Enhancing Ionic Conductivity in In Situ‐Polymerized Solid‐State Sodium Metal Batteries

ABSTRACT Solid‐state sodium metal batteries (SSMBs) are promising for next‐generation large‐scale energy storage due to their low cost and high safety. Polymer electrolytes (PEs) fabricated via in situ polymerization offer distinct advantages such as facile processing, excellent interfacial contact, and compatibility with existing battery manufacturing processes, garnering significant attention. Despite the promising application prospects, the ionic conductivity of most in situ polymerized PEs remains relatively low, especially at room temperature, which severely limits the performance of SSMBs. Herein, as a complement to the existing reviews, a deep understanding of the ion transport mechanism and identification of key influencing factors are provided for advancing the practical application of in situ polymerized PEs. This review comprehensively examines the fundamental principles, conduction mechanisms, influencing factors, and evaluation methods related to ion transport in in situ polymerized PEs. This is followed by a critical summary of the recent advances in in situ polymerization strategies for SSMBs, with an emphasis on the role of electrolyte components in enhancing ionic conductivity, including monomer design as well as the incorporation of various additives and inorganic fillers. Furthermore, we propose some practical optimization strategies to offer valuable insights for the development of in situ polymerized PEs and high‐performance SSMBs.