Nanoconfined LiBH4 as a Fast Lithium Ion Conductor

• Published in: Advanced functional materials Vol. 25; no. 2; pp. 184 - 192
• Main Authors: Blanchard, Didier, Nale, Angeloclaudio, Sveinbjörnsson, Dadi, Eggenhuisen, Tamara M., Verkuijlen, Margriet H. W., Suwarno, Vegge, Tejs, Kentgens, Arno P. M., de Jongh, Petra E.
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 14.01.2015
• Subjects: impedance spectroscopy; ionic conductors; nanoconfinement; nuclear magnetic resonance; solid electrolytes
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201402538

Designing new functional materials is crucial for the development of efficient energy storage and conversion devices such as all solid‐state batteries. LiBH4 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. Confining LiBH4 inside nanopores of mesoporous silica results in stable and high Li+ mobilities persisting to room temperature. The mobility is associated with a LiBH4 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.