One day of beamtime on GEM will be used to analyse the structure of a new superionic conductor composed of both mixed cations and mixed anions. The stability and ion conductivity in these phases is of interest to both the hydrogen storage and solid state battery communities. The lithium sodium borohydride is formed by partially substituting the hydrogen storage material NaBH4 with Li+ for Na+. The cubic structure (adopted by the parent NaBH4) is only stabilised, however by the co-substitution of a small amount of Br-. We will collect diffraction data for this compound at temperatures up to 325 °C in order to characterise the structure crystallographically for the first time. The requested beamtime will also provide information on the mechanism of formation of this phase and identify the role of the dopant ions in modifying the thermal stability of this material.