NONAQUEOUS ELECTROLYTE SECONDARY BATTERY AND METHOD FOR FABRICATING THE SAME ( as amended

Abstract

A nonaqueous electrolyte secondary battery includes: a positive electrode 4 including a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material and a binder, the positive electrode mixture layer being provided on the positive electrode current collector; a negative electrode 5 ; a porous insulating layer 6 interposed between the positive electrode 4 and the negative electrode 5 ; and a nonaqueous electrolyte. The positive electrode 4 has a tensile extension percentage of equal to or higher than 3.0%. The positive electrode current collector is made of aluminium containing iron. In this manner, the tensile extension percentage of the positive electrode is increased without a decrease in capacity of the nonaqueous electrolyte secondary battery. Accordingly, even when the nonaqueous electrolyte secondary battery is destroyed by crush, occurrence of short-circuit in the nonaqueous electrolyte secondary battery can be suppressed.

1 . A nonaqueous electrolyte secondary battery, comprising:
 a positive electrode including a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material and a binder, the positive electrode mixture layer being provided on the positive electrode current collector;   a negative electrode;   a porous insulating layer interposed between the positive electrode and the negative electrode; and   a nonaqueous electrolyte, wherein   the positive electrode has a tensile extension percentage of equal to or higher than 3.0%.   
     
     
         2 . The nonaqueous electrolyte secondary battery of  claim 1 , wherein the negative electrode has a tensile extension percentage of equal to or higher than 3.0%, and
 the porous insulating layer has a tensile extension percentage of equal to or higher than 3.0%.   
     
     
         3 . The nonaqueous electrolyte secondary battery of  claim 1 , wherein the tensile extension percentage of the positive electrode is calculated from a length of a sample positive electrode formed out of the positive electrode and having a width of 15 mm and a length of 20 mm immediately before the sample positive electrode is broken with one end of the sample positive electrode fixed and the other end of the sample positive electrode extended along a longitudinal direction thereof at a speed of 20 mm/min, and from a length of the sample positive electrode before the sample positive electrode is extended. 
     
     
         4 . The nonaqueous electrolyte secondary battery of  claim 1 , wherein the positive electrode current collector has a dynamic hardness of equal to or less than 70, and
 the positive electrode mixture layer has a dynamic hardness of equal to or less than 5.   
     
     
         5 . The nonaqueous electrolyte secondary battery of  claim 1 , wherein measurement of stress on a sample positive electrode whose circumferential surface is being pressed at a given speed shows that no inflection point of stress arises until a gap corresponding to the sample positive electrode crushed by the pressing reaches 3 mm, inclusive, and
 the sample positive electrode is formed out of the positive electrode, has a circumference of 100 mm, and is rolled up in the shape of a single complete circle.   
     
     
         6 . The nonaqueous electrolyte secondary battery of  claim 5 , wherein the given speed is 10 mm/min. 
     
     
         7 . The nonaqueous electrolyte secondary battery of  claim 1 , wherein the positive electrode current collector is made of aluminium containing iron. 
     
     
         8 . The nonaqueous electrolyte secondary battery of  claim 7 , wherein an amount of iron contained in the positive electrode current collector is in the range from 1.20 wt % to 1.70 wt %, both inclusive. 
     
     
         9 . The nonaqueous electrolyte secondary battery of  claim 1 , wherein the binder is one of poly vinylidene fluoride and a derivative of poly vinylidene fluoride. 
     
     
         10 . The nonaqueous electrolyte secondary battery of  claim 1 , wherein the binder is a rubber-based binder. 
     
     
         11 . The nonaqueous electrolyte secondary battery of  claim 1 , wherein an amount of the binder contained in the positive electrode mixture layer is in the range from 3.0 vol % to 6.0 vol %, both inclusive, with respect to 100.0 vol % of the positive electrode active material. 
     
     
         12 . The nonaqueous electrolyte secondary battery of  claim 1 , wherein the positive electrode active material has an average particle diameter in the range from 5 μm to 20 μm, both inclusive. 
     
     
         13 . A method for fabricating a nonaqueous electrolyte secondary battery including: a positive electrode including a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material and a binder, the positive electrode mixture layer being provided on the positive electrode current collector; a negative electrode; a porous insulating layer interposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte, the method comprising the steps of:
 (a) preparing the positive electrode;   (b) preparing the negative electrode;   (c) either winding or stacking the positive electrode and the negative electrode with the porous insulating layer interposed therebetween, after steps (a) and (b), wherein   step (a) includes the steps of:   (a1) coating the positive electrode current collector with positive electrode material mixture slurry containing the positive electrode active material and the binder, and drying the slurry;   (a2) rolling the positive electrode current collector coated with the dried positive electrode material mixture slurry, thereby forming the positive electrode having a given thickness; and   (a3) performing heat treatment on the positive electrode at a given temperature, after step (a2).   
     
     
         14 . The method of  claim 13 , wherein the positive electrode current collector is made of aluminium containing iron. 
     
     
         15 . The method of  claim 14 , wherein an amount of iron contained in the positive electrode current collector is in the range from 1.20 wt % to 1.70 wt %, both inclusive. 
     
     
         16 . The method of  claim 13 , wherein the given temperature is higher than a softening temperature of the positive electrode current collector. 
     
     
         17 . The method of  claim 13 , wherein the given temperature is lower than a decomposition temperature of the binder. 
     
     
         18 . The method of  claim 13 , wherein an amount of the binder contained in the positive electrode material mixture slurry is in the range from 3.0 vol % to 6.0 vol %, both inclusive, with respect to 100.0 vol % of the positive electrode active material. 
     
     
         19 . The method of  claim 13 , wherein in step (a3), the heat treatment is performed on the positive electrode at the given temperature with hot air subjected to low humidity treatment. 
     
     
         20 . The method of  claim 19 , wherein in step (a3), the given temperature is in the range from 250° C. to 350° C., both inclusive, and
 the heat treatment is performed in a period of time ranging from 10 seconds to 120 seconds, both inclusive.   
     
     
         21 . The method of  claim 19 , wherein in step (a3), the given temperature is in the range from 220° C. to 250° C., both inclusive, and
 the heat treatment is performed in a period of time ranging from 2 minutes to 60 minutes, both inclusive.   
     
     
         22 . The method of  claim 19 , wherein in step (a3), the given temperature is in the range from 160° C. to 220° C., both inclusive, and
 the heat treatment is performed in a period of time ranging from 60 minutes to 600 minutes, both inclusive.   
     
     
         23 . The method of  claim 13 , wherein in step (a3), the heat treatment is performed on the positive electrode by bringing a heated roll heated at the given temperature into contact with the positive electrode. 
     
     
         24 . The method of  claim 23 , wherein in step (a3), the given temperature is 280° C., and
 the heat treatment is performed in a period of time equal to or less than 10 seconds.