Ion-Selective Membrane Derived from Ionic Block Copolymers with Controlled Nanostructure for Non-Aqueous Redox Flow Batteries

The Department of Energy is seeking the development of innovative ion-selective membranes for advanced electrochemical energy storage systems. Non-aqueous redox flow batteries are of particular interest for their potential in grid-scale energy storage. However, the membrane used in these batteries are mainly adopted from other commercial processes, such as fuel cells, lithium-ion batteries, and desalination processes. Existing membranes are limited in stability, selectivity, and compatibility, which significantly hinders non-aqueous redox flow battery development. During the proposed project, the company will develop an innovative nanophase-separated ion- selective membrane for non-aqueous redox flow batteries based on a carefully designed block copolymer, taking advantage of its highly controllable and versatile chemistry. The membrane will provide: (1) reliability and stability, resisting swelling and degradation, (2) high ionic conductivity for enhanced electrochemical performance, and (3) excellent ion-selectivity to prevent unwanted crossover minimizing self-discharging. Our systematic study of block copolymer synthesis, and the fabrication and testing of the membrane will promote in-depth understanding of the structural-property relationship for redox flow battery membranes and expand the application of the polymer and membranes to various energy storage systems. In Phase I, the project team will develop the polyelectrolyte-containing membrane for non- aqueous redox flow battery systems. Polyelectrolyte and copolymer components will be screened to determine the optimal membrane composition. Then the nanodomain size and structure will be engineered to boost membrane performance at full cell level. The fabrication process and the physical, chemical and electrochemical performance will be characterized and evaluated to demonstrate feasibility and better understand the structural-property relationship. The proposed membrane could potentially remove a bottleneck to commercializing advanced energy storage systems, especially non-aqueous redox flow batteries. In addition, the in-depth understanding on the structure-property relationship and nanodomain control of the membrane could have broader impacts for the development of other membranes for various energy related applications: aqueous and non-aqueous redox flow batteries with different chemistries; other storage systems (e.g., lithium ion, sodium ion and magnesium ion batteries); and energy conversion systems (e.g., fuel cells and solar fuel generation).