Issue 55 Uncrewed Systems Technology Apr/May 2024 Sellafield’s UAV equipment l Applied EV Blanc Robot l Battery tech l Robotican’s Goshawk l UGVs l UAVHE RW1 rotary l Roboat UVD l Autopilots l Arkeocean UVD l UMEX 2024 l CycloTech UVD

42 Focus | Battery technology pulse equivalent to 15 C is applied for 45 s. Subsequent discharge is carried out at a nominal C/3 current. For the batteries investigated here, 1 C corresponds to ~0.08 A, while 15 C corresponds to roughly 1.2 A. The team found that none of the tested cells lasted more than 100 cycles under these high-stress conditions, with most starting to show decreased performance at around 85 cycles. After being stressed, the cells were subjected to a more normal, lowerrate power draw. This showed the cells partially retained their capacity under low-rate conditions, but failed quickly when placed under rapid current drain conditions again. This shows that existing fast-charging cells might not have the characteristics necessary for long-term, high-stress usages, but they could be retired and meet more typical power demands in other applications, such as battery back-ups for power supplies and energy-grid storage. Maritime power Increasing the power density with cathodes using NMCA and silicon anodes brings more safety considerations. Adding a fire-retardant additive to the water-soluble electrolyte formula composition lowers the risk of a thermal event by close to 80%. This has been demonstrated in industry standard nail-penetration tests on a 60 Ah cell. Despite the test cells being punctured with the resulting internal short circuit, they exhibited a far lower risk of fire than the same cells without the flameretardant additives. This is particularly important for electric uncrewed maritime systems. With the higher energy density, liquid cooling technology is needed in the marine battery systems to manage the increased heat generated. This method efficiently dissipates heat, maintaining optimal operating temperatures and prolonging the life of the battery. Additionally, liquid cooling enhances safety by reducing the risk of overheating and thermal runaway events, which is crucial for marine safety. These systems are integrated into the vessel’s infrastructure to minimise the need for space. Underwater power A cylindrical battery pack is providing power for uncrewed underwater vehicles (UUVs) and underwater charging stations. The design started out with a 180 mmdiameter cylinder in a titanium housing using lithium ion cells. This operates to a depth of 6000 m for ocean monitoring and seawater quality control. The 6 m long, 361 Ah cylinder weighs 17 kg in the air and 9 kg in water. However, demand for higher voltages up to 600 V are driving the need for a modular system with larger diameters for various UUV platforms – beginning with a 310 mm diameter to target the majority of underwater applications, and then a smaller, 260 mm version and a larger one of 416 mm. These are all built with smart power modules using the same standard, 18650 cylindrical lithium-ion NMC cells that are used in electric vehicles. Arranged in concentric circles, the cells are always one cell deep and come from the same manufacturing batch to maintain consistency as much as possible. A standard stencil is used to arrange the batteries in the modules, and the length of the pack depends on the capacity required. There are about 300 cells for a 6.6 kW module. All the data from the sensors in the module runs through a 12-pin connector to a monitoring module at the end of the cylinder. Current monitoring is on the April/May 2024 | Uncrewed Systems Technology A liquid-cooled NMCA battery pack for maritime applications (Image courtesy of Leclanche) Using lithium ion cells for power underwater (Image courtesy of SubCTech)