Search

Solid-state ionics, the study of fast ion transport in solids, expanded explosively after the discovery of sodium ion transport in β-alumina 50 years ago and has revolutionized energy storage. Lithium-ion batteries have come from a dream with titanium disulfide to enabling the communications revolution and are enabling renewable energy. Much can be learned from these early studies that will allow the attainment of a fossil-free society and a sustainable environment.

In this work, we study the electronic properties of mono- and multilayer titanium disulfide (TiS2) with the aid of first-principles calculations based on density functional theory. We find that the band gap can slightly be tuned as a function of the number (N) of stacked layers, ranging from 0.49 eV in the monolayer down to 0.40 eV in the bulk form—as a result of quantum confinement and the formation of sub-bands. However, the introduction of external agents such as biaxial strain and electric fields can significantly change the electronic properties of the system and induce strong gap modifications. Compressive strains and electrical fields are found to reduce the indirect band gap and induce a semiconductor to semimetal transition beyond a critical value, which is a decreasing function of N. In contrast, under tensile strains, the gap increases up to a maximum value and can reach about 0.90 eV under a 5% strain. Furthermore, we also report the optical properties of these systems, which display strong absorption peaks in both visible and UV regions of the spectrum, thus making the most of incident solar light. These properties also display a good tunability, as the peak intensities increase with N and the peak positions show a strong dispersion with strain. However, the spectra are less sensitive to electrical fields, despite their response being very similar to that found under compressive strains. Finally, k-resolved band structure calculations suggest the existence of both intralayer and interlayer excitons in optical transitions in the visible range. In light of these results, we believe that TiS2 can efficiently be explored in the design of novel vdW heterostructures in combination with other 2D materials, thus opening the way to novel applications in future nano- and optoelectronic devices.

Titanium disulfide (TiS2) was adopted as a negative electrode material for the asymmetric sodium-ion supercapattery of TiS2/activated carbon using Na+-based organic electrolytes. This type of supercapattery possesses a working voltage as high as 3 V. The physical properties of the negative electrode were characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The electrochemical performance tests revealed that the supercapattery had a relatively high rate performance and good cycle stability, displaying 77% capacity retention after 1000 cycles at a current density of 0.2 A g−1.

It is now almost 50 years since the first rechargeable lithium batteries, based on the reversible intercalation of lithium into layered structured titanium disulfide, were conceived. They were the precursor to the structurally related layered oxides that now dominate energy storage for electronics, the grid and vehicles.

Lithium-intercalated titanium disulfide Li x TiS2 had been extensively studied as prototypical cathode material for high-energy-density reversible lithium batteries with moderate voltage. Today, this phase is one of the leading candidates for all-solid-state lithium batteries with durable high energy and high rate performance. However, fundamental knowledge of Li+ insertion into TiS2 is still incomplete; available information on the phase diagram of the Li–TiS2 system is limited by x = 1 due to difficulties in preparing lithium-rich equilibrated samples. The goals of this work were to re-examine Li x TiS2 single phase boundaries and to clarify the existence of lithium-rich intercalates with x > 1. А new preparation technique was developed to obtain 1T-Li x TiS2 samples as good-quality equilibrated products with desirable lithium content. Phase equilibria in a quasibinary Li–TiS2 system were studied by X-ray diffraction, emf measurements (25 °C) and thermal analysis (25–350 °C) over a wide range of Li:Ti ratios (0 to 4).

Mixed conductors show significant mobility of both electronic and ionic species and were the subject of an earlier review in MRS Bulletin. The current review is restricted to those mixed conductors of interest for use in lithium batteries, with an emphasis on commercialization. The first lithium batteries were primary cells using pure lithium anodes and carbon monofluoride or manganese oxide as the cathode. Both were developed in Japan, the former for use in fishing floats and the latter for calculators and similar small devices. Such primary cells based mainly on MnO{sub 2} or FeS{sub 2} cathodes are still extensively used in watches, cameras, and so on. Lithium primary cells are also the main power source for many medical devices, such as pacemakers. In some of these applications, silver vanadate is the cathode. The recognition of the role of intercalation/ insertion reactions in battery electrodes just over 25 years ago allowed significant progress to be made in secondary (rechargeable) lithium batteries. From the first prototypical titanium disulfide cells, the technology has more recently been commercialized by Sony Corp. in the Li-ion cell, using a cobalt oxide insertion cathode and a carbon insertion anode. In the former, commercialized by Exxon, the reactionmore » is the simple intercalation of lithium ions between sheets of TiS{sub 2}.« less

