Enhancing energy storage capacity of iron oxide-based anodes by adjusting Fe (II/III) ratio in spinel crystalline

Abstract

Supercapacitors, as promising energy storage candidates, are limited by their unsatisfactory anodes. Herein, we proposed a strategy to improve the electrochemical performance of iron oxide anodes by spinel-framework constraining. We have optimized the anode performance by adjusting the doping ratio of Fe (II/III) self-redox pairs. Structure and electronic state characterizations reveal that the Ni x Fe 3−x O 4 was composed of Fe (II/III) and Ni (II/III) pairs in lattice, ensuring a flexible framework for the reversible reaction of Fe (II/III). Typically, when the ratio of Fe (II/III) is 0.91:1 (Fe (II/III)-0.91/1), the Ni x Fe 3−x O 4 anode shows a remarkable electrochemical performance with a high specific capacitance of 1694 F g −1 at the current density of 2 A g −1 and capacitance retention of 81.58%, even at a large current density of 50 A g −1 . In addition, the obtained material presents an ultra-stable electrochemical performance, and there is no observable degradation after 5000 cycles. Moreover, an assembled asymmetric supercapacitor of Ni-Co-S@CC//Ni x Fe 3−x O 4 @CC presents a maximum energy density of 136.82 Wh kg −1 at the power density of 850.02 W kg −1 . When the power density was close to 42 500 W kg −1 , the energy density was still maintained 63.75 Wh kg −1 . The study indicates that inherent performance of anode material can be improved by tuning the valence charge of active ions.

Ag(e)ing and Degradation of Supercapacitors: Causes, Mechanisms, Models and Countermeasures

“…The beneficial effect of careful voltage/potential control for slower ageing of MnO 2 -based electrodes has been addressed in general terms [ 232 ]. When a material is available in several sufficiently redox-active crystalline types (e.g., Ni x Fe 3−x O 4 ), a flexible spinel framework seems to be beneficial for higher stability [ 233 ]. Seamless graphidyne layers on metal oxides have been proposed as a way of mitigating degrading effects of structural and interfacial instabilities of metal oxides in electrodes [ 234 ].…”