Meaning
Systematic testing of battery components to determine the temperature at which uncontrolled chemical reactions begin. This process identifies the safety limits of electrolytes, separators, binders and active materials. Results from thermal stability screening dictate the maximum operating temperature for the finished battery pack.
Test Procedure
Differential scanning calorimetry provides a map of heat flow as the sample is warmed. The onset of an exothermic reaction during thermal stability screening marks the point where the material becomes unstable. Scientists look for the temperature where the self heating rate exceeds the cooling capacity of the system.
This data is used to set the software limits in the battery management system.
Safety Validation
Full cells are subjected to oven tests to verify that they do not catch fire under extreme heat. If the thermal stability screening of the individual parts is accurate, the behavior of the whole cell can be predicted. Materials that pass these tests are more likely to survive a short circuit without entering thermal runaway.
This validation is a legal requirement for transporting lithium batteries across international borders.
Material Selection
High performance cells require a balance between high energy and high safety. Sourcing teams use thermal stability screening to compare different suppliers of cathode powder. A material that is stable up to two hundred degrees is preferred over one that breaks down at one hundred and fifty degrees.
Better stability allows for faster charging and higher discharge rates in hot environments. Choosing the right material reduces the need for heavy and expensive cooling systems in the final product.
