Cathode material based on sulfur-MWCNTs-PPy-nanopipes for Li-S batteries

We report the synthesis of S-MWCNTs-PPy-nanopipes as a cathode material for Li-S batteries. The synthesis was accomplished using a simple chemical oxidative polymerization of pyrrole monomer by adding the anions azo dye methyl orange (MO) and FeCl₃. To characterize the cathode material cyclic voltammetry, galvanostatic charge/discharge measurements or electrochemical impedance spectroscopy were carried out. As shown in Fig. 1, MWCNTs formed agglomerates among the PPy-nanopipes. Our goal was to accommodate sulfur inside these agglomerates to control volumetric increase during the charge/discharge process. Homogeneous sulfur distribution in PPynanopipes and also in MWCNTs agglomerates was confirmed by EDX elemental map analysis and by TEM. STEM analysis confirmed a presence of sulphur inside the MWCNT tube. The improved electrochemical performance of S-MWCNTs-PPy-nanopipes was attributed to the stable network between the sulfur and MWCNTsPPy-nanopipes that effectively facilitates Li⁺ ion diffusion which inhibited shuttle effect. Combination of PPynanopipes and MWCNTs provides additional conductivity and delivers extra capacity. (authors)