Flat battery

Abstract

A flat battery of the present invention is a flat battery including an exterior can and a sealing can with which an opening of the exterior can is sealed, wherein the exterior can and the sealing can include a bottom portion and a circumferential wall extending upright from an outer circumference of the bottom portion and have a cylindrical shape that is open at one end; a distal end portion of the circumferential wall of the exterior can is bent toward a central axis of the sealing can to form a curve, whereby the exterior can is fixed to the sealing can by crimping; in a cross-sectional shape of the sealing can in the direction of the central axis, the circumferential wall of the sealing can is a single layer wall without being folded back, and the circumferential wall of the sealing can includes a rectilinear portion that is connected to the bottom portion via a corner portion; and the rectilinear portion has a Vickers hardness greater than the Vickers hardness of the corner portion.

What is claimed is: 
     
         1 . A method for manufacturing a flat battery, comprising:
 (a) a step of obtaining an exterior can that comprises a bottom portion and a circumferential wall extending upright from an outer circumference of the bottom portion and has a cylindrical shape that is open at one end;   (b) a step of obtaining a sealing can that comprises a bottom portion and a circumferential wall extending upright from an outer circumference of the bottom portion and has a cylindrical shape that is open at one end, the circumferential wall is a single layer wall without being folded back;   (c) a step of fitting the exterior can on the sealing can so that the circumferential wall of the exterior can is positioned outside the circumferential wall of the sealing can; and   (d) a step of bending a distal end portion of the circumferential wall of the exterior can toward a central axis of the sealing can to form a curve, whereby the exterior can is fixed to the sealing can by crimping,   wherein the step (b) comprises:   (b1) a step of obtaining a disk-like member from a plate material;   (b2) a step of drawing the disk-like member so as to form the bottom portion and the circumferential wall having a first rectilinear portion connected to the bottom portion via a corner portion; and   (b3) a step of beating the circumferential wall so that the first rectilinear portion has a Vickers hardness greater than a Vickers hardness of the corner portion.   
     
     
         2 . The method for manufacturing a flat battery according to  claim 1 , wherein in the step (b3), the circumferential wall is beaten so that the Vickers hardness of the corner portion is 150 or more and the Vickers hardness of the first rectilinear portion is 200 or more. 
     
     
         3 . The method for manufacturing a flat battery according to  claim 1 , wherein in the step (b3), the circumferential wall is beaten so that the Vickers hardness of the corner portion is 210 or less. 
     
     
         4 . The method for manufacturing a flat battery according to  claim 1 , wherein in the step (b3), the circumferential wall is beaten so that the Vickers hardness of the first rectilinear portion is 1.05 times or more greater than the Vickers hardness of the corner portion. 
     
     
         5 . The method for manufacturing a flat battery according to  claim 1 , wherein in the step (b3), the circumferential wall is beaten so that the Vickers hardness of the first rectilinear portion is 1.6 times or less greater than the Vickers hardness of the corner portion. 
     
     
         6 . The method for manufacturing a flat battery according to  claim 1 , wherein in the step (b3), the circumferential wall is beaten so that that throughout the circumferential wall of the sealing can, the Vickers hardness is greater than the Vickers hardness of the corner portion. 
     
     
         7 . The method for manufacturing a flat battery according to  claim 1 , wherein in the step (b3), the circumferential wall is beaten so that the circumferential wall is deformed under compression and work hardened. 
     
     
         8 . The method for manufacturing a flat battery according to  claim 1 , wherein the step (b) comprises further (b4) a step of forming a second rectilinear portion and a shoulder portion stepped between the first rectilinear portion and the second rectilinear portion in the circumferential wall of the sealing can,
 in the step (d), the exterior can is fixed to the sealing can by crimping so that the second rectilinear portion is sandwiched between the distal end portion of the circumferential wall of the exterior can and the bottom portion of the exterior can.   
     
     
         9 . The method for manufacturing a flat battery according to  claim 8 , wherein the second rectilinear portion has a Vickers hardness greater than the Vickers hardness of the corner portion. 
     
     
         10 . The method for manufacturing a flat battery according to  claim 8 , wherein the Vickers hardness of the second rectilinear portion is 200 or more. 
     
     
         11 . The method for manufacturing a flat battery according to  claim 8 , wherein the Vickers hardness of the second rectilinear portion is 1.05 times or more greater than the Vickers hardness of the corner portion. 
     
     
         12 . The method for manufacturing a flat battery according to  claim 8 , wherein the second rectilinear portion has a thickness greater than a thickness of the corner portion. 
     
     
         13 . The method for manufacturing a flat battery according to  claim 8 , wherein the thickness of the second rectilinear portion is 1.01 times or more greater than the thickness of the corner portion. 
     
     
         14 . The method for manufacturing a flat battery according to  claim 8 , wherein the second rectilinear portion has a thickness greater than a thickness of the first rectilinear portion. 
     
     
         15 . The method for manufacturing a flat battery according to  claim 1 , wherein in the step (c), a gasket is interposed between the circumferential wall of the exterior can and the circumferential wall of the sealing can, and the sealing can is fitted against the exterior can.