The Rate Equation for Oxygen Evolution by Decomposition of LixCoO₂at Elevated Temperatures

The oxygen evolution from Li0.5CoO2 cathodes at elevated temperatures was investigated by mass spectrometry coupled with thermogravimetry (TG-MS). The rate equation for the oxygen evolution from Li0.5CoO2 (particle diameters: 1−5 μm) was found to be dα/dt = 1.88 × 108 (exp(-114 × 1000/RT))(1- α)1.62, where α is the fractional degree of conversion of reactants; the values obtained using this equation showed a good agreement with the experimental ones for the dependency of the oxygen evolution speed on the temperature rising speed. With minor parameter changes of the rate equation, the equations could explain the dependence of the oxygen evolution speed on x in LixCoO2. Nano-sized Li0.5CoO2 (particle diameters: 200–400 nm) was prepared and the influence of the particle size on the oxygen evolution speed was investigated. The nano-sized Li0.5CoO2 showed a shift of the onset temperatures of O2 evolution from 240°C to 210°C. When the frequency factor is optimized, the values calculated using the modified equation were coincident with the experimental ones for the nano-sized Li0.5CoO2.