Vanadium redox flow batteries are being developed for shipping applications by corporate and research partners in Germany, the Netherlands, Australia and Canada, and cost-competitiveness could be enhanced by leasing the 100% reusable electrolyte to shipowners.
Vanadium is a soft, grey, plentiful metal mainly produced from magnetite. It has the highest strength to weight ratio of any metal, and it also defies the Wiedemann-Franz Law which states that good conductors of electricity are also good conductors of heat.
The use of vanadium dates back to the third Century BC when high-strength “Damascus steel” was used for forging swords. The first wide-scale industrial use of vanadium occurred in 1905 when Henry Ford used vanadium-enriched steel to make the Model-T stronger and lighter. Today, it continues to be used to strengthen steel rebar, to dissipate heat in engines, computers, robotics and energy storage and as a key component in the manufacture of smart glass, aviation alloys, manufacturing and health formulations.
REDOX FLOW BATTERY TECHNOLOGY
Vanadium redox flow battery technologies date back to the 1980s, with work led by Professor Maria Skyllas-Kazacos of the University of NSW (UNSW Sydney) in Australia. The first patent for the All-Vanadium Redox Flow Battery was filed in 1986, and this was the start of a 35-year program at UNSW that continues today.
Unlike conventional batteries, redox flow batteries have electrolyte liquids stored in separated storage tanks, not in the power cell of the battery system. During operation, the electrolytes are pumped through the stack of power cells to produce electricity.
Vanadium redox flow batteries are non-flammable, reusable over hundreds of thousands of cycles (compared to several thousand for lithium-ion batteries) and last more than 20 years. They can be scaled up to deliver energy for a wide range of applications without generating significant waste heat, and they can extend energy storage time well beyond lithium-ion’s typical four to eight hour operating time. However, so far, researchers have not been able to match the power density of lithium-ion technology.
In January this year, Canada-based VanadiumCorp Resource Inc., with its wholly-owned subsidiary, Germany-based VanadiumCorp GmbH, announced engineering partnerships for the application of zero-emission ships using the design of next-generation vanadium redox flow batteries and electrolyte suitable for mobile applications. The move comes after VanadiumCorp’s research and development cooperation with CENELEST, the German-Australian Alliance for Electrochemical Technologies for the Storage of Renewable Energy, which combines the research and engineering strengths of both UNSW Sydney and the Fraunhofer Institute for Chemical Technology.
Generation 1 vanadium redox flow batteries contain vanadium dissolved in acid, typically sulphuric acid. Generation 2 technology uses a vanadium bromide solution instead and next-generation technology being developed by CENELEST for VanadiumCorp will involve further development of this to achieve higher energy density. The partners conducted work in 2020 that is anticipated to increase stored energy potential to around two times as much as a conventional vanadium redox flow battery. The technology can be scaled to any size, says VanadiumCorp CEO Adriaan Bakker.
He says recent key advancements in energy density have helped form a strong business case for the technology, targeting higher than 50 watts per litre (Wh/l), that can be obtained with vanadium bromide electrolyte. Along with advances in stack architecture, such as the development of wedge-shaped cells and additive manufacturing techniques, this means that the advantages of vanadium redox flow batteries, which include higher range, reusable electrolyte, simple management, fuelling instead of charging, and no risk of thermal runaway or fire, can be realized in marine propulsion systems, says Bakker.
Phase I of his plan will see the formalization of a trilateral partnership with Conoship International Projects from the Netherlands and Vega Reederei and Partners from Germany. VanadiumCorp will contribute new flow-battery designs, a high-energy-density electrolyte formulation, manage research and development and provide its network of manufacturing partners. Conoship will contribute marine engineering designs to integrate a compact redox flow-battery into propulsion systems, and Vega will arrange project financing, contribute fleet operations expertise and conduct field testing of the prototype.
