The role of glass fiber separators on the cycling of zinc metal anodes

Aqueous zinc-ion batteries (AZIBs) have shown promising suitability for grid-scale energy storage due to their affordability, intrinsic safety, and environmental-friendliness. However, the commercialization of AZIBs has been hindered by the dissolution of the cathode and instabilities of the Zn metal anode. Researchers have worked to improve the cathode, anode, and electrolyte, but relatively little attention has been given to the glass fiber (GF) membrane often used as the separator. As such, we compare four commonly used GF membranes (Whatman™ GF/A, GF/B, GF/C, and GF/D) to examine the influence of their average pore size, nominal thickness, and the use of varying electrolyte quantities on the cycling of Zn|Zn symmetric cells. We found that a minimized average pore size improves Zn accumulated capacity by restraining Zn deposits from forming within the pores of the separator. Varying the electrolyte volume showed minimal influence on the Zn accumulated capacity, suggesting that limiting the electrolyte quantity to 75 μL can maximize a cell's energy density. In contrast, an increased separator thickness was found to increase the mean accumulated Zn capacity, but degrades cell-to-cell stability between trials. Finally, using micro-computed X-ray tomography (micro-CT) for post-characterization reveals the failure-inducing Zn dendrites, compositional changes of Zn metal with cycling, and improved Zn plating/stripping homogeneity with decreased pore size.