Low-temperature synthesis of LiNiO2 - Reaction mechanism, stability, and electrochemical properties

A thorough study was made concerning the formation of LiNiO2 by a low-temperature ion-exchange reaction under hydrothermal conditions. LiNiO2 with a low degree of cationic mixing and good electrochemical performance was prepared either from pure beta-NiOOH, gamma-NiOOH, or a mixture of both where the gamma phase was the majority. The synthesized product (LT-LiNiO2) presents electrochemical properties similar to LiNiO2 prepared by conventional powder synthesis (HT-LiNiO2) in spite of the difference in Brunauer, Emmett, and Teller (BET) surfaces, around 20 m(2)/g for LT-LiNiO2 and 0.7 m(2)/g for HT-LiNiO2. The thermal and moisture stabilities of LT-LiNiO2 were studied and turned out to be much lower than those of HT-LiNiO2. This moisture instability was found (i) to be intrinsic to LiNiO2, since ground HT-LiNiO2 samples presented a similar behavior, (ii) to be enhanced by decreasing the LiNiO2 particle size, and (iii) to be much larger than that of LiCoO2. In view of electrochemical applications, cobalt-substituted products should be used in order to ensure the stability against both reduction-delithiation and hydrolysis.