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

Abstract 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.