Influence of Water on Poly(propylene glycol)- Lithium Triflate Electrolytes, Studied by Impedance and Infrared Spectroscopy
Examensarbete för masterexamen
Physics and astronomy (MPPAS), MSc
In this thesis, Poly(propylene glycol)4000-LiCF3SO3-water electrolytes were studied with thermogravimetry, impedance and infrared spectroscopy. A method for drying the compounds and adding water was developed success- fully. Among the samples without water, the medium concentration 0.63 mol/kg LiCF3SO3 (LiTf) had the highest conductivity of 2.9 10−4 S/m. Water increased the conductivity for all samples. The conductivity increased the most for the high concentration 2.7 mol/kg LiTf sample, from 8.4 10−6 S/m dry to 1.5 10−2 S/m wet. Water in PPG4000 above saturation sepa- rates into a wet polymer phase and an aqueous phase, but LiTf enables more water to be mixed into the electrolyte without phase separation. The limited molecular interaction between PPG4000 chain and water explains the phase separation. The PPG4000 hydrophilic OH endgroups can explain the ability to form emulsion with water. The SO3 1041 cm−1 and 1031 cm−1 symmetric stretch IR bands show that OH and Li+ compete in interacting with SO3. The ion pair dissociation could explain part of the conductivity increase with added water.
Polymer electrolytes , Impedance Spectroscopy , Conductivity , Permittivity , FTIR Infrared Spectroscopy , Lithium Triflate LiCF3SO3 , Poly(propylene glycol) PPG PPG4000 , Poly(propylene glycol)-Water Mixtures , Poly(propylene glycol)-Lithium Triflate electrolytes , Poly(propylene glycol)-Lithium Triflate-Water Mixtures , Macrophase and Microphase Separation , Phase Separation , Ion Pairs , Aqueous electrolytes