| 摘要 |
PROBLEM TO BE SOLVED: To provide a separator for a lithium ion secondary battery, low in basis weight and low in thickness, high in mechanical strength, low in internal resistance and rate of internal short-circuit failure, and also excellent in cycle characteristics, and a lithium ion secondary battery using the separator.SOLUTION: There is provided a separator for a lithium ion secondary battery, containing 50 mass% or more of a fibrillated solvent-spun cellulose fiber which is increased in freeness such that a fiber diameter of a stem part of the fibrillated solvent-spun cellulose fiber is reduced to less than 9.0 μm. There is also provided a lithium ion secondary battery using the separator. |
