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Doping engineering is an effective modification strategy to enhance the electrochemical performance of electrode materials. In this paper, the impacts of heteroatom doping in monolayer titanium disulfide (TiS2) by substituting the S atom with the heteroatoms (B, C, N, O, F, and P) on the adsorption and diffusion capabilities of alkali metals (Li, Na, and K) have been systematically investigated using first-principles calculations to evaluate the material performance for application in alkali metal-ion batteries. The doping of most heteroatoms can promote the adsorption capability of alkali metal atoms on monolayer TiS2 as their adsorption energies decrease compared with the pristine system, particularly for p-type doping with C, N, and P. The diffusion energy barriers decrease when alkali metals approach the doping site of most heteroatom-doped TiS2, and the barriers near the doping site are extremely small (0.00-0.08 eV), whereas they slightly increase as alkali metals move away from the doping site. P doping has the lowest overall diffusion energy barrier for each metal. Thus, monolayer TiS2 with heteroatom doping, especially P doping, can be used as a potential anode material for alkali metal-ion batteries. This study can help comprehend the impacts of heteroatom doping and design high-performance electrode materials for rechargeable batteries.

Promoting the reversible structural transformation and carrier migration dynamics simultaneously in a multiple ion-involved process is vital for sulfide electrode materials. Herein, TiS2 with a sulfide cluster vacancy (CV–TiS2−x) has been calculated and prepared to explore a novel strategy to improve the electrochemistry reversibility of sulfide electrodes. It is found that the cluster vacancy can serve as an effective control factor for the improvement of the Fermi level, and enhances the electrochemical stability of CV–TiS2−x in the liquid organic electrolyte system. Moreover, owing to the plentiful positively charged S-vacancies, the CV–TiS2−x samples exhibit an extended interplanar spacing and retain their structural integrity during the lithium ion insertion process. The integrated HRTEM, in situ XRD, XPS analysis and electrochemical study reveal that the cluster vacancy is not only responsible for an increase in reversible performance, but also boosting the anionic redox reaction of (S2)2− species. Therefore, the CV–TiS2−x electrode delivers a reversible capacity of 650 mA h g−1 for 300 cycles at a current density of 1C (220 mA g−1). Our study provides a novel strategy of introducing sulfur cluster vacancies to improve the electrochemical activity of TiS2, which can be applied to other sulfide electrodes.

A relatively new and promising method to tune properties of monolayers is by forming a heterostructure of them. Here, the van der Waals heterostructure of graphene-like zinc oxide (g-ZnO) and 1-trigonal titanium disulfide (1T-TiS2) was formed and its structural, electronic, and optical properties were studied in the framework of density functional theory. The dynamical stability of the heterostructure was confirmed based on its phonon band structure. An indirect (Γ → M) bandgap of 0.65 eV, a large built-in electric field (or a large potential drop of 3.12 eV), a type-II (staggered) band alignment, and a large conduction band offset of 2.94 eV were found to form across the interface, which are all desirable for potentially efficient separation of charge carriers. We showed also that the formation of the heterostructure largely enhances the almost-zero optical absorption of g-ZnO in visible and near-infrared regions, which is desirable for optoelectronic applications. By applying a perpendicular electric field, we could tune the bandgap value and the band alignment type (type-II → type-I) of the heterostructure. Finally, we showed that by applying compressive strain, one can change the band alignment type (type-II → type-I) and by applying tensile strain, the bandgap value could be tuned and a crossover occurs in the bandgap type (indirect → direct → indirect).

The rapid capacity loss caused by the shuttling effect of polysulfides is one of the great challenges of Li–S batteries. In this work, we adopted a simple solid-phase sintering method to synthesize titanium disulfide (TiS2) and further demonstrated it as a superior modifier of separators for Li–S batteries. Two commonly adopted modification processes of separators, including vacuum filtration (VF) and slurry casting (SC) have been used to prepare TiS2/Celgard separators. TiS2-VF/Celgard can better restrain the polysulfide shuttling effect compared with TiS2-SC/Celgard. A TiS2-VF/Celgard-based Li–S battery has a reversible capacity of 771.6 mA h g−1, with a capacity retention of 645.6 mA h g−1 after 500 cycles at 2.0 C, corresponding to a capacity fading rate of ∼0.033% per cycle. This study has shown the potential of TiS2 as a multifunctional modifier of separators for high performance and long cycle life Li–S batteries.

Titanium disulfide (TiS2) with high electric conductivity, fast rate capability, and good cycling performance is a promising candidate for electrode material in sodium (Na)-ion batteries. Despite the well-studied electrochemical behaviors of TiS2 in Li-ion batteries, the detailed reaction mechanism of TiS2 in Na-ion batteries is not yet fully understood due to a more complex multi-phase conversion process. In this work, reactions of TiS2 in Na-ion batteries are investigated via a multi-modal synchrotron approach: operando X-ray Absorption Spectroscopy (XAS) – including X-ray Absorption Near-Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) – and ex situ X-ray Powder Diffraction (XPD), coupled with computational modeling. Operando XANES spectra indicate that the redox reactions occur in both Ti and S during the electrochemically driven phase transformation. Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) analysis of XAS suggests that different numbers of components are involved in the lithiation and sodiation of TiS2, with the sodiation including at least one intermediate phase in addition to the starting material and the final sodiation product. Ex situ XPD and Rietveld refinement further determined and quantified the unknown phases, showing that three phases, TiS2, Na0.55TiS2, and NaTiS2, participate in the sodiation of TiS2. Operando EXAFS results show the changes in the Ti–Ti coordination number and interatomic distance. This explains the coulombic efficiency decay due to the incomplete recovery of the coordination number of Ti after cycling. Overall, this work reveals the reaction mechanism occurring in Na–TiS2 batteries with a greater quantitative understanding of the structural evolution. By combining the multi-modal synchrotron approach and computational work, this study provides a framework for studying a broader range of electrochemically driven phase-transformation systems towards advanced energy storage and conversion applications.

