(Invited) New Concepts for Sodium Metal Halogenide Batteries Towards a Highly Economic and Ecologic Storage Technology
Authors: Schulz Matthias , Hofacker Martin , Herold Daniela , Schüssler Benajamin , Dirksen Cornelius , Richter Maria , Pfeifer Thomas , Weidl Roland , Stelter Michael 
Published: December 2020

NaNiCl2 batteries are member of the sodium metal halogenide battery family and represent a robust, save and environmentally friendly storage technology, which is in operation all over the world from small to large scale for decades. In particular, the high cycle stability, lifetime and the excellent safety predestine the technology for large scale stationary applications.
Nevertheless, a significant marked penetration has so far failed to materialize. The dominating obstacle are the costs for conventional NaNiCl2 in competition with the dramatically falling prices for Li-Ion batteries. The energy intensive ceramic electrolyte manufacturing and the usually used high amount of nickel are mainly responsible. Beside this, some high power technical applications, such as peak shaving, are currently not accessible for NaNiCl2 batteries. The limited C-rates permit an economic operation of these business cases.
To overcome these obstacles material scientific and engineering approaches are under development in workgroups all over the world. In the presentation, a technological review of new concepts for sodium metal halogenide batteries will be given. This will include new materials, designs and production methods along the battery value chain.
The high economical impact from solid electrolyte manufacturing was tackled by lowering the sintering temperature by material doping. By 1.5 % TiO2 doping the sintering temperature for the Na-ß-alumina electrolyte was lowered by 150 °C. By optimizing the microstructure, an ionic conductivity of 0.25 S/cm and a mechanical toughness of 210 MPa were reached at the same time.
Different cell designs matching different requirements in terms of power and energy will be presented. This will include 25 Ah plate cells and large tubular cells with high energy contents. Using the plate cell approximately, 100 % DoD can be discharged with an elevated current of 1 C which pushes NaNiCl2 close to Li-Ion cells. By a simple stacking of the cells, the capacity and the voltage level of a module can easily be adjusted to different applications.
For high-energy applications tubular 100 Ah cells and 5 kWh battery packs were successfully developed. The simplification of the cell and module design with the simultaneous use of innovative production methods ended up in calculated costs of 300 to 400 €/kWh for a large scale production. An intermediate temperature NaNiCl2-like cell concept was developed. A fundamentally different cathode composition and a liquid sodium anode opens the door to a batteries with improved round trip efficiency, compared to high temperature NaNiCl2.
Metal halogenid batteries have a high development potential. Away from the classic high temperature NaNiCl2 technology, a several approaches are under development and on the way to become a product in the near future. A successful implementation of the described approaches will yield in excellent batteries for large-scale stationary energy storage.