Breaking the 4.6 V Barrier in LiCoO2 Cathodes: Synergistic Effects of Bulk and Surface Structure Modification

Abstract Overcoming the 4.6 V barrier for LiCoO2 (LCO) cathodes necessitates concurrent mitigation of bulk structural degradation and interfacial side reactions. Herein, a bulk‐surface synergistic stabilization strategy is proposed integrating Fe/F dual‐site doping with an ultrathin LiCPON solid electrolyte coating (≈2 nm) deposited via magnetron sputtering. Fe substitution at Co sites strengthens Co–O bonds to alleviate irreversible O3‐to‐H1‐3 phase transitions, while F doping at O sites can stabilize lattice oxygen and enhance electronic conductivity. The conformal LiCPON layer constructs an inorganic‐rich artificial cathode‐electrolyte interphase (CEI), effectively suppressing transition metal dissolution and lattice oxygen evolution. The optimized LCO‐FeF‐LiCPON cathode delivers exceptional electrochemical performance: 85.5% capacity retention after 200 cycles at 4.6 V (vs 55.1% for pristine LCO), 81.1% retention in pouch‐type full‐cells (3.0–4.55 V), and 72.7% retention after 100 cycles at 4.7 V. Density functional theory (DFT) calculations reveal that Fe/F co‐doping increases the Co 3d–O 2p band center separation from 0.31 to 0.57 eV at 4.6 V, inhibiting oxygen redox activity. The work not only enriches the regulation of LiCoO2 electrochemical performance through bulk and surface structure modification, but also provides new directions for future more sophisticated composite control of LiCoO2 electrochemistry.