Effect of Anions on the Delithiation of [Li-Al] Layered Double Hydroxides: Thermodynamic Insights

The utilization of lithium aluminum [Li-Al] layered double hydroxides (LDHs) is explored for direct lithium extraction (DLE) from geothermal brines and minerals. Following extraction, the Li⁺ ions need to be removed from the LDH structure and converted into LiOH or Li₂CO₃ products, making them suitable for battery applications. The research investigates the delithiation of [Li-Al-X] LDHs (where X = Cl^-, OH^-, and SO₄^2-), which were synthesized and dried under different conditions. The study aims to understand how the choice of anions and drying conditions affects the delithiation process. To determine the stability of these [Li-Al] LDHs, high-temperature oxide melt solution calorimetry is employed. The results reveal that the stability of LDHs varies significantly based on postdrying conditions, anion choice, and the water content in the interlayer. The order of stability, as indicated by the enthalpy of formation values, is found to be OH-LDH-O > OH-LDH-A > SO₄-LDH-O > SO₄-LDH-A > Cl-LDH-O > Cl-LDH-A. This trend is attributed to the interactions among the interlayer species and the metal hydroxide layers.