Laser Scanning Method for High-Resolution Thickness Mapping of Lithium-Ion Pouch Cells

A precise understanding of the physical properties of lithium-ion cells including the cell thickness distribution during cycling and its connection with lifetime is important for cell improvement. A laser scanning instrument has been developed to perform contact-free thickness measurements in operando for small 250 mAh lithium-ion pouch cells and a large 60 Ah automotive format pouch cell. LiNi0.83Mn0.07Co0.10O2/silicon-graphite cells with 20 and 10 wt% micron-sized silicon particles, a LiNi0.8Mn0.1Co0.1O2/natural graphite cell, and a medium-Ni/graphite automotive cell were either cycled in the laser scanning setup with continuous operando thickness mapping or aged at elevated temperature on separate battery cyclers with intermittent operando thickness mapping using the new laser scanning instrument. During the operando cycles, the cell thickness was measured periodically every 1 h and a graphical quantification method was developed to determine reversible and irreversible swelling of the silicon-containing and silicon-free cells. Using the high-resolution laser scanning technique, irreversible cell swelling could be correlated with capacity loss, especially in cells with high silicon content. Graphite-based cells with mature interface like the large automotive pouch cell showed a fully reversible swelling profile indicative of a long-lived cell.