Thermal management system enhancement by characterization between Psychrometrics and Lithium-ion polymeter battery lifespan

Lithium-ion polymer (LiPo) battery shows a promising future as energy storage due to higher energy density by weight among other rechargeable batteries. Recently, thermal issues are concerned, which prevent LiPo battery to be fully commercialized as an energy storage of electric vehicle (EV). It is expected that establishing thermal comfort in a battery compartment would help LiPo battery to perform better in terms of its life cycle. Previous studies only concentrate on Tdb as the key environmental factor contributing to battery’s capacity fade. New exploration studies are needed since little work has been carried out to investigate other psychrometric properties such as Twb and RH of air. Hence, this research attempts to bridge the gaps by investigating the relation between psychrometry conditions and the cycling performance of LiPo battery. The first objective was to investigate and compare the cycling performance of tested LiPo battery based on different psychrometry conditions, i.e. Tdb, Twb, and RH. The second objective was to evaluate the thermal behaviour of tested LiPo battery. The third objective was to characterize important mechanical parameters by proposing a hypothetical design of forced air cooling for a single LiPo battery pack. Cycling experiments (CLE) were performed using Revolectrix Cellpro PowerLab 8 (v2) battery workstation, which battery was cycled at 6.0 A charging/discharging rates up to 300 cycles at voltage window of 3.3–4.2 V. Besides, the selected psychrometry conditions were controlled by using an environmental chamber. Next, infrared thermography experiments (ITE) were performed by capturing infrared (IR) images of LiPo battery’s surfaces when cycled at various charging/discharging rates with FLIR E6 thermal imaging camera. The captured images were analysed based on surface temperature distribution, maximum surface temperature, and temperature rise. The maximum surface temperature was further compared with thermocouples data to determine the critical surface temperature location. The forced air cooling system was hypothetically designed by determining the thermal comfort zone and heat load of tested LiPo battery first. Then the mechanical parameters were characterized. At the end of this research, study found that the cycling performance of tested LiPo battery was strongly related to the Twb of surrounding air. With an acceptable range of uncertainty (U% < 10 %), a similar trend of capacity fade was observed in case of battery cycled at the same Twb, different Tdb and different RH. Based on the captured IR images, no critical surface temperature location detected either during charging/discharging modes. The surface temperature distribution became more spatially uniform at the end of ITE, with final maximum surface temperature difference of ± 0.3 °C and ± 0.5 °C during charging and discharging modes, respectively. The hypothetical design of forced air cooling for a single LiPo battery pack was proposed to have 4.0 W of required cooling capacity. In conclusion, the cycling performance of tested LiPo battery was found to be more favourable in dry and cool condition, which the changes in enthalpy (which mostly depends on the changes of Twb) play an important role in heat transfer process. The characterization of mechanical parameters also could serve as a good foundation to develop a full design if the same refrigeration cycle approach is used.