40 A new generation of materials is boosting the performance of lithium battery cells in commercial production, reducing weight while increasing power. The use of silicon anodes, nickel manganese cobalt aluminium oxide (NMCA) cathodes, lithium sulfur and solid-state electrolytes are all improving the energy density of cells. Increasing the safety of lithium cells through additives or solid-state electrolytes reduces the need for additional sensing and protection, further reducing the weight of the battery pack. 3D printing with solid-state materials opens up new ways to use batteries in different shapes, while AI is identifying thousands of new substances that could lead to improvements in gravimetric specific energy, as measured in Wh/kg, and volumetric energy density, as measured in Wh/L for smaller cells. All of this is helping designers of uncrewed aerial vehicles (UAVs) and autonomous electric vehicle take-off and landing (eVTOL) aircraft to boost mission times, often doubling performance, and providing faster charging rates for quicker turnarounds and more time in the air. Silicon anodes A key technology for batteries in uncrewed systems is using silicon as the anode. While silicon has twice the energy capacity of carbon, it suffers from significant expansion of many times its original size when charging. This leads to safety issues as a cell will swell when charging and discharging, risking the lithium-based liquid electrolyte leaking out and catching fire. The current approach is to use silicon alongside various types of carbon, from 3D structures to encasing the silicon in carbon nano-structures, which provide an incremental increase in energy capacity. However, for airborne applications, particularly High-Altitude Pseudo Satellites (HAPS) that operate at altitudes above 60,000 ft and need to store power from solar cells for operation overnight, this requires significantly higher energydensity battery cells and a new approach. Nick Flaherty explores the new wave of battery tech, boosted by AI, 3D printing and enhanced materials Packing power April/May 2024 | Uncrewed Systems Technology Silicon nanowires for high-performance batteries in the air (Image courtesy of Amprius)
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