Synergistic effects of coating and doping for lithium ion battery cathode materials: synthesis and characterization of lithium titanate-coated LiCoO2 with Mg doping

Abstract

Lithium titanates are introduced as coating materials on the surface of Mg-doped LiCoO2 in which the residual Li2CO3 after synthesis of the active materials is used as a lithium source. It is revealed that two completely different lithium titanate phases (monoclinic Li2TiO3 and spinel Li4Ti5O12) can be obtained as the coating materials depending on the concentration of a titanium source. Characterization of the coating materials is performed with various experimental techniques including XRD, nano SIMS, TEM, EELS and current measurement using nano probe. The Li4Ti5O12 coating layer from the high concentration of titanium source secures better electrochemical performances than the Li2TiO3 one from the low concentration of titanium source due to its "zero-strain" characteristic. In addition, it is shown that the doped ions (Mg2+) from the active materials move to the coating layer and strongly enhance the conductivity of Li4Ti5O12. Consequently, synergistic effects on the cell performances of cyclability and rate capability from coating and doping for the LiCoO2 cathode materials are rigorously investigated. (C) 2015 Elsevier Ltd. All rights reserved.