Ultrafast cathode assembled using small reduced graphene oxide sheets enables a 2,000 C rate supercapacitor with high energy density

Abstract

To realize ultrafast supercapacitors, a series of ultrahigh-rate (≥1,000 mV s⁻¹) anodes that break a well-known “energy vs. power dilemma” in aqueous electrolytes have been successfully developed over the past five years. However, their matching cathodes are still limited by slow ion transport dynamics and oxidation. Here, we report a series of hydrated films that comprise small sheets of reduced graphene oxide (SSs−rGO, <100 nm in average lateral size) and feature short interlayered pathways (∼100 nm) for rapid ion transport and high oxidation resistance. As the first ultrahigh-rate cathode with areal capacitance (C_a) satisfying an industrial requirement (>0.6 F cm⁻²), the SSs−rGO electrode (5.0 mg cm⁻²) delivers a C_a of 0.61 F cm⁻² and a gravimetric capacitance of 123 F g⁻¹ at an ultrahigh-rate of 3,000 mV s⁻¹. Combining with a Ti₃C₂T_x anode, the cathode enables a 1.8 V ultrafast aqueous supercapacitor that delivers energy densities of 0.14 and 0.09 mWh cm⁻² for discharges in 1.79 and 0.97 s (∼2,000 and 3,700 C rate), respectively. These values double (at 2,000 C) and almost ten-fold (at 3,700 C) those of the ever-reported supercapacitors operating at the corresponding rates. The present strategy paves a road to ultrafast (>1,000 C) and high-energy-density supercapacitors, by which energy charge/discharge can finish within 3.6 s.