Enhanced electrochemical performance in an aluminium doped δ-MnO2 supercapacitor cathode: experimental and theoretical investigations.

One of the biggest challenges faced by the layered manganese oxide MnO2 used as a supercapacitor cathode is the capacity fading caused by chemo-mechanical degradation and/or structural transformation occurring in the discharging/charging process. Here, based on systematical experimental measurements and theoretical calculations, we show that both the stability and rate performance of the δ-MnO2 supercapacitor cathode can be significantly enhanced by Al doping. Compared with pure δ-MnO2, Al doping (δ-Al0.06MnO2) clearly improves the specific capacitance (7% enhancement at 0.1 mA cm-2) and cycling stability (12% enhancement after 5000 cycles) simultaneously. These improvements can be attributed to the enhanced electronic transport and formation of more active sites, which are introduced by Al doping. Additionally, our calculations demonstrate that the doped systems (Al atoms located at Mn or O sites) show smaller surface energies than that of pure δ-MnO2, which hinders side reactions or structure transformations and leads to a better cycling lifetime. Our work gives a comprehensive understanding of the impacts on the performance of δ-MnO2 introduced by Al doping, and provides a feasible scheme to study the electrochemical mechanism of metal-doped δ-MnO2.