Chloride molten salts are promising candidates for high temperature thermal storage applications, owing to their energy storage density and thermal stability. Nevertheless, the main disadvantage of them is their corrosive behaviour with metal containers, which narrows down the range of applications. Encapsulation is considered a favourable method to prevent the corrosion. In this work, composite thermal storage materials consist of a phase change material (PCM) and a encapsulation material are studied, where the PCM is a mixture of sodium and potassium eutectic salts and the encapsulation material is diatomite. The composite materials which consist of PCMs & encapsulation materials are fabricated using a micro encapsulation method which is a combination of mixing and sintering. After applying the aforementioned method, it is observed that the PCMs are distributed homogeneously in the composite materials. With the help of XRD, it is found that the compounds stay unchanged after the encapsulation process, which indicates that the materials are compatible to each other. In this study, the composite material containing 70 wt% PCM exhibits the most favourable thermal energy storage properties, stability and capsule integrity as it is shown that the latent heat of the aforementioned composite material is observed 179.3 J/g and no significant decline or salt leakage is found after hundreds of heating-cooling cycles.