Hierarchical Nanosheet-Built CoNi₂S₄Nanotubes Coupled with Carbon-Encapsulated Carbon Nanotubes@Fe₂O₃Composites toward High-Performance Aqueous Hybrid Supercapacitor Devices

A hybrid supercapacitor system was designed with ternary Ni–Co sulfides (CoNi2S4) as cathode materials and Fe-based composites [carbon nanotubes (CNTs)@Fe2O3@C] as anode materials to achieve excellent overall electrochemical performance with high energy and power density as well as long lifespan. Here, hierarchical CoNi2S4 nanotubes were synthesized by a solvothermal route followed by sulfidation reaction for the first time, in which nanotubes were composed of interconnected ultrathin nanosheets. Consequently, such a unique nanosheet-built nanoarchitecture enables the CoNi2S4 cathode with multidimensional synergistic effect from one-dimensional nanotubes, two-dimensional nanosheets, and three-dimensional frameworks. Profiting from its structural merits, the as-prepared CoNi2S4 nanotubes deliver a high capacitance of 2552 F g–1 at 1 A g–1 with a high rate capacity of 81% at 25 A g–1. In addition, the CNTs@Fe2O3@C anode materials—incorporating carbon-encapsulated ultrafine Fe2O3 nanoparticles into CNT matrices—were achieved by atomic layer deposition and acetylene thermal decomposition, which realize excellent electrochemical properties (678 F g–1 at 1 A g–1 and capacity retention of 82% at 25 A g–1) that matched well with CoNi2S4 cathode materials. With the well-designed nanostructure and matching of materials and properties, the corresponding aqueous hybrid device exhibits a wide output voltage window of 0–1.75 V with a maximum energy density of 90.5 W h kg–1 at a power density of 1.84 kW kg–1. Meanwhile, a high energy density of 73.1 W h kg–1 can be retained at an ultrahigh power density of 26.9 kW kg–1. Moreover, the hybrid device has a stable cycling ability with 82.1% retention over 5000 cycles. This coordinative design strategy integrating the cathode and anode electrodes developed in this work provides a novel way to manufacture next-generation energy-storage device with high performance and safety.