Formation of Lithium-Manganates in a Complex Slag System Consisting of Li2O-MgO-Al2O3-SiO2-CaO-MnO—A First Survey

Abstract

Due to the increasing demand for electromobility, the recovery of technologically relevant elements from spent Li-ion batteries is becoming increasingly important. Pyrometallurgical processing can deal with a broad range of input materials. Unfortunately, ignoble elements such as Li and Mn enter the slag. A novel approach to facilitate this processing is the Engineered Artificial Minerals (EnAM) strategy for the recovery of critical elements. The aim of this study is to investigate whether it is possible to stabilize Li in Li-manganates as the first crystallizate. For this purpose, synthetic oxide slags (Li, Mg, Al, Si, Ca, Mn) of varying compositions were made. The constituting compounds were identified using inductively coupled plasma optical emission spectrometry, powder X-ray diffraction, X-ray absorption near-edge structure analysis, and electron probe microanalysis. These results provide an understanding of the solidification process and the behavior of the elements of concern. Lithium-manganate(III) (LiMnO2) crystallized first, next to hausmannite (Mn2+Mn3+2O4) in a matrix consisting of wollastonite (CaSiO3) and larnite (Ca2SiO4). Within the structure of LiMnO2, Li and Mn can replace each other in certain proportions. By adding Al and Mg spinel, solid solutions between Mn2+Mn3+2O4, MnAl2O4, MgAl2O4 and LiMnO2 are expected and described by the stoichiometry formula: (Li(2x),Mg(1x),Mn(2+(1–x)))1+x(Al(2–z),Mn3+(z))2O4.

Stabilization of Mn4+ in Synthetic Slags and Identification of Important Slag Forming Phases

“…In addition, small amounts of Mg and Al in LiMnO 2 and Li 2 MnO 3 are expected to promote intralayer diffusion and Mg should also promote interlayer diffusion [14]. For this reason, current research is focusing on the stabilization of Li in Li-manganates as a potential EnAM [8]. The difficulties here are the redox-sensitive behavior of Mn and the Jahn-Teller effect on the Mn 3+ at temperatures above 1445 K [12,13].…”

“…The difficulties here are the redox-sensitive behavior of Mn and the Jahn-Teller effect on the Mn 3+ at temperatures above 1445 K [12,13]. Schnickmann et al [8] showed that it is possible to stabilize a Li-manganate in a complex synthetic oxide slag system (Li, Mg, Al, Si, Ca, Mn). Under a normal atmosphere, a mixture between Mn 2+ and Mn 3+ was present and pure LiMnO 2 was formed.…”

“…In a follow-up experiment, pure oxygen (100% O 2 ) was used to stabilize a higher Mn oxidation stage in the slag. For this experiment, the same batch precursors were used as in Schnickmann et al [8]. This experiment is designed to investigate whether it is possible to stabilize higher Mn oxidation states in synthetic slags and whether Mn 4+ forms a compound with the other elements, especially with Mg and/or Al.…”

“…In addition, this phase should have a high Li-content as well as good processing properties (e.g., habitus, crystal size, magnetic properties). The stabilization of Li in a single phase for an efficient recovery of critically relevant elements is the idea behind engineered artificial minerals (EnAMs) [8] (Figure 1).…”

Enhancing Lithium Recycling Efficiency in Pyrometallurgical Processing through Thermodynamic-Based Optimization and Design of Spent Lithium-Ion Battery Slag Compositions

“…Furthermore, applying gel-combustion for synthesizing artificial minerals leads to the extra LiMnO 2 phase in the slag. 42 This work was motivated to improve the lithium recovery efficiency of LIBs with lithium-nickel-manganese-cobalt-oxide cathodes (NMC). To achieve this goal, we develop and present a new approach for optimizing lithium enrichment due to artificial engineering phases during solidification for a manganese-containing slag system (Li−Al−Si−Ca−Mn−O system) within a particular and varying chemical composition field and based on thermodynamic modeling.…”