Synthesis and electrical properties of the polymer electrolytes based on polyetheresters

Abstract

A series of polyetheresters(PES) containing the different length of ethylene oxide(EO) units or methylene units in the polymer backbone was synthesized by solution polycondensation and was characterized by $^1H$＆$^{13}C$ NMR, DSC, GPC, X-ray diffraction, polarizing microscopy experiments. Most of polyetheresters synthesized had a relatively flexible chain to assist the ion transport, and the degree of crystallinity was significantly reduced by alternating introduction of methylene units into EO chains, as compared with that of the poly(ethylene oxide)(PEO) homopolymer. The polyetheresters were complexed with lithium salts to obtain a novel class of solid polymer electrolytes, and the relationships between the structures and properties of these polymer electrolytes were investigated. These polymer electrolytes showed the ionic conductivities up to the range of $10^{-5}~10^{-4}$S/cm at 25℃. The enhanced conductivities of these polymer electrolytes are attributed to the reduced crystallinity of a matrix polymer. The $^7Li$ NMR spin-spin relaxation studies were carried out to investigate the local environments and dynamics of ions in the polymer electrolytes. The $^7Li$ NMR relaxation results revealed the coexistence of two separate components with substantially different spin-spin relaxation times($T_2$), indicating that the presence of mobile lithium species as well as tightly bound lithium species. From these results, the relative ionic mobility and the fraction of free mobile ions contributing to the ionic conductivity could be monitored. The combination of the ionic conductivity and $^7Li$ NMR relaxation data of the polyetherester complexes containing a $LiClO_4$ salt provided the evidence that the controlling factor for ionic conductivity in these systems was a solvating capacity caused by the difference in the density of polar groups. An increase of conductivity with temperature proved to be mainly attributed to the increase of the mobility of the charge car...