Unlocking the Potential of Iron Sulfides for Sodium‐Ion Batteries by Ultrafine Pulverization

Abstract Iron sulfides have attracted tremendous research interest for the anode of sodium‐ion batteries due to their high capacity and abundant resource. However, the intrinsic pulverization and aggregation of iron sulfide electrodes induced by the conversion reaction during cycling are considered destructive and undesirable, which often impedes their capacity, rate capability, and long‐term cycling stability. Herein, an interesting pulverization phenomenon of ultrathin carbon‐coated Fe1‐xS nanoplates (Fe1‐xS@C) is observed during the first discharge process of sodium‐ion batteries, which leads to the formation of Fe1‐xS nanoparticles with quantum size (≈5 nm) tightly embedded in the carbon matrix. Surprisingly, no discernible aggregation phenomenon can be detected in subsequent cycles. In/ex situ experiments and theoretical calculations demonstrate that ultrafine pulverization can confer several advantages, including sustaining reversible conversion reactions, reducing the adsorption energies, and diffusion energy barriers of sodium atoms, and preventing the aggregation of Fe1‐xS particles by strengthening the adsorption between pulverized Fe1‐xS nanoparticles and carbon. As a result, benefiting from the unique ultrafine pulverization, the Fe1‐xS@C anode simultaneously exhibits high reversible capacity (610 mAh g−1 at 0.5 A g−1), superior rate capability (427.9 mAh g−1 at 20 A g−1), and ultralong cycling stability (377.9 mAh g−1 after 2500 cycles at 20 A g−1).