Nonmonotonic Li-Content Evolution and Size-Dependent Lithium Accessibility in Degraded High-Nickel Cathodes

Abstract Understanding how degradation reshapes lithium (de)insertion pathways in high-nickel cathodes is crucial for extending battery lifetime. Here, we integrate operando synchrotron X-ray diffraction (sXRD) with electrode-level transmission X-ray microscopy (TXM) to quantitatively resolve how degradation redistributes lithium accessibility in Ni-rich NCA cathodes. Using a 26-state deconvolution framework, we show that degraded electrodes exhibit nonmonotonic Li-content population evolution: delithiation kinetics are initially suppressed, transiently synchronized, and ultimately diverge, leaving ∼7% discharge-like states and ∼13% intermediate Li-content states at the end of charge. Spatially resolved TXM reveals that this divergence originates from size-dependent accessibility constraints—large particles develop persistent intra-particle state-of-charge gradients, while small particle…