Hierarchical Manganese-Nickel Sulfide Nanosheet Arrays as an Advanced Electrode for All-Solid-State Asymmetric Supercapacitors

In this work, hierarchical manganese-nickel sulfide nanosheet arrays (Mn-Ni-S NAs) were designed through a cost-effective hydrothermal method, followed by an ion-exchange technique. Among the various electrode samples prepared, Mn-Ni-S NAs with a Mn/Ni feeding ratio of 1:2 (denoted Mn-Ni-S NAs (1:2)) were found to possess outstanding electrochemical properties, including a superb areal capacity of 0.687 mAh cm^-2 (286.3 mAh g^-1 specific capacity) and a splendid cycling stability. Furthermore, Mn-Ni-S NAs (1:2) can be coupled with iron oxide embedded in reduced graphene oxides (Fe₂O₃@rGO) to assemble all-solid-state asymmetric supercapacitor devices. The resultant device demonstrated superior volumetric capacity and a superb energy density of 76.6 W h kg^-1 with a prominent cycling stability. The current synthesis protocol provides a meritorious reference for the synthesis of other kinds of transition-metal sulfide electrode materials for energy storage applications.