Bio-waste chicken eggshells to store energy

Abstract

Bio-waste in the form of chicken eggshells, which contain high amounts of calcium carbonate (CaCO₃), is used to store energy. The fine eggshell powders are used as an electrode against a metallic lithium anode in a non-aqueous electrolyte. The initial discharge capacitance of the eggshell system was found to be 232 F g⁻¹, while the reversible capacitance was 120 F g⁻¹. Thereon, the cell maintained an excellent capacitance retention of 92% over 1000 cycles. The electrochemical performance obtained is comparable to that of commercially available classical activated carbon (AC) material. CaCO₃ showed a non-faradaic behaviour and the shape of the electrochemical curves resembles that of the AC electrode. The preliminary findings suggest that CaCO₃ from eggshells can be used as the electrode in Li-ion capacitors to store and release charges effectively over a wide electrochemical stability window of 4 V. Using chicken eggshells in this manner not only reduces the amount of bio-waste, but also adds considerable value. A detailed understanding of the electrochemical and physical behaviour of the material is needed in order to improve its performance and to enable its widespread use.