High temperature versus low temperature Zebra (Na/NiCl2) cell performance

The effect of operating temperature on performance and aging of Zebra cells was investigated. The cells were cycled at 260 degrees C and 350 degrees C using a modified charging regime to accelerate damage. The cathode and solid electrolyte of degraded cells at the end of cycling were analyzed by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. It is hypothesized that the formation of AlF3 on the surface of the beta '' alumina electrolyte contributes to the failure of cells at low temperatures. A mechanism based on the overcharge reaction is proposed for the formation of this phase. At 350 degrees C, a significant capacity loss was observed with cycle life, which correlates to nickel particle growth as the cause of this phenomenon. The factors responsible for Ni grain growth are discussed. (C) 2012 Elsevier B.V. All rights reserved.