Operando analysis of commercial battery cells: surface-scan MRI and plug-and-play multi-nuclear magnetic resonance spectroscopy

Abstract: Advancements in portable electrochemical energy storage devices rely on analytical tools capable of revealing the mechanisms behind the function and degradation of electrochemical materials in situ. Nuclear magnetic resonance (NMR) spectroscopy and imaging have shown exceptional sensitivity to local environments and dynamics of electrochemically relevant elements. The jelly roll architecture remains the most energy-efficient design used in battery cells, but a significant challenge for NMR lies in the limited penetration of radio frequency (RF) fields through conductive casings and current collectors. Two experimental approaches that enable in situ/operando analysis of commercial cells have been recently proposed.

Surface-scan Magnetic Resonance Imaging (MRI) is an operando method designed for the accurate detection of substandard battery cells and for monitoring electrochemical processes with high spatial and temporal resolutions. Intercalation-dependent magnetism and charge transfer processes in the cell's electrodes give rise to characteristic magnetic field patterns outside the cell. For accurate mapping of such patterns, we proposed the concept of a unilateral radio-frequency (RF) sensor, a flat thin resonator encapsulating a proton-rich solid-state detection medium. When the pouch cell is placed in direct contact with the sensor, the magnetic field patterns propagate inside the sensor's detection medium, and the corresponding spatial distribution of Larmor precession frequencies can be detected with MRI. The magnetic field map can show contributions originating from state-of-charge (SoC) dependent magnetic susceptibility variations and the coherent motion of charged particles in the cell. The proposed technology provides an ultimate sensitivity to a variety of battery degradation mechanisms (both mechanical and chemical) and is suitable for a high-throughput screening of large capacity pouch cells.

Plug & play NMR allows for direct RF wave transmission through the battery terminals, thus enabling efficient excitation and detection of signals from active electrochemical materials. A specialized RF adapter transforms the battery into an NMR probe tunable across a broad range of Larmor frequencies. This device offers detailed insights into the chemical environments of electrochemically active elements and introduces new metrics for accurately assessing states of charge (SoC) and health (SoH). Preliminary tests revealed electrochemical transformations between intercalated and metallic forms of charge carriers such as lithium (Li) and sodium (Na), along with bulk magnetic susceptibility effects in electrodes of commercial pouch cells. The magnetism of battery cell components is a sensitive indicator of electrodes' chemistry, SoC, SoH, current distribution, and defects.

Lab's webpage: https://iramis.cea.fr/en/nimbe/lsdrm/

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