Spatially Inhomogeneous Delithiation in LiNiO ₂ Positive Electrode: The Effect of X-ray Dose

Operando synchrotron X-ray techniques have become essential tools for investigating rechargeable batteries, as they provide real-time insights into electrochemical processes. However, the high brilliance of synchrotron radiation can alter the electrochemical mechanisms within the battery, thereby compromising the reliability and reproducibility of the operando measurements. In this study, we introduce a methodology that directly correlates the local X-ray dose with the Ni4+/Ni3+ redox activity in a LiNiO2 positive electrode. Full-field transmission X-ray absorption spectroscopy imaging (FFI-XAS) is employed to probe the charge-compensation mechanism during lithium extraction at the micrometer scale, using two beam configurations with different focal distances (far-focus and near-focus). While the spatially averaged XAS spectra exhibit sluggish reactions, regions exposed to lower dose rates show the expected electrochemical evolution. This contrast enables the identification, in our case, of a dose threshold for reliable operando measurements; however, determining a universal criterion remains complex because several parameters influence the material behavior, such as cathode thickness and electrolyte formulation. Our approach, including the definition of dose masks, provides a powerful framework to capture and rationalize the consequences of different experimental configurations in battery studies, enabling the design of more robust and reliable operando experiments.