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

• Published in: Advanced energy materials Vol. 14; no. 5
• Main Authors: Weiling, Matthias, Lechtenfeld, Christian, Pfeiffer, Felix, Frankenstein, Lars, Diddens, Diddo, Wang, Jian‐Fen, Nowak, Sascha, Baghernejad, Masoud
• Format: Journal Article
• Language: English
• Published: 02.02.2024
• Subjects: 2‐sulfobenzoic acid anhydride; lithium‐ion batteries; operando ATR‐FTIR spectroscopy; silicon oxide; solid‐electrolyte interphase
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.202303568

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. This study introduces 2‐Sulfobenzoic acid anhydride as an effective SEI‐forming additive for high‐voltage NMC811||AG+20% SiOx lithium‐ion battery cells. The additive implementation improves the electrochemical performance, resulting in a significantly longer cell cycle life and accumulated specific energy. An operando ATR‐FTIR setup is developed to gain a mechanistic understanding of the SEI formation. By combining results of operando, ex‐situ, and post‐mortem investigations with theoretical calculations, multiple reaction mechanisms for additive degradation are presented.