Synthesis and electrochemical properties of Na-doped Li3V2(PO4)3 cathode materials for Li-ion batteries

Na-doped Li3-xNaxV2(PO4)(3)/C (x = 0.00, 0.01, 0.03, and 0.05) compounds have been prepared by using sol-gel method. The Rietveld refinement results indicate that single-phase Li3-xNaxV2(PO4)(3)/C with monoclinic structure can be obtained. Among three Na-doped samples and the undoped one, Li2.97Na0.03V2(PO4)(3)/C sample has the highest electronic conductivity of 6.74 x 10(-3) S cm(-1). Although the initial specific capacities for all Na-doped samples have no much enhancement at the current rate of 0.2 C, both cycle performance and rate capability have been improved. At the 2.0 C rate, Li2.97Na0.03V2( PO4)(3)/C presents the highest initial capacity of 118.9 mAh g(-1) and 12% capacity loss after 80 cycles. The partial substitution of Li with Na (x = 0.03) is favorable for electrochemical rate and cyclic ability due to the enlargement of Li3V2(PO4)(3) unit cells, optimizing the particle size and morphology, as well as resulting in a higher electronic conductivity. (C) 2011 Elsevier B.V. All rights reserved.