| 摘要 |
PROBLEM TO BE SOLVED: To obtain a porous membrane which contains polyethylene and polypropylene, and is useful in the production of lithium ion secondary cells because it has specific temperature characteristics, shows excellent current-breaking properties as a battery separator, when used as a cell separator and stably works without ignition of fire by the external short-circuit. SOLUTION: This membrane is porous membrane containing (A) polyethylene and (B) polypropylene (for example, a simple porous membrane of a mixture of A and B or a porous membrane formed by alternately laminating a porous membrane of an A and B mixture and a porous membrane of B). When the porous membrane is impregnated with an electrolyte solution, electrodes are arranged onto both main faces of the porous membrane and an alternating voltage is applied to the electrodes to raise the temperature of the membrane at a rate of 10-50 deg.C/second by the resistance heat of the electrolyte solution, the maximum temperature to be reached is adjusted to be equal to or less then (the melting point of the component A +20 deg.C). This porous membrane is prepared, for example, by mixing component A of >=60% crystallinity with component B of <=70% crystallinity so that the proportion of component A becomes >=12wt.% and by monoaxially orienting the membrane of the mixture. |
