1. Field of the Invention
The present disclosure relates to a secondary battery and a battery pack, and particularly relates to a secondary battery including a current cut-off device, and a battery pack configured by connecting a plurality of secondary batteries of this type.
2. Description of Related Art
Japanese Patent Application Publication No. 2011-258550 discloses a secondary battery having a configuration that deforms a short-circuiting member by increase in inner pressure of a case so as to short-circuit a positive electrode terminal and a negative electrode terminal to fuse a fuse portion by an overcurrent, thereby cutting off an electric connection between the positive electrode terminal and an electrode body.
In the configuration as described in JP 2011-258550 A, the short-circuiting member is formed to be thin enough to be easily inverted by the pressure. Hence, the short-circuiting member might be fused before the fuse portion is fused due to a large current flowing in a moment at the time of the short circuit.
If the short-circuiting member is fused but the fuse portion does not work, connection between the terminal and the electrode body is maintained, so that increase in inner pressure of the case is continued. Consequently, the secondary battery might be damaged.
On the other hand, if the short-circuiting member is fused and the fuse portion works, the connection between the terminal and the electrode body is cut off, and no short circuit between the positive electrode terminal and the negative electrode terminal is formed, and thus a cut-off of conduction among batteries is caused by an abnormal secondary battery. Consequently, it becomes impossible to pick up electric power from normal batteries, which disables charging and discharging in the whole battery pack.