Highly Selective Lithium Extraction from Shale Gas Wastewater Using Al- and F-Doped LiMn2O4 Electrode in Rocking-Chair Capacitive Deionization

Abstract Selective lithium extraction from shale gas wastewater (SGW) offers a promising strategy to expand lithium supply while reducing wastewater-management burdens. However, low Li+ concentrations and overwhelming competition from Na+ and Mg2+ make selective and energy-efficient extraction challenging. Lithium manganese oxide (LMO) is attractive for electrochemical Li extraction but remains limited by insufficient cycling stability and selectivity in complex ionic matrices. Here, we investigate the effects of Al and F modification of LMO on lithium extraction in a rocking-chair capacitive deionization system. Structural and spectroscopic characterizations show that the optimized modification contracts the spinel lattice and produces near-surface enrichment of F-containing species, improving electrochemical reversibility. Electrochemical analyses and density functional theory calculations further indicate favorable Li+ transport and stronger migration restrictions for Na+ and Mg2+ after lattice entry. In a simulated SGW matrix with a Li/Na/Mg molar ratio of 1:100:1, LMO-Al-F achieves a Li adsorption capacity of 9.54 mg g–1, Li/Na and Li/Mg separation factors of 2216 and 1509, and an energy consumption of 4.21 Wh mol–1 Li. Strong Li selectivity is also maintained in real SGW. After 100 competitive-ion cycles, 78% of adsorption capacity is retained, supporting repeated Li-selective extraction under high-salinity conditions.