A novel carbamide-assistant hydrothermal process for coating Al2O3 onto LiMn1.5Ni0.5O4 particles used for cathode material of lithium-ion batteries

High-voltage spinel LiMn1.5Ni0.5O4 material is successfully coated by Al2O3 via a novel carbamide-assistant hydrothermal process followed by a heat treatment. Carbamide is used as a slow-release alkali in the high temperature autoclave reaction so that a homogeneous coating layer can be obtained without intense grinding or stirring. Thus the morphology of pristine materials can be prevented from destroying. The structure and morphology of the pristine and Al2O3-coated samples synthesized by this process are characterized by XRD, SEM and TEM analysis. Compared with pristine sample, the coated ones show no change on crystal structure as well as microstructure. The capacity retentions delivered by the coated samples are enhanced remarkably compared to that of the pristine one, especially at elevated-temperature. It is proved that the 1 at.% Al2O3-coated sample has not only improved capacity retention but acceptable initial capacity. At 0.5 C rate, the bare, 1 and 2 at.% coated samples have their respective capacity retentions of 64.4%, 76.6% and 75.8% after 300 cycles at room-temperature. Meanwhile, their capacity retentions at 55 degrees C are 22.4%, 78.5% and 73.4% after 100 cycles. Furthermore, through electrochemical impedance spectroscopy, the 1 and 2 at.% coated samples are proved to have lower aging rate. (C) 2013 Elsevier B.V. All rights reserved.