An Investigation on the Electrical Energy Capacity of Cylindrical Lithium-Ion and Lithium Iron Phosphate Battery Cells for Hybrid Aircraft

Improving the energy performance of batteries can increase the reliability of electric aircraft. To achieve this goal, battery management systems (BMS) are required to keep the temperature within the battery pack and cells below the safety limits and make the temperature distribution as even as possible. Batteries have a limited service life as a result of unwanted chemical reactions, physical changes that cause the loss of active materials in the structure, and internal resistance increase during the charging and discharging cycle of the battery. These changes usually affect the electrical performance of batteries. Battery life can be increased only by reducing or preventing unwanted chemical reactions. Lithium-ion (Li-ion) batteries are a suitable option due to their high specific energy and energy density advantages. In this study, the necessity of heat management is emphasized. The discharge tests of the Li-ion battery provided 94.6 Wh under 10C and 90.9 Wh under 1C. The differences in these values were due to the energy consumed by the battery management system (BMS) for functions such as balancing and shearing rather than the high energy discharge rates of Li ions. Li-ion batteries could be supplied with 98.3 Wh under 10C and 91.7 Wh under 1C during charging experiments. The increase of charge/current ratio reduces the energy that the battery can receive. The discharge tests of the lithium iron phosphate (LiFePO₄) battery provided 83.25 Wh below 10C and 81.2 Wh below 1C. The differences in these values were observed in LiFePO₄ due to its chemical structure and suitability for fast charging and discharging. During the charging tests, the battery could be supplied with 88.2 Wh below 10C and 82.7 Wh below 1C. It was seen that the energy differences between charge and discharge in the batteries were the lost energy emitted to the environment.