The role of the transition metal nature and Al2O3 coating on the surface reactivity of LiCoO2 and LiNi(1/3)Mn(1/3)Co(1/3)O2 (NMC) materials were studied by coupling chemisorption of gaseous probes molecules and X-ray photoelectron (XPS) spectroscopy. The XPS analyses have put in evidence the low reactivity of the LiMO2 materials toward basic gaseous probe (NH3). The reactivity toward SO2 gaseous probe is much larger (roughly more than 10 times) and strongly influenced by the nature of metal. Only one adsorption mode (redox process producing adsorbed sulfate species) was observed at the LiCoO2 surface, while NMC materials exhibit sulfate and sulfite species at the surface. On the basis of XPS analysis of bare materials and previous theoretical work, we propose that the acid-base adsorption mode involving the Ni(2+) cation is responsible for the sulfite species on the NMC surface. After Al2O3 coating, the surface reactivity was clearly decreasing for both LiCoO2 and NMC materials. In addition, for LiCoO2, the coating modifies the surface reactivity with the identification of both sulfate and sulfite species. This result is in line with a change in the adsorption mode from redox toward acid-base after Al/Co substitution. In the case of NMC materials, the coating induced a decrease of the sulfite species content at the surface. This phenomenon can be related to the cation mixing effect in the NMC.

Density Functional Theory is applied to understand the large difference in surface reactivity of LiCoO 2 due to Al/Co substitution which is experimentally observed. In this way, we explore the SO 2 and CO 2 adsorption modes on the (110) surface of LiCoO 2 and α-LiAlO 2 . For SO 2 adsorption, chemisorption produces sulfite species (for LiCoO 2 and α-LiAlO 2 ) and sulfate species (in the case of LiCoO 2 ). We demonstrate that the modification of the surface reactivity when Co 3+ ions are substituted by Al 3+ ions is due to a change from an adsorption mode controlled by redox properties for LiCoO 2 to a less energetically favorable adsorption mode controlled by acid−base properties for α-LiAlO 2 . For CO 2 adsorption, the formation of carbonate species is observed for both compounds, illustrating the fundamental difference in the factors controlling SO 2 adsorption compared to CO 2 adsorption.

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