LiPF₆ Stabilizer and Transition-Metal Cation Scavenger: A Bifunctional Bipyridine-Based Ligand for Lithium-Ion Battery Application

Because of its well-balanced properties, lithium hexafluorophosphate (LiPF6) remains the most widely adopted conducting salt in state-of-the-art nonaqueous, aprotic liquid electrolytes used in lithium-ion batteries (LIBs). However, the relatively high reactivity of LiPF6 can cause issues such as bulk electrolyte deterioration including formation of toxic compounds, solid electrolyte interphase and cathode electrolyte interphase growth, and transition-metal dissolution–migration–deposition because of the strong Lewis acidity of PF5. LiPF6-related aging processes are one of the major reasons for specific capacity and energy decay of LIBs. To address these issues, a bifunctional insoluble ligand, 2,2′-bipyridine-4,4′-dicarboxylato dilithium salt (Li2BPy), is employed to (1) stabilize LiPF6 via its Lewis basicity and (2) to block transition-metal migration through electrolyte via ligand–transition-metal complexation.