Electrochemical properties of Sn-doped Li3V2(PO4)3 cathode material synthesized via a citric acid assisted sol-gel method

A series of Sn-doped Li3V2-xSnx(PO4)(3)/C (x = 0, 0.1, 0.15, 0.2) samples were synthesized via a citric acid assisted sol-gel method. XRD patterns indicated that all the Li3V2-xSnx(PO4)(3)/C samples were pure single phase with a monoclinic structure (space group P2(1)/n) and well crystallized. The structural refinement results and HRTEM analysis both indicated that Sn-doping did not alter the lattice structure of Li3V2(PO4)(3), but increased the unit cell volume. SEM images revealed that Sn-doping has no obvious effects on the morphology and particle size of Li3V2(PO4)(3). HRTEM, XRF and Raman results demonstrated that a thin carbon layer was coated on the surface of Li3V2-xSnx(PO4)(3)/C samples with a similar carbon content and good quality. The electrochemical performance was evaluated using coin-type half cells. Among the samples synthesized in this work, Li3V1.85Sn0.15(PO4)(3)/C exhibited the electrochemical performance in terms of specific capacity, rate capability, cycling performance. CV and EIS results implied that optimizing Sn-doping contents with x = 0.15 could greatly enhance the structural stability of Li3V2(PO4)(3) during the charge-discharge processes, as well as increase electrical conductivity with a lower charge transfer resistance and a higher Li+ diffusion coefficient. (C) 2015 Elsevier B.V. All rights reserved.