Controlling Sulfur Vacancies in TiS_2–x Cathode Insertion Hosts via the Conversion of TiS₃ Nanobelts for Energy-Storage Applications

The electronic properties of titanium(IV) sulfide (TiS 2 ) 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 TiS 3 to TiS 2– x nanobelts as a means to control the nonstoichiometry of TiS 2– x nanostructures is reported. Careful structural, optical, and electronic studies were performed to elucidate the real nature of TiS 2 (i.e., semimetal or semiconductor). Experimental evidence gathered by diffraction, spectroscopy, and electrical measurements for TiS 2– 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 TiS 2– x nanobelts with increasing nonstoichiometry deviations. Electrical transport measurements suggest an increase in the electrical conductivity of TiS 2– x nanobelts with increasing sulfur vacancies. Furthermore, we also report the influence of nonstoichiometries on the electrochemical performance of lithium ion batteries based on TiS 2– x nanobelt-assembled film cathodes. Our results demonstrate that cathodes based on sulfur-deficient TiS 2– 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.