Carbon additive structure influence on electrochemical double-layer capacitor electrode behavior

Abstract

Electrochemical double-layer capacitors (EDLC) are widely used as power sources for peak load or peak generation leveling in transport and stationary applications sometimes in combination with accumulator battery. For such applications EDLC need low sensitivity (from lifetime and capacity point of view) to high current mode operation, which is usually crucial for traditional accumulators’ types. Capacity loss in high current mode operation due to both transport and resistive limitations is observed both for accumulators and supercapacitors but much less for latter due to initial low internal resistance and electrochemical reactions absence. Carbon nanotubes (CNT) and nanofibers (CNF) as alternative to carbon blacks as conductive additive for electrodes are good possibility to improve high current operation both for accumulators and EDLC. This paper is devoted to investigation of carbon nanotubes and nanofibers comparison with traditional carbon black additive. CNF structure usually contains more defects and has lower aspect ratio than single-walled nanotubes but this kind of materials is less expensive than CNT, that is also important for final customer. Electrode samples with Vulcan XC72R carbon black were prepared for reference measurements. All electrode samples were tested in galvanostatic charge-discharge mode at different current levels in laboratory-scale EDLC cell, characterized by impedance spectroscopy. Obtained results showed improved high-current operation for CNT-containing electrodes. Economic estimation for different kinds of additives has also been carried out.