4-Isopropyl phenyl diphenyl phosphate as flame-retardant additive for lithium-ion battery electrolyte

To improve the safety of lithium-ion batteries, 4-isopropyl phenyl diphenyl phosphate (IPPP) was used as a flame-retardant additive in a LiPF6 electrolyte solution. The flammability and thermal stability of IPPP-containing electrolytes were investigated by means of burning test and microcalorimetry. It was found that the addition of IPPP can reduce the flammability, and delay the onset temperature of a major exothermal reaction of the electrolyte. Furthermore, the electrochemical performances of LiCoO2/Li cells become slightly worse after using IPPP additive in the electrolyte. This alleviated trade-off between electrolyte flammability, thermal stability, and cell performance provides a possibility to formulate a nonflammable electrolyte containing 5-15 % of IPPP and improve the electrolyte thermal stability with a minimal sacrifice in performance. (c) 2005 The Electrochemical Society. All rights reserved.