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

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.