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. LiNiO 2 with a low degree of cationic mixing and good electrochemical perfor mance was prepared either from pure beta-NiOOH, gamma-NiOOH, or a mixt ure of both where the gamma phase was the majority. The synthesized pr oduct (LT-LiNiO2) presents electrochemical properties similar to LiNiO 2 prepared by conventional powder synthesis (HT-LiNiO2) in spite of th e 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 mo isture 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 parti cle size, and (iii) to be much larger than that of LiCoO2. In view of electrochemical applications, cobalt-substituted products should be us ed in order to ensure the stability against both reduction-delithiatio n and hydrolysis.