Batteries with good tolerance to high gamma-radiation environments are critical to NASA's future exploration missions to the outer planets, particularly Jupiter and its neighbors. Lithium-ion cells are generally expected to be less tolerant to radiation, due to their organic electrolyte solutions, polymer binders, and separators. Our earlier studies on aerospace lithium-ion prototype cells reveal a fairly good tolerance of the lithium-ion chemistry. A more detailed experimental evaluation has been carried out here on Sony/AEA/ComDev's 18650 cells to determine the effects of exposure to various levels of cumulative radiation levels, up to about 18 Mrad, and at different levels of intensities, on the performance of lithium-ion cells. The discharge performance, at ambient temperatures and at 0degreesC, and the electrochemical impedance spectroscopic (EIS) responses at ambient temperature were determined after each exposure. The ISIS data were analyzed for the electrochemical rate parameters and their changes upon irradiation, In addition, such measurements were made on control cells that went through the same degree of storage and/or cycling as the irradiated cells, without being subjected to radiation. Thus, these studies serve to quantify the performance loss sustained by lithium-ion cells subjected to gamma-radiation, in contrast to the previous studies, in which there are no control cells. Postradiation cycling tests were also carried out on these cells to assess their cyclability subsequent to radiation exposure. (C) 2005 The Electrochemical Society. All rights reserved.