Niobium carbide nanofibers as a versatile precursor for high power supercapacitor and high energy battery electrodes

Abstract

This study presents electrospun niobium carbide/carbon (NbC/C) hybrid nanofibers, with an average diameter of 69 ± 30 nm, as a facile precursor to derive either highly nanoporous niobium carbide-derived carbon (NbC–CDC) fibers for supercapacitor applications or niobium pentoxide/carbon (Nb₂O₅/C) hybrid fibers for battery-like energy storage. In all cases, the electrodes consist of binder-free and free-standing nanofiber mats that can be used without further conductive additives. Chlorine gas treatment conformally transforms NbC nanofiber mats into NbC–CDC fibers with a specific surface area of 1508 m² g⁻¹. These nanofibers show a maximum specific energy of 19.5 W h kg⁻¹ at low power and 7.6 W h kg⁻¹ at a high specific power of 30 kW kg⁻¹ in an organic electrolyte. CO₂ treatment transforms NbC into T-Nb₂O₅/C hybrid nanofiber mats that provide a maximum capacity of 156 mA h g⁻¹. The presence of graphitic carbon in the hybrid nanofibers enabled high power handling, maintaining 50% of the initial energy storage capacity at a high rate of 10 A g⁻¹ (64 C-rate). When benchmarked for an asymmetric full-cell, a maximum specific energy of 86 W h kg⁻¹ was obtained. The high specific power for both systems, NbC–CDC and T-Nb₂O₅/C, resulted from the excellent charge propagation in the continuous nanofiber network and the high graphitization of the carbon structure.