## 6 Conclusions  
This paper reports research carried out on the encapsulation of phase change materials for energy storage applications. Several requirements must be considered for selecting PCMs, such as the temperature of phase change transitions, density, and their associated enthalpies. The TES applications can be classified as high-, medium-, and low-temperature areas. In high-temperature applications, inorganic materials are the most used, while on the lower and medium side, organic materials such as commercial paraffin and fatty acids are employed. For practical use, microencapsulation techniques were employed to enhance the thermal properties of materials and limit leakage and contamination during application. The PCM microencapsulation methods were classified into three categories, i.e., (i) chemical, (ii) physical, and (iii) physicochemical ones. The choice of one of these microencapsulation techniques is not only based on the desired characteristics of the microcapsules, such as their size, core and shell materials, and thermal and mechanical properties, but also by taking into account the advantages and the drawbacks of the different processes. In recent years, research has focused not only on the development of more environmentally friendly processes and the choice of new materials for membrane synthesis but also on new functionalities. Thus, mPCMs have become multifunctional, where the membrane protects the active from the external environment, improves heat transfer, or provides a complementary activity to that of energy storage. These new functionalities are either brought by a modification of the PCMs formulation with notably the incorporation of additives or by new membranes, whether hybrid or multilayer. Thus, the development of multifunctional microcapsules extends application areas (e.g., pollutants degradation by photocatalytic activity, antibacterial for medical application, photoluminescence for thermosensitive and photosensitive sensors, etc.).  
The efficiency of thermal energy storage technology is strongly dependent on the cost-effectiveness of the technology and the selected raw materials. In the large-scale application of thermal energy storage, the essential areas are reducing the cost of storage materials and maintaining high energy storage efficiency. Thus, improving the thermal conductivity of thermal energy storage materials is a significant priority. Therefore, our future study will focus on optimizing the thermophysical properties of PCMs and investigating conductor materials that improve the heat transfer and stabilize the shape of PCMs. In addition, exploring the cost-effectiveness of microencapsulated PCMs manufacturing technologies will be beneficial and contribute significantly to the future direction of phase change materials research.  
**Author Contributions:** Conceptualization, all authors; methodology, F.S. and G.B.H.; validation, all authors; formal analysis, all authors; investigation, all authors; resources, all authors; data curation, all authors; writing--original draft preparation, G.B.H.; writing--review and editing, G.B.H. and F.S.; visualization, F.S.; supervision, F.S.; project administration, Z.Y. and H.N.; funding acquisition, Z.Y. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by \"JUNIA-Hautes etudes d'ingenieur (HEI)\", the \"Hauts de France\" region and PROSPA group, CACCTHESE HEI_PROSPA_10012019.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** The authors are thankful for the technical support from Ensait, Gemtex-Laboratoire de Genie et Materiaux Textiles.  
**Conflicts of Interest:** The authors declare no potential conflicts of interest regarding authorship and/or publication of this paper.