Last January is an interesting article in the prestigious journal Nature that speaks of a system of accumulation of electricity that draws its inspiration from what make living things. I get curious and sending a message to the authors. Prof. Michael J. Aziz, of the Harvard School of Engineering and Applied Sciences, answer me almost instantly and we agree that, at the first opportunity to visit Boston, I’m going to find it.
Last May I introduce myself to the fourth floor of No. 9 Oxford Street and Prof. Aziz is accompanied by Prof. Roy G. Gordon teaches Materials Science, and Dr. Murray McCutcheon, head of technology transfer and business development. That’s what they tell me.
Q: How is the energy is stored in your flow-battery?
R: Unlike conventional, solid-electrode batteries, flow batteries store energy outside the battery container itself in chemical storage tanks. Energy is stored reversibly in the form of reduced and oxidized species that circulate from the external tanks into the main battery stack. In the stack, reduction-oxidation reactions across a membrane convert the electrochemical energy into electrical energy (or vice versa). Compared to alternatives such as lithium-ion batteries, flow batteries have the major advantage that the energy capacity can be increased simply by increasing the size of the chemical storage tank. As a result, they are a promising technology for long-discharge duration applications (up to 8h), which are in increasing demand for the electrical grid.
The Harvard research group around their “Organic mega flow battery”
Q: Are the chemicals/materials that constitute your battery easy to find?
R: Many flow batteries rely on rare elements or precious metal catalysts. Our battery is distinguished by its use of common, low-cost materials that can dramatically lower system costs compared to competitive approaches. Although half of the twelve leading venture-backed flow battery start-ups are using vanadium as the electrolyte, it has an unsustainable cost structure. We calculate that our electrolytes are less than 10% of the cost of vanadium, and do not suffer from the same resource scarcity issues. Although the anthraquinone used in one half of our system is unfamiliar to most people, it is used at scale as an oxidizing agent in the pulp and paper and petrochemical industries. As a result, it can be readily sourced at low cost in large volumes. Similarly, hydrogen bromide is a common industrial chemical available widely and cheaply.
Q: Any of these materials are dangerous, harmful or polluting? Or may be released without problems for the environment?
R: For the past year, we focused our efforts on developing a metal-free material for the negative half-cell of the flow battery. We studied a class of molecules called quinones that are found in all plants and animals, and can undergo rapid reversible oxidation and reduction over many cycles without degradation. That’s exactly the kind of functionality you want in a battery. We modified them to give them high solubility in water and put them in a flow battery. The key material we have used is non-toxic and is similar to one of the constituents of rhubarb, leading many to dub our invention the “rhubarb” battery.
For the positive half-cell of our battery, we have used a well-known chemical architecture based on hydrogen bromide. This is a mature chemical system suitable for a first demonstration of our technology, but it does require safe-handling procedures and should not be released to the environment. One of the major goals for our three-year grant from the U.S. Department of Energy (ARPA-E) is to develop a quinone-based electrolyte to replace the hydrogen bromide, which will result in an inexpensive, non-toxic all-quinone flow battery.
Q: How much power can accumulate this flow-battery? Have you been imagining scalability of the product?
R: Due to its scalable architecture, the individual unit cells of a flow battery can be coupled together to yield high power, high energy capacity systems. A pilot system capable of delivering one megawatt (MW) of power for five hours (total energy capacity of 5 MWh) has been demonstrated by Sumitomo Electric in Japan, and systems ten times larger than that are under construction. Our invention can be scaled in the same manner, and we believe the cost-performance benefits of our chemistry will provide a disruptive advantage.
The Harvard flow battery
Q: This battery might therefore serve in places like homes but also hospitals, hotels and shopping malls … What is the maximum size you imagine would be for these batteries? What are the pro and cons of large batteries vs a small size batteries?
The value proposition of flow batteries is most compelling at medium (100 kW) to large scales (1+ MW) – roughly on the scale of a commercial or industrial facility up to electrical substations for the grid and wind or photovoltaic farms. Uniquely amongst competitive storage technologies, the energy capacity of a flow battery can be increased at low cost by increasing the volume of the chemical tanks, without changing the size of the power delivery system (the stack). This translates to the potential for unrivalled cost per kilowatt-hour for large, long-discharge systems.
There are many compelling applications for large flow batteries. To give one example, the biggest technical obstacle preventing wind and solar energy from supplying more of our electricity is their intermittency. If we can mass produce a battery at large scale that could safely and cost-effectively store large amounts of energy, we could solve this problem by making wind and solar power dispatchable.
Dr. Michael J. Aziz
Q: How close you are to an industrialized product? Are you collaborating with companies that are helping you to achieve it?
R: We reported our research results in the journal Nature in January, and are currently in conversations with potential partners as part of our commercialization roadmap. Because flow batteries have been in development since the 1970s, there are companies with extensive know-how in the system design and engineering. We plan to leverage this expertise to build value around our innovation.
from left: Murray McCutcheon, io, Roy G. Gordon, Michael J. Aziz.
Q: I imagine that you have had many interests from Chemical Industry and energy producers. How will you transfer this technology in the market?
R: There has been an extraordinary level of interest from potential partners since we published our work. To us, this speaks both to the large potential of our invention as well as the compelling market opportunity in energy storage. To effectively transfer the technology, we recognize we cannot do all the work ourselves. It is important to engage entities across the value chain, from chemical companies to systems integrators and energy service providers. Our plan is to assemble the right network of partners that will accelerate the development and adoption of quinone-based flow batteries. At the same time, we are continuing to pursue breakthrough research in our lab that will feed into the next generation systems.