Characteristics of Conducting Polymer-Coated Nanosized LiFePO 4 Cathode in the Li + Batteries

Both nano-sized and micron-sized LiFePO4 crystalline particles with rhombus structure were synthesized by a hydrothermal method for the cathode materials. Coating conductive polymers, such as polypyrrole (PPy) and poly-3,4-ethylenedioxythiophene (PEDOT), on the surfaces of LiFePO4 particles improved the battery capacities by increasing the ionic and electric conductivities of the cathode materials. The nano-sized LiFePO4 coated with PEDOT shows the largest specific capacity (167 mAhg-1 for initial to 158 mAhg-1 after 50 cycles), compared to the cases coated with PPy (165 mAhg-1 to 127 mAhg-1) and with carbon (152 mAhg-1 to 147 mAhg-1). Compared to the nano-sized particles, the micron-sized particles have much smaller surface-to-volume ratios, which resulted in increased diffusion distance requirements for lithium ions and, also, reduced accessibility of lithium ions.