Pulsed sonication for alumina coatings on high-capacity oxides: Performance in lithium-ion cells

High-capacity xLi(2)MnO(3)center dot(1 - x)LiMO2 (M = Ni, Mn, Co) oxides show relatively rapid performance degradation when cycled at voltages >4.5 V vs. Li/Li+. Previous research has indicated that modifying the oxide surfaces with coatings, such as alumina, reduces cell impedance rise and improves capacity retention. In this article, we demonstrate pulsed-sonication as a rapid and effective approach for coating alumina on Li(1.2)Ni(0.17)sMn(0.525)Co(0.1)O(2) (0.5Li(2)MnO(3)center dot 0.5LiNi(0.44)Mn(0.31)Co(0.25)O(2)) particles. Oxide integrity and morphology is maintained after the sonochemical process and subsequent heat-treatment. Energy dispersive spectroscopy (EDS) X-ray elemental maps show uniform coating of all secondary particles. Al-27 Magic Angle Spinning (MAS) NMR data confirm the presence of alumina and mainly indicate octahedral aluminum occupancy in a six-coordinate environment with oxygen. Full cells containing electrodes with the alumina-coated particles demonstrate lower initial impedance rise and better capacity retention during extended cycling to high voltages. However, the coating has a negligible effect on the voltage hysteresis and voltage fade behavior displayed by these oxides. The various data indicate that the pulsed sonochemical technique is a viable approach for coating oxide particles. The methodology described herein can easily be extended beyond alumina to include coatings such as AlF3, MgO, and MgF2. (C) 2014 Elsevier B.V. All rights reserved.