CROSS REFERENCE TO RELATED APPLICATIONS

The present invention application claims priority to Japanese Patent Application No. 2018-162756 filed in the Japan Patent Office on Aug. 31, 2018, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to a secondary battery.

Description of Related Art

Japanese Published Unexamined Patent Application No. 2017-41299 (Patent Document 1) discloses a typical secondary battery in itsFIG. 4. This secondary battery includes an exterior package that has a substantially cuboid recess and a sealing plate that seals an opening. The sealing plate has a pair of through-holes, and negative electrode terminal has been inserted into one of the through-holes. The negative electrode terminal has a first region formed of aluminum and a second region formed of copper. The second region is on the recess side relative to the first region in the height direction, and the upper end surface of the second region joins the lower end surface of the first region in the height direction. The boundary between the first region and the second region overlies the upper surface of the sealing plate, the joint part has an exposed part that is exposed to the outside on the side surface of the negative electrode terminal.

In such a secondary battery, the negative electrode terminal has the first region formed of aluminum on the upper side thereof in the height direction and can be therefore readily welded to a light aluminum bus bar, which enables a reduction in the weight of the bus bar.

A salt spray test, in which salt water is sprayed on a secondary battery, is performed to examine the corrosion of the secondary battery, and it is found that some of the salt water adheres to the exposed part in the negative electrode terminal. Some adhering salt water causes galvanic corrosion, and aluminum having a higher ionization tendency than copper is dissolved into the salt water around the exposed part in the negative electrode, which promotes the corrosion of the part formed of aluminum around the exposed part.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present disclosure to provide a secondary battery that includes a terminal having two or more regions formed of different materials and that enables a reduction in the corrosion of the terminal around the boundary between the different regions.

In order to address the above-mentioned problem, a secondary battery according to an aspect of the present disclosure includes an exterior package having an opening at one end in a height direction, a sealing plate that seals the opening and that has a through-hole, an electrode body that is disposed inside the exterior package and that includes a positive electrode and a negative electrode, and a terminal that is inserted into the through-hole to be electrically connected to the positive electrode or the negative electrode, wherein the terminal has a first region formed of a first material and a second region formed of a second material having a different ionization tendency from the first material; the terminal has a flange having an outer diameter larger than the inner diameter of the through-hole; the flange is disposed so as to face the outer surface of the sealing plate; an insulating member is disposed between the flange and the outer surface of the sealing plate; and a boundary between the first region and the second region has an exposed part that is exposed to the outside, and the exposed part is positioned at an opposite corner on the periphery of the flange to the sealing plate.

The term “corner” herein refers to a vicinity of the part at which the upper surface of the flange joins the side surface of the flange. In particular, the corner can be a region within 2 mm from the part at which the upper surface of the flange joins the side surface of the flange.

A secondary battery according to another aspect of the present disclosure includes an exterior package having an opening at one end in a height direction, a sealing plate that seals the opening and that has a through-hole, an electrode body that is disposed inside the exterior package and that includes a positive electrode and a negative electrode, and a terminal that is inserted into the through-hole to be electrically connected to the positive electrode or the negative electrode, wherein the terminal has a first region formed of a first material and a second region formed of a second material having a different ionization tendency from the first material; the terminal has a flange having an outer diameter larger than the inner diameter of the through-hole; the flange is disposed so as to face the outer surface of the sealing plate; an insulating member is disposed between the flange and the outer surface of the sealing plate; the insulating member has a base disposed along the outer surface of the sealing plate and a protruding insulating part that protrudes from the base and that faces the side surface of the flange; a boundary between the first region and the second region has an exposed part that is exposed to the outside, and the exposed part is positioned on the side surface of the flange; and the exposed part is positioned on the upper surface side of the flange relative to an end of the protruding insulating part that is on the upper surface side of the flange.

A secondary battery according to the present disclosure includes a terminal having two or more regions formed of different materials and enables a reduction in the corrosion of the terminal around the boundary between the different regions.

