Ultra-stable Mn_1-xNi_xCO₃ nano/sub-microspheres positive electrodes for high-performance solid-state asymmetric...

Long-term cycling performance of electrodes for application in supercapcitor has received large research interest in recent years. Ultra-stable Mn_1-xNi_xCO₃ (x-0, 0.20, 0.25 and 0.30) nano/sub-microspheres were synthesized via simple co-precipitation method and the Mn_1-xNi_xCO₃ was confirmed by XRD, FT-IR, XPS and their morphology was studied by SEM and TEM analysis. Among the various Mn_1-xNi_xCO₃ electrodes, the Mn_0.75Ni_0.25CO₃ electrode exhibited the higher specific capacitance (364 F g^-1 at 1 A g^-1) with capacity retention of 96% after 7500 cycles at 5 A g^-1. Moreover, the assembled solid-state asymmetric supercapacitor based on Mn_0.75Ni_0.25CO₃//graphene nanosheets performed a high specific capacity of 46 F g^-1 and energy density of 25 Wh kg^-1 at a power density of 499 W kg^-1 along with high capacity retention of 87.7% after 7500 cycles. The improved electrochemical performances are mainly owing to the intrinsic conductivity and electrochemical activity of MnCO₃ after Mn_1-xNi_xCO₃ (x-0.20, 0.25 and 0.30) with appropriate Ni concentration. This study highlights the potentiality of the Mn_0.75Ni_0.25CO₃//GNS asymmetric supercapacitor device for promising energy storage applications.