In Situ Analytical and Spectroscopic Characterizations of the Electrode-Electrolyte Interfacial Chemistry in Lithium-Ion Batteries with Next-Generation Electrodes
Authors: Tremolet de Villers Bertrand J. , Fink Kae , Yang Junghoon , Palmer Jack , Han Sang-Don 
Published: July 2021

Next-generation electrodes for rechargeable lithium-ion batteries (LiBs) promise higher energy and power storage at lower cost. For example, silicon has a theoretical capacity approximately 10 times higher compared to current state-of-the-art anodes based on graphite, 3580 mAhg-1 vs 372 mAhg-1, respectively.1 On the other side of the cell, it has been shown that increasing the Ni content in cathodes based on lithium nickel manganese cobalt oxide (LiNi1-x-yMnxCoyO2 or NMC) increases their specific capacity up to 280 mAhg-1.2, 3. Unfortunately, the improvements in energy storage provided by these next-gen materials is currently offset by their rapid degradation due to the undesirable (electro)chemical reactions, taking place at electrode surface in contact with a reactive liquid organic electrolyte, which form the unstable electrode-electrolyte interphase (EEI).2, 4-8 Understanding the complex reactions taking place in each phase, as well as the compositional, morphological, and structural formation and evolution of the EEI is essential to the development of mitigation strategies enabling longer battery life. Over the decades of battery R&D, many spectroscopic and analytical techniques have been developed to characterize the properties of battery components and understand cell capacity fade, but most often, these techniques are applied ex situ to a component of the battery that has been harvested from a disassembled cell after testing.9, 10 While informative, ex situ measurements cannot elucidate changes happening to the cell during testing, thus potentially failing to provide critical information about correlated processes underpinning the cell performance.
Here we present a summary of our recently-developed in situ Raman and FTIR spectroscopic techniques and in situ gas chromatography-mass spectrometry-flame-ionization detection (GC-MS-FID) analytical methods applied to custom battery cells under test11-13. By monitoring the EEI “in real-time” during cell charging and discharging cycles, we gain a better understanding of the critical mechanisms occurring near the electrode surfaces. For example, with our in situ FTIR spectroscopic methods, we have investigated the voltage dependent electrolyte solution structure changes at the interface, electrode changes correlated to redox chemistry, and the electrode/electrolyte interfacial layer evolution in LiBs employing high-Ni cathodes. In an electrochemical cell, gas evolution from electrolyte degradation is controlled by many factors, including the electrolyte’s physical and (electro)chemical properties, electrode compositions, and the applied stress to the cell (voltage, current, temperature, etc.), and we have used GC-MS-FID to elucidate mechanistic relationships between gas evolution/interface formation in novel Si-anode LiBs. Our various in situ cell designs provide both sensitive detection and reliable electrochemical device testing. Ultimately, we aim to develop in-situ gas analysis tools to be coupled with in situ spectroscopic techniques enabling a holistic understanding of the battery.
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