Heat-generation estimation in a cylindrical lithium-ion cell using direct heat-flux measurements, inverse thermal and electrochemical models

Reliable quantification of heat generation in lithium-ion batteries remains challenging, especially under realistic cycling conditions where calorimeters are impractical and thermal models depend on uncertain boundary conditions. This study presents a time-resolved method to quantify the heat released by a 5 Ah commercial NMC811/G–Si cylindrical cell using a calibrated heat-flux sensor covering the lateral surface. A dedicated calibration campaign using a custom cylindrical resistor enabled determination of the Measured Heat-Flow Ratio (MHFR), allowing conversion of local heat-flux measurements into total heat output. To assess the robustness of this approach, two additional heat-generation estimates were obtained independently: one from an inverse lumped thermal model using an experimentally identified overall heat capacity of 61 J K − 1 and an external thermal resistance that decreased from 12 . 47 K W − 1 at 1C to 10 . 97 K W − 1 at 2C under natural convection, and another from an electrochemical model incorporating a pseudo-OCV curve measured at C/50 and an entropy-coefficient profile. All three methods were applied to the same cell across C-rates of 1C, 1.5C, and 2C. Quantitative error metrics validate the excellent agreement between direct heat-flux measurements and the inverse thermal model (max RMSE: 1.7% at 2C). Conversely, the electrochemical model deviated significantly at high C-rates (RMSE: 15.4% at 2C), reflecting the sensitivity of reversible heat and overpotentials to internal gradients and thermodynamic hysteresis. These results establish calibrated heat-flux sensing as an experimentally robust alternative for characterizing battery thermal behavior and provide benchmark data for improving electrochemical–thermal models.