Non-flammable electrolytes for high-safety sodium-ion batteries

Sodium-ion batteries (SIBs) have emerged as strong candidates for next-generation electrochemical energy storage systems due to their high resource abundance and low cost. However, traditional SIBs rely on flammable organic liquid electrolytes (LEs), which are prone to battery fires and explosions under abusive conditions, hindering the wide application of SIBs. The frequent occurrence of battery safety incidents is closely related to the properties of the electrolytes, which has driven the development of non-flammable electrolytes. This review summarizes the recent developments in non-flammable electrolytes for SIBs. Firstly, the electrolyte system of SIBs is briefly summarized. Then, a comprehensive discussion of the flame-retardant mechanisms of non-flammable and flame-retardant solvents to guide the design of non-flammable electrolytes is provided. Afterward, the development of non-flammable LEs is reviewed, including organic non-flammable electrolytes, aqueous electrolytes, and ionic liquid electrolytes. For non-flammable solid-state electrolytes, we summarize the characteristics of inorganic solid-state electrolytes, polymer solid-state electrolytes, and composite solid-state electrolytes. Lastly, the critical importance of non-flammable electrolytes in SIBs is underscored and the potential research directions and remaining challenges for the next generation of intrinsically safe SIBs are outlined. This review offers a valuable reference for scientific and practical issues to promote the development of advanced SIBs.