Fikile Brushett

Abstract:

Robust, scalable and low cost stationary energy storage is needed to stabilize the electric grid against the intermittency common to solar and wind-generated power, thus improving grid reliability and thereby enabling the broader use of renewable resources. Redox flow batteries are well-suited to storing megawatt-hours of electrical energy that is meant to be discharged over the course of hours. While a large number of aqueous flow batteries have been developed, a number of technical and economic challenges have prevented widespread commercial success. Transitioning from aqueous to non-aqueous electrolytes offers a wider window of electrochemical stability that enables operation at higher cell voltage (> 4 V) leading to higher energy density. Moreover, a greater selection of redox materials may be available due to either the wider potential window or the variety of non-aqueous solvents. Together, these benefits promise to reduce the cost of energy as well as to shrink the system footprint, enabling storage in confined spaces. However, this promise must be balanced with the challenges associated with non-aqueous electrolytes including increased solvent cost, reduced ionic conductivity and other undesirable physical properties. Furthermore, as compared to their aqueous counterparts, non-aqueous flow batteries are in their infancy and many unknowns still exist. Understanding and balancing these competing factors will be key to determining the true prospects for non-aqueous flow batteries. Here, we will present the challenges and opportunities in the science and engineering of non-aqueous flow batteries capable of meeting US Department of Energy established grid storage costs. Specifically, we will describe system-level techno-economic analyses which yield materials-level benchmarks to guide molecular discovery. We will then highlight the development of several promising new materials which begin to lay a credible pathway to low cost electrochemical technologies.