Development of a NMR Device Adapted to Operando Analysis of Electrochemical Commercial Cells

Abstract

NMR (Nuclear Magnetic Resonance) spectroscopy is a common analytical technique for analysing electrode materials. Most of these analyses are ex situ NMR measurements, a post mortem analysis of the cell. Yet, development of in situ and operando NMR considerably increased. Since the first in situ measurement reported by Gerald et al [1] in 2000, a large variety of operando NMR approaches have been developed and applied to batteries [2–5].Two levers of improvement remain for operando NMR: the battery-casing design, usually home-made, and the geometry of the NMR resonator used to detect the spectrum.Battery-casing goes from flexible cells in a clear pouch to capsule, Swagelok or coin cells. Home-made casings are usually used to avoid distortion and sensitivity loss in the NMR measurement, attributed to the conductive casings. Another way of improvement is the type of NMR resonator to fit a larger variety of cell geometries. Solenoids, saddle coil, hairpin coil or parallel plates are currently used.Electrochemistry is sensitive to cell fabrication, so home-made cells are intrinsically less reproducible than commercial cells. To increase the repeatability for a higher number of cycles and from one cell to another, we collaborate with a cell maker to get industrial pouch cells and we use commercial protocols. Nevertheless, studying such cells implies new challenges. First, strong and controlled pressure must be applied on the cell. An innovative pressure system was created to be compatible with the NMR requirements, mainly low available space and the absence of magnetic or strongly paramagnetic materials. It also involved adapting the resonator to the commercial cell geometry. The second challenge is the attenuation and distortion of the NMR signal by conductors (skin effect for radio-frequency fields).Recently, Walder [6]. arose our interest with their report on operando NMR measurement for a stainless steel coin cell. We will present measurements that quantify the influence of the components of a commercial battery (casing material, electrodes, current collector and number of stacks).This development and these measurements will lead in close future to performing operando NMR of commercial cells in fast charging conditions (for example on silicon Li-ion batteries).[1] R. E. Gerald et al., J. Power Sources 89, 237 (2000).[2] X. Liu et al., Adv Mater 33, 2005878 (2021).[3] O. Pecher et al., Chem. Mater. 29, 213 (2017).[4] K. Gotoh et al., J. Mater. Chem. A 8, 14472 (2020).[5] K. J. Sanders et al., Carbon 189, 377 (2022).[6] B. J. Walder et al., Sci. Adv. 7, eabg8298 (2021).