| 摘要 |
PROBLEM TO BE SOLVED: To provide a fine porous membrane wound body made of polyolefin for realizing a battery showing a performance with less fluctuations in capacity and cycle characteristics when the membrane is used as a separator of a lithium ion secondary battery. SOLUTION: This is a wound body in which fine porous membrane of polyolefin is wound around, and the absolute value (%) of the difference between an average porosity P(%) of the wound body as calculated by a formula (1) P=[1-äM/(V×ρ)}]×100 and the average porosity p(%) of a plane membrane as calculated by a formula (2) p=[1-äm/(v×ρ)}]×100 is 3% or less. Here, in the above formula (1), M shows a mass (g) of the wound body, V shows a volume (cm<SP>3</SP>) of the wound body,ρshows a specific gravity (g/cm<SP>3</SP>) of polyolefin. In the formula (2), m shows a mass (g) of the plane membrane of 10 cm square extracted from the polyolefin fine porous membrane, v shows a volume (cm<SP>3</SP>), andρshows a specific gravity (g/cm<SP>3</SP>) of polyolefin. COPYRIGHT: (C)2009,JPO&INPIT
|
