Effect of fluoride (CoF2) based electrode material for high energy and power density asymmetric flexible supercapacitors

Herein, an asymmetric supercapacitor (ASC) device was assembled by employing the pristine CoF 2 as active positive electrode material and activated carbon (AC) as negative electrode material. The CoF 2 electrode exhibited an outstanding electrochemical behavior with enhanced specific capacitance (C s ) of 872 F/g at 1 A/g current density in three electrode configurations. The reversible Faradaic redox reactions in CoF 2 instigate the formation of cobalt-oxyfluorides and generating the mixed valence state of Co (Co 2+ and Co 3+ ) which improves its electrical conductivity and electrochemical behaviors. Furthermore, the room temperature paramagnetic nature of CoF 2 increases the gradient force of ions which could possibly increase the redox reactions at the electrolyte/electrode interface. The constructed asymmetric device structure of CoF 2 //AC revealed a quasirectangular shaped cyclic voltametric curve and symmetrical semi-triangular shaped galvanostatic chargedischarge profiles, respectively, which affirms the combined electric double layer capacitance and pseudocapacitive nature by its hybrid assembly. Hence, the constructed CoF 2 //AC ASC demonstrated a remarkable specific capacitance of 141 F/g, energy density of 44.06 Wh.Kg -1 , and power density of 422.97 W.Kg -1 at 1 A/g with the high cell voltage of 1.5 V. The CoF 2 //AC ASC device retained c.a. 92 % of its initial capacitance and attained over 96 % of Coulombic efficiency after 2000 cycles of charge-discharge profiles at 1 A/g, which suggests the high electrochemical stability. This admirable electrochemical performance and the origin towards the magneto-capacitance of CoF 2 could pave a new way to explore next generation high -performance supercapacitors.