Protective element and secondary battery device

1. A protection element comprising:

a low-melting metal conductor which is provided between a pair of electrodes disposed at both ends of a top face of an insulation baseboard, which is connectable to a power supply path of a device targeted to be protected, and which causes a blowout when a predetermined abnormal electric power amount is supplied;

an insulation cover member which is mounted on the baseboard, and which covers the low-melting metal conductor with a predetermined space; and

a flux coated on a surface of the low-melting metal conductor and positioned in the space before the blowout;

wherein, in a case where the abnormal electric power amount is supplied to the device targeted to be protected, the low-melting metal conductor causes the blowout, and a current path thereof is shut off;

wherein said protection element further comprises a stepped portion which is formed by a protrusion on an interior face of the insulation cover member opposite to a center part of the low-melting metal conductor, for adhering to and retaining the flux before the blowout such that the flux remains in contact with both a surface of the protrusion and the center part of the low-melting metal conductor by means of surface tension and wettability;

wherein the protrusion comprises a cylindrical protrusive stripe which is formed with a circular stepped portion at a position facing the center part of the low-melting metal conductor; and

wherein the insulation cover member is formed in the shape of a box which opens at one side face part thereof, and which is adapted to cover the baseboard with the predetermined space being formed relative to the low-melting metal conductor.

2. The protection element as set forth in claim 1 , wherein when the low-melting metal conductor causes the blowout, an end face of the stepped portion at a side of the low-melting metal conductor is provided at a position at which a top part of the blowout low-melting metal conductor does not come into contact.

3. The protection element as set forth in claim 1 , further comprising a second protrusion, which is provided opposite to the stepped portion, at an end of the low-melting metal conductor.

4. The protection element as set forth in claim 1 , wherein a cutout portion communicating with a space at a back side of the insulation cover member is formed in the protrusive stripe.

5. The protection element as set forth in claim 4 , wherein the cutout portion is provided at a position which is symmetrical to a center axis of the insulation cover member.

6. The protection element as set forth in claim 1 , wherein:

the low-melting metal conductor is laminated on the baseboard via an insulation layer and a heating element;

the low-melting metal conductor and the heating element are connected between a plurality of electrodes including the pair of electrodes formed on the baseboard; and

a number of the electrodes formed on the baseboard is three or less.

7. The protection element as set forth in claim 1 , wherein dimensional ratios of a size of the baseboard meet a condition that a length to thickness ratio is 1080%:50 to 78% and a width to thickness ratio is 640%:50 to 78%.

8. The protection element as set forth in claim 7 , wherein the dimensional ratios further meet a condition that the width to thickness ratio is 640%:50 to 56%.

9. A secondary battery device, wherein the protection element as set forth in claim 1 is provided in a power supply path of a secondary battery.

10. The protection element as set forth in claim 1 , wherein the protrusion comprises two protrusive stripes which are formed in concentric circular shapes on the interior face of the insulation cover member.