Battery Types - Sodium Batteries - High-Temperature Sodium Batteries | Sodium-Nickel Chloride

The sodium-metal chloride (NaMCl2) battery has its origin in the mid-70s of the last century in South Africa which is responsible for the common name ZEBRA - "Zeolite Battery Research Africa" and later the “Zero Emission Battery Research Activity” project. ZEBRA cells comprise a liquid sodium negative electrode separated from a transition metal chloride positive electrode by a sodium ion conducting Na-β-alumina ceramic solid electrolyte. In the positive electrode compartment, a second but liquid electrolyte of sodium tetrachloroaluminate (NaAlCl4) mediates the transfer of sodium ions between the solid metal chloride and the Na-β-alumina. The transition metal predominantly utilized is nickel or mixtures of nickel and iron which also leads to the frequently used designation NaNiCl2 battery. The melting point of the NaAlCl4 determines the minimum operating temperature of the cell to 157°C while the maximum operating temperature is limited to 350°C to avoid cell failures from pressure build up or corrosion. The normal operating temperature range is 250-350°C while the set point temperature often is set to 270°C. This represents the optimum regarding a low cell resistance and a long lifetime and is responsible for the frequently utilized term "high temperature battery". In consequence, the cells are housed in a heated and insulated module to secure the required operation temperature and to minimize the thermal losses and guarantee an efficiency of around 90% at the same time. ZEBRA cells based on tubular Na-β-alumina electrolytes were the starting point of cell development and the commercialization was successfully done in the late 90s. The first industrial production for ZEBRA cells, modules and battery systems was installed in Stabio (Switzerland). Planar cell designs provide different performance characteristics and are currently under development. A specific energy of 140Whkg-1 is possible for the cell and pulse powers in excess of 150Wkg-1 for the battery are applicable. A calendar life of 15years has been demonstrated and a cycle life of 5000 nameplate cycles has been achieved over a period of 7years of laboratory testing. Due to the capability of high-power charging and discharging of Li-Ion batteries that were developed in the last decades the main applications of the ZEBRA battery altered from mobile to multipurpose stationary applications with moderate power requirements.