Flow battery balancing

In the case of sealed systems with internal rebalancing, the balance can be fully restored so that in principal, steady-state operation can be achieved. Development of sealed flow batteries with internal rebalancing is thus an important step toward the ideal "maintenance-free" operation.

Abstract Principles of sealed iron flow batteries are introduced and a semi-empirical model that incorporates the hydrogen evolution reaction and electrolyte rebalancing is developed. Hydrogen generation rates are measured using pressure measurements in sealed vessels.

The model is validated with own measurements and can therefore predict the battery capacity as a function of time. This is used to analyse the battery performance by applying an overflow from one half-cell to the other. Different constant overflow rates were analysed with regard to an impact of the performance and electrolyte stability.

Regarding both, the DoD and the electrolyte stability, the battery shows the best performance with an overflow rate of 0.3 mL h −1 since the DoD is higher until cycle 180 compared to an overflow rate of 0.25 mL h −1.

Therefore, a dynamic overflow was determined in such a way that the capacity of the battery is maximised while the electrolytes remain stable for 200 cycles. The vanadium redox flow battery (VFB) is an attractive storage technology for large-scale storage applications because of its decoupled power and energy rating.

Conclusions Hydrogen side-reactions lead to an electrolyte imbalance in all-iron flow batteries, and this occurs simultaneously for iron and hydrogen species. Fortunately, this problem can be corrected using an appropriate rebalancing system.