EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Solid-state electrolytes (SSEs) are promising candidates for resolving the intrinsic limitations of the organic liquid electrolyte currently employed in Li-ion batteries. Nevertheless, an SSE must fulfil several requirements to be employed in an all-solid state battery (SSB), such a high ionic conductivity. Complex hydrides (e.g. LiBH4) are suggested as solid-state electrolytes. Among the different polymorphs of LiBH4, only the hexagonal phase, which is stable at temperatures above 110°C, has a remarkable high ionic conductivity (~10-3 S cm-1 at 120 °C).
In this work, different approaches to enhance the RT Li+ conductivity in LiBH4 are presented, such as halide substitution and oxide-LiBH4 composites synthesis. Firstly, the effect of the halogenation on the electrochemical properties in the LiBH4-LiBr-LiCl system has been investigated. The LiBH4-LiBr-LiCl ternary phase diagram has been determined at RT, showing that a ternary hexagonal solid solution containing chloride anion was stabilized at RT. The Li-ion conductivity has been enhanced by the LiBH4 halogenation and the insertion of the chloride decreases the weight of the electrolyte and hence increases the energy density.
Secondly, the effect of the mixture composition on Li-ion conductivity in the LiBH4-SiO2 system was analysed showing that a clear effect of the SiO2 volume fraction is present. In addition, different oxides were tested and all increased the Li-ion conductivity of the LiBH4, achieving the highest conductivities for the samples containing ZrO2 and MgO.
Finally, the possibility to have a synergetic effect between these two approaches has been highlighted.