attributed to a stronger binding of oxygen to Ti and a decrease in the metal oxygen covalence due to a larger charge transfer gap between the Ti3+/4+ 3d and O2- 2p bands, the latter is attributed to a weaker binding of oxygen to Co and an increase in the metal oxygen covalence due to an overlap of the Co3+/4+ t(2g) band with the top of the O2- 2p band.