Studies of physical properties of novel lithium polymer electrolytes
Polymer electrolyte systems using thermoplastic polyester polyurethane (TPU), modified natural rubbers and modified natural rubbers/polyethylene oxide polymer hosts have been investigated. Three types of modified natural rubber, namely 2S percent epoxidised natural rubber (ENR2S), SO percent epoxidised natural rubber (ENRSO) and polymethyl methacrylate grafted natural rubber were employed as polymer hosts. In this study the ionic conductivity, thermal, FTIR spectroscopy and morphology have been determined for both unplasticised and plasticised polymer electrolyte systems understudied. The following characterization results explain the effect of the polymer electrolyte films made by systematic compositional ratio of lithium triflate and ECIPC plasticisers introduced into the polymer aided by volatile solvent. Without any plasticiser, the TPUlLiCF3S03, modified natural rubber and modified natural rubberIPEO blend based polymer electrolyte systems have ionic conductivity in the range 10-6 to 10-s S cm-1 at ambient temperature. Incorporating SO-100% of ECIPC by weight to the understudied polymer electrolyte systems yielded mechanically stable films and ionic conductivities in the range of 10-4 to 10-3 S cm-1 at ambient temperature. Thermal analyses have shown the detection of single glass transition temperatures for the TPU and modified natural rubber based polymer electrolyte system. FTIR spectroscopy indicates that the interaction of lithium salt with polymer hosts occurred by the increasing band intensities within polymer electrolyte system. The mechanical properties of the systems showed that at low plasticiser content the stiffiless of the polymer electrolytes is less affected but has a low ionic conductivity. In summary, results from SEM spectroscopic data in conjunction with thermal analysis show that the degree of crystallinity, melting temperature, crystallisation rate and microstructure of PEO in PEOIENR blends have been perturbed weakly by the presence of ENR. In addition SEM images showed a rather complicated blend morphology, which is composition dependent, arising from phase separation.