Nanocomposite Polymer Electrolyte Materials Based on Polyether, LiBF4 and Nanofibers for Renewable Electrochemical Devices

Abstract

Nanocomposite polymer electrolytes are promising materials for the manufacture of modern renewable electrochemical devices. The development and improvement of the properties of such materials is an urgent task today. The methods of differential scanning calorimetry and impedance spectroscopy were used for studying the thermophysical and electrical properties of the developed nanocomposite polymer electrolytes. Polyelectrolytes were based on polyether, nanofibers and lithium tetrafluoroborate. The analysis of thermophysical data showed that the melting point and crystallinity of the studied polymer electrolytes decrease with increasing salt content. The addition of nanofibers to the composition of the system further reduces the melting point and crystallinity due to the formation of a gel network. At 20% salt content, polyelectrolyte systems are completely amorphized, which is explained by the formation of electrostatic complexes between cations and ether oxygens of the polymer macromolecules. Analysis within the framework of the classical theory of polymer solutions showed that PEG has a better dissolving capacity than the PEG-nanofiber system, due to its lower molecular weight and the absence of a gel-like network. Values for entropy, enthalpy and Gibbs's energy of solvation were obtained. The analysis of these parameters showed that dissolution occurs spontaneously in the polyether-salt system. The higher Gibbs energy values for the PEG-nanofiber-salt system indicate that the gel-like network of nanofibers hinders the processes of salt dissolution, therefore, it is likely to reduce the mobility of charges inside the polymer matrix.