Structural characterization of polymer-salt complexes and the role of plasticizers in ionic transport

Polymer electrolytes, a novel class of superionic conductors, are polymer-salt complexes with a wide range of electrochemical applications. Ion-polymer and ion-ion interactions play a significant role in the ion-transport mechanism. Research is therefore focused on understanding these factors that determine the ionic conductivity of the complexes. In turn, this understanding will aid in the synthesis of electrolytes with better electrochemical properties.; Polyether-(ZnBr{dollar}sb2{dollar}+LiBr) complexes have been studied in poly(propylene oxide), tetraethylene glycol, tetraethylene glycol dimethyl ether and high molecular weight poly(ethylene oxide) systems. The nature of ionic association in these complexes was studied as a function of O:(Zn+Li) and Zn:Li ratios. Direct evidence for the speciation in these complexes has been obtained using Raman spectroscopy. The local structure around the Zn{dollar}sp{lcub}2+{rcub}{dollar} has been studied in the high molecular weight PEO-salt complexes using extended x-ray absorption fine structure (EXAFS). Temperature variation EXAFS studies have provided further information regarding polymer segmental motion and local coordination around the Zn{dollar}sp{lcub}2+{rcub}{dollar} ion.; The effect of end group and salt concentration on ionic association has been studied in lithium triflate complexes of tetraethylene glycol and its dimethyl ether. The poly(ethylene oxide)-lithium triflate system, PEO-LiCF{dollar}rmsb3SOsb3{dollar}, has been systematically studied using infrared and Raman spectroscopy, differential scanning calorimetry and impedance spectroscopy. This system is characterized by a compound with a 3:1 ether oxygen to lithium cation ratio, (PEO){dollar}rmsb3LiCFsb3SOsb3{dollar}. Kinetic effects in the ionic association of PEO-LiCF{dollar}rmsb3SOsb3{dollar} complexes, showing crystallization of the compound, are being reported for the first time. A plausible mechanism to explain the kinetic phenomena has also been postulated. In addition, the local structure of the (PEO){dollar}rmsb3LiCFsb3SOsb3{dollar} compound in its amorphous phase has been described using the results of a temperature variation infrared spectroscopic study of the 3:1 complex. This is the first time that local structure in an amorphous polymer electrolyte has been described in any level of detail beyond the average coordination number of a target cation obtained via EXAFS.; The effect of plasticizers such as ethylene carbonate, propylene carbonate, tetraethylene glycol and its dimethyl ether has been extensively studied in the PEO-LiCF{dollar}rmsb3SOsb3{dollar} system. A vibrational spectroscopic study of this system has not been reported before. The plasticizer study has also been extended to other PEO-triflate salt systems, PEO-MCF{dollar}rmsb3SOsb3{dollar}, with cations being Na{dollar}sp{lcub}+{rcub}{dollar}, K{dollar}sp{lcub}+{rcub}{dollar}, NH{dollar}sb4sp{lcub}+{rcub}{dollar} and tetrabutyl ammonium (TBA). These studies were also carried out for the non-plasticized systems. The cation dependence studies showed the variation in the cation-polyether, cation-anion and cation-plasticizer interactions as a function of cation size and charge density. A systematic study of the high molecular weight PEO-NH{dollar}rmsb4CFsb3SOsb3{dollar} system showed the presence of three compounds with O:NH{dollar}sb4{dollar} stoichiometries of 8:1, 4:1 and 1:1. Although the first two compounds have been reported in the literature, the presence of the 1:1 compound is reported here. Finally, evidence for the likely presence of compounds with high O:M stoichiometries is reported in several PEO-triflate salt systems.