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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

TiO2 Nanocrystal-Framed Li 2 TiSiO 5 Platelets for Low-Voltage Lithium Battery Anode

Titanium-based anode materials are attracting considerable attention for use in high-performance lithium-ion batteries, but the compromised energy density caused by high voltage plateaus and unsatisfactory capacities severely retards their practical applications. Herein, a molten-salt synthesis of Li 2 TiSiO 5 crystalline platelets and a subsequent selective facet modification by in situ growth of TiO 2 nanocrystal frames are facilely achieved. The discharge voltage plateau at around 0.5 V renders the Li 2 TiSiO 5 anode safe compared with graphite and confers a high energy density compared with zero-strain Li 4 Ti 5 O 12 anode. With the optimized size, structure, and content of modified TiO2 nanocrystals associated with the exposed (001) plane of Li 2 TiSiO 5 , the Li 2 TiSiO 5 -based anodes can deliver a capacity of above 300 mAh g -1 , enhanced rate performance, and a capacity retention of 66% after 10 000 cycles. In situ X-ray diffraction and ex situ transmission electron microscopy have demonstrated the structural stability of the anodes upon charge/discharge. Further theoretical calculation reveals 3D migration paths of Li + ions in Li 2 TiSiO 5 . The selective modification of in situ grown TiO2 nanocrystals on certain facets of crystallites opens a new door for the development of electrode materials possessing superior electrochemical properties.

anodes↗
DOE OSTI2020

Materials Data on TiSiOs by Materials Project

TiOsSi crystallizes in the orthorhombic Ima2 space group. The structure is three-dimensional. there are three inequivalent Ti3+ sites. In the first Ti3+ site, Ti3+ is bonded in a 5-coordinate geometry to five Si4- atoms. There are a spread of Ti–Si bond distances ranging from 2.62–2.93 Å. In the second Ti3+ site, Ti3+ is bonded to five Si4- atoms to form distorted TiSi5 square pyramids that share corners with six OsSi4 tetrahedra, corners with five equivalent TiSi5 trigonal bipyramids, edges with two equivalent TiSi5 square pyramids, edges with six OsSi4 tetrahedra, and edges with two equivalent TiSi5 trigonal bipyramids. There are three shorter (2.63 Å) and two longer (2.64 Å) Ti–Si bond lengths. In the third Ti3+ site, Ti3+ is bonded to five Si4- atoms to form TiSi5 trigonal bipyramids that share corners with five equivalent TiSi5 square pyramids, corners with six OsSi4 tetrahedra, edges with two equivalent TiSi5 square pyramids, edges with six OsSi4 tetrahedra, and edges with two equivalent TiSi5 trigonal bipyramids. There are four shorter (2.64 Å) and one longer (2.68 Å) Ti–Si bond lengths. There are two inequivalent Os1+ sites. In the first Os1+ site, Os1+ is bonded to four Si4- atoms to form OsSi4 tetrahedra that share corners with two equivalent TiSi5 square pyramids, corners with ten OsSi4 tetrahedra, corners with two equivalent TiSi5 trigonal bipyramids, edges with two equivalent TiSi5 square pyramids, edges with two equivalent OsSi4 tetrahedra, and edges with two equivalent TiSi5 trigonal bipyramids. There are two shorter (2.48 Å) and two longer (2.49 Å) Os–Si bond lengths. In the second Os1+ site, Os1+ is bonded to four Si4- atoms to form OsSi4 tetrahedra that share corners with two equivalent TiSi5 square pyramids, corners with ten OsSi4 tetrahedra, corners with two equivalent TiSi5 trigonal bipyramids, edges with two equivalent TiSi5 square pyramids, edges with two OsSi4 tetrahedra, and edges with two equivalent TiSi5 trigonal bipyramids. There are one shorter (2.41 Å) and three longer (2.47 Å) Os–Si bond lengths. There are two inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 10-coordinate geometry to three Ti3+ and six Os1+ atoms. In the second Si4- site, Si4- is bonded in a 9-coordinate geometry to six Ti3+ and three Os1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The Influence of Alkalinity on the Uptake of Cs{sup +} and Sr{sup 2+} by Cation-substituted Natisites in Sodium-bearing Conditions - 20336

The titanosilicate natisite (Na{sub 2}TiSiO{sub 5}) is a kinetic phase of the mineral sitinakite (Na{sub 2}Ti{sub 2}O{sub 3}SiO{sub 4}.2H{sub 2}O), which is a reference material in the removal of Cs and Sr from radioactive high-level waste. Natisite is disregarded in the literature as a candidate sorbent for Cs and Sr, despite being more thermally stable than sitinakite, which is a critical property for this application. Replacing portion of the Ti in natisite by other metals is believed to enhance natisite sorption properties. In nuclear waste remediation, Cs and Sr are contained in high-salinity liquid wastes that can either be highly acidic or alkaline. In the present study, Al-, Sn-, and Zr-natisites were synthesized, and compared to pure natisite and sitinakite in batch experiments. Five concentrations of NaOH and NaNO{sub 3} (i.e. source of Na{sup +}) mimicking conditions of high alkalinity, and competing Na{sup +} ions, respectively, were evaluated. Sorption results demonstrate that sitinakite is generally more effective than all four natisites in removing Cs and Sr. However, sitinakite uptake mechanism seems to deteriorate at increasing concentrations of base and Na{sup +}. Although less selective than sitinakite, all natisite sorbents provided a less dramatic decline in Cs and Sr uptake through increasing molarities. Overall, there was an improvement in the sorption of Cs and Sr by the metal-substituted materials over natisite and, in neither of the testing solutions, natisite outperformed its substituted variants. In highly alkaline solutions, Sn- and Zr-Natisite provided for exceptional removal for Sr, removing more than twice the amount sorbed by sitinakite at 0.1 M NaOH. The results obtained for Sr uptake by all four natisite materials in alkaline solutions are promising, especially considering the highly alkaline nature of wastes from the nuclear industry. Future studies should investigate the sorption mechanisms responsible for natisite selectivity for Sr at high pH. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