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Li-ion cells were cycled as part of a program to assess commercial technologies for space applications. Cells showing capacity loss were disassembled and compared with new cells using scanning electron microscopy (SEM) x-ray diffraction (XRD), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) to determine the underlying cause for the capacity loss. Results indicate a loss of lithium from the cathode and a thicker, non-active, fluorine-rich layer on the surface of the anode.

Nickel-metal hydride cells use AB5, AB2, AB, and A2B compounds for the negative electrode. These intermetallic compounds differ in the ease with which they are activated and their kinetics in forming the hydride phase. Various techniques are used to optimize the storage capacities of these different classes of materials. Long cycle lives are difficult to attain primarily due to surface oxidation and the large expansion of the intermetallic lattice caused by the formation of the hydride phase. This article reviews the different failure modes active in intermetallic hydrides and the recent ways researchers have tried to increase the cycle life.