Lithium-excess transition metal oxide materials are
promising cathode candidates for future secondary batteries due to their
relatively high energy density, which is commonly related to redox-active
oxygen centers. First-principle computations are crucial for the understanding
of the underlying redox mechanism in these compounds, with plane-wave density
functional theory being the most frequently used setup. An important tool for
the assignment of the redox-active species is the projected density of states,
although the atomic contributions postulated this way do not strictly
correspond to any observable physical quantity. By directly analyzing the computed
real-space charge density changes, on the other hand, oxygen redox activity can
be found to be substantial in most transition metal oxide compounds, although a
projection onto atomic states would suggest otherwise. This can be linked to
the shortcomings of the commonly employed spherical approximation for ions in
crystalline compounds used to compute the projected density of states, which
fails to describe the charge density topology in covalent transition metal
oxides and leads to a qualitatively different picture from a charge
density-based approach, specifically, the underrepresentation of oxygen
contributions and exaggeration of transition metal contributions to the density
of states The density based approach,
due to the non-spherical nature of Bader domains, is more apt to properly
describe oxygen redox contributions. This raises the question how meaningful
the descriptors of oxygen redox activity are and how it should be acknowledged
for transition metal oxide compounds in general.
Front Cover: Carbon Transition‐metal Oxide Electrodes: Understanding the Role of Surface Engineering for High Energy Density Supercapacitors (Chem. Asian J. 11/2020)
