Electrolyte Engineering for Safer Lithium-Ion Batteries: A Review

Despite being widely used in people's daily life, the safety issue of lithium-ion batteries (LIBs) has become the major barrier for them to be applied in electrical vehicles (EVs) or large-scale energy storage. Typically, due to the use of liquid electrolytes containing flammable solvents which are easily oxidized by excessive and accumulated heat, the potential thermal runaway is a major safety concern for traditional LIBs. A strategy for a safer electrolyte design is controlling the flammability and volatility of the liquid electrolytes, to effectively prevent thermal runaway, thus avoiding fire or other risks. Through this study, the mechanisms of thermal runaway and the recent progress in electrolyte engineering toward LIBs were summarized, covering the major strategies including adding flame-retardants, the utilization of ionic liquid electrolytes and solid electrolytes. The characteristics, strengths and weaknesses of different strategies were discussed. New designing directions of safer electrolytes for the LIBs were also provided.