Pressure‐Induced Degradation Effects in Large‐Format Lithium‐Ion Pouch Cells

The electrochemical aging of large-format pouch cells (LG E78 type) is systematically studied under varying external pressure. The cells are cycled at high current while combining reference performance testing, direct current internal resistance measurements, and temperature monitoring to track the degradation. Further synchrotron-based powder X-ray diffraction radiography measurements of the cells are carried out in a fresh and aged state, resolving the spatial lithium concentration in the graphite anodes and NMC cathodes. Cycling under external pressure strongly influences cycling stability, resistance evolution, and thermal behavior. Without pressure, the tested cell shows the highest initial depth-of-discharge (DOD) but rapid capacity fade, accelerated resistance growth, and elevated temperatures. Under pressure, the cells exhibit longer lifetimes and improved heat dissipation but also show pressure-induced ionic transport limitations and pronounced lithiation inhomogeneities, including a ring-like lithium distribution linked to electrolyte redistribution and pore size reduction. It is shown that reduced pressure emerged as the most favorable compromise, balancing structural stability, lithium homogeneity, and cycle life.