Abstract
Redox flow batteries are receiving wide attention for electrochemical energy storage due to their unique architecture and advantages, but progress has so far been limited by their low energy density (~25 Wh l−1). Here we report a high-energy density aqueous zinc-polyiodide flow battery. Using the highly soluble iodide/triiodide redox couple, a discharge energy density of 167 Wh l−1 is demonstrated with a near-neutral 5.0 M ZnI2 electrolyte. Nuclear magnetic resonance study and density functional theory-based simulation along with flow test data indicate that the addition of an alcohol (ethanol) induces ligand formation between oxygen on the hydroxyl group and the zinc ions, which expands the stable electrolyte temperature window to from −20 to 50 °C, while ameliorating the zinc dendrite. With the high-energy density and its benign nature free from strong acids and corrosive components, zinc-polyiodide flow battery is a promising candidate for various energy storage applications.
Highlights
Redox flow batteries are receiving wide attention for electrochemical energy storage due to their unique architecture and advantages, but progress has so far been limited by their low energy density (B25 Wh l À 1)
It is generally believed that the energy density is not a critical performance criterion for stationary applications, the low energy density of flow-based batteries has largely excluded themselves from other energy storage market
Progress has been made to achieve high V value (42.0 V) through a variety of non-aqueous redox flow batteries (RFBs) designs[3], such as those based on all-organic active materials[9] and redox non-innocent ligands[10], the redox species concentration currently is limited to around 0.1 M or less resulting in an energy density o10 Wh l À 1, even for higher cell voltages
Summary
Redox flow batteries are receiving wide attention for electrochemical energy storage due to their unique architecture and advantages, but progress has so far been limited by their low energy density (B25 Wh l À 1). Flow-based electrochemical energy storage systems separate the energy storage and power generation by storing the electro-active species in externally flowing electrolytes (that is, the anolyte and catholyte), while maintaining the redox reactions at the electrode surface inside a stack[1,2]. This unique architecture permits the redox flow batteries (RFBs) to independently scale the power and/or energy—a characteristic advantage along with high safety coveted by the energy industry for intermittent renewable energy integration and other grid services[3]. Progress has been made to achieve high V value (42.0 V) through a variety of non-aqueous RFB designs[3], such as those based on all-organic active materials[9] and redox non-innocent ligands[10], the redox species concentration currently is limited to around 0.1 M or less resulting in an energy density o10 Wh l À 1, even for higher cell voltages
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