Understanding electrochemical performance improvement with Nb doping in lithium-rich manganese-based cathode materials

This study synthesizes pristine and Nb-doped lithium-rich manganese-based cathode materials by solvothermal and high-temperature solid-phase methods. Analysis by focused ion beam scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy indicates successful Nb doping into the material's bulk structure. Electrochemical evaluation reveals that electrochemical performance is significantly enhanced by Nb doping. The discharge capacity of Nb-0.02 can maintain 271.7 mAh.g(-1), and its cycle retention rate is up to 98.50% after 300 cycles at 0.2C; however, under the same parameters, the pristine material's discharge capacity and cycle retention rate are 212.8 mAh.g(-1) and 86.68%. The initial coulombic efficiency and initial discharge capacity of Nb-0.02 is 86.94% and 287.5 mAh.g(-1), while that of the pristine material is 73.59% and 234.2 mAh.g(-1). Density functional theory calculations demonstrate that Nb doping accelerates Li-ion diffusion and stabilizes material structure due to stronger Nb-O bonds from reduced Li-ion migration barrier energy. Thus, the proposed modification strategy for Nb doping can illuminate the structural design of lithium-rich manganese-based cathode materials.