Effect of multi-walled carbon nanotubes on the thermal stability and surface morphology of LiFePO4 cathode material

A novel network composite cathode was prepared by mixing LiFePO4 particles with multiwalled carbon nanotubes (MWCNTs). LiFePO4 particles were connected by MWCNTs and a polymer binder, polypyrrole-polyethylene glycol (PPy-PEG), to form a three-dimensional network. The surface morphology and thermal stability of the LiFePO4-MWCNT/PPy-PEG composite cathode were investigated by scanning electron microscopy, thermogravimetric analysis and pyrolysis capillary gas chromatography. It was found by scanning electron microscopy that the particle size of LiFePO4 in the LiFePO4-MWCNT sample was smaller than that of the pure LiFePO4 and the structure in the LiFePO4-MWCNT/PPy-PEG sample was more homogeneous than in the LiFePO4-MWCNT/PPy sample. Thermogravimetric analysis indicated that PPy-PEG blend polymer in combination with MWCNTs considerably improves the thermal stability of the final cathode material. Pyrolysis capillary gas chromatography measurements at 500 °C showed a decreased thermal stability of organic species contained in the composite cathode material. The addition of MWCNTs was an effective way to increase homogeneity and thermal stability of the LiFePO4-MWCNT/PPy-PEG cathode material.