The present invention relates to a method of making a polymeric porous
separation membrane for a lithium ion polymer battery, the method
comprising: providing a porous polyolefin membrane and a polymer solution
of the concentration of 1 20 weight % in an organic solvent fabricated by
dissolving in an organic solvent a polymer compound that is stable in an
electrolyte containing a lithium salt and can be gelled in the
electrolyte, at the temperature of 10 40.degree. C.; and fabricating a
polymeric porous separation membrane by coating the polymeric porous
polyolefin membrane with the polymer solution. Thus, the porous
separation membrane for a lithium ion polymer battery is fabricated by
using the polymer solution fabricated at the low temperatures of 10
40.degree. C., and the size of the pores of the coated is proper, so that
the containing capacity of the electrolyte and the ion conductivity are
good. Further gelling at low pressure is enabled and cohesive force to
the electrodes is improved. In the lithium ion battery containing the
porous separation membrane, the gelling is accomplished at atmospheric
pressure or at low pressure for a few hours, so that problems caused by
gelling for a short period at high pressure and high temperature such as
the non uniform gelling of the battery, the deformation of the separation
membrane and the weakened cohesion can be avoided. Moreover, the
high-rate discharge, the cycle life becomes excellent.