In electric vehicle applications, ensuring the safety of batteries and battery modules is the most important thing to protect the lives and property of vehicle occupants. The design and manufacturing of these battery modules primarily address the heat management issues of the battery pack, keeping safety in mind. Even it has passed safety standard tests, connected in series to form a battery module, the reduction in the heat dissipation area can pose risks. If a battery module is misused, it can lead to the internal battery experiencing thermal runaway. Therefore, controlling the risk (Failsafe) to keep the battery module within an acceptable range without comprehensive burnout is essential to protect lives and property.

Battery thermal energy measurement:

The thermal change state of the cell comes from the power consumption of the electric current flowing in the Lithium-ion battery impedance and the electronic impedance during operation, so that the temperature of the battery rises.

Taking the experimental measurement of 18650 Li-ion battery discharge in an open environment as an example, the voltage when discharge and temperature of 18650 Li-ion batteries at various C-rates will change and show that the battery temperature rises rapidly with the increase of C-rate; the temperature change status of the battery is within the average operating voltage range, and the battery temperature rises slowly.  Oppositely, when the battery capacity is reduced to about 1.5 Ah, the voltage will drop, and the temperature of cells rises rapidly.

Since the module is formed by connecting multiple batteries in series and parallel, each battery is a heat source. When the batteries are stacked, the heat dissipation becomes uneven which makes the temperature of the batteries inside higher than outside. The higher the heat generation of the batteries, the higher degree of the non-uniformity.

However, the decay rate of the high-temperature batteries is higher than that of the low-temperature. As a result, it is necessary to control the temperature difference to less than 5˚C.

Therefore, the maintenance of temperature uniformity and the control of the maximum temperature is an important factor in increasing the lifetime of the batteries.

 

Author

Professor Wei-Keng Lin

Education｜Ph.D., University of Maryland

Occupation｜Professor, National Tsing Hua University 

Specialty｜Electronic package heat dissipation, Heat pipe, Loop heat pipes(CPL，LHP，PHP), Energy-saving design, Solar heat storage and cooling, Heat flow system, Cooling of electronic components, Two-phase flow, Heat transfer elements of artificial satellite and high-altitude flying object