Mechanisms elucidation of secondary seawater batteries: From ion migration to conversion for sustainable energy storage

• Comprehensive surveyed the current secondary seawater batteries (SSWBs) with various underlying working mechanisms. • Categorized the current SSWBs into two major types, internal ion-migration type and interfacial substance-conversion type. • Discussed and summarized the latest progress and design strategies of various types of SSWBs. • Provided an overview on the applications of SSWBs, especially in terms of large-scale applications. • Concluded the current challenges and outlook the future development of SSWBs. Secondary seawater batteries (SSWBs) are cost-effective, safe, and sustainable alternatives to lithium batteries, suitable for various energy storage applications. Despite the considerable advancement of high-performance SSWBs, the increasing diversity in SSWB types as the technology progresses has introduced new challenges to achieving further improvements in performance. This review categorized various types of SSWBs by dividing them into two primary types based on the redox mechanisms on their cathode, internal ion-migration type and interfacial substance-conversion type, and systematically covers recent advancements in design strategies of the anode and cathode that enhance the overall performance of SSWBs, including their capacity, energy density, and cycle life. We delve into the fundamental principles underlying these mechanisms, elucidating the intricate process involved in energy conversion and storage with these types of SSWBs. Current and future applications of SSWBs are subsequently discussed. At last, the challenges and prospects of SSWBs are addressed, highlighting the needs for ongoing research to realize their full potential in sustainable energy future.