摘要
The pre-edges of oxygen-K X-ray absorption spectra have been ubiquitous in transition metal(TM)oxide studies in various fields,especially on the fervent topic of oxygen redox states in battery electrodes.However,critical debates remain on the use of the O-K pre-edge variations upon electrochemical cycling as evidences of oxygen redox reactions,which has been a popular practice in the battery field.This study presents an investigation of the O-K pre-edge of 55 oxides covering all 3d TMs with different elements,structures,and electrochemical states through combined experimental and theoretical analyses.It is shown unambiguously that the O-K pre-edge variation in battery cathodes is dominated by changing TM-d states.Furthermore,the pre-edge enables a unique opportunity to project the lowest unoccupied TM-d states onto one common energy window,leading to a summary map of the relative energy positions of the low-lying TM states,with higher TM oxidation states at lower energies,corresponding to higher electrochemical potentials.The results naturally clarify some unusual redox reactions,such as Cr^(3+/6+).This work provides a critical clarification on O-K pre-edge interpretation and more importantly a benchmark database of O-K pre-edge for characterizing redox reactions in batteries and other energy materials.
基金
supported by the LDRD program at the LBNL and facilitated by a User Program at The Molecular Foundry(TMF)
provided by the TMF clusters(managed by the High Performance Computing Services Group,at LBNL)
by the National Energy Research Scientific Computing Center(NERSC)
supported by the Office of Science of the US DOE under Contract No.DE-AC02-05CH11231
support from EERE VTO under the Applied Battery Materials Program of the US DOE with Contract No.DE-AC02-05CH11231
supported by the DOE VTO at Argonne National Laboratory
