Benzene-bridged anthraquinones as a high-rate and long-lifespan organic cathode for advanced Na-ion batteries

Abstract Organic electrodes in principle possess the “single-molecule-energy-storage” capability for rechargeable batteries. By proper molecule engineering, a new insoluble organic cathode namely 1,4-bis(9,10-anthraquinonyl)benzene (BAQB) with a high theoretical specific capacity (CT) of 218 mAh g−1 is designed and reported for sodium-ion batteries (SIBs). It is found that the high-concentration electrolyte (4 M) is effective to restrain the phase separation within the electrode composition, leading to the improved cycle stability. In the fabricated SIBs (0.2–3.2 V) with Bi-Na alloy (Na3Bi) as the inorganic anode, the resulting BAQB II Na3Bi SIBs can deliver the peak discharge capacity of 242 mAh g−1cathode with an average voltage of 1.2 V, holding the capacity of 182 mAh g−1cathode after 400 cycles. Meanwhile, the SIBs can run over 8000 cycles with the capacity retention of 54% at 2 A g−1. Impressively, our SIBs can deliver the discharge capacity of 140 mAh g−1cathode (64% retention to its CT value) at the ultra-high current density of 20 A g−1cathode, which is currently the world record for all SIBs reported. To the best of our knowledge, the integrated performance of our BAQB II Na3Bi SIBs is among the best SIBs reported to date.