Ultra-stable Mn(1-)(x)Ni(x)CO(3) nano/sub-microspheres positive electrodes for high-performance solid-state asymmetric supercapacitors

Long–term cycling performance of electrodes for application in supercapcitor has received large research interest in recent years. Ultra-stable Mn(1-)(x)Ni(x)CO(3) (x-0, 0.20, 0.25 and 0.30) nano/sub-microspheres were synthesized via simple co-precipitation method and the Mn(1-)xNi(x)CO(3) was confirmed by XRD, FT-IR, XPS and their morphology was studied by SEM and TEM analysis. Among the various Mn(1-x)Ni(x)CO(3) electrodes, the Mn(0.75)Ni(0.25)CO(3) 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(0.75)Ni(0.25)CO(3)//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 MnCO(3) after Mn(1-)(x)Ni(x)CO(3) (x-0.20, 0.25 and 0.30) with appropriate Ni concentration. This study highlights the potentiality of the Mn(0.75)Ni(0.25)CO(3)//GNS asymmetric supercapacitor device for promising energy storage applications.