Microwave-assisted in-situ isomorphism via introduction of Mn into CoCo2O4 for battery-supercapacitor hybrid electrode material

Abstract Introducing secondary metal ions into host electrode materials may result in extra redox sites and regulating the electronic structure to increase electrochemical properties. With the assistance of microwave, Mn cation was in-situ isomorphism doped into porous CoCo2O4 nanowires during a hydrothermal process. Ex-situ characterizations reveal that the doped Mn2+ and Mn3+ in CoCo2O4 provides additional redox reaction by forming reversible Mn4+, which effectively improved electrochemical storage capacity. The added redox reaction of Mn cations is also helpful to effectively suppress the water-splitting, which expanded the operating voltage window. As a result, the as-obtained Mn-doped CoCo2O4 nanowire array electrodes exhibited an enlarged specific capacity (1528.0 C g-1/424.4 mA h g-1 at 1 A g-1) with a widened operating voltage window of 1.1 V and superior cycling stability (91.5 % retention after 5000 cycles). Correspondingly, the battery-supercapacitor hybrid device constructed by Mn2CoCo2O4 porous nanowire array electrode and biomass-derived N doped porous carbon delivered a stable working voltage of 1.9 V and superior energy density of 58.6 Wh kg-1 at power density of 950 W kg-1 as well as excellent stability (83.7 % specific capacity retained at 10 A g-1 for 8000 cycles). This work provides a feasible route for the construction of energy storage devices with high energy density and high power density.