Mechanistic Understanding of Additive Reductive Degradation and SEI Formation in High-Voltage NMC811||SiOx-Containing Cells via Operando ATR-FTIR Spectroscopy

Weiling, Matthias; Lechtenfeld, Christian; Pfeiffer, Felix; Frankenstein, Lars; Diddens, Diddo; Wang, Jian-Fen; Nowak, Sascha; Baghernejad, Masoud

Abstract

The implementation of silicon (Si)-containing negative electrodes is widely discussed as an approach to increase the specific capacity of lithium-ion batteries. However, challenges caused by severe volume changes and continuous (re-)formation of the solid-electrolyte interphase (SEI) on Si need to be overcome. The volume changes lead to electrolyte consumption and active lithium loss, decaying the cell performance and cycle life. Herein, the additive 2-sulfobenzoic acid anhydride (2-SBA) is utilized as an SEI-forming electrolyte additive for SiOx-containing anodes. The addition of 2-SBA to a state-of-the-art carbonate-based electrolyte in high-voltage LiNi0.8Mn0.1Co0.1O2, NMC811||artificial graphite +20% SiOx pouch cells leads to improved electrochemical performance, resulting in a doubled cell cycle life. The origin of the enhanced cell performance is mechanistically investigated by developing an advanced experimental technique based on operando attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy. The operando ATR-FTIR spectroscopy results elucidate the degradation mechanism via anhydride ring-opening reactions after electrochemical reduction on the anode surface. Additionally, ion chromatography conductivity detection mass spectrometry, scanning electron microscopy, energy dispersive X-ray analysis, and quantum chemistry calculations are employed to further elucidate the working mechanisms of the additive and its degradation products.