Secondary battery and secondary battery manufacturing method

Abstract

In a secondary battery, for providing a structure which can enable a welding operation even when a gap is formed between a current collecting plate and a winding assembly, recessed portions are formed in a positive current collecting plate. The recessed portions are disposed opposite to the winding assembly. A laser beam is irradiated to welding protrusions located between the recessed portions to melt the welding protrusions. Here, since the end surface of a positive electrode foil is uneven in height, the positive electrode foil does not contact the positive current collecting plate necessarily. The welding operation is performed by heating, melting, and dropping the welding protrusions by the use of a YAG laser under the welding condition of a laser power of 900 W and a welding speed 2 m/min.

1 . A secondary battery with a structure in which a wound assembly formed by winding a positive electrode and a negative electrode with a separator interposed therebetween is received in a battery container along with an electrolyte and in which electricity which is charged in and discharged from the wound assembly can be taken from positive and negative electrode terminals to an outside,
 wherein a positive or negative metal foil protrudes from at least an end of the wound assembly, and   wherein said second battery has connected portions in which portions of a current collecting plate protruding in a direction contacting with the wound assembly are connected to portions of the metal foil protruding in a direction contacting with the current collecting plate,   an area to which said connected portion of the current collecting plate belongs is thicker than an area surrounding said connected portion of the current collecting plate, and   an area outside of said area surrounding the connected portion of the current collecting plate is thicker than the area surrounding the connected portion of the current collecting plate.   
     
     
         2 . The second battery according to  claim 1 ,
 wherein a surface of the area surrounding the connected portion of the current collecting plate, opposite to a surface in contact with the wound assembly, is lower than a surface of the area outside of the area surrounding the welding portion of the current collecting plate, opposite to a surface in contact with the wound assembly.   
     
     
         3 . The second battery according to  claim 1 ,
 wherein the areas surrounding the connected portion of the current collecting plate are an area which, before being connected, were a plurality of recessed areas provided on a surface of the current collecting plate opposite to a surface in contact with the wound assembly, and   wherein the area which the connected portion of the current collecting plate belongs is an area which, before being connected, was a convex portion formed between the plurality of recessed portions.   
     
     
         4 . The second battery according to  claim 1 ,
 wherein the connected portions of the current collecting plate are formed on the current collecting plate on the same side.   
     
     
         5 . The second battery according to  claim 1 ,
 wherein the connected portions of the current collecting plate are formed to connect two outer peripheral ends of the wound assembly.   
     
     
         6 . The second battery according to  claim 1 ,
 wherein the current collecting plate has at the outer periphery an outer peripheral bent portion which is bent toward the wound assembly.   
     
     
         7 . The second battery according to  claim 1 ,
 wherein a hole is formed at a center portion of the current collecting plate by punching and an inner peripheral bent portion which is bent toward the wound assembly is formed around the hole.   
     
     
         8 . The second battery according to  claim 1 ,
 wherein said connected portions are provided on both of the positive and negative metal foils.   
     
     
         9 . The second battery according to  claim 1 ,
 wherein said connected portions are connected by means of welding.   
     
     
         10 . The second battery according to  claim 1 ,
 wherein the portions of said current collecting plate protruding in the direction contacting with said wound assembly is formed by melting the current collecting plate.