In conventional generation, 1 vanadium redox flow batteries, two tanks of vanadium, one containing the negative electrolyte (V2+ and V3+ ions) and the other containing the positive electrolyte (V4+ and V5+ ions) are connected to the battery stacks. Pumps are used to circulate the electrolytes through the battery stacks where power conversion takes place. Most batteries use different chemicals in the positive and negative half-cells which can cross-contaminate and therefore degrade over time. This does not occur in conventional vanadium redox flow batteries as the single element, vanadium, is used to store and release charge.
“The electrolyte never actually degrades,” says Associate Professor Chris Menictas, Head of the Energy Storage and Refrigeration Research Group at UNSW. “It doesn’t change physical state or be used up. When you start from a discharge state, you have V3+ on the negative side and V4+ on the positive side. When you charge it up to 100%, V3+ will be converted to V2+ on the negative side, and V4+ will be converted to V5+ on the positive side. Those processes can just keep going, almost indefinitely. You’re only changing the oxidation state in the electrolyte, you aren’t actually degrading it.” In the Generation 2 technology, the electrolyte is composed of vanadium ions in mixed chloride and bromide acidic solutions. This allows for potentially higher energy density due to higher concentrations of vanadium and utilization of the bromine reaction.
Having a common electrolyte flowing to every cell is advantageous because it allows all cells in the battery system to be at the same condition, Menictas says. “Quite often, when you have other technologies where you’ve got thousands of cells, some cells may be 60%, some may be 100%. This can cause issues such as imbalance and cell reversal in larger battery arrays.
Additionally, power and energy can be scaled independently. “If I had, say, 2,000 lithium-ion batteries, the amount of power and the amount of time that I can use that power for is fixed, and if I want to add more capacity, for example I need a few extra hours, I’ve got to add more batteries,” explains Menictas. “With the vanadium flow battery, because all the energy is stored in liquid form and the battery stacks are only used for power, if I need more energy or I need power to be provided for a longer time, I can just add more electrolytes. Take a 10 megawatt battery and storage for four hours, so 40 megawatt hours, and if I need 60 megawatt hours, I don’t have to change the battery stacks, I just add more volume of electrolytes. No other system can really do that, other than a flow battery.”
Menictas says most batteries need to be recycled after their useful lifetime, generating an end-of-life financial and environmental cost. “However, in flow batteries, your electrolyte could be worth more and be an asset at that time than it was in the beginning, which is a huge benefit.” Bakker and Menictas anticipate that shipping companies could lease electrolyte, bringing the cost of the technology down dramatically.
Another costly issue for other types of batteries is thermal management, Menictas says. The liquid electrolyte going through the stacks of a vanadium redox flow battery can be used to cool the stacks. “It doesn’t have flammability or explosion issues, so it can be used in a contained environment where it would be an issue with other battery technology that has a flammability limitation that you need to be careful of.
“With lithium-ion, lead-acid, or other types of sealed systems, you get heat build-up in the different stacks, especially when you’re drawing a lot of current. And the problem is you need ventilation, active cooling and a lot of active management, which becomes very expensive. In a closed environment, such as a ship, the need for this equipment means the battery system can actually take up more space than an equivalent vanadium redox flow battery.”
The vanadium electrolyte can be stored in a different part of a ship to the stack, making for a flexible installation that facilitates change out of the electrolyte, which could be much like any other bunkering operation. The electrolyte could then be charged using renewable energy sources without the need for costly portside infrastructure and without the vessel needing to remain alongside in port while it occurs.
A SUSTAINABLE RESOURCE
Despite its advantages, the use of vanadium in energy storage technology has been held back by a lack of supply of high-purity metal and by a lack of green production technology. Conventional pyrometallurgical processes are capital intensive, have high operating costs and emit significant amounts of greenhouse gases. “You can’t really have renewable energy unless you have a truly renewable and sustainable energy storage technology,” says Bakker.
As well as owning one of the largest and most metallurgically favourable vanadium mineral deposits in the world, located in Quebec, Canada, VanadiumCorp owns a novel chemical process, invented by Dr. Francois Cardarelli, that overcomes production problems by digesting feedstocks into concentrated sulfuric acid. “Vanadium redox flow battery technology is 100% green when the contained vanadium is produced sustainably,” says Bakker.