Lithium loss kinetics from polycrystalline LixNi1-xO at high temperatures

Lithium loss kinetics from polycrystalline LixNi1-xO has been investigated in the temperature range 900-1500 degrees C by measuring the time and temperature dependence of the weight and lattice constant change of the samples. At 900 degrees C the rate of Li2O evaporation was controlled by lithium ion diffusion in LixNi1-xO. An initial region of fast diffusion followed by a region of slower diffusion was observed in the thermogravimetric measurements. This observation can be interpreted as the rapid diffusion of lithium ions along the grain boundaries and subsequent diffusion into the bulk of the grain. A plot of the logarithm of lithium loss following 2 h of thermal treatment at different temperatures vs, the reciprocal of absolute temperature consisted of two straight lines, the slope depending on the activation energy of the process and the change of slope occurred at 1300 degrees C. This behaviour suggests that up to 1300 degrees C lithium ion diffusion from the bulk to the surface of LixNi1-xO particles was the rate-determining step. Above 1300 degrees C, instead, the evaporation process depended on the demixing reaction of Li2O (g) and NiO(s) at the surface of the particles.