Effect of Polymer Binders with Single-Walled Carbon Nanotubes on the Electrochemical and Physicochemical Properties of the LiFePO4 Cathode

We report the development of high-energy-density LiFePO4 cathodes incorporating single-walled carbon nanotubes (SWCNTs) and a series of alternative polymer binders, including poly­(3,4-ethylenedioxythiophene):poly­(4-styrenesulfonate) (PEDOT:PSS), polyacrylonitrile copolymer (PAN), and sulfonated poly­(2,6-dimethyl-1,4-phenylene oxide), which are processed through environmentally benign solvents. The binders ensured uniform distribution and excellent dispersion stability of the SWCNTs within the slurries, which resulted in enhanced electrical conductivities as compared to traditional polyvinylidene fluoride-bound composite cathode formulations. The characteristics of polymer–SWCNT composite binders were studied on cathodes with a high content of active material (95 wt % LiFePO4/C). Introduction of SWCNTs as low as 0.25 wt % into the slurry and the resultant composite cathode provided a good rate capability (beyond 110 mA h g–1 at 10 C charge/discharge rates). Among the composite binders studied and benchmarked, PEDOT:PSS–SWCNT composites with LiFePO4 exhibited good electrical conductivity and rate capability at 10–50 C, while PAN–SWCNT composites exhibited better electrochemical stability and cyclability.