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

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 HO-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 HO solvents (labelled LiTFSI-12C4@TTE/HO) demonstrates low impedance (2.7 Ω cm) at the TTE/HO interface and enabling 2,000 cycles of prelithiated graphite||LiFePO coin cells at 850 mA g with an average Coulombic efficiency of 99.8%. Single-layer 22.5 mAh Li||LiMnO pouch cells using LiTFSI-12C4@TTE/HO electrolyte with G4 delivered a stable discharge capacity of about 1.3 mAh cm for 80 cycles at 0.5 mA cm.