Symmetric/Asymmetric Supercapacitor Based on the Perovskite-type Lanthanum Cobaltate Nanofibers with Sr-substitution.

In this study, we synthesize the La x Sr 1−x CoO 3−δ (0.3≤x≤1) nanofibers (LNF-x) by Electrospun method to improve the energy density of supercapacitor. As well, the structure and electrochemical properties of LNF-x are investigated in detail. As a result, LNF-0.7 sample with high specific surface area possesses the maximum specific capacitance value of 747.75   F·g −1 at a current density of 2   A·g −1 in 1   M Na 2 SO 4 aqueous electrolyte. In addition, a symmetric supercapacitor and an asymmetric supercapacitor are constructed using the LNF-0.7 as the positive electrode, while the LNF-0.7 and activated carbon (AC) are applied to the negative electrode, respectively. The LNF-0.7//LNF-0.7 device with an extended operating voltage range of 0-1.6   V displays excellent electrochemical performance with a high energy density of 34.8   Wh·kg −1 at a low power density of 400   W·kg −1 . On the other hand, the LNF-0.7//AC supercapacitor is operated reversibly at a high cell voltage of 2.0   V and exhibits a high energy density of 27.7 Wh·kg −1 with a low power density of 500   W·kg −1 . Furthermore, the LNF-0.7//LNF-0.7 and LNF-0.7//AC devices have superior cycling stability with ∽97% and ∽80% specific capacitance retention after 2000 cycles, respectively.