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

LIN Shih-Pin, FUNG Kuan-Zong, HON Yi-Ming, HON Min-Hsiung

doi:10.2109/jcersj.110.1038

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:<br>Citrate complex→Li₂CO₃+NiO+Ni₂O₃<br>Ni₂O₃→2NiO+1/2 O₂<br>x/2Li₂CO₃+(2-x)NiO+x/4 O₂→Li_xNi_2-xO₂+x/2 CO₂ (0<x≤1)<br>This reaction is rationalized on the basis of the instability of Ni₂O₃ and the structural similarity between NiO and LiNiO₂.

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

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