A furan-based organic cathode material for high-performance sodium ion batteries

Organic materials have potential to be applied as electrode materials for sodium ion batteries, due to their easily tunable molecular structures and low costs. However, the dissolution of the organic materials in electrolyte tends to result in poor performance, which is also one of the main obstacles for development of organic electrode materials. Herein, 2,5-bis-(p-benzoquinonyl) furan (QFQ) with two p-benzoquinone units connected by an electron-rich furan bridge is developed. The introduction of a furan core structure leads to a planar conformation of QFQ, making it almost insoluble in common organic electrolytes, thus contributing to stable electrochemical performance. Density functional theory (DFT) calculations and ex Situ techniques are conducted to support our conclusions. QFQ shows a reversible specific capacity of 223 mA h g(-1) at a current density of 0.1 A g(-1), and the capacity retention rate after 200 cycles retains 97.7%. It is noteworthy that the furan unit could also be used as a p-type material for reversible insertion and extraction of PF6- at high potentials (>3.5 V), thereby providing additional capacity. To the best of our knowledge, this is the first report that the furan unit works as an additional anion storage site, which might be helpful for future design of efficient organic cathode materials.