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

Redox flow batteries (RFBs) based on lithium polysulfide (Li-PS) chemistry present great opportunities for largescale 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.

Automated summary

Redox flow batteries (RFBs) based on lithium polysulfide (Li-PS) chemistry offer great opportunities for large-scale energy storage and electric vehicles due to abundant raw materials and higher energy density. The novel multifunctional electrochemical membrane (mECM) with high Li+/PS ion selectivity provides stable electrochemical performance and significantly enhanced capacity retention compared to traditional commercial separators. This suggests that mECM is a promising membrane separator for developing high-performance Li-PS RFB systems.