Ultrahigh coulombic efficiency in alkali metal incorporated biomass derived carbon electrode

In order to facilitate higher stability and fast charging of the energy storage devices, it is also essential to increase their coulombic efficiency. The most common approaches to increase the coulombic efficiency are either by (i) introducing capacitive behaviour or (ii) tuning parasitic electrochemical reactions in batteries. Here we demonstrate a novel approach to facilitate ultra high coulombic efficiency in supercapacitors by introducing parasitic electrochemical processes in biomass derived carbon (BDC) based electrodes. Three different BDCs were synthesized by varying activating agents (KOH and NaOH) and carbonization temperatures (600 and 800 degrees C). These carbon samples captured some portion of alkali metals from their respective activating agents. The trapped alkali metals in the carbon matrix eventually participate in parasitic electrochemical processes to provide ultrahigh coulombic efficiency (>115 %) for the first few thousand charge discharge cycles. Finally, an asymmetric supercapacitor (ASC) was fabricated using the prepared BDC as the negative electrode and a comparatively slow V2O5 electrode as a positive. The ASC can retain about 98 % of its initial capacitance even after 10,000 cycles and exhibits high coulombic efficiency. It provides an energy density of 0.196 mWhcm(-3) while maintaining a high power density of 190.41 mWcm(-3).