Physical examination of high capacity nickel-hydrogen battery cells

In order to assess cell cycle performance and possible failure modes, some randomly selected nickel-hydrogen (Ni/H₂) battery cells of 83 Ah capacity were put through a rapid cycle test at 80% depth of discharge (DOD) using simulated low-earth-orbit conditions. A destructive physical analysis (DPA) was performed on several cells following the cycle tests. After nearly 1000 charge/discharge cycles, the cells from one manufacturer exhibited significant voltage performance degradation and internal stack damage. The cells from another manufacturer exhibited little voltage degradation and no significant internal damage. The authors summarize the important results of the cell DPAs. In particular, polarization test results show that active material extrusion from the pores of the positive plates can cause cell voltage performance degradation. Also, electrolyte (KOH) concentration gradients within a stack can be caused by a cell dome-to-dome temperature gradients, and nonuniform stack wearout can result