Phase diagram and electrochemical behavior of lithium sodium vanadium phosphates cathode materials for lithium ion batteries

摘要

A series of Li3-xNax V-2(PO4)(3)/C (0 <= x <= 3) is successfully synthesized through a simple solid-state reaction method. The structures of these lithium sodium vanadium phosphate compounds are investigated by the X-ray diffraction. It can be found that Li3-xNaxV2(PO4)(3)/C is composed of one monoclinic phase with 0 <= x <= 0.2, two monoclinic phases with 0.2 < x <= 0.4, two monoclinic phases and two rhombohedral phases with 0.4 < x <= 0.6, one monoclinic phase and two rhombohedral phases with 0.6 < x < 1.5, two rhombohedral phases with 1.5 <= x < 2.8 and one rhombohedral phases with 2.8 <= x <= 3.0. By using as cathode materials for lithium ion batteries, the electrochemical performances of Li3-xNaxV2(PO4)(3)/C are studied by galvanostatic charge-discharge tests. The electrochemical results show that the lithiation/delithiation plateaus of Li3-xNaxV2(PO4)(3)/C gradually evolve with the increase of Na content in the formula, which is induced by different phases formed in the as-prepared samples. As lithium storage materials, Li2NaV2(PO4)(3)/C shows the best electrochemical property among all the as-obtained samples. It can deliver a reversible capacity of 115.1 mAh g(-1) with capacity retention of 98.21% after 50 cycles. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.