Thick lamellar textures and high ambient conductivity in de-blended mixtures of low-dimensional systems of two polymers and Li salts

The three-component low-dimensional polymer electrolyte complexes of blends of the amphiphilic helical polymer poly[2,5,8,11,14-pentaoxapentadecamethylene(5-hexadecyloxy-1,3-phenylene)] (I), the block copolymer of poly(tetramethylene oxide)-co-dodecamethylene (II) with LiClO₄, LiBF₄ and Li(CF₃SO₂)N have been studied by polarised light optical microscopy, DSC and SAXS together with AC complex impedance measurements using ITO glass, silver and lithium electrodes. In systems with LiClO₄ a well-defined spherulitic morphology with lamellae of 1-3 μm in thickness were observed following heat treatment. The lamellae were shown to consist of de-blended polymer I:LiClO₄ complex with polymer II forming an interlamellar ion-conducting layer. Complex impedance measurements with ITO and Ag electrodes give σ∼10^-3 S cm^-1 with low temperature dependence over ambient to 100°C and Z′ versus Z″ planes featuring a new small semicircle on de-blending consistent with a Maxwell series layered dielectric system. A galvanic cell with LiCoO₂ composite cathode discharged at 20°C with 0.1 mA cm^-2. In corresponding systems with LiBF₄, blocks of lamellae separate from a blended matrix which give temperature-dependent AC conductivities. DC polarisation of LiBF₄ based systems between Li electrodes give ambient conductivities 10^-3-10^-2 S cm^-1 in good accord with AC impedance measurements. Long spacings from SAXS measurements indicate the I-salt occupancies in blends with the various salts, which correlates to their de-blending tendency.