Covalent organic framework membranes for lithium extraction: facilitated ion transport strategies to enhance selectivity

Abstract

The surging global demand for lithium, driven by the proliferation of electric vehicles and energy storage technologies, has exposed significant limitations in conventional lithium extraction methods, including inefficiency and environmental harm. Covalent organic frameworks (COFs) have emerged as a promising platform to address this challenge and enable more sustainable lithium extraction, owing to their unique advantages such as precisely tunable pore sizes, robust stability, and the ability to incorporate functional binding sites for selective ion transport. This review focuses on structural design and functionalization strategies in COFs to optimize lithium-ion separation, highlighting how pore confinement effects, tailored interlayer stacking arrangements, and strategic functional group modifications can dramatically enhance Li⁺ selectivity over competing ions present in brine solutions. A particular emphasis is placed on the fundamental energy barriers associated with lithium-ion transport. In particular, we discuss how appropriately designed pore environments and lithium-binding functional groups reduce the dehydration energy required for Li⁺ to enter and traverse COF nanochannels, thereby facilitating faster and more selective Li⁺ conduction. We also survey recent advancements in COF-based lithium separation technologies, such as high-performance COF membranes and sorbents for extracting lithium from brines and seawater, evaluating their potential, as well as remaining challenges, for sustainable industrial implementation. This review provides a comprehensive understanding of how advanced COF engineering can enable efficient and selective lithium-ion transport, offering valuable insights for the development of next-generation lithium extraction materials and technologies.