An in-depth understanding of Al doping homogeneity affecting the performance of LiCoO2 at cut-off voltage over 4.6 V

The increasing demand for energy density pushes LiCoO2 (LCO) to work at higher voltage (≥4.5 V), which brings a series of problems including detrimental phase transition and structural instability. Various elemental doping has been proven an effective strategy to improve its structure stability. However, the understanding of elemental doping homogeneity effect is not enough, whether in terms of the controllability of doping homogeneity or its complex consequences. In this work, LCO powders with different Al doping homogeneity were synthesized and tested under high voltage (≥4.5 V) in both half and full cell at room and high temperature, respectively. The results show that the Al homogeneously doped LCO showed better cycling stability and rate performance compared to the inhomogeneous LCO sample. Particularly, the discharge capacity of Al homogeneously doped LCO after 500 cycles under 4.5 V in full cells could reach 160.1 mAh/g at 1.0 C with 94.1% capacity retention. Postmortem characterization demonstrates that a better doping homogeneity favors the stability of both the bulk and interface as well as the kinetic conditions. This study provided new insights about LCO performance fading, which sheds new light on the development of high-voltage LCO products The homogeneous Al doping effectively suppresses the irreversible phase transition, promote the reaction kinetics and stabilize the electrode/electrolyte interface, and therefore shows better cycling stability (94.1% capacity retention after 500 cycles at 0.1 C in full cells) and rate performance than the heterogenous one. [Display omitted]