Improved structural stability and adsorption capacity of adsorbent material Li1.6Mn1.6O4 via facile surface fluorination

Li1.6Mn1.6O4 (LMO) is deemed as the most promising candidate for Li+ extraction from brine. However, it suffers from structural collapses and capacity fading during lithium adsorption/desorption cycles. To solve this problem, an effortless one-step dry method was adopted to prepared surface-fluorinated Mn-based ion-sieve materials using NH4F at low temperatures. XRD, FIB-SEM, HRTEM, XPS, and chemical analyses were used to characterize the crystal structure, morphology, surface information, chemical composition, and adsorption properties of the materials. The surface-fluorinated LMO showed an adsorption capacity of up to 31.86 mg g−1, a low dissolution loss ratio of Mn, and remarkable long cycle stability with a capacity retention rate of 91.29%. The main reason for the improved adsorption capacity was that the surface fluorination eroded the material outside and increased the specific surface area. Furthermore, the bond energy and structural stability of the material were enhanced by the F–Mn bond, which partially replaced the surface O–Mn bond. In addition, DFT simulation was theoretically performed to understand the improvement mechanism of the material properties by fluorination. These results provide insights into the surface fluoridation effect in the optimization of Mn-based adsorbents, and the proposed simple modification strategy has the potential to be applied to large-scale production.