Lithium Ion Cells

Where applications demand the greatest energy density and minimum weight, Lithium Ion (Li-Ion) rechargeable cells have quickly become the battery of choice despite their continued high cost. Recent advances in the cells and recharging methods are described in this article.The ideal rechargeable battery is still a long way off. For high current application the established Nicad (Nickel Cadmium or NiCd) cell has always been preferred. Recent tests have established that the so-called memory effect (see box) is no longer a problem with this type of cell. From a cost standpoint Nicads are the cheapest cell but they do incur an environmental cost. They contain the heavy metal cadmium and should therefore not be consigned to landfill sites at the end of their life. For this reason Europe is committed to cease production of Nicads by 1998. Nickel metal Hydride (NiMH) cells are becoming increasingly seen as a better alternative. They have the advantage of not containing harmful heavy metals and offer a better energy density (cell size to stored energy ratio). We have seen a doubling of their energy density since they were first introduced with the prospect of a 2.0 Ah AA sized cell not far off.