Controlling Sulfur Vacancies in TiS2–x Cathode Insertion Hosts via the Conversion of TiS₃ Nanobelts for Energy-Storage Applications

The electronic properties of titanium(IV) sulfide (TiS2) have been scrutinized for many decades due to its strong tendency toward nonstoichiometry with either titanium excess or sulfur deficiency in its crystal structure. Here, the systematic solid-state transformation of TiS3 to TiS2–x nanobelts as a means to control the nonstoichiometry of TiS2–x nanostructures is reported. Careful structural, optical, and electronic studies were performed to elucidate the real nature of TiS2 (i.e., semimetal or semiconductor). Experimental evidence gathered by diffraction, spectroscopy, and electrical measurements for TiS2–x as a function of sulfur deficiencies indicates it behaves as a semimetal even at nonstoichiometry ranges as low as x = 0.15. Optical characterization shows a decrease in the bandgap of TiS2–x nanobelts with increasing nonstoichiometry deviations. Electrical transport measurements suggest an increase in the electrical conductivity of TiS2–x nanobelts with increasing sulfur vacancies. Furthermore, we also report the influence of nonstoichiometries on the electrochemical performance of lithium ion batteries based on TiS2–x nanobelt-assembled film cathodes. Our results demonstrate that cathodes based on sulfur-deficient TiS2–x nanobelts deliver efficient Li+ intercalation/insertion activity, excellent cycling life, enhanced specific capacity, and excellent rate capability pointing to the importance of carefully controlling defects and stoichiometries in materials as a way to favorably tune their electronic properties.