Investigation and optimization of Ni/NaCl granules for Na-NiCl2 high temperature batteries

Sodium-nickel chloride batteries are a highly efficient and intrinsically safe energy storage technology. [1] The research activities at the Fraunhofer IKTS addresses the overall investigation of all related materials, components and processes. This covers in particular the electrochemical cell behaviour that basically can be described with the given equation. Ni + 2 NaCl ⇌ NiCl2 + 2 Na E0=2.58 V at 300 °C The cathode material, which consists of nickel, sodium chloride and some additives is crucial for the later full cell performance. Thus, the cathode composition and the granulation process were thoroughly investigated to find a low internal resistance and a high performance Ni/NaCl granule type material. The cathode samples were prepared by mixing and dry compaction. By adjusting the process parameters systematically, the bulk density of the granules was optimized which corresponds to an increasing capacity of the cell. High energy capable cathode granules with bulk densities of 2.0 g/cm³ were obtained after an additional spheronizing treatment. [2] The cathode properties were characterized with density measurements, mercury intrusion porosimetry and SEM analysis. For cathode testing high temperature 5 Ah sodium nickel chloride test cells were assembled. The impact from granulometric material properties to electrochemical cell performance was investigated. Correlations between the granule properties, the cycling stability and the durability were derived.