TiO₂ top layer improving the performance of sulfur/carbon composite cathode in Li-sulfur cells

Facile preparation of the TiO2 top layer on the sulfur/carbon cathode in a Li-sulfur battery is presented. The layer significantly improves the initial charge capacity of composite cathodes. To demonstrate the versatility of the TiO2 top layer, its effect is evaluated on the sulfur composite cathodes with three kinds of carbonaceous addi-tives. The electrochemical performance of these sulfur composite cathodes in the Li-sulfur battery is studied by cyclic voltammetry, galvanostatic chronopotentiometry, and electrochemical impedance spectroscopy. The sulfur/composite cathode with TOB carbon provides the highest charge capacity of 816 mAh g(-1) from cyclic voltammetry, however, due to its structural disorder, exhibits the most pronounced capacity fade during gal-vanostatic cycling at 0.1C rate. The graphene nanoplatelets/sulfur composite cathode provides a charging ca-pacity of 739 mAh g(-1) in cyclic voltammetry and excellent cycling stability over 100 cycles of galvanostatic charging/discharging. A TiO2 top layer on the cathode and a TiO2-modified separator increase substantially the initial charge capacities of sulfur composite cathodes with all three kinds of carbon. The voltammetric charge capacities are 1427 mAh g(-1), 1349 mAh g(-1), and 952 mAh g(-1) for TOB carbon, graphene nanoplatelets, and Penta carbon, respectively. This represents the relative enhancement by 75%, 83%, and 44%, respectively, as referenced to the cells with titania-free materials. Galvanostatic chronopotentiometry confirms the beneficial effect of inorganic additive on the charge capacity of Penta carbon and graphene nanoplatelets, however, the long-term cycling stability of the composite electrode is determined exclusively by the carbonaceous additive.