Fe-doping engineered MnO2 cathode with ultrahigh energy density and exceptional cycling stability for aqueous magnesium-ion hybrid supercapacitors

The key challenge impeding the advancement of aqueous MHS lies the fabrication of structurally stable electrode materials with exceptional reaction kinetics and superior cycling performance. In this study, we employed elemental doping strategies to synthesize MnFe-6, which has wide interlayer spacing and an abundance of oxygen vacancies, by modulating its morphology and optimizing its structure. The MnFe-6 demonstrated superior electrochemical performance (199.4 F g −1 at 1 A g −1 ) in three-electrode tests. Systematic ex-situ XRD and XPS analysis reveal that the material's exceptional electrochemical properties originate from the pseudo capacitance generated by the reactions involving Mn 2+ and Mn 3+ /Mn 4+ , combined with the charge compensation facilitated by oxygen vacancies. An asymmetric MHS with MnFe-6 as the cathode material exhibits a specific capacitance of 171.2 F g −1 at 1 A g −1 .The MHS attained an excellent energy density of 160.7 Wh kg −1 at power density of 1299.8 W kg −1 . Moreover, it exhibited exceptional cyclability, retaining 96.5% of primary capacitance after 60,000 cycles tests at 10 A g −1 . This study establishes elemental doping as a viable and efficient strategy for the development of advanced MHS electrode materials.