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

46 300 C in a 3 Ah cell. This high-temperature operation is key for airborne applications, where the battery can be closer to the high-temperature inverter, and operate at atmospheric pressure and below. Other important aspects include the ability to use commercial cathode materials such as NMC lithium and to fit the application of the electrolyte into existing commercial cell-manufacturing processes, rather than requiring high pressure to compress the anode during manufacturing or high pressure in sealed cells during operation. Using lithium metal as an anode is only becoming possible with a solid electrolyte due to previous safety issues, but the ability of the solid electrolyte to transfer the lithium ions from the cathode to the anode is crucial. In a liquid electrolyte, this is much easier as the ions move in the liquid. The solid electrolytes need to have a structure that allows ions to move through it to give higher conductivity and support higher current rates, but this leads to more heating effects. The nano-composite matrix, which is similar to a polymer, has a conductivity of 1-10 mS/cm (milliSiemens per cm) at room temperature, which is close to a liquid electrolyte. The matrix includes lithium ions and allows them to move on the walls of the nanopores in the matrix, acting as highways for the lithium ions to move along. Before it becomes solid, the material is a liquid precursor, so it can be added to the existing battery cell manufacturing process before it solidifies. The nano-composite matrix is a family of materials with additives to tune the performance for conductivity for faster charge/discharge, thermal behaviour, and how soft or hard it is for the interface to the lithium metal anode and the cathode. This allows the solid electrolyte to be used with conventional cathodes, such as NMC 622 and 811, and high-nickel cathodes that have more power and less cobalt, while still being as close as possible to the existing manufacturing lines as a drop in replacement material. The first-generation cell with an NMC cathode shows an energy density of 340 Wh/kg and >800 Wh/L to be on a par with current liquid cells, with a charging and discharging rate of 1 C and 500 cycles. The second-generation cells are targeting 385 Wh/kg and 1100 Wh/L, with a 3 C-Rate and a lifetime of 7501000 cycles. Meanwhile, the third-generation cells are aiming to be above 450 Wh/kg and 1100 Wh/L, with the same or higher C-Rate. This is a bigger challenge, as the current density is much higher, and that higher current has an impact on cycle life. This is particularly important with a 3 C discharge rate, according to the mission profile for the aircraft, with higher power requirements at take-off and landing, rather than during horizontal flight. Performance in a module is also important to assess, as cells can start to behave differently when placed together, so there is a need to optimise the module. April/May 2024 | Uncrewed Systems Technology The first-generation nanocomposite solid state battery cells (Image courtesy of Solithor) Manufacturing solid-state battery cells in a dry room (Image courtesy of Solithor)