The influence of silica surface groups on the Li-ion conductivity of LiBH₄/SiO₂ nanocomposites

Abstract

The lithium ion conductivity of LiBH4 nanoconfined in mesoporous silica is strongly influenced by the types and concentration of the silica surface groups.

The effect of nanoscaffold porosity and surface chemistry on the Li-ion conductivity of LiBH4–LiNH2/metal oxide nanocomposites

“…In previous studies it has been found that the silanol vibrations disappear when the pores of the scaffold are lled with an electrolyte salt, as the hydroxyl vibrations are supressed by interactions or reaction between the silanol groups and the conned electrolyte. 43,48 This is clearly also the case for nanoconned LiBH 4 -LiNH 2 , implying that for the used compositions, the melt inltration process results in the successful incorporation of LiBH 4 -LiNH 2 in the oxide pores. Further evidence for the incorporation of LiBH 4 -LiNH 2 into the oxide pores is provided by XRD and N 2 physisorption (Fig.…”

“…The broadening effect was observed in previous studies on nanoconned LiBH 4 , and was attributed to increased rotational freedom of the [BH 4 À ] anion due to the structural changes induced by nanoconnement. 43 Secondly, two sharp bands related to [N-H] stretching vibrations of LiNH 2 are typically present at 3260 and 3310 cm À1 . 65 In the nanocomposites spectra, these sharp peaks are no longer observed.…”

“…For pure LiBH 4 , the enhancement in conductivity upon nanoconnement in a mesoporous oxide has been attributed to the interactions between surface groups of the oxide and the conned metal hydride, which leads to the formation of a space-charge region or highly defected layer at the LiBH 4 /oxide interface. 39,43,51 In this case, the chemical nature of the scaffold, especially the surface chemistry, is crucial for the interface effects, and thereby the conductivity of the LiBH 4 /oxide nanocomposite. Alternatively, it is also known that nanoconnement can lead to a reduction in phase transition temperature, which can profoundly inuence the properties of nanoconned complex hydrides.…”

“…In the second method, the lithium salt is intimately mixed with a high surface area non-conducting oxide scaffold, such as SiO 2 or Al 2 O 3 . [35][36][37][38][39][40][41][42][43][44] Close contact can be achieved through nanoconnement by melt inltration of the metal hydride in the nanopores of the oxide, thereby forming a nanocomposite. 45 Interestingly, this method was originally used to improve hydrogen sorption properties of metal hydrides.…”

“…LiBH 4 /SiO 2 , it is known that their ionic conductivity is greatly affected by the surface properties of the scaffold, such as the nature and density of the surface groups. [40][41][42][43][44] For nanoconned anion-substituted metal hydrides, on the other hand, the impact of the mesoporous scaffold properties on the scaffold/hydride interactions, and consequently ion mobility in the nanocomposites, have not yet been investigated.…”