We have been developing lithium-ion batteries for electric power storage and have chosen cell chemistries having a high energy density and long life. The cell chemistry consisted of a positive electrode containing a lithium-manganese spinel or a mixture of it with a layered-manganese-based material, and a negative electrode containing a hard carbon. The 8 Ah-class cells consisting of these cell chemistries showed that their extrapolated lives were long enough to withstand a cycling load for 10 years of use. A comparison of the cycle life data with the storage life data suggested the possibility to separate the capacity fading caused only by the storage and that only by the cycling, which is expected to be the basis of a prediction method for the calendar life. However, much work still needs to be done to achieve it. We also manufactured two types of 100 Ah-class cells as an experiment based on the results for the 8 Ah-class cells. They showed specific energies of 100 Wh kg(-1) and 106 Wh kg(-1). (C) 2010 Elsevier B.V. All rights reserved.