Extraction of lithium from brine, seawater and spent lithium-ion batteries: a review

The rapid expansion of the new energy vehicle and energy storage industry has led to a surge in lithium demand, intensifying concerns regarding the sustainability of its supply. Nowadays, lithium is mainly acquired from abundant brine and seawater sources, yet effectively separating magnesium ions and lithium ions is critical for producing high-purity lithium products. Concurrently, with the increasing number of spent lithium-ion batteries (LIBs), recycling valuable metals has become the top priority in achieving a sustainable circular economy. Given the compositional variation among LIBs designed for different applications, developing suitable and sustainable recycling processes is essential for efficiently recovering metals from all LIB types. Most existing reviews only discuss lithium extraction from brine and seawater, or lithium recovery from spent LIBs separately, rarely connecting their separation principles and technical commonalities. For the first time, this review systematically integrates the two major technical systems, with a focus on the separation challenges in high magnesium systems and the core pain point of inhomogeneous feedstock for spent cathodes, thereby overcoming the limitations of conventional reviews that only concentrate on a single lithium source or a single technical route. It begins by a systematic description of various separation techniques for brine and seawater-including precipitation, adsorption, solvent extraction, nanofiltration membranes, and electrochemical methods—while integrating the latest modification and coupling research of these lithium extraction technologies. Subsequently, it provides a comprehensive survey of established lithium recovery processes, such as pyrometallurgical and hydrometallurgical rotes, sorting out their process optimization and bottleneck breakthroughs, and also covers other recycling technologies like direct regeneration as well as cutting-edge technical routes including electrochemical coupling and supercritical fluid extraction. Finally, it discusses future research directions aimed at advancing lithium extraction and recycling technologies, with the goal of providing a more comprehensive technical reference for the sustainable utilization of lithium resources.