| PolyPyrrole(PPy) is one of the typical conducting Polymers. It can be used as cathode of lithium secondary batteries because of its high conductivity, high electrical charge reserving ability and good stability in air or water. In this paper, LiFePO4/C-PPy composites were prepared by using chemical liquid deposition method and chemical vapor-phase deposition method, respectively. The prepared LiFePO4/C-PPy composites showed obviously improved electrochemical performance.The constitutions, structures and morphologies of these materials were characterized by TEM, TGA, FT-IR. The conductivities of these materials were measured by four-probe instrument; The electrochemical properties and high-temperature stability of the sample materials were investigated and characterized by galvanostatic charge-discharge test, a.c.impedance spectroscopy. The results showed that PPy coating remarkably enhance the high rate performance of LiFePO4/C. The capacities of LiFePO4/C–PPy-Chem cathode and LiFePO4/C–PPy-CVD cathode were 145(1C), 138(2C), 132(5C), 123(10C), 115mAh/g(20C) and 145(1C), 133(2C), 118(5C), 108(10C), 80mAh/g(20C), respectively. The rate capacities of both cathodes are greater than that of LiFePO4/C, 150(1C), 147(2C), 127(5C), 60mAh/g(8C).Moreover, LiFePO4/C–PPy-Chem cathode and LiFePO4/C–PPy-CVD cathode showed excellent high-temperature stability. Investigation result indicates that PPy coating could prevent undesirable electrode/electrolyte reactions and reduce the dissolution of Fe ion, thus improving the cycling stability of composites at high temperature.The effects of oxidants and dopants for Py polymerization on the properties of LiFePO4/C–PPy composites were also studied. Results show that the LiFePO4/C–PPy samples prepared by using Fe(III)tosylate as oxidant as well as dopant demonstrate better electrochemical performance than those prepared suing FeCl3 as oxidant and sodium p-toluenesulfonate as dopant for preventing the influence of chlorin ion.
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