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

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 (C-T) of 218 mAh g(-1) is designed and reported for sodiumion 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(cathode)(-1) with an average voltage of 1.2 V, holding the capacity of 182 mAh g(cathode)(-1) 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(cathode)(-1) (64% retention to its C-T value) at the ultra-high current density of 20 A g(cathode)(-1), 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.

Automated summary

The study introduces a new organic cathode BAQB with high theoretical specific capacity for sodium-ion batteries. The use of high-concentration electrolyte enhances cycle stability, leading to the excellent performance of BAQB II Na3Bi SIBs with the highest capacity retention among reported SIBs.