Research progress of electrolytes for aluminum-ion batteries

Aluminum-ion batteries are considered as an attractive candidate for "post-lithium" energy storage system due to their low cost of raw materials, high theoretical capacity of aluminum metal anode, and high safety of the whole battery system. At present, more researches for aluminum-ion batteries are focused on the cathode materials. However, as an important component, the electrolyte plays a crucial role in electrochemical performance and safety of aluminum-ion batteries, no matter in liquid or solid-state systems. In recent years, there is a rapid increase of research reports on electrolytes for aluminum-ion batteries. Herein, this paper reviewed the research progress of electrolytes for aluminum-ion batteries, including aqueous electrolytes and non-aqueous ionic liquid, inorganic molten salt, and gel polymer electrolytes. Furthermore, the advantages and disadvantages of different electrolyte systems in the aspect of electrochemical window, stability, operating temperature conditions, ionic conductivity and cost were discussed. Finally, some prospects of the future development direction were put forward in this paper.