Sr- and Fe-substituted LaMnO3 Perovskite: Fundamental insight and possible use in asymmetric hybrid supercapacitor

The symmetry or structural stability of ABO(3)-type perovskite oxides depends largely 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 La3+ with Sr2+ with a larger ionic radius and Mn3 + with Fe3+ with a similar ionic radius favored both the crystal symmetry and the mixed ionic-electronic conductivity of the perovskite. Electrodes based on La0.7Sr0.3Mn0.5Fe0.5O3 (LSMFO55) exhibited a faradaic behavior with a specific capacity of 330 C g(-1) (92 mAh g(-1)) at 12C rate, while this electrode maintained a capacity of 259 C g(-1) at 240C (charge or discharge in 15 s). 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 the use of 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 adopting an appropriate carbon-derived negative electrode (such as CNO) can provide a practical high-rate hybrid device using various perovskites.

Automated summary

The symmetry and conductivity of perovskite oxides are greatly influenced by the size and valence states of cations. By substituting La3+ with Sr2+ and Mn3+ with Fe3+, the crystal symmetry and ionic-electronic conductivity of the perovskite can be improved. The use of carbon nano-onions as a negative electrode in an asymmetric hybrid supercapacitor greatly enhances its rate capability. Tuning the conductivities and using appropriate carbon-derived negative electrodes can pave the way for high-rate hybrid devices using different perovskites.