The role of boracic polyanion substitution on structure and high voltage electrochemical performance of Ni-Rich cathode materials for lithium ion batteries

The bottleneck for large-scale application of Nickel-rich layered LiNi0.6Co0.2Mn0.2O2 (NCM) cathode material for lithium-ion batteries is their severe capacity fading, especially at high voltage. Herein, we modify the NCM cathode materials by substituting the boracic polyanion to suppress capacity degradation and improve power performance. The crystal structure, morphology, elemental states and surface elemental composition of the cathode materials are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM), respectively. Compared to the bare NCM, the I-(003)/I-(104) ratio of the B3-NCM sample increases from 1.58 to 1.66, and the cation mixing declines from 4.65% to 3.21%, as known by XRD and Rietveld refinement. The results of electrochemical tests indicate that the B1-NCM exhibit superior rate property at the high current density (131.02 mAh g(-1) at 5 C), and the higher capacity retention (76.07% after 100 cycles at 1 C). Further electrochemical impedance spectra (EIS) and galvanostatic intermittent titration technique (GITT) demonstrate that boracic polyanion doping decreases impedance value and enhances lithium ion diffusion coefficient. These consequences reveal that the boracic polyanion modified LiNi0.6Co0.2Mn0.2O2 cathode material has better electrochemical performance. (C) 2019 Elsevier B.V. All rights reserved.