Comparative studies of the electrochemical and thermal stability of two types of composite lithium battery electrolytes using boron-based anion receptors

Comparative studies were done on two new types of boron based anion receptors, tris(pentafluorophenyl) borane (TFPB) and tris(pentafluorophenyl) berate (TFPBO), regarding conductivity enhancement, and electrochemical and thermal stability when used as additives in composite electrolytes for lithium batteries. Both additives enhance the ionic conductivity of electrolytes of simple lithium salts, LiF CF3CO2Li, and C2F5CO2Li in several organic solvents. The electrochemical windows of TPFB based electrolytes in ethylene carbonate-propylene carbonate-dimethyl carbonate (1:1:3, v/v) are up to 5, 4.76, and 4.96 V for LiF CF3CO2Li, and C2F5CO2Li, respectively. TPFBO has Tower electrochemical stability compared to TPFB. The thermal stability of pure TFPB is better than TFPBO. Complexation with the salt improves the thermal stability of these additives. TPFB based electrolytes showed high cycling efficiencies and good cycleability when they were tested in Li/LiMn2O4 cells. TFPBO based electrolytes were tested in Li/LiNiO2 cells; the cells delivered high discharge capacity and good cycling efficiencies. The capacity retention of the cells using TFPB based electrolytes during multiple cycling is better than those using TFPBO based electrolytes. (C) 1999 The Electrochemical Society. S0013-4651(99)04-036-7. All rights reserved.