Enhanced 4.5 V/55 °C cycling performance of LiCoO2 cathode via LiAlO2[sbnd]LiCo1-xAlxO2 double-layer coatings

Abstract

Surface structural engineering has been widely applied to improve the electrochemical performances of LiCoO2 cathodes, especially for applications at high operation voltages (>4.4 V vs. Li) and elevated working temperature (≥50 °C). In this report, Al2O3 layer with an average thickness of 8 nm was firstly obtained on the LiCoO2 surface, and then was transformed into LiAlO2/LiCo1-xAlxO2 double-layers by a facile heating treatment. This novel double-layers structure was clearly presented by high resolution transmission electron microscopy (HRTEM) and depth profile of X-ray photoelectron spectroscopy (XPS). Due to the chemical/electrochemical stability of the LiAlO2 layer and high Li+ conductivity of the LiCo1-xAlxO2 layer, this cathode with hierarchical structure achieved higher capacity and better cycling stability than the Al2O3 coated LiCoO2 cathode at both 25 and 55 °C. In addition, this LiAlO2/LiCo1-xAlxO2/LiCoO2 cathode maintained the capacity of 178.1 mA h g−1 (73% capacity retention) after 500 cycles (3.0–4.5 V, 1C), which is very promising to be used in severe operation conditions such as high temperature and voltage.