Recyclable liquid metal – Graphene supercapacitor

Abstract

Because of their high electrical conductivity, fluidic deformability, self-healing properties, and the possibility of recycling, Ga-based liquid metal alloys like eutectic gallium indium (EGaIn) have tremendous potential as electrodes for stretchable energy storage devices. However, EGaIn droplets could never be used as electrodes in thin-film supercapacitors (SCs) at the desired micro/nano scale, because they rapidly coalesce into bulk EGaIn when contacting acidic/alkaline electrolytes. Here, we show that coating EGaIn droplets with only 0.08 wt% of reduced graphene oxide (GO) nanosheets tremendously improves their chemical stability. We fabricated binder-free GO-coated EGaIn nanocomposite electrodes that show excellent stability in a strong alkaline electrolyte. We demonstrated a symmetric soft-matter pseudo-SC with areal capacitances of 1200mF/cm2@0.3 mA/cm2 and 220mF/cm2@1mA/cm2, which is > 10 × compared to previous SCs based on bulk EGaIn. This SC retains 98.4 % of the initial capacitance after 4000 electrochemical cycles and exhibits comparable self-discharge rates to state-of-the-art flexible pseudo-SCs. Surprisingly, applying mechanical strain results in improved areal capacitance. We demonstrate rapid, laser-based fabrication of a wirelessly chargeable elastic film with an integrated energy harvesting antenna and energy-storage SC that can be used in wearable biomonitoring patches, and e-textiles. Finally, we demonstrate the recovery of the metals from the disposed of SCs through an electrowinning technique.