Preparation and electrochemical study of Mn-doped Li9V3(P2O7)3(PO4)2 cathode material for lithium ion batteries

A series of Mn-doped Li9V3−xMnx(P2O7)3(PO4)2/C (x = 0.00, 0.02, 0.05, 0.08, and 0.10) compounds have been successfully prepared by using sol–gel method. ICP, XRD, and Rietveld refinement results analyses indicate that Mn ions were sufficiently doped in Li9V3(P2O7)3(PO4)2 without changing its trigonal structure, and the cell parameters (including a, c, and V) of Li9V3−xMnx(P2O7)3(PO4)2/C (x = 0.00, 0.05, and 0.10) increase with the increasing of x. The X-ray photoelectron spectroscopy (XPS) analysis reveals that the manganese oxidation state was +2 and both V4+ and V3+ ions were present in the Li9V2.9Mn0.1(P2O7)3(PO4)2 compound. The electronic conductivity increases monotonically with Mn-doped content x. The electrochemical insertion/extraction properties of Li9V3−xMnx(P2O7)3(PO4)2/C (x = 0.00, 0.02, 0.05, 0.08, and 0.10) phases are also presented. The Mn-doped phases exhibit smaller redox voltage polarization, higher cycle performance and better rate capability than that of the pristine one. Particularly, Li9V2.9Mn0.1(P2O7)3(PO4)2/C shows both good rate capability and best capacity recovered ability among all the samples. The enhancement of rate performance and cyclic capability may be attributed to the optimizing particle size, enhancement of electronic conductivity, lithium ion mobility and structural stability owing to the proper amount of Mn-doping in V sites.