Structures and electrochemical properties of Li_(1.075)V_(0.925-x)M_xO_2 (M = Cr or Fe, 0 ≤ x ≤ 0.025) as new anode materials for secondary lithium batteries

摘要

Li_(1.075)V_(0.925-x)M_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+x)V_(1-x)M_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+x)V_(1-x)M_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_(1.075)V_(0.925)O_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_(1.075)V_(0.925-x)M_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_(1.075)V_(0.925)O_2, iron-doped materials give improved electrical conductivities and electrochemical properties. Li_(1.075)V_(0.9)Fe_(0.025)O_2 sample exhibits the highest discharge capacity, an excellent rate capability, and an improved cyclability due to the high strength of the individual particles.