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

摘要

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 LiClO{sub}4, LiBF{sub}4 and Li(CF{sub}3SO{sub}2)N have been studied by polarized light optical microscopy DSC dud SAXS together with AC complex impedance measurements using ITO glass silver and lithium electrodes. In systems with LiClO{sub}4 well-defined spherulitic morphology with lamellae of 1-3μm in thickness were observed following heat treatment. The lamellae were shown to consist of de-blended polymer I: LiClO{sub}4 complex with polymer II forming an interlamellar ion-conducting layer. Complex impedance measurements with ITO and Ag electrodes give σ～10{sup}(-3)Scm{sup}(-1) with low temperature dependence over ambient to 100 ℃ 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 LiCoO{sub}2 composite cathode discharged at 20℃ with 0.1 mA cm{sup}(-2). In corresponding systems with LiBF{sub}4. blocks of lamellae separate from a blended matrix which give temperature-dependent AC conductivities. DC polarization of LiBF{sub}4 based systems between Li electrodes give ambient conductivities 10{sup}(-3) 10{sup}(-2) S cm{sup}(-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 dc-blending tendency.