Secondary battery
A first electrode current collector is joined to a multilayer of a positive electrode core in a part including no positive electrode active material layer of the first electrode core, by ultrasonic welding in a joint area. The joint area, at which the multilayers of the first electrode core where the first electrode cores are stacked is joined to the first electrode current collector by ultrasonic welding, includes a plurality of core recesses. A core projection is formed between each adjacent pair of the plurality of core recesses of the multilayer of the first electrode core with the first electrode core flexed in a convex shape. A gap in an arc shape is formed between the adjacent pair of the layers of the first electrode core forming the core projection. The gap has a length decreasing from an apex to a bottom of the core projection.
1 . A secondary battery comprising:
an electrode body including a first electrode plate, and a second electrode plate with a different polarity from the first electrode plate; and
a first electrode current collector electrically connected to the first electrode plate;
the first electrode plate including a first electrode core and a first electrode active material layer on the first electrode core,
the first electrode core being made of aluminum or an aluminum alloy,
the first electrode current collector being made of aluminum or an aluminum alloy,
the electrode body including a multilayer of the first electrode core where the first electrode cores are stacked,
the first electrode current collector being joined to the multilayer of the first electrode core by ultrasonic welding in a joint area,
the joint area, at which the multilayers of the first electrode core is joined to the first electrode current collector by ultrasonic welding, including a plurality of core recesses,
a core projection being formed between the core recesses with the first electrode core flexed in a convex shape,
a gap in an arc shape being formed between an adjacent pair of layers of the multilayer of the first electrode core forming the core projection,
the core projection has a height of n×0.5×t or less from bottoms of the core recesses, where n is the number of layers of the first electrode core in the multilayer of the first electrode core, and t is a thickness of the first electrode core.
2 . The secondary battery of claim 1 , wherein
the core projection is obtained by flexing at least n×0.3 or more layers of the first electrode core, where n is the number of layers of the first electrode core in the multilayer of the first electrode core.
3 . The secondary battery of claim 1 , wherein
the core projection has a height of n×0.3×t or more from bottoms of the core recesses, where n is the number of layers of the first electrode core in the multilayer of the first electrode core, and t is a thickness of the first electrode core.
4 . The secondary battery of claim 1 , wherein
the gap is left under the core projection in the multilayer of the first electrode core.
5 . The secondary battery of claim 1 , wherein
the core projection has an apex angle ranging from 60° to 90°.
6 . The secondary battery of claim 1 , wherein
the first electrode plate has a long shape,
the second electrode plate has a long shape,
the electrode body is a wound electrode body in a flat shape obtained by winding the first electrode plate and the second electrode plate with a long separator interposed therebetween, and
the wound electrode body includes, at one end, the multilayer of the first electrode core including an exposed part for the first electrode core that is wound.