Solid‐State and Gel Electrolytes for Sodium‐Ion Batteries

One of the frontiers in the development of SIBs is to replace flammable organic liquid electrolytes with solid electrolytes to improve safety. However, several challenges, including inadequate ionic conductivity and poor stability of the interface between the electrode and solid electrolyte, have prevented the large-scale development of all-solid SIBs. This chapter provides an overview of the current advances of both solid polymer electrolytes and inorganic solid-state electrolytes for SIBs, with focuses on their structures, ionic conductivities, chemical/electrochemical stabilities, thermal stabilities, and electrochemical performances. Specifically, polymer solid electrolytes with different Na salts, as well as inorganic solid electrolytes, including beta-alumina, NASICON, sulfides, and complex hydrides with high Na + ion conductivity, are systematically discussed.