Patent ID: 7540991

Claim:
A method for manufacturing an electrolyte membrane formed of an ion conductive composition containing a lyotropic liquid crystalline polymer having an ionic dissociative group and molecular chains orientated in a specific direction in which a degree of orientation α of the liquid crystalline polymer is in a range of 0.45 or more and less than 1, as defined by an equation (1) as follows: Degree of orientation α=(180−Δβ)/180 (1) wherein Δβ is a full width at half maximum of a peak in an X-ray diffraction intensity distribution pattern obtained by measuring an intensity distribution from 0 to 360 degrees in the azimuthal angle direction, at a peak scattering angle, in an X-ray diffraction image of the electrolyte membrane; and wherein an anisotropy ratio of ionic conductivity of the membrane determined from equation (2) below falls within a range of more than 1 and less than 60, anisotropy ratio of ionic conductivity γ=(ionic conductivity in thickness direction)/(ionic conductivity in direction parallel to surface) (2), the method comprising: preparing the ion conductive composition containing the lyotropic liquid crystalline polymer having an ionic dissociative group and a solvent, each molecular chain including a main chain and the ionic dissociative group being bonded to the main chain; developing liquid crystallinity of the liquid crystalline polymer in the composition, wherein said developing includes heating the composition once to a temperature range in which liquid crystallinity is not developed in order to transform the lyotropic liquid crystalline polymer into a uniform isotropic phase and then cooling the composition to a temperature range in which liquid crystallinity is developed; orientating the molecular chains of the lyotropic liquid crystalline polymer having developed liquid crystallinity, in a thickness direction of the membrane; and solidifying the ion conductive composition while the orientation of the molecular chains of the liquid crystalline polymer is maintained.