Gel Polymer Electrolytes for Flexible LiXPO4 (X=Mn,Fe,Co)-Fractal-like Fe2O3 Hybrid Supercapacitor Devices

Abstract

In the recent years, the development of electrochemical energy storage device has been widely investigated. Supercapacitors are known for their excellent power density and superb cycling stability but restricted by low charge storage capacity, on the other hand batteries provide high energy density, limited by low power density. Here, olivine-structured LiXPO4 (X=Mn,Fe,Co) possessing high energy storage capability is used as a positive electrode. Our recent research demonstrated that Fe2O3-based Fractal-like structures supported on Ni Foam exhibit extremely high specific capacitance of ~2708 F g-1 at 1 A g-1 in 1 M KOH electrolyte, when used as negative electrode [1]. Hence, the Fractal-like Fe2O3 is used as the negative electrode for the envisaged hybrid supercapacitor device. The flexibility is imparted to these devices by employing carbon cloth as the current collector. The choice of suitable electrolyte is crucial for supercapacitor applications as it decides the working potential window, electrode-electrolyte interaction, and ionic conductivity. Here, PVA based gel polymer electrolyte (GPE) is used due to the ease in gel formation and non-toxicity to make flexible hybrid supercapacitor device. Different PVA based GPEs are synthesized using H3PO4, H2SO4 and KOH with Ionic liquids viz. EMIMBF4 and EMIMCl. The role of GPEs in the performance of LiXPO4 (X=Mn,Fe,Co)//GPE//Fe2O3 hybrid supercapacitors is understood through charge storage mechanisms deciphered from galvanostatic charge-discharge (GCD) experiments, Electrochemical Impedance Spectroscopy (EIS).