Multi-Functional Metal/Ceramic Separators for Nonaqueous Redox Flow Batteries

Redox flow batteries (RFBs) are considered one of the most promising electrochemical technologies for the large-scale storage of renewable electrical energy. They can store large amount of energy up to megawatt-hours (MWh). Despite of the tremendous success, however, RFBs employing aqueous electrolytes are fundamentally limited by the narrow electrochemical window of water leading to low cell voltages energy density. By contrast, nonaqueous RFBs with organic electrolytes offer much wider electrochemical window (e.g., over 5 V) and potentially higher solubility for redox compounds, both of which can lead to high energy density. As a critical component in RFB, the separator with highly selective Li+ ion conductivity is an “enabler” of nonaqueous RFBs. Polymeric ion exchange membranes suffer from low ionic conductivity, redox organic-active material (ROM) crossover, and/or membrane fouling by ROM entrapment. Porous separators have high conductivity but limited selectivity causing irreversible ROM crossover and capacity decay. Dense ceramic separator is a promising option to achieve absolute permselectivity and zero ROM crossover in nonaqueous RFBs but suffer from limited mechanical properties. These drawbacks bring significant challenges for delivering high power density and reliable RFB assembly and operations. Therefore, increasing the Li+ conductivity and mechanical strength is the most critical need for ceramic separators to enable high-power, stable nonaqueous RFBs. Storagenergy Technologies Inc. (Storagenergy) and Indiana University - Purdue University Indianapolis (IUPUI) will continue R&D efforts to enable commercial supported ceramic separators for high energy efficiency, high power, and long cycling life nonaqueous RFBs. As the number of generation sources from intermittent renewable technologies on the electric grid increases, the need for large-scale electrical energy storage devices is becoming essential to ensure grid stability and sustainability. Solid-electrode batteries maintain discharge at peak power for far too short a time to fully regulate wind or solar power output. In contrast, RFBs offer an advantage over conventional batteries, as their energy and power can be scaled independently by maintaining all of the electro-active species in fluid form. The successful development of this technology will enable a new family of American batteries of all scales for both commercial and government sectors. And, finally, this technology will serve to re-establish the U.S. technological lead in batteries that has migrated overseas.