Iron Porphyrin Organic Frameworks Derived Bionic-Tree-Nodule-like Fe7S8 with Ultralong Potassium Ion Storage

Transition metal sulfides (TMSs) serve as anodes for potassium-ion batteries (PIBs) because of their high conductivity, high capacity, and requirement of cheap raw materials. However, their volume expansion, agglomeration, and crushing often lead to limited cycle life and inferior structural stability. Here, inspired by biological tree nodules, S, N-codoped carbon-coated Fe7S8 particles (Fe7S8@SNC) originated from metalloporphyrins and were rationally designed for PIBs after being vulcanized by a one-pot method. Fe7S8@SNC as an anode delivered a high reversible capacity of 410 mAh g–1 at 50 mA g–1, an extremely long cycle up to 2000 cycles with a capacity of 214 mAh g–1 maintained at 1000 mA g–1, and excellent rate performances (287 mAh g–1 at 500 mA g–1 and 181 mAh g–1 at 2000 mA g–1). Significantly, ex situ TEM can still capture the stable structure of Fe7S8 after 500 cycles. In this unique structure, prominent Fe7S8 particles reduce the mechanical stress and shorten the transport path of K+, alleviating the pulverization during repeated insertion/extraction of K+. The S, N-codoped carbon decoration protects the structural stability and inhibits the agglomeration of internal Fe7S8, alleviates the volume change caused by the K+ reaction, and greatly improves the stability of PIBs. This study provides a new strategy for the realization of TMSs with ultralong cycling stability and lays a foundation for the commercial application of PIBs.