Structures and electrochemical properties of Li _1.075V _0.925-xM _xO ₂ (M = Cr or Fe, 0 ≤ x ≤ 0.025) as new anode materials for secondary lithium batteries

Li _1.075V _0.925-xM _xO ₂ (M = Cr or Fe, 0 ≤ x ≤ 0.025) compounds are investigated as new anode materials for secondary lithium batteries. Previous research suggests Li _1+xV _1-xO ₂ (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 Li _1+xV _1-xO ₂ (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 Li _1.075V _0.925O ₂, 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. Li _1.075V _0.925-xM _xO ₂ 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 Li _1.075V _0.925O ₂, iron-doped materials give improved electrical conductivities and electrochemical properties. Li _1.075V _0.9Fe _0.025O ₂ sample exhibits the highest discharge capacity, an excellent rate capability, and an improved cyclability due to the high strength of the individual particles.