Improved thermal stability of lithium ion battery by using cresyl diphenyl phosphate as an electrolyte additive

To enhance the safety of lithium ion battery, cresyl diphenyl phosphate (COP) is explored as an additive in 1.0 M LiPF(6)/ethylene carbonate (EC) + diethyl carbonate (DEC) (1:1 wt.). The electrochemical performances of LiCoO(2)/CDP-electrolyte/C cells are tested. At the thermal aspect, the thermal stability of the electrolyte with COP is detected firstly by using a C80 micro-calorimeter, and then the charged LiCoO(2)/CDP-electrolyte/C cells are disassembled and wrapped to detect the thermal behaviors. The results indicate that CDP-containing electrolyte enhances the thermal stabilities of electrolyte and lithium ion battery, and the electrochemical performances of LiCoO(2)/CDP-electrolyte/C cell become slightly worse by using COP in the electrolyte. Furthermore, the cell with 10% (wt.) CDP-containing electrolyte shows better cycle efficiency than that of other CDP-containing electrolyte, such as containing 5% (wt.) COP and 15% (wt.) CDP. This maybe because that the mass ratio between COP and electrolyte is close to the reaction stoichiometric ratio in the 10% (wt.) COP-containing electrolyte, where stable solid electrolyte interphase (SEI) is formed. Therefore, 10% COP-containing electrolyte improves the safety of lithium ion battery and keeps its electrochemical performance. (C) 2010 Elsevier B.V. All rights reserved.