3D yolk-shell NiGa₂S₄ microspheres confined with nanosheets for high performance supercapacitors

Recent advances in the development of two-dimensional transition-metal chalcogenides (2D TMCs) have opened up new avenues for supercapacitor applications. However, they still suffer from limited specific capacitance and poor rate capability due to their poor interfacial properties and simple geometry. Here, we propose a facile strategy for the synthesis of yolk-shell NiGa₂S₄ microspheres comprising crumpled nanosheets supported on nickel foam. The robust structure not only highly facilitates the electron and charge transportation but also efficiently alleviates the volume expansion during redox reactions, contributing to excellent electrochemical behaviors in terms of specific capacitance and rate capability. Significantly, an asymmetric supercapacitor based on the prepared NiGa₂S₄ as the positive electrode and N,S-codoped graphene/Fe₂O₃ (N,S-G/Fe₂O₃) as the negative electrode delivers a high energy density of 43.6 W h kg^-1 at a power density of 961 W kg^-1 and retains an energy density of 22.2 W h kg^-1 even at 15 974 W kg^-1. These impressive results may provide a new perspective to develop high energy and power density storage systems for practical applications.