A Highly Ion‐Selective Zeolite Flake Layer on Porous Membranes for Flow Battery Applications

Abstract

Zeolites are crystalline microporous aluminosilicates with periodic arrangements of cages and well-defined channels, which make them very suitable for separating ions of different sizes, and thus also for use in battery applications. Herein, an ultra-thin ZSM-35 zeolite flake was introduced onto a poly(ether sulfone) based porous membrane. The pore size of the zeolite (ca. 0.5 nm) is intermediary between that of hydrated vanadium ions (>0.6 nm) and protons (<0.24 nm). The resultant membrane can thus be used to perfectly separate vanadium ions and protons, making this technology useful in vanadium flow batteries (VFB). A VFB with a zeolite-coated membrane exhibits a columbic efficiency of >99 % and an energy efficiency of >81 % at 200 mA cm(-2), which is by far the highest value ever reported. These convincing results indicate that zeolite-coated membranes are promising in battery applications.

Thin skinned asymmetric polybenzimidazole membranes with readily tunable morphologies for high-performance vanadium flow batteries

“…An ideal nonionic porous membrane in VFBs is expected to satisfy the following criteria: pore size should be proper to separate vanadium ions from protons to guarantee high ion selectivity; pores should be interconnected and porosity should be high enough to promote proton transport. 35 However, the sizes of the ions are so tiny (diameters of hydrated vanadium ions and protons are around 0.6 nm and 0.3 nm, respectively) [38][39][40] that it is difficult to precisely control the pore size and the membrane morphology (e.g., porosity and pore connectivity) to meet the requirements. 31,33,34,36,41,42 Recently, polybenzimidazoles (PBI) as membrane materials have attracted much attention in VFB applications.…”

Theoretical Investigation into Suitable Pore Sizes of Membranes for Vanadium Redox Flow Batteries

“…Membranes with anionic exchange groups showed good performance for VRB application . Excellent performance of the membranes with good pore size distribution on a nanoscale or even smaller level has been reported in VRB applications . It has been proven that the membranes with smaller pores (<5 Å) allow only hydrated ion transport based on a molecular dynamics study for various types of membranes .…”

“…Their main advantages are high energy efficiency, long cycle life, and reasonable costs . Global demand for VRBs is increasing year by year, but its commercial applications have been limited due to the high costs of the key materials, especially the ion‐exchange membranes (IEMs) …”

“…Over the past several years, researchers mainly focused on non‐fluorinated and partially fluorinated membranes with ion‐exchange groups due to their low cost and good conductivity, such as poly(vinylidene fluoride) (PVDF), polysulfone (PSF), poly(ether ether ketone) (PEEK), polybenzimidazole (PBI), etc. The conduction mechanisms of IEMs in VRBs is very complicated because of the diversity of electrolyte components, which in turn has great influence on the selection and preparation of IEMs . IEMs should prevent the cross‐over of positive and negative electrolyte ions (VO 2+ / and V 2+ /V 3+ , respectively), while they enable the transport of charge‐balancing ions such as H + , H 3 O + , and ) to complete the current circuit .…”

A Bunch-Like Tertiary Amine Grafted Polysulfone Membrane for VRFBs with Simultaneously High Proton Conductivity and Low Vanadium Ion Permeability

“…To address this challenge, several kinds of novel concept membranes have recently been fabricated for potential application in VRFBs. These membranes are based on the conducting proton and V‐blocking synergy design, such as the amphoteric ion exchange membrane and porous membranes . Although these membranes achieved superior ionic selectivity, the lower proton conductivity compared to PEMs and AEMs, and the heterogeneous pore size is still a challenge for large‐scale application in VRFBs …”