Abstract
Air stability caused by the H(2)O/CO(2) reaction at the layered oxide NaTMO(2) surface is one of the main obstacles to commercializing sodium-ion batteries (SIBS). The H(2)O and CO(2) adsorption properties on the (100) surface of sodium layered transition metal oxide NaTMO(2) (TM = Co, Ni, Mo, Nd) are calculated using the DFT method to study the surface air stability. This study showed that the material bulk phase (symmetry), surface site, element type, and surface termination are all (though not the only) important factors that affect the adsorption strength. Contrary to previous studies, the P phase is not always more air-stable than the O phase; our calculations showed that the NaNiO(2) O phase is more stable than the P phase. The calculated band center and occupation showed a direct relationship with the adsorption energy. The Na site adsorption for CO(2) and H(2)O showed the same V-shape trend. However, the TM adsorption for CO(2) and H(2)O showed a different trend. With an increased t(2)g band center, CO(2) adsorption strength increases. There is no clear trend for H(2)O adsorption. Our calculations showed that the electronic structure of the surface atomic of adsorption site plays a decisive role in CO(2) and H(2)O adsorption strength. This study demonstrated an effective method for obtaining a stability parameter regarding the electronic structure, which can be used to screen the air-stable layered oxide sodium cathode in the future.