Journal of Power Sources 161 (2006) 1486–1492 Short communication Enhanced electrochemical stability of all-polymer redox supercapacitors with modified polypyrrole electrodes A.M.P. Hussain ∗ , A. Kumar Department of Physics, Tezpur University, Napaam, Tezpur 784 028, Assam, India Received 4 March 2006; accepted 29 May 2006 Available online 24 July 2006 Abstract Redox supercapacitors are attracting increasing attention as high power electrochemical sources and can either be coupled with batteries to provide peak power or replace batteries for memory back-up. In the present work, all-polymer solid-state supercapacitors with LiClO 4 and LiCF 3 SO 3 doped polypyrrole electrodes and P(VDF-HFP)-PMMA based polymer gel electrolyte are fabricated. The polypyrrole electrodes are irradiated with 160 MeV Ni 12+ ions at 5 × 10 10 ,5 × 10 11 and 5 × 10 12 ions cm -2 . A comparative study is made between unirradiated and irradiated supercapacitors with polypyrrole-based electrodes. An average capacitance of about 200 F gm -1 is obtained. On successive charging and discharging, the capacitance decreases for supercapacitors with unirradiated electrodes but remains stable when irradiated electrodes are used. In addition, the capacitance is slightly decreased compared with that for unirradiated electrodes. Charge–discharge studies show a decrease in total charge–discharge time for supercapacitors with irradiated electrodes. The capacitance values calculated from cyclic voltammograms are higher than those determined from charge–discharge plots due to the added contribution of a leakage current. The coulombic efficiency of all the supercapacitors is about 90%. © 2006 Elsevier B.V. All rights reserved. PACS: 82.47.Uv; 61.80.–x Keywords: Polypyrrole; Supercapacitor; Ion irradiation; Charge–discharge; Specific energy; Coulombic efficiency 1. Introduction There is increasing interest in the application of electrochem- ical systems under conditions in which the electrical power demand is highly time-dependent, often in the form of short-term pulses. Because of the general observation that capacitors can be used to provide short electrical pulses, attention has focused on the use of electrochemical systems that exhibit capacitor- like characteristics. The concept of providing large quantities of electrical power, comparable in magnitude with that attainable in batteries, in reasonably small capacitors was proposed about five decades ago [1,2]. Only in the past 15 years or so, however, has the electrochemical charge-storage device variously called a ‘supercapacitor’ or an ‘ultra capacitor’ [3] become the subject of practical and commercial development for use in a hybrid mode ∗ Corresponding author. Tel.: +919435081078 (Mobile). E-mail address: abu@tezu.ernet.in (A.M.P. Hussain). with batteries for electric vehicle power systems for the starting, lighting and ignition of internal combustion engine vehicles, and for small-scale consumer electronics [3]. Electrochemical supercapacitors bridge the gap between con- ventional capacitors and batteries. Supercapacitors have two unique characteristics, namely, large capacitance and high stor- age and delivery of power. Conducting polymers are very promising electrode materials for redox capacitors as they are less expensive than other electrode materials, e.g., noble metal oxides, may be easily synthesized in the form of extended sur- face thin films, and can store charge throughout their entire volume [4]. Swift heavy ion (SHI) irradiation of polymers has been found to produce useful modifications in their phys- ical and chemical properties. Increases in hardness, strength and wear resistance [5–7], electrical conductivity [8–10], den- sity [9], chain length [6–8], crystallinity [7–9] and solubility [5–9], as well as improvements in optical transmission [7–10] properties of the polymers have been reported. Many studies of ion irradiation with low energy (<1 MeV) on intrinsically 0378-7753/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2006.05.051