Effect of Cobalt and Nickel Contents on the Performance of Lithium Rich Materials Synthesized in Glycerol Solvent

Abstract

Lithium-rich cathode materials in the form of Li1.2Mn0.51Ni0.145+xCo0.145-xO2 (x = 0 (LR2), 0.0725 (LR1)) have been successfully synthesized by a sol-gel method using glycerol as solvent. These materials were characterized by X-ray diffractions (XRD), scanning electron microscopy (SEM), and electrochemical measurements. XRD patterns showed that both materials have typical diffraction peaks of Li-rich material with a well-crystallized structure, but the LR1 sample with less Co has a well-distinguished Li2MnO3 peak between 20°–25°. SEM images demonstrate that LR1 also has a more uniform particle distribution. Electrochemical measurements revealed that LR2 with more Co has a higher initial discharge capacity of 223 mAh/g than LR1 of 185 mAh/g at 0.1 C between 2 and 4.8 V. However, LR1 was observed to have an increasingly improved capacity over several dozens of cycles. The specific discharge capacity of LR1 increased from 185 to 213 mAh/g after 20 cycles. This is ascribed to a gradual activation of the Li-rich phase from the surface of the particles. It is shown that the smaller Co/Mn ratio (1:7.134) of LR1 plays an important role in its continuous activation. Its capacity retention is 98% at 100 cycles at 1C rate, better than that of LR2 and most previously reported lithium-rich materials.