High-Rate LiFePO₄ Lithium Rechargeable Battery Promoted by Electrochemically Active Polymers

LiFePO 4 is a promising cathode material for the next generation of a lithium-ion rechargeable battery because of its low-cost, safety, excellent cyclability, and large capacity. Moreover, its voltage, 3.45 V versus lithium, is compatible with the window of a solid-polymer Li-ion electrolyte. Of particular interest for commercial applications is its safety and energy capacity at high power output and at short recharge times. We report here a systematic investigation of the enhancement of capacity at high rates of charge and discharge by substitution of a conductive, electrochemically active polymer for some or all of the deadweight conductive carbon and binder used conventionally to enhance performance of a secondary battery. Polypyrrole (PPy) and polyaniline (PANI) were used as the conductive polymers; two methods, electrochemical deposition and simultaneous chemical polymerization, were used to prepare the LiFePO 4 /polymer composite cathodes. Our results show that significantly improved capacity and rate capability can be achieved in such composite cathodes and that the electrodeposited carbon-coated LiFePO 4 /PPy composite exhibits the best performance.