Microporous Polymer Sorbents for Direct Lithium Extraction

Lithium extraction from brines is essential to onshoring battery supply chains. Yet, cation-exchange sorbents often exhibit poor selectivity and require pH swings, contributing to increased capital and operating expenditures. Here, we develop lithium extraction sorbents that obviate pH swings by reversibly binding Li⁺ within aqueous brine-compatible polymers of intrinsic microporosity (AquaPIMs) bearing metal-complexing aza-crown-ether pendants. We conduct selectivity screens with synthetic and natural brines, the latter obtained from oilfield and salt lake sites across North America. Sorption selectivities for Li⁺/Na⁺, Li⁺/K⁺, Li⁺/Mg²⁺, and Li⁺/Ca²⁺change with respect to sorbent and brine composition due to pH, mixed-ion effects, and ion-polymer interactions; this behavior was pronounced for natural brines. Using an AquaPIM sorbent embodying aza-12-crown-4 pendants, we demonstrated a lithium extraction process for Smackover Formation brine (Arkansas, USA), enriching Li by a factor of 3.7 when desorbing it with pure water. Our work underscores the importance of designing sorbents based on brine composition and Li⁺/Mⁿ⁺ separation priorities.