Synthesis of polyanionic anthraquinones as new insoluble organic cathodes for organic Na-ion batteries

Abstract

A new polyanionic organic cathode, namely sodium 2,6-dihydroxyanthraquinone (AQ26ONa), is synthesized and fully characterized for sodium-ion batteries (SIBs). Due to the two ionic Na–O bonds, the polyanionic AQ26ONa is found almost insoluble in ether-type electrolytes. Meanwhile, AQ26ONa can deliver a two-electron redox mechanism and thus a high specific capacity of 189 mAh g−1 for SIB. In half cells, the AQ26ONa electrode delivers a reversible capacity of 217 mAh g−1 for 150 cycles (50 mA g−1) and ~128 mAh g−1 for 2500 cycles (0.5 A g−1). In the full cells with the reduced state (Na4TP) of sodium terephthalate (Na2TP) as the organic anode, the resulting Na4TPIIAQ26ONa organic SIBs (OSIBs) can display an average discharge capacity of 150 mAh g−1cathode for 50 cycles and ~66 mAh g−1 for 1000 cycles during the working voltage of 0.01–3.0 V. Currently, the performance of the Na4TPIIAQ26ONa full cells is among one of the best OSIBs reported to date.