Nonflammable trimethyl phosphate solvent-containing electrolytes for lithium-ion batteries - II. The use of an amorphous carbon anode

In order to improve the cycling performance of lithium-ion batteries with nonflammable trimethyl phosphate (TMP)-based electrolytes, amorphous carbon (AC) was used as the anode material. It was found that the reduction decomposition of TMP solvent, which occurred without limit on a natural graphite anode and concomitantly generated a large amount of methane (CH4) and ethylene (C2H4) gases, was considerably suppressed on amorphous carbon anode. This improvement was attributed to the disordered structure of amorphous carbon, which hindered the cointercalation of TMP solvent. The charge/discharge result and cyclic voltammetry further disclosed that a highly stable and passivating surface film, called the solid electrolyte interphase film, was formed on the AC surface at the potential near 1 V. As a result, an AC/LiCoO2 ion cell with 1 mol/dm(3) LiPF6/ethylene carbonate (EC) + propylene carbonate (PC) + diethylcarbonate (DEC) + TMP (30:30:20:20) nonflammable electrolyte exhibited promising cycling performance. Furthermore, this electrolyte was also found to have good low-temperature performance with the freezing point of <-40C. Thermal test results disclosed that a lithium-ion cell with 1 mol/dm(3) LiPF6/EC + PC + DEC + TMP (30:30:20:20) exhibited good thermal stability. (C) 2001 The Electrochemical Society.