Structures and electrochemical properties of Li1.075V0.925-xMxO2 (M = Cr or Fe, 0 <= x <= 0.025) as new anode materials for secondary lithium batteries

Li1.075V0.925-xMxO2 (M = Cr or Fe, 0 <= x <= 0.025) compounds are investigated as new anode materials for secondary lithium batteries. Previous research suggests Li1+xV1-xO2 (0.075 <= x <= 0.1) samples exhibit the first discharge capacities of 240-250 mAh g(-1) at 0.2 C-rate. Although the lithiation of Li1+xV1-xO2 (0.075 <= x <= 0.1) offer high initial capacities, a major difficulty for the anode application lies in the cycle life. In an attempt to improve Li1.075V0.925O2, doping with chromium and iron are systemically carried out to investigate its effect on the crystal structures, valence state of vanadium ions, electrical conductivities, mechanical strengths, and electrochemical properties. Li1.075V0.925-xMxO2 samples are successfully synthesized by solid-state reaction in a reducing atmosphere and the products give a single phase of the hexagonal layered structure with a space group of R-3m. Compared to Li1.075V0.925O2, iron-doped materials give improved electrical conductivities and electrochemical properties. Li1.075V0.9Fe0.025O2 sample exhibits the highest discharge capacity, an excellent rate capability, and an improved cyclability due to the high strength of the individual particles. (C) 2012 Elsevier B.V. All rights reserved.