| Summary: | Electrochemical energy storage devices (EESDs) have caused widespread concern, ascribed to the increasing depletion of traditional fossil energy and environmental pollution. In recent years, nickel cobalt bimetallic sulfides have been regarded as the most attractive electrode materials for super-performance EESDs due to their relatively low cost and multiple electrochemical reaction sites. In this work, NiCo-bimetallic sulfide Ni<sub>x</sub>Co<sub>3−x</sub>S<sub>4</sub> particles were synthesized in a mixed solvent system with different proportion of Ni and Co salts added. In order to improve the electrochemical performance of optimized Ni<sub>2.5</sub>Co<sub>0.5</sub>S<sub>4</sub> electrode, the Ni<sub>2.5</sub>Co<sub>0.5</sub>S<sub>4</sub> particles were annealed at 350 °C for 60 min (denoted as Ni<sub>2.5</sub>Co<sub>0.5</sub>S<sub>4</sub>-350), and the capacity and rate performance of Ni<sub>2.5</sub>Co<sub>0.5</sub>S<sub>4</sub>-350 was greatly improved. An aqueous NiCo-Zn battery was assembled by utilizing Ni<sub>2.5</sub>Co<sub>0.5</sub>S<sub>4</sub>-350 pressed onto Ni form as cathode and commercial Zn sheet as anode. The NiCo-Zn battery based on Ni<sub>2.5</sub>Co<sub>0.5</sub>S<sub>4</sub>-350 cathode electrode delivers a high specific capacity of 232 mAh g<sup>−1</sup> at 1 A g<sup>−1</sup> and satisfactory cycling performance (65% capacity retention after 1000 repeated cycles at 8 A g<sup>−1</sup>). The as-assembled NiCo-Zn battery deliver a high specific energy of 394.6 Wh kg<sup>−1</sup> and long-term cycling ability. The results suggest that Ni<sub>2.5</sub>Co<sub>0.5</sub>S<sub>4</sub>-350 electrode has possible applications in the field of alkaline aqueous rechargeable electrochemical energy storage devices for supercapacitor and NiCo-Zn battery.
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