New-generation iron–titanium flow batteries with low cost and ultrahigh stability for stationary energy storage

Abstract

New-generation iron–titanium flow battery (ITFB) with low cost and high stability is proposed for stationary energy storage, where sulfonic acid is chosen as the supporting electrolyte for the first time. In the design, the complexation between the sulfate ion and TiO2+ inhibits the hydrolysis of TiO2+ ions and improves the stability of the electrolyte. Combining the experimental characterization and the theory calculation, the stabilization mechanism of the electrolyte and the existing forms of TiO2+ ions in the electrolyte are explored deeply. Moreover, by electrodepositing metal Bi on the surface of the electrode, the electrochemical activity of the Ti3+/TiO2+ couple is effectively improved. As a result, the new-generation ITFB demonstrates coulombic efficiency of 99.7% and energy efficiency of 85.6% at the current density of 40 mA/cm2 and can run stably for more than 1000 cycles without obvious efficiency decay. Most importantly, after 1000 cycles, the discharge capacity still keeps 80% of the initial capacity, stating the extremely slow capacity decay (0.193 mAh/cycle). Furthermore, a low-cost and easily prepared sulfonated poly(ether ether ketone) (SPEEK) membrane, instead of the expensive Nafion membranes, is successfully used in the ITFB, feathering a very competitive cost advantage (less than 88.22 $/kWh). Therefore, considering the ultrahigh stability and low cost, it is easy for the new-generation ITFB to scale up and industrialize, thus new-generation ITFB is expected as a large-scale energy storage device in the foreseeable future.