Thin-film composite membrane breaking the trade-off between conductivity and selectivity for a flow battery

Qing Dai,Chao Wang,Anmin Zheng,Qiang Fu,Zhiqiang Liu,Xianfeng Li,Ling Huang,Huamin Zhang,Yuyue Zhao

doi:10.1038/s41467-019-13704-2

Abstract

A membrane with both high ion conductivity and selectivity is critical to high power density and low-cost flow batteries, which are of great importance for the wide application of renewable energies. The trade-off between ion selectivity and conductivity is a bottleneck of ion conductive membranes. In this paper, a thin-film composite membrane with ultrathin polyamide selective layer is found to break the trade-off between ion selectivity and conductivity, and dramatically improve the power density of a flow battery. As a result, a vanadium flow battery with a thin-film composite membrane achieves energy efficiency higher than 80% at a current density of 260 mA cm−2, which is the highest ever reported to the best of our knowledge. Combining experiments and theoretical calculation, we propose that the high performance is attributed to the proton transfer via Grotthuss mechanism and Vehicle mechanism in sub-1 nm pores of the ultrathin polyamide selective layer.

Highlights

Large-scale energy storage is the key technology to solve the issues of intermittency and instability of renewable energies like wind power and solar energy
The ion selectivity is high and the conductivity of the Thin-film composite membranes (TFCMs) in 3 M H2SO4 far exceeds that of Nafion 115
This thin and compact layer with proper pore size can break the trade-off between ion conductivity and selectivity and achieve a dramatically improved performance for vanadium flow battery (VFB)

Summary

Introduction

Large-scale energy storage is the key technology to solve the issues of intermittency and instability of renewable energies like wind power and solar energy. According to our calculation and previous supports[17,18], the ultrathin polyamide selective layer owns very compact cross-linked structures and sub 1 nm pores, which are perfectly in-between the radius of hydrated vanadium ions (V) and protons (H). These sub 1 nm pores endow the ultrathin selective layer with high resistance to hydrated vanadium ions and low resistance to proton transfer, the TFCM can break the trade-off between the selectivity of V/H and the proton conductivity, and produce a VFB with super high power density

Methods

Results

Conclusion