Nonaqueous electrolyte secondary battery

Abstract

The invention provides a nonaqueous electrolyte secondary battery excellent in output characteristic such as large current discharge or pulse discharge in ordinary use, high in safety by preventing destruction due to suppression of current in an abnormality such as external short-circuiting, and further large in capacity. The nonaqueous electrolyte secondary battery comprises an external can opened at one end thereof, an electrode assembly contained in the external can, and comprising a negative electrode, a separator and a positive electrode, a nonaqueous electrolyte contained in the external can, and a sealing lid group tightly sealed at the opening of the external can by way of an insulating member, wherein the sealing lid group includes an intact plate-like PTC element having a fragile portion to be easily broken due to elevation of internal pressure by gas generation.

1 . A nonaqueous electrolyte secondary battery comprising: 
 an external can opened at one end thereof;    an electrode assembly contained in the external can, and comprising a negative electrode, a separator and a positive electrode;    a nonaqueous electrolyte contained in the external can; and    a sealing lid group tightly sealed at the opening of the external can by way of an insulating member,    wherein the sealing lid group comprises an intact plate-like PTC element having a fragile portion to be easily broken due to elevation of internal pressure by gas generation.    
     
     
         2 . The nonaqueous electrolyte secondary battery according to  claim 1 , wherein the PTC element has a structure in which a resin sheet containing conductive carbon is interposed between a pair of electrodes composed of a metal thin film.  
     
     
         3 . The nonaqueous electrolyte secondary battery according to  claim 2 , wherein the fragile portion is a notch formed at least in one of the pair of electrodes in the PTC element.  
     
     
         4 . The nonaqueous electrolyte secondary battery according to  claim 3 , wherein the notch has a depth of 4% or more of the electrode thickness, and not more than the total of the electrode thickness and 20% of the thickness of the resin sheet.  
     
     
         5 . The nonaqueous electrolyte secondary battery according to  claim 3 , wherein the notch has a width of 5 μm or more.  
     
     
         6 . The nonaqueous electrolyte secondary battery according to  claim 3 , wherein the notch has an opening area of 1 mm 2  or more.  
     
     
         7 . The nonaqueous electrolyte secondary battery according to  claim 1 , wherein the fragile portion is a recess formed in the PTC element.  
     
     
         8 . The nonaqueous electrolyte secondary battery according to  claim 7 , wherein the recess has a depth of 20 μm or more.  
     
     
         9 . The nonaqueous electrolyte secondary battery according to  claim 1 , wherein the sealing lid group further comprises a rupture plate whose outer periphery is fixed to the insulating member, the rupture plate having a fragile portion to be broken easily by elevation of internal pressure by gas generation.  
     
     
         10 . The nonaqueous electrolyte secondary battery according to  claim 9 , wherein the fragile portion is a notch formed at least in one side of the rupture plate.  
     
     
         11 . The nonaqueous electrolyte secondary battery according to  claim 1 , wherein the sealing lid group further comprises a battery breaking member.  
     
     
         12 . The nonaqueous electrolyte secondary battery according to  claim 1 , wherein the sealing lid group further comprises a conductive support plate positioned at one side of the PTC element and fixed in the insulating member at a peripheral edge thereof.  
     
     
         13 . The nonaqueous electrolyte secondary battery according to  claim 12 , wherein the support plate has an intact fragile portion to be broken easily by elevation of internal pressure by gas generation.  
     
     
         14 . The nonaqueous electrolyte secondary battery according to  claim 13 , wherein the support plate is a ring.  
     
     
         15 . The nonaqueous electrolyte secondary battery according to  claim 12 , wherein the support plate is composed of a ring plate to be fixed by the insulating member, a thin plate fixed to cover a hollow space at least at one side of the ring plate excluding the fixed portion by the insulating member, and a fragile portion to be broken easily by elevation of internal pressure by gas generation, the fragile portion being formed in the thin plate.  
     
     
         16 . The nonaqueous electrolyte secondary battery according to  claim 12 , wherein the support plate is composed of a ring plate, and a circular high molecular resin layer disposed in tight contact with the inner side of a hollow space of the ring plate.