Metal-organic frameworks and zeolite materials as active fillers for lithium-ion battery solid polymer electrolytes

The efforts to decarbonize the economies, with particular focus on renewable energies, must be accompanied by the development of more efficient and environmentally friendlier energy storage systems. In this context, all solid-state batteries emerge as one of the most promising candidates for this purpose due to their potentially higher energy density and improved safety with respect to conventional systems. With this objective, the development of solid electrolytes, with high ionic conductivity and low interfacial resistance, is a critical step to achieve the needed performances of all solid-state batteries. The three-component approach for composite solid polymer electrolytes (SPEs), which relies on the use of one polymer and two complementary fillers, attracted a great interest in recent years, due to the possibility of incorporating different fillers to impart simultaneously distinct properties to the SPEs, such as enhanced ionic conductivity and improved mechanical stability. Microporous materials are an effective option for application in this technology, due to their thermal and mechanical stability, as well as their tuneable structure, high porosity and surface area, which make them suitable materials to adsorb and encapsulate other components. In this work, the main advantages and disadvantages of SPEs are discussed, together with the critical issues to be addressed in the near future, namely the low room temperature ionic conductivity and the interfacial compatibility issues. Some solutions are proposed, with special focus on microporous materials, particularly metal-organic frameworks (MOFs) and zeolites. Their main properties and advantages for application in this field are presented. A comprehensive state-of-the-art of this exciting topic of research is also provided, highlighting the most recent advances in the area.