1D MnSe@carbon nanofiber as a high-rate anode for sodium-ion batteries: electrochemical and ex situ mechanistic investigation of Na+ charge storage

Abstract

One-dimensional manganese selenide@carbon nanofibers (MnSe@CNF) were synthesized by means of an electrospinning technique involving in situ selenization. The synthesized MnSe@CNF was characterized using various material characterization techniques. The surface morphology of MnSe@CNF was investigated using field-emission scanning electron microscopy and further substantiated with high-resolution transmission electron microscopy analyses. A sodium-ion battery was constructed using MnSe@CNF as the anode, which exhibited an enhanced specific capacity of 725 mA h g⁻¹ at 0.1C rate with a better rate capability. Furthermore, the Na⁺ charge storage kinetics was evaluated using Dunn's method. It was revealed that Na⁺ charge storage was a combination of diffusion storage and significant capacitive storage. Explicitly, the deconvoluted current response at the peak potential region of the cyclic voltammetry profile affirmed that Na⁺ charge storage is dominated by diffusion, whereas the non-peak potential region had a blend of capacitance and diffusion. Further, the postmortem analyses using the XRD performed at different depths-of-discharges (DoDs) confirmed the occurrence of the conversion/reconversion reaction and the robust stability of the MnSe@CNF anode. MnSe@CNF underwent the diffusive conversion/reconversion reaction while the carbon nanofibre facilitated the capacitive Na⁺ charge storage, leading to enhanced specific capacity.