Investigation of Mg(BH₄)(NH₂)-Based Composite Materials with Enhanced Mg²⁺ Ionic Conductivity

Abstract

Nowadays, the development of rechargeable Mg batteries remains a challenge, especially due to the difficulty to find a noncorrosive liquid electrolyte with suitable ionic transport properties. A possible improvement could come from a solid electrolyte, such as Mg(BH4)(NH2), which has been recently reported as a solid-state Mg-ion conductor. In this study, its synthesis parameters are carefully investigated. The formation of an additional phase is reported, whose amount is decreased by optimizing the synthesis parameters and especially by increasing the ball-milling speed. For the first time, 11B MAS NMR spectroscopy is applied to this Mg–B–N–H system: it reveals that an additional phase is always present even in an amorphous state. Interestingly, it strongly influences the ionic conduction properties. Indeed, the as-obtained borohydride–amide composite exhibits a high conductivity of 3 × 10–6 S·cm–1 at 100 °C, one of the highest ever-reported ionic conductivities for a Mg2+ solid conductor at such a low temperature.