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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Zn(BH4)2 by Materials Project

Zn(BH4)2 crystallizes in the orthorhombic Pmc2_1 space group. The structure is two-dimensional and consists of one Zn(BH4)2 sheet oriented in the (0, 1, 0) direction. Zn2+ is bonded in a 6-coordinate geometry to eight H+0.50+ atoms. There are a spread of Zn–H bond distances ranging from 1.88–2.22 Å. There are two inequivalent B3- sites. In the first B3- site, B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. There are a spread of B–H bond distances ranging from 1.19–1.26 Å. In the second B3- site, B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. There are a spread of B–H bond distances ranging from 1.22–1.24 Å. There are six inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to two equivalent Zn2+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in a water-like geometry to one Zn2+ and one B3- atom. In the third H+0.50+ site, H+0.50+ is bonded in a distorted L-shaped geometry to one Zn2+ and one B3- atom. In the fourth H+0.50+ site, H+0.50+ is bonded in a distorted L-shaped geometry to one Zn2+ and one B3- atom. In the fifth H+0.50+ site, H+0.50+ is bonded in an L-shaped geometry to one Zn2+ and one B3- atom. In the sixth H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zn(BH4)2 by Materials Project

Zn(BH4)2 crystallizes in the tetragonal I4_122 space group. The structure is three-dimensional. Zn2+ is bonded in a 8-coordinate geometry to eight H+0.50+ atoms. There are four shorter (1.88 Å) and four longer (2.18 Å) Zn–H bond lengths. B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. There is two shorter (1.22 Å) and two longer (1.24 Å) B–H bond length. There are two inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to one Zn2+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in an L-shaped geometry to one Zn2+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Ca-dimers, solvent layering, and dominant electrochemically active species in Ca(BH4)2 in THF

Abstract Divalent ions (Mg, Ca, and Zn) are being considered as competitive, safe, and earth-abundant alternatives to Li-ion electrochemistry, but present challenges for stable cycling due to undesirable interfacial phenomena. We explore the formation of electroactive species in the electrolyte Ca(BH 4 ) 2 ∣THF using molecular dynamics coupled with a continuum model of bulk and interfacial speciation. Free-energy analysis and unsupervised learning indicate a majority population of neutral Ca dimers and monomers with diverse molecular conformations and an order of magnitude lower concentration of the primary electroactive charged species – the monocation, $${\rm{CaBH}}_{4}^{+}$$ CaBH 4 + – produced via disproportionation of neutral complexes. Dense layering of THF molecules within ~1 nm of the electrode surface strongly modulates local electrolyte species populations. A dramatic increase in monocation population in this interfacial zone is induced at negative bias. We see no evidence for electrochemical activity of fully-solvated Ca 2+ . The consequences for performance are discussed in light of this molecular-scale insight.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on KZnB(H2Cl)2 by Materials Project

KZnB(H2Cl)2 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. K1+ is bonded in a 7-coordinate geometry to two H+0.50+ and five Cl1- atoms. There are one shorter (2.79 Å) and one longer (2.83 Å) K–H bond lengths. There are a spread of K–Cl bond distances ranging from 3.25–3.65 Å. Zn2+ is bonded to two equivalent H+0.50+ and two Cl1- atoms to form distorted ZnH2Cl2 tetrahedra that share an edgeedge with one BH4 tetrahedra. Both Zn–H bond lengths are 1.85 Å. There are one shorter (2.24 Å) and one longer (2.25 Å) Zn–Cl bond lengths. B3- is bonded to four H+0.50+ atoms to form BH4 tetrahedra that share an edgeedge with one ZnH2Cl2 tetrahedra. There is two shorter (1.21 Å) and two longer (1.26 Å) B–H bond length. There are three inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to one K1+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in an L-shaped geometry to one Zn2+ and one B3- atom. In the third H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to one K1+ and one B3- atom. There are two inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to two equivalent K1+ and one Zn2+ atom. In the second Cl1- site, Cl1- is bonded in a 4-coordinate geometry to three equivalent K1+ and one Zn2+ atom.

36 MATERIALS SCIENCE↗