Lithium-sulfur batteries have a poor cyclability and inferior rate capability due to the shuttle effect of lithium polysulfides. To solve these problems, a sulfur coated MWCNTs composite (S/MWCNTs) was coated with conductive polypyrrole (PPy) to trap the polysulfides and facilitate charge and lithium ion transport. From the contact angle measurement, it is found that the PPy coating improves the wettability of the S/MWCNTs composite. Compared with the bare S/MWCNTs composite, the PPy coated S/MWCNTs composite cathode exhibited improved cycle stability and high rate performance. A reversible discharge capacity of 671 mAh g-1 was maintained after 50 cycles at 3 C for the PPy coated composite. The effect of PPy coating on kinetic property was investigated by electrochemical impedance spectroscopy (EIS). The electrolyte resistance, surface film resistance, charge transfer resistance, lithium ion diffusion coefficient and exchange current density were evaluated from the EIS measurements. The EIS results reveal that the PPy coating increases both Li ion diffusion into the cathode and exchange current density. The as-prepared PPy coated S/MWCNTs composite can be considered to be a promising candidate for high capacity and high rate performance cathode material.
