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

A series of Sn-doped Li 3 V 2− x Sn x (PO 4 ) 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 Li 3 V 2− x Sn x (PO 4 ) 3 /C samples were pure single phase with a monoclinic structure (space group P 2 1 / n ) and well crystallized. The structural refinement results and HRTEM analysis both indicated that Sn-doping did not alter the lattice structure of Li 3 V 2 (PO 4 ) 3 , but increased the unit cell volume. SEM images revealed that Sn-doping has no obvious effects on the morphology and particle size of Li 3 V 2 (PO 4 ) 3 . HRTEM, XRF and Raman results demonstrated that a thin carbon layer was coated on the surface of Li 3 V 2− x Sn x (PO 4 ) 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, Li 3 V 1.85 Sn 0.15 (PO 4 ) 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 Li 3 V 2 (PO 4 ) 3 during the charge–discharge processes, as well as increase electrical conductivity with a lower charge transfer resistance and a higher Li + diffusion coefficient .