High-efficient multifunctional electrochemical membrane for lithium polysulfide redox flow batteries

Abstract

Redox flow batteries (RFBs) based on lithium polysulfide (Li-PS) chemistry present great opportunities for large-scale energy storage and electric vehicles because of their use of abundant raw materials and their higher energy density compared with traditional flow batteries. However, to successfully implement Li-PS RFBs, issues related to the crossover of PS species through a membrane separator must be resolved. In this work, we demonstrate a facile method for fabricating a novel multifunctional electrochemical membrane (mECM) consisting of an organic ion exchange membrane reinforced with a porous carbon nanotube layer and a boron nitride layer. This rational design endows the membrane with remarkable ion selectivity and dimensional stability in organic electrolyte, leading to a greatly enhanced Li+/PS ion selectivity, which exceeds that of a commercial polyolefin separator (i.e., Celgard 2325) by three orders of magnitude. A Li-PS RFB with the mECM exhibited stable electrochemical performance (0.05% capacity decay per cycle after 40 cycles) with 78% capacity retention over 100 cycles at 0.75C, while a reference cell with a Celgard 2325 membrane rapidly lost its capacity (0.33% capacity decay per cycle and 33% capacity at 100 cycles). Our results strongly suggest that the mECM with its high Li+/PS ion selectivity is a promising membrane separator for developing high-performance Li-PS RFB systems.