The electrical conductivity and thermoelectric power of titanium disulfide were measured at temperatures ranging from 77 to 300 K on samples exhibiting different deviations from stoichiometry. It was found that Ti1+yS2 has metallic properties at the temperatures studied, the effective mass of the carriers varying with the deviation from stoichiometry. It was shown that the character of the discharge curve for the Li/Li+/LixTi1+yS2 cell was correlated with the electronic structure of titanium disulfide.

A study has been made of the influence of the sulfide substrate on the rate and direction of thermal decomposition, in an argon atmosphere, of Fe3(CO)12 deposited on the surface of crystalline MoS2, TiS2, and Co0.5TiS2 in amounts K=0.5−10 monolayers. It has been shown that the decomposition rate increases in the series MoS2

Titanium disulfide films were prepared by plasma CVD. Crystalline orientation of layered TiS2 was investigated in relation to deposition rate, film thickness, and kinds of substrate. The preferred orientation of TiS2 basal plane perpendicular to substrates was obtained on the films with their thickness of more than ca. 10 μm at the deposition rate of ca. 4 ⊠ 10−3 g/cm2·h on all kinds of substrate. This orientation resulted in a large discharge capacity in a lithium battery cathode application.

Deintercalation processes for the model neutral intercalation system HgxTiS2 (1.25≥x>0.00) have been investigated using dynamic high-resolution transmission electron microscopy. X-ray powder diffraction and thermogravimetric analysis demonstrated the intercalation process is thermally reversible, both structurally and compositionally. In situ deintercalation of stage- 1 compounds was induced by thermal/electron-beam heating during DHRTEM observation. The resulting deintercalation processes were followed with 0.03 second time resolution. The deintercalation processes observed possess a strong similarity to nucleation and growth processes. Deintercalation was observed to “nucleate” by the initial deintercalation of an external-most or internal guest layer, with further deintercalation of the guest “growing” away from the onset layers. This results in generally randogmuelsyt lsatyaegresd greengeiroanllsy, occasionally containing regions of short-range order, that expand away from the deintercalation onset layers.

The synthesis of oxides by the use of metal alkoxides is well known in the sol-gel process. However, little is known regarding the use of alkoxides as starting materials for nonoxides. In this work titanium isopropoxide has been reacted with different sulfidizing agents to form alkoxy sulfide precursors. In all the processes the transformation of the precursors to form TiS2 has been studied and the morphologies of the sulfide powders have also been compared. Gas chromatography and infrared spectroscopy have been used to study the molecular processes that occur in one of the reactions.

Titanium disulfide is a particularly promising cathode material for very high cycle life applications in secondary lithium batteries due to the reversible nature of the intercalation of lithium into the host TiS2 lattice. It has long been known that the mechanical stress of the intercalation process is minimized if TiS2 crystal size is kept below 10μm. It has also been suspected that minimizing crystal thickness would improve the kinetics of at the onset of lithiation by minimizing the forces which would have to be overcome in expanding the host lattice. We have synthesized three different types of microcrystalline TiS2, two thin film and one powder, and have compared their performances to that of a large crystalline powder. Lithium ion diffusivity and pulse power performance of the four materials were compared. It was found that the two thin film materials exhibited extraordinary pulse power rate capabilities while the two powder materials were limited in their performance by the constraints of the composite cathode matrix.

The titanium disulfide intercalation compounds obtained that contained both lithium and transition metals with the composition LixMyTiS2 (M=Ti, Fe, Ni) had an interlayer distance that was greater than in the original MyTiS2, but less than in LixTiS2 with the same lithium content.

The addition of water, Bu4NI, lithium amides, and n-BuLi to amines capable of intercalation into TiS2 as well as amines with lower basicity accelerate the formation of intercalation compounds.

1. In TiS2-amine insertion compounds the nitrogen atom is coordinated directly with the titanium atom. 2. The presence of water accelerates the insertion of the amine and leads to the coordination of oxygen-containing compounds to the titanium atoms of TiS2. 3. The TiS2-amine insertion compounds are easily oxidized by atmospheric oxygen at ∼20°C to give TiO2 and S8.