Redox flow batteries for energy storage: their promise, achievements and challenges

Abstract

Redox flow batteries continue to be developed for utility-scale energy storage applications. Progress on standardisation, safety and recycling regulations as well as financing has helped to improve their commercialisation. The technical progress of redox flow batteries has not considered adequately the significance of electrolyte flow velocity, mass transfer and plug flow reactor modelling, despite steps in the right direction. 3D simulations of fluid flow, pressure drop, current distribution and mechanical resistance using commercial software are becoming more common, but satisfactory validation by experiments is still unusual. The majority of research tends to report short term studies on small electrodes, often in poorly defined flow channels; long term evaluation of electrode and membrane durability on a pilot scale is needed. Digital imaging of electrode structure using X-ray computed tomography is increasingly being used. Much activity is directed to organic and non-aqueous systems. However, scale-up and high, sustained charge capacity using electrolytes of moderate cost which are environmentally acceptable to source, store, transport and handle require considerable attention. Recommendations for future work are discussed.

Modelling of redox flow battery electrode processes at a range of length scales: a review

“…To enable numerical models to give physically meaningful results of RFB operational parameters, precise transport properties are needed, in addition to a sound formulation. 281 An important transport property is the effective diffusivity, which is necessary to model the mass transport at the representative elementary volume level of porous electrodes in the context of Darcy's law. The widelyused effective diffusivity 210,214,282 is a simple association equation with the inherent diffusivity and the material porosity using a Bruggemann correction; 211 a concern with this correlation, however, is that the inuence of the pore morphology of various porous structures is missed.…”

Solute transport and reaction in porous electrodes at high Schmidt numbers

“…The mechanism of solute transport through redox flow battery porous electrodes is traditionally modelled via the Nernst-Planck equation, which describes the motion of ions under the influence of ionic concentration gradients and electric fields (Probstein 2005;Arenas, de León & Walsh 2019). Such an approach is applied via numerical simulations to a scale larger than the characteristic pore size of the electrode and the microstructural effects are neglected.…”

Research Frontiers in Energy‐Related Materials and Applications for 2020–2030

“…For these reasons, in the future, we foresee a differentiation of storage technologies depending on the final application of the battery system (Figure 2). [61,62] Last but not the least, in recent years different metal-ion chemistries such as Zn-ion, Al-ion, and Mg-ion batteries have been proposed as promising technologies for wearable devices. [55][56][57] Moreover, redox flow batteries are a recent technology that shows encouraging results for its application in the stationary large-scale energy sector.…”

“…Driven by the need for higher energy density and cycle life and lower costs, alternative technologies to the Li‐ion concept are increasingly explored, which focus on cheaper, more abundant, and environment‐friendly materials. Post‐Li‐ion batteries such as Li–sulfur, Li–air, all‐solid‐state Li‐ion, metal‐ion (Na‐ion, K‐ion, Zn‐ion, Al‐ion, and Mg‐ion), redox flow batteries, and all‐organic batteries are being developed . Among the many post‐Li‐ion systems that are under current development, here we will focus on Li–S and Li–air because specific advancements in these technologies could enable extremely high energy densities batteries.…”