In Operando Evaluation of Heterogeneity Development in Fast-Cycled Single-Layer Pouch Cells

Investigating Li-ion batteries during high current rates is becoming increasingly important to advance fast charging of electric vehicles. Here, we use a state-of-the-art synchrotron instrument and detector to measure spatially resolved X-ray diffraction in operando on single-layer pouch cells at 1C and 3C. Using batch refinement on the hundreds of thousands of obtained diffractograms, the electrode lithiation inhomogeneity across the cells induced by cell cycling could be probed. The inhomogeneity was found to depend significantly on C-rate, and the cells were generally more electrochemically active in the center than close to the edges. At high current rates, the expected sequence of lithiated stages in the graphite anode was found to no longer hold. Areas of the electrodes were also found to behave very differently from others, probably due to local differences in resistance. These behaviors are detectable only at high C-rates using in operando methods. Using the methods developed in this work allows for investigating pouch cells that are close to commercial sizes.