NONAQUEOUS ELECTROLYTE SECONDARY BATTERY AND METHOD FOR MANUFACTURING THE SAME

1 . A nonaqueous electrolyte secondary battery, comprising:

a positive electrode including a positive electrode current collector and a positive electrode material mixture layer containing a positive electrode active material and a binder and 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 3.0% or more,

the binder is made of polyvinylidene fluoride, and

the positive electrode current collector has a softening temperature lower than a crystalline melting point of the binder.

2 . 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 by using 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.

3 . The nonaqueous electrolyte secondary battery of claim 1 , wherein the positive electrode current collector is made of aluminium containing iron.

4 . The nonaqueous electrolyte secondary battery of claim 3 , wherein an amount of iron contained in the positive electrode current collector is 1.40 weight percent (wt. %) or more.

5 . The nonaqueous electrolyte secondary battery of claim 1 , wherein the positive electrode current collector has a dynamic hardness of 70 or less.

6 . The nonaqueous electrolyte secondary battery of claim 1 , wherein measurement of stress on a sample positive electrode whose circumferential surface is being pressed at 10 mm/min 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 by using the positive electrode, has a circumference of 100 mm, and is rolled up in the shape of a single complete circle.

7 . The nonaqueous electrolyte secondary battery of claim 1 , wherein

the negative electrode has a tensile extension percentage of 3.0% or more, and the porous insulating layer has a tensile extension percentage of 3.0% or more.

8 . A method for fabricating a nonaqueous electrolyte secondary battery including a positive electrode including a positive electrode current collector and a positive electrode material mixture layer containing a positive electrode active material and a binder and 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; and

(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 predetermined thickness, and

(a3) performing heat treatment on the positive electrode coated with the dried positive electrode material mixture slurry at a predetermined temperature after step (a2),

the binder is made of polyvinylidene fluoride, and

the predetermined temperature is higher than or equal to a softening temperature of the positive electrode current collector and lower than a crystalline melting point of the binder.

9 . The method of claim 8 , wherein the positive electrode current collector is made of aluminium containing iron.

10 . The method of claim 9 , wherein an amount of iron contained in the positive electrode current collector is 1.40 weight percent (wt. %) or more.

11 . The method of claim 8 , wherein in step (a3), the heat treatment is performed on the positive electrode by bringing the positive electrode and a heated roll into contact with each other.

12 . A method for fabricating a nonaqueous electrolyte secondary battery including a positive electrode including a positive electrode current collector and a positive electrode material mixture layer containing a positive electrode active material and a binder and 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; and

(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 predetermined thickness, and

(a3) performing heat treatment on the positive electrode coated with the dried positive electrode material mixture slurry at a predetermined temperature after step (a2),

the binder is made of polyvinylidene fluoride, and

the predetermined temperature is higher than or equal to a crystalline melting point of the binder and lower than a decomposition temperature of the binder.

13 . The method of claim 12 , wherein the positive electrode current collector is made of aluminium containing iron.

14 . The method of claim 13 , wherein an amount of iron contained in the positive electrode current collector is 1.40 weight percent (wt. %) or more.

15 . The method of claim 12 , wherein in step (a3), the heat treatment is performed on the positive electrode by bringing the positive electrode and a heated roll into contact with each other.