Construction of Se-doped MnS with sulfur-bridged bonds in N, S-codoped carbon nanofibers as an anode for robust sodium-ion capacitors

Manganese sulfide (MnS) has emerged as a promising anode material for sodium-ion capacitor owing to its significant theoretical capacity, abundant reserves, and non-toxic characteristics. Nevertheless, the sluggish reaction kinetics, coupled with low electrical conductivity and substantial volume expansion, result in inferior rate capabilities and a relatively short cycle life, which severely hinders its practicality. In response to these challenges, Se-doped MnS confined within N, S-codoped carbon nanofibers (Se–MnS@CNFs) has been precisely engineered. Experimental results reveal that Se doping enhances both the lattice spacing and electrical conductivity of MnS. Furthermore, the CNF coating facilitates the formation of Mn–S–C bonds between Se–MnS and CNFs, effectively promoting Na⁺/electron migration while preventing agglomeration and volumetric change of Se–MnS during the (de)sodiation processes. These advantageous properties endow the Se–MnS@CNFs anode with a supernormal capacity (609.8 mAh g⁻¹ at 0.05 A g⁻¹), remarkable rate performance (355.1 mAh g⁻¹ at 20 A g⁻¹), and unparalleled cycle lifespan (retaining 89.1 % of its capacity after 800 cycles). Moreover, a comprehensive investigation into the sodium storage mechanism of Se–MnS@CNFs was conducted utilizing a series of in-situ and ex-situ characterization techniques alongside rigorous theoretical calculations. As expected, when coupled with a nitrogen-doped carbon (NC) cathode, the constructed Se–MnS@CNFs//NC sodium-ion capacitor delivered outstanding energy and power densities (146.1 Wh kg⁻¹/22000 W kg⁻¹) along with excellent cycling life (79.6 % capacitance retention after 6000 cycles). This research contributes novel perspectives on the exploration of non-metallic atom-doped MnS and offers an efficient approach to designing fast kinetic anodes for advanced energy storage systems.