Reconciling strong coordination and anion-reinforced solvation structure enables nonflammable electrolytes for potassium-ion batteries

Abstract

Nonflammable electrolytes are pivotal for improving the safety of potassium-ion batteries. However, their broad adoption has been hindered by the inadequate electrode compatibility of conventional nonflammable electrolytes, which typically result from strong solvation and excessive free solvent molecules. Here, we employ a molecular design strategy that integrates strong coordination capability with anion-reinforced solvation structure, thereby enabling the effective deployment of nonflammable phosphate solvents. By incorporating lengthened functionalized side-chains into the phosphate backbone, the tailored molecule tri(2-butoxyethyl) phosphate achieves robust multi-site chelation via synergistic interactions between the ether oxygen (C-O-C) and the phosphoryl (P=O) groups. Concurrently, its large molecular structure effectively increases the anion-to-solvent ratio in the electrolyte, promoting the formation of stable electrode-electrolyte interphases, and resulting in high compatibility with both the negative and positive electrodes. Consequently, the optimized tri(2-butoxyethyl) phosphate-based electrolyte enables stable cycling of graphite negative electrode (92.7% capacity retention after 800 cycles at 100 mA g−1) and Prussian blue positive electrode (4.2 V, 88.6% capacity retention after 3200 cycles at 100 mA g−1). Furthermore, the assembled graphite||Prussian blue full cell also maintains 80.3% capacity retention after 1500 cycles at 500 mA g−1. This work provides a strategy for electrolyte design in potassium-ion batteries. Nonflammable electrolytes are key to safe potassium-ion batteries but suffer from poor electrode compatibility. Here, authors design a phosphate molecule with long side-chains enabling strong chelation and anion-reinforced solvation, leading to high electrode compatibility.