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

White. This is a framework material consisting of sodium, iron, carbon and nitrogen and a variant of a dye called Prussian Blue. The large pores inside the material enable the capture and storage of a range of atoms or molecules, making the compound highly interesting for a range of applications. Altris has developed a method of producing a cathode material called Fennac in a form that is suitable for use as a positive electrode material in NIBs. Using iron as a source of electrons and completely filling the material with sodium provides a theoretical capacity of 170 mAh/g and an average voltage output of 3.2 V. Fennac is produced using a patented low-temperature and pressure synthesis process, in a fully sodiated form, which is necessary for a cathode material. This can be dropped into existing battery production lines. Altris has built a production plant in Sandviken, Sweden, called Ferrum, to make the material and plans to open it next year. It will produce 2000 t of Fennac a year, enough to make 1 GWh of NIBs. Ahlstrom-Munksjo, a French manufacturer of fibre products, will provide heat-resistant separators for the Fennac-based cells. CIDAUT, the Foundation for Transport and Energy Research and Development in Spain, will develop and perform safety and performance cell testing. Anodes Anodes can be made from layered oxides, variants of Prussian Blue mixed with sodium- or vanadium-based polyanionic compounds, and used with aqueous and non-aqueous electrolytic solutions, says Dr Nuria Tapia-Ruiz at the Department of Chemistry at Lancaster University and the Faraday Institution in the UK. Elsewhere, researchers at the Korea Maritime and Ocean University set out to find a suitable non-graphite anode material for NIBs. “Because NIBs have low performance – only 1/10th the capacity of a lithium-ion battery – it is crucial to find an efficient anode that retains graphite’s low cost and stability,” says Dr Jun Kang, the lead researcher. The anode they developed uses a hierarchical porous structure that allows rapid movement of sodium ions from the bulk zone of the electrolyte to the interface of the active material. The structure has large specific surface areas where sodium ions migrate to the interface, which can be easily accessed in the active material and makes use of the surface defects and pore structures that enable co- intercalation from the surface to the interior. This reduces the diffusion paths and increases the number of active sites to boost the performance. “These factors afford good capacity retention, reversible capacity, ultra-high cycling stability, high initial coulombic efficiency – 80% – and remarkable C-rate capability,” Dr Kang says. “That means they can be used for a long time, even with intense battery use.” This approach gives an energy density of 101 mAh/g and a very high cycling stability of 11,000 cycles at currents of 100 A/g. Other researchers have developed a 3D-printing process for carbon micro- lattice anodes in NIBs. Battery cells tend to be built using layers of materials, usually laid down as a slurry and dried off or as a metal foil. The layers are stacked up in a pouch or prismatic cell or rolled up for a cylindrical cell, and all these formats are suitable for sodium cells in e-mobility designs. However, the slurry approach for carbon anodes means there are limited opportunities to develop structures in the electrode that could be used to boost the performance. So researchers at Tohoku University in Japan are looking at ways to achieve high-performance, low-cost batteries by increasing the loaded amount of active materials used to make a battery in a single cell. This would reduce the inactive materials that are used for binding multiple cells together but requires the fabrication of thicker electrodes, which would restrict ion movement within the battery. + printing micro lattice structures create more eɈective carIon anodes *ourtesy of ;oOoku <niversity Autumn 2022 | E-Mobility Engineering 61 Deep insight | Sodium batteries