Thermal Stability of the Li(Ni[sub 0.8]Co[sub 0.15]Al[sub 0.05])O[sub 2] Cathode in the Presence of Cell Components

The 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 powder was studied by thermal gravimetric analysis (TGA), gas chromatography/mass spectrometry, and X-ray diffraction techniques under different gas flows. The transformation of -layered material to the -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 occurred. Differential scanning calorimetry measurements were performed on powder in the presence of solvent, salt, or binder independently. The reactivity at between and ethylene carbonate (EC) solvent was found to be dependent on the 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 salt, when added to the charged oxide powder, was found to shift the exothermic reaction to when it was dissolved in the electrolyte and when it was added in the solid form. When polyvinylidene fluoride binder was added to powder, the exothermic reaction occurred at high temperatures . The initiation of the exothermic reaction has been primarily attributed to the oxidation of the electrolyte by the oxygen gas released from after the collapse of its layered structure.