Boosting fast and stable potassium storage of iron selenide/carbon nanocomposites by electrolyte salt and solvent chemistry

Abstract

Metal selenides with good electronic conductivity and high theoretical capacities are regarded as potential anodes for potassium-ion batteries (PIBs). But the large radius and heavy weight of K-ion, and inefficient electrolyte lead to sluggish reaction kinetics and structure collapse of the electrode. Herein, the enhanced rate capability and cycling performance of FeSe/C nanocomposites are achieved by electrolyte salt and solvent engineering. The introduction of KFSI-EC/DEC electrolyte significantly boosts the charge transfer, K-ion diffusion, and capacitive behavior of FeSe/C electrode, which can be attributed to the stable solvation structure and the inorganic compound-rich solid electrolyte interphase layer demonstrated by computational studies on molecular orbital energy levels, X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) characterizations. Consequently, the FeSe/C electrode shows superior rate performance (230 mA h g−1 at 10 A g−1) and stable cycling performance (550 mA h g−1 at 0.2 A g−1 over 100 cycles). Additionally, ex-situ X-ray diffraction, HRTEM and XPS characterizations throw light on the reversible conversion reaction mechanism between FeSe and K-ion.