The Nature of Interface Interactions Leading to High Ionic Conductivity in LiBH₄/SiO₂ Nanocomposites

Abstract

Complex metal hydride/oxide nanocomposites are a promising class of solid-state electrolytes. They exhibit high ionic conductivities due to an interaction of the metal hydride with the surface of the oxide. The exact nature of this interaction and composition of the hydride/oxide interface is not yet known. Using 1 H, 7 Li, 11 B, and 29 Si NMR spectroscopy and lithium borohydride confined in nanoporous silica as a model system, we now elucidate the chemistry and dynamics occurring at the interface between the scaffold and the complex metal hydride. We observed that the structure of the oxide scaffold has a significant effect on the ionic conductivity. A previously unknown silicon site was observed in the nanocomposites and correlated to the LiBH 4 at the interface with silica. We provide a model for the origin of this silicon site which reveals that siloxane bonds are broken and highly dynamic silicon–hydride–borohydride and silicon–oxide–lithium bonds are formed at the interface between LiBH 4 and silica. Additionally, we discovered a strong correlation between the thickness of the silica pore walls and the fraction of the LiBH 4 that displays fast dynamics. Our findings provide insights on the role of the local scaffold structure and the chemistry of the interaction at the interface between complex metal hydrides and oxide hosts. These findings are relevant for other complex hydride/metal oxide systems where interface effects leads to a high ionic conductivity.

Superionic Conductivity in Sodium Zirconium Chloride‐Based Compounds

“…Therefore, the origin of the high conductivity observed in Na 0.67 Zr(SO 4 ) 0.33 Cl 4 might be weak Na−Cl bonds due to the strong Lewis acidity on Zr connected to SO 4 2− polyanion, which strongly withdraw electron. This is similar with high ionic conductivity observed in interfacial interaction of metal oxide and borohydride [28,29] . In the case of LiBH 4 /SiO 2 , siloxane bonds are broken and highly dynamic silicon‐hydride‐borohydride and silicon‐oxide‐lithium bonds are formed at the interface between LiBH 4 and silica [28] .…”

Enhanced Li-ion conductivity in LiBH4–ZrO2 nanocomposites and nanoscale Li imaging by energy-filtered transmission electron microscopy

“…Another possible reason is the formation of interfacial side-reaction phases between LiBH 4 and oxide. This also has been proposed in a recent study, 23 where silicon-hydride–borohydride and silicon-oxide–lithium bonds are formed at the interface between LiBH 4 and SiO 2 . The ion dynamics study of LiBH 4 in silica nanopores revealed the two distinct fractions.…”

“…A recent study revealed a strong correlation between the thickness of silica pore walls and the fraction of LiBH 4 that shows fast dynamics. 23 The effect is considered to originate from charge distributions within the silica scaffold. Another possible reason is the formation of interfacial side-reaction phases between LiBH 4 and oxide.…”

A Wide Temperature 10 V Solid-state Electrolyte with a Critical Current Density of over 20 mA cm-2

“…1a), LiBH 4 displays a space group (s.g.) Pnma (PDF#27-0287). 35 In addition, HT150-0PMMA shows the weakened diffraction peaks of s.g. P6 3 mc (PDF#27-0286) 21 after incorporating γ-Al 2 O 3 and LiI via continuous shearing and crushing in ball milling, as a sign of the completion of the orthorhombic-to-hexagonal transitions at RT. 22 After the in situ melting reaction with PMMA at 150 ℃ for 1 h, HT150-5PMMA preserves an obvious amorphous structure.…”

“…Recently, researchers have proven that the high electronic conductivity in bulk SE accelerates oxidative decomposition kinetically, 18 and it is the leading cause of severe dendrite growth. 19,20 Many studies have been devoted to resolving disturbing electronic percolations by adding a second phase with low electronic conductivity, e.g., SiO 2 , 21 Al 2 O 3 , 22 TiO 2 , 23 and ZrO 2 . 24 The decreases in electronic conductivities in the composite SEs can be understood based on percolation theories in which electronic percolations can be turned off once the volume fractions of the llers exceed a certain point.…”