Controlling high-voltage failure pathways through interfacial regulation in Ni-rich single-crystal cathodes

High-voltage degradation of Ni-rich single-crystal layered oxide cathodes (SC-NCM) is closely coupled with the cathode–electrolyte interface, where parasitic reactions, surface reconstruction, and kinetic deterioration are readily activated during deep delithiation. To clarify the role of interfacial reaction pathways in this degradation process, electrolyte additive chemistry was used as a molecular tool to regulate the initial interfacial reaction pathway without altering the bulk structure of the cathode. The results reveal that an uncontrolled interface accelerates electrolyte decomposition, charge-transfer resistance growth, Li⁺ transport deterioration, high-voltage phase irreversibility, and layered-to-rock-salt surface reconstruction. In contrast, additive-regulated cathode–electrolyte interphase (CEI) formation stabilizes the interfacial reaction environment, suppresses parasitic surface reactions, and preserves charge-transfer and Li⁺ diffusion kinetics during deep delithiation. Moreover, the regulated interface maintains the reversibility of the H2–H3-related phase evolution and mitigates stress concentration during the structurally sensitive phase-transition stage. This work demonstrates that regulating the initial cathode–electrolyte reaction pathway can mitigate interface-triggered degradation in SC-NCM, highlighting interfacial chemistry regulation as an effective strategy for stabilizing SC-NCM under high-voltage operation.