Compositional Gradient Engineering of LiNi 0.75 Co 0.05 Mn 0.20 O 2 Greatly Enhances High-Voltage Cycling Stability for Li-Ion Batteries

Ni-rich Co-poor layered oxide cathodes enable high energy density under high-voltage operation (upper cutoff of ≥4.5 V) but suffer from severe structural and interfacial degradation under high-voltage operation. Herein, we propose a synergistic strategy that integrates trace W doping with an island-type Li x CoO 2 surface coating to construct a full-concentration-gradient LiNi 0.75 Co 0.05 Mn 0.20 O 2 cathode. The W dopant effectively suppresses transition-metal interdiffusion during high-temperature lithiation to preserve a sharp gradient with a Ni-rich core and Mn-rich surface, enhancing the structural stability and relieving the mechanical stress. Simultaneously, the conductive Li x CoO 2 coating scavenges residual lithium, accelerates interfacial charge transfer, and enhances Li + diffusion. Consequently, the optimized cathode delivers a high reversible capacity of 220 mAh·g –1 at 0.1C and remarkable rate capability (100.0 mAh·g –1 at 10C). In pouch-type full cells cycled up to 4.6 V, it retains 92.6% capacity after 1000 cycles, significantly outperforming its unmodified counterpart (75.9%). This work demonstrates a synergistic structural–interfacial engineering to achieve both high-power and long-life Ni-rich Co-poor cathodes toward high-energy Li-ion batteries.