Ionic conductivity in complex hydrides for energy storage applications: A comprehensive review

In recent years, complex hydrides have been extensively studied for energy storage and conversion applications. In particular, the possibility of using this class of materials as solid ionic electrolytes is attracting increasing interest. This review aims at providing a comprehensive overview of ionic conduction in complex hydrides containing various monovalent (Li+, Na+, and K+) and multivalent (Mg2+) ions. Possible approaches to enhance the ionic conductivity of complex hydrides such as ionic substitution, nanoconfinement, interface engineering, and composite formation are highlighted, and the associated conduction mechanisms are discussed. The use of complex hydrides as solid electrolytes for electrochemical conversion and storage applications is then reviewed, including potential applications, challenges, and our perspectives. Finally, the relationship between ionic conduction and hydrogen sorption properties of complex hydrides is briefly discussed.