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

Abstract

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.

Highly efficient monovalent ion transport enabled by ionic crosslinking‐induced nanochannels

“…Dried PEEK (15 g) was added to concentrated sulfuric acid (150 ml), and the mixture was stirred at 35°C for 12 h. Subsequently, SPEEK was precipitated by extruding the homogeneous solution into a large amount of deionized water and washed several times until neutralization 35 . Finally, the SPEEK was dried overnight at 20°C and for another 24 h at 100°C in a vacuum oven.…”

“…The resultant solution was cast onto a glass plate and first dried at 60 C for 18 h; after that, the heating temperature was gradually increased to 100 C for another 6 h. The obtained membrane was first immersed in deionized water for 24 h, then transferred to a 1 M HCl solution for another 24 h to convert the exchange group to an H-type, and finally transferred to deionized water, where it was stored for later use. The ICMs fabricated by introducing a certain QPPO content (20,30,35,40, and 50 wt%) were labeled as ICM Q/S_X , where X represents the mass content of QPPO. 15 It should be noted that the quaternary ammonium group contents were 23, 34, 39, 44, 54 (mol %), which were calculated according to the following Equation (1) based on the IEC difference of two ionomers, as follows:…”

Advances and challenges in metal ion separation from water

“…Due to the high demand of lithium for the battery industry, various types of specific membranes for lithium have been proposed. Despite the general lack of selectivity for a specific ion in nanofiltration, metal ions such as lithium can be selectively recovered by ion-imprinted membranes [35][36][37][38][39] and ionsieve membranes [40,41]. Electrodialysis using ion exchange membranes can also separate metal ions into different streams.…”

Anionic MOFs Embedded in Anion-Exchange Membranes for the Separation of Lithium/Magnesium Cations

“…For the separation of Li + and Mg 2+ , neutral polymeric matrices with little ionic conductivity, such as polyvinyl chloride (PVC), usually hinder the ion transport between fillers and exhibit a low ion permeation flux . Cation-exchange membranes (CEMs) with abundant cation-exchange sites, such as sulfonated polyether ether ketone (SPEEK), usually exhibit a fast ion permeation rate but low ion selectivity . Besides, the cations could prefer to transport through the CEM matrix but not the filler phase.…”

“…9 Cationexchange membranes (CEMs) with abundant cation-exchange sites, such as sulfonated polyether ether ketone (SPEEK), usually exhibit a fast ion permeation rate but low ion selectivity. 22 Besides, the cations could prefer to transport through the CEM matrix but not the filler phase. Particularly, anion-exchange membranes (AEMs) with a high anion conductivity could also be used for the separation of cations by the diffusion dialysis (DD) method, such as H + /Fe 2+ separation in acid recovery.…”