Ultrastable organic cathode derived by pigment/rGO for aqueous zinc-ion batteries

Carbonyl compounds have been widely used for cathodes of aqueous zinc-ion batteries (ZIBs) nowadays, however, poor electrical conductivity has limited its development. Reduced graphene oxide (rGO) could easily interact with carbonyl compounds by π-π stacking to achieve good conductivity. Herein, a carbonyl compound, 6,15-dihydrodinaphtho[2,3-a:2′,3′-h]phenazine-5,9,14,18-tetraone (DNPT, pigment blue 60), interacts with rGO to obtain DNPT/rGO as cathode for ZIBs, which shows excellent stability with capacity of 120 mAh g−1 after 1000 cycles at current density of 500 mA g−1, as well as good rate performance (20C). Through ex-situ analysis and density functional theory calculation, synergistic mechanism of proton and zinc ion in DNPT/rGO has been detailed discussed with three possible discharging processes of DNPT(H+)4, DNPT2(H+)6(Zn2+), DNPT2(H+)4(Zn2+)2. The combination of two adjacent DNPT molecules with one zinc ion and six protons suggests optimal structure of DNPT2(H+)6(Zn2+) during charge–discharge process. Prospectively, DNPT/rGO material with good electrical performance and high cycling stability would inspire development of carbonyl compounds used for ZIBs.