Atomic-Scale Signatures of Structural Irreversibility during Oxygen Redox in Li-Rich Layered Oxide Cathodes

Li-rich layered oxides access high capacity through transition-metal and oxygen redox, but oxygen loss and structural reconstruction cause large first-cycle irreversibility. Here, we examine Li1.2Ni0.13Co0.13Mn0.54O2 at four states of the first charge–discharge cycle using atomic-resolution STEM, nanobeam electron diffraction with electron pair distribution function (NBED-ePDF) analysis, electron energy-loss spectroscopy (EELS), image simulations, and DFT. Up to 4.3 V, Li extraction is dominated by interlayer sites and the slab framework remains largely preserved. At 4.8 V, changes in Li/O contrast and O K-edge features coincide with a short ePDF correlation near 1.57 Å. Seeded DFT relaxations stabilize short O–O pairs near vacancies in the transition-metal slab. After discharge, incomplete spectroscopic recovery accompanies near-surface reconstruction and oxygen-related contrast changes consistent with oxygen depletion. Together, the results implicate Li depletion from the transition-metal slab in high-voltage oxygen rearrangement and suggest that controlling this site occupancy may improve oxygen-redox reversibility.