Full-field experimental characterization of charging-induced swelling in lithium-ion pouch cells using surround digital image correlation

Lithium plating is a major degradation mechanism in lithium-ion cells influenced by local pressure, rate- and state-of-charge. In this work, heterogeneous plating in 4 Ah graphite/LiCoO2 pouch cells is investigated using surround three-dimensional digital image correlation (DIC), enabling full-field measurements of in-plane strain and thickness evolution on both faces during charging. Cells are charged using CC–CV protocols at 0.5C, 1.0C, and 1.5C under unconstrained conditions and constant compressive loads of 0.026 MPa and 1 MPa. Full-field thickness maps reveal an early onset of heterogeneous swelling with increasing charge rate, showing strain localization at cell edges and center. The maximum swelling overshoots during the CV/rest stages followed by partial relaxation, consistent with plating and stripping, whereas a plateau region of low-variance strain accompanies intercalation-dominated swelling. At 1.5C, strain relaxation is observed over essentially the full surface, indicating widespread plating, while most of the surface remain within the plateau regime at lower charge rates. Applying ∼1 MPa pressure reduces the plating-associated contribution, yielding thickness evolution close to the plateau strain at low charge rate. These results demonstrate that surround DIC provides a direct, high-throughput route to spatially resolve lithium plating in pouch cells and quantify how mechanical constraint mitigates plating-induced swelling. • Surround 3D DIC enables full-field thickness mapping in pouch cells during charging. • Heterogeneous swelling is observed with localization at the cell's edge and center. • CV/rest stages show swelling overshoot increasing with C-rate implying Li stripping. • Mechanically constrained charging shows lower swelling and hence reduced plating.