Lithium-based batteries stand out as a crucial technology for energy storage. Between 2020 and 2022, lithium production surged from 77,000 to 100,000 tons. The majority of the world's lithium reserves are situated in water resources. Nevertheless, the direct extraction of lithium requires additional chemical processes due to the presence of other salts. Nanofiltration is recommended as an environmentally friendly and economical method for lithium purification. The main objective of this thesis is to develop a nanofiltration membrane for efficient Li+ and Mg2+ separation. The support membrane was prepared through the phase inversion technique using polyamide-imide (PAI) in the casting solution and polyethyleneimine in the coagulation bath. In-situ dopamine polymerization under oxygen backflow formed an intermediate layer on the support surface for further modification. PDA-modified support was first coated with polyethyleneimine (PEI) functionalized alumina particles and then low molecular weight PEI (800Da). The final membrane design was optimized for Li+purity and Li+ recovery. The produced nanofiltration membrane exhibited significant rejection rates, notably around ~90% % for Mg2+and approximately ~ -21% for Li+. Additionally, it demonstrated a pure water permeability of 9.7 L/m2 hbar. Each membrane layer underwent characterization through various techniques, including SEM, EDX, zeta potential analysis, AFM, and contact angle measurements. The membrane was subjected to stability tests under dynamic and static conditions. Li+ and Mg+2 rejections, separation factor, and salt solution flux did not change after 30 days of storage in 2000 ppm salt solution and during 72 h dynamic filtration test.