A computational chemistry approach to modelling conducting polymers in ionic liquids for next generation batteries

Abstract

An overview of modern quantum chemical methods is presented followed by a discussion of their application in the field of conducting organic polymers (COPs), with a view towards modelling the cathodic half-cell of a poly(3,4-ethylenedioxythiophene) (PEDOT) cathode in an AlCl3-1-ethyl-3-methylimidazolium chloride (EMImCl) ionic liquid electrolyte. The most popular combination of hybrid DFT functional and polarized moderate basis set has been broadly and successfully applied to COPs in the literature. However, in the presence of anions and intermolecular interactions, diffuse functions and dispersion corrections must also be included. A comprehensive specification of these elements appears well suited to the determination of many relevant parameters including molecular geometry, bandgap of oligomers and energies for systems including multiple chains and chloroaluminate anions. However, range-separated hybrid functionals may be more suitable for determining electron transport properties of very long chains. The clearest benefit of DFT to this system is the ability to visualize charge distribution and the interaction between charged PEDOT and the active species, which will help to explain the specific capacity, voltage and charge/discharge characteristics — insights that may help identify further improvements.