Tungsten-consolidated crystal structure of LiNi_0.6Co_0.2Mn_0.2O₂ cathode materials for superior electrochemical performance

Tungsten-consolidated LiNi0.6Co0.2Mn0.2O2 cathode materials (NCMWs) are successfully synthesized by Ni0.6Co0.2Mn0.2O2(OH)(2) @W precursor via a facile polyvinyl pyrrolidone (PVP)-assisted wet coating process followed by heat treatment. Experimental results demonstrate that a proper tungsten (W) content can migrate into transition metal layer to form W-gradient cathode material, while the excess W can induce the formation of a disordered Li-Ni-Co-Mn-W mixed layer on the surface due to the interdiffusion, finally forming core-shell cathode material. The physical-electrochemical properties of particles surface can also be optimized by W introduction. The W introduction would increase the Li/Ni mixing due to charge compensation of the high-valence W6+. The increased Ni2+ in lithium layers and the doped W6+ jointly consolidate the layered structure. As a result, the W modified sample with 8000 ppm W shows the capacity retention of 86.89% (72.68% for the pristine) at 165 mA g(-1) after 100 cycles over 3.0-4.6 V. Even at 1320 mA g(-1), the W modified sample can deliver 150.6 mAh g(-1), far higher than that of the pristine (119.9 mAh g(-1)).