Preparation and electrochemical properties of high-voltage cathode materials, LiM_yNi_(0.5-y)Mn_(1.5)O_4 (M = Fe, Cu, Al, Mg; y = 0.0-0.4)

摘要

Solid-state synthesized LiNi_(0.5-y)M_yMn_(1.5)O_4 spinels, where M = Fe, Mg, Al, or Cu, and y = 0.0―0.4, have been studied as high-voltage cathode materials. Powder X-ray diffraction studies showed that all the substituents displayed a propensity for the 8a tetrahedral site at high concentrations. Cyclic voltammetric studies showed electrochemical activity around 4 Vas well as above 4.4 V. While the 4-V activity was related solely to the Mn~(4+)/Mn~(3+) couple, the 5-V activity was due to the redox reactions of Ni and the other transition metal ions. The co-substituents reduced the 5-V capacity and shifted the redox potentials in the 5-V region to higher values. At high concentrations, the co-substituents tended to occupy the 8a sites, which may lead to a blockage of lithium transport during the charge-discharge processes. LiNi_(0.4)Fe_(0.1)Mn_(1.5)O_4 registered the best performance with a first-cycle capacity of 117 mAh/g and 78% capacity retention over 60 cycles. Electrochemical impedance spectroscopic studies showed a decrease in the charge transfer resistance at high deintercalation levels.