Microwave-irradiation synthesis of Li1.3NixCoyMn1-x-yO2.4 cathode materials for lithium ion batteries

Li1.3NixCoyMn1-x-yO2.4 (typically Li1.3Ni1/6Co1/6Mn4/6O2.4, Li1.3Ni1/5Co1/10Mn7/10O2.4 and Li1.3Ni1/4Mn3/4O2.4) cathode materials have been synthesized by microwave irradiation at 800 degrees C in a rapid calcination period of 1.5 h. The influence of transition metal ratios on the structure and electrochemical performance of the samples have been carefully investigated by powder X-ray diffraction (XRD) together with Rietveld refinement, inductive coupled plasma (ICP), scanning electron morphology (SEM), galvanostatically charge/discharge test, cyclic voltammetry (CV) in conjunction with electrochemical impedance spectroscopy (EIS) measurements. The as-prepared Li1.3Ni1/6Co1/6Mn4/6O2.4, Li1.3Ni1/5Co1/10Mn7/10O2.4 and Li1.3Ni1/4Mn3/4O2.4 materials can deliver discharge capacities of 291, 287 and 217 mAh g(-1), respectively, at a charge/discharge current density of 12.5 mA g(-1) in the voltage range of 2.5-4.7 V. These cathode materials have a relatively small initial irreversible capacity loss (around 50 mAh g(-1)), comparing with the commonly reported values (70-100 mAh g(-1)). When the charge/discharge current density increases to 50 mA g(-1), they have initial discharage capacities of 267, 236 and 166 mAh g(-1), which are 92%, 82% and 76% of the corresponding capacity values at 12.5 mA g(-1). The Li1.3Ni1/6Co1/6Mn4/6O2.4 cathode exhibits the largest discharge capacity value and best rate capability due to the highest hexagonal ordering, the lowest cation mixing, content of spinel impurity phase, and charge transfer resistance. The cobalt-free cathode material, Li1.3Ni1/4Mn3/4O2.4, shows better cycling performance than the cobalt-contained counterparts. (C) 2012 Elsevier Ltd. All rights reserved.