Nickel and cobalt Co-substituted spinel ZnMn2O4@N-rGO for increased capacity and stability as a cathode material for rechargeable aqueous zinc-ion battery

Rechargeable aqueous zinc-ion batteries (ZIBs) are possible future replacements for large-scale energy storage devices because of their safety, low cost, and abundance of materials. Finding a competitive cathode material suitable for zinc-ion insertion/de-insertion, needed to achieve high reversible capacity and long cycle stability, is one of the most important and arduous challenges. For the first time, nickel and cobalt co-substituted spinel ZnMn2O4 nanoparticles, homogeneously loaded onto N-doped reduced graphene oxide (ZnNixCoyMn2-x-yO4@N-rGO), were synthesised through a one-step hydrothermal method and applied as a cathode material to accommodate the intercalation of zinc ions. The as-prepared ZnNixCoyMn2-x-yO4@N-rGO displayed excellent electrochemical performance, with a reversible capacity of 95.4 mA h g−1, achieved at 1000 mA g−1 after 900 cycles, and a capacity retention ratio of 79%. When the current density increased from 10 mA g−1 to 1500 mA g−1, high capacity (200.5 mA h g−1 to 93.5 mA h g−1) was achieved, which was much higher than that of [email protected] without nickel and cobalt co-substituting (184 mA h g−1 to 59.2 mA h g−1), demonstrating excellent rate performance. These excellent electrochemical properties are attributed to the co-substituting of nickel and cobalt elements, which is an effective approach to promote Zn2+ de-intercalation and to stabilize the spinel structure in order to suppress the Jahn-Teller distortion of Mn3+. Therefore, nickel and cobalt co-substituting of spinel ZnMn2O4@N-rGO with a stable structure opens up new possibilities for large-scale application of rechargeable, aqueous ZIBs.