Recent Progress on In Situ Polymerized Electrolytes for Lithium‐Ion Batteries

Rechargeable lithium batteries, including lithium-ion batteries, lithium metal batteries, and lithium-sulfur batteries, face significant safety concerns such as electrolyte leakage, flammability, and explosion when using conventional organic liquid electrolytes. Therefore, developing high-safety polymer electrolytes (PEs) is an urgent necessity. From the perspective of the preparation process, PEs fabricated via the solution-casting method or blade-casting process often suffer from poor solid/solid interfacial contact between the PEs and electrodes. This issue leads to high interface impedance and degraded cell performance. Compared to other methods, the in situ polymerization strategy is particularly advantageous for achieving excellent interfacial contact between the PEs and electrodes. This approach significantly reduces the interfacial resistance and efficiently promote Li-ion transport. This review aims to provide a comprehensive summary of the in situ polymerization processes, including free-radical polymerization, ion-initiated polymerization, as well as the materials involved, such as backbone materials, monomers, lithium salts, and initiators. Through this analysis, the review highlights how these processes can be optimized to improve the safety performance and achieve good interface stability between the PEs and electrodes. Additionally, this review evaluates the challenges and development trends of in situ polymerized electrolytes for high safety lithium batteries in the future.