Abstract: The essence of the safety problem of lithium-ion battery is the internal thermal runway. Inside the battery, the heat is continuously accumulated, causing the sustaining rise of temperature. Its external performances are combustion and explosion. Therefore, the safety of lithium-ion battery has certain contradictions with specific energy, operating temperature and rate performance. Higher energy density, higher rate performance and harsher operating environment are usually the causes to a more violent energy release, leading to the greater impact on the battery system and more serious safety problems. In general, the electrolyte of lithium-ion battery consists of carbonates with low flash point, lithium salt LiPF₆ with high sensitivity to H₂O and temperature, and other additives at present. Besides, the destruction of the interface film between the electrolyte and the electrode is considered to be the starting point of the battery thermal runway. Thus, electrolyte modification is a significant method to promote battery safety. In this paper, the enhancing effects of modified solvents such as ionic liquid and fluorinated solvent on the safety of electrolyte were analyzed. The positive impacts of various lithium salts on the safety of electrolyte were compared. The safety improvements by the electrolyte additives such as flame retardant, overcharge protector, lithium dendrite inhibitor and solid-electrolyte interface stabilizer were introduced. At last, from the perspective of the overall application performance of the battery, the further research and development directions of high-safety lithium-ion battery electrolyte were discussed.

Key words: safety electrolyte, lithium-ion battery, solvent, lithium salt, additive