Pendent Persubstituted Imidazolium and a Polyimidazolium Cross-Linked Polymer as Robust Alkaline Anion Exchange Membranes for Solid-State Zn-Air Batteries

Alkaline anion exchange membranes (AEMs) were developed from a series of persubstituted imidazolium cations with varying alkyl chains (Im-nC, nC = (CH2)(n-1)CH3; n = 4, 12, and 16) tethered on poly(vinylbenzyl chloride-co-acrylonitrile) (PVC-co-AN) to prepare a comb-shaped polymer membrane (M1-nC) and a cross-linked polymer membrane from polyimidazolium cations and PVC-co-AN (M3). The PVC-co-AN polymer backbone shows high stability after curing, and the water uptake and swelling ratio are controlled by varying the alkyl chain length in M1-nC even with temperature variation. Results show that M1-16C retains the highest ion exchange capacity (IEC) of 95% among the M1-nC series of membranes after exposure to 1 M KOH solution at 80 degrees C for 30 days. However, the longer alkyl chains hindered the interconnected ion channels limiting the hydrophobic/hydrophilic phase separation and the hydroxide ion conductivity. Meanwhile, M3 exhibits a distinct microphase-separated morphology and a high ionic conductivity of 54.5 mS/cm for a 2.02 IEC with high stability to retain an IEC of 97% after storage in 1 M KOH solution at 80 degrees C for 30 days. In addition, all the AEMs exhibit high oxidation stability and retain >96% weight after immersion into 4 ppm Fenton's reagent at 80 degrees C. Moreover, the flexible solid-state zinc-air batteries comprising an M3 membrane displayed a peak power density of 165 mW cm(-2) and superior cycling stability (30 h at 10 mA cm(-2)) demonstrating very promising applications in solid-state flexible rechargeable Zn-air batteries.

Automated summary

A series of novel alkaline anion exchange membranes (AEMs) have been developed with high stability and ionic exchange capacity (IEC), demonstrating promising applications in solid-state flexible rechargeable Zn-air batteries. The membranes show controlled water uptake and swelling ratio by adjusting the alkyl chain length, while longer chains hinder ion channel connectivity and phase separation affecting hydroxide ion conductivity. Additionally, the membranes exhibit high oxidation stability and retention rate after exposure to harsh conditions, showcasing their potential for long-term battery performance.