Issue 37 Unmanned Systems Technology April/May 2021 Einride next-gen Pod l Battery technology l Dive Technologies AUV-Kit l UGVs insight l Vanguard EFI/ETC vee twins l Icarus Swarms l Transponders l Sonobot 5 l IDEX 2021 report

34 T here are a number of key engineering trade-offs for the battery technology used in unmanned systems. The main one is the balance between high energy density for lightweight cells and high specific energy for delivering high power, and that challenge is at the heart of the development of battery materials. The trade-offs are also critical for cell lifetime and charging rate. A high-power cell that delivers power quickly can take a charge just as quickly, leading to fast charging. But that requires thicker elements in the cell, adding to its weight and reducing its energy density. The material for these elements, and hence the performance of the cells, determines the architectures that can be used in unmanned systems. There are crucial distinctions between the materials used for the cathode (the negative electrode in normal operation) and the positive anode, as well as the electrolyte that sits between the electrodes to facilitate the transfer of ions that provide the power. Some battery materials, such as silver zinc for underwater applications and lithium iron phosphate (LFP) are at the bottom end of the scale of energy density. They can be heavy but support many hundreds of cycles and have a high level of reliability and ruggedness. Moving up the scale, there are lithium cells with silicon to boost the power density, ‘anode-free’ metal batteries and solid-state materials for cells with a different balance of energy density and power delivery. Nick Flaherty sets out the competing factors in unmanned systems battery design, and explains the various cell technologies for addressing them Power challenge April/May 2021 | Unmanned Systems Technology The Zephyr high-altitude UAV originally used lithium sulphur cells that were charged by solar cells to release power overnight to keep it in position (Courtesy of Qinetiq)