A Bifunctional Boron‐Ester Anion Receptor to Stabilize LiPF _6‐ Containing Carbonate Electrolyte for Lithium Metal Batteries

The instability of LiPF₆-containing carbonate electrolytes hinders its application in lithium (Li) metal anodes. Although anion receptors can introduce LiNO₃ to improve electrolyte stability, commonly used anion receptors such as tris(pentafluorophenyl)borane (TPFPB) can paradoxically accelerate the hydrolysis of PF₅ and generate corrosive HF. This study proposes nitro-triol borate (NTB), a novel bifunctional boron-ester anion receptor designed to suppress PF₅ hydrolysis while introducing LiNO₃ to enhance Li reversibility. Density functional theory (DFT) calculations and experimental results demonstrate that, unlike the sterically hindered TPFPB, NTB effectively binds PF₅, thereby significantly reducing its chemical activity and increasing the energy barrier to hydrolysis. This stabilization, coupled with the introduced LiNO₃, promotes the formation of a dense, homogeneous, and inorganic-rich solid electrolyte interphase. Consequently, Li||Cu cells with the NTB-modified electrolyte present stable cycling exceeding 400 cycles and achieve a high average Coulombic efficiency (ACE) of 99.1%. Li||NCM811 full cells also exhibit enhanced cycling stability under a low N/P ratio of 2.5, retaining 74.3% capacity after 200 charge and discharge cycles. This work elucidates the previously overlooked detrimental effects of anion receptors and presents a new strategy for engineering novel anion receptors to achieve stable, high-performance lithium metal batteries in LiPF₆-containing carbonate electrolytes.