Quantitative analysis of molecular surface: systematic application in the sodiation mechanism of a benzoquinone-based pillared compound as a cathode

Abstract

Against the background of great attention on linear polymers and covalent organic frameworks, some small-molecule organic compounds have shown great potential as cathodes for sodium-ion batteries due to their high redox potentials and high specific capacity. However, limited by the fact that most of the current theoretical research methods are aimed at organic crystals, it is challenging to reasonably elaborate the sodium storage mechanisms of single-molecule organic compounds. Herein, we conceptualize a novel research approach for such small-molecule organic materials possessing complex structures by taking the benzoquinone-based compound pillar[5]quinone as an example. The redox-active sites for the sodiation process were predicted systematically by multiple quantitative analyses of molecular surfaces. In addition, the reasonable sequences of discharge sites were verified based on factors such as the single-point energy, degree of molecular structure deformation, chemical bonding, molecular orbital energy gaps, etc. Moreover, the theoretical reduction potentials calculated by this approach showed high consistency with the experimental data. These results are expected to inspire the theoretical investigation of the reduction mechanism and redox potential of small-molecule organic materials.