A Dynamic Duo: Fast ion conduction in metal hydride/oxide nanocomposites

This thesis discusses the development of novel electrolytes for all-solid-state batteries. These next generation batteries are expected to play a key role in the global transition from fossil fuel-based energy to a society that runs mostly on renewable energies as they enable high-capacity electricity storage with improved safety compared to conventional Li-ion batteries. Due to their light weight and the ability to form a good interface with most electrode materials, metal hydrides (e.g., LiBH4) have been proposed as promising candidates for this application. Unfortunately, their poor room temperature ionic conductivity hinders their use in all-solid-state batteries. Hence, the main goal of the research described in this thesis has been to improve the ionic transport in metal hydrides. To this end, the effect of interactions between metal hydrides and metal oxides (in metal hydride/oxide nanocomposites) on the ionic conductivity of metal hydrides was investigated. This work shows that the conductivity of monophasic metal hydrides (LiBH4, NaBH4, NaNH2), as well as ion-substituted metal hydrides (LiBH4-LiI, LiBH4-LiNH2) can be greatly enhanced via nanocomposite formation with oxide scaffolds. The conductivity of the nanocomposites depends strongly on the properties of the mesoporous oxide, i.e., the chemical and physical properties. Generally, the conductivity enhancement originates from the formation of a conductive layer at the hydride-oxide interface, but in the case of LiBH4-LiNH2/oxide nanocomposite, the conductivity enhancement arises from stabilization of a conductive high temperature phase at ambient temperature. This illustrates that nanocomposite formation offers more than one way to improve ionic transport in solid electrolytes.