Sr and Fe-Substituted LaMnO₃ Perovskite for High-Rate Asymmetric Hybrid Supercapacitors

Perovskite has been getting significant attention in solar cells, photocatalysts, and hybrid supercapacitors. The symmetry or structural stability of ABO 3 -type perovskite oxides depends mainly on the size of ‘A’ and ‘B’ cations, which determines the material properties. The partial substitution of these cations may be used to tune these properties. The ionic sizes and valence states of the cations play an important role in improving the properties of perovskite. In this study, the substitution of La 3+ with Sr 2+ with a larger ionic radius and Mn 3+ with Fe 3+ with a similar ionic radius favored both the crystal symmetry and the mixed ionic-electronic conductivity of the perovskite. Electrodes based on La 0.7 Sr 0.3 Mn 0.5 Fe 0.5 O 3 (LSMFO55) exhibited a faradaic behavior with a specific capacity of 330 C g -1 (92 mAh g -1 ) at a 12C rate, while this electrode maintained a capacity of 259 C g -1 at 240C (charge or discharge in 15s). Additionally, exohedral carbon nano-onions (CNO) were introduced as a negative electrode to design an asymmetric hybrid supercapacitor (AHS) with a widened cell voltage. The use of CNO as a negative electrode in the AHS improved the rate capability drastically compared to rGO. This device maintained a good energy density even at an extra-high charging rate (600C), owing to its outstanding rate capability. The high-rate performance of the LSMFO55//CNO AHS can be elucidated by successful fabrication with a mixed ionic-electronic conductive positive electrode and a CNO negative electrode. Tuning the electronic and ionic conductivities by cationic substitution and introducing CNO negative electrodes can provide a practical high-rate hybrid device using various perovskites.