Inhibition Mechanism of Weakly Solvating Electrolyte against Capacity Fade Caused by Mn (II) Deposition in Lithium-Ion Batteries

The dissolution and deposition of Mn (II) are considered to be non-negligible factors of capacity fade in lithium-ion batteries. The high-concentration electrolytes (HCEs) can inhibit the deposition of Mn (II), but the high cost and viscosity limit their practical application. Herein, the weakly solvating solvent tetrahydrofuran (THF) is selected to regulate the solvation structure, inspired by the inhibition mechanism of HCEs. We find that the high proportion of contact ion pairs and aggregates formed in THF-based weakly solvating electrolyte brings about a significant increase in the lowest unoccupied orbital value of the solvation structure of Mn (II) and achieves almost 100% capacity retention during the first 100 cycles at the charge–discharge rate of 0.5 C. Moreover, the binding energy between Mn (II) and other components in the solvation structure remarkably increases due to more anions coordinating with Mn (II). This immobilizes Mn (II) in the bulk electrolyte and inhibits its deposition on the anode. Besides, benefiting from anion-rich solvation structure in weakly solvating electrolyte, a stable and uniform solid electrolyte interphase rich in inorganics is formed. It not only suppresses the reduction and deposition of Mn (II), but also promotes the migration kinetics of Li+ across the interfaces, consequently inhibiting the capacity fade. This study provides a new strategy for designing electrolyte systems with low viscosity, low cost, and high resistance to Mn (II) deposition.