B-Site-Substituted Rhombohedral LaMnO₃ Nanoparticle-Decorated Electrodes for Stable 2 V Aqueous Symmetric Supercapacitors

The material properties, symmetry, and structural properties of ABO 3 -type perovskite oxides are strongly influenced by the nature of A- and B-site cations. The electrochemical properties of this material can be tuned by the partial substitution in either the A-site or the B-site. The ionic radii and valence states of these cations are critical factors in optimizing the performance of perovskites. In this work, the electrochemical activity of rhombohedral LaMnO 3 is improved by substituting cobalt for manganese at the B-site. Various levels of Co substitution (25, 50, and 75%) are carried out and optimized using a sol–gel method. Among the different electrodes fabricated using these samples, LMC 25 (LaMn 0.75 Co 0.25 O 3 ) shows the best performance, which is attributed to the synergistic effects and improved electronic as well as ionic conductivities of the sample. This electrode exhibits a specific capacitance of 85 F g –1 at a current density of 1 A g –1 . A symmetric device is also fabricated with the LMC 25 electrodes, which is operated in a potential window of 2 V. The device is found to exhibit a capacitance of 37 F g –1 at a current density of 0.5 A g –1 and delivers an energy density of 20.5 Wh kg –1 at a power density of 1 kW kg –1 . High capacitance retention of 92% even after 20000 charge–discharge cycles and the ability to deliver an appreciable energy density of 10 Wh kg –1 even at a high power density of 10 kW kg –1 highlight the potential of these electrodes in efficient energy storage applications with long cycle life.