Flame-Retardant Electrolyte Composition for Stable Graphite Anodes

The patent changes the chemical composition parameters of the electrolyte by introducing fluorinated cyclic carbonate solvents (FEC, FPC, FDC) with specific fluorine-containing functional groups. This parameter change enables the electrolyte to achieve both flame retardancy and good battery performance by modifying the molecular structure rather than simply adding flame retardant additives. The fluorinated solvents create a stable SEI film that prevents further decomposition while maintaining ionic conductivity.

The patent uses composite electrolyte systems combining fluorinated cyclic carbonate solvents with lithium salts (LiPF6, LiBF4, LiTFSI) and optionally other additives. This composite approach creates a synergistic effect where the fluorinated solvent provides flame retardancy and stable SEI formation, while the lithium salts provide ionic conductivity, and other components supplement specific functions, achieving both safety and performance.

The fluorinated cyclic carbonate solvents perform preliminary action by forming a stable solid electrolyte interface (SEI) film on the graphite electrode surface during initial cycles. This pre-formed SEI film acts as a protective barrier that prevents further electrolyte decomposition and graphite exfoliation, stabilizing the system while allowing the high-capacity graphite electrode to function properly.

The fluorinated cyclic carbonate solvents act as intermediaries between the graphite electrode and the electrolyte. They form a stable SEI film that mediates the interaction, preventing direct contact and harmful reactions between the electrolyte and graphite, while still allowing lithium ion transport. This intermediary layer resolves the contradiction between using high-capacity graphite and maintaining electrolyte stability.