Electrochemical performance and 7Li NMR studies on an inverse spinel LiNi1/3Co1/3Mn1/3VO4 for Li-ion batteries

A new inverse spinel LiNi1/3Co1/3Mn1/3VO4 cathode material was synthesized through a citric acid assisted polyethylene glycol (CA:PEG; 3:1, 3:0.5 and 3:0) polymeric method, followed by calcination at 723 K for 5 h in air. The synthesized compound was characterized by TG/DTGA, XRD, FTIR, TEM, and 7Li NMR techniques. TG/DTGA curves showed that the formation of LiNi1/3Co1/3Mn1/3VO4 occurred between 523 and 673 K and the phase pure crystalline formed at 723 K, as also confirmed by XRD analysis which showed that the crystalline phase peaks formed when heated at 723 K for 5 h in air. TEM images revealed that nanosized particles ranged ~170–190 nm. FTIR spectra showed that all organic residues were removed and LiNi1/3Co1/3Mn1/3VO4 formed. The 7Li MAS NMR spectrum of the LiNi1/3Co1/3Mn1/3VO4 sample revealed that the paramagnetic effect is small and small side band manifolds were observed. The galvanostatic cycling study suggests that the cycle stability and capacity retention were enhanced for LiNi1/3Co1/3Mn1/3VO4 prepared with a CA:PEG molar ratio of 3:1 when it was cycled between 2.8 and 4.9 V (versus Li) at a 0.15C rate. The electrochemical impedance behavior suggested that a passive layer was formed on the surface of the cathode materials during continuous cycling.