Effects of Cr Contents on the Physical and Electrochemical Properties of LiNi_(0.5-x)Cr_(2x)Mn_(0.5-x)O_2 Cathode Materials for Lithium-Ion Batteries

摘要

Layered LiNi_(0.5-x)Cr_(2x)Mn_(0.5-x)O_2 materials with various Cr contents have been successfully prepared by a coprecipitation method. X-ray diffraction, scanning electron microscopy (SEM), Brunauer-Emmett-Teller method, and charge-discharge tests have been adopted to study the physical and electrochemical performance of LiNi_(0.5-x)Cr_(2x)Mn_(0.5-x)O_2. A single-phase product was obtained in the range of 2x > = 0.1 in LiNi_(0.5-x)Cr_(2x)Mn_(0.5-x)O_2, although some impurity phases were found for 2.x s= 0.2. SEM observation shows that Cr doping in LiNi_(0.5-x)Cr_(2x)Mn_(0.5-x)O_2has obviously changed the morphologies of its particles and the agglomeration of primary particles becomes tighter with the increasing of Cr contents. The specific surface area of LiNi_(0.5-x)Cr_(2x)Mn_(0.5-x)O_2 decreases linearly from 5.8 m~3/g (2x > = 0) to 0.34 m~3/g (2x > = 0.2) with the addition of Cr. Moreover, we have found that the presence of Clean greatly improve the density of LiNi_(0.5-x)Cr_(2x)Mn_(0.5-x)O_2powder. The electric conductivity of LiNi_(0.5-x)Cr_(2x)Mn_(0.5-x)O_2 abruptly increases with the addition of a small amount of Cr (2x> =s 0.1) and decreases with the further increase of Cr contents (2x > = 0.2). An electrochemical test indicates that the addition of a small amount of Cr can improve the cycling performance of LiNi_(0.5-x)Cr_(2x)Mn_(0.5-x)O_2, although it has no significant effects on the reversible capacity of the sample. However, the electrochemical performance of LiNi_(0.5-x)Cr_(2x)Mn_(0.5-x)O_2 becomes worse when the content of Cr further increases (2x > = 0.2).