Tetraphenylethene-Containing Nanofilm via Interfacial Confinement Self-Assembly for Fluorescent Monitoring of SOCl₂ Leakage in a Li–SOCl₂ Battery Electrolyte

Lithium thionyl chloride (Li-SOCl₂) batteries are widely used due to their high energy density and long shelf life. However, the corrosive nature of SOCl₂ poses a safety hazard, necessitating effective leak detection methods. We report an approach for real-time fluorescent detection of SOCl₂ leakage in Li-SOCl₂ batteries using a tetraphenylethene-based nanofilm. The nanofilms were prepared through the interfacial confined self-assembly method and exhibit excellent flexibility, homogeneity, tunable size and thickness, and adaptability to various substrates, enabling easy integration into sensor devices. They possess high photochemical stability and a photoluminescence quantum yield exceeding 25%, demonstrating their potential as high-performance fluorescent sensing material. The nanofilms also exhibit high sensitivity, good reproducibility, and selectivity toward SOCl₂ detection. Upon exposure to SOCl₂ vapor, the nanofilm shows a red-shifted and fluorescence quenching response, attributed to the protonation of the acylhydrazone bond in the nanofilm by the hydrolysis product of SOCl₂, which disrupts the electronic structure of the nanofilm and leads to a decrease in the fluorescence intensity and a shift in the emission wavelength. A detection limit of ∼1.31 ppt and excellent repeatability over 300 cycles are demonstrated, highlighting their high sensitivity and reliability. This work paves the way for a highly sensitive and reliable leak detection system for Li-SOCl₂ batteries, enhancing their safety and reliability in various applications.