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

The 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 H-2 and C3H6 from PC decomposition play a dominant role in destroying the graphitic structure. The evolution of H-2 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, approximate to 2.6 Ah, approximate to 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.

Automated summary

The use of noncoordinating flame retardant FPPN improves the compatibility and stability of PC-based electrolytes with graphite anode, enhancing the safety performance of high-energy-density LIBs.