Current estimates predict that over half of the generated thermal energy is lost as process heat. Hence, in order to reduce heat loss and to increase the overall system efficiency, there is an urgent need for materials which are capable of capturing and storing thermal energy at temperature levels adapted to the respective conversion process. Established and widely-used materials for this purpose include metal-salt hydrates and paraffins. To facilitate the capture and release of thermal energy, these materials rely on solid-to-liquid phase transitions for latent heat storage on the scale of 10 4 -10 5 J/kg. A major design target of such phase change materials (PCMs) is the accessible temperature window. Drawbacks and limitations include their cycling stability, toxicity, and corrosivity. Furthermore, the rate dependence and supercooling propensity are factors which affect the practical applicability of a solid-to-liquid PCM. As a possible alternative, metal-organic PCMs were recently introduced for thermal energy storage applications, based on coordination compounds forming hydrogen-bonding networks similar to metal-salt hydrates. These materials exhibit reversible melt-to-crystal phase transitions for a couple of cycles, with a volumetric latent heat storage capability comparable to that of soft paraffins. However, the current metal-organic PCMs, metal-salt hydrates, paraffins and other PCMs based on solid-liquid transitions underlie practical constraints in terms of geometrical stability and liquid handling. In many cases, these materials therefore require support structures, blending, or carrier confinement. Alternatively, solid-solid or other shape-preserving phase transitions often exhibit significantly lower latent heat capacity. Hybrid PCMs based on an IL@MOF composite for solid-state latent heat storage are a promising alternative to overcome these limitations. We combine in situ structural and thermal characterization to explore and quantify the nature of reversible phase transformations in this IL@MOF material during cyclic heating. Both the IL, [EMIM][TFSI], and the MOF, CuBTC (also known as HKUST-1: Hong Kong University of Science and Technology 1, and Basolite® C300, comprising copper and BTC: benzene-1,3,5-tricarboxylate), are widely used compounds. They are commercially available and produced on large scale, facilitating implementation of the IL@MOF composite approach on a larger scale.