BATTERY MODULE AND BATTERY SYSTEM

PROBLEM TO BE SOLVED: To provide a battery module or the like having large energy density per unit volume. SOLUTION: This battery module is composed by arranging, in spaces formed in arranging a plurality of cylindrical sodium secondary batteries 10A in a heat insulation vessel 30, a plurality of sodium secondary batteries 20A each having a diameter smaller than that of each sodium secondary battery 10A. Although the spaces are naturally formed when a plurality of the secondary batteries 10A are arranged in the insulation vessel 30, total battery capacity as the entire battery module can be increased without changing the size of the insulation vessel 30, and the energy density per unit volume as the entire battery module can remarkably be improved by arranging a plurality of the small-diameter sodium secondary batteries 20A in the spaces. COPYRIGHT: (C)2005,JPO&NCIPI