Tunable Synthesis of 3D Niobium Oxynitride Nanosheets for Lithium-Ion Hybrid Capacitors with High Energy/Power Density

Lithium-ion hybrid capacitors (LIHCs), as a novel energy storage device combining the mechanism of lithium-ion batteries and supercapacitors, can achieve high energy and power density simultaneously. Pseudocapacitive materials with rapid lithium-ion storage characteristics have great potential for improving the kinetic mismatch between cathodes and anodes in LIHCs. Herein, we successfully synthesized niobium oxynitride (NbOxNy) nanosheets with a three-dimensional (3D) architecture and tunable nitrogen and oxygen contents through solvothermal treatment followed by a controllable solid-state nitridation process. Benefiting from the resulting short transport path, 3D morphology, optimized N/O atom ratio, and the enhanced electrical conductivity, the NbOxNy electrode with pseudocapacitive lithium-ion storage characteristics exhibits excellent rate capability and cycling stability. By matching with an activated carbon (AC) cathode, a novel NbOxNy//AC LIHC device was fabricated, which delivers an ultrahigh energy density of 158.3 W h kg-1 at 200 W kg-1. A convincing energy density of 45 W h kg-1 could also be achieved at 20 kW kg-1. Furthermore, the NbOxNy//AC LIHC demonstrates superior cycling performance after 10,000 cycles at 1 A g-1.