MgxCo1-x(OH)2@C as electrode for supercapacitor: Effect of doping level on energy storage capability

Abstract

Incorporating non-electrochemically-active elements (such as Zn, Mg, etc.) into the framework of active components can enhance structural stability, leading to improved cycling performance. However, limited research has been conducted on the impact of varying doping concentrations. In this study, we conducted a comprehensive analysis of how different levels of Mg doping in Co(OH)2 affect supercapacitor performance. We synthesized a range of cobalt hydroxides with precisely controlled Mg content using a cation ion-exchange reaction method. Our findings suggest that the Mg component can be evenly distributed in the composite material, and when the Co/Mg ratio exceeds 1:1, the formation of Mg-O-Co bonds can be observed. When used as an electrode for a supercapacitor, the doped cobalt hydroxides exhibit superior performance compared to the un-doped version and some recently reported cobalt hydroxide based devices, including a high specific capacitance of 700.2 C/g@ 1.0 A/g versus 448.2 F/g@ 1.0 A/g, a large energy density of 48 Wh/kg@800 W/kg versus 39 Wh/kg@775 W/kg, and excellent cycling stability with only slight fluctuations around 100% capacitance retention after 30,000 cycles of continuous charge and discharge. This research not only offers guidance on the optimal doping level of redox-active metal hydroxides for improving supercapacitor performance, but also presents a novel method for preparing various metal hydroxides/oxides and their composite forms.