Spiropyran‐Based Luminescent Polymer Artificial SEI for Interphase Visualization and High‐Performance Lithium Metal Batteries

Ester‐based electrolytes offer high ionic conductivity but suffer from insufficient stability against lithium metal, leading to continuous electrolyte decomposition and lithium dendrite growth. This study proposes the design and construction of a luminescent polymer P‐FMA as an artificial solid electrolyte interphase (SEI) for lithium metal anodes. Integrating a unique spiropyran‐derived fluorescent moiety, fluorine‐containing groups, and flexible methoxyethoxy segments, the polymer features dual functional advantages: the spiropyran fluorescent moiety provides an optical readout associated with the evolution of the electrode‐electrolyte interface through its fluorescence response; meanwhile, the fluorine‐containing groups facilitate the formation of a LiF‐rich SEI layer with high mechanical strength and ionic conductivity, while the flexible methoxyethoxy segments optimize interfacial compatibility. Collectively, these functional components synergistically regulate lithium‐ion deposition behavior and effectively suppress lithium dendrite growth. The Li||Li symmetric cells assembled with P‐FMA@Li anodes exhibited stable cycling for over 1200 h at 1 mA cm −2 and 1 mAh cm −2 in carbonate‐based electrolytes. Additionally, P‐FMA@Li||LiFePO 4 full cells retained 82.2% of the initial capacity after 480 cycles, demonstrating significantly improved cycling stability and electrochemical performance compared to bare lithium anodes. This work provides a novel strategy for developing intelligent SEI materials that combine interface visualization with performance enhancement.