Nafion/aquivion-based composite lithium ion exchange membranes for high capacity Li-S batteries

Abstract

Lithiated Nafion (Li-Naf) and lithiated Aquivion (Li-Aqu) ion exchange membranes are applied as electrolyte and separator to prevent the polysulfide shuttle effect in Li?S batteries. The production and characterization of Li-Naf, Li-Aqu, and their composites (2 : 1, 1 : 1, and 1 : 2; w/w) are carried out. The ion exchange capacity and polysulfide transition of the produced membranes are examined and structural characterizations are conducted via Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and field emission scanning electron microscopy (FESEM). CR2032 half cells are assembled in order to perform electrochemical analysis. The electrochemical performances of the membranes are investigated by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge tests. Due to the low equivalent weight of Aquivion, the ion exchange capacity and ionic conductivity of the membrane enhance with the increasing amount of Li-Aqu in the composite membrane. Because of the synergistic effect of Nafion and Aquivion, Li-Naf : Li-Aqu/1 : 2 composite offers 61.2 % capacity retention and the best electrochemical discharge capacity of 826 mAhg?1 after 100 charge-discharge cycles. As a result, Nafion and Aquivion composite membranes can successfully inhibit the shuttle movement of negatively charged polysulfide species while allowing the transition of positively charged lithium ions for high performed Li?S batteries.