Donor Number‐Driven Solvation Manipulation of Ether‐Aided Ionic Liquid Electrolytes Enables Stable K‐Storage for FeNCN Anode

ABSTRACT Highly concentrated electrolytes (HCEs) were successfully developed for perspective iron‐based anode materials in potassium ion batteries (PIBs) to achieve excellent K‐storage cycling stability, however, which was usually achieved at the expense of compromised K‐storage kinetics, presenting a significant challenge in reconciling the trade‐off between K‐storage kinetics and cycling stability. Herein a donor number (DN)‐driven solvation manipulation strategy was proposed to develop weakly polar and various‐DN ether‐assisted ionic liquid electrolytes (ILE) for iron carbodiimide (FeNCN) anode. The optimized HDILE via introducing high‐DN anisole (AS) into ILE demonstrated high ionic transport kinetics and FSI ⁻ ‐rich dominant solvated structures, which can provide multi‐scale guarantees for the rapid and stable K‐storage behaviors. Consequently, the FeNCN anode in HDILE electrolyte delivered a high reversible specific capacity of 420.5 mAh/g after 250 cycles at 200 mA/g with an average Coulombic efficiency of more than 99.5%, attributed to the accelerated K‐storage kinetics via locally dispersing solvation structures as well as formation of inorganic‐dominated robust solid‐electrolyte‐interphase (SEI) via trapping the organic cation by high‐DN ether solvent. This work provides novel insights into the electrolyte design principle for reconciling the trade‐off between kinetics and stability in energy storage devices.