Transformed Solvation Structure of Noncoordinating Flame‐Retardant Assisted Propylene Carbonate Enabling High Voltage Li‐Ion Batteries with High Safety and Long Cyclability

Abstract

AbstractThe evolution of high‐energy‐density lithium‐ion batteries (LIBs) urgently requires the development of high‐safety electrolytes with high voltage resistance. Here, noncoordinating flame retardant pentafluoro‐(phenoxy)‐cyclotriphosphazene (FPPN) endows propylene carbonate (PC, 70 vol%)‐based electrolytes with high graphite anode compatibility, non‐flammability, high voltage stability, and excellent separator/electrode wettability. Theoretical calculations reveal that FPPN significantly affects Li+‐PC‐anion interactions and favors Li+ desolvation. Based on in situ optical microscopy and in situ differential electrochemical mass spectrometry, it is innovatively proposed that large amounts of H2 and C3H6 from PC decomposition play a dominant role in destroying the graphitic structure. The evolution of H2 and C3H6 is dramatically alleviated and totally suppressed, respectively, when FPPN prevents PC‐induced graphite exfoliation. More encouragingly, an optimized PC/FPPN‐based electrolyte (70 vol% PC) enables a high voltage LiCoO2/graphite pouch cell (4.35 V, ≈2.6 Ah, ≈242 Wh kg−1) with excellent cycle life and high safety. This work deepens the understanding of PC‐graphite compatibility and opens a new avenue of realizing practical application of PC‐based electrolytes (PC content over 50 vol%) in high capacity (over 2 Ah) LIBs.