E-Mobility Engineering 016 l Aurora Powertrains eSled dossier l In Conversation: Thomas de Lange l Automated manufacturing focus l Torque sensing insight l Battery Show Europe 2022 report l Sodium batteries insight l User interfaces focus

This approach involves using 3D stereolithography to print micro- lattice structures made from resin. The micro-lattices are then shrunk by carbonising them using a process called pyrolysis. The resulting hard carbon anodes were found to allow fast transportation of energy- generating ions. The micro-lattices have a width of 32.8 µm and reach an areal capacity of 21.3 mAh/cm 2 at a loading of 98 mg/cm 2 without degrading performance, which is much higher than conventional monolithic electrodes with 5.2 mAh/cm 2 at 92 mg/cm 2 . Avoiding the use of binding materials also enables structural changes in hard carbon to be tracked, to help understand the mechanisms of ion penetration into hard carbon. Sodium cells CATL has also used Prussian White for the cathode, and redesigned the bulk structure of the material by rearranging the electrons, which it says has solved the worldwide problem of rapid capacity fading upon material cycling. In terms of anode materials, CATL has developed a hard carbon material that features a unique porous structure that enables the storage and fast movement of sodium ions. Cycle performance is reported to be up to 3000 cycles as a result of the change in the cathode structure, but further details of that are unclear at the moment. The first-generation NIB cells have an energy density of up to 160 Wh/kg, and can charge to 80% at room temperature in 15 minutes. More important, at -20 ºC they have a capacity retention rate of more than 90%, and their system integration efficiency can reach more than 80%. CATL is aiming the cells at various transportation electrification applications, especially in regions with extremely low temperatures, and is working on the next generation of them to raise the energy density to more than 200 Wh/kg. Using sodium cells also changes the battery pack’s design. CATL has developed an ‘AB’ battery system that mixes NIB and LIB cells in a particular proportion, integrates them into one battery system, and controls the different systems using a BMS algorithm. The AB design compensates for the energy density shortage of sodium-ion batteries, and takes advantage of the high power and performance in low temperatures, providing power to heat the LIB batteries to make them ready for use. Conclusion Sodium batteries have key advantages for e-mobility applications if the lifetime issues can be overcome. The low- temperature operation in particular appeals for heavy-duty applications where lithium-ion cells will just not work. Using a hybrid approach that mixes sodium and lithium-ion batteries means the sodium batteries are not used as much, so the cycle life is not as much of an issue. Meanwhile, research continues into new materials for the cells. Variants of Prussian Blue for the cathodes and new anode materials are increasing the energy density of the cells, while careful optimisation of the electrolyte and solvent can help increase the cycle life to a more useful level. All of this is driving the development of sodium-ion battery cells for commercial use in e-mobility applications in different ways, from hybrid battery packs with lithium cells to supporting regenerative energy capture in vehicles powered by fuel cells. Deep insight | Sodium batteries Chinese battery giant CATL is planning to produce sodium cells in volume (Courtesy of CATL) 62 Autumn 2022 | E-Mobility Engineering