FePO₄-coated Li[Li_0.2Ni_0.13Co_0.13Mn_0.54]O₂ with improved cycling performance as cathode material for Li-ion batteries

Li[Li_0.2Ni_0.13Co_0.13Mn_0.54]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[Li_0.2Ni_0.13Co_0.13Mn_0.54]O₂ particle, which helps to protect the cathode from chemical attacks by HF and thus suppresses the large increase in charge transfer resistance.