Electric storage device, manufacturing method of electric storage device, and bus bar used for electric storage device

1. An electric storage device, comprising:

an electric storage element including an external terminal; and

a bus bar connected to the external terminal, a face of the bus bar which opposes the external terminal being flat,

wherein the bus bar includes a thin-walled portion and a thick-walled portion, the thin-walled portion being located around outer edges of the thick-walled portion,

wherein the thin-walled portion and the external terminal are directly welded together,

wherein a thickness of the thin-walled portion is less than a thickness of a remaining portion of the bus bar including the thick-walled portion, and

wherein the thin-walled portion has a circular shape that encircles the thick-walled portion.

2. The electric storage device according to claim 1 , wherein the electric storage device comprises at least two electric storage elements, and

wherein the thin-walled portions are provided to at least two portions of the bus bar and welded to the external terminals of the two electric storage elements.

3. The electric storage device according to claim 1 , wherein the thin-walled portion is formed at least at a portion of the bus bar in contact with the external terminal.

4. The electric storage device according to claim 1 , wherein the thin-walled portion is formed at a central portion in a width direction of the bus bar.

5. The electric storage device according to claim 1 , wherein the bus bar includes a main body portion and a connection portion continuous with the main body portion and to be connected to the external terminal, and

wherein the thin-walled portion is formed at the connection portion.

6. The electric storage device according to claim 5 , wherein the connection portion has a smaller width than the main body portion.

7. The electric storage device according to claim 5 , wherein the electric storage device comprises at least the two electric storage elements, and

wherein a pair of the connection portions are provided to both ends of the main body portion to connect the external terminals of the two electric storage elements.

8. The electric storage device according to claim 7 , wherein each of the electric storage elements includes a case and is in a shape of a flat prism, one face of the case on which the external terminal is disposed is in a rectangular shape, and at least the two electric storage elements are disposed so that the one faces are arranged in a longitudinal direction,

wherein the main body portion is formed to correspond to a width of the one face, and

wherein the connection portions are formed to correspond to a width of the external terminal which is smaller than the width of the one face.

9. The electric storage device according to claim 7 , wherein each of the electric storage elements includes a case and is in a shape of a flat prism, one face of the case on which the external terminal is disposed is in a rectangular shape, the plurality of electric storage elements are disposed in lines and rows so that the one faces are arranged in a longitudinal direction and a short-side direction,

wherein the main body portion of the bus bar for connecting the external terminals of the two electric storage elements arranged in the longitudinal direction out of the bus bars is formed to correspond to a width of the one face, and

wherein the connection portions of the bus bar are formed to correspond to a width of the external terminal which is smaller than the width of the one face.

10. The electric storage device according to claim 1 , wherein the thin-walled portion is formed in a stepped shape.

11. The electric storage device according claim 1 , wherein an entirety of the face of the bus bar which opposes the external terminal is flat.

12. An electric storage device, comprising:

an electric storage element including an external terminal; and

a bus bar connected to the external terminal, a face of the bus bar, which opposes the external terminal, being flat,

wherein the bus bar has a substantially rectangular shape in a plan view and includes a main body portion and a connection portion, the connection portion being connected to the external terminal,

wherein a thin-walled portion is formed at a center portion in a width direction of the connection portion,

wherein a thick-walled portion of the connection portion is formed inside the thin-walled portion such that the thin-walled portion is located around outer edges of the thick-walled portion,

wherein the thin-walled portion and the external terminal are directly welded together,

wherein the thin-walled portion is formed in a stepped shape and a thickness of the thin-walled portion is less than a thickness of a remaining portion of the bus bar including the thick-walled portion, and

wherein the thin-walled portion has a circular shape that encircles the thick-walled portion.

13. The electric storage device according to claim 1 , wherein the bus bar further includes another thick-walled portion located around outer edges of the thin-walled portion, the thickness of the thin-walled portion being less than a thickness of said another thick-walled portion.