Fiber Bragg Grating Array-Based Synchronous Monitoring of Spatiotemporal Surface Temperature–Strain Fields in a 314 Ah Energy Storage Battery

Lithium-ion batteries undergo coupled thermal and mechanical responses during operation, which are closely related to their safety and reliability. However, simultaneously monitoring the surface temperature and strain fields of large-format prismatic batteries remains challenging. In this study, a fiber Bragg grating (FBG) array-based dual-parameter sensing system was developed to synchronously measure the temperature and strain of a 314 Ah lithium iron phosphate battery during charge–discharge cycling under different power conditions. Continuous surface temperature and strain fields were reconstructed from the measured data to investigate their spatiotemporal evolution. The results reveal significant differences between the temperature and strain distributions as well as asynchronous dynamic responses. Spatially, with increasing power, temperature hotspots shifted toward the central region, whereas strain extrema migrated toward the positive electrode side, revealing distinct spatial heterogeneity in the thermo-mechanical response. Temporally, the strain extrema consistently appeared tens to hundreds of seconds earlier than the temperature peaks. These findings provide direct experimental evidence of the thermo-mechanical coupling behavior of large-capacity lithium-ion batteries, establish baseline temperature–strain distributions under normal operating conditions, and offer valuable guidance for battery state evaluation, thermal management, and early fault diagnosis.