Impact of Fluorination on the Anodic Performance of Disodium Terephthalate: an Experimental and Computational Study

Advancing research into organic electrode materials is conducive for the development of affordable and sustainable Na-ion battery (NIB) technology owing to the low cost, abundance, and high structure tunability of organic materials. To obtain high-performance organic electrode materials, an in-depth understanding of the correlation between dynamic geometries of redox active functional groups in organic materials and electrochemical performance is critical but remains elusive. In this work, three fluorinated derivatives of disodium terephthalate (DTP) were synthesized to explore how fluorine substitutions altered the geometry and performance of the carboxylate groups in reversible sodiation/desodiation. Matching computational models, the monofluorinated disodium 2-fluoroterephthalate derivative outperformed disodium 2,3-difluoroterephthalate (196 mAh g-1 vs 88 mAh g-1), and disodium tetrafluoroterephthalate was found to not be redox active. The difference in performance is attributed to the dynamic geometry caused by the fluorine substituents that disrupt the planarity of the molecules, preventing favorable redox reactions of the carboxylate functional groups. This effect is more pronounced with higher degrees of fluorination.