Solvent-dependent electrochemical performance of UPyMA–PETEA supramolecular gel polymer electrolytes for lithium–oxygen batteries

Abstract

Supramolecular gel polymer electrolytes (SGPEs) based on UPyMA and PETEA were prepared with 1 M LiTFSI and 10 wt% TTE using sulfolane, dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMA), or N,N-dimethylformamide (DMF) as the solvent. Structural characterization supported polymer formation and retention of the UPy hydrogen-bonding motifs. The solvent-dependent physicochemical and electrochemical characteristics of the formulations were compared by thermal analysis, viscosity measurements, electrochemical characterization, and Li–O2 cell testing. Among the tested SGPEs, the sulfolane-based formulation exhibited the highest apparent anodic oxidation onset, approximately 5.5 V vs. Li/Li+ under the employed linear-sweep voltammetry conditions. At 0.05 mA cm−2, the DMSO-based cell delivered a full-discharge capacity of 3135 mAh g−1, compared with 2133 mAh g−1 for the sulfolane-based cell. In contrast, under capacity-limited cycling at 500 mAh g−1, the sulfolane-based cell showed the longest cycling among the tested formulations, with the reported trace maintaining discharge capacities above 400 mAh g−1 through 30 cycles. Post-cycling FE-SEM and XRD revealed cathode deposits and changes in detectable crystalline products between discharge and charge. These results demonstrate divergent solvent-dependent performance within a common SGPE framework: DMSO favored full-discharge capacity, whereas sulfolane favored extended capacity-limited cycling under the tested conditions. The findings highlight that maximizing discharge capacity and sustaining repeated cycling represent distinct considerations in solvent selection for Li–O2 SGPEs.