Highly dispersed FeSe2 nanoparticles in porous carbon nanofibers as advanced anodes for sodium and potassium ion batteries

Abstract Sodium and potassium ion batteries (SIBs and PIBs) have received a substantial amount of attention in large-scale applications due to the abundance and low price of sodium and potassium metals. However, large-sized Na+ and K+ ions can cause sluggish kinetics, large volume change and unsatisfactory cycling behaviors. Herein, highly dispersed FeSe2 nanoparticles confined in mesoporous carbon nanofibers (FeSe2@C) were prepared via a novel selenization strategy and utilized as an anode material in both SIBs and PIBs for the first time. The mesoporous FeSe2@C nanocomposite possesses unique structural features including a large surface area and the presence of highly dispersed FeSe2 nanoparticles and a 1D mesocarbon nanofiber matrix, which can efficiently enhance electrical conductivity, facilitate electron/ion transportation and alleviate volume variations, thereby enabling fast Na/K storage kinetics, an outstanding structural integrity and a superior Na/K storage performance. For SIBs, FeSe2@C shows a high charge capacity of 483 mAh g−1 at 0.2 A g−1 over 100 cycles, which retains a capacity of 359 mAh g−1 after 200 cycles at 1.0 A g−1. When employed as anode for PIBs, FeSe2@C displays a high charge capacity of 352 mAh g−1 at 0.1 A g−1. Moreover, the electrochemical kinetic analysis confirms that the excellent pseudocapacitive behavior accounts for the superior sodium/potassium storage performance at high current densities.