Cylindrical Lithium-Ion Structural Batteries for Drones

The increasing use of battery-powered multirotor aircraft for industrial applications has allowed for advancements in a wide range of fields. These aircraft, however, have limited payloads and shorter endurance and range than fuel-powered conventional aircraft. To extend these key performance metrics, we have developed an optimized structural battery that uses commercially available battery cells as load bearing and power source elements for weight critical applications. Multifunctional lithium-based batteries have been previously proposed for the efficient use of space and mass in electric vehicles [1]. Lithium batteries offer an energy density high enough for most small multirotor flight applications [2], however these batteries often constitute a significant portion of the aircraft’s mass. This implementation is proposed to decrease the structural frame mass and thus increase multirotor performance characteristics such as payload capacity and flight time [3]. In this work, structural lithium-ion batteries were integrated into the design of a commercial drone to improve hover time. Hover tests were first performed with the original lithium polymer batteries for comparison purposes. Battery voltage was measured every 2 minutes to monitor voltage decrease versus hover time. With no payload, the original hover time of the drone was 34 minutes. For payloads of 0.5, 1.0, and 1.5 kg, hover times decreased to 28.7, 22.7, and 19.1 minutes, respectively. Standard 18650 cylindrical battery cells (Panasonic NCR18650B) were then integrated into the carbon fiber arms of the drone, to replace the original lithium polymer batteries. This design modification reduced the weight of the drone from 1242 g to 848 g, while also improving the structural integrity of the carbon fiber arms. For both designs, the velocity of the drone was related to the impact force experienced in the case of a crash. The carbon fiber arms would fracture at 4 m/s when hollow, and 7 m/s when reinforced with lithium-ion batteries. Hover tests for this modified design are being performed currently, and times are expected to be on the order of 40% longer [4]. Ongoing efforts to investigate the relationship between the intensity of power usage and the angular inertia of the drone will help to characterize the optimal battery distribution. [1] Zhang YC, Ma J, Singh AK, et al. (2017) Multifunctional structural lithium-ion battery for electric vehicles. Journal of Intelligent Material Systems and Structures 28: 1603-1613. [2] Vikstrom, H.; Davidsson, S.; Hook, M., Lithium availability and future production outlooks. Applied Energy 2013, 110 , 252-266. [3] Dughir, C.; Ieee, Power wire thickness influence on the multicopters flight time. 2016 12th Ieee International Symposium on Electronics and Telecommunications (Isetc'16) 2016, 239-242. [4] Hollinger AS, McAnallen DR, Brockett MT, DeLaney SC, Ma J, Rahn CD. Cylindrical lithium‐ion structural batteries for drones. International Journal of Energy Research . 2020; 44:560–566. Figure 1