A Novel Safe and Ultrahigh-Energy-Density Aqueous Redox Flow Battery System

Redox flow batteries (RFBs), as one of the most promising electrical energy storage systems, provide an alternative solution to the problems of balancing power generation and consumption. RFBs are designed to convert and store electrical energy into chemical energy and release it in a controlled fashion when required. Many redox couples, such as all-vanadium, iron/chromium, iron/vanadium, bromide/vanadium systems, have been used as active materials for various RFB designs. Of them, all vanadium system (VRBs), utilizing vanadium-containing chemicals as positive V(IV)/V(V) and negative V(II)/V(III) electrolytes, is one of the most promising redox systems due to its high efficiency.^[1] Especially, recently invented mix-acid based all vanadium system by Li and co-workers^[2]at PNNL largely improved the energy density and temperature stability window of vanadium electrolytes. However, the energy density is still too low as compared with other secondary batteries, such as Li ion battery, which is very important especially in the application of large-scale energy storage system.

Here we report a novel aqueous redox flow battery system, which is safe and exhibits high discharge energy density. As shown in Fig. 1, the discharge energy density is around 135 Wh/L, which is about 5 times of that in VRB system. In addition, the chemistry and transportation mechanism of this system are investigated in detail.

Acknowledgements

The authors would like to acknowledge financial support from the U.S. Department of Energy’s (DOE’s) Office of Electricity Delivery and Energy Reliability (OE) (under Contract No. 57558). We also are grateful for insightful discussions with Dr. Imre Gyuk of the DOE-OE Grid Storage Program. The S/TEM work was conducted in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by DOE's Office of Biological and Environmental Research and located at PNNL. Pacific Northwest National Laboratory is a multi-program national laboratory operated by Battelle for DOE under Contract DE-AC05-76RL01830.

References

[1] Wang, W., Luo, Q., Li, B., Wei, X., Li, L. and Yang, Z. (2013), Recent Progress in Redox Flow Battery Research and Development. Adv. Funct. Mater., 23: 970–986.

[2] Li, L., Kim, S., Wang, W., Vijayakumar, M., Nie, Z., Chen, B., Zhang, J., Xia, G., Hu, J., Graff, G., Liu, J. and Yang, Z. (2011), A Stable Vanadium Redox-Flow Battery with High Energy Density for Large-Scale Energy Storage. Adv. Energy Mater., 1: 394–400.