Enhanced initial coulombic efficiency of Li1.14Ni0.16Co0.08Mn0.57O2 cathode materials with superior performance for lithium-ion batteries

Abstract

Enhanced initial coulombic efficiency (above 90%) of Li1.14Ni0.16Co0.08Mn0.57O2 (LMO) cathode materials are achieved by utilizing a NaCl molten-salt method. Anaerobic environment can be controlled via adjusting the weight ratio of LMO and NaCl molten-salt. The morphology and structure of all samples are detected by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The modified samples have smaller particle sizes and abundant mesopores, compared with the pristine LMO sample. The change of crystal parameters, XPS analysis and HRTEM images demonstrate the effect of anaerobic environment offered by NaCl molten-salt on the structure of LMO material. More oxygen vacancies could exist in the modified LMO materials due to the anterobic environment offered by a lot of NaCl molten-salt. It should be responsible for the enhanced initial coulombic efficiency. The higher reversible capacities mainly come from smaller particle size and abundant mesopores of the modified LMO samples, in which the utilization ratio of active mass is improved due to the shortened diffusion length for Li ions. A tiny spinel phase generates in the modified samples controlled by the amount of NaCl additive. The excellent cycling stability and improved rate capacity of the modified materials are also achieved due to its good thermal stability and the 3D structure of the spinel phase. These results give a new insight into preparing lithium-rich cathode materials with high initial coulombic efficiency as well as superior performance for advanced lithium-ion batteries.