Reaction Mechanism of LiNiO2 Synthesized in Oxygen Atmosphere by Pechini Method.

Abstract

Pechini process was known as an excellent method for the synthesis of LiNiO2 powder. Compared with the result of solid state reaction using NiO and Li2CO3 as reactants, Ni2O3 was the new compound found in Pechini-processed powder. In the present work, the role of Ni2O3 and the reaction mechanism for the synthesis of Pechini-processed LiNiO2 were studied. XRD and DTA/TG analysis were used to investigate the phases present and the thermal reaction in the Pechini process studied. It was found that Ni2O3 was obtained from nickel citrate and nickel acetate which released a large amount of heat during calcination. Based on the thermodynamic calculation, Ni2O3 is not a stable compound in the oxidizing environment. As a result, Ni2O3 decomposes into NiO, and the decomposed NiO reacts with Li2CO3 and forms LiNiO2 at 700°C. An isothermal kinetics study was performed on the mixture of NiO, Ni2O3 and Li2CO3 at 700°C. The result indicates that the decomposition of Ni2O3 into NiO takes place at the beginning hour of the isothermal reaction. Consequently, NiO and Li2CO3 are consumed due to the formation of LiNiO2. Based on the results obtained, the reactions for Pechini-processed LiNiO2 may be described by the following reactions:Citrate complex→Li2CO3+NiO+Ni2O3Ni2O3→2NiO+1/2 O2x/2Li2CO3+(2-x)NiO+x/4 O2→LixNi2-xO2+x/2 CO2 (0<x≤1)This reaction is rationalized on the basis of the instability of Ni2O3 and the structural similarity between NiO and LiNiO2.