Electrochemical Analysis of Conductive Polymer-Coated LiFePO4 Nanocrystalline Cathodes with Controlled Morphology

Nanocrystalline LiFePO4 particles and donut- and dumbbell-shaped LiFePO4 microstructures hierarchically constructed with the nanoparticles were synthesized. Coating the surfaces of the LiFePO4 particles with conductive polymers, poly-3,4-ethylenedioxythiophene (PEDOT), improved battery characteristics, such as specific capacity, capacity retention, and impedances, by increasing the ionic and electric conductivities of the cathode materials as well as by enhancing the accessibility of lithium ions. The nanocrystalline LiFePO4 that was coated with PEDOT exhibited even larger values than the theoretical value of LiFePO4 at a rate of 1 C or lower rates were observed, with its largest specific capacities of 190 mAhg(-1) and 175 mAhg(-1) at the rates of 0.2 C and 1 C, respectively, due to the compatibility of the redox characteristics of LiFePO4 and PEDOT. The cathode composed of nanocrystalline LiFePO4 that was coated with PEDOT exhibited the lowest value of the charge transfer resistances (R-ct) from the electrochemical impedance analysis.