  Untangling the relationship between reactions, mass transfer, and temperature
within lithium-ion batteries enables control approaches that mitigate thermal
hot spots and slow degradation. Here, we develop an efficient physics-based
pouch-cell model to simulate lock-in thermography experiments, which
synchronously record the applied current, cell voltage, and surface-temperature
distribution. Prior modelling efforts have been confounded by experimental
temperature profiles whose characteristics suggest anisotropic heat conduction.
Accounting for a multiscale coupling between heat flow and solid-state
diffusion rationalizes this surface-temperature nonuniformity. We extend an
earlier streamlined model based on the popular Doyle--Fuller--Newman theory,
augmented by a local heat balance. The reduced-order model is exploited to
parametrize and simulate commercial 20 Ah lithium iron phosphate (LFP) cells at
currents up to 80 A. This work highlights how microscopic intercalation
processes produce distinctive macroscopic heat signatures in large-format
cells, as well as how heat signatures can be exploited to fingerprint material
properties.
