Lithium-Ion Conduction in a Class of Aluminoborates LinMAlB12O24 (M = Ba, Sr, Ca, or La; n = 7 or 6)

Abstract

With diverse structures and high ambient stability, Li-containing borate materials are promising candidates as Li solid-state conductors. Here, we report a group of aluminoborate compounds, LinMAlB12O24 (n = 6 for M = La; n = 7 for M = Ba, Sr, Ca), which were synthesized by a conventional solid-state method. Their crystal structures feature a common three-dimensional framework consisting of B6O14 clusters and AlO6 octahedra and the Li ions are positioned around the chained B6O14 clusters. The Li content n can be modified, i.e. either 6 or 7, depending on the chosen metal species M to keep the overall charge balance. The Li-ion conduction properties of the series were studied by bond valence site energy calculation and electrochemical impedance spectroscopy. We observed much higher ionic conductivity and a lower migration barrier in Li7BaAlB12O24 than in Li6LaAlB12O24, suggesting that the Li-ion site configuration plays an important role in determining ion transport.