Redox flow batteries—Concepts and chemistries for cost-effective energy storage

Abstract

Electrochemical energy storage is one of the few options to store the energy from intermittent renewable energy sources like wind and solar. Redox flow batteries (RFBs) are such an energy storage system, which has favourable features over other battery technology, e.g. solid state batteries, due to their inherent safety and the independent scaling of energy and power content. However, because of their low energy-density, low power-density and the cost of components such as redox species and membranes, commercialised RFB systems like the all-vanadium chemistry cannot make full use of the inherent advantages over other systems. In principle, there are three pathways to improve RFBs and to make them viable for large scale application: First, to employ electrolytes with higher energy density. This goal can be achieved by increasing the concentration of redox species, employing redox species that store more than one electron or by increasing the cell voltage. Second, to enhance the power output of the battery cells by using high kinetic redox species, increasing the cell voltage, implementing novel cell designs or membranes with lower resistance. The first two means reduce the electrode surface area needed to supply a certain power output, thereby bringing down costs for expensive components such as membranes. Third, to reduce the costs of single or multiple components such as redox species or membranes. To achieve these objectives it is necessary to develop new battery chemistries and cell configurations. In this review we focus on a comparison of promising cell chemistries, be they all-liquid, slurries or hybrids combining liquid, gas and solid phases.Aim is to elucidate which redox-system is most favourable in terms of energy-density, power-density and capital cost. Also the choice of solvent and the selection of an inorganic or organic redox couples with the entailing consequences are discussed.

In situ NMR metrology reveals reaction mechanisms in redox flow batteries

“…Application considerations in RFBs and beyond. Organic RFBs based on inexpensive (the estimated price of, for example, anthraquinone disulfonic acid is currently in the range of US$0.9/kg to US$3.9/kg for industrial-scale production 35 Because of the simplicity of the on-line NMR setup, which consists essentially of a lab-scale RFB and a flow NMR sampling tube, we expect wide adoption of this technique to advance the understanding of a variety of redox chemistry, such as quinone- 37,38 , carbonyl-nitrogen- 39 , radical-40 , polymer- 41 , and metal complex- 42 based redox chemistries in flow and other battery systems, [3][4][5]39,[43][44][45][46][47][48][49][50][51][52] e.g. lithium-air batteries that involve organic redox shuttles.…”

Dihydrophenazine‐Based Copolymers as Promising Cathode Materials for Dual‐Ion Batteries

“…In the last years, the postlithium battery technologies have been developed tremendously, in particular, sodium‐ion, [ 7 ] potassium‐ion, [ 8 ] dual‐ion, [ 9 ] redox‐flow [ 10 ] batteries and supercapacitors [ 11 ] based on inorganic and organic electrode materials. In our opinion, organic batteries deserve a special attention due to a number of reasons.…”

Asymmetric polyoxometalate electrolytes for advanced redox flow batteries

“…[Fe(CN) 6 ] 4-/[Fe(CN) 6 ] 3-8 ) as electron carriers (all three will be called metal ions for simplicity), while the second proposes to employ organic redox active materials. 4,5,9 Both approaches come with their distinct advantages and drawbacks. The champion of the dissolved metal chemistries is the all-vanadium redox flow battery (VRFB).…”