Titanium disulfide is a promising material for a range of applications, including lithium-ion battery (LIB) anodes. However, its application potential has been severely hindered by the tendency of exfoliated TiS2 to rapidly oxidize under ambient conditions. Herein, we confirm that, although layered TiS2 powder can be exfoliated by sonication in aqueous surfactant solutions, the resultant nanosheets oxidise almost completely within hours. However, we find that upon performing the exfoliation in the solvent cyclohexyl-pyrrolidone (CHP), the oxidation is almost completely suppressed. TiS2 nanosheets dispersed in CHP and stored at 4 °C in an open atmosphere for 90 days remained up to 95% intact. In addition, CHP-exfoliated nanosheets did not show any evidence of oxidation for at least 30 days after being transformed into dry films even when stored under ambient conditions. This stability, probably a result of a residual CHP coating, allows TiS2 nanosheets to be deployed in applications. To demonstrate this, we prepared lithium ion battery anodes from nano : nano composites of TiS2 nanosheets mixed with carbon nanotubes. These anodes displayed reversible capacities (920 mA h g−1) close to the theoretical value and showed good rate performance and cycling capability.

Pseudocapacitive materials offer an opportunity to bridge the energy storage gap between supercapacitor and battery technologies. Herein is chronicled the first report of pseudocapacitance in a system devoid of liquid electrolytes, using the cathode material LiTiS2. It is demonstrated that due to extreme crystallite reduction to less than 3 nm, additional charge storage is derived by reducing surface Ti3+ to Ti2+ at higher voltages and more reversibly than traditionally shown. Due to facile diffusion pathways in 3-fold coordinated lithium along the TiS2 surfaces, disordered LiTiS2 can be used as a singular cathode without conductive additives. The result is a system exhibiting nearly 300 mA h g−1 at a rate of C/2 for 1000 cycles. Whereas active materials in liquid cells typically have size limitations before irreversibilities appear, the high pseudocapacitance demonstrated in this report indicates that active materials used in the solid-state could benefit from size reduction. Hopefully, a new avenue of research stems from this work to investigate mixed conductor nano-domains for solid-state battery/capacitor hybrids. The prospect of a solid-state pseudocapacitor unlocks a series of new applications that offer long shelf life, high temperature capabilities, and enhanced safety.

The synthesis of inorganic fullerene (IF) nanoparticles and IF hollow spheres of titanium disulfide by a simple colloidal route is reported. The injection temperature of the titanium precursor into the solvent mixture was found to be important in controlling the morphology.

Solid state reaction of metal halides MXn (n = 1 or 2) with stoichiometric amounts of sodium chalcogenide (Na2S2 or Na2E where E = S, Se or Te) at 300 °C for 48 h in evacuated ampoules affords a range of transition and main-group metal chalcogenides: ME2 (M = Fe or Co, E = S or Te); M(1 − x)E (M = Fe or Co, E = S); Ag2E (E = S, Se or Te), Ni(1 − x)E (E = S, Se or Te); NiS2, MnS, FeSe, SnSe and SnTe along with co-formed salt. Washing of the highly sintered, fused product mixture with water resulted in isolation of crystalline binary chalcogenides, typically of a single phase in good yield (90%). The products were characterised by X-ray powder diffraction, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA) and i nfrared spectroscopy.

Titanium disulfide, TiS2, has been successfully prepared via a thio ‘sol–gel’ process using titanium(IV) thiolate precursors as the metal source. Four precursors have been investigated, namely [Ti(SBut)4], [Et2NH2][Ti2(SCH2Ph)9], [Et2NH2][Ti(SC6F5)4(NEt2)] and [Et2NH2]3[Ti(SC6F5)5][SC6F5]2. The titanium(IV) thiolate reacts at room temperature with H2S to form a precipitate which upon annealing at 800 °C under H2S results in the formation of crystalline TiS2. The TiS2 produced was analysed by powder X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA) and Raman spectroscopy. Annealing the precipitate obtained from the thio ‘sol–gel’ process at 600 °C under H2S results in the formation of a mixture of crystalline TiS2 and Ti1.25S2.

Investigations pertaining to the synthesis of titanium disulfide (TiS 2 ) have so far been focused on solid state reactions, low temperature chemical techniques and vapor phase reactions using titanium tetrachloride (TiCl 4 ) as the starting material. In this paper, we have investigated the potential of titanium tetraalkoxides [Ti(OR) 4 ], which have been widely used for the synthesis of oxides by the sol-gel approach, for the synthesis of TiS 2 via the thio-sol-gel process. The mechanism of the reaction of titanium isopropoxide {Ti(OPr i ) 4 } with H 2 S in benzene has been studied using infrared spectroscopy (FTIR), gas chromatography (GC) and chemical analysis. Based on these studies, it has been determined that the precipitate obtained from the reaction forms following a thiolysis-condensation mechanism similar to the hydrolysis-condensation mechanism that operates in the oxide sol-gel process. The precipitate, which is an alkoxysulfide, can be converted to TiS 2 by heat treatments in flowing H 2 S. The influence of modifying agents, the role of solvents and the alkoxy group [in Ti(OR) 4 ] on the formation of the alkoxysulfide precipitate have also been presented and discussed. Finally, the applicability of this process for the synthesis of NbS 2 has also been demonstrated.

A low-temperature gas reaction was used to successfully synthesize TiS2 nanotubes with an outer diameter of approximately 20 nm, an inner diameter of approximately 10 nm, an interlayer spacing of approximately 0.57 nm, and an average length of 2-5 microm.