Hybrid Cation Exchange Membranes with Lithium Ion‐Sieves for Highly Enhanced Li+ Permeation and Permselectivity

Cation exchange membranes (CEMs) hold promise for efficient and environment‐friendly lithium extraction from salt‐lake brine. However, development and practical application of CEMs are significantly hindered by the low Li⁺ permeation and permselectivity. Herein, novel hybrid CEMs are developed by dispersing lithium ion‐sieves (LMO) into sulfonated poly(ether ether ketone) matrix. Two kinds of LMOs are synthesized including acidified LMO (HMO) and its sulfonation compound (HMO‐S). The physicochemical property and separation performance of hybrid membranes are systematically investigated. The uniformly dispersed HMO and HMO‐S enhance the thermal, mechanical stability, and swelling resistance of hybrid membranes. Furthermore, these fillers obviously reduce the area resistance from 8.0 to less than 6.0 Ω cm^?2. Importantly, the unique Li⁺ transfer channels in HMO/HMO‐S efficiently elevate the Li⁺ permeation by up to 66%. While the “ion‐sieve effect” of the channels weakens the migration of Mg²⁺ and K⁺, thus notably rising Li⁺/Mg²⁺ and Li⁺/K⁺ permselectivities by ≈5 times, which is difficult to realize with conventional fillers. Comparing with HMO, HMO‐S shows higher improvement for permselectivity because of the reduced area resistance of the resultant hybrid membrane. This study paves a way to design and development of selective Li⁺ exchange membranes for transport and separation applications.