Solvating power regulation enabled low concentration electrolyte for lithium batteries

Li⁺ solvation structures have a decisive influence on the electrode/electrolyte interfacial properties and battery performances. Reduced salt concentration may result in an organic rich solid electrolyte interface (SEI) and catastrophic cycle stability, which makes low concentration electrolytes (LCEs) rather challenging. Solvents with low solvating power bring in new chances to LCEs due to the weak salt-solvent interactions. Herein, an LCE with only 0.25 mol L^-1 salt is prepared with fluoroethylene carbonate (FEC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (D₂). Molecular dynamics simulations and experiments prove that the low solvating power solvent FEC not only renders reduced desolvation energy to Li⁺ and improves the battery kinetics, but also promotes the formation of a LiF-rich SEI that hinders the electrolyte consumption. Li||Cu cell using the LCE shows a high coulombic efficiency of 99.20%, and LiNi_0.6Co_0.2Mn_0.2O₂||Li cell also exhibits satisfying capacity retention of 89.93% in 200 cycles, which demonstrates the great potential of solvating power regulation in LCEs development.