Synthesis and lithium-ion storage performances of LiFe0.5Co0.5PO4/C nanoplatelets and nanorods

Abstract

Carbon-coated olivine-structured LiFe0.5Co0.5PO4 solid solution was synthesized by a facile rheological phase method and applied as cathode materials of lithium-ion batteries. The nanostructure’s properties, such as morphology, component, and crystal structure for the samples, characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer, Emmett, and Teller (BET) determination, X-ray photoelectron spectroscopy (XPS), and the electrochemical performances were evaluated using constant current charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results indicate that nanoplatelet- and nanorod-structured LiFe0.5Co0.5PO4/C composites were separately obtained using stearic acid or polyethylene glycol 400 (PEG400) as carbon source, and the surfaces of particles for the two samples are ideally covered by full and uniform carbon layer, which is beneficial to improving the electrochemical behaviors. Electrochemical tests verify that the nanoplatelet LiFe0.5Co0.5PO4/C shows a better capacity capability, delivering a discharge specific capacity of 133.8, 112.1, 98.3, and 74.4 mAh g−1 at 0.1, 0.5, 1, and 5 C rate (1 C = 150 mA g−1); the corresponding cycle number is 5th, 11th, 15th, 20th, and 30th, respectively, whereas the nanorod one possesses more excellent cycling ability, with a discharge capacity of 83.3 mAh g−1 and capacity retention of 86.9% still maintained after cycling for 100 cycles at 0.5 C. Results from the present study demonstrate that the LiFe0.5Co0.5PO4 solid solution nanomaterials with favorable carbon coating effect combine the characteristics and advantage of LiFePO4 and LiCoPO4, thus displaying a tremendous potential as cathode of lithium-ion battery.