Multiple structural and surface modifications stabilize LiCoO₂ cathodes to 4.7 V

Raising the charge cut-off voltage is an efficient strategy to enhance the energy density of LiCoO₂ (LCO) based lithium-ion batteries. However, irreversible phase transitions and severe interfacial degradation at highly delithiated states largely undermine cycle stability. Herein, a multiple modification strategy integrating bulk Ni doping, sub-surface Zr/P doping, and interfacial Nafion-Rb coating is proposed to stabilize LCO to a voltage as high as 4.7 V. The bulk Ni doping can act as pillar to stabilize the layer structure, while sub-surface Zr/P doping can significantly improve the sub-surface metal–O bonding, thereby suppressing the irreversible phase transitions from O3 to H1-3/O1 at highly delithiated state. Meanwhile, a Nafion-Rb polymer coating on the surface can efficiently alleviate side reactions from electrolyte decomposition. Theoretical calculations further confirm that the reduced O band center and band gap in the modified LCO (the Nafion-Rb coated and Ni, Zr, and P co-doped LCO particles (R-LCONZP)) are responsible for the stable Co–O bond within the LCO surface and enhanced electronic conductivity. The R-LCONZP demonstrates a high capacity of 245.9 mAh·g⁻¹ at 0.1 C and superior capacity retention of 71.9% after 200 cycles. This integrated modification approach is enlightening and feasible to eventually tackle the complicated structural and interfacial problems of LCO cathodes under high voltage.