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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Li(TiS2)2 by Materials Project

LiTi2S4 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. Li1+ is bonded to six S2- atoms to form LiS6 octahedra that share corners with twelve equivalent TiS6 octahedra, edges with two equivalent LiS6 octahedra, and faces with two equivalent TiS6 octahedra. The corner-sharing octahedra tilt angles range from 43–51°. There are a spread of Li–S bond distances ranging from 2.58–2.69 Å. Ti+3.50+ is bonded to six S2- atoms to form TiS6 octahedra that share corners with six equivalent LiS6 octahedra, edges with six equivalent TiS6 octahedra, and a faceface with one LiS6 octahedra. The corner-sharing octahedra tilt angles range from 43–51°. There are a spread of Ti–S bond distances ranging from 2.39–2.56 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a rectangular see-saw-like geometry to one Li1+ and three equivalent Ti+3.50+ atoms. In the second S2- site, S2- is bonded to two equivalent Li1+ and three equivalent Ti+3.50+ atoms to form a mixture of distorted edge and corner-sharing SLi2Ti3 trigonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiTi(SO)2 by Materials Project

LiO2TiS2 crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of one LiO2 sheet oriented in the (0, 0, 1) direction and one TiS2 sheet oriented in the (0, 0, 1) direction. In the LiO2 sheet, Li1+ is bonded to six equivalent O2- atoms to form edge-sharing LiO6 octahedra. There are four shorter (1.91 Å) and two longer (2.51 Å) Li–O bond lengths. O2- is bonded in a 4-coordinate geometry to three equivalent Li1+ and one O2- atom. The O–O bond length is 1.37 Å. In the TiS2 sheet, Ti3+ is bonded to six equivalent S atoms to form edge-sharing TiS6 octahedra. There are two shorter (2.42 Å) and four longer (2.46 Å) Ti–S bond lengths. S is bonded in a distorted T-shaped geometry to three equivalent Ti3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiTi(SO)2 by Materials Project

LiO2TiS2 crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of one LiO2 sheet oriented in the (0, 0, 1) direction and one TiS2 sheet oriented in the (0, 0, 1) direction. In the LiO2 sheet, Li1+ is bonded to six equivalent O2- atoms to form edge-sharing LiO6 octahedra. There are four shorter (1.91 Å) and two longer (2.56 Å) Li–O bond lengths. O2- is bonded in a 4-coordinate geometry to three equivalent Li1+ and one O2- atom. The O–O bond length is 1.38 Å. In the TiS2 sheet, Ti3+ is bonded to six equivalent S atoms to form edge-sharing TiS6 octahedra. There are two shorter (2.42 Å) and four longer (2.46 Å) Ti–S bond lengths. S is bonded in a distorted T-shaped geometry to three equivalent Ti3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiTiS2O by Materials Project

Li2O2(TiS2)2 crystallizes in the trigonal R3m space group. The structure is two-dimensional and consists of three Li2O2 sheets oriented in the (0, 0, 1) direction and three TiS2 sheets oriented in the (0, 0, 1) direction. In each Li2O2 sheet, Li1+ is bonded in a trigonal planar geometry to three equivalent O2- atoms. All Li–O bond lengths are 1.95 Å. O2- is bonded in a trigonal planar geometry to three equivalent Li1+ atoms. In each TiS2 sheet, Ti4+ is bonded to six S+1.50- atoms to form edge-sharing TiS6 octahedra. There are three shorter (2.41 Å) and three longer (2.43 Å) Ti–S bond lengths. There are two inequivalent S+1.50- sites. In the first S+1.50- site, S+1.50- is bonded in a 3-coordinate geometry to three equivalent Ti4+ atoms. In the second S+1.50- site, S+1.50- is bonded in a 3-coordinate geometry to three equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

First-Principles Modeling of Sodium Ion and Water Intercalation into Titanium Disulfide Interlayers for Water Desalination

Recent experiments revealed the possibility of using titanium disulfide (TiS 2 ) as the cathode material in capacitive deionization (CDI) devices for water desalination. Although it performed stably up to 70 cycles with a salt removal capacity of 14 mg/g (corresponding to a sodium ion removal capacity of 35.8 mg/g) at high molar concentration (600 mM NaCl), the maximum capacity of TiS 2 as a CDI electrode was much lower (~70 mAh/g) than as a supercapacitor (239 mAh/g). Understanding why the ion capacities of these two configurations of the same material differ will entail elucidating detailed charge/discharge mechanisms at the atomic scale. Here, we present density functional theory simulations of sodium intercalation into TiS 2 interlayers in order to gain such understanding. We systematically investigated TiS 2 stacking patterns and ion intercalation sites, energetics of the intercalated compounds, and phase transformation during sodium intercalation. The calculated structural evolution and capacitance–voltage curve agree quite well with previous measurements. We conclude that the different maximum capacities of TiS 2 measured in aqueous and dry environments originate from weaker interlayer interactions with respect to shear strain after ~33% intercalation of Na + –H 2 O pairs, which is detrimental to the mechanical stability of TiS 2 . In conclusion, this study sheds light on the underlying mechanisms of ion intercalation into layered materials and contributes to understanding requirements for future design and optimization of CDI electrode materials for water desalination.

36 MATERIALS SCIENCE↗