Plentiful abutting functional groups boosting sodium storage in a small molecule

Abstract

Organic electrode materials (OEMs), particularly small molecules, are promising for use in future large-scale batteries due to their advantages of mass production with potentially low cost, flexibility, high capacity, and facile molecular design. However, small molecules usually have high solubility in organic electrolytes, resulting in low actual capacity and poor cyclability. Herein, we demonstrated a strategy that abutting functional groups could boost the electrochemical performance of small molecules via several aspects by utilizing a small molecule (QAP) as a proof-of-concept. The QAP contains plentiful abutting functional groups. We found that the abundant abutting functional groups could on one hand guarantee high specific capacity, induce strong intermolecular interactions and inhibit the dissolution of QAPs, and on the other hand effectively boost the sodium storage by chelating with sodium ions. Moreover, due to the strong chelation effect, the complete extraction of Na ions required high potential, which led to the existence of ionic intermolecular interactions and hence insolubility and high cyclability. As a result, the QAP electrodes underwent a reversible five-electron redox process, delivering a high capacity of 562 mA h g⁻¹ at 100 mA g⁻¹, excellent rate capability and long-term cyclability. The presence of the chelation effect was substantially verified by high resolution mass spectrometry, control experiments and theoretical calculations.