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

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.