Abstract
Aqueous redox flow batteries (ARFBs) are a promising technology for large-scale energy storage. Developing high-capacity and long-cycle negolyte materials is one of major challenges for practical ARFBs. Inorganic polysulfide is promising for ARFBs owing to its low cost and high solubility. However, it suffers from severe crossover resulting in low coulombic efficiency and limited lifespan. Organosulfides are more resistant to crossover than polysulfides owing to their bulky structures, but they suffer from slow reaction kinetics. Herein, we report a thiolate negolyte prepared by an exchange reaction between a polysulfide and an organosulfide, preserving low crossover rate of the organosulfide and high reaction kinetics of the polysulfide. The thiolate denoted as 2-hydroxyethyl disulfide+potassium polysulfide (HEDS+K 2 S 2 ) shows reduced crossover rate than K 2 S 2 , faster reaction kinetics than HEDS, and longer lifespan than both HEDS and K 2 S 2 . The 1.5 M HEDS+1.5 M K 2 S 2 static cell demonstrated 96 Ah L -1 negolyte over 100 and 200 cycles with a high coulombic efficiency of 99.2% and 99.6% at 15 and 25 mA cm -2 , respectively. The 0.5 M HEDS+0.5 M K 2 S 2 flow cell delivered a stable and high capacity of 30.7 Ah L -1 negolyte over 400 cycles (691 h) at 20 mA cm -2 . This study presents an effective strategy to enable low-crossover and fast-kinetics sulfur-based negolytes for advanced ARFBs.
Highlights
The redox flow batteries (RFBs) are a promising energy storage technology owing to the decoupled power and energy, high scalability, and high safety compared to commercial Li-ion batteries [1,2,3,4,5,6,7,8]
Sulfur-containing materials receive remarkable attention in both aqueous [9,10,11,12,13] and nonaqueous flow systems [14,15,16,17,18,19,20,21] owing to their low cost and high solubility compared with vanadium-based flow battery [22,23,24,25]
We report a thiolate negolyte prepared by an exchange reaction between a polysulfide and an organosulfide for aqueous RFBs, preserving low crossover rate of the organosulfide and high reaction kinetics of the polysulfide
Summary
The redox flow batteries (RFBs) are a promising energy storage technology owing to the decoupled power and energy, high scalability, and high safety compared to commercial Li-ion batteries [1,2,3,4,5,6,7,8]. Previous studies have shown some effective methods to alleviate polysulfide crossover and improve coulombic efficiency. Gao et al [13] reported that CuS was deposited on graphite felt electrode using successive ionic layer adsorption and reaction method, which absorbs polysulfides and promotes the redox reaction of the polysulfides. Membrane engineering is another way to alleviate crossover of polysulfides. Li et al [10] and Ma et al [11] employed two layers of membranes (Nafion) to mitigate the crossover of polysulfides thereby improving coulombic efficiency. Gross and Manthiram [12] further applied a solid-electrolyte
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