The sodium-based battery is one of the most advanced post-lithium technologies. Compared to other post-Li technologies, it is already closer to market introduction, but offers a storage performance that is lower than that of lithium-ion batteries. On the other hand, sodium is much more readily available, which could lead to lower costs and higher production volumes compared to current lithium-ion batteries. The market introduction of sodium-ion batteries will therefore initially be limited to niche applications, e.g. in power tools and for stationary applications. In order to further develop this system, POLiS will take a holistic approach to the fundamental factors that limit the performance of electrode materials and electrolytes in terms of energy density, safety and cost. This includes the understanding of insertion and conversion mechanisms in inorganic and organic materials and ionic transport.