Hollow Co9S8 cores encapsulated in hierarchical MXene@Bi2O3 multiple shells for constructing binder-free electrodes of foldable supercapacitors

Abstract

Rational structure design and regulation are of paramount importance for obtaining electrode materials with desirable electrochemical performance. Here, a novel binder-free electrode with the hollow Co9S8 core@multi-shell structure (CS-x@MXene@Bi2O3) derived from metal-organic frameworks (MOFs) precursor is well designed by the electrospinning, sulfuration, carbonization, and hydrothermal processes. In this architecture, the concentration of Co9S8 (CS-x) is optimized for an ideal flexible substrate, which alleviates the dimensional variation for long cycle life. The unique cores and the MXene flakes engineered by Bi2O3 multiple shells can be responsible for the superior characteristics, including a fast electronic pathway, large specific surface area, enhanced electrical conductivity, and improved electrochemical performance. As expected, the obtained CS-2@MXene@Bi2O3 binder-free electrode exhibits a high discharge capacitance of 646.1 F g–1 (1 A g–1). Two binder-free electrodes can be assembled into a solid-state supercapacitor with desirable energy and power density, and long-term cyclic stability is demonstrated through 5000 cycles. Given these advantages, the CS-2@MXene@Bi2O3 is selected as the electrode in a foldable supercapacitor. More importantly, the specific capacitance is reserved after various deformations. Therefore, it is expected that binder-free electrode materials with the unique core@shell structure design could be applied in wearable and portable energy conversion devices.