In the present work, phase equilibria in the Li $$_2$$2 O–Al $$_2$$2 O $$_3$$3 system were experimentally studied and calorimetric measurements were performed. Based on obtained results and data from literature, thermodynamic parameters of the system were assessed. The solid solution phases were modeled using Compound Energy Formalism (CEF) and liquid phase was described by two-sublattice partially ionic liquid model. The experimental investigations for selected compositions of isothermally heat-treated samples were performed using x-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC) were used to measure the temperature of the reactions as well as the heat capacities, respectively. After DTA, the microstructure was analyzed using SEM. Temperature of peritectic melting of h-LiAl $$_5$$5 O $$_8$$8 was determined to be 2222 K and temperature of eutectic reaction Liq $$\leftrightarrow$$↔ $$\gamma$$γ -LiAlO $$_2$$2 + h-LiAl $$_5$$5 O $$_8$$8 to be 1965 K. Heat capacity of LiAlO $$_2$$2 and LiAl $$_5$$5 O $$_8$$8 was measured in the temperature range of 100-1300 K. The degree of inversion of spinel phase (Al $$^{+3}$$+ 3 , Li $$^{+1}$$+ 1 ) $$_1^T$$1 T :(Al $$^{+3}$$+ 3 , Li $$^{+1}$$+ 1 , Va) $$_2^O$$2 O :O $$_4$$4 was modelled assuming Al $$^{+3}$$+ 3 and Li $$^{+1}$$+ 1 can occupy tetrahedral (T) and octahedral (O) cationic sublattices while its composition extension in Al $$_2$$2 O $$_3$$3 enriched region was described by introducing vacancies in octahedral sites. Thermodynamic description derived in the present study reproduces the degree of inversion close to that of the high-temperature spinel phase, which means that Al $$^{+3}$$+ 3 ions preferentially occupy the tetrahedral sites. The calculated phase diagram satisfactorily agrees with the experimental results. Available experimental thermodynamic data are also reproduced within uncertainty limits.

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 Mn⁴⁺ 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 LiMn³⁺O₂, Li₂Mn⁴⁺O₃ was also stabilized. Both phases crystallized in a Ca-silicate-rich matrix. In the structures of Li₂MnO₃ and LiMnO₂, Li and Mn can substitute each other in certain proportions. As long as a mix of Mn²⁺ and Mn³⁺ is present in the slag, spinels form through the addition of Mg and/or Al.

Phase equilibria studies were performed in the Li₂O-SiO₂ system for heat-treated samples using Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD). The temperature of the eutectic reaction (Liq. ⇌ Li₄SiO₄ + Li₂SiO₃) was experimentally determined at 1289 K using Differential Thermal Analysis (DTA). No evidences of the Li₆Si₂O₇ formation was found by the experimental investigation and therefore, it was not considered. Heat capacity of the Li₈SiO₆ phase was measured using Differential Scanning Calorimetry (DSC). Solid phases of the Li₂O-SiO₂ system were described as stoichiometric compounds and liquid phases by two-sublattice partially ionic liquid model. Four stoichiometric intermediate compounds were considered to be stable (Li₈SiO₆, Li₄SiO₄, Li₂SiO₃ and Li₂Si₂O₅). The polymorphic transformation in Li₂Si₂O₅ phase was accounted and the metastable liquid miscibility gap on SiO₂-rich side was reproduced. The calculated phase diagram satisfactorily agrees with the experimental phase equilibria as well as calculated thermodynamic properties reproduces experimental values within uncertainty limits.