Mechanistic Mapping of Additive Cracking for Hybrid SEI Construction in Aqueous Zinc‐Ion Batteries

ABSTRACT Electrolyte additives represent a promising strategy for regulating the solid‐electrolyte interphase (SEI) in aqueous zinc‐ion batteries. However, the underlying molecular mechanisms by which these additives mediate SEI formation remain insufficiently understood. Here, we employ 1‐acetyl‐2‐pyrrolidone (APD) as a model organic additive to mechanistically map molecular cracking pathways involved in constructing a robust SEI on zinc anodes. Using in situ synchrotron radiation vacuum ultraviolet photolysis mass spectrometry (SR‐VUPM), for the first time, we reveal the dynamic cleavage process of the additive to form a hybrid SEI. The in situ synchrotron radiation X‐ray diffraction and Fourier transform infrared spectroscopy further indicate that the resulting hybrid SEI serves as a hydrophobic barrier and regulates the uniform deposition of zinc. The functional SEI plays a crucial role in optimizing interfacial reaction kinetics and deposition/stripping reversibility. As a result, the Zn/Zn symmetric cells deliver over 1500 h at 5.0 mA cm −2 and 5.0 mA h cm −2 . The cycle life of the Zn/I 2 @AC full battery is extended to 6000 cycles, while the optimized pouch cell also displays excellent cyclic stability. These findings provide mechanistic insight into additive‐derived SEI formation for developing durable metal anodes.