Self-Cross-linking Nanocomposite Membranes for Green Recycling of the Solvent during Lithium-Ion Battery Manufacturing

Abstract

Polyvinyl alcohol (PVA)/CNT composite membranes were prepared without adding cross-linkers; herein, carboxylated CNTs served as alternative cross-linkers. A molecular simulation confirmed the cross-linking capability between CNTs and PVA chains, which led to the prediction that the cross-linked PVA/CNT complex would be stable in water. To realize the simulated outcome, the multiwalled CNTs were activated and functionalized via sonication methods and subsequent acid treatment. The PVA/CNT composite membranes, including the CNTs treated by probe sonication, exhibited sufficient stability against dissolution in water at 80 °C when the CNT loading reached 1.5 wt %, thus substantiating the proposed idea. The composite membranes exhibited a high separation performance for green recycling of 1-methyl-2-pyrrolidone (NMP) during manufacturing of lithium-ion batteries (LIBs). Long-term operations using membranes with 1.5 wt % CNTs also exhibited a steady combination of total flux and water/NMP selectivity of approximately 0.06 kg/m2·h and 3500, respectively. Thus, the membranes developed here and the corresponding NMP dehydration performance could contribute to increasing the sustainability of the LIB manufacturing industry.

Nanostructural Engineering of Electrospun Poly(vinyl alcohol)/Carbon Nanotube Mats into Dense Films for Alcohol Dehydration

“…Figure c shows the images of dense PVA/CNT films after 10 min of water treatment and subsequent annealing at 130 °C. According to the literature, annealing was performed to cross-link the PVA chains with CNTs . As shown in Figure c, an almost transparent film was obtained for the PVA/CNT film with 0.1 wt % CNT loading, indicating that porous structures that scatter visible light collapsed into the dense film .…”

“…All of the membranes possessed a higher DS in water than in ethanol due to their hydrophilic nature . The DS gradually decreased with more CNT loading, where the PVA/CNT films became tightly packed and less hydrophilic because of a high degree of cross-linking . However, as shown in Table S2, although the electrospun PVA/CNT films had better CNT dispersion, their degree of swelling was insignificant compared to that of the solution-cast films.…”

“…Measuring the pervaporation of PVA/CNT membranes with CNT loading above 2.0 wt % was not possible because the membranes were brittle and tended to crack and cleave during operation. In the PVA/CNT composite films prepared from the conventional approach, the film with 2.0 wt % CNT loading exhibited high stability in pervaporation operation Figure b–d shows the ethanol dehydration performance by PVA/CNT membranes.…”

“…The samples were dried at 60 °C for 24 h. Finally, the membranes were placed in a convection oven at 130 °C for 4 h to allow the cross-linking between PVA and CNTs. For comparison, a PVA/CNT composite membrane was also prepared through a conventional solution-casting method …”

“…Electrospun mats were then prepared using pure PVA and PVA/CNT mixture solutions. CNTs were used both as a nanofiller and a cross-linker because pure PVA membranes are unstable in water-based separation processes and typically exhibit low liquid permeation in pervaporation operations . Alcohols and water were used as nonsolvents and solvent, respectively, for the interfacial engineering of the PVA/CNT electrospun mats into dense membranes.…”