Synthesis and electrochemical studies on Al2O3 coated LiNi0.5Co0.44Fe0.06VO4 for lithium ion batteries

LiNi0.5Co0.44Fe0.06VO4 cathode material has been synthesized by a citric acid:polyethylene glycol polymeric method at 723 K for 5 h in air. The surface of the LiNi0.5Co0.44Fe0.06VO4 was coated with various wt.% of Al2O3 by a wet chemical procedure and heat treated 873 K for 2 h in air. The samples were characterized by XRD, FTIR, SEM, and TEM techniques. XRD patterns expose that the complete crystalline phase occurred at 723 K and there was no indication of new peaks for the coated samples. FTIR spectra show that the complete removal of organic residues and the formation of LiNi0.5Co0.44Fe0.06VO4. TG/DTGA results reveal that the formation of LiNi0.5Co0.44Fe0.06VO4 occurred between 480 and 670 K and the complete crystalline occurred at 723 K. SEM micrographs show the various morphological stages of the polymeric intermediates. TEM micrographs of the pristine LiNi0.5Co0.44Fe0.06VO4 reveal that the particle size ranged from 130 to 150 nm and Al2O3 coating on the fine particles was compact and had an average thickness of about 15 nm. The charge–discharge experiments were carried out between 2.8 and 4.9 V (versus Li) at a current rate of 0.15 C. The 1.0 wt.% Al2O3 coated sample had the best electrochemical performance, with an initial capacity of 65 mAh g−1 and capacity retention of 60% after 50 cycles. The electrochemical impedance behavior suggests that the failure of pristine cathode performance is associated with an increase in the impedance growth on the surface of the cathode material upon continuous cycling.