Polymeric Species in Solid Electrolyte Interphase Identified with MALDI-TOF-MS Assisted By on-Electrode Chromatography

Abstract

The solid electrolyte interphase (SEI) is a passivating layer on the electrode surface produced by decomposition of the electrolyte, which has key impact on the battery’s long-term cycling performance. The inorganic species in SEIs have been extensively investigated but the organic SEI components, especially the polymeric molecules, often remain a mystery partially due to the difficulties in identifying these organics of small to trace quantities in a complicated chemical environment. Here, we propose matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for detection of organic and polymer species in SEIs. MALDI is suitable for characterization of organic and polymer molecules at trace amount but is inconvenient to couple with chromatography methods for separation of the analytes. Therefore, on-electrode chromatography is introduced for fractionating different species on electrode surfaces, where the electrode itself serves as the stationary phase to realize separation upon solvent elution. This strategy has proved indispensable for effective MALDI characterization of organic species in SEIs. High-mass polyethylene oxide (PEO) and polymethacrylate molecules have been identified as electrolyte and additive decomposition products. The combination of MALDI-TOF-MS and on-electrode chromatography methods presents a promising strategy for identification of the organic and polymeric species in SEIs.