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Larger battery cell formats increase usable energy but promote inhomogeneities that affect degradation. This work examines aging in 21700-type cells with NCM cathodes and graphite/SiOx anodes using cyclic aging combined with in operando neutron diffraction, neutron depth profiling, and X-ray computed tomography. Prolonged cycling leads to Li loss, visible on the cathode through reduced NCM unit cell expansion and on the anode by suppressed formation of fully lithiated LiC₆. Differential voltage analysis reveals both loss of active anode material and Li inventory, corroborated by diffraction data showing the LiC₆ and LiC₁₂ transitions shifted to lower capacity values. Li concentration profiles confirm cathode depletion, while elevated anode Li content indicates increased solid–electrolyte interphase formation, consistent with cathode-derived Li consumption at the anode. Spatially resolved X-ray imaging analysis shows stronger degradation in the cell center than at the bottom edge, underscoring the role of electrode inhomogeneities in large-format cells.