Large-Molecule Decomposition Products of Electrolytes and Additives Revealed by On-Electrode Chromatography and MALDI

The solid-electrolyte interphase (SEI) produced by the decomposition of electrolyte has critical impact on battery performance. However, the precise makeup of SEI, including the composition of organic and polymeric species, is one of the least understood aspects of lithium-ion batteries. Here, we probe SEIs using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) assisted by on-electrode chromatography. On-electrode chromatography utilizes the electrode itself as the stationary phase for fractionating the molecules on the electrode surfaces, thus realizing separation of different molecular species prior to MALDI analysis. This strategy has proven important for effective MALDI measurements of SEI components directly on the electrode surfaces. With on-electrode chromatography, large-molecule decomposition products of carbonate electrolytes containing vinylene carbonate and methacrylate additives are unambiguously illustrated in each case with clear structure assignment. This work provides a simple, powerful, and universal solution for the identification of the organic components in SEIs.