Eco-friendly and scalable synthesis of micro-/mesoporous carbon sub-microspheres as competitive electrodes for supercapacitors and sodium-ion batteries

Abstract

Cost-efficiency utilization of carbon sub-microspheres is greatly significant for their versatile energy-related applications. However, eco-friendly synthesis and moderate activation protocols for enhancing their electrochemical performances are still challenging. Herein, we explore a facile two-step methodology, i.e., hydrothermal carbonization and subsequent mild activation, for bottom-up fabrication of KHCO3 activated micro-/mesoporous carbon microspheres (MCMS-K) as competitive electrodes towards electrochemical capacitors (ECs) and sodium-ion batteries (SIBs) by using the soluble starch as a low-cost precursor. Benefitting from its high specific surface area (~1972.8 m2 g−1), abundant micropores (~88.8%), and high graphitization degree, the MCMS-K electrode obtains a specific capacitance of ~369.8 F g−1 (~266.3 F cm−3) at 1 A g−1 in 1 M H2SO4, higher than that in 6 M KOH, thanks to the surface oxygen functional groups involved pseudocapacitance. More remarkably, the MCMS-K based organic symmetrical ECs deliver a high-rate energy density of 34.4 Wh kg−1 at 12.5 kW kg−1, and ultra-long cycling stability. Besides, the MCMS-K anode renders a high-rate capacity of ~78.6 F g−1 at 5.0 A g−1via Na+ surface adsorption and intercalation accompanying with excellent cycling behaviors for SIBs. It strongly highlights the promising applications of our MCMS-K product in ECs and SIBs.