Effects of Nd-doping on the structure and electrochemical properties of Li3V2(PO4)3/C synthesized using a microwave solid-state route

Abstract

Abstract Nd-doped Li 3 V 2 − x Nd x (PO 4 ) 3 /C (x = 0, 0.01, 0.02, 0.04, 0.06 and 0.08) cathode materials are successfully and fast synthesized by a microwave solid-state route. The effects of Nd-doping on the structure and electrochemical properties of Li 3 V 2 (PO 4 ) 3 /C are investigated. Compared with the X-ray diffraction (XRD) pattern of the undoped sample, these Nd-doped samples have no extra reflections, which indicate that Nd enters the structure of the Li 3 V 2 (PO 4 ) 3 /C cathode. Scanning electron microscope (SEM) images show that Nd-substitution in Li 3 V 2 (PO 4 ) 3 /C has regular and uniform particles. According to the results of charge/discharge measurements at 0.1 C rate, the initial capacities of the Nd-doped samples are all higher than that of the undoped sample which is 140 mAh g − 1 . Among all the doped samples, Li 3 V 1.96 Nd 0.04 (PO 4 ) 3 /C shows the best rate capability and cycling stability. The initial discharge capacity of Li 3 V 1.96 Nd 0.04 (PO 4 ) 3 /C is 157 mAh g − 1 with the capacity retention ratio of 92.5% after 50 cycles at 0.1 C. Especially, it still shows a high discharge capacity of 126 mAh g − 1 even at a higher rate of 5.0 C. Electrochemical impedance spectroscopy (EIS) reveals that the charge transfer resistance of as-prepared samples is reduced through Nd-substitution and its reversibility is enhanced as proved by the cyclic voltammograms (CV). The improved electrochemical properties of Nd-doped Li 3 V 2 (PO 4 ) 3 /C can be attributed to the optimizing particle size and structural stability due to the proper amount of Nd-doping in V sites.