Calorimetry, based on the First Law of Thermodynamics, has been extensively used to measure the energy change in the system during thermal runaway.
Techniques such as accelerating rate calorimetry (ARC), copper slug calorimetry, and cone calorimetry have all been applied to quantify thermal runaway. Despite their utility, traditional calorimetric techniques struggle to differentiate between the total energy released through the cell casing and the ejected solids, liquids, and gases.
To address these issues, engineers at the NASA Johnson Space Center and Science Applications International Corporation (SAIC) developed the Fractional Thermal Runaway Calorimeter (FTRC). This innovative device allows for discernment between the total heat output due to thermal runaway and the fraction of the total heat that is released through a cell’s casing versus its ejecta material.
FTRC can accommodate a range of cell formats, from cylindrical 18650 and 21700 cells to D cells and small pouch cells. It can also be paired with high-speed x-ray videography for in-situ imaging of thermal runaway events. Its design allows for multiple experiments per day, enabling extensive evaluation of cell safety across cell formats and manufacturers.
Currently, FTRC research is conducted by collaborators at the NASA Johnson Space Center, the National Renewable Energy Laboratory (NREL), and the University College London (UCL). This collaborative effort generates data that not only aids in the development of safer batteries for space exploration applications, but is also shared publicly to support the design of safe batteries for mobility and other applications.
To further enhance the understanding of Li-ion batteries and their failure mechanisms, the FTRC team employs synchrotron facilities such as the Diamond Light Source (DLS) in the UK and the European Synchrotron Radiation Facility (ESRF) in France. These facilities offer a high-intensity x-ray beam that enables detailed visualization of the internal structure and failure mechanism of Li-ion cells during thermal runaway.
The research conducted using FTRC and synchrotron facilities offers insights into the safety characteristics of Li-ion batteries, especially concerning thermal runaway events. As our reliance on Li-ion batteries continues to grow, the knowledge gained through these advanced testing methodologies will become increasingly critical to developing safer and more reliable energy storage solutions for a wide range of applications.
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