Solubility-Limited Small Molecule for Stable High-Capacity Potassium Storage

Small molecule electrode materials with superb redox activity have significant applied implications for K-ion storage, but they face significant challenges like high solubility in electrolytes and low conductivity, limiting their capacity, rate, and cycling stability. Herein, a series of Ni-bis(dithiolene) (NiS₄)-based small molecules are designed with control of various redox-active substitutional groups for K-ion batteries anode materials. It is identified that bis[1,2-di(pyridine-4-yl) ethylene-1,2-dithiolate] nickel Ni[C₂S₂Py₂]₂ demonstrates a high reversible specific capacity (399 mAh g^-1 at 0.03 A g^-1) with an impressive rate capability and an exceptional cycling stability (over 99% capacity retention after 1600 cycles). Its extraordinary performance is attributed to the synergy between the NiS₄ unit and pyridine group, providing abundant K⁺ storage sites, impressive conductivity, and low solubility. The comprehensive characterizations and theoretical simulation confirm the multistep K⁺ storage mechanism in Ni[C₂S₂Py₂]₂, enabling fast charge transfer and excellent rate performance. This work offers new perspectives in building solubility-limited and conductive small molecule electrode materials with high redox activity for non-aqueous rechargeable batteries.