Destabilization of LiBH4 by the infusion of Bi2X3 (X = S, Se, Te): an in situ TEM investigation

Abstract

Lithium borohydride is a potential candidate not only for hydrogen storage (high hydrogen capacity ∼18.5 wt%), but it can also be used as a solid electrolyte due to the high conductivity (∼10⁻³ S cm⁻¹) of its high-temperature phase. However, it cannot be utilized as a hydrogen storage material practically because of its high stability and high decomposition temperature. During our recent work on LiBH₄ as a solid electrolyte for Bi₂X₃ anode materials in all-solid-state Li-ion batteries, a thermochemical side reaction was observed. This thermochemical reaction restricted the potential window of electrochemical cycling, thus lowering the overall capacity of the electrode material. However, on the other hand, it allowed a significant destabilization of LiBH₄. This motivated us to investigate the effect of bismuth chalcogenides on the stability of LiBH₄ in detail. In this work, we prepared LiBH₄ composites with bulk and nanostructures of Bi₂X₃ and investigated the minimum decomposition temperature of LiBH₄. In order to understand the detailed reaction mechanism, X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) were performed after milling as well as at different temperatures according to TG-DTA experiments. The onset desorption temperature of LiBH₄ could be lowered down to 50 °C by the infusion of 50 wt% Bi₂S₃ nanoflowers. This work not only enabled us to achieve efficient destabilization of LiBH₄ but also provided a significant understanding of the side reaction during the use of LiBH₄ as a solid electrolyte for Bi₂X₃ chalcogenides. It will be helpful in tuning the electrolyte–electrode combination without any side reaction, thus improving the cycling stability.