Low-Temperature, High Energy Density Non-Aqueous Redox Flow Battery

Redox flow battery (RFB) is a well-known storage technology. Commercial RFBs are based on aqueous electrolytes, but also several organic electrolytes are evaluated. Organic solvents provide a number of advantages due to their physicochemical properties, such as a wider operating temperature window and a wider stable potential window. Limiting factor in these systems is the solubility of the redox-active species.

In our study the solubility of vanadium(III) acetylacetonate as redoxactive species and tetrabutylammonium hexafluorophosphate as supporting electrolyte were investigated in a ternary solvent mixture containing acetonitrile, 1,3-dioxolane and dimethyl sulfoxide. The solubility could be almost doubled compared to the well-known acetonitrile system [1]. Furthermore the non-aqueous redox flow battery demonstrated good performance at -25°C (Figure 1).

Further studies to improve the solubility of redox-active species and to optimize battery tests are still under research.

Figure 1: Energy efficiency (EE) and coulombic efficiency (CE) of the V(acac)₃ RFB in acetonitrile-1,3-dioxolane-dimethyl sulfoxid solvent mixture at -25°C. 

Literature:

[1] Shinkle, A. A.; Sleightholme, Alice E. S.; Griffith, L. D.; Thompson, L. T.; Monroe, C. W., Journal of Power Sources 206 (2012) 490–496.