The effects of FePO4-coating on high-voltage cycling stability and rate capability of Li[Ni0.5Co0.2Mn0.3]O2

Abstract

Li[Ni0.5Co0.2Mn0.3]O2 was prepared using nickel–cobalt–manganese hydroxide as the precursors, then resultant Li[Ni0.5Co0.2Mn0.3]O2 was surface modified by FePO4 through co-precipitation routine. The samples of bare and FePO4-coated Li[Ni0.5Co0.2Mn0.3]O2 were characterized with various techniques such as X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectrometer (EDS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results demonstrated that the thickness of FePO4-coating layer is about 5nm, and FePO4-coating layer not affects the crystal structure of the pristine Li[Ni0.5Co0.2Mn0.3]O2. Thus FePO4-coating layer is only a thin layer with amorphous structure. Furthermore, the FePO4-coated Li[Ni0.5Co0.2Mn0.3]O2 exhibits much better cycle performance, higher capacity retention ratios of 91.2% at 1C after 50 cycles since the FePO4-coating effectively prevents the reaction between active material and electrolyte on the process of charge/discharge under a high charge cutoff voltage of 4.6V. Meanwhile, the rate capability of FePO4-coated Li[Ni0.5Co0.2Mn0.3]O2 is enhanced, and it obtained at 0.2, 0.5, 1, 2, 5 and 10C rates are 213.1, 207.9, 203.8, 190.2, 171.2 and 151.6mAhg−1, respectively.