Redox Flow Battery Cost Modeling: Bridging Techno-Economic Analysis to Materials Selection Criteria

Growing adoption of renewable energy technologies, combined with a desire to improve electrical grid efficiency, is driving the development of grid-scale energy storage devices. Redox flow batteries (RFBs) offer an attractive solution to grid-scale storage due to independent scaling of power and energy, long service life, and simple manufacturing. 1 Despite these attractive features, RFBs have failed to reach widespread deployment due to high prices; in 2014, RFB prices exceeded $500 kWh -1 . 2 The United States Department of Energy (DOE) has established that decreasing RFB system price (including the battery, inverter, and installation) to below $150 kWh -1 , in the near-term, could enable market penetration for 2 – 4 h grid-scale discharge applications. 3 Despite existing high prices, recent studies indicate that RFBs could achieve the aggressive DOE target by minimizing reactor and materials costs. 2 Techno-economic modeling provides a powerful tool for evaluating the price performance of energy storage systems by relating system price to materials properties, electrochemical performance, and component cost parameters. Prior techno-economic studies on RFBs have considered cost reductions afforded by decreasing manufacturing costs 2,4,5 and improving reactor performance, 6 but no studies systematically evaluate cost and performance tradeoffs from varying electrolyte materials selection. To address this literature gap, we develop a techno-economic model that accounts for the reactor, electrolyte, balance-of-plant, and additional cost contributions to RFB price. In particular, a detailed electrolyte cost model, accounting for the constituent active material, salt, and solvent costs, allows for cost-driven electrolyte materials selection. After solidifying the techno-economic model, we quantify cost constraining variables for both aqueous (Aq) and nonaqueous (NAq) RFBs, which span a broad design space with a wide array of materials options. AqRFBs take advantage of low area specific resistance (ASR) cells and inexpensive electrolytes employing water as the solvent and inorganic salts (e.g., H 2 SO 4 , NaCl). One drawback to AqRFBs is that the typical electrochemical stability window of aqueous electrolytes (≤ 1.5 V) limits energy density. Contrastingly, NAqRFBs offer the possibility of much higher energy densities by utilizing nonaqueous solvents with wide electrochemical windows (3 – 4 V), but suffer from high solvent and salt costs, as well as high react