Epitaxial growth of a single hexagonal layered alpha-LiAlO2 coating on a high-voltage LiCoO2 cathode material for enhanced stability

High-voltage LiCoO2 (LCO) cathodes with high theoretical capacity and compact density are an ideal choice for lithium-ion batteries with high energy densities. However, the high cutoff charging voltage causes structural damage to the LCO particles. The LiAlO2 (LAO) coating on the LCO surface has been considered as an artificial passivation layer and stabilizes its performance at high voltages. However, to date, the phase and structure of these LAO coatings have not been studied in detail. Therefore, in this study, a hexagonal-layered alpha-LAO coating is epitaxially grown on bulk LCO via an in situ sol-gel method. The electrochemically inert coating protects the LCO cathode from electrolyte corrosion and prevents structural degradation in a highly charged state. The stoichiometric ratio of the coating is maintained even in a highly delithiated state, decreasing the activity of lattice O2- in LCO and suppressing the slip of the layered structure. The lattice-matched alpha-LAO/LCO interface facilitates continuous 2D Li+ diffusion channels, resulting in an excellent capacity retention (94.5% after 100 cycles at 4.6 V) and rate capacity performance (128.1 mA h g(-1) at 10C). This epitaxial growth of an alpha-LAO coating on LCO particles is a simple and scalable route for the development of high-voltage cathode materials.