Lithium extraction from low-grade brines via strain-induced electronic structure modulation of MnO2 nanorods through Mg incorporation

Abstract

In this study, the incorporation of Mg²⁺ induced the transformation of MnO₂ from the original cubic [MnO₆] octahedron to a flattened conformation (FLA-MnO₂). The flattened conformation mitigated structural deformation of the [Mn³⁺·O₆] octahedron by inhibiting the J–T aberration during the reduction process of Mn⁴⁺, thereby improving the selective adsorption capacity of lithium. When used in hybrid capacitive deionization (HCDI), FLA-MnO₂ exhibited a high Li⁺ adsorption capacity of 30.14 mg g⁻¹ in 32.74 mg L⁻¹ Li⁺ ion solution, with low energy consumption of 0.45 Wh g⁻¹. Notably, the FLA-MnO₂‖AC HCDI cell exhibited high stability, maintaining 82% of its capacity over 100 cycles. This was evidenced by the 82% capacity retention and low Mn loss (1.3%) over 100 cycles. Finally, the excellent selective extraction performance of Li⁺ ions was demonstrated in Lop Nor, the low-grade original brine of the XieLi salt flats. The calculated separation factors for Li⁺/Na⁺, Li⁺/K⁺, Li⁺/Ca²⁺, and Li⁺/Mg²⁺ reached impressive values of 4.37, 3.75, 3.24, and 2.11, respectively, making the Lop Nor a candidate electrode for lithium extraction from low-grade raw brines.