Enhancing electrochemical performances of LiNi0.5Co0.2Mn0.3O2 cathode materials derived from NiF2 artificial interface at elevated voltage

Herein, NiF2 artificial interface was proposed for the first time to enhance the electrochemical performances of LiNi0.5Co0.2Mn0.3O2 (NCM523) under 4.5 V. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images verify NiF2 layer is successfully constructed on the surface of NCM523. The 1.0 wt% NiF2-modified NCM523 delivers a much higher capacity retention (86.9%) than pristine sample (69.0%) after 100 cycles under 4.5 V at 30 degrees C, even exceeding pristine NCM523 under 4.2 V (82.2%). Beyond that, the cycling stability of NCM523 under 4.5 V at 55 degrees C is also visibly improved due to the NiF2 protective layer. Electrochemical impedance spectroscopy analyses confirm that NiF2 suppresses the increase of interface resistance and therefore makes for the interface kinetics behaviors during cycling. In addition, the measurements of SEM, TEM and XPS support that the inhibition of the SEI (solid electrolyte interphase) growth can be attributed to the restrained side reactions between electrolyte and NCM523 by NiF2 artificial layer at 4.5 V. (C) 2019 Elsevier B.V. All rights reserved.