Abstract
Transition-metal oxides have shown renewed interest as promising electrode materials for high-performance electrochemical energy storage devices. However, applications of these devices are hindered by the instability of the electrode materials, which is originated from the electrochemical redox reactions induced phase transition between materials with different chemical stoichiometries. Herein, the Pourbaix diagram was constructed to predict ways of inhibiting this undesirable phase transition by using iron oxides as a prototypical model. Appropriate metal dopant (e.g., Ni) doping in the iron oxide was theoretically and experimentally found to present single phase under an extra-wide range of applied potential in alkaline aqueous solutions. Typically, the designed material (NixFe3-xO4) presents high cycling stability with capacitance retention of 94.3% over 5,000 cycles at a current density of 20 A/g when working as a supercapacitor anode. A configured asymmetric supercapacitor with the designed anode exhibits an almost 100% performance retention after 10,000 charging-discharging cycles. This success proposed a new perspective to enhance the stability of electrochemical electrodes for energy storage devices.