Synthesis and Characterization of Li₄(OH)₃Br for Thermal Energy Storage

The peritectic compound Li₄(OH)₃Br has been suggested as a candidate material for latent heat thermal energy storage (TES), due to its high calculated melting enthalpy (804 J g^–1) around 300 °C, however experimental reports have obtained much lower values (≤250 J g^–1). In this work, we show that the crystal structure established for Li₄(OH)₃Br in literature corresponds to a metastable hydrated compound, and instead propose that the thermodynamically stable phase belongs to the Pmnm space group. The hydrated phase dehydrates at ∼175 °C, rendering the exceptional previous predictions inapplicable. An experimentally measured melting enthalpy of 263 ± 3 J g^–1 is found for high-purity Li₄(OH)₃Br. Theoretical modeling is used to suggest a crystal structure for Li₄(OH)₃Br, from which a melting enthalpy of 260 J g^–1 is calculated, in good agreement with the experimental work, and supporting that nonetheless impressive storage capacity at ∼290 °C can be offered by Li₄(OH)₃Br.