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Abstract This report describes the status of advanced redox flow battery research being performed at Pacific Northwest National Laboratory for the U.S. Department of Energy’s Energy Storage Systems Program. In FY16 we target a redox flow battery system operating with 25% increased current density over FY15 targets. The redox flow battery system will be developed and designed to maximize the stack energy efficiency at 400 mA/cm2. A prototype kW scale system will be demonstrated to show the targeted improvements in performance. Cost projections for a 1 MW/ 4 MWh commercial system will be based on the performance and materials used in the demonstration stack. • Target reached: A 3-cell redox flow battery was constructed and tested using the all vanadium mixed acid electrolyte developed under the OE program. The 3-cell stack was operated at 400 mA/cm2, a 25% increase over the FY15 target (320 mA/cm2). A thinner, lower resistant membrane, Nafion NR-211, was utilized along with a new monolithic bipolar plate design with an interdigitated flow pattern. Both additions to the FY16 stack improved performance and lowered the cost of the stack design. The resulting 3-cell stack exceeded target metrics by achieving an average power of 1.1 kW and a stack energy efficiency of ~ 74% when operated at 400 mA/cm2. The prototype stack maintained similar stack energy efficiency (~74%) in comparison to FY15 targets. The system cost for a commercial 1MW/4MWh redox flow battery system is projected to be ~$290/kWh for the all vanadium mixed acid electrolyte. Q1 Milestone: Evaluate performance of existing redox flow battery technology at 400 mA/cm2 and determine efficiency/performance tradeoffs. • Milestone completed. A single cell with active area of 780 cm2 was constructed using the FY15 design and evaluated at 25% greater current density (400 mA/cm2) to determine the impact on the stack energy efficiency. When operated at the FY15 current density target of 320 mA/cm2, the stack energy efficiency was ~75% with a flow rate of 800 cc/min/cell and a temperature of 35°C. The stack energy efficiency was decreased by ~ 5% at the same flow rate and temperature when the current density was increased to 400mA/cm2. The pressure drop was maintained below 10 psi and was nearly identical for both current densities evaluated. Optimization of components will be further investigated in FY16 to increase the stack energy efficiency at 400 mA/cm2. Q2 Milestone: Complete evaluation of experimental 3-cell stacks with component improvements to improve stack performance at higher current density. 3PDF Image | High Current Density Redox Flow Batteries
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