BACKGROUND High efficiency membrane extraction (ME) of lithium from brine has been constrained by membrane mass transfer resistance. We report here a new solvent-resistant membrane produced from ethylene vinyl alcohol (EVAL) and sulfonated polyether ether ketone (SPEEK). RESULTS The effect of the SPEEK on the thermodynamics and kinetics of demixing to the membrane morphology was investigated systematically. Addition SPEEK created extra resistance to the movement of the polymer chains in solution which was reflected in the reduced gelation diffusion coefficient. About 0.5 wt% of SPEEK was sufficient to reduce the mass transfer resistance of lithium ions (Li+). Membrane thickness showed linear correlation with Li+ flux, but was limited by its weak mechanical strength. Finally, a composite EVAL/SPEEK membrane supported by a thin loose nonwoven fabric showed a stress of 12.5 MPa, nearly 10-fold greater than the unsupported membrane, and the highest lithium extraction flux of 4.80 x 10(-8) mol cm(-2) s(-1). CONCLUSION The work provides a rationale for developing mechanically stable, high extraction flux membranes for ME. (c) 2020 Society of Chemical Industry