Composite cathode for Li-sulfur system: Effect of inorganic additives on electrochemical performance

Abstract

The influence of five different inorganic additives with different composition and morphology, viz. nanofibrous rutile/TiOxNy, Li4Ti5O12 (LTS) from Altair, TiO2-P90 from Evonik, TiOxNy-anatase and nano-TiO2 on the electrochemical performance of the activated carbon/sulfur composite cathode is evaluated by cyclic voltammetry at the scan rate of 0.1 mV s-1 and by galvanostatic chronopotentiometry at the 0.1 C rate. The composites are prepared by facile mechanical mixing of activated carbon with the inorganic additive and subsequent melting-diffusion with sulfur. The addition of nano-TiO2 from titanium isopropoxide, TiOxNy-anatase, rutile/TiOxNy, and LTS Altair to the carbon/sulfur composite cathode increased the charge capacity of the corresponding Li-sulfur cell. The negative effect of the P90 additive can be attributed to the blocking of its surface by Al2O3 and SiO2, hindering the adsorption of polysulfides. TiOxNy-anatase additive exhibits the highest capacity improvement due to its surface-enhanced redox chemistry of conductive and sulphiphilic surface resulting in a 7 % increase of the voltammetric charge capacity. In addition, this additive has a beneficial effect on the cycling stability of the sulfur composite cathode during galvanostatic cycling.