Operando X-ray Absorption Spectroscopy and Emission Kβ1,3 Study of the Manganese Redox Activity in High-Capacity Li4Mn2O5 Cathode

The electrochemical performance of nanostructured Li4Mn2O5 (or rather the 0.93Li3.6–xMn2.4O5.4–0.07Li2O composite) displaying an outstanding charge capacity of 350 mA h/g was recently reported. Interestingly, the removal of lithium from Li4Mn2O5 is found to take place beyond the oxidation limit of +4 for Mn in an octahedral environment. To characterize the nature of this extra capacity, we have approached the study of the redox chemistry and local structure of manganese in Li4Mn2O5 via a combination of X-ray absorption and emission spectroscopies at the manganese K-edge. To support our results, we have thoroughly characterized the composition of the materials at several potential values by inductively coupled plasma and online electrochemical mass spectrometry. Additionally, operando X-ray absorption near-edge structure studies, in excellent agreement with ex situ data, were carried out for the charge and discharge of the battery. Our results unequivocally rule out the participation of the Mn4+/Mn5+ redox couple and indicate the participation of oxygen in the electrochemistry. After the first charge, the battery cycles reversibly between the charged and discharged states, where the lithium exchange is mainly compensated by anionic redox.