Improved electrochemical performances of yttrium oxyfluoride-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 for lithium ion batteries

The Li-rich layered oxides show a higher discharge capacity over 250 mAh/g and have been developed into a promising positive material for lithium ion batteries. A rare earth metal oxyfluoride YOF-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O-2 composites have been synthesized by a simple wet chemical method. Crystal structure, micro-morphology and element valence of the pristine and YOF-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O-2 materials are characterized by XRD, SEM, TEM, and XPS. The results indicate that all materials exhibit a typical layered structure, and are made up of small and homogenous particles ranging from 100 nm to 200 nm. In addition, YOF layer with a thickness of approximately 3-8 nm is precisely coated on the surface of the Li[Li0.2Mn0.54Ni0.13Co0.13]O-2. Constant current charge/discharge tests at various current densities show that the electrochemical performance of 2 wt% YOF-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O-2 has been improved significantly. 2 wt% YOF-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O-2 delivers the highest discharge capacity of 250.4 mAh/g at 20 mA/g among all the samples, and capacity retention of 87% after 100 charge/discharge cycles at 200 mA/g while that of the pristine one is only 81.6%. The superior electrochemical performance of 2wt% YOF-coated sample is ascribed to YOF coating layer, which could not only reduce side reactions between the electrode and liquid electrolyte, but also promote lithium ion migration. (C) 2017 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.