Nonflammable electrolytes for Li-ion batteries based on a fluorinated phosphate

In this work we demonstrate that the fluorination of alkyl substituents on phosphate can reduce the viscosity, enhance flame-retarding efficiency, and increase electrochemical stability of the cosolvents. Therefore the new flame retardant can be used at a concentration greater than 20% in the electrolyte, as a cosolvent, in order to formulate a completely nonflammable electrolyte that works in lithium-ion cells. This new electrolyte formulation not only increases the safety feature of the lithium-ion battery, while maintaining the capacity utilization and rate capability, but also improves the capacity retention of the cell. The trade-off between electrolyte nonflammability and performance in the cell is thus alleviated by the introduction of fluorine in the structure of the flame retardants. (C) 2002 The Electrochemical Society.