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DOE OSTI2022

Hydrogenated and Carbon-coated Na2Ti6O13 Nanowires as High-Rate Anode Materials for Lithium Ion Batteries

The main disadvantage for sodium titanate as an anode material for LIBs is its low electronic conductivity, resulting in poor rate capability. Several approaches have been taken in an attempt to improve the electronic conductivity of sodium/lithium titanate, such as electronic material coating/mixing, ionic doping, comminution, etc.; but as of yet there has been no uniform carbon coating reported on sodium titanate for LIBs. In this work, we detail a facile technique to create uniform thin carbon coating layers on Na2Ti6O13 nanowires (NTO-C). In addition, we also explored self-doped Ti3+ on carbon coated Na2Ti6O13 nanowires (H-NTO-C) in an effort to further improve its electronic conductivity. The detailed results of the synthesis, characterization, and electrochemical performance of the NTO-based materials (NTO, NTO-C and H-NTO-C) will be presented.

25 ENERGY STORAGE↗

DOE OSTI2020

Materials Data on Na2Ti6O13 by Materials Project

Na2Ti6O13 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.48–3.00 Å. There are three inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded to six O2- atoms to form a mixture of distorted edge and corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles are 34°. There are a spread of Ti–O bond distances ranging from 1.82–2.24 Å. In the second Ti4+ site, Ti4+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 0–28°. There are a spread of Ti–O bond distances ranging from 1.84–2.19 Å. In the third Ti4+ site, Ti4+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ti–O bond distances ranging from 1.77–2.28 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to two equivalent Na1+ and two Ti4+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to three Ti4+ atoms. In the third O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two equivalent Na1+ and two Ti4+ atoms. In the fourth O2- site, O2- is bonded to four Ti4+ atoms to form distorted OTi4 trigonal pyramids that share corners with three equivalent ONa2Ti2 tetrahedra, corners with three OTi4 trigonal pyramids, and edges with four OTi4 trigonal pyramids. In the fifth O2- site, O2- is bonded in a linear geometry to two equivalent Ti4+ atoms. In the sixth O2- site, O2- is bonded to four Ti4+ atoms to form distorted OTi4 trigonal pyramids that share corners with three OTi4 trigonal pyramids, an edgeedge with one ONa2Ti2 tetrahedra, and edges with two equivalent OTi4 trigonal pyramids. In the seventh O2- site, O2- is bonded to two equivalent Na1+ and two Ti4+ atoms to form distorted ONa2Ti2 tetrahedra that share corners with two equivalent ONa2Ti2 tetrahedra, corners with three equivalent OTi4 trigonal pyramids, and an edgeedge with one OTi4 trigonal pyramid.

36 MATERIALS SCIENCE↗

NASA NTRS1973

Selection and preliminary evaluation of three structures as potential solid conductors of alkali ions: Two hollandites, a titanate, and a tungstate

Utilization of crystal-chemical criteria has suggested three structure types in which alkali ions may be mobile: (1)hollandites K(x)Mg(x/2)Ti(8-x/2)O16 and K(x)Al(x)Ti(8-x)O16 for 1.6 less than or equal to x less than or equal to 2.0 tungstate K2W4013; and (3) sodium hexatitante Na2Ti6O13. Each is a tunnel structure. An electrical screening procedure, previously tested on beta-alumina, has indicated high K(+) ion mobility in the hollandites and in the tungstate, but not in the hexatitanate. Specimens were polycrystalline disks near 90 percent of theoretical density. The ac conductivity calculated from dielectric and capacitance measurements has been attributed to ion mobility. This ac conductivity was up to 0.01/ohm-cm for hollandites and about 0.0001/ohm-cm for the tungstate, with approximate activation energies of 21 to 25 and 16 kJ/mole (5 to 6 and 4 kcal/mole), respectively. Electronic conduction and chemical reactivity have eliminated the tungstate from further consideration. The hollandites have been considered worthy of further development and evaluation.

Singer, J.↗