Lithium Hexastannate: A Potential Material for Energy Storage

Abstract

The prediction of a new lithium compound, Li2Sn6O13, is made from a combined first‐principles and classical force‐field approach. The electronic, structural, and mechanical properties of monoclinic Li2SnO3, Li2Ti6O13, and Li2Sn6O13 are explored. The calculated results for the equilibrium lattice parameters are in agreement with the available experimental data. The thermodynamic stabilities of Li2Ti6O13 and Li2Sn6O13 are evaluated. Both compounds are demonstrated to be thermodynamically stable with standard molar formation enthalpies of −5553 and −6740 kJ mol−1, respectively. Reaction energies for delithiation of 6.41 and 6.90 eV atom−1 are also determined for Li2Sn6O13 and Li2Ti6O13, respectively. The predicted voltage of Li insertion/extraction process per Li+/Li is 1.6 V for Li2Sn6O13, comparable to its isostructural counterpart Li2Ti6O13. Electronic band structure calculations indicate the insulating character of Li2SnO3 with an indirect band gap of 4.4 eV, whereas both Li2Ti6O13 and Li2Sn6O13 appear to be semiconductor compounds with band gaps of 3.1 and 3.0 eV, respectivley. The energy barriers for Li+ migration amount to ≈0.5 eV for both materials. Elastic stiffness coefficients and bulk, shear and Young's moduli were also calculated. The Li2Sn6O13 derivative is mechanically stable and can be predicted to be a brittle compound that is more resistant to volume change than Li2Ti6O13. If the Li2Sn6O13 compound could experimentally be prepared by using ion exchange, it could potentially be an efficient material for anodes in lithium‐ion batteries.

Implications of Oxygen–Sulfur Exchange on Structural, Electronic Properties, and Stability of Alkali‐Metal Hexatitanates

“…The lower values reveal the possibility of Na + /Li + , K + /Li + , and Na + /K + ion exchange. In addition, these values are comparable and even lower with respect to the well‐known Li 2 Ti 6 O 13 . The values of and have a small difference between structures, revealing a permanency and strong bonding interaction of the TiS 6 octahedral form upon change of the A + ion in the A 2 Ti 6 S 13 structures.…”

“…Figure depicts the band structure of A 2 Ti 6 S 13 in the equilibrium ground state. All structures have large energy bands near the Fermi level (red lines), representative of semiconductor compounds . K 2 Ti 6 S 13 has a metallic character considering the presence of bands crossing the valence band limit.…”

“…For the Li 2 Ti 6 S 13 and K 2 Ti 6 S 13 structures, the energy band spectra are similar, resulting in a low or indistinguishable Eg. In view of the common underestimation of DFT for band gap calculations, and the lack of further experimental measurements of these compounds, the values of the Eg should be considered as lower bounds …”

“…The second approach deals with the exploration of other thermodynamics data, such as the standard molar and formation enthalpies. In order to explore the thermodynamic stability of the A 2 Ti 6 S 13 compounds, the stoichiometry of A 2 Ti 6 S 13 is multiplied by 2 as the Z formula unit is 2 for the C 2/ m ‐type structure …”

“…With the available information of the standard molar formation enthalpy of Na 2 S, K 2 S, Li 2 S, and TiS 2 ; the standard molar enthalpies and standard molar formation enthalpies of A 2 Ti 6 S 13 compounds are obtained and listed in Table . Table also include the available data of standard molar and formation enthalpies for the oxygen containing material, including their respective Eg taken from the literature . Since thermodynamic stability point of view, while the values of behave more negative, then the structure is more stable .…”