Enhanced Lithium Adsorption on an Anion- and Cation-Codoped Lithium Manganese Oxide Ion Sieve with a Thin Fluoride-Protective Coating Layer

In this work, novel lithium manganese oxide ion sieves (LISs) H1.6Mn1.54Al0.02Cr0.04FyO4–y codoped with Al, Cr, and F ions were synthesized to improve their lithium adsorption performance. The resulting anion- and cation-codoped LISs maintain the spinel structure. Particularly, the introduction of F ions forms a fluoride coating layer on the surface of LISs, playing an important role in stabilizing the LIS structure. Moreover, some Mn3+ ions are partially replaced by Al3+ and Cr3+ ions and some of the surface O2– ions are replaced by F– ions, forming the stronger Al–O, Cr–O, and metal–fluorine bonds. The synergistic effect of the anion and cation codoping enhances the structural stability of LIS. Compared with undoped and double-doped LISs, the triple-doped LIS H1.6Mn1.54Al0.02Cr0.04F0.1O3.9 (HMACFO-10) exhibits a lower manganese dissolution loss, enhanced Li+ adsorption performance, and better reusability. In addition, HMACFO-10 affords good adsorption selectivity for Li+ ions from brines.