Effect of substrate on the performance of flexible energy storage devices based on surface modified C60 – β Ni(OH)2 nanocomposite

Abstract

Aim of this study is to find the effect of the current collector in the performance of flexible energy storage devices based on surface modified organic-inorganic composite. As a part of our pursuit to develop flexible supercapacitive electrodes, we recently reported the fabrication of an electrode from an organic-inorganic composite slurry of surface functionalized fullerene and nickel hydroxide coated onto a copper sheet substrate using simple doctor blade method. We reported that the electrodes deliver specific energy and specific power of 661.5 Wh/kg and 8.8 KW/kg, respectively, and a specific capacitance of 675 Fg−1, which showed excellent cycling stabilities. In an effort to search for various combinatorial combinations of the composite and the substrate, in lieu of copper, in the present study, we incorporate nickel sheet as the current collector. The structure and composition of the binder-free, flexible super capacitive electrodes were characterized using XRD, TEM, FTIR, XPS, BET, Raman Spectroscopy, and their electrochemical properties were characterized using cyclic voltammetry, galvanostatic charge-discharge measurements, chronoamperommetry and impedance spectroscopy. The as-prepared films stuck readily onto the substrate without the need of any binder material, exhibited remarkable flexibility, and were proven to be crack-free when subjected to repeated bending and twisting. The developed flexible super capacitive electrodes deliver a specific capacitance of 296 F g−1, maximum energy density of 82.2 Wh kg−1, and a maximum power density of 1056 W kg−1. The device retains 91.2 % of its capacitance when subjected to 1000 charge-discharge cycles. Our observations indicate that copper is the better choice as the current collector, which can be ascribed to the better electrical conductivity of copper compared to nickel. We conclude that the poor electrical conductivity of nickel sheet compared to copper substrate make the bottleneck for the performance of electrodes made using nickel substrate. To recapitulate, judicious choice of a current collector with high electrical conductivity along with a suitable surface modification strategy to form a composite in an amorphous form that forms smooth slurry are vital to the fabrication of binder-free, flexible supercapacitive devices.