Redox Flow Batteries: Innovations and Projects: Vanadium Flow Batteries Show Grid Storage and Overgeneration Management Capabilities: EV-Powering Other Potential Apps

      What exactly is a flow battery, and how does it differ from other batteries? Wikipedia explains:

“A flow battery, or redox flow battery (after reduction–oxidation), is a type of electrochemical cell where chemical energy is provided by two chemical components dissolved in liquids that are pumped through the system on separate sides of a membrane. Ion transfer inside the cell (accompanied by current flow through an external circuit) occurs across the membrane while the liquids circulate in their respective spaces.”

“Various flow batteries have been demonstrated, including inorganic and organic forms. Flow battery design can be further classified into full flow, semi-flow, and membraneless.”

“The fundamental difference between conventional and flow batteries is that energy is stored in the electrode material in conventional batteries, while in flow batteries it is stored in the electrolyte.”

“A flow battery may be used like a fuel cell (where new charged negolyte (a.k.a. reducer or fuel) and charged posolyte (a.k.a. oxidant) are added to the system) or like a rechargeable battery (where an electric power source drives regeneration of the reducer and oxidant).”

     Redox-flow batteries are very efficient and have a longer service life than conventional batteries. Since the energy is stored in external tanks, the battery capacity can be scaled independently of the rated battery power. Liquid is utilized as the storage medium. There are many different kinds of flow batteries with different anodes, cathodes, and electrolytes. Energy conversion in flow batteries is similar to energy conversion in fuel cells. Energy density is typically similar to that of lead-acid batteries. Lifespan, however, is much longer for flow batteries. A flow battery’s capacity is determined by the volume of electrolyte. The surface area and number of cells (the cell stack) determine the power.

Flow batteries provide long-lasting, rechargeable energy storage, particularly for grid reliability. Unlike solid-state batteries, flow batteries store energy in liquid electrolyte, shown here in yellow and blue. Researchers at PNNL developed a cheap and effective new flow battery that uses a simple sugar derivative called β-cyclodextrin (pink) to speed up the chemical reaction that converts energy stored in chemical bonds (purple to orange), releasing energy (electrons) to power an external circuit. A parallel reversible process (red-green) in the positive catholyte solution balances the positive and negative charges during charge and discharge. Credit: Animation by Sara Levine, Pacific Northwest National Laboratory

     

     The Fraunhofer Institute for Chemical Technology (ICT) in Germany tests materials, redox chemistry, cell stack development, and performs modeling and simulations for redox flow batteries. The Institute hosts Europe’s largest vanadium redox flow battery. They recently reached an important milestone in utilizing the battery to integrate variable wind and solar generation. They utilized their own storage platform to smooth the integration of curtailed wind and solar into energy storage. According to TechXplore:

"We have shown that renewable energy can be managed intelligently with our storage platform. This is a decisive step toward a stable, flexible and resilient electricity system based on renewable sources," explains Adj. Assoc. Prof. (UNSW, UQ) Dr. Jens Noack, Team Manager for Flow Batteries at Fraunhofer ICT.

     Apparently, the key to success is feeding the energy into the battery when appropriate and back into the grid when appropriate in a systematic, predictable way. Flow batteries, particularly vanadium flow batteries, could be one of the best means of storing and reintegrating curtailed wind and solar generation. As always with batteries, cost is a significant hurdle.

     Meanwhile, Swiss company nanoFlowcell is working on a flow battery for EVs that requires periodic electrolyte fill-ups but is also aiming for a 1200-mile range per tank of electrolytes. The battery is refueled rather than recharged. The external storage of electrolyte in redox flow battery design enables refueling. However, the flow battery technology still faces challenges regarding cost-effectiveness and scalability for mass EV adoption. They note that the concentration and volume of the electrolyte determine the range. The company’s technology is deployed in several car models and one aircraft with vertical takeoff capabilities. According to their website, nanoFlowcell’s bi-ION electrolyte is:

“…a precise mixture of metallic and non-metallic salts. The solution is then enriched with the specially designed bi-ION® molecule, our proprietary energy carrier.”

“Our specially formulated aqueous salt solution ensures that bi-ION® is easily transportable, pumpable, and performs reliably under extreme temperature conditions.”

“Flow cells, like nanoFlowcell®, differ from traditional batteries by separating energy conversion from storage. The energy output depends on the concentration and volume of the electrolyte solution, not the cell size. This allows nanoFlowcell® to be infinitely scalable, making it adaptable to a wide range of applications.”

nanoFlowcell - Functional Animation on Vimeo

     Other potential uses for flow batteries include drones, household energy storage, and consumer electronics. It should be interesting to see what comes from redox-flow battery tech. China deployed some vanadium flow batteries, beginning several years ago, for grid balancing capabilities. Research is ongoing for flow battery materials that are easier to obtain than mined materials like vanadium. Research in 2023 showed that additives such as the common food and medicine additive called β-cyclodextrin, derived from starch, can increase flow battery capacity and longevity by 60%. I am guessing that nanoFlowcell’s bi-ION has “proprietary” additives that enhance its capabilities.      

 

 

References:

 

New EV Battery Promises 1,200-Mile Range but Requires Fuel-Style Fill-Ups. Kathrine Frich, Dqgens News. October 27, 2024. New EV Battery Promises 1,200-Mile Range but Requires Fuel-Style Fill-Ups

Flow battery. Wikipedia. Flow battery - Wikipedia

Scientists make game-changing breakthrough with tech that could transform power grids: 'A decisive step'. Hannah Slusher. The Cool Down. August 26, 2025. Scientists make game-changing breakthrough with tech that could transform power grids: 'A decisive step'

Redox-flow batteries. Fraunhofer Institute for Chemical Technology ICT. Redox-flow batteries - Fraunhofer ICT

New storage platform delivers predictable renewable power regardless of weather conditions. Manuel Fuchs and Fraunhofer-Gesellschaft. edited by Lisa Lock, reviewed by Andrew Zinin. TechXplore. June 24, 2025. New storage platform delivers predictable renewable power regardless of weather conditions

Record-Breaking Advances in Next-Generation Flow Battery Design. Pacific Northwest National Laboratory, SciTechDaily. July 14, 2023. Record-Breaking Advances in Next-Generation Flow Battery Design