A positive electrode plate, a negative electrode plate and a separator, all of which are formed into bands each with a predetermined width, are wound flat with the separator interventing between the positive and negative electrode plates, and this group 1a of electrode plates, being square in top view, has its corners cut into straight or arc to improve space factor within a circular negative electrode case 5. 一定幅の帯状に形成された正極極板、負極極板、セパレータを、正極極板と負極極板との間にセパレータを介して偏平に巻回し、平面形状が四角形になった極板群1aの角部を直線または円弧にカットして、円形の負極ケース5内でのスペース効率を向上させる。 - 特許庁