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 (LaMn_0.75Co_0.25O₃) 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.