Luisa Whittaker-Brooks1,Edwin Miller1
University of Utah1
Luisa Whittaker-Brooks1,Edwin Miller1
University of Utah1
Realizing fast ion kinetics in solid-state materials is of critical interest for the development of technologies including energy storage, neuromorphic computing, water desalination, and selective ion extraction. Development in these areas hinges on one fundamental challenge: facilitating ion transport through a host material. Layered van der Waals (vdW) structures stand out as a promising class of materials for reversible ion insertion, as ion intercalation can occur in the interstitial layers without permanent structural alterations. Of these vdW materials, titanium disulfide (TiS<sub>2</sub>) is an attractive candidate for study due to its wide inter-lamellar spacing, continuous single-phase solid-solution lithiation, and material stability. While Li<sup>+</sup> ion kinetics in TiS<sub>2</sub> itself have been well-characterized, our group seeks to further advance its development by studying the effect of selenium (Se) doping on Li<sup>+</sup> ion kinetics in TiS<sub>2</sub> nanobelts. To pursue this goal, a synthesis of TiS<sub>1.8</sub>Se<sub>0.2</sub> nanobelts has been developed. Since both TiS<sub>2</sub> and TiS<sub>1.8</sub>Se<sub>0.2</sub> share the same nanobelt morphology, differences in ion kinetics between the two materials can purely be ascribed to the doping process. Compositional changes to nanostructured materials become important as it become increasingly apparent that nanostructured materials improve ion kinetics; thus, by realizing the need for nanoscaling <i>and </i>altering composition, we are including factors that will allow this study to remain relevant in the fast-paced development of ion kinetics.<br/>Our synthesis of TiS<sub>1.8</sub>Se<sub>0.2</sub> nanobelts predictably increases the interlayer spacing and electronic conductivity of the doped material versus pure TiS<sub>2</sub>; both properties are expected to improve ion kinetics in these doped systems. Rate-dependent cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) are both used to investigate the effect of Se doping on ion kinetics in layered TiS<sub>2</sub> nanobelt systems. Analysis via these methods indicates that TiS<sub>1.8</sub>Se<sub>0.2</sub> nanobelts do indeed display a charge storage process that is less diffusion-limited than their TiS<sub>2</sub> analogues. Lower electrochemical impedance across faster frequency ranges for TiS<sub>1.8</sub>Se<sub>0.2</sub> also indicates a decrease in resistances across the cell for the doped material. This insight into the effects of chalcogen doping on the charge storage process of TiS<sub>2</sub> nanobelts informs future development of layered vdW materials.