An Ultrastable RA-LiMn<sub>2</sub>O<sub>4</sub> Lithium-Ion\nSieve for Lithium Extraction from Brine

The\nsurging demand for lithium, driven by the expanding market\nfor electric vehicles and electronic devices, necessitates efficient\nlithium extraction methods. A reverse lithium-ion battery (RLiB) method,\nutilizing a lithium-ion sieve to directly extract Li<sup>+</sup> from\nbrine, offers the advantages of high selectivity and environmental\nfriendliness. However, implementation of RLiB systems has been hindered\nby the limited cycling stability of the LiMn<sub>2</sub>O<sub>4</sub> material. This study addresses this challenge by introducing a novel\nRA-LiMn<sub>2</sub>O<sub>4</sub> material with a core–shell\nstructure, incorporating rutile-anatase (RA) as the shell and spinel\nLiMn<sub>2</sub>O<sub>4</sub> as the core to enhance stability. Remarkably,\nthe RA-LiMn<sub>2</sub>O<sub>4</sub> material demonstrates exceptional\ncycling stability, maintaining full capacity even after 100 cycles\nof charging–discharging in an aqueous LiCl electrolyte. Moreover,\nconcentration polarization during lithium extraction is alleviated,\nand Li<sup>+</sup> is successfully extracted from real brine (309\nppm of Li<sup>+</sup>) using RA-LiMn<sub>2</sub>O<sub>4</sub> as the\nworking electrode. This work presents an ultrastable RA-LiMn<sub>2</sub>O<sub>4</sub> material for lithium extraction from real brine.