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 n onflammable trimethyl phosphate (TMP)-based electrolytes, amorphous carbon (AC) was used as the anode material. It was found that the reduction decomp osition of TMP solvent, which occurred without limit on a natural graphite anode and concomitantly generated a large amount of methane (CH4) and ethyl ene (C2H4) gases, was considerably suppressed on amorphous carbon anode. Th is improvement was attributed to the disordered structure of amorphous carb on, which hindered the cointercalation of TMP solvent. The charge/discharge result and cyclic voltammetry further disclosed that a highly stable and p assivating 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/LiCo O2 ion cell with 1 mol/dm(3) LiPF6/ethylene carbonate (EC) + propylene carb onate (PC) + diethylcarbonate (DEC) + TMP (30:30:20:20) nonflammable electr olyte exhibited promising cycling performance. Furthermore, this electrolyt e was also found to have good low-temperature performance with the freezing point of <-40<degrees>C. Thermal test results disclosed that a lithium-ion cell with 1 mol/dm(3) LiPF6/EC + PC + DEC + TMP (30:30:20:20) exhibited go od thermal stability. (C) 2001 The Electrochemical Society.