Enhanced hazard characterization of lithium-ion batteries subject to destructive overcharge conditions

During a failure event, electrochemical cells can exhibit such characteristics as extreme high temperatures, deflagration, fire, venting of electrolyte and rapid uncontrolled disassembly. The cell's characteristics prior to, during, and after a destructive event are important in developing preventive and mitigating hazard steps. A novel measuring system based on isothermal calorimetry has been developed and utilized to further understand the worst-case event produced by large format electrochemical cells. This system allows for the containment of the reaction and its products while measuring the pressure and release rate of the gaseous product, as well as a complete thermal profile of the reaction. This paper provides a description of the calorimeter, calibration test results on its performance, test results, and empirical model from a selection of cells tested. The cells utilized in this developmental testing were Lithium Iron Phosphate and Lithium Cobalt Oxide cells ranging from 6 to 38 Ampere hour capacities and approximately 40 mm diameter, 170 mm height, and 0.35 kg each. This analytical system allows for a wide range of cells, chemistries, failure mechanisms and testing environments for lithium-ion cells, static or under load. Empirical models developed from this flexible and adaptive system will enable researchers to compare larger samples across material property boundaries to better predict the outcome of destructive chemical reactions.