Alkylammonium-Intercalated 2D Mackinawite FeS as Electrode Materials for Rechargeable Batteries

Although electrode materials for batteries show high energy density, sluggish kinetics originated from the diffusion-controlled charge storage mechanism result in low power density and limit potential applications. Here, we report the synthesis of alkylammonium-intercalated mackinawite iron sulfides (M-FeS) as electrode materials for batteries. Well-defined layered structures with an interlayer distance controlled from 0.5 to 1.3 nm were formed by the intercalation of various alkylammonium ions into M-FeS, and the density of intercalated ions was controlled by varying the mass of the intercalated molecules, resulting in controlled electrochemical properties. M-FeS with increased interlayer distance and controlled density of intercalated molecules exhibited enhanced capacity, ion diffusion flux, rate capability, and structural stability. These improved electrochemical properties were explained by the effect of electrical conductivity, the density of intercalated molecules, diffusion coefficient, and concentration of electrolyte ions. This analysis suggests factors to consider when selecting two-dimensional materials and intercalants in order to enhance electrochemical performance.