Lithium extraction via capacitive deionization: AlF₃ coated LiMn₂O₄ spheres for enhanced performance

The escalating demand within the lithium battery sector has intensified the pursuit of efficient methods for lithium's selective extraction from brines. Particularly, LiMn₂O₄ (LMO) emerges as a prime candidate, celebrated for its robust redox properties and considerable theoretical adsorption capacity. Nonetheless, its application is hampered by structural instability due to Jahn-Teller distortion, which triggers a phase shift from cubic to tetragonal and Mn dissolution, undermining the material's lithium extraction efficiency. In response, this study introduces an innovative, multifunctional amorphous AlF₃ coating on LMO spheres, employing a novel synthesis approach combining co-precipitation, solid-phase transformation, and a final AlF₃ deposition. This method not only mitigates Mn leaching but also curtails the adverse effects of Jahn-Teller distortion by integrating trace amounts of Al³⁺ into the LMO lattice, thus fortifying both the surface and bulk structure of the material. Significantly, the AlF₃-coated LMO demonstrates an enhanced lithium extraction capacity of 31.5 mg g⁻¹ at 1.2 V with feedwater concentration of 150 mg L⁻¹. Additionally, the optimally coated sample exhibits superior cycling stability, maintaining high-capacity retention and minimal manganese dissolution across multiple absorption-desorption cycles. Furthermore, the optimized electrode exhibits exceptional selectivity for lithium over magnesium in solutions with high Mg²⁺/Li⁺ ratios, achieving a notable separation factor of 7.66. Additionally, this electrode demonstrates efficient separation capabilities in synthetic brine, effectively distinguishing Li⁺ from competing ions such as Na⁺, K⁺, Ca²⁺, and Mg²⁺, which underscores its substantial potential for effective lithium recovery from complex brines.