Separator for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery using the same

1. A separator for a non-aqueous electrolyte secondary battery, the separator comprising a biaxially-oriented polyolefin porous film including extended-chain crystals and folded-chain crystals, wherein:

the extended-chain crystals and the folded-chain crystals form a biaxially-oriented structure in which the extended-chain crystals are rod-like crystals oriented in a first direction corresponding to an orientation direction of molecules, and the folded-chain crystals are plate-like crystals whose planes are oriented so as to cross the first direction,

an average distance between the extended-chain crystals adjacent to each other is 1.5 μm or more and less than 11 μm, and

an average distance between the folded-chain crystals adjacent to each other is 0.3 μm or more and less than 0.9 μm.

2. The separator for a non-aqueous electrolyte secondary battery in accordance with claim 1 , the separator further comprising a heat resistant porous film laminated on the polyolefin porous film, the heat resistant porous film including a resin having heat resistance or a melting point higher than a melting point of the polyolefin porous film.

3. The separator or a non-aqueous electrolyte secondary battery in accordance with claim 2 , wherein

the polyolefin porous film has a shutdown function to close pores under an abnormal condition, and

a shrinkage percentage when shutdown occurs is 10% or less.

4. The separator for a non-aqueous electrolyte secondary battery in accordance with claim 2 , wherein the heat resistant porous film includes 50 to 400 parts by mass of an inorganic filler per 100 parts by weight of the resin.

5. The separator for a non-aqueous electrolyte secondary battery in accordance with claim 1 , the separator having a Gurley value of 180 sec/100 ml or more and less than 260 sec/100 ml, and a porosity of 50% or more and less than 62%.

6. The separator for a non-aqueous electrolyte secondary battery in accordance with claim 1 , wherein the polyolefin porous film includes a mixture of a first polyethylene having an average molecular weight of 2,500,000 or more and a second polyethylene having an average molecular weight of less than 2,000,000.

7. A non-aqueous electrolyte secondary battery comprising: an electrode group including a positive electrode, a negative electrode, and the separator of claim 1 interposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte.

8. The non-aqueous electrolyte secondary battery in accordance with claim 7 having a capacity density of 44,000 mAh/kg or more.