Manipulating Molecular Structure to Trigger Ultrafast and Long-Life Potassium Storage of Fe_0.4 Ni_0.6 S Solid Solution

Currently, the main obstacle to the widespread utilization of metal chalcogenides (MS_x ) as anode for potassium-ion batteries (PIBs) is their poor rate capability and inferior cycling stability as a result of the undesirable electrical conductivity and severe pulverization of the nanostructure during large K-ions intercalation-extraction processes. Herein, an ultrafast and long-life potassium storage of metal chalcogenide is rationally demonstrated by employing Fe_0.4 Ni_0.6 S solid-solution (FNS/C) through molecular structure engineering. Benefiting from improved electroactivity and intense interactions within the unique solid solution phase, the electrical conductivity and structure durability of Fe_0.4 Ni_0.6 S are vastly improved. As anticipated, the FNS/C electrode delivers superior rate properties (538.7 and 210.5 mAh g^-1 at 0.1 and 10 A g^-1 , respectively) and long-term cycle stability (180.8 mAh g^-1 at 5 A g^-1 after 2000 cycles with a capacity decay of 0.011% per cycle). Moreover, the potassium storage mechanisms of Fe_0.4 Ni_0.6 S solid solution are comprehensively revealed by several in situ characterizations and theoretical calculations. This innovative molecular structure engineering strategy opens avenues to achieve high-quality metal chalcogenides for future advanced PIBs.