Polycrystalline phases grown in-situ engendering unique mechanism of charge storage in polyaniline-graphite composite

Abstract

We report on a simple surfactant/template free chemical route for the synthesis of semi-polycrystalline polyaniline-graphite (SPani-graphite) composite and its application as an electroactive material in electrochemical charge storage. The synthesized material exhibits well-defined poly-crystallographic lattices in high resolution transmission electron micrographs and sharp peaks in x-ray diffraction spectra suggesting crystalline nature of the material. The specific capacitance computed from the galvanostatic charge-discharge (GCD) data obtained from 3-electrode cell configuration using 1 M aq. Na2SO4 as an electrolyte was 111.4 F g−1 at a current density of 0.1 A g−1 which rises to 269 F g−1 at an elevated current density of 1.0 A g−1. A similar pattern of increase in the specific capacitance values with an increase in the current density was observed in the results obtained from 2-electrode symmetric device configuration using polymer gel electrolyte (xanthan gum in 1 M aq. Na2SO4). The specific capacitance computed from the GCD data obtained from the device configuration was 20 F g−1 at the current density of 1.0 A g−1. The device delivers an energy density of 1.7 Wh kg−1 and a power density of 2.48 kWh kg−1 at an applied current density of 0.5 A g−1 suggesting an excellent rate capability and power management. In addition, the device exhibits ⁓92 % specific capacitance retention up to 8000 continuous GCD cycles and ⁓80 % coulombic efficiency up to 10,000 continuous GCD cycles indicating excellent cycling stability. The unique feature of increasing specific capacitance with respect to applied current density is attributed to the presence of semi-polycrystalline phases in the SPani-graphite matrix. The material behaves as a surface redox supercapacitor and its unique mechanism of charge storage is discussed in detail in the article.