Jul
13
Combining The Supercapacitor and Flow Battery
July 13, 2012 | 1 Comment
A team of researchers from Drexel University’s College of Engineering has developed a new method for quickly and efficiently storing large amounts of electrical energy. Their target is supporting efficient use of intermittent renewable energy resources, a goal that hinges on the ability to store the energy when it is produced and dispense it when it’s needed.
The Drexel’s team of researchers is putting forward a plan to integrate into the grid an electrochemical storage system that combines principles behind the flow batteries and supercapacitors that power our daily technology.
The team’s research has yielded a novel solution that combines the strengths of batteries with supercapacitors plus taking away the scalability problem. Their new “electrochemical flow capacitor” (EFC) consists of an electrochemical cell connected to two external electrolyte reservoirs – a design similar to existing redox flow batteries which are used in electrical vehicles.
Electrochemical Flow Capacitor Diagram. Click image for more info.
The Drexel team’s new technology is unique because it uses small carbon particles suspended in the electrolyte liquid to create a slurry of particles that can carry an electric charge. The uncharged slurry is pumped from its tanks through a flow cell, where energy stored in the cell is then transferred to the carbon particles. The charged slurry can then be stored in reservoirs until the energy is needed, at which time the entire process is reversed in order to discharge the EFC.
The EFC design allows it to be constructed on a scale large enough to store large amounts of energy and allows for rapid disbursal of the energy when the demand load needs it.
Dr. Yury Gogotsi, director of the A.J. Drexel Nanotechnology Institute and the lead researcher on the project said, “A liquid storage system, the capacity of which is limited only by the tank size, can be cost-effective and scalable. By using a slurry of carbon particles as the active material of supercapacitors, we are able to adopt the system architecture from redox flow batteries and address issues of cost and scalability.”
The team’s concept for the EFC was recently published in a special issue of Advanced Energy Materials focusing on next-generation batteries with a flow cell design by the Materials Research Center of the Ukraine used for the cover design artistic rendering by Kristi Jost.
Electrochemical Flow Capacitor Artists Rendering from the cover of Advanced Energy Materials. Used for news purposes and referral to the source. © John Wiley & Sons, Inc.
In the EFC, as well as flow battery systems, the energy storage capacity is determined by the size of the reservoirs that store the charged slurry material. If a larger capacity is desired, the tanks can simply be scaled up in size. In the same principle, the power output of the system is controlled by the size of the electrochemical cell, with larger cells producing more power.
Dr. E.C. Kumbur, director of Drexel’s Electrochemical Energy Systems Laboratory explains a unique attribute with, “Flow battery architecture is very attractive for grid-scale applications because it allows for scalable energy storage by decoupling the power and energy density. Slow response rate is a common problem for most energy storage systems. Incorporating the rapid charging and discharging ability of supercapacitors into this architecture is a major step toward effectively storing energy from fluctuating renewable sources and being able to quickly deliver the energy, as it is needed.”
The team’s work has yielded a design also giving the EFC a relatively long usage life compared to currently used flow batteries. According to the researchers, the EFC can potentially be operated in stationary applications for hundreds of thousands of charge-discharge cycles.
Kumbur adds an understatement, “This technology can potentially address cost and lifespan issues that we face with the current electrochemical energy storage technologies.”
Dr. Volker Presser, who was an assistant research professor in the Department of Materials Science and Engineering at the time the initial work was done is back with, “We believe that this new technology has important applications in (the renewable energy) field. Moreover, these technologies can also be used to enhance the efficiency of existing power sources, and improve the stability of the grid.”
The team’s future is developing new slurry compositions based on different carbon nanomaterials and electrolytes, as well as optimizing their flow capacitor design. The group is also designing a small demonstration prototype to illustrate the fundamental operation of the system.
Gogotsi winds up with, “We have observed very promising performance so far, and being close to that of conventional packaged supercapacitor cells. However, we will need to increase the energy density per unit of slurry volume by an order of magnitude, and achieve it using very inexpensive carbon and salt solutions to make the technology practical.”
The team is doing pretty well for a lab bench concept. The supporting information link on the abstract webpage has videos with a look at the slurry and its viscosity. Yes, there is a long way to go for commercial use. It’s still a fully new concept awaiting lots of innovation beyond proof of concept. But the disconnection between the power and the energy density has powerful and quantitative opportunities yet to be imagined.
Its step one, big one and those coming are sure to impress as well. It not hard to surmise that as well as a massive grid size, downsizing will be very attractive as well. After all, flow batteries without supercapacitor attributes are already being tested in vehicles.
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There are many wonderful nano-particle based super batteries and capacitors out there. Unfortunately, the manufacturing technology to scale up a micron level process up to just a few inches is not mature enough. Gaps and misallignments at the molecular level are introduced that quickly degrade the process – or – they cost $10,000 each to manufacture.
Here is hoping the manufacturing process can mature enough to actually scale.