Pseudocapacitive sodium storage of Fe1−xS@N-doped carbon for low-temperature operation

Abstract

Constructing potential anodes for sodium-ion batteries (SIBs) with a wide temperature property has captured enormous interests in recent years. Fe1−xS, a zero-band gap material confirmed by density states calculation, is an ideal electrode for fast energy storage on account of its low cost and high theoretical capacity. Herein, Fe1−xS nanosheet wrapped by nitrogen-doped carbon (Fe1−xS@NC) is engineered through a post-sulfidation strategy using Fe-based metal-organic framework (Fe-MOF) as the precursor. The obtained Fe1−xS@NC agaric-like structure can well shorten the charge diffusion pathway, and significantly enhance the ionic/electronic conductivities and the reaction kinetics. As expected, the Fe1−xS@NC electrode, as a prospective SIB anode, delivers a desirable capacity up to 510.2 mA h g−1 at a high rate of 8000 mA g−1. Additionally, even operated at low temperatures of 0 and −25°C, high reversible capacities of 387.1 and 223.4 mA h g−1 can still be obtained at 2000 mA g−1, respectively, indicating its huge potential use at harsh temperatures. More noticeably, the full battery made by the Fe1−xS@NC anode and Na3V2(PO4)2O2F cathode achieves a remarkable rate capacity (186.8 mA h g−1 at 2000 mA g−1) and an impressive cycle performance (183.6 mA h g−1 after 100 cycles at 700 mA g−1) between 0.3 and 3.8 V. Such excellent electrochemical performance is mainly contributed by its pseudocapacitive dominated behavior, which brings fast electrode kinetics and robust structural stability to the whole electrode.