The temperature profiles of the battery packs with PCM at different discharge
rates are shown in Figure 3. The packs were tested at an ambient temperature of 30°C. As
the discharge rate increases from 1C to 2.08C, the heat generated by the battery pack
increased significantly causing cell temperature to increase fast. As shown in Figure 3,
the PCM was capable of removing heat due to its high latent heat of fusion, while the
high thermal conductivity of the graphite used to contain the PCM, insured high rate of
the removal of heat and minimized the temperature distribution in the battery pack. PCM
starts to melt when the temperature of the module exceeds the melting point of the PCM,
and regulates the temperature around the melting point of the PCM, which is around 55
°C. This behavior can be seen clearly in Figure 4 as the change of slopes of the
temperature-time curve happens during melting of the PCM. The utilized capacities at 4.8
A and 10 A discharge were 4.48 Ah and 4.28 Ah, respectively. These results clearly
demonstrate that with PCM, it is possible to utilize the full capacity of the battery at high
discharge rates even at elevated temperatures. At the end of the test, the packs were not
affected by the heat and no disintegration was observed. Afterwards, the packs were
cycled several times at normal operating conditions during which full capacity utilization
was observed