Improving lithium batteries by tethering carbon-coated LiFePO4 to polypyrrole

The demand for rechargeable lithium batteries, which have ushered in the wireless revolution and have found a place in the hybrid electric vehicle, is rapidly expanding. Commercial use commonly requires high power, high energy density, and high rate capability. However, achieving a high capacity at a high charge/discharge rate has proven difficult. In this paper, we show a remarkable improvement in the rate capability and capacity of cathodes using carbon-coated LiFePO4 by replacing the carbon plus Teflon additives with polypyrrole (PPy) bonded to the oxide particles by the carbon coat. An excellent charge/discharge performance at a rate as high as 10C, and even a 3 min (20C) charge, is demonstrated with a C-LiFePO4/PPy cathode containing 16 wt % PPy. Attaching a conductive polymer to an active oxide particle is a general strategy that also promises to enhance the rate capability of other cathode composites used in rechargeable lithium batteries. (c) 2006 The Electrochemical Society.