Carboxylate-alumoxanes as precursors for alumina coatings to enhance the cyclability of LiCoO2

LiCoO2 cathodes coated with Al2O3 derived from carboxylate-alumoxanes have been shown to possess improved cyclability. The carboxylate-alumoxanes were prepared by reacting pseudo-boehmite with acetic and substituted acetic acids. TEM images of the coated powders revealed that the alumina formed a compact kernel of thickness averaging about 20 nm. XRD data on the coated materials suggested the formation of solid solutions of the composition LiAlyCo1-yO2 on the surface, a conclusion attested by ESCA depth profiles. Galvanostatic cycling studies suggested that a coating formed from (methoxyethoxy)acetate-alumoxane enhanced the cyclability 13-fold. The improved cyclability is attributed to suppression of the cycle-limiting phase transitions accompanying the charge-discharge processes. The coating procedure based on carboxylate-alumoxanes is economical and environmentally benign, features attractive for industrial exploitation. (c) 2005 Elsevier B.V. All rights reserved.