The Li(Ni0.8Co0.15Al0.05)O-2 cathode, a potential candidate for hybrid electric vehicle applications, has been electrochemically charged in powder form without a carbon additive and binder. The thermal stability of the resulting Li-0.53 (Ni0.8Co0.15Al0.05)O-2 powder was studied by thermal gravimetric analysis (TGA), gas chromatography/mass spectrometry, and X-ray diffraction techniques under different gas flows. The transformation of Li-0.53 (Ni0.8Co0.15Al0.05)O-2-layered material to the NiO-type structure material and/or to nickel metal was correlated to the oxidizing/reducing properties of the TGA gas flow under which the thermal decomposition of the Li-0.53(Ni0.8Co0.15Al0.05)O-2 occurred. Differential scanning calorimetry measurements were performed on Li-0.53(Ni0.8Co0.15Al0.05)O-2 powder in the presence of solvent, salt, or binder independently. The reactivity at 170 degrees C between Li-0.53(Ni(0.8)Co(0.15)A1(0.05))O-2 and ethylene carbonate (EC) solvent was found to be dependent on the Li-0.53(Ni0.8Co0.15Al0.05)O-2 oxide/EC weight ratio. The exothermic reaction observed in the presence of other solvents was not greatly affected, as long as the oxide/solvent weight ratios were kept very close to one another. The LiPF6 salt, when added to the charged oxide powder, was found to shift the exothermic reaction to 220 degrees C when it was dissolved in the electrolyte and 270 degrees C when it was added in the solid form. When polyvinylidene fluoride binder was added to Li-0.53(Ni0.8Co0.15Al0.05)O-2 powder, the exothermic reaction occurred at high temperatures (340 degrees C). The initiation of the exothermic reaction has been primarily attributed to the oxidation of the electrolyte by the oxygen gas released from Li-0.53(Ni0.8Co0.15Al0.05)O-2 after the collapse of its layered structure. (c) 2006 The Electrochemical Society.