High-rate aqueous/ionic liquid dual electrolyte supercapacitor using 3D graphene sponge with an ultrahigh pore volume

Highlights: • High-rate ionic liquid/aqueous dual electrolyte EDLC using 3D graphene sponge. • 3D graphene shows an ultrahigh volume of 5.6 cm³ g⁻¹ with macropores. • Dual electrolyte supercapacitor employs ion exchange membrane-free configuration. • EDLC deliver the maximum rate of 30 A g⁻¹ and the cell potential of 2.0 V. • Differential electrochemical mass spectrometry is used for In situ gas analysis. -- Abstract: Non-traditional electrolytes like "water-in-salt" and dual electrolyte are emerging as promising electrolytes for next-generation energy storage devices. However, their low rate capability is a major obstacle for their extensive employment. Here, we achieve a high-rate aqueous/ionic liquid dual electrolyte supercapacitor using 3D interconnected graphene sponge with a high pore volume of 5.6 cm³ g⁻¹. It delivers a high rate of 30 A g⁻¹ and the maximum cell potential of 2.0 V. The maximum specific energy of 9.1 Wh kg⁻¹ at 0.5 A g⁻¹ and the specific power of 16.3 kW kg⁻¹ at 30 A g⁻¹ are achieved for the dual electrolyte. Excellent long-term stability of 85% is estimated for the applied cell potential of 2.0 V after 50,000 cycles at 5 A g⁻¹. In situ gas analysis using differential electrochemical mass spectrometry identifies three gases (H₂, CO₂ and CO) at the critical cell potentials. The possible cell potential-limiting electrode in the full cell is identified by the type of gas evolved at the maximum cell potentials. This high-rate supercapacitor may be useful for high-power applications.