High-temperature all-solid-state batteries with LiBH₄ as electrolyte - a case study exploring the performance of TiO₂ nanorods, Li₄Ti₅O₁₂ and graphite as active materials

The hexagonal high-temperature form of LiBH₄ is known as a fast ion conductor. Here, we investigated its suitability as a solid electrolyte in high-temperature all-solid-state cells when combined with the following active materials: Li metal, graphite, lithium titanium oxide (Li₄Ti₅O₁₂, LTO), and nanocrystalline rutile (TiO₂). First results using lithium anodes and rutile nanorods as cathode material show that a cell constructed by simple cold-pressing operates at reversible discharge capacities in the order of 125 mA h g^-1 at a C-rate of C/5 and at temperatures as high as 393 K. Besides TiO₂, the compatibility of the LiBH₄ with other active materials such as graphite and LTO was tested. We found evidence of possible interface instabilities that manifest through rare, yet still detrimental, self-charge processes that may be relevant for hydrogen storage applications. Moreover, we investigated the long-term cycling behavior of the cells assembled and demonstrate the successful employment of LiBH₄ as an easily processable model solid electrolyte in practical test cells.