Heat Metrics and Heat-Release Pathways Change Thermal Runaway Rankings of Commercial Cylindrical Lithium-Ion Cells

Thermal runaway (TR) severity can be ranked using absolute or energy-normalised heat and by the pathway through which heat leaves the cell, but whether these definitions identify the same high-hazard cells remains unclear. We analysed 98 non-ISC heater-triggered tests from 13 commercial or near-commercial cylindrical cell models in the Battery Failure Databank. Cathode chemistry was not analysed because it was incompletely documented. Total, body, and ejecta heat were evaluated using allometric scaling, S-FTRC-generation-adjusted fixed-effects models, hierarchical bootstrap ranking, and isometric log-ratio analysis. Scaling exponents for total, ejecta, and body heat were 0.899, 1.003, and 0.879, respectively, with all 95% bootstrap intervals including b = 1. Despite this approximate proportional scaling, generation-adjusted absolute-total and total-kJ/Wh rankings disagreed for 46.2% of cell-model pairs. Body- and ejecta-heat rankings diverged even more strongly, with 62.8% point discordance, a bootstrap median of 61.5% (95% interval 53.8–67.9%), and 28 of 78 pairs showing reversal probabilities ≥95%. These findings show that absolute heat, energy-normalised heat, body heat, and ejecta heat address different engineering questions and should be reported and interpreted separately rather than combined into a universal cell-safety ranking.