Aluminum-based coatings are commonly used in lithium-ion batteries to modify the surface of LiCoO₂ particles, to limit cobalt dissolution in the electrolyte at high voltage. It was shown that the formation of a LiCo_1−xAl_xO₂ solid solution occurs at the interface between the coating and the core material. In this paper, we investigated the surface properties of LiCo_1−xAl_xO₂ materials by X-ray photoelectron spectroscopy. We explored the surface acid−base properties of these materials by adsorption of gaseous probe molecules (NH₃ and SO₂) followed by XPS analyses. We showed that the basic character of the LiCo_1−xAl_xO₂ surface strongly decreases when x increases, which makes these materials less reactive than LiCoO₂ toward acidic species (such as HF) that are present in LiPF₆-based electrolytes. This is a possible explanation for the efficiency of Al-based coatings to protect LiCoO₂ against cobalt dissolution in the electrolyte.