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

Abstract

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.