In situ NMR spectroscopy of batteries enables fundamental electrochemical investigations. In situ NMR spectroscopy can also be used for applied investigations of batteries, such as tracking degradation products during cycling and calendar aging. These applied studies are best performed on realistic and high-fidelity battery cells as slight modifications in cell construction can alter degradation routes in surprising ways. We use specialized radio frequency (RF) probes in the “skimming” configuration to perform studies on coin cell batteries with metal casings [1]. Counterintuitively, spectra of solutions are often broader than solid components in coin cell batteries, as the solutions squeeze throughout the cell and experience a more varied magnetic field in the metal case. We show that heteronuclear multidimensional correlation techniques and processing can reduce these linewidths by up to 100x. This resolution improvement coupled with other sensitivity enhancement schemes enables us to track the evolution of trace amounts of fluorophosphate degradation products in aging silicon-anode based batteries. At the heart of these methods are dual-channel broadband heteronuclear correlation pulse sequences. The correlation methods are built using new pulse elements containing six adiabatic inversion pulses, called SCRAM blocks, that enable broadband and arbitrary coupled spin evolution. Sandia National Laboratories is managed and operated by NTESS under DOE NNSA contract DE-NA0003525
1. Walder, B. J. et. al. Sci Adv 2021, 7 (37) DOI: 10.1126/sciadv.abg8298