Adiabatic calorimetry has been the cornerstone of chemical process safety for the last 30 years. More recently, adiabatic calorimetry has been widely used in measuring the potential of thermal runaway of Li-ion cells. These cases are similar in that they require measuring both the amount of heat released (thermodynamics) and the rate at which the heat is released (kinetics). In both cases there can be a significant increase in the sample pressure and the combination of the temperature and pressure rise can lead to an explosion. Therefore adiabatic calorimeters are generally designed to be much more robust than many of other types of calorimeters.
When looking at a thermal runaway, whether it is within a battery cell or part of a chemical process in a plant, the reaction produces heat which increases the temperature of the reaction and further increases the rate. There can come a point when the rate of heat release from the reaction exceeds the rate at which the heat can be lost to the surroundingenvironment- the point at which thermal runaway inevitable. Obviously the worst case is when there is little or no ability for the heat to be lost to the environment. Any heat, even small amounts of heat, cause the temperature to rise and accelerates the reaction producing even more heat. This is the adiabatic condition and it is this precise condition that adiabatic calorimeters can safely measure in the small scale. It is this same condition that can be found inside large processing vessels as well as inside a Li-ion pack running inside a laptop computer.
The energy release from chemical reactions (decomposition etc.) is a point of focus in chemical research, battery research and other industries. When energy is generated by a thermally induced chemical reaction and the heat transfer to the outside is smaller than the generated amount, runaway reactions can occur. In the worst case this can cause catastrophic effects (explosions). Adiabatic calorim-eters are ideal tools for analyzing such questions as they simulate the worst case scenario with no heat exchange with the surroundings.
For decades accelerating rate calorim-eters have been widely used by researchers in this field, offering the capability to measure temperatures, enthalpy changes and pressure changes quantitatively.The use of adiabatic systems has theadvantage that no heat loss is allowedfrom the sample; the behavior in real large scale chemical reactors can therefore be simulated (worst case scenario).
A sample (several grams) is placed in a spherical vessel. The vessel is surrounded by a sophisticated heating system. Depending on the working mode, the surroundings of the vessel are controlled to the same temper-ature as the sample. If there is no temperature difference between the heaters and the sample, then all the heat generated by the sample stays within the sample. This is the adiabatic condition.
A thermal runaway reaction is usually investigated with the Heat‐Wait‐Search mode (HWS). The temperature of reaction as well as the temperature and pressure increase are measured. Additionally, the temperature and pressure increase rates can be deter-mined. These are important values in order to characterize the worst casescenario of a substance.