Long-run in-operando NMR to investigate the evolution and degradation of battery cells

Nuclear magnetic resonance (NMR) investigations of electrochemical systems require gas-tight and non-metallic cell housings. This contribution reports on the development and evaluation of a cylindrical battery container in combination with a numerically optimized saddle coil that is suitable for NMR investigations of battery cells over hundreds of charge-discharge cycles. The reliability of the new cell container design and its long-time gas-tight sealing are shown by rate capability comparisons to standard housings with LiCoO$_{2}$ (LCO) vs. Li-metal electrodes as well as a charge-discharge experiment of a LCO vs. graphite batteries over more than 2000 hours. To demonstrate the performance of the entire NMR setup, long-run in-operando measurements on a Li-metal vs. graphite cell are presented. The NMR data reveal the formation and evolution of mossy and dendritic Li microstructures over a period of 1000 h. Analyzing the measured rate of microstructure growth could help to identify dendrite mitigation strategies, such as enhanced cell pressure or additives, and could enable a method for battery lifetime prediction.