Evaluation of a new lithium complex hydride: a derivative of BH4− and NH2− for fast Li-ion conduction and H2 sorption

Abstract

A new ternary complex hydride is synthesized by the interaction between Li₂NH and LiBH₄. The crystal structure of this new hydride is tentatively indexed using an orthorhombic cell with a space group of Pna2₁ and lattice parameters of a = 9.643 Å, b = 6.228 Å, and c = 5.563 Å. The Li₂NH-2LiBH₄ sample shows excellent hydrogenation properties with hydrogen absorption starting at near-ambient temperature (50 °C), which is more than 100 °C lower than that of pristine Li₂NH. Furthermore, it attains 100% hydrogenation under isothermal conditions at 60 °C and 50 bar hydrogen pressure. Such superior low-temperature hydrogen absorption may be due to the formation of this new complex hydride. Interestingly, above 97 °C, the lithium-ion conductivity of this new hydride is higher than those of Li₂NH and LiBH₄ and reaches 10⁻² S cm⁻¹ at 114 °C. Meanwhile, the ionic conductivity of this new hydride is ∼30 times higher than that of LiBH₄ reaching 10⁻⁵ S cm⁻¹ at room temperature. The interaction between imides and borohydrides described in this work expands the options for strategic design of novel hydrogen storage materials and solid ionic conductors.