Understanding cross-talk-induced anode slippage in high-voltage mid-Ni NCM/graphite full cells.

While high-voltage operation of mid-Ni layered oxide cathodes in full-cell Li-ion batteries is essential for achieving high energy density, it inevitably accelerates electrode degradation, ultimately resulting in capacity loss. However, the underlying degradation mechanisms under high-voltage conditions remain poorly understood. In this study, we reveal that anode slippage - induced by cross-talk-driven surface degradation - is the dominant factor in capacity fade during high-voltage (4.35 or 4.40 V) cycling of single-crystal mid-Ni layered oxide (SC-NCM)/graphite pouch full-cells. Electrochemical and post-mortem analyses show that, although high-voltage operation induces cathode surface degradation, including lattice oxygen loss and phase transitions, its direct impact on capacity loss is relatively minor compared to that of the anode. Instead, anode degradation is primarily caused by cross-talk effects from cathode Ni dissolution, which promote the accumulation of irreversible organic byproducts - such as LiO and LiCO - within the solid electrolyte interphase (SEI) layer of the graphite anode. This leads to increased resistance and reduced anode electrochemical activity, disrupting electrode balance and accelerating full-cell capacity fade. These findings highlight the critical role of anode degradation in high-voltage operation and emphasize the importance of mitigating cross-talk effects. A comprehensive understanding of cross-talk-induced anode slippage is therefore critical for the rational design of high-voltage mid-Ni full-cell systems with long-term durability.