Non-invasive internal pressure measurement of 18650 format lithium ion batteries during thermal runaway

The dynamics of 18650 format lithium ion battery pressure build-up during thermal runaway is investigated to inform understanding of the subsequent pressure-driven venting flow. Battery case strain and temperature were measured on cells under thermal abuse which was used to calculate internal pressure via hoop and longitudinal stress relations. Strain measurement is a non-invasive approach with no impact on the chemical decomposition within batteries that leads to thermal runaway. The experimental methodology and test apparatus were developed and validated through predictable, representative test specimens of open cases and pressurized gas cylinders. Live battery experiments reliably captured the final pressure rise before venting onset. The pressure build up was observed to coincide with the beginning of thermal runaway.