This work investigates structural changes and macroscopic expansion in a commercial lithium-ion cell under operando conditions. Synchrotron X-ray diffraction (XRD) and interferometric dilatometry are combined to study the relationship between electrochemical processes and mechanical cell deformation during cycling.

A commercial LiFePO₄/graphite cell was studied under controlled temperature and constant mechanical pressure. Structural measurements were performed at the PETRA III synchrotron (DESY) using high-resolution XRD, while cell current, voltage, and temperature were recorded simultaneously. In parallel, cell thickness changes were measured using a high-precision interferometric dilatometer.

The results reveal a clear dependence of structural phase evolution on temperature and current rate. In particular, the LiC₆ phase appears at lower states of charge at low temperatures and high C-rates. This early phase formation correlates with a broadened macroscopic cell expansion during charging.

These observations indicate inhomogeneous lithium intercalation in the graphite anode and demonstrate that macroscopic expansion effects are directly linked to microscopic structural changes in the electrode material.