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℃ 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.