Thermal Behavior of Charged Graphite and Li[sub x]CoO[sub 2] in Electrolytes Containing Alkyl Phosphate for Lithium-Ion Cells

The thermal behavior of charged graphite anode and Li x Co O 2 cathode was investigated focusing on nonflammable electrolytes containing alkyl phosphates as a flame retardant by differential scanning calorimetry. Trimethyl phosphate improved the thermal stability on the cathode side, while a violent exothermic reaction occurred on the anode side. It was demonstrated that the additive technique provides important improvements electrochemically and thermally even in a unique Li B F 4 ∕ γ -butyrolactone-based electrolyte containing a reductive phosphate solvent. The flame retardant concept of liquid electrolytes is intrinsically ineffective inside a cell, because the excellent flame retardant, tris(2,2,2-trifluoroethyl) phosphate did not make the anode and cathode more thermally stable.