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

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(OCH2CH2)n (modified KEO), is designed by tailoring cation-anion coordination in 1 m carbonate electrolyte based on the main salt-potassium perfluorinated pinacolatoborate, (KB(O2C2(CF3)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 -CF3 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. A potassiumperfluorinated pinacolatoborate is unprecedentedly investigated as a main salt in conventional carbonate electrolytes, tuning the K+-anions interactions through fluorine atoms instead of oxygen atoms. The tailored cation-anion coordination in carbonate electrolytes facilitate the formation of a rigid-flexible compact solid-electrolytes interphase, empowering long-life and low-cost potassium batteries. image