Filling the gaps in the LiBr-LiOH phase diagram: a study on the high-temperature Li3(OH)2Br phase

In this paper we build on previous work to characterise a new phase with stoichiometry Li3(OH)2Br existing between ∼225 degC and ∼275 degC in the LiBr-LiOH phase diagram. Diffraction studies indicate that the phase takes a hexagonal unit cell, and theoretical mod- elingisusedtosuggestapossiblecrystalstructure. Nuclearmagneticresonancespectroscopy and electrochemical impedance spectroscopy measurements demonstrate excellent lithium- ion dynamics in this phase, with an ionic conductivity of 0.12 S/cm at 250 degC. Initial attempts to stabilise this phase at room temperature through quenching were not successful. 1 Instead, a metastable state demonstrating poor lithium-ion conductivity is found to form. This is an important consideration for the synthesis of Li2OHBr solid-state electrolytes (also found in the LiBr-LiOH phase diagram) which are synthesised by cooling through phase fields containing Li3(OH)2Br, and are hence susceptible to these impurities.