Impact of unsolvated lithium salt concentration on the ions transport pathway in polymer electrolyte (LiTFSI-PEO): empirical mathematical model to predict the ionic conductivity.

The effect of the lithium salt LiTFSI molality into the PEO-based electrolyte on the ionic conductivity was investigated in this work. To begin, the experimental evolution of LiTFSI-PEO electrolyte's ionic conductivity as a function of molality was analyzed, and hypotheses were put out to explain how ionic transport occurs in a heterogeneous microstructure of polymer electrolytes. To forecast the ionic conductivity in the electrolyte LiTFSI-PEO as a function of molality, an empirical mathematical model was then proposed, taking the phenomena predicted to occur into account. The proposed theoretical model presupposes that lithium salt's solvation state (total or partial solvation) and the steric effect brought on by heterogeneous areas are related to the conduction of ions (at the microscopic scale). The model is adjusted to accurately depict the entire experimental curve, which is thought to have three distinct domains. In the first domain, where the molality m is less than 1 mol/kg, the oxygen atoms completely solvate the lithium salt. The conduction is believed to be favorable in this situation since the released solvated lithium ions linearly fluctuate against the molality. The partial solvation of lithium corresponds to the second domain (1 mol/kg ≾ m ≾ 2 mol/kg), where the conductivity of the polymer electrolyte slightly increases with increasing molality. In the third domain, where m is greater than 2 mol/kg, the loss in ionic conductivity is caused by steric effects, as some of the lithium salt (LiTFSI) does not ionize and becomes immobilized, obstructing the transport pathway. Finally, the model was expanded to include how temperature affects ionic conductivity. The prediction model was effectively validated when it was put up against the findings of experiments conducted by various authors. [ABSTRACT FROM AUTHOR]