Low Cost, Low Surface Area Activated Carbon As Anode Material for Neutral pH Aqueous Asymmetric Supercapacitor Applications Via a Simple Surface Modification

Surface modified activated carbon has been developed for use as a low-cost electrode material in aqueous asymmetric electrochemical supercapacitors.  Specifically, wood-based activated carbon with a surface area of under 500 m²/g was modified using an intermediate temperature acid exposure step that more than doubled the specific capacitance in a neutral aqueous electrolyte. After the modification step, the carbon was analyzed using x-ray photoelectron spectroscopy, BET, and combustion analysis. The material thus developed gave approximately 200% improvement in the specific capacitance in 1 M Na₂SO₄; namely 109 F/g when compared against the precursor activated carbon which showed 38 F/g. To prove the possible utility of this material, full asymmetric energy storage cells were made using the modified carbon as the anode active material and Lithium Manganese Oxide as the cathode active material and Na₂SO₄ aqueous electrolyte.  The test cells displayed excellent reversible capacity greater than 40 Ah/kg of activated carbon in anode for over 1000 cycles, which is an effective capacitance of approximately 160 F/g delivered over relatively slow  charge/discharge rates.   A Simple economic analysis shows that this material is over an order of magnitude more cost effective on a $/Ah basis than off-the-shelf electrochemical double-layer capacitor materials.  These encouraging results show great promise in developing low cost energy storage devices while incorporating non-toxic and environmentally benign materials.