Characteristic signatures of aerospace nickel-cadmium cells on life-cycle testing

NASA-Goddard Spaceflight Center (GSFC) is continuing its long-standing program of life-cycle tests of nickel-cadmium (Ni-Cd) cells from various battery cell vendors at the Naval Surface Warfare Center (NSWC) in Crane, Indiana in order to predict on-orbit performance and develop onboard management strategies for both nominal and anomalous batteries. Testing is in progress on several packs and different sizes of the two types of Ni-Cd cells manufactured by Eagle-Picher Industries, Inc. (EPI). These two designs are the Super Ni-Cd cell and the Magnum Ni-Cd cell, the significant difference between the two types being the type of separator material. Anomalous charge voltage divergences have been observed in cells from both designs, particularly at cold temperatures and fairly low depths-of-discharge. A similar divergence has also been observed in the one on-board battery of the LEO SAMPEX (Solar Anomalous Magnetospheric Particle Explorer) spacecraft. This paper illustrates the life-cycle test voltage divergences, shows how they differ from divergences observed on previous life-cycle tests of EPI cells, and report the data from at least one attempt to manage the voltage divergence.