Although chemical doping has been extensively employed to improve the electrochemical performance of Li-rich layered oxide (LLO) cathodes for Li ion batteries, the correlation between the electrochemical kinetics and local structure and chemistry of these materials after chemical doping is still not fully understood. Herein, gradient surface Si/Sn-doped LLOs with improved kinetics are demonstrated. The atomic local structure and surface chemistry are determined using electron microscopy and spectroscopy techniques, and remarkably, the correlation of local structure-enhanced kinetics is clearly described in this work. The experimental results suggest that Si/Sn substitution decreases the TMO2 slab thickness and enlarges the interslab spacing, and the concentration gradient of Si/Sn affects the magnitude of these structural changes. The expanded interslab spacing accounts for the enhanced Li+ diffusivity and rate performance observed in Si/Sn-doped materials. The improved understanding of the local structure-enhanced kinetic relationship for doped LLOs demonstrates the potential for the design and development of other high-rate intercalated electrode materials.
Keywords: HAADF-STEM; cathode materials; gradient chemical doping; interslab spacing; lithium-rich layered oxide.