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

Abstract

Li[Li0.2Ni0.13Co0.13Mn0.54]O2 cathode materials were synthesized by carbonate-based co-precipitation method, and then, its surface was coated by thin layers of FePO4. 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 FePO4 coating layer does not make any major change in the crystal structure. The FePO4-coated sample exhibits both improved initial discharge capacity and columbic efficiency compared to the pristine one. More significantly, the FePO4 coating layer has a much positive influence on the cycling performance. The FePO4-coated sample exhibits capacity retention of 82 % after 100 cycles at 0.5 °C 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 FePO4 on the surface of Li[Li0.2Ni0.13Co0.13Mn0.54]O2 particle, which helps to protect the cathode from chemical attacks by HF and thus suppresses the large increase in charge transfer resistance.