Synergy of VN and FeO Enables High Performance Anodes for Asymmetric Supercapacitors.

FeO 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 FeO@VN core-shell structure. The FeO@VN/CC exhibits a much higher areal capacity of 254.8 mC cm at 5 mA cm (corresponding to 318.5 mF cm, or 265.4 F g) than the individual VN (48 mC cm, or 60 mF cm) or FeO/CC (93.36 mC cm, or 116.7 mF cm), along with enhanced stability. Moreover, the assembled asymmetric supercapacitor devices based on FeO@VN/CC anode and RuO/CC cathode show a high stack energy density of 0.5 mWh cm at a power density of 12.28 mW cm along with good stability (80% capacitance retention after 14000 cycles at 10 mA cm). This work not only establishes the FeO@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.