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 °C and 350 °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 β″ 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 °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.

► Rapid cycling of Zebra cells is examined at 260 and 350 °C.
► The cells cycled at 260 °C failed in discharge after 300 cycles.
► Significant capacity loss occurred in cells cycled at 350 °C after 600 cycles.
► The failure at 260 °C is linked to the formation of AlF3 phase on β″ electrolyte.
► At 350 °C, growth of Ni particles is found to be the cause of capacity loss.