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

• New-generation iron–titanium flow battery with good performance was proposed. • The stabilization mechanism of the electrolyte in ITFB was explored deeply. • ITFB showed excellent cycle stability (over 1000 cycles). • ITFB exhibited a very competitive cost advantage (less than 88.22 $/kWh). 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 TiO 2+ inhibits the hydrolysis of TiO 2+ 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 TiO 2+ ions in the electrolyte are explored deeply. Moreover, by electrodepositing metal Bi on the surface of the electrode, the electrochemical activity of the Ti 3+ /TiO 2+ 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/cm 2 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.