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

The material properties, symmetry, and structural properties of ABO3-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 LaMnO3 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 (LaMn0.75Co0.25O3) 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.