Li+(ionophore) nanoclusters engineered aqueous/non-aqueous biphasic electrolyte solutions for high-potential lithium-based batteries

Abstract

The use of aqueous/non-aqueous biphasic electrolyte solutions in Li-based battery systems circumvents the limitations of poor reductive stability of aqueous electrolyte solutions, broadening their electrochemical stability window. However, aqueous/non-aqueous electrolytes suffer from biphasic mixing and high impedance when Li ions cross the biphasic interface. Here we propose the use of 12-crown-4 (12C4) and tetraglyme (G4) as lithium ionophores to form Li⁺(ionophore) nanoclusters in both non-aqueous and aqueous phases to overcome the interface challenges in biphasic electrolytes. The Li⁺(ionophore) nanoclusters have the H₂O-excluding inner Li⁺ solvation structure in non-polar 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), allowing fast charge transport across the biphasic interface without solvent mixing or water shuttling. A tailored electrolyte formulation comprising the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, 12C4, TTE and H₂O solvents (labelled LiTFSI−12C4@TTE/H₂O) demonstrates low impedance (2.7 Ω cm⁻²) at the TTE/H₂O interface and enabling 2,000 cycles of prelithiated graphite||LiFePO₄ coin cells at 850 mA g⁻¹ with an average Coulombic efficiency of 99.8%. Single-layer 22.5 mAh Li||LiMn₂O₄ pouch cells using LiTFSI−12C4@TTE/H₂O electrolyte with G4 delivered a stable discharge capacity of about 1.3 mAh cm⁻² for 80 cycles at 0.5 mA cm⁻².