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

fleet operator that wants the cars out on the road all the time.” These sodium cells could also be used alongside hydrogen fuel cells that need a battery pack to incorporate the energy from regenerative braking, so the company is developing a proof of concept at 48 V. It is also working with Plastic Omnium to develop a 48 V sodium battery pack for mild hybrid vehicles with a view to incorporating hydrogen systems. Also in France, Sodium Cycles is developing an e-bike based around Tiamat’s cells. The Xubaka has a 4 kW motor and a top speed of 50 mph (80.5 kph) in the US, although this will be limited to 45 kph in the EU. The pack will charge in 4 hours from a standard plug and give a range of 60 to 80 km. In the UK, technology from Faradion uses mixed-phase O3/P2-type Na- Mn-Ni-Ti-Mg layered oxide cathodes, hard carbon anodes and non-aqueous electrolytes, and has achieved a 3000- 4000 cycle lifetime. Batteries based on this design are being used in trucks and e-bikes in India, where the lower maintenance requirements and higher safety of sodium over lithium-ion are key advantages. The next generation of the technology is aiming for 2 kW/kg and 210 Wh/kg, with a lifetime of up to 8000 cycles. This compares to the existing cells with an energy density in excess of 140 Wh/kg, with a design performance of 155 Wh/ kg in 10 Ah pouch cells. Meanwhile, US-based Natron Energy has built its sodium-ion technology around aqueous solvents and PBA- based cathodes and anodes, but this is more suited to stationary energy storage system (ESS) applications rather than e-mobility. AMTE Power in the UK has similar plans with a sodium battery line for ESS alongside its lithium-ion cells for e-mobility applications. For cathodes for e-mobility cells, Altris uses a material called Prussian “Higher energy storage capacity is just one advantage of this material. It also enables the cathode to operate at lower ambient temperatures, which is particularly relevant for Russia,” he says. The team used solid-state chemistry design rather than trial and error. “That means we relied on hard science, using the fundamental laws and principles of solid-state chemistry to arrive at the material with desired properties,” says researcher Semyon Shraer at Skoltech “Theoretical considerations led us to the basic formula for a material that might provide high energy storage capacity,” he adds. “We then needed to determine which crystal structure would unlock that potential. “The one we chose is known as the KTP-type framework, which comes from non-linear optics; it’s not very common in battery engineering. We realised that this particular compound with that particular crystal structure should work, then we managed to synthesise it via low-temperature ion exchange. And there it is, with its superior characteristics now confirmed by an experiment.” The cathode material is produced by combining a NaVPO 4 F composition and KTiOPO 4 -type framework using low- temperature ion-exchange synthesis at 190 °C. When tested in a coin cell configuration in combination with a sodium metal negative electrode and a NaPF 6 -based non-aqueous electrolyte solution, the cathode active material enables a discharge capacity of 136 mAh/g at 14.3mA/g with an average cell discharge voltage of about 4.0V. A specific discharge capacity of 123 mAh/g at 5.7A/g is also reported for the same cell configuration. Last year, the team at Skoltech developed a cathode with a reversible specific discharge capacity of 190 mAh/g, a relatively high value for sodium-ion battery cathode materials, by using layers of sodium, lithium and manganese, NaLi/Mn 2 /O 2 Elsewhere, Tiamat Energy in France is using cathodes based on the polyanionic Na 3 V 2 (PO 4 )2F 3 material. The company is a spin-off of France’s CNRS research laboratory that developed the technology. The key is that the sodium family is as wide as the lithium-ion family, and that allows layers of oxides, says Herve Beuffe, founder and president of Tiamat Energy. Tiamat’s polyanionic compound uses fluoride and vanadium to support fast charging at rates of 40-50C so that a cell can be fully charged in 10 minutes, exactly the same as NMC lithium-ion cells. The downside is its lower energy density, from 90-120 Wh/kg, compared with the 400-800 Wh/kg of lithium metal cells, which restricts the range of possible e-mobility applications. “A 100% EV using sodium batteries would have a restricted range, despite allowing a full charge in 10 minutes,” says Beuffe. “That could benefit small cars used in cities, especially with a A team at the Korea Maritime and Ocean University has developed an anode that allows rapid movement of sodium ions from the bulk zone of the electrolyte to the interface of the active material (Courtesy of Korea Maritime and Ocean University) 60 Autumn 2022 | E-Mobility Engineering