Low‐Temperature Synthesis of LiNiO2 : Reaction Mechanism, Stability, and Electrochemical Properties

Abstract

A thorough study was made concerning the formation of LiNiO, by a low-temperature ion-exchange reaction under hydrothermal conditions. LiNiO, with a low degree of cationic mixing and good electrochemical performance was prepared either from pure 3-NiOOH, y-NiOOH, or a mixture of both where the y phase was the majority. The synthesized product (LT-LiNiO,) presents electrochemical properties similar to LiNiO, prepared by conventional powder synthesis (HT-LiNiO) in spite of the difference in Brunauer, Emmett, and Teller (BET) surfaces, around 20 m2/g for LT-LiNiO and 0.7 m2/g for HT-LiNiO2. The thermal and moisture stabilities of LT-LiNiO, were studied and turned out to be much lower than those of HT-LiNiO,. This moisture instability was found (i) to be intrinsic to LiNiO,, since ground HT-LiNiO, samples presented a similar behavior, (ii) to be enhanced by decreasing the LiNiO, 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.