Operando FTIR Characterization of Interphases from Organosulfur Electrolytes in High Voltage Lithium-Ion Batteries

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The widespread adoption of renewable energy storage technologies like electric vehicles and grid storage largely relies on the improvements of the energy density of the batteries inside those devices. Lithium-ion batteries (LIBs) are typically used for these applications due to their high energy density,[1] but the operating voltage of LIBs is limited by the electrochemical stability windows of the electrolyte. Resistive interphase layers form as a result of the breakdown of electrolyte molecules and limit LIB cycling stability. However, there is significant difficulty in the study and characterization of both the components and structure of the electrode-electrolyte interphases formed via electrolyte degradation.[2] Traditional characterization techniques provide information on what the interphase layers look like after cell disassembly, but sample preparations are difficult and destructive.[3] Therefore, it is crucial to develop in operando techniques to better understand the relationship between the interphase layers and battery performance.In this work, we develop a custom surface-enhanced infrared absorption spectroscopy in the attenuated total reflectance mode (ATR-SEIRAS) setup for in operando studies of the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) in organosulfur electrolyte systems. Organosulfur molecules are potential components for high voltage LIBs due to their excellent performance.[4] We apply our custom ATR-SEIRAS setup to study ethyl methyl sulfone (EMS) containing electrolytes and propose possible reduction routes with the help of ex situ and postmortem characterization techniques. We study both SEI and CEI formed and correlate favorable interphase components with contributing molecules to identify important functional groups for novel molecular design. The work provides an opportunity to elevate our understanding of currently elusive electrochemical phenomena like the structure-reactivity relationships of SEI and CEI, and why certain sulfone systems outperform other formulations. Furthermore, it will provide molecular design principle for electrolyte systems in high performing and high voltage LIBs.References S. Chu, Y. Cui, and N. Liu, Nat. Mater., 16, 16–22 (2017).H. Wan, J. Xu, and C. Wang, Nat. Rev. Chem., 8, 30–44 (2024).A. Dopilka, Y. Gu, J. M. Larson, V. Zorba, and R. Kostecki, ACS Appl. Mater. Interfaces, 15, 6755–6767 (2023).M. A. Dato et al., Adv. Energy Mater., 2303794 (2024).