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With the continuous advancement of electrodialysis (ED) technology, there arises a demand for improved monovalent cation exchange membranes (CEMs). However, limitations in membrane materials and structures have resulted in the low selectivity of monovalent CEMs, posing challenges in the separation of Li + and Mg 2+ . In this investigation, a designed CEM with a swelling-embedded structure was created by integrating a polyelectrolyte containing N-oxide Zwitterion into a sulfonated poly(ether ether ketone) (SPEEK) membrane, leveraging the notable solubility characteristic of SPEEK. The membranes were prepared by using N-oxide zwitterionic polyethylenimine (ZPEI) and 1,3,5-benzenetrlcarbonyl trichloride (TMC). The as-prepared membranes underwent systematic characterization and testing, evaluating their structural, physicochemical, electrochemical, and selective ED properties. During ED, the modified membranes demonstrated notable permeability selectivity for Li + ions in binary (Li + /Mg 2+ ) systems. Notably, at a constant current density of 2.5 mA cm -2 , the modified membrane PEI-TMC/SPEEK exhibited significant permeability selectivity ( P Mg 2 + Li + = 5.63 ) in the Li + /Mg 2+ system, while ZPEI-TMC/SPEEK outperformed, displaying remarkable permeability selectivity ( P Mg 2 + Li + = 12.43 ) in the Li + /Mg 2+ system, surpassing commercial monovalent cation-selective membrane commercial monovalent cation-selective membrane (CIMS). Furthermore, in the Li + /Mg 2+ binary system, Li + flux reached 9.78 × 10 -9 mol cm -2 s -1 for ZPEI-TMC/SPEEK, while its Mg 2+ flux only reached 2.7 × 10 -9 mol cm -2 s -1 , showing potential for lithium-magnesium separation. In addition, ZPEI-TMC/SPEEK was tested for performance and stability at high current densities. This work offers a straightforward preparation process and an innovative structural approach, presenting methodological insights for the advancement of lithium and magnesium separation techniques.

Ion-conductive polymers having a well-defined phase-separated structure show the potential application of separating mono- and bivalent ion separation. In this work, three side-chain-type poly(arylene ether sulfone)-based anion exchange membranes (AEMs) have been fabricated to investigate the effect of the stiffness of the polymer backbone within AEMs on the Cl - /NO 3 - and Cl - /SO 4 2- separation performance. Our investigations via small-angle X-ray scattering (SAXS), positron annihilation, and differential scanning calorimetry (DSC) demonstrate that the as-prepared AEM with a rigid benzimidazole structure in the backbone bears subnanometer ion channels resulting from the arrangement of the rigid polymer backbone. In particular, SAXS results demonstrate that the rigid benzimidazole-containing AEM in the wet state has an ion cluster size of 0.548 nm, which is smaller than that of an AEM with alkyl segments in the backbone (0.760 nm). Thus, in the electrodialysis (ED) process, the former exhibits a superior capacity of separating Cl - /SO 4 2- ions relative to latter. Nevertheless, the benzimidazole-containing AEM shows an inability to separate the Cl - /NO 3 - ions, which is possibly due to the similar ion size of the two. The higher rotational energy barrier (4.3 × 10 -3 Hartree) of benzimidazole units and the smaller polymer matrix free-volume (0.636%) in the AEM significantly contribute to the construction of smaller ion channels. As a result, it is believed that the rigid benzimidazole structure of this kind is a benefit to the construction of stable subnanometer ion channels in the AEM that can selectively separate ions with different sizes.

Binder, as one of the key components, plays a crucial role in improving the capacity and cycling performance of lithium-sulfur (Li-S) batteries. In this work, commercially available, low-cost, water-soluble polyvinyl alcohol (PVA) has been systematically investigated as a functional polymer binder for high-sulfur-loading cathodes, with the aim of enhancing sulfur utilization, reducing capacity decay, and extending cycling life of the cathodes. In comparison with polyvinylidene fluoride as a conventional binder, PVA shows a valuable polysulfide entrapping ability and a much stronger binding strength. Its superior polysulfide entrapping ability has been verified through theoretical density functional theory calculations and an experimental ex situ adsorption study. In electrochemical Li-S battery performance evaluation, at a sulfur loading density of 3.5 mg cm -2 , the sulfur cathode assembled with the PVA binder displays at 0.5 C a very slow capacity decay of only 0.010% per cycle over 250 cycles. Additionally, the strong binding strength of PVA allows the fabrication of thick sulfur cathodes with a high sulfur loading density of 10.5 mg cm -2 , which shows a high areal capacity of 4.0 mA h cm -2 and a high cycling stability (capacity decay of 0.1% per cycle). In consideration of the superior capacity retention and cycling performance of its enabled cathodes, the cost-effective PVA is a promising candidate for high-sulfur-loading cathodes in practical applications., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

Surface modification has been proven to be an effective approach for ion exchange membranes to achieve separation of counterions with different valences by altering interfacial construction of membranes to improve ion transfer performance. In this work, we have fabricated a series of novel cation exchange membranes (CEMs) by modifying sulfonated polysulfone (SPSF) membranes via codeposition of mussel-inspired dopamine (DA) and 4'-aminobenzo-15-crown-5 (ACE), followed by glutaraldehyde cross-linking, aiming at achieving selective separation of specific cations. The as-prepared membranes before and after modification were systematically characterized in terms of their structural, physicochemical, electrochemical, and electrodialytic properties. In the electrodialysis process, the modified membranes exhibit distinct perm selectivity to K + ions in binary (K + /Li + , K + /Na + , K + /Mg 2+ ) and ternary (K + /Li + /Mg 2+ ) systems. In particular, at a constant current density of 5.0 mA·cm -2 , modified membrane M-co-0.50 shows significantly prominent perm selectivity [Formula: see text] in the K + /Mg 2+ system and M-co-0.75 exhibits remarkable performance in the K + /Li + system [Formula: see text], superior to commercial monovalent-selective CEM (CIMS, [Formula: see text], [Formula: see text]). Besides, in the K + /Li + /Mg 2+ ternary system, K + flux reaches 30.8 nmol·cm -2 ·s -1 for M-co-0.50, while it reaches 25.8 nmol·cm -2 ·s -1 for CIMS. It possibly arises from the effects of pore-size sieving and the synergistic action of electric field driving and host-guest molecular recognition of ACE and K + ions. This study can provide new insights into the separation of specific alkali metal ions, especially on reducing influence of coexisting cations K + and Na + on Li + ion recovery from salt lake and seawater.