| 摘要 |
A battery separator of the invention is obtained by press forming a meltblown nonwoven fabric comprising 4-methyl-1-pentene polymer or a 4-methyl-1-pentene/alpha-olefin copolymer, the battery separator having an average fiber diameter of 0.8 to 5 mum, a basis weight of 9 to 30 g/m<SUP>2</SUP>, a porosity of 30 to 60%, and a load at 5% elongation in the MD direction (longitudinal direction) of not less than 1.2 (kg/5 cm width). A lithium ion secondary battery of the invention includes the battery separator.
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