Electrochemical performance of the carbon coated Li 3V 2(PO 4) 3 cathode material synthesized by a sol–gel method

Abstract

A carbon coated Li 3V 2(PO 4) 3 cathode material for lithium ion batteries was synthesized by a sol–gel method using V 2O 5, H 2O 2, NH 4H 2PO 4, LiOH and citric acid as starting materials, and its physicochemical properties were investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), transmission electron microscope (TEM), and electrochemical methods. The sample prepared displays a monoclinic structure with a space group of P2 1/ n, and its surface is covered with a rough and porous carbon layer. In the voltage range of 3.0–4.3 V, the Li 3V 2(PO 4) 3 electrode displays a large reversible capacity, good rate capability and excellent cyclic stability at both 25 and 55 °C. The largest reversible capacity of 130 mAh g −1 was obtained at 0.1 C and 55 °C, nearly equivalent to the reversible cycling of two lithium ions per Li 3V 2(PO 4) 3 formula unit (133 mAh g −1). It was found that the increase in total carbon content can improve the discharge performance of the Li 3V 2(PO 4) 3 electrode. In the voltage range of 3.0–4.8 V, the extraction and reinsertion of the third lithium ion in the carbon coated Li 3V 2(PO 4) 3 host are almost reversible, exhibiting a reversible capacity of 177 mAh g −1 and good cyclic performance. The reasons for the excellent electrochemical performance of the carbon coated Li 3V 2(PO 4) 3 cathode material were also discussed.