Abstract
The widespread utilization of nonaqueous redox flow batteries is hindered by the low performance. Including some kinds of additives in electrolyte is a possible and facile solution. In this chapter, the effects of carbon dioxide gas, EC/DMC, and antimony ions on the electrochemical performance of nonaqueous redox flow batteries are disclosed. The results show that the ohmic resistance of the deep eutectic solvent (DES) electrolyte reduces significantly when adding carbon dioxide gas and EC/DMC, the percentage of reduction increases with the volume percentage of EC/DMC in electrolyte, and the reaction kinetics almost keeps unchanged for carbon dioxide gas and EC/DMC additives. For the additive of antimony ions, the electrochemical reaction kinetics of active redox couple is enhanced, the diffusion coefficient of active ions also increases, and the charge transfer resistance decreases. The antimony ions electrodeposited on the surface of graphite felt contribute a catalytic effect on the electrochemical reaction so as to improve the performance. However, due to the trade-off between the enhanced kinetics and reduced active surface area, the optimum concentration of antimony ions is found to be 15 mM. In addition, the flow battery assembled with negative electrolyte containing antimony ions exhibits 31.2% higher power density than that of pristine DES electrolyte.
Highlights
Recent years, with the development of energy storage technology, people prefer to use the redox flow battery (RFB) in large-scale energy storage
The results indicate that when the concentration of SO2 increases, the viscosity of conventional ionic liquids will decrease sharply
For the pristine deep eutectic solvent (DES), the plot shows a semicircle in the high-frequency region, and in the low-frequency region, there is a straight line upward; the semicircle corresponds to the charge transfer reaction at the electrode/ electrolyte interface, and the straight line upward corresponds to the diffusion of iron species in the electrolyte, suggesting electrochemical reaction and diffusion steps mix-control the Fe(III)/Fe(II) redox reaction
Summary
With the development of energy storage technology, people prefer to use the redox flow battery (RFB) in large-scale energy storage. Organic solvents show potential safety hazards because of their volatility, toxicity, and flammability; moisture or oxygen contamination can adversely affect battery performance [6] To this point, some ionic liquids (ILs) have advantages to solve the problem. Ionic liquids have high thermal and electrochemical stability, and the conductivity is higher than aqueous electrolytes [7]. Because of these advantages, ILs have been applied to a lot of fields, such as lithium-ion batteries [8], dye-sensitized solar cells [9], electrolytes in sensors [10], electrochemical capacitors [11], lead acid batteries [12], and fuel cells [13], and even applied to flow batteries recently as electrolyte solutions [14]. The results here disclose an effective and convenient approach to improve the cell performance of nonaqueous redox flow batteries
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