Annual Review 2024-2025

D I A M O N D L I G H T S O U R C E L I M I T E D 23 RIXS shows why Li-rich batteries fade The net zero transition necessary to limit the effects of climate change requires dramatic cuts to carbon emissions. One of the cornerstones of the UK’s transition will be switching to fossil-free transport, with electric vehicles (EV) one of the most developed options. However, the cathode is a critical limiting factor in efforts to increase the energy density of lithium-ion (Li-ion) batteries for EV applications. Cathodes have layered structures with alternating layers of transition metal oxide and lithium ions. Lithium-rich cathodes are next-generation materials which have higher concentrations of lithium within the cathode structure, replacing some of the transition metals. They have a higher capacity because they store energy via oxidation of the oxygen in the structure as well as the transition metal. However, a long-standing question has been how the oxygen undergoes charge storage. Using high-resolution resonant inelastic X-ray scattering (RIXS) spectroscopy on beamline I21, researchers from the Faraday Institution and the University of Oxford followed the oxygen redox reaction in Li-rich cathodes over cycling and quantitatively measured the O2 trapped within the material. Their results show that a gradual increase in electrochemically inactive O2 and the loss of O2 from voids near the cathode surface leads to a reduction in the O redox capacity and the observed voltage fade. These important insights could lead to innovations in cathode chemistry and aid the transition to low-carbon energy sources. DOI: 10.1038/s41563-024-01833-z M A G N E T I C M AT E R I A L S G R O U P Imaging and measurements demonstrated the battery fade. 2nd Charge 100th Charge Energy Loss (eV) Energy Loss (eV)