Operando spatiotemporal reconstruction of surface thermo-mechanical fields in a lithium-ion pouch cell using a quasi-distributed fiber Bragg grating sensor network

Lithium-ion batteries exhibit complex thermo-mechanical behavior during operation, and the spatiotemporal evolution of temperature and strain is closely related to performance degradation and structural safety. However, existing sensing methods remain limited in achieving high-precision operando decoupled monitoring of multiple physical fields, restricting a deeper understanding of cell behavior under non-steady-state conditions. Here, an operando temperature–strain monitoring method for lithium-ion pouch cells is developed by combining a quasi-distributed fiber Bragg grating sensor (FBG) network and ordinary Kriging interpolation. The method enables spatiotemporal reconstruction of the surface temperature and strain fields and tracks their evolution during cycling and post-charge/discharge rest. Under 1C cycling, the cell surface shows pronounced thermo-mechanical non-uniformity: the positive-tab region emerges as the main hotspot during charging, whereas the geometric center exhibits the strongest strain response. Strain hysteresis appears after charging, which is mainly attributed to solid-state diffusion kinetics in the graphite anode, whereas the strain rebound in the later stage of post-discharge rest reflects the competition between lithium-ion redistribution and thermal contraction. These results demonstrate the feasibility of the proposed quasi-distributed FBG network as a cell-level operando thermo-mechanical characterization platform and provide a proof-of-concept basis for future spatially resolved operando monitoring of lithium-ion cells.