Lithium-Ion (liquid electrolyte) batteries are considered as long life and reliable systems. This paper:introduces discussion about aging and degradation mechanism both for storage and cycling,illustrates the proposed phenomena from results based on several years experimentation and obtained on scale one cells,shows the behaviour of several kinds of active materials,proposes some trends for life prediction.Aging in Li-Ion cells may mainly come from:reactions of active materials with electrolyte at electrodes interfaces,self degradation of active materials structure on cycling,aging of non active components (ex: electrodes binders).These phenomena lead to energy and/or power losses.Reaction rates on depending on:type of materials and reactivityimpuritiesmanufacturing processescell designtype of application and profile of use.On the negative electrode side the main parameters are passivation layer stability, the layer structure/composition (effect of additives in electrolyte and formation process), polluting agents.On the positive electrode side key factors seem to be the material structure evolution and organic solvent oxidation.These phenomena are highly dependent of voltage and temperature.So far, according to experimentation for electric (EV) and hybrid (HV) vehicles applications, using scale 1 cells built with nickel based positive material the results show:more than 1200 deep cycle (80% d.o.d. EV cycle) with only few percent of energy and power losses,more than 500000 shallow cycles (3% d.o.d. HV cycle) with negligible power losses,2 years of storage testing at full charge and various temperature (20 degreesC/40 degreesC/60 degreesC) leading to a life expectation of 10 years for EV applications and 15 years for HV applications. (C) 2003 Elsevier B.V. All rights reserved.