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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on LiAlH4 by Materials Project

LiAlH4 crystallizes in the monoclinic C2/c space group. The structure is two-dimensional and consists of two LiAlH4 sheets oriented in the (0, 1, 0) direction. Li1+ is bonded in a 6-coordinate geometry to six H1- atoms. There are a spread of Li–H bond distances ranging from 2.02–2.10 Å. Al3+ is bonded in a tetrahedral geometry to four H1- atoms. All Al–H bond lengths are 1.65 Å. There are two inequivalent H1- sites. In the first H1- site, H1- is bonded in a trigonal planar geometry to two equivalent Li1+ and one Al3+ atom. In the second H1- site, H1- is bonded in a bent 120 degrees geometry to one Li1+ and one Al3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiAlH4 by Materials Project

LiAlH4 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Li1+ is bonded to five H1- atoms to form LiH5 trigonal bipyramids that share corners with five equivalent AlH4 tetrahedra and an edgeedge with one LiH5 trigonal bipyramid. There are a spread of Li–H bond distances ranging from 1.87–2.01 Å. Al3+ is bonded to four H1- atoms to form AlH4 tetrahedra that share corners with five equivalent LiH5 trigonal bipyramids. There are a spread of Al–H bond distances ranging from 1.62–1.64 Å. There are four inequivalent H1- sites. In the first H1- site, H1- is bonded in a bent 150 degrees geometry to one Li1+ and one Al3+ atom. In the second H1- site, H1- is bonded in a trigonal planar geometry to two equivalent Li1+ and one Al3+ atom. In the third H1- site, H1- is bonded in a bent 150 degrees geometry to one Li1+ and one Al3+ atom. In the fourth H1- site, H1- is bonded in a bent 150 degrees geometry to one Li1+ and one Al3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiAlH4 by Materials Project

LiAlH4 is Zircon-like structured and crystallizes in the tetragonal I4_1/a space group. The structure is three-dimensional. Li1+ is bonded in a 8-coordinate geometry to eight equivalent H1- atoms. There are four shorter (2.06 Å) and four longer (2.19 Å) Li–H bond lengths. Al3+ is bonded in a tetrahedral geometry to four equivalent H1- atoms. All Al–H bond lengths are 1.65 Å. H1- is bonded in a distorted trigonal planar geometry to two equivalent Li1+ and one Al3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiAlH4 by Materials Project

LiAlH4 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Li1+ is bonded to six H1- atoms to form LiH6 octahedra that share corners with six equivalent AlH4 tetrahedra and edges with two equivalent LiH6 octahedra. There are a spread of Li–H bond distances ranging from 1.96–2.11 Å. Al3+ is bonded to four H1- atoms to form AlH4 tetrahedra that share corners with six equivalent LiH6 octahedra. The corner-sharing octahedra tilt angles range from 45–63°. There is one shorter (1.63 Å) and three longer (1.64 Å) Al–H bond length. There are three inequivalent H1- sites. In the first H1- site, H1- is bonded in a distorted bent 150 degrees geometry to one Li1+ and one Al3+ atom. In the second H1- site, H1- is bonded in a bent 120 degrees geometry to one Li1+ and one Al3+ atom. In the third H1- site, H1- is bonded in a trigonal non-coplanar geometry to two equivalent Li1+ and one Al3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Electrolyte-Assisted Hydrogen Cycling in Lithium and Sodium Alanates at Low Pressures and Temperatures

An investigation of electrolyte-assisted hydrogen storage reactions in complex aluminum hydrides (LiAlH4 and NaAlH4) reveals significantly reduced reaction times for hydrogen desorption and uptake in the presence of an electrolyte. LiAlH4 evolves ~7.8 wt% H2 over ~3 h in the presence of a Li-KBH4 eutectic at 130 °C compared to ~25 h for the same material without the electrolyte. Similarly, NaAlH4 exhibits 4.8 wt% H2 evolution over ~4 h in the presence of a diglyme electrolyte at 150 °C compared to 4.4 wt% in ~15 h for the same material without the electrolyte. These reduced reaction times are composed of two effects, an increase in reaction rates and a change in the reaction kinetics. While typical solid state dehydrogenation reactions exhibit kinetics with rates that continuously decrease with the extent of reaction, we find that the addition of an electrolyte results in rates that are relatively constant over the full desorption window. Fitting the kinetics to an Avrami-Erofe’ev model supports these observations. The desorption rate coefficients increase in the presence of an electrolyte, suggesting an increase in the velocities of the reactant-product interfaces. In addition, including an electrolyte increases the growth parameters, primarily for the second desorption steps, resulting in the observed relatively constant reaction rates. Similar effects occur upon hydrogen uptake in NaH/Al where the presence of an electrolyte enables hydrogenation under more practical low temperature (75 °C) and pressure (50 bar H2) conditions.

25 ENERGY STORAGE↗
DOE OSTI2021

Reversing the Irreversible: Thermodynamic Stabilization of LiAlH 4 Nanoconfined Within a Nitrogen-Doped Carbon Host

A general problem when designing functional nanomaterials for energy storage is the lack of control over the stability and reactivity of metastable phases. Using the high-capacity hydrogen storage candidate LiAlH4 as an exemplar, we demonstrate an alternative approach to the thermodynamic stabilization of metastable metal hydrides by coordination to nitrogen binding sites within the nanopores of N-doped CMK-3 carbon (NCMK-3). The resulting LiAlH 4 @NCMK-3 material releases H 2 at temperatures as low as 126 °C with full decomposition below 240 °C, bypassing the usual Li 3 AlH 6 intermediate observed in bulk. Moreover, >80% of LiAlH 4 can be regenerated under 100 MPa H 2 , a feat previously thought to be impossible. Nitrogen sites are critical to these improvements, as no reversibility is observed with undoped CMK-3. Density functional theory predicts a drastically reduced Al–H bond dissociation energy and supports the observed change in the reaction pathway. Finally, the calculations also provide a rationale for the solid-state reversibility, which derives from the combined effects of nanoconfinement, Li adatom formation, and charge redistribution between the metal hydride and the host.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