Lithium Extraction in Confined Channels.

The sustainable extraction of lithium (Li+) from aqueous resources is increasingly vital for next-generation energy storage technologies. Conventional technologies are usually limited by intensive cost and complicated process demands, and poor efficiency in handling low-concentration sources such as seawater. Membrane-based lithium extraction has emerged as a transformative alternative, offering low energy consumption, environmental-friendly operation, and potential for high lithium selectivity. The key to this technology is the concept of confined channels, where ion transport is regulated within nano- or subnanometer-scale pathways. Unlike conventional bulk-phase separation, confined channels show distinct mechanisms, including size effects, pore-wall effects, and special interactions that enable discrimination between Li+ and competing ions with similar ionic size. This review categorizes confined channel membranes into three main classes: 2D layered systems (e.g., graphene oxide, MXenes, clays), porous crystalline frameworks (e.g., metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and porous organic cages (POCs)), and polymer with engineered nanoconfinement. We summarize recent progress in materials design, pore structure tuning, and separation mechanism insights. Finally, we highlight emerging three type separation processes (diffusion, nanofiltration, and electrodialysis) equipped with confined channel membranes and future potential possibilities toward scalable fabrication, emphasizing the integration of advanced materials, membrane engineering, and computational modeling.