High‐Throughput Study of the Phase Constitution of the Thin Film System Mg–Mn–Al–O

The increasing importance of recycling makes the recovery of valuable elements from slags interesting. The concept of engineered artificial minerals aims at the formation of phase(s) with a high content of the to‐be‐recovered element(s) from slags of pyrometallurgical recycling processes. For this, understanding the phase constitution of the slag systems, such as the spinel‐forming subsystem Mg–Mn–Al–O from Li‐ion battery recycling, is of great importance. Herein, the phase constitution is investigated using a thin film materials library (ML) that covers the composition space (Mg₁₄₋₆₉Mn₁₁₋₃₈Al₁₄₋₇₄)O_x. High‐throughput energy‐dispersive X‐ray spectroscopy and X‐ray diffraction confirm the formation of the spinel solid solution phase for a wide composition space. The Mn oxidation state is shown to be a mixture of Mn²⁺ and Mn³⁺ by analyzing Mn 2p3/2 spectra from X‐ray photoelectron spectroscopy. For one measurement area of the ML containing equal atomic amounts of Mg, Mn, and Al, transmission electron microscopy shows columnar spinel grains with Mg, Mn, and Al evenly distributed. Based on these results, it is suggested that the high likelihood of spinel formation in slags can be influenced by controlling the Mn oxidation state to allow the formation of desirable engineered artificial minerals for Li recovery.