Effect of heating rates on thermal runaway and gas composition in large Li-ion battery cell formats – An experimental study

The growing use of high-energy lithium-ion batteries for energy storage raises fire safety concerns, especially under high charge/discharge rates or external heating. This work presents an experimental investigation of different heating rates into the thermal runaway behavior of two large cell formats, a 64 Ah NMC pouch cell and a 100 Ah LFP prismatic cell, focusing on key parameters such as surface temperature evolution, propagation time across cell surfaces, total mass loss, gas composition and volume, and total heat release. The tests were conducted in inert atmosphere in a pressurised vessel. Different heating rates, from 4 °C/min to 24 °C/min, and a test with an initial 24 °C/min increase followed by a plateau, were employed for fully charged cells. Results demonstrated for both cells that heating rates influenced the time to reach thermal runaway, the onset temperature, and the maximum temperatures, but had a minor impact on the total gas volume. The gas composition from LFP prismatic cells was found to correlate with the studied heating rates. The findings provide valuable empirical data that support the development of predictive models for thermal runaway initiation and heat propagation in battery modules, contributing to improved safety strategies and system-level design for energy storage applications.