Oxygen Redox Activity in Cathodes: A Common Phenomenon Calling for Density-Based Descriptors

First-principle computations are crucial for the understanding of the oxygen redox mechanism in lithium-excess transition metal oxide materials. An important tool for the assignment of the redox-active species is the projected density of states (PDOS). A topological analysis of the charge density, on the other hand, suggests substantial oxygen redox activity in many transition metal oxide compounds beyond the ones commonly associated with it. This can be linked to the shortcomings of the spherical approximation for ions in crystalline compounds used to compute the PDOS, which fails to describe the charge density topology in transition metal oxides and leads to an erroneous description of the nature of charge transfer compared to a charge density-based approach. The density-based approach, due to the nonspherical nature of its domains, is more apt to properly describe oxygen redox contributions. This raises the question how meaningful the commonly employed descriptors of oxygen redox activity are.