Advantages
The advantage of redox-flow batteries in general is the separate scalability of power and energy, which makes them good candidates for stationary energy storage systems.[3] This is because the power is only dependent on the stack size while the capacity is only dependent on the electrolyte volume.[5]
As the electrolyte is based on water, it is non-flammable. All electrolyte components are non-toxic and abundantly available. The reactants in both half-cells are soluble salts of the same species and only differ in their oxidation state (Fe0, Fe2+, Fe3+). This means that unwanted membrane crossover of the active species does not lead to irreversible reactant loss,[2] but can be rebalanced using either a trickle-bed reactor or a fuel cell.[3][9] Iron chloride is cheaply and widely available as it is a by-product for steel production.[1]
The IRFB is stable within different temperature ranges, therefore, the stationary energy storage can be used in regions with higher temperature without the need of a thermal management system. [5] The battery efficiency would even benefit from higher temperatures. Other battery types (e.g. Vanadium-Redox-Flow Batteries (VRFB)) cannot perform at higher temperatures. For instance, toxic Vanadium pentoxide (V2O5) in VRFBs precipitates at ~ 40 °C.[13]
Overall, the components are low in cost (2 $/kg iron) and abundantly available. All the other parts (e.g. membrane, bipolar plate, monopolar plate, frames, gaskets, pumps) are widely available on the market and associated costs can be expected to decrease as production of these batteries scales up.
Additionally, compared to lithium-ion batteries with expected lifetimes of ~1000 cycles, the IRFB promises a potential battery lifetime of > 20 years with over 10.000 cycles.[1]
Disadvantages
The capacity is not solely dependent on the electrolyte volume as is the case with other RFBs which are only based on electrochemical reactions in solution (e.g. VRFB). Rather, in an IRFB the plating iron volume within the negative half-cell has an influence on the capacity. Thus, the energy capacity and stack size are not completely decoupled as is the case with other RFB.[7]
During the charge reaction, hydrogen evolves on the negative side, reducing coulombic efficiency. Additionally, the pH increase leads to insoluble Fe(OH)3 (rust) precipitation which untreated can lead to cell death. However, a rebalancing system can bring the IRFB back to a state of health.[3]
Compared to non-RFB systems, all flow batteries include auxiliary components such as pumps and valves, which do require a regular maintenance cycle.
Leave a Reply