High-Performance Non-Aqueous Redox Flow Batteries at Pnnl

With the potential applications in power grid stabilization, redox flow battery has been widely considered as a promising large- and middle-scale stationary energy storage technology. The cell architecture enables separation of the energy capacity and power rating, offering excellent scalability and tremendous design flexibility to meeting different energy-to-power ratio requirements. Traditional aqueous flow batteries have been extensively developed, but the limited voltage window narrows down the intrinsic capacity to achieve high energy density. Therefore, alternative nonaqueous redox flow techniques are rapidly emerging because of their wider voltage window that has a direct impact on the energy density. Currently, the primary focus of the nonaqueous flow research is on the flow chemistry study. Most of these efforts use organic electroactive materials taking advantage of the structural diversity and tunability.¹

Here we update the flow battery community with our recent development in nonaqueous flow chemistries. The first type is the hybrid lithium-organic flow battery, which uses Li-based anode and organic catholyte materials including ferrocene and TEMPO.^2,3 High solubilities in the supporting carbonate electrolytes were obtained to TEMPO (2M) and structurally modified ferrocene (0.8M). Taking advantage of the low potential of the Li anode, cell voltages of ~3.5V were achieved. Consequently, these flow cells delivered high volumetric energy densities of 50Wh/L for ferrocene and 126Wh/L for TEMPO, respectively.

Because of the limitations of the Li anode, organic anolyte materials were explored coupled with another organic catholyte material in the second type. Cell voltages of >2V were obtained in these total-organic flow batteries. Electrolyte optimization was performed to achieve improved cycling stability and gain mechanistic understandings of capacity fading. The flow cell tests demonstrated remarkable cell efficiencies and high operational current densities that exceed those of most reported non-aqueous flow chemistries.

References

                (1)           Wang, W.; Luo, Q. T.; Li, B.; Wei, X. L.; Li, L. Y.; Yang, Z. G. Advanced Functional Materials 2013, 23, 970.

                (2)           Wei, X.; Cosimbescu, L.; Xu, W.; Hu, J. Z.; Vijayakumar, M.; Feng, J.; Hu, M. Y.; Deng, X.; Xiao, J.; Liu, J.; Sprenkle, V.; Wang, W. Adv Energy Mater 2014.

                (3)           Wei, X.; Xu, W.; Vijayakumar, M.; Cosimbescu, L.; Tianbiao, L.; Sprenkle, V.; Wang, W. Adv Mater 2014.