Synergy of VN and Fe₂O₃ Enables High Performance Anodes for Asymmetric Supercapacitors

Fe₂O₃ is one of the most common anode materials beyond carbons but suffers from unsatisfactory capacity and poor stability, which are associated with the insufficient utilization of active material and the structural instability caused by the phase transformation. In this work, we report an effective strategy to overcome the above issues through electronic structure optimization by constructing delicately designed Fe₂O₃@VN core-shell structure. The Fe₂O₃@VN/CC exhibits a much higher areal capacity of 254.8 mC cm^-2 at 5 mA cm^-2 (corresponding to 318.5 mF cm^-2, or 265.4 F g^-1) than the individual VN (48 mC cm^-2, or 60 mF cm^-2) or Fe₂O₃/CC (93.36 mC cm^-2, or 116.7 mF cm^-2), along with enhanced stability. Moreover, the assembled asymmetric supercapacitor devices based on Fe₂O₃@VN/CC anode and RuO₂/CC cathode show a high stack energy density of 0.5 mWh cm^-3 at a power density of 12.28 mW cm^-3 along with good stability (80% capacitance retention after 14000 cycles at 10 mA cm^-2). This work not only establishes the Fe₂O₃@VN as a high-performance anode material but also suggests a general strategy to enhance the electrochemical performance of traditional anodes that suffer from low capacity (capacitance) and poor stability.