The expected shortage of Li due to the strong increase in electromobility is an important issue for the recovery of Li from spent Li-ion batteries. One approach is pyrometallurgical processing, during which ignoble elements such as Li, Al and Mn enter the slag system. The engineered artificial mineral (EnAM) strategy aims to efficiently recover critical elements. This study focuses on stabilizing Li-manganates in a synthetic slag and investigates the relationship between Mnsup.4+ and Mg and Al in relation to phase formation. Therefore, three synthetic slags (Li, Mg, Al, Si, Ca, Mn, O) were synthesized. In addition to LiMnsup.3+Osub.2, Lisub.2Mnsup.4+Osub.3 was also stabilized. Both phases crystallized in a Ca-silicate-rich matrix. In the structures of Lisub.2MnOsub.3 and LiMnOsub.2, Li and Mn can substitute each other in certain proportions. As long as a mix of Mnsup.2+ and Mnsup.3+ is present in the slag, spinels form through the addition of Mg and/or Al.