Nanoconfined LiBH sub(4) 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 sub(4) is a promising solid electrolyte for Li-ion batteries. It displays high lithium mobility, although only above 110 degree C at which a transition to a high temperature hexagonal structure occurs. Herein, it is shown that confining LiBH sub(4) in the pores of ordered mesoporous silica scaffolds leads to high Li super(+) conductivity (0.1 mS cm super(-1)) at room temperature. This is a surprisingly high value, especially given that the nanocomposites comprise 42 vol% of SiO sub(2). Solid state super(7)Li NMR confirmed that the high conductivity can be attributed to a very high Li super(+) mobility in the solid phase at room temperature. Confinement of LiBH sub(4) in the pores leads also to a lower solid-solid phase transition temperature than for bulk LiBH sub(4). 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 SiO sub(2) 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. Confining LiBH sub(4) inside nanopores of mesoporous silica results in stable and high Li super(+) mobilities persisting to room temperature. The mobility is associated with a LiBH sub(4) phase that does not undergo a structural phase transition, a phase probably located within 1.0 nanometer of the pore walls. This presents a new strategy to design efficient electrolytes for all solid-state rechargeable lithium batteries.