Al2O3-surface modification of LiCoO2 cathode with improved cyclic performance

In this article, Al2O3-coated LiCoO2 cathode is synthesized by high-temperature solid-state reaction method, i.e. sintering the mixture of Al2O3 and LiCoO2 powder. X-ray diffraction (XRD) analysis shows that there is no Al2O3 impurity being found in the final product. Scanning electron spectroscopy (SEM) and transmission electron spectroscopy (TEM) measurements show that the micro-morphology of pristine LiCoO2 grains is sustained after coating Al2O3. We analyze the surface chemistry of the pristine and Al2O3-coated LiCoO2 by X-ray photoelectron spectroscopy (XPS) technique. The electrochemical behavior is systematically investigated. The cathodes are cycled in different potential ranges (3.70 V-4.30, 4.35, 4.40, 4.45, 4.50, 4.55 and 4.60 V). The charge-discharge, cyclic voltammetry (CV) and Electrochemical impedance spectroscopy (EIS) measurements show that coating Al2O3 can obviously improve the cyclic stability and decrease the total interfacial resistance. We could conclude that Al2O3-coated LiCoO2 cathode is suitable for practical application in the potential range of 3.70-4.50 V vs. Li/Li+. The discharge capacity can reach 113 mAh/g after 500 cycles. It is very possible that the LiCo1 − xAlxO2-like surface phase, formed on the surface of LiCoO2, prevents Co-dissolution. As results, the operation potential range is extended and the cyclic stability is improved.