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.