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Low Cost, Optimized Redox Flow Battery Electrolytes, Novel Solid Ionic Conducting Membranes, and Rechargeable Air-Breathing Cathodes for Batteries for Stationary Storage


The projected doubling of world energy consumption within the next 50 years, along with resource constraints and environmental concerns about using fossil fuels , have spurred great interest in generating electrical energy from renewable sources such as wind and solar. The variable and stochastic nature of renewable sources, however, makes solar and wind power difficult to manage, especially at high levels of penetration. To effectively use the intermittent renewable energy and enable its delivery demand electrical energy storage (EES). For example, storage operating near an intermittent, renewable wind energy source can smooth out wind variability, lessen the slope on ramp rates, and, at sufficient scale, can store off peak wind energy. EES is also an effective tool to improve the reliability, stability, and efficiency of the future electrical grid, i.e. smart grid that enables real-time, two-way communication to balance demand and generation and supports plug-in electrical vehicles. Electrical energy storage can shave peaks from a user or utility load profile, increase asset utilization by improving duty factor and delaying utility upgrades, decrease fossil fuel use for ancillary services, provide high levels of power quality, and increase grid stability. Distributed energy storage near load centers can reduce congestion on both the distribution and transmission systems.

Among the most promising electrical storage technologies are redox flow batteries (RFBs) and sodium (Na) batteries. RFBs have the advantage of allowing separationof power and energy. The power (kW) of the system is determined by the size of the electrodes and the number of cells in a stack, whereas the energy storage capacity (kWh) by the concentration and volume of the electrolyte. Varied RFBs have been developed, including the all vanadium redox flow batteries (VRBs) that have recently demonstrated operation at multi-MWs with unlimited cycle life. The use of abundant, low cost Na makes the Na-batteries attractive to further cost reduction for the grid applications. Sodium batteries typically come with either a polysulfide or metal halide cathode. Both deliver good performance but at high capital and levelized costs (>$3,000/kW and >30ยข/kWh, respectively). One of the major cost drivers for sodium batteries is the solid-state electrolyte membrane, while for VRBs the cost is attributed to the electrolyte. Finally, the ultimate in low-cost, high energy density energy storage are the metal-air systems, which have been demonstrated in the laboratory but suffer from drastically limited cycle life and low efficiency at the discharge and recharge cathode half-reactions.

Particularly sought this year are research efforts related to novel, high performance and low-cost electrolytes in RFBs, high conductivity solid-state electrolyte membranes either for sodium or for other abundantly available lightweight multivalent cation systems (e.g., aluminum or magnesium), and technologies with promise to extend the life of metal-air cathodes to thousands of cycles at low cost and high cycle efficiencies.

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