Li-Driven Electrochemical Conversion Reaction of AlH₃, LiAlH₄, and NaAlH₄

Abstract

The conversion reaction of AlH3, LiAlH4, and NaAlH4 complex hydrides with lithium has been examined electrochemically. All compounds undergo a conversion reaction in which one equivalent of LiH is formed for each equivalent of hydrogen contained in the hydride material. Decomposition of the hydrides follows different paths depending on the nature of the alkali metal but leads in all cases to pure metallic aluminum. Such very fine and reactive Al particles are able to readily form an alloy with Li at a lower potential. Alternatively, thermal decomposition of alane has been used to produce highly porous aluminum able to react with lithium to form the AlLi alloy directly. Constant current charge/discharge cycling, cyclic voltammetry, and in-operando XRD were utilized to characterize the performance of these materials and to interpret the reaction paths depending of the complex hydride compositions.