Patent ID: 7745041

Claim:
An electrochemical element comprising a case, an electrolyte, and an electrode assembly accommodated in the case with the electrolyte, the electrode assembly including a positive electrode having a current collector strip with a positive electrode active material deposited thereon, and a negative electrode having a current collector strip with a negative electrode active material deposited thereon, the positive and negative electrodes being wound around a separator interposed therebetween to form the electrode assembly, positive and negative leads respectively connected to portions of the positive and negative electrodes to serve as respective positive and negative external connection terminals, wherein the positive and negative electrodes include respective exposed current collector portions at both ends in a lengthwise direction where respective positive electrode active material and negative electrode active material have not been deposited; the exposed current collector portions are bent from a lengthwise direction along a bending line of a predetermined angle, the bending direction of one electrode being opposite from that of the other electrode, such that edges of the exposed current collector portions in the lengthwise direction protrude beyond an edge of the electrodes in a width direction to form welding pieces; the positive and negative electrodes with the separator interposed therebetween are wound to form the electrode assembly having an ellipsoidal cross-section, such that the welding pieces are located in a linear portion of the ellipsoidal shape; and a welding piece of the positive electrode protruding out from one end of the electrode assembly is pressed together in a shorter side direction of the ellipsoidal cross-section and is welded together with the positive lead to form a welding joint, and a welding piece of the negative electrode protruding out from the other end of the electrode assembly is pressed together in the shorter side direction of the ellipsoidal cross-section and is welded together with the negative lead to form a welding joint, wherein exposed current collector portions at the ends of the positive and negative electrodes are split in a widthwise direction such that split portions are approximate rectangles having a predetermined ratio of long and short sides to protrude from the edge of the electrode assembly by a predetermined distance.