SOC Mismatch–Driven Inter‐Particle Synchronization via Internal Li‐Ion Transfer: An Unrecognized Electrode‐Emergent Degradation Pathway in Ni‐Rich Composite Cathodes

Non‐uniform reaction dynamics are ubiquitous in composite electrodes of lithium‐ion batteries (LIBs), yet they are commonly regarded as transient kinetic effects that relax and average out over time, rather than as drivers of long‐term degradation. Here, using a deliberately designed bimodal Ni‐rich NCM811 model system comprising two particle populations with identical chemistry but distinct reaction kinetics—polycrystalline and single‐crystal NCM811—we systematically tune inter‐particle kinetic mismatch at the electrode‐ensemble level. We show that the resulting non‐uniform dynamics generate inter‐particle state‐of‐charge (SOC) mismatch, creating electrochemical potential gradients that drive spontaneous internal Li‐ion transfer—a controlled mechanistic example of electrode‐emergent degradation in a composite cathode. Although this redistribution synchronizes particle SOC across the ensemble, it proceeds through transient internal currents associated with more severe surface degradation, including organic‐rich cathode–electrolyte interphase (CEI) formation and rock‐salt‐type surface reconstruction. These findings show that collective electrode‐level dynamics can provide an additional degradation contribution beyond material‐intrinsic processes, suggesting that performance decay in kinetically mismatched composite cathodes may be better understood as an emergent consequence of interacting particle populations rather than a simple summation of material‐intrinsic failure modes. Our work highlights the importance of explicitly accounting for reaction heterogeneity and inter‐particle kinetic mismatch in composite electrode design and optimization.