FePO4-coatedLi[Li0.2Ni0.13Co0.13Mn0.54]O2withimprovedcyclingperformanceascathodematerialforLi-ionbatteries

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 ℃ 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.