The pyrometallurgical recycling of lithium-ion batteries allows the recovery of critical elements into an alloy of noble elements. Ignoble elements such as lithium are transferred into an industrial slag or dust. The extensive application and everyday use of high-tech devices bring about the need to recycle lithium, and possible study of interactions of Li2O-containing slag systems with refractories. MgO and MgO-Cr2O3 refractories are among the top candidates for research on the interfacial reaction when magnesia comes in contact with a Li-bearing slag. Synthetic slags with four variations of Li2O content were poured into magnesia and magnesia chromite crucibles, and held at 1450 ¿C for up to 60 minutes. These experiments allowed the study of the dissolution and corrosion resistance of magnesia-based refractories in the presence of Li¿O in Umicore¿s lithium-ion batteries recycling slag. XRD analysis revealed amorphous phases were formed in the slag samples due to non-equilibrium solidification. The dissolution of MgO into the slag, confirmed by XRF and ICP-OES, was found to increase with longer holding times and higher initial Li¿O content. ICP-OES data showed significant Li¿O loss during the experiments, with loss percentages varying by slag composition. For Li-free slag (C1), an intermediate layer containing solid spinel phases, (Mg, Fe, Mn)(Fe, Al, Mn)¿O¿, was identified, acting as a diffusion barrier and moderating MgO dissolution. Similar characteristics were observed in C2 slag due to 100% evaporation of Li¿O, including an Al- and Fe-enriched intermediate layer. In C1 and C2 slags, indirect dissolution led to the formation of a thicker intermediate layer, which decelerated the infiltration of the slag. The thickness of the intermediate layer increased over time and was thicker for C1 and C2 compositions with no or lower Li¿O content, correlating with higher slag viscosity and less diffusion. In contrast, samples with higher Li¿O content (C3 and C4) contained thinner intermediate layers, and exhibited dendritic microstructures with Al-rich dendrites surrounded by Si(Ca)-rich melts further through the slag bulk. The higher lithium-containing slags facilitated the formation of lithium aluminate and eucryptite-like phases, suggesting distinct reaction mechanisms due to network-breaking properties of lithium. Viscosity calculations confirmed that increased Li¿O content reduces slag viscosity, enhancing ion mobility and accelerating MgO dissolution, while reducing the effectiveness of the intermediate layer as a diffusion barrier. The rapid dissolution of magnesia at the presence of Li could reduce the buildup of a protective intermediate layer, and MgO is readily absorbed into the slag. MgO-Cr¿O¿ crucibles showed significantly better corrosion resistance compared to pure MgO crucibles, with the stability of the MgCr¿O¿ spinel phase playing a crucial role in enhancing chemical stability and minimizing dissolution in the presence of Li¿O.