Structure and formation mechanism of polymer byproducts in vinyl carbonate synthesis

Vinyl carbonate (VC) is a crucial film-forming additive for lithium-ion batteries, but its low industrial yields remain a significant challenge. This study investigated the causes of low yield by analyzing the structure and formation mechanism of polymer byproducts. Characterization, which included attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy, gas composition analysis, elemental analysis, 13C solid-state NMR spectroscopy, and 1H NMR spectroscopy, revealed that triethylamine (TEA)-initiated polymerization was a major contributor to the low yield. These polymer byproducts exhibited structural similarities to those constituting the solid–electrolyte interface (SEI) film reported in the literature, containing structural units such as cyclic carbonate, C–O, and O–C–O moieties. Density functional theory (DFT) calculations indicated that the chain initiation featured a termolecular reaction of TEA with two VC molecules. During chain propagation, intramolecular backbiting reactions drove decarboxylation, producing C–O and O–C–O structural units. This study not only provides important guidance for the synthesis of VC but may also offer theoretical insights into the formation mechanism of the SEI film.