Tailored Cation–Anion Coordination in Carbonate Electrolyte Enabling a Rigid‐Flexible Compact Solid‐Electrolyte Interphase for Potassium Batteries

Abstract Potassium batteries have received extensive attention as a promising grid‐level storage technology. However, the anodes in potassium batteries using conventional carbonate‐based electrolyte systems always suffer from severe capacity deterioration, due to the heterogeneous and highly swollen solid‐electrolyte interphase (SEI) layer. Herein, a rigid‐flexible compact SEI consisting of rigid inner KF layer and flexible crosslinked oligomeric K–B(OCH 2 CH 2 ) n (modified KEO), is designed by tailoring cation–anion coordination in 1 m carbonate electrolyte based on the main salt—potassium perfluorinated pinacolatoborate, (KB(O 2 C 2 (CF 3 ) 4 ) 2 , abbreviated as KPFB). Specifically, the KPFB tunes K + −anions coordinated configuration in K + solvation sheaths by unique spatial structure and strong electron‐withdrawing effect of its eight −CF 3 groups. With the assistance of rigid‐flexible compact SEI layer, the potassium metal symmetric cells stably cycle for more than 1600 hours in the conventional carbonate electrolyte (1 m KPFB‐EC/DEC). Moreover, K||graphite and K||Prussian blue (PB) batteries adopting this conventional carbonate electrolyte can operate for more than 500 and 120 cycles with high average Coulombic efficiency of 99.7% and 99.4%, respectively. The work provides new insights in customizing salt anion structure to reinforce SEI layer for high‐performance potassium batteries.