Poly(ionic liquid) membranes preserving liquid crystalline microstructures for lithium-ion enrichment

The combination of membrane separation technology and hydrometallurgy has opened up new possibilities for the recovery and recycling of lithium from ever-growing spent lithium-ion batteries. Herein, we prepared a series of positively charged poly(ionic liquid) membranes preserving liquid crystal mesophases and investigated the monatomic ion separation capacity of the liquid crystalline membranes by diffusion dialysis experiments using the simulative spent battery leachate. The results revealed that liquid crystalline membranes with bicontinuous cubic liquid crystal structure possessed great potential as precise ion separation membranes for lithium-ion enrichment. Compared to the other topological structures, the bicontinuous cubic liquid crystal structure enhanced both the Li+ flux and ion selectivity of the membranes. The ion flux of the membrane with this structure was three times higher than that of amorphous membranes. Meanwhile, the Li+/Ni2+ selectivity was up to 7.40, which was significantly higher than that of hexagonal liquid crystalline membranes (2.59) and commercial membranes AMI-7001S (5.71). Moreover, the preservation of liquid crystal structures obviously improved the water management capacity and mechanical strength of the membranes.