2015 Articles

Galvanostatic Intermittent Titration Study of the Positive Electrode of a Na|Ni(Fe)-Chloride Cell

Zhu, Ruixing; Vallance, Michael; Rahimian, Saeed Khaleghi; West, Alan C.

The response to open-circuit interrupts of porous mixed iron-nickel cathodes operating in NaCl-buffered, molten NaAlCl4 electrolyte has been characterized as a function of state of charge (SOC) for different iron loadings and different charge and discharge rates. After discharge, the open-circuit potential (OCP) can evolve in time from the iron plateau to the nickel plateau, and this behavior can be explained by galvanic interactions between iron metal and Ni2+. Characteristic times of the OCP transients depend on SOC and can be large. When the OCP has converged on a steady state during discharge, its value may provide an estimate of the mole fraction of NiCl2 at the interface of the triclinic (Ni,Fe)Cl2 film that resulted from metal oxidation. Detailed analyses of the experiment require modeling of the galvanic conversion rates, which depend on both charge-transfer and mass-transfer phenomena.