  Understanding the lattice oxygen dimerization is quite essential for the
optimal design for the Li-rich Mn-based cathode materials. In this work, based
on the density functional theory (DFT) calculations, a Ni-honeycomb Li-Ni-Mn
cation configuration for Li$_{1.22}$Ni$_{0.22}$Mn$_{0.56}$O$_2$ cathode was
carefully proposed and examined, which can coexist with the well-known
Li-honeycomb structure in the experimentally synthesized
Li$_{1.2}$Ni$_{0.2}$Mn$_{0.6}$O$_2$ samples. Li-Ni-Mn cation configurations
have significant impacts on oxygen redox activities and oxygen dimerizations in
the delithiated Li$_x$Ni$_{0.22}$Mn$_{0.56}$O$_2$. There is no necessary
consistency between the high lattice oxygen redox activity and easy oxygen
dimerization, such as the Li-honeycomb structures showing higher redox
activities and higher activation energy barriers to prohibit oxygen
dimerizations than Ni-honeycomb structures. Avoiding the Ni-honeycomb
structures with more favorable lattice oxygen dimerization and making full use
of the Li-honeycomb structures with better redox activities is important to
optimally design the high-performance Li-rich Mn-based cathode materials.
