Medium ion-association electrolyte enables fast and stable K-storage for ferrocene-based organic anodes

Abstract

High-concentration electrolytes have demonstrated promise in improving the cycling stability of organic K-storage materials via suppressing dissolution of the organic active materials and enhancing interfacial stability. However, the improved cycling stability has been achieved at the expense of diminished K-storage kinetics. To overcome this challenge, herein, a green and environmentally friendly medium ion-association electrolyte (MIAE) with high ionic conductivity and anion-rich solvation structures was designed for organic ferrocene (Fc) K-storage anodes. The medium ion-association properties for the tailored solvation structures of MIAE can provide multiple benefits for fast and stable K-storage of Fc anodes via suppressing the dissolution of Fc, promoting the formation of a stable solid-electrolyte interphase (SEI), as well as accelerating the ion-transfer kinetics at the same time. As a result, the Fc anode in an ethylene carbonate (EC)-based MIAE delivered a reversible discharge capacity of 209.1 mAh g⁻¹ after 200 cycles at 50 mA g⁻¹ with an average coulombic efficiency (CE) of above 99.7%. This work provides valuable insights into the rational design of customized electrolytes for advanced organic potassium-ion batteries (PIBs).