Nanoconfined LiBH₄ as a Fast Lithium Ion Conductor

Designing new functional materials is crucial for the development of efficient energy storage and conversion devices such as all solid-state batteries. LiBH 4 is a promising solid electrolyte for Li-ion batteries. It displays high lithium mobility, although only above 110 °C at which a transition to a high temperature hexagonal structure occurs. Herein, it is shown that confining LiBH₄ in the pores of ordered mesoporous silica scaffolds leads to high Li⁺ conductivity (0.1 mS cm⁻¹ ) at room temperature. This is a surprisingly high value, especially given that the nanocomposites comprise 42 vol% of SiO₂. Solid state ⁷Li NMR
confirmed that the high conductivity can be attributed to a very high Li⁺ mobility in the solid phase at room temperature. Confinement of LiBH4 in the pores leads also to a lower solid-solid phase transition temperature than for bulk LiBH₄. However, the high ionic mobility is associated with a fraction of the confined borohydride that shows no phase transition, and most likely located close to the interface with the SiO₂ pore walls. These results point to a new strategy to design low-temperature ion conducting solids for application in all solid-state lithium ion batteries, which could enable safe use of Li-metal anodes.