Nanocrystalline TiO₂/Carbon/Sulfur Composite Cathodes for Lithium-Sulfur Battery

This paper evaluates the influence of the morphology, surface area, and surface modification of carbonaceous additives on the performance of the corresponding cathode in a lithium-sulfur battery. The structure of sulfur composite cathodes with mesoporous carbon, activated carbon, and electrochemical carbon is studied by X-ray diffraction, nitrogen adsorption measurements, and Raman spectroscopy. The sulfur cathode containing electrochemical carbon with the specific surface area of 1606.6 m² g^-1 exhibits the best electrochemical performance and provides a charge capacity of almost 650 mAh g^-1 in cyclic voltammetry at a 0.1 mV s^-1 scan rate and up to 1300 mAh g^-1 in galvanostatic chronopotentiometry at a 0.1 C rate. This excellent electrochemical behavior is ascribed to the high dispersity of electrochemical carbon, enabling a perfect encapsulation of sulfur. The surface modification of carbonaceous additives by TiO₂ has a positive effect on the electrochemical performance of sulfur composites with mesoporous and activated carbons, but it causes a loss of dispersity and a consequent decrease of the charge capacity of the sulfur composite with electrochemical carbon. The composite of sulfur with TiO₂-modified activated carbon exhibited the charge capacity of 393 mAh g^-1 in cyclic voltammetry and up to 493 mAh g^-1 in galvanostatic chronopotentiometry. The presence of an additional Sigracell carbon felt interlayer further improves the electrochemical performance of cells with activated carbon, electrochemical carbon, and nanocrystalline TiO₂-modified activated carbon. This positive effect is most pronounced in the case of activated carbon modified by nanocrystalline TiO₂. However, it is not boosted by additional coverage by TiO₂ or SnO₂, which is probably due to the blocking of pores.