PURPOSE: To provide a good cycle characteristic by using specific metallic oxides as active materials for both positive and negative electrodes.

CONSTITUTION: A carbon electrode is used as a negative electrode, and an oxide of lithium and manganese is used as an active material for a positive electrode. 4 parts by weight of acetylene black and 10 parts by weight of polyvinylidene fluoride(PVDF) serving as a binding agent are added to 86 parts by weight of meso-carbon microbeads (d002 = 3.37) which are heat treated at 2800°C, and this mixture is wet mixed with N-methyl-2-pyrolidone and formed into a slurry (paste), the N-methyl-2-pyrolidone serving as a solvent. The slurry is applied uniformly to both sides of 0.02-mm thick copper foil serving as a collector, and after drying pressure molding is performed with a roller press to form a 0.15-mm thick sheet-shaped negative electrode 1. The negative electrode 1 has its length adjusted to 51 1mm and has two kinds of widths, large and small (57mm and 52mm, respectively). Since the battery performance is not deteriorated by overdischarge, a battery assembly comprising a number of unit cells connected together can have a good cycle characteristic even if the batteries differ in capacity from one another.