Quantitative Investigation of Spatial Inhomogeneity of Transition Metal Deposition in Commercial Automotive Cylindrical Cells under Overvoltage Conditions

Abstract Transition metal (TM) dissolution from the cathode and deposition on the anode in lithium−ion batteries is a key degradation mechanism, yet its spatial distribution in commercial cylindrical automotive-grade cells remains insufficiently understood. In this study on lithium−ion cells 18650 with a NMC811/graphite technology, we reveal a pronounced radial inhomogeneity in cathode metal deposition on the anode, with significantly higher accumulation in the inner windings of the jelly roll compared to the outer regions, identifying a critical vulnerability in the cell design while operating in overvoltage conditions. Spatially resolved near-edge edge X-ray absorption fine structure measurements further highlight this geometry dependence, revealing a higher fraction of Ni4+ in the inner windings, whereas the outer regions are dominated by Ni2+. This radial gradient correlates with intrinsic geometric characteristics of cylindrical cells, where the smaller bending radius in the inner windings may plausibly contribute to elevated mechanical stress, higher compressive pressure, and reduced heat dissipation in the cell core. The findings directly link cell geometry to both the extent and chemical state of TM deposition, proving its central role in degradation processes.