Effects of metal oxide coatings on the thermal stability and electrical performance of LiCoCO2 in a Li-ion cell

A study is made of the effects of MgO and Al2O3 coatings on the electrical properties of LiCoO2 cathode material on the thermal stability (differential scanning calorimetry (DSC)) of the charged cathode, and on the safety characteristics of 18650 Li-ion cells. Powdery active material is coated with Mg or Al alkoxide solutions followed by heat treatment in air at temperatures between 300 and 800degreesC. The presence of the coating is confirmed by an elemental depth-profile analysis of the powder surface using secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS). Both oxide coatings, especially the Al2O3 coating, substantially improve the charge-discharge voltage characteristics, rate capability, capacity and rate-capability retention on cycling and thermal stability of the LiCoO2 cathode. These beneficial effects are demonstrated in 18650 Li-ion cells. (C) 2003 Elsevier B.V. All rights reserved.