Promoting Persistent Superionic Conductivity in Sodium Monocarba--dodecaborate NaCBH via Confinement within Nanoporous Silica.

Superionic phases of bulk anhydrous salts based on large cluster-like polyhedral (carba)borate anions are generally stable only well above room temperature, rendering them unsuitable as solid-state electrolytes in energy-storage devices that typically operate at close to room temperature. To unlock their technological potential, strategies are needed to stabilize these superionic properties down to subambient temperatures. One such strategy involves altering the bulk properties by confinement within nanoporous insulators.

Anion and Cation Dynamics in Polyhydroborate Salts: NMR Studies.

Polyhydroborate salts represent the important class of energy materials attracting significant recent attention. Some of these salts exhibit promising hydrogen storage properties and/or high ionic conductivities favorable for applications as solid electrolytes in batteries. Two basic types of thermally activated atomic jump motion are known to exist in these materials: the reorientational (rotational) motion of complex anions and the translational diffusion of cations or complex anions.

Structural and Dynamical Properties of Potassium Dodecahydro-monocarba--dodecaborate: KCBH.

MCBH (M: Li, Na) dodecahydro-monocarba--dodecaborate salt compounds are known to have stellar superionic Li and Na conductivities in their high-temperature disordered phases, making them potentially appealing electrolytes in all-solid-state batteries. Nonetheless, it is of keen interest to search for other related materials with similar conductivities while at the same time exhibiting even lower (more device-relevant) disordering temperatures, a key challenge for this class of materials. With this in mind, the unknown structural and dynamical properties of the heavier KCBH congener were investigated in detail by x-ray powder diffraction, differential scanning calorimetry, neutron vibrational spectroscopy, nuclear magnetic resonance, quasielastic neutron scattering, and AC impedance measurements.

Low-Temperature Rotational Tunneling of Tetrahydroborate Anions in Lithium Benzimidazolate-Borohydride Li(bIm)BH.

To investigate the dynamical properties of the novel hybrid compound, lithium benzimidazolate-borohydride Li(bIm)BH (where bIm denotes a benzimidazolate anion, CNH ), we have used a set of complementary techniques: neutron powder diffraction, ab initio density functional theory calculations, neutron vibrational spectroscopy, nuclear magnetic resonance, neutron spin echo, and quasi-elastic neutron scattering. Our measurements performed over the temperature range from 1.5 to 385 K have revealed the exceptionally fast low-temperature reorientational motion of BH anions.

Tracking the Progression of Anion Reorientational Behavior between -Phase and -Phase Alkali-Metal Silanides, MSiH, by Quasielastic Neutron Scattering.

Quasielastic neutron scattering (QENS) measurements over a wide range of energy resolutions were used to probe the reorientational behavior of the pyramidal SiH anions in the monoalkali silanides (MSiH, where M = K, Rb, and Cs) within the low-temperature ordered -phases, and for CsSiH, the high-temperature disordered -phase and intervening hysteretic transition region. Maximum jump frequencies of the -phase anions near the - transitions range from around 10 s for -KSiH to 10 s and higher for -RbSiH and -CsSiH. The -phase anions undergo uniaxial 3-fold rotational jumps around the anion quasi- symmetry axis.

Exceptional superionic conductivity in disordered sodium decahydro-closo-decaborate.

Na2 B10 H10 exhibits exceptional superionic conductivity above ca. 360 K (e.g.

Sodium superionic conduction in Na2B12H12.

Impedance measurements indicate that Na2B12H12 exhibits dramatic Na(+) conductivity (on the order of 0.1 S cm(-1)) above its order-disorder phase-transition at ≈529 K, rivaling that of current, solid-state, ceramic-based, Na-battery electrolytes. Superionicity may be aided by the large size, quasispherical shape, and high rotational mobility of the B12H12(2-) anions.