Lithium loss kinetics from polycrystalline LixNi1–xO at high temperatures

Abstract

Lithium loss kinetics from polycrystalline Li _x Ni _1–x O has been investigated in the temperature range 900-1500°C by measuring the time and temperature dependence of the weight and lattice constant change of the samples. At 900°C the rate of Li ₂ O evaporation was controlled by lithium ion diffusion in Li _x Ni _1–x O. 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°C. This behaviour suggests that up to 1300°C lithium ion diffusion from the bulk to the surface of Li _x Ni _1–x O particles was the rate-determining step. Above 1300°C, instead, the evaporation process depended on the demixing reaction of Li ₂ O(g) and NiO(s) at the surface of the particles.