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 LiBH 4 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 (Li 4 Ti 5 O 12 , LTO), and nanocrystalline rutile (TiO 2 ). 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 TiO 2 , the compatibility of the LiBH 4 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 LiBH 4 as an easily processable model solid electrolyte in practical test cells.