Structural Stabilization of 4.6 V LiCoO₂ Through Tri-Site Co-Doping with Al-Mg-F

Uplifting the charging voltage of LiCoO₂ is crucial for surpassing current energy density thresholds in Li-ion batteries. However, the structural and chemical instability of LiCoO₂ in the deeply delithiated state is a major obstacle to the practical implementation of high-voltage LiCoO₂. This study proposes a multi-element co-doped LiCoO₂ that exhibits enhanced electrochemical performances at 4.6 V (vs Li/Li⁺). Al, Mg, and F are doped at three distinct lattice sites, and the contributions of each dopant are investigated using advanced synchrotron X-ray analyses and electron microscopies. Al and Mg delay the detrimental transition to the H1-3 phase and facilitate a smoother phase transition, thereby preserving particle robustness. The electronegative anion dopant F mitigates oxygen oxidation and ensures a wider range of transition metal redox reactions. These enhancements enable the particles to withstand numerous cycles without severe cracking or surface degradation, thereby significantly improving cyclability. Consequently, the tri-site doping strategy effectively minimizes capacity sacrifice and bolsters battery performance, with every dopant functioning synergistically.