Mechanism of high-concentration electrolyte inhibiting the destructive effect of Mn(II) on the performance of lithium-ion batteries

By optimizing electrolyte formulation to inhibit the deposition of transition metal ions (TMIs) on the surface of the graphite anode is an effective way to improve the electrochemical performance of lithium-ion batteries. At present, it is generally believed the formation of an effective interfacial film on the surface of the anode electrode is the leading factor in reducing the dissolution of TMIs and prevent TMIs from being embedded in the electrode. It ignores the influence of the solvation structures in the electrolyte system with different composition, and is not conducive to the design of the electrolyte formulation from the perspective of changing the concentration and the preferred solvent to inhibit the degradation of battery performance caused by TMIs deposition. In this work, by analyzing the special solvation structures of the high-concentration electrolyte, we study the main reason why high-concentration electrolyte inhibits the destructive effect of Mn (II) on the electrochemical performance of LIBs. By combining the potential-resolved in-situ electrochemical impedance spectroscopy technology (PRIs-EIS) and density functional theory (DFT) calculation, we find that Mn (II) mainly exists in the form of contact ions pairs (CIPs) and aggregates (AGGs) in high-concentration electrolyte. These solvation structures can reduce the destructive effect of Mn (II) on battery performance from two aspects: on the one hand, it can rise the lowest unoccupied orbital (LUMO) value of the solvation structures of Mn (II), thereby reducing the chance of its reduction; on the other hand, the decrease of Mn2+ ions reduction can reduce the deposition of metallic manganese in the solid electrolyte interphase (SEI), thereby avoiding the continuous growth of the SEI. This study can be provided inspiration for the design of electrolytes to inhibit the destructive effect of TMIs on LIBs.