Thermal Management Data//iso-BTC
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Principle of isothermal BTC

Basic principles of isothermal BTC

Isothermal heat measurement from batteries can be performed by balancing the heating and cooling duties necessary to hold the sample temperature constant, see figure opposite. Thus, the iso-BTC consists of a chamber (which holds the battery sample) into which cold air blown from all sides. Provided the air flow and temperature are constant, the cooling effect on the battery will also be constant. At the same time, the battery surface is warmed by a thermal controller (fine heaters coated on to a conducting sheet) to counter the effect of cooling. The controller is software controlled and reports changes in thermal duty.

There are two temperature sensors, on either side the battery sample and the thermal controller keeps the average of these two temperatures, at the user defined value. In a typical experiment, the cooling is started and the average temperature allowed to stabilise before any charging/discharging of the battery is started.

When the cycler is then operated, leading to either heating or cooling of the battery, the&nbsp controller ensures that the average temperature of the battery remains constant and this directly provides a measure of the heat being generated by the battery. With Li-ion batteries, charging often leads to an endothermic reaction (cooling of the battery) and discharging results in a exotherm (heating of the battery).

When charging starts, a small fall in battery temperature is observed but further change is prevented as the controller adds heat. When charging is complete, the temperature stabilises. During the discharge step, the battery temperature is seen to rise slightly &ampndash the controller reduces power input to prevent further rise &ampndash to compensate for the heating (exotherm) within the battery. This is what is measured and displayed while the experiment is performed. These changes in the controller performance can be directly related to the heat effects within the battery and translated to the thermal duty needed to keep the battery temperature under control.

The commercial of the iso-BTC is shown in image 3 on the left