Recent Progress of Single‐Ion Conducting Polymer Electrolytes for Rechargeable Mono‐ and Multivalent Cation‐Based Metal Batteries

Lithium metal batteries (LMBs) have been extensively studied due to their high energy density; however, their practical application is limited by the scarcity of lithium resources. Emerging mono- and multivalent cation-based metal batteries offer promising alternatives that may overcome this limitation owing to their high abundance. Nevertheless, the development of these batteries using conventional liquid electrolytes (LEs) faces challenges such as safety concerns, parasitic reactions and dendrite formation. Replacing LEs with polymer electrolytes (PEs) can significantly improve battery safety and interfacial compatibility. Among various PEs, single-ion conducting polymer electrolytes (SICPEs) are particularly attractive due to their high cation transference numbers, flexibility, and easy processability. Despite this, systematic strategies for immobilizing anions across different battery systems remain insufficiently discussed and summarized. In addition, the design of SICPEs often depends on experimental trial and error, and the prevalent use of fluorine-containing components in their molecular structures raises significant environmental concerns. This review provides a comprehensive summary of strategies for developing anion-immobilizing SICPEs, highlighting the similarities and differences of different SICPEs for lithium and other emerging battery systems. Finally, we outline existing challenges and future research directions to inspire innovative solutions for tailoring SICPE properties and advancing their practical applications.