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

초록

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.

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