Divalent closo -monocarborane solvates for solid-state ionic conductors.

Li-ion batteries have held the dominant position in battery research for the last 30+ years. However, due to inadequate resources and the cost of necessary elements ( e.g. , lithium ore) in addition to safety issues concerning the components and construction, it has become more important to look at alternative technologies. Multivalent metal batteries with solid-state electrolytes are a potential option for future battery applications. The synthesis and characterisation of divalent hydrated closo -monocarborane salts - Mg[CB 11 H 12 ] 2 · x H 2 O, Ca[CB 11 H 12 ] 2 · x H 2 O, and Zn[CB 11 H 12 ] 2 · x H 2 O - have shown potential as solid-state electrolytes. The coordination of a solvent ( e.g. H 2 O) to the cation in these complexes shows a significant improvement in ionic conductivity, i.e. for Zn[CB 11 H 12 ] 2 · x H 2 O dried at 100 °C (10 -3 S cm -1 at 170 °C) and dried at 150 °C (10 -5 S cm -1 at 170 °C). Solvent choice also proved important with the ionic conductivity of Mg[CB 11 H 12 ] 2 ·3en (en = ethylenediamine) being higher than that of Mg[CB 11 H 12 ] 2 ·3.1H 2 O (2.6 × 10 -5 S cm -1 and 1.7 × 10 -8 S cm -1 at 100 °C, respectively), however, the oxidative stability was lower (<1 V (Mg 2+ /Mg) and 1.9 V (Mg 2+ /Mg), respectively). Thermal characterisation of the divalent closo -monocarborane salts showed melting and desolvation, prior to high temperature decomposition.