FePO4-coated Li[Li0.2Ni0.13Co0.13Mn0.54]O2 with improved cycling performance as cathode material for Li-ion batteries

Li[LiNiCoMn]Ocathode materials were synthesized by carbonate-based co-precipitation method, and then, its surface was coated by thin layers of FePO. The prepared samples were characterized by X-ray diffraction(XRD), field emission scanning electron microscope(FESEM), energy-dispersive spectroscopy(EDS), and transmission electron microscopy(TEM). The XRD and TEM results suggest that both the pristine and the coated materials have a hexagonal layered structure, and the FePOcoating layer does not make any major change in the crystal structure. The FePO-coated sample exhibits both improved initial discharge capacity and columbic efficiency compared to the pristine one. More significantly, the FePOcoating layer has a much positive influence on the cycling performance. The FePO-coated sample exhibits capacity retention of 82 % after 100 cycles at 0.5 ℃ between 2.0 and 4.8 V, while only 28 % for the pristine one at the same charge-discharge condition. The electrochemical impedance spectroscopy(EIS) results indicate that this improved cycling performance could be ascribed to the presence of FePOon the surface of Li[LiNiCoMn]Oparticle, which helps to protect the cathode from chemical attacks by HF and thus suppresses the large increase in charge transfer resistance.