Self-assembled layered lithium manganese oxide shows ultra-large adsorption capacity and high selectivity for lithium

Lithium manganese oxides (LMOs) are competitive materials for lithium extraction from aqueous resources. However, traditional LMOs are yet to be industrialized based on their existing lithium adsorption capacities. In this work, Li1.90Mn1.52O4, a self-assembled layered LMO, is innovatively synthesized with an accurately measured structure using multiple high-precision characterization technologies, and its adsorbent has an ultra-large lithium adsorption capacity of 66 mg/g. Synthesis experiments and related density functional theory (DFT) calculations show that the self-assembled synthesis of Li1.90Mn1.52O4 occurs during the hydrothermal process and is abstracted into three steps: first, manganese oxide dissolves into manganese oxide octahedron [MnO6] groups; second, the [MnO6] groups form metastable and thin-layer δ-type manganese oxide (δ-MnO2) by self-assembly; third, the pre-product of Li1.90Mn1.52O4 is formed by the reaction between the δ-MnO2 and the hydroxide ions with lithium ions embedded between layers. The selectivity experiments and corresponding DFT calculations show that the selective adsorption process of H1.90Mn1.52O4 follows the selectivity order “Li+ ≫ Na+ > K+ > Ca2+ > Mg2+” and is divided into two steps: first, the hydrated metal ions from the liquid resources leave the water molecules and transfer to the surface of H1.90Mn1.52O4; second, the metal ions migrate into the adsorption sites via the ultra-narrow ion transfer channels